Risks of Malathion Use to the Federally Threatened Delta Smelt (Hypomesus transpacificus) and California Tiger Salamander (Ambystoma californiense), Central California Distinct Population Segment, and the Federally Endangered California Tiger Salamander, Santa Barbara County and Sonoma County Distinct Population Segments


Risks of Malathion Use to the Federally Threatened Delta

Smelt (Hypomesus transpacificus) and California Tiger
Salamander (Ambystoma californiense), Central California
Distinct Population Segment, and the Federally Endangered
California Tiger Salamander, Santa Barbara County and
Sonoma County Distinct Population Segments



° ^ °

H3Cv ^tr /c — c—CH3	H3C Y C — c—ch3

o—p-s—CH H2	O—p—S—CH H2

I \	I \

A h2C^	' h2c.

o c—c—ch3	,o c—c—ch3

H3C II H2	H3C II H2

J o	o

Malathion (Parent Compound)	Maloxon (Degradate of Concern)

Pesticide Effects Determinations
PC Code: 057701
CAS Number: 121-75-5

Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460

September 29,2010

l

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Acknowledgement

We would like to acknowledge the contribution of the Litigation Steering Committee in
compiling detailed information on the species. Additionally, the Steering Committee has
provided invaluable guidance toward achieving greater consistency in format and content
between chemicals being assessed.

2

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Primary Authors:

Nicholas Mastrota, Ph.D., Biologist
Stephen P. Wente, Ph.D., Biologist
Faruque Khan, Ph.D. Senior Scientist

Secondary Review:

Melissa Panger, Wildlife Biologist
Reuben Baris, Environmental Scientist

Acting Branch Chief, Environmental Risk Assessment Branch 1:
Brian Anderson

3

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Table of Contents

1.	EXECUTIVE SUMMARY	14

1.1.	Purpose of Assessment	14

1.2.	Scope of Assessment	14

1.2.1.	Uses Assessed	14

1.2.2.	Environmental Fate Properties of Malathion	16

1.2.3.	Evaluation of Degradates and Stressors of Concern	16

1.3.	Assessment Procedures	17

1.3.1.	Exposure Assessment	17

1.3.2.	Toxicity Assessment	19

1.3.3.	Measures of Risk	19

1.4.	Summary of Conclusions	19

2.	PROBLEM FORMULATION	23

2.1.	Purpose	23

2.2.	Scope	25

2.2.1.	Evaluation of Degradates and Other Stressors of Concern	25

2.2.2.	Evaluation of Mixtures	28

2.3.	Previous Assessments	29

2.3.1.	Malathion Registration Eligibility Decision, 2006	29

2.3.2.	Organophosphate Cumulative Assessment, and Malathion Reregistration
Eligibility Decision, 2006	30

2.3.3.	California Red-legged Frog Endangered Species Assessment	30

2.3.4.	Pacific Anadromous Salmonids Endangered Species Assessment	31

2.4.	Environmental Fate Properties	32

2.4.1.	Environmental Transport Mechanisms	39

2.4.2.	Mechanism of Action	41

2.4.3.	Use Characterization	42

2.5.	Assessed Species	53

2.6.	Designated Critical Habitat	58

2.7.	Action Area and LAA Effects Determination Area	60

2.7.1.	Action Area	60

2.7.2.	LAA Effects Determination Area	60

2.8.	Assessment Endpoints and Measures of Ecological Effect	61

2.8.1.	Assessment Endpoints	61

2.8.2.	Assessment Endpoints for Designated Critical Habitat	63

2.9.	Conceptual Model	64

2.9.1.	Risk Hypotheses	64

2.9.2.	Diagram	64

2.10.	Analysis Plan	66

2.10.1.	Measures of Exposure	67

2.10.2.	Measures of Effect	67

2.10.3.	Data Gaps	68

3.	EXPOSURE ASSESSMENT	68

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3.1.	Label Application Rates and Intervals	68

3.2.	Aquatic Exposure Assessment	69

3.2.1.	Modeling Approach	69

3.2.2.	Aquatic Exposure Modeling Results	79

3.2.3.	Existing Monitoring Data	85

3.3.	Terrestrial Animal Exposure Assessment	93

3.3.1.	Exposure to Residues in Terrestrial Food Items	93

3.3.2.	Exposure to Terrestrial Invertebrates	96

3.4.	Terrestrial Plant Exposure Assessment	99

4.	EFFECTS ASSESSMENT	99

4.1.	Ecotoxicity Study Data Sources	99

4.2.	Toxicity of Malathion to Aquatic Organisms	101

4.2.1.	Toxicity to Freshwater Fish and Aquatic-Phase Amphibians	103

4.2.2.	Toxicity to Freshwater Invertebrates	110

4.2.3.	Toxicity to Estuarine/Marine Fish	113

4.2.4.	Toxicity to Estuarine/Marine Invertebrates	114

4.2.5.	Toxicity to Aquatic Plants	115

4.3.	Toxicity of Malathion to Terrestrial Organisms	116

4.3.1.	Toxicity to Birds, Reptiles, and Terrestrial-Phase Amphibians	117

4.3.2.	Toxicity to Mammals	120

4.3.3.	Toxicity to Terrestrial Invertebrates	122

4.3.4.	Toxicity to Terrestrial Plants	123

4.4.	Toxicity of Chemical Mixtures	125

4.5.	Incident Database Review	125

4.5.1.	Aquatic Animal Incidents	126

4.5.2.	Terrestrial Animal Incidents	127

4.5.3.	Plant Incidents	128

4.6.	Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern	128

5.	RISK CHARACTERIZATION	129

5.1.	Risk Estimation	129

5.1.1.	Exposures in the Aquatic Habitat	129

5.1.2.	Exposures in the Terrestrial Habitat	146

5.1.3.	Primary Constituent Elements of Designated Critical Habitat	151

5.2.	Risk Description	151

5.2.1.	Delta Smelt	154

5.2. I.e. Modification of Designated Critical Habitat	161

5.2.1 .d. Spatial Extent of Potential Effects	162

5.2.2.	California Tiger Salamander	164

5.2.3.	Modification of Designated Critical Habitat	169

5.2.4.	Spatial Extent of Potential Effects	170

5.3.	Effects Determinations	172

5.3.1.	Assessed Species	172

5.3.2.	Addressing the Risk Hypotheses	173

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6.	UNCERTAINTIES	174

6.1.	Exposure Assessment Uncertainties	174

6.1.1.	Aquatic Exposure Modeling of Malathion	174

6.1.2.	Exposure in Estuarine/marine Environments	182

6.1.3.	Modeled Versus Monitoring Concentrations	183

6.1.4.	Maloxon formation, environmental fate, and toxicity	184

6.2.	Effects Assessment Uncertainties	185

6.2.1.	Data Gaps and Uncertainties	185

6.2.2.	Use of Surrogate Species Effects Data	185

6.2.3.	Sublethal Effects	186

7.	RISK CONCLUSIONS	186

8.	REFERENCES	190

9.	MRID LIST	196

Appendices

Appendix A. Multi-Active Ingredients Product Analysis
Appendix B. Verification Memo for Malathion

Appendix C. Risk Quotient (RQ) Method and Levels of Concern (LOCs)

Appendix D. Details on Aquatic Exposure Assessment

Appendix E. Example Output from PRZM/EXAMS

Appendix F. Example Output from T-REX and T-HERPS

Appendix G. Summary of Ecological Incidents Linked to Malathion

Appendix H. Bibliography of ECOTOX Open Literature

Appendix I. Accepted ECOTOX Data

Appendix J. Revised Human Health Risk Assessment for the Reregi strati on Eligibility
Decision Document (RED) for Malathion (PC Code 057701, Case No. 0248).

Attachments

Attachment I. Supplemental Information on Standard Procedures for Threatened and
Endangered Species Risk Assessments on the San Francisco Bay Species
Attachment II: Status and Life History for the San Francisco Bay Species
Attachment III: Baseline Status and Cumulative Effects for the San Francisco Bay Species
Attachment IV. Supplemental Information on the California Right-of-Way Scenario

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List of Tables

Table 1-1. Effects Determination Summary for Effects of Malathion on the Delta Smelt and

California Tiger Salamander 20

Table 1-2. Effects Determination Summary for the Critical Habitat Impact Analysis 21

Table 1-3. Malathion Use-specific Risk Summary for Delta Smelt and California Tiger

Salamander 22

Table 2-1. Impurities and degradates reported in technical malathion (CalEPA 1981) 26

Table 2-2. Summary of Maloxon Environmental Fate Properties 38

Table 2-3. Malathion uses, application information, and modeling scenarios used in exposure

assessment1 43

Table 2-4. Summary of California Department of Pesticide Registration (CDPR) Pesticide Use
Reporting (PUR) data from 1999 to 2007 for currently registered malathion uses1.... 49

Table 3-1. Field monitored runoff a from the Cotton Boll Weevil Control Program 87

Table 3-2. Southeast Boll Weevil Eradication Program monitoring data of spray drift to adjacent

moving water (USDA 1993)a 88

Table 3-3. Texas Lower Rio Grande Valley Boll Weevil Eradication Program monitoring data of

spray drift to adjacent moving water (USDA 1995a)a 89

Table 3-4. Southern Rolling Plains Boll Weevil Eradication Program monitoring data of spray

drift to adjacent moving water (USDA 1994-5)a 89

Table 3-5. Malathion levels in bodies of water in relation to medfly control sprayinga 90

Table 3-6. Malathion level in 29 ponds in Florida exposed to direct (unprotected aquatic sites) or

indirect (protected aquatic sites) malathion spray in medfly controf 91

Table 3-7. Malathion and maloxon concentrations in creeks after malathion applications in the

Santa Clara Valley 93

Table 4-1. Aquatic Toxicity Profile for Malathion 101

Table 4-2. Categories of Acute Toxicity for Fish and Aquatic Invertebrates 103

Table 4-3-13. Aquatic plant toxicity studies (sourced from OPP data and ECOTOX studies

meeting minimum quality for database and OPP) 116

Table 5-1. Acute and Chronic RQs for Freshwater Fish. Risk quotients that exceed the LOC are
shown in bold. The acute LOC is 0.1 for the acute effects and 1.0 for chronic effects.

130

Table 5-2. Summary of Acute and Chronic RQs for Aquatic Invertebrates. Risk quotients that
exceed the LOC are shown in bold. The acute LOC is 0.1 for the acute effects and 1.0

for chronic effects 133

Table 5-3. Summary of Acute RQs for Aquatic Plants 143

Table 5-4. Acute and Chronic RQs Derived Using T-REX for Malathion and Birds and

Amphibians. Risk quotients that exceed the LOC are shown in bold. The acute LOC
is 0.1 for the CTS (direct effect) and 0.5 for other amphibians and mammals; the

chronic LOC is 1.0 for all species 147

Table 5-5. Acute and Chronic RQs for Amphibians Derived Using T-HERPS. Risk quotients

that exceed the LOC are shown in bold. The acute LOC is 0.1 and the chronic LOC is

1.0 148

Table 5-6. Summary of RQs for Terrestrial Invertebrates. Risk quotients that exceed the LOC of

0.1 are shown in bold 150

Table 5-7. Risk Estimation Summary for Malathion - Direct and Indirect Effects 152

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Table 5-8. Risk Estimation Summary for Malathion - Effects to Designated Critical Habitat.

(PCEs)	152

Table 6-1. Percentage of pesticide expected to be applied on application dates when estimated
environmental concentrations (EECs) are expected to exceed Agency levels of

concern (LOCs) for the aquatic impacts of legal uses of malathion in California	176

Table 6-2. Within species comparisons of malathion and maloxon acute toxicity	184

Table 7-1. Effects Determination Summary for Effects of Malathion on the DS and CTS	186

Table 7-2. Effects Determination Summary for the Critical Habitat Impact Analysis	188

Table 7-3. Malathion Use-specific Risk Summary for Delta Smelt and California Tiger

Salamander	189

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List of Figures

Figure 2-1. Malathion Use in Total Pounds per County	48

Figure 2-2. Critical Habitat and Occurrence Sections of the Delta smelt identified in Case No.

07-2794-JCS	56

Figure 3-1. Variation in 90th percentile peak, 21-day average, and 60-day EECs across first
application dates for ground application to pecan compared to a 15-day moving
average of pounds of malathion applied per day. (Based on CDPR PUR data from

years 1990 through 2008.)	 70

Figure 3-2. Variation in estimated environmental concentration (EEC) of malathion and area of

cull piles in the standard PRZM watershed	72

Figure 3-3. Variation in estimated environmental concentration (EEC) of malathion and area of

fence row in the standard PRZM watershed	74

Figure 3-4. Deposition curve for a malathion application at a release height of 75 ft and a Dvo.s of

60 |im and wind speed of 10 mph	76

Figure 3-5. Variation in estimated environmental concentration (EEC) of malathion and area of
trash bins in the standard PRZM watershed	79

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List of Commonly Used Abbreviations and Nomenclature

|ig/kg	Symbol for "micrograms per kilogram"

|ig/L	Symbol for "micrograms per liter"

°C	Symbol for "degrees Celsius"

AAPCO	Association of American Pesticide Control Officials

a.i.	Active Ingredient

AIMS	Avian Monitoring Information System

Acc#	Accession Number

amu	Atomic Mass Unit

BCB	Bay Checkerspot Butterfly

B CF	B i oconcentrati on F actor

BEAD	Biological and Economic Analysis Division

bw	Body Weight

CAM	Chemical Application Method

CARB	California Air Resources Board

CAW	California Alameda Whipsnake

CBD	Center for Biological Diversity

CCR	California Clapper Rail

CDPR	California Department of Pesticide Regulation

CDPR-PUR California Department of Pesticide Regulation Pesticide Use
Reporting Database

CFWS	California Freshwater Shrimp

CI	Confidence Interval

CL	Confidence Limit

CTS	California Tiger Salamander

CTS-CC	Central Valley DPS of the California Tiger Salamander

CTS-SB	Santa Barbara County DPS of the California Tiger Salamander

CTS-SC	Sonoma County DPS of the California Tiger Salamander

DPS	Distinct population segment

DS	Delta Smelt

EC	Emulsifiable Concentrate

ECos	5% Effect Concentration

EC25	25% Effect Concentration

EC50	50% (or Median) Effect Concentration

ECOTOX	EPA managed database of Ecotoxicology data

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EEC	Estimated Environmental Concentration

EFED	Environmental Fate and Effects Division

e.g.	Latin exempli gratia ("for example")

EIM	Environmental Information Management System

EPI	Estimation Programs Interface

ESU	Evolutionarily significant unit

et al.	Latin et alii ("and others")

etc.	Latin et cetera ("and the rest" or "and so forth")

EXAMS	Exposure Analysis Modeling System

FIFRA	Federal Insecticide Fungicide and Rodenticide Act

FQPA	Food Quality Protection Act

ft	Feet

GENEEC	Generic Estimated Exposure Concentration model

HPLC	High Pressure Liquid Chromatography

IC05	5% Inhibition Concentration

IC50	50% (or median) Inhibition Concentration

i.e.	Latin for id est ("that is")

IECV1.1	Individual Effect Chance Model Version 1.1

KABAM	K0w (based) Aquatic BioAccumulation Model

kg	Kilogram(s)

kJ/mole	Kilojoules per mole

km	Kilometer(s)

KAw	Air-water Partition Coefficient

Kd	Solid-water Distribution Coefficient

KF	Freundlich Solid-Water Distribution Coefficient

K0c	Organic-carbon Partition Coefficient

K0w	Octanol-water Partition Coefficient

LAA	Likely to Adversely Affect

lb a.i./A	Pound(s) of active ingredient per acre

LC50	50% (or Median) Lethal Concentration

LD50	50% (or Median) Lethal Dose

LOAEC	Lowest Observable Adverse Effect Concentration

LOAEL	Lowest Observable Adverse Effect Level

LOC	Level of Concern

LOD	Level of Detection

LOEC	Lowest Observable Effect Concentration

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LOQ	Level of Quantitation

m	Meter(s)

MA	May Affect

MATC	Maximum Acceptable Toxicant Concentration

m2/day	Square Meters per Days

ME	Microencapsulated

mg	Milligram(s)

mg/kg	Milligrams per kilogram (equivalent to ppm)

mg/L	Milligrams per liter (equivalent to ppm)

mi	Mile(s)

mmHg	Millimeter of mercury

MRID	Master Record Identification Number

MW	Molecular Weight

n/a	Not applicable

NASS	National Agricultural Statistics Service

NAWQA	National Water Quality Assessment

NCOD	National Contaminant Occurrence Database

NE	No Effect

NLAA	Not Likely to Adversely Affect

NLCD	National Land Cover Dataset

NMFS	National Marine Fisheries Service

NOAA	National Oceanic and Atmospheric Administration

NOAEC	No Observable Adverse Effect Concentration

NOAEL	No Observable Adverse Effect Level

NOEC	No Observable Effect Concentration

NRCS	Natural Resources Conservation Service

OPP	Office of Pesticide Programs

OPPTS	Office of Prevention, Pesticides and Toxic Substances

ORD	Office of Research and Development

PCE	Primary Constituent Element

pH	Symbol for the negative logarithm of the hydrogen ion activity
in an aqueous solution, dimensionless

pKa	Symbol for the negative logarithm of the acid dissociation
constant, dimensionless

ppb	Parts per Billion (equivalent to |ig/L or |ig/kg)

ppm	Parts per Million (equivalent to mg/L or mg/kg)

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PRD	Pe sti ci de Re-Evaluati on Di vi si on

PRZM	Pesticide Root Zone Model

ROW	Right of Way

RQ	Risk Quotient

SFGS	San Francisco Garter Snake

SJKF	San Joaquine Kit Fox

SLN	Special Local Need

SMHM	Salt Marsh Harvest Mouse

TG	Tidewater Goby

T-HERPS	Terrestrial Herpetofaunal Exposure Residue Program
Simulation

T-REX	Terrestrial Residue Exposure Model

UCL	Upper Confidence Limit

USD A	United States Department of Agriculture

USEPA	United States Environmental Protection Agency

USFWS	United States Fish and Wildlife Service

USGS	United States Geological Survey

VELB	Valley Elderberry Longhorn Beetle

WP	Wettable Powder

wt	Weight

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1. Executive Summary

1.1. Purpose of Assessment

The purpose of this assessment is to evaluate potential direct and indirect effects on the delta
smelt (Hypomesus transpacificus) (DS) and California tiger salamander (Ambystoma
californiense) (CTS) arising from FIFRA regulatory actions regarding use of malathion (PC
code: 057701) on agricultural and non-agricultural sites. In addition, this assessment evaluates
whether these actions can be expected to result in modification of designated critical habitat for
the DS and CTS. The CTS is comprised of three threatened or endangered distinct population
segments (DPS's): Central California (CTS-CC), Santa Barbara County (CTS-SB), and Sonoma
County (CTS-SC). Except where noted, this assessment addresses risk to all three DPSs jointly.
This assessment was completed in accordance with the U.S. Fish and Wildlife Service (USFWS)
and National Marine Fisheries Service (NMFS) Endangered Species Consultation Handbook
(USFWS/NMFS, 1998) procedures outlined in the Agency's Overview Document (USEPA,
2004) and is consistent with a suit in which malathion was alleged to be of concern to the DS and
CTS (Center for Biological Diversity (CBD) vs. EPA et al. (Case No. 07-2794-JCS)).

The DS was listed as threatened on March 5, 1993 (58 FR 12854) by the USFWS (USFWS,
2007). DS are mainly found in slightly brackish water of the Suisun Bay and the Sacramento-
San Joaquin Delta Estuary near San Francisco Bay. During spawning DS move upstream into
freshwater habitats.

1.2. Scope of Assessment
1.2.1. Uses Assessed

Malathion is one of the most widely used insecticides in the U. S. for residential as well as
agricultural pest control. It is used throughout the state of California. Historically a predominant
agricultural use was cotton for the Boll Weevil Eradication Program. Currently, it is applied to a
large number of other agricultural commodities, including various vegetable, grain, fruit, nut
crops, and stored grains. Malathion is also used extensively in non-agricultural settings for adult
mosquito control by municipal vector control programs. Several uses of malathion were
removed during the recent reregi strati on process either because the uses were not supported or
were discontinued as part of the implementation of risk mitigation (see Appendix B, Verification

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Memorandum for Malathion for SF Bay Species). The remaining registered uses of malathion in
the United States are listed below.

Agricultural Uses

Grains, stored

Radish

Intermittently

Alfalfa

Grapes, raisin,

Rutabagas

flooded areas

Apricot

table, wine

Rice

Non-agricultural

Asparagus

Grass, forage, hay

Rye

rights-of-

Avocado

Grasses,

Salsify

way/fencerows

Barley

Bermuda,

Shallot

Non-agricultural

Beans, dry, snap,

Guava

Sorghum

uncultivated

lima

Hops

Spinach

areas/soil

Beets, garden

Horseradish

Squash, summer

Ornamental

Blueberry

Kale

Squash, winter

and/or shade

Broccoli, Chinese

Kohlrabi

Strawberry

trees

broccoli,

Kumquats

Sweet potatoes

Ornamental

broccoli rabb

Leeks

Swiss chard

herbaceous

Brussels sprouts

Lespedeza

Tomatoes,

plants

Cabbage

Lettuce, head

Tomatillos

Ornamental non-

Cantaloupe

Lettuce, leaf

Trefoil, birdsfoot

flowering plants

Caneberries

Lupine

Turnips

Ornamental

Carrots

Macadamia nut

Vetch

woody shrubs

Cucumber

Mango

Walnuts

and vines

Cauliflower

Melons

Watercress

Pine seed orchards

Celery

Mint

Watermelons

Refuse/solid

Cherries, sweet

Mushrooms

Wheat, spring and

waste containers

Cherries, tart

Mustard greens

winter

Refuse/solid

Citrus fruits

Nectarines

Wild Rice

waste sites

Clover

Oats

Yams

Swamps/marshes/

Collards

Okra

Agricultural,

stagnant water

Corn, field

Onions, bulb, and

uncultivated

Wide Area -

Corn, sweet and

green

areas

Public Health

pop

Papaya



Use

Chayote fruit

Parsley

Non-agricultural



Chayote root

Parsnip

Uses



Chinese greens

Passion fruit

Christmas tree



Clover

Pasture and

plantations



Cotton

rangeland

Cull piles



Currant

Peaches

Fence rows/hedge



Dandelion

Pears

rows



Dates

Peas, dried

Grain/cereal/ fl our



Eggplant

Peas, green

bins



Eggplant, oriental

Pecans

Grain/cereal/fl our



Endive (escarole)

Peppers

elevators



Fig

Pineapple

Household/



Flax

Potatoes

domestic



Garlic

Pumpkins

dwellings



15

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Malathion is registered for use to control a wide variety of insects and arachnids. Most
malathion products are formulated as an emulsifiable concentrate (EC) spray, ultralow-volume
(ULV) concentrate, or a dust. A few products are formulated as a powder or wettable powder.

1.2.2. Environmental Fate Properties of Malathion

Several open literature studies (Mulla et al 1981, Howard 1991) are consistent with data
presented by the registrant showing that malathion degradation is much slower under acidic
conditions compared to alkaline conditions. This is likely due to the extreme variation in
malathion hydrolysis rates with pH (hydrolysis Tm = 107, 6, and 0.5 days at pH 5, 7, and 9,
respectively). Malathion is stable to aqueous photolysis (Ti/2 = 98 and 143 days, corrected for
dark control) and soil photolysis (Ti/2 =173 days). It is likely that malathion can be metabolized
by soil microorgaisms, but the rate at which this occurs is somewhat uncertain due to the
necessary presence of water and the complications of factoring out the effects of hydrolysis.
Additional open literature studies suggest persistence on soil is longer under dry, sandy, low
nitrogen, low carbon, and acidic conditions (Walker and Stojanovic 1973).

The importance of other dissipation pathways must consider the conditions of use. For example,
volatilization (<5.1% of applied volatilized after 16 days) would be an important dissipation
pathway under dry and/or acidic conditions (urban environment or acidic soils), but would be
much less important under wet and basic conditions (typical of agricultural use). A complete
discussion of the environmental fate properties of malathion is given in Section 2.4.

1.2.3. Evaluation of Degradates and Stressors of Concern

The hydrolysis, metabolism, demethylation reactions that malathion undergoes under most use
conditions are similar to the biological reactions used by most biological entities to breakdown
and detoxify malathion. Therefore, the majority of malathion degradates are less toxic than the
parent. The major exception is the oxidation reaction that produces maloxon, which is more
toxic than malathion. (Maloxon is the active cholinesterase inhibiting metabolite of malathion.)

Other stressors of potential concern are impurities (chemicals that are not intentionally included
in the technical pesticide formulation). In general, impurity concentrations tend to decrease as
pesticide formulation methods improve over time. Because malathion has a long history
extending back to the 1950s, impurities have been reported in relatively high concentrations (see
section 2.2.1). However, EFED assumes modern malathion formulations contain much lower
concentrations of impurities.

Therefore, EFED considers maloxon, produced directly through oxidation of malathion, to be the
only degradate of concern. Maloxon has not been observed to form during any of the registrant-
submitted fate studies. However, it has been observed in urban surface runoff monitoring data
associated with the USDA's Medfly Eradication Program, and has been found to occur in
California rainwater (Vogel et al., 2008) and fog (Schomburg el al., 1991). Additionally,
California Department of Pesticide Regulation has measured maloxon production on dry,
microbially-inactive surfaces (steel plates) of up to 10%.

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A potential explanation of these observations is that malathion oxidation to maloxon in the
environment is slower than hydrolysis or metabolism. Therefore, under the environmental
conditions typical for agricultural uses and most nonagricultural uses (presence of water and
microorganisms), malathion is converted to hydrolysis or metabolism products before it can be
oxidized to maloxon. However under environmental conditions in which hydrolysis and/or
metabolism are not favored, EFED believes there may be potential for maloxon production (i.e.,
on dry, microbially-inactive surfaces such as the steel plates in the CDPR study or concrete,
glass or metal surfaces in malathion-treated urban and suburban areas). As part of the agency's
registration review process, a data call-in was issued for a study of maloxon production on dry
surfaces. This study has not been completed at this time.

Because EFED does not have the maloxon production estimates yet, and inclusion of maloxon
exposure would not alter the endangered species affect determination made by this assessment,
EFED has chosen to include maloxon in the risk assessment qualitatively, rather than to consider
it quantitatively. Therefore for those uses in which malathion is or may be applied to dry,
microbially-inactive surfaces (most notably, mosquito adulticide and refuse/solid waste
containers), the Estimated Environmental Concentrations (EECs) and Risk Quotients (RQs)
should be considered as low estimates as they do not account for the potential additional impact
of maloxon. However, for most uses on wet and microbially-active surfaces (most agricultural
and non-agricultural uses), little maloxon production is expected.

1.3. Assessment Procedures

A description of routine procedures for evaluating risk to the San Francisco Bay Species is
provided in Attachment 1.

1.3.1. Exposure Assessment

1.3.1.a. Aquatic Exposures

Aquatic exposure assessments were conducted to predict exposure of malathion to the delta
smelt, the California tiger salamander, and aquatic prey of these species. Tier-II aquatic
exposure models were used to estimate high-end exposures of malathion in aquatic habitats
resulting from runoff and spray drift. The models used to predict aquatic EECs for all uses
except aquatic agriculture (rice, wild rice, and water cress) are the Pesticide Root Zone Model
coupled with the Exposure Analysis Model System (PRZM/EXAMS). The AgDRIFT and
AGDISP models were used to estimate deposition of malathion on aquatic habitats from spray
drift. Peak PRZM/EXAMS estimated environmental concentrations (EECs) resulting from
malathion uses ranged from 0.614 to 89.8 |ig/L. EECs for aquatic agriculture were estimated
using the Tier-I Rice Model which calculates the upper limit of concentrations on a flooded field
based on direct application. This model does not account for degradation. Since malathion
degrades rapidly in soil and water, these estimates are likely overestimates of actual exposure.
The maximum peak EEC estimated for aquatic agriculture was 1120 |ig/L.

-------
These model estimates were supplemented with analysis of available California surface water
monitoring data from U. S. Geological Survey's National Water Quality Assessment (NAWQA)
program and the California Department of Pesticide Regulation (Section 3.2.3.a). The maximum
concentration of malathion reported by monitoring of surface waters in agricultural watersheds
since 1991 was 6.00 |ig/L (Gorder et al., 1996). This value is approximately 15 times less than
the maximum non-rice model-estimated environmental concentration. Because these samples
were not specifically targeted to malathion use areas and were not collected at sites similar to the
standard EXAMS pond (which is designed to present a high EEC scenario), these detections are
not expected to be directly comparable to PRZM/EXAMS EECs.

Monitoring targeted specifically to malathion applications was available from the various
monitoring and pest eradication efforts (Section 3.2.3.b). The highest concentrations measured
were in runoff samples associated with medfly eradication efforts in California, which resulted in
maximum concentrations of 583 |ig/L for malathion and 328 |ig/L for maloxon. This malathion
concentration is 6.5 times the highest PRZM/EXAMS EEC and approximately half the highest
Rice Model concentration estimate. Again because the application rates and use characteristics
vary between these studies and currently allowed applications, these targeted monitoring values
cannot be directly compared to the model estimates and non-targeted monitoring values.
However, the similarity in measured and modeled values should dispel any notion that the
modeled values are biased by orders of magnitude in one direction or another.

A number of studies have documented atmospheric transport and re-deposition of pesticides,
including malathion, from the Central Valley to the Sierra Nevada Mountains (Fellers et al.,
2004; LeNoir et al., 1999; McConnell et al., 1998; Sparling et al., 2001). Prevailing winds blow
across the Central Valley eastward to the Sierra Nevada Mountains, transporting airborne
industrial and agricultural pollutants into the Sierra Nevada ecosystems, where they are
deposited in rain and snow. Thus, long range transport may be an additional source of exposure
to CTS that breed in ponds which are located in higher elevations, especially in the foothills of
the Sierra Nevada Mountains to the east of the intensive use areas of the Central Valley.

1.3.1.b. Terrestrial Exposures

Terrestrial exposure assessments were conducted to estimate malathion exposures to the
terrestrial stage of the CTS and its terrestrial prey (small birds and mammals). The T-REX
model (ver. 1.4.1) was used for estimating exposure for screening level risk assessments, using
small mammals and birds as surrogates for amphibians. The T-HERP model (ver. 1.1) was used
to refine the exposure assessment for the CTS and to characterize dietary exposures of terrestrial-
phase salamander relative to the bird and mammal surrogates. The AgDisp model was also used
to estimate deposition of malathion on terrestrial habitats from aerial ULV spraying done for
adult mosquito control and other wide-area public health uses. For these uses, maximum
deposition rates estimated from aerial ULV spraying were input into the T-REX and T-HERPS
models in place of the typical application rates. The TerrPlant model was not used in this
assessment.

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1.3.2. Toxicity Assessment

The assessment endpoints include direct toxic effects on survival, reproduction, and growth of
individuals, as well as indirect effects, such as reduction of the food source and/or modification
of habitat. Federally-designated critical habitat has been established for the DS and CTS.

Primary constituent elements (PCEs) were used to evaluate whether malathion has the potential
to modify designated critical habitat. The Agency evaluated registrant-submitted studies and
data from the open literature to characterize malathion toxicity. The most sensitive toxicity
value available from acceptable or supplemental studies for each taxon relevant for estimating
potential risks to the assessed species and/or their designated critical habitat was used.

Section 4 summarizes the ecotoxicity data available on malathion. In general, malathion is
extremely toxic to fish, aquatic invertebrates, and terrestrial invertebrates, but is less toxic to
terrestrial vertebrates. Malathion is classified as very highly toxic to all freshwater and
estuarine/marine fish and invertebrates on an acute exposure basis. With chronic exposure, the
NOAEL and LOAEL for sublethal effects to freshwater invertebrates were determined to be
0.060 ppb and 0.10 ppb, respectively. Chronic toxicity levels for fish were higher (NOAEL =
8.6 ppb and LOAEL = 11 ppb). Malathion is classified as moderately toxic to birds on an acute
oral basis and slightly toxic to birds on a subacute dietary exposure basis. On a chronic basis, the
NOAEL and LOAEL for sublethal effects to birds are 110 mg/kg and 350 mg/kg, respectively.
For mammals, malathion is also classified as slightly toxic on an acute oral exposure basis. On a
chronic basis, the NOAEL and LOAEL for sublethal effects to mammals are 240 mg/kg and
1000 mg/kg, respectively. Malathion is classified as very highly toxic to honey bees on an acute
contact exposure basis. Data available from the open literature indicate that malathion has low
toxicity to plants.

1.3.3. Measures of Risk

Acute and chronic risk quotients (RQs) were compared to the Agency's Levels of Concern
(LOCs) to identify instances where malathion use has the potential to adversely affect the
assessed species or adversely modify their designated critical habitat. When RQs for a particular
type of effect were below the LOCs, malathion was considered to have "no effect" on that
species and its designated critical habitat. Where RQs exceeded one or more LOC, a potential to
cause adverse effects or habitat modification was identified, leading to a conclusion of "may
affect". If malathion use "may affect" the assessed species, and/or may cause effects to
designated critical habitat, the best available additional information was considered to refine the
potential for exposure and effects, and distinguished actions that were Not Likely to Adversely
Affect (NLAA) from those that were Likely to Adversely Affect (LAA).

1.4. Summary of Conclusions

Based on the best available information, the Agency makes a May Affect and Likely to
Adversely Affect determination for the Delta smelt (DS) and for all three DPSs of the California
tiger salamander (CTS) from the use of malathion. All uses of malathion are predicted to have
potential to cause mortality of aquatic and terrestrial invertebrates, thereby reducing the
availability of prey to both the DS and the CTS. For the DS, most uses of malathion are also

-------
predicted to have the potential to cause direct adverse effects by way of acute and chronic
toxicity. For the CTS, all uses of malathion are also predicted to have the potential to cause
direct adverse effects by way of acute toxicity, and most uses are predicted to have the potential
to cause chronic effects as well. Additionally, the Agency has determined that there is the
potential for modification of designated critical habitat of the DS and CTS from the use of this
pesticide. Malathion is predicted to have the potential to adversely affect the habitat of the DS
by contributing to degradation of water quality and by reducing prey availability. Malathion is
predicted to have the potential to adversely affect the habitat of the CTS by reducing prey
availability and potentially causing acute and chronic toxic effects on small mammals, thereby
potentially reducing the availability of small mammal burrows that the CTS uses for refugia. A
summary of the risk conclusions and effects determinations for each listed species assessed and
their designated critical habitat is presented in Table 1-1 and Table 1-2. Use-specific
determinations are provided in Table 1-3. Further information on the results of the effects
determination is included as part of the Risk Description in Section 5.2. Given the LAA
determination for the DS and the CTS, and the potential modification of designated critical
habitat for the DS and CTS, a description of the baseline status and cumulative effects for these
two species is provided in Attachment 2.

Table 1-1. Effects Determination Summary for Effects of Malathion on the Delta Smelt and
California Tiger Salamander

Species

Effects
Determination

Basis for Determination

Delta Smelt

Likely to

Potential for Direct Effects

(Hypomesus
transpacificus)

Adversely Affect
(LAA)

Aquatic-phase (Eggs, Larvae, and Adults):

Exposure from uses of malathion is expected to occur throughout the
entire range of the DS. Risk quotients exceed the Agency LOCs for listed
species. Mortality was observed in the rainbow trout (a freshwater fish)
and the sheepshead minnow (an estuarine/marine fish) with acute
exposure to malathion at concentrations less than one-twentieth the
malathion EEC, and reproductive impairment was observed in the flagfish
(a freshwater fish) and the bullhead (an estuarine/marine fish) with
chronic exposure to malathion at concentrations less than the chronic
EEC. In addition, numerous fish kills have been linked to malathion use.

Potential for Indirect Effects

Aquatic prey items, aquatic habitat, cover and/or primary productivity

Exposure from uses of malathion is expected to occur throughout the
entire range of the DS. Risk quotients exceed the Agency LOCs for taxa
that comprise the prey of the DS and indicate that use of malathion is
likely to reduce abundance of prey of the DS. Mortality was observed in
the water flea (a freshwater crustacean) and the mysid (an
estuarine/marine crustacean) with acute exposure to malathion at
concentrations much less than less than one-tenth the malathion EEC.
Reproductive impairment was predicted in the water flea (a freshwater
crustacean) and the mysid (an estuarine/marine crustacean) with chronic
exposure to malathion at concentrations much less than the chronic EEC
and less than some malathion concentrations from surface water samples
taken within the range of the DS.

California Tiger

Likely to

Potential for Direct Effects

Salamander

(Ambystoma

adversely affect
(LAA)

Aquatic-phase (Eggs, Larvae, and Adults):

-------
Species

Effects
Determination

Basis for Determination

californiense),
including Central,
Santa Barbara, and
Sonoma County
distinct population
segments



Aquatic exposure from uses of malathion is expected to occur throughout
the entire range of the CTS, including all DPSs. Risk quotients exceed the
Agency LOCs for listed species. Mortality was observed in the rainbow
trout (a freshwater fish, surrogate for freshwater amphibians) with acute
exposure to malathion at concentrations less than one-twentieth the
malathion EEC, and reproductive impairment was observed in the flagfish
(a freshwater fish, surrogate for freshwater amphibians) with acute
exposure to malathion at concentrations less than less than the chronic
malathion EEC.





Terrestrial-phase (Juveniles and Adults) :





Terrestrial exposure from uses of malathion is expected to occur
throughout the entire range of the CTS, including all DPSs. Risk
quotients exceed the Agency LOCs for listed species. Mortality was
predicted for CTS (based on acute toxicity data for the ring-neck pheasant
and Japanese quail, surrogates for the CTS) at dietary concentrations less
than one-tenth the acute EEC, and reproduction impairment was predicted
for CTS (based on reproduction toxicity data for the northern bobwhite) at
dietary concentrations less than the chronic EEC.





Potential for Indirect





Aquatic prey items, aquatic habitat, cover and/or primary productivity





Aquatic exposure from uses of malathion is expected to occur throughout
the entire range of the CTS, including all DPSs. Risk quotients exceed the
Agency LOCs for taxa that comprise the prey of the CTS and indicate that
use of malathion is likely to reduce abundance of prey of the CTS.
Mortality was observed in the water flea (a freshwater crustacean) with
acute exposure to malathion at concentrations much less than less than
one-tenth the malathion EEC. Reproductive impairment was predicted in
the water flea (a freshwater crustacean) with chronic exposure to
malathion at concentrations much less than the chronic EEC.





Terrestrial prey items, riparian habitat





Terrestrial exposure from uses of malathion is expected to occur
throughout the entire range of the CTS, including all DPSs. Risk
quotients exceed the Agency LOCs for taxa that comprise the prey of the
CTS. Mortality was observed in the honey bee and the rat (surrogates for
terrestrial prey of the CTS) at concentrations less than one-tenth the acute
EEC. Reproduction impairment was observed in the rat at concentrations
less than the chronic EEC.

Table 1-2. Effects Determination

Summary for the Critical Habitat Impact Analysis

Designated Critical
Habitat for:

Effects
Determination

Basis for Determination

Delta Smelt

(Hypomesus
transpacificus)

Habitat
Modification

Use of malathion has the potential to cause degradation of water quality in
the estuarine and freshwater habitats used by the DS.

California Tiger
Salamander

(Ambystoma
californiense),

Habitat
Modification

Use of malathion has the potential to cause acute and chronic effects to
small mammals, thereby potentially reducing the availability of burrows
on which the CTS depends for underground refugia.

21

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including Central,
Santa Barbara, and

Sonoma County
distinct population
segments

Table 1-3. Malathion Use-specific Risk Summary for Delta Smelt and California Tiger
Salamander



Species r.l'l'eels

( rilical llahilal

Polcnlial lor HITccls

1 sow

Dclcrminaliun1

Modil'icalion

Direct

Indirccl

Delta Smelt

All uses except passion
fruit, ULV application on
citrus, and ULV

LAA

Yes

Acute toxicity (all uses)
and chronic toxicity

Acute and chronic
toxicity, reduced prey
abundance, and

application for adult
mosquito control





(some uses)

degradation of water
quality

Passion fruit, ULV
application on citrus, and
ULV application for adult
mosquito control







Acute and chronic

LAA

Yes

None

toxicity, reduced prey
abundance, and
degradation of water
quality

California Tiger Salamander

All uses except ULV
application on citrus, and
ULV application for adult
mosquito control

LAA

Yes

Acute toxicity and
chronic toxicity

Acute toxicity to insects,
chronic toxicity to
mammals, acute toxicity
to mammals (some uses),
reduced prey abundance,
and reduction of mammal
burrows

ULV application on
citrus, and ULV
application for adult
mosquito control

LAA

Yes

Acute toxicity

Acute toxicity to insects
and reduced prey
abundance

1LAA = Likely to adversely affect

Based on the conclusions of this assessment, a formal consultation with the U. S. Fish and
Wildlife Service under Section 7 of the Endangered Species Act should be initiated.

When evaluating the significance of this risk assessment's direct/indirect and adverse habitat
modification effects determinations, it is important to note that pesticide exposures and predicted
risks to the listed species and its resources {i.e., food and habitat) are not expected to be uniform
across the action area. In fact, given the assumptions of drift and downstream transport {i.e.,
attenuation with distance), pesticide exposure and associated risks to the species and its resources
are expected to decrease with increasing distance away from the treated field or site of
application. Evaluation of the implication of this non-uniform distribution of risk to the species
would require information and assessment techniques that are not currently available. Examples
of such information and methodology required for this type of analysis would include the
following:

22

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• Enhanced information on the density and distribution of DS and CTS life stages
within the action area and/or applicable designated critical habitat. This
information would allow for quantitative extrapolation of the present risk
assessment's predictions of individual effects to the proportion of the population
extant within geographical areas where those effects are predicted. Furthermore,
such population information would allow for a more comprehensive evaluation of
the significance of potential resource impairment to individuals of the assessed
species.

• Quantitative information on prey base requirements for the assessed species.

While existing information provides a preliminary picture of the types of food
sources utilized by the assessed species, it does not establish minimal
requirements to sustain healthy individuals at varying life stages. Such
information could be used to establish biologically relevant thresholds of effects
on the prey base, and ultimately establish geographical limits to those effects.

This information could be used together with the density data discussed above to
characterize the likelihood of adverse effects to individuals.

• Information on population responses of prey base organisms to the pesticide.
Currently, methodologies are limited to predicting exposures and likely levels of
direct mortality, growth or reproductive impairment immediately following
exposure to the pesticide. The degree to which repeated exposure events and the
inherent demographic characteristics of the prey population play into the extent to
which prey resources may recover is not predictable. An enhanced understanding
of long-term prey responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and together
with the information described above, a more complete prediction of effects to
individual species and potential modification to critical habitat.

2. Problem Formulation

Problem formulation provides a strategic framework for the risk assessment. By identifying the
important components of the problem, it focuses the assessment on the most relevant life history
stages, habitat components, chemical properties, exposure routes, and endpoints. The structure
of this risk assessment is based on guidance contained in U.S. EPA's Guidance for Ecological
Risk Assessment (USEPA, 1998), the Services' Endangered Species Consultation Handbook
(USFWS/NMFS, 1998) and is consistent with procedures and methodology outlined in the
Overview Document (USEPA, 2004) and reviewed by the U.S. Fish and Wildlife Service and
National Marine Fisheries Service (USFWS/NMFS/NOAA, 2004).

2.1. Purpose

The purpose of this endangered species assessment is to evaluate potential direct and indirect
effects on individuals of the DS and CTS arising from FIFRA regulatory actions regarding use of
malathion for a wide variety of agricultural and non-agricultural uses. In addition, this
assessment evaluates whether these actions can be expected to result in modification of
designated critical habitat of the DS and CTS. For the California Tiger Salamander, the
assessment jointly discusses the Central California, Santa Barbara County, and Sonoma County

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distinct population segments (DPS's) except where noted. This ecological risk assessment has
been prepared consistent with the settlement of a suit in which malathion was alleged to be of
concern to the DS and CTS (Center for Biological Diversity (CBD) vs. EPA et al. (Case No. 07-
2794-JCS)).

In this assessment, direct and indirect effects to the DS and CTS and potential modification to
designated critical habitat for the DS and CTS were evaluated in accordance with the methods
described in the Agency's Overview Document (USEPA, 2004). Adverse effects to the Primary
Constituent Elements (PCEs) of each species were considered.

The DS was listed as threatened on March 5, 1993 (58 FR 12854) by the USFWS (USFWS,
2007). DS are mainly found in the Suisun Bay and the Sacramento-San Joaquin estuary near San
Francisco Bay. During spawning DS move into freshwater. The PCEs for DSs are shallow fresh
or brackish backwater sloughs for egg hatching and larval viability, suitable water with adequate
river flow for larval and juvenile transport, suitable rearing habitat, and unrestricted access to
suitable spawning habitat.

There are currently three CTS Distinct Population Segments (DPSs): the Sonoma County (SC)
DPS, the Santa Barbara (SB) DPS, and the Central California (CC) DPS. Each DPS is
considered separately in the risk assessment as they occupy different geographic areas. The
main difference in the assessment will be in the spatial analysis. The CTS-SB and CTS-SC were
downlisted from endangered to threatened in 2004 by the USFWS, however, the downlisting was
vacated by the U.S. District Court. Therefore, the Sonoma and Santa Barbara DPSs are currently
listed as endangered while the CTS-CC is listed as threatened. CTS utilize vernal pools, semi-
permanent ponds, and permanent ponds, and the terrestrial environment in California. The
aquatic environment is essential for breeding and reproduction and mammal burrows are also
important habitat for estivation. The PCEs for CTSs are standing bodies of freshwater sufficient
for the species to complete the aquatic portion of its life cycle that are adjacent to barrier-free
uplands that contain small mammal burrows. An additional PCE is upland areas between sites
(as described above) that allow for dispersal of the species.

In accordance with the Overview Document, provisions of the ESA, and the Services'
Endangered Species Consultation Handbook, the assessment of effects associated with
registrations of malathion is based on an action area. The action area is the area directly or
indirectly affected by the federal action, as indicated by risk quotients exceeding of the Agency's
Levels of Concern (LOCs). It is acknowledged that the action area for a national-level FIFRA
regulatory decision associated with a use of malathion may potentially involve numerous areas
throughout the United States and its Territories. However, for the purposes of this assessment,
attention was focused on relevant sections of the action area including those geographic areas
associated with locations of the DS and CTS and their designated critical habitat within the state
of California. As part of this assessment, "effects determination" identified one of the following
three conclusions for each of the assessed species in the lawsuits regarding the potential use of
malathion in accordance with current labels:

-------
• "No effect";

• "May affect, but not likely to adversely affect"; or

• "May affect and likely to adversely affect".

Additionally, for habitat and PCEs, a "No Effect" or "Habitat Modification" determination is
made.

A description of routine procedures for evaluating risk to the San Francisco Bay Species is
provided in Attachment 1.

2.2. Scope

The end result of the EPA pesticide registration process {i.e., the FIFRA regulatory action) is an
approved product label. The label is a legal document that stipulates how and where a given
pesticide may be used. Product labels (also known as end-use labels) describe the formulation
type {e.g., liquid or granular), acceptable methods of application, approved use sites, and any
restrictions on how applications may be conducted. Thus, the use or potential use of malathion
in accordance with the approved product labels for California is "the action" relevant to this
ecological risk assessment.

Historically, malathion has been one of the most widely used insecticides in the U. S. for
residential as well as agricultural pest control. It is used throughout the state of California. A
major historical use was on cotton in the boll weevil eradication program. However, it is also
applied to a large number of other agricultural commodities, including various vegetable, grain,
fruit, and nut crops, as well as stored grains. It has also been used extensively in non-agricultural
settings for residential insect control and for adult mosquito control by municipal vector control
programs.

Although current registrations of malathion allow for use nationwide, this ecological risk
assessment and effects determination address currently registered uses of malathion in portions
of the action area that are reasonably assumed to be biologically relevant to the DS and CTS and
their designated critical habitat. Because of the wide variety of agricultural and nonagricultural
uses of malathion, including residential uses, the action area for this assessment is considered to
be the entire state of California. Thus the spatial scope of this assessment is limited only by the
distribution of the DS and CTS, not by the action area for the use of malathion. Further
discussion of the action area relative to the DS and CTS and their critical habitat is provided in
Section 2.7.

2.2.1. Evaluation of Degradates and Other Stressors of Concern

Malathion degrades and transforms into a large number of chemicals (Table 2-1). Additionally,
technical malathion has historically contained impurities that account for up to 5% of the
insecticide. California Department of Food and Agriculture reported 15 impurities (Table 2-1) in
a representative ultra low volume malathion formulation (CalEPA 1981).

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Table 2-1. Impurities and Degradates Reported in Technical Malathion (CalEPA 1981)

Impurity as Listed in CalEPA (1.981)

% in
Technical

Synonym as in Appendix Table
D-l

Diethyl fumarate

0.90

Diethylfumarate (DEF)

Diethylhydroxy succinate

0.05

Diethylmaleate

0,0-dimethylphosphorothioate

0.05

Ion not in Appendix

0,0,0-trimethyl phosphorothioate

0.45

CAS No. 1186-09-0 Not in
Appendix

0,0,S-trimethyl phosphorodithioate

1.20

CAS No. 2953-29-9 Not in
Appendix

Ethyl nitrite

0.03

Not in Appendix

Diethyl-bis (ethoxycarbonyl) mercaptosuccinate

0.15

Cannot Identify1

S-1,2-ethyl-0,S-dimethyl phosphorodithioate

0.20

Isomalathion

S-( 1 -methoxycarbonyl-2-ethoxycarbonyl)ethyl-0,0-dimethyl
phosphorodithioate

0.60

Cannot Identify1

Bis-(0,0-dimethyl thionophosphoryl) sulfide

0.30

Cannot Identify1

Diethyl methylthiosuccinate

1.00

Cannot Identify1

S-ethyl-0,0-dimethyl phosphorodithioate

0.10

Cannot Identify1

S-l,2-bis (ethoxycarbonyl) ethyl-0,0-dimethyl phosphorothioate

0.10

Maloxon

Diethyl ethylthiosuccinate

0.10

Cannot Identify1

Sulfuric acid

0.05

Not in Appendix

1 Web-based searches for chemical synonyms only returned quotations of the original document (no synonyms).

Some malathion (and other organophosphate) impurities can potentiate malathion toxicity and
also are toxic alone, but there is almost no data available on their environmental fate. The
persistence of a phosphorothioate impurity (0,0,S-trimethyl phosphorothioate) was shown to be
18.7 times longer than malathion in an aerobic soil metabolism study (Miles and Takashima
1991). Some phosphorothioates and -dithioates have been intensively studied and induce a
delayed toxic effect to mammals at much lower levels than pure malathion (Ali Fouad and
Fukuto 1982, Umetsu et al 1977, Fukuto 1983, Aldridge et al 1979, Toia et al 1980). A
phosophorothioate and -dithioate impurity identified by CalEPA (1981) is of lower toxicity than
impurities reported in older formulations (Toia et al 1980). One hydrolysis product, diethyl
fumarate, which is also present as an impurity in technical malathion is approximately three
times more toxic to fathead minnows than malathion (Bender 1969). No guideline studies have
been conducted and little open literature data exist to define the fate and persistence of impurities
of malathion; however, most of the highly toxic impurities identified in past studies on malathion
(Ali Fouad and Fukuto 1982, Umetsu et al 1977, Fukuto 1983, Aldridge et al 1979, Toia et al
1980) have not been identified or are present only at low levels in more recently produced
technical malathion (CaEPA 1981 and confidential information provided by the registrant).

The relative concentration of malathion impurities can vary dramatically depending not only on
manufacturing processes but also storage conditions. Umetsu et al (1977) concluded "Storage of
technical malathion for 3 to 6 months at 40 degrees C resulted in materials which were
noticeably more toxic to mice." Therefore, the composition and toxicological properties of the
technical malathion are not only affected by initial purity, but also by storage conditions.

Similar to several other organophosphate insecticides, malathion degrades and is metabolized
into an oxon product that is more toxic than the parent compound. The oxon product of
malathion is called maloxon in this document, but also called malaoxon elsewhere. Chemically,
the only difference between malathion and maloxon is the substitution of oxygen for sulfur at its

26

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double bond to phosphorous (Structures provided in Table D-l of Appendix D). Metabolic
conversion of malathion into maloxon is called activation because it is the maloxon metabolite
that is responsible for most of the insecticidal activity of malathion, as well as most of its toxicity
to other nontarget animals. All other non-oxon degradation and metabolic products of malathion
exhibit much lower toxicity than maloxon. Thus, maloxon is the primary degradation
product/metabolite considered to be a significant concern for ecological risk. Although little or
no maloxon production is observed in registrant submitted aquatic and terrestrial exposure
studies, maloxon has been detected in surface waters, rain water, and fog (Schomburg et al.,
1990). Maloxon is also expected to form in the bodies of prey animals through
biotransformation processes.

Malathion impurities and degradates were evaluated for inclusion in the current risk assessment.
The hydrolysis, metabolism, demethylation reactions that malathion undergoes under most use
conditions are similar to the biological reactions used by most biological entities to breakdown
and detoxify malathion. Therefore, the majority of malathion degradates are less toxic than the
parent with the exception being maloxon.

Other stressors of potential concern are impurities (chemicals that are not intentionally included
in the pesticide formulation). In general, impurity concentrations tend to decrease as pesticide
formulation methods improve over time. Because malathion has a long history extending back
to the 1950s, impurities have been reported in relatively high concentrations. However, EFED
assumes modern malathion formulations contain much lower concentrations of impurities.

Historically, EFED has assessed maloxon based on study results showing a maximum maloxon
concentration observed in a soil aerobic metabolism study (MRID 41721701) of 1.8% of applied
malathion (USEPA 2006a, USEPA 2007a). However, this maloxon is present from the beginning
of this study and therefore, likely indicates that this maloxon is an impurity in the specific batch
of technical grade malathion rather than a degradate produced in this study.

A CDPR study (1981) found a 10% conversion of malathion to maloxon on dry surfaces in a
study that was cut short due to wet weather. The observation of maloxon production on dry
surfaces is a potential explanation of the high maloxon concentrations (up to 328 |ig/L) observed
in runoff water collected in conjunction with the Medfly Eradication Program in California.
EPA has requested a dry surface maloxon production study as well as several environmental fate
and effect studies from the registrant as part of the registration review process.

Due to uncertainty in the production of maloxon, EFED elected to consider maloxon
qualitatively rather than quantitatively in this assessment. Based on the findings in the CRLF
assessment, it is assumed that a quantitative assessment based on the parent chemical alone will
be sufficient to trigger a "likely to adversely affect" determination for all uses for indirect effects
as well as many of the uses for direct effects to the CTS and DS in the current assessment. In the
risk characterization section (5.2), the qualitative assessment of additional potential effects to the
CTS and DS of exposure to environmental sources of maloxon will be factored in to provide an
assessment of both malathion and maloxon.

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2.2.2. Evaluation of Mixtures

The Agency does not routinely include, in its risk assessments, an evaluation of mixtures of
active ingredients, either those mixtures of multiple active ingredients in product formulations or
those in the applicator's tank. In the case of the product formulations of active ingredients (that
is, a registered product containing more than one active ingredient), each active ingredient is
subject to an individual risk assessment for regulatory decision regarding the active ingredient on
a particular use site. If effects data are available for a formulated product containing more than
one active ingredient, it may be used qualitatively or quantitatively in accordance with the
Agency's Overview Document and the Services' Evaluation Memorandum (U.S., EPA 2004;
USFWS/NMFS/NOAA 2004).

Malathion has registered products that contain multiple active ingredients. Analysis of the
available acute oral mammalian LD50 data for multiple active ingredient products relative to the
single active ingredient is provided in Appendix J. Data were only available on a few products
and all measured values were nondefinitive (e.g., no effects were observed at the highest dose
tested). Given that the formulated products for malathion do not have LD50 data available, it is
not possible to undertake a quantitative or qualitative analysis for potential interactive effects.
Therefore, this assessment was based on the toxicity of the malathion alone.

In addition, several studies were located in the open literature that evaluated the potential
toxicological interactions of malathion and other pesticides. These studies are summarized in
Table 2-2. According to the available data, other pesticides may combine with malathion to
produce synergistic, additive, and/or antagonistic toxic effects. Greater than additive effects
have been demonstrated in birds, fish, and invertebrates when exposure to malathion was paired
with exposure to other pesticides, including atrazine, carbaryl, carbofuran, chlorpyrifos,
coumaphos, diazinon, EPN, fenthion, parathion, and trichlorfon (Table 2-2). If chemicals that
show such effects are present in the environment in combination with malathion, the toxicity of
malathion may be increased, offset by other environmental factors, or even reduced by the
presence of antagonistic contaminants if they are also present in the mixture. The variety of
chemical interactions presented in the available data set suggest that the toxic effect of
malathion, in combination with other pesticides used in the environment, can be a function of
many factors including but not necessarily limited to: (1) the exposed species, (2) the co-
contaminants in the mixture, (3) the ratio of malathion and co-contaminant concentrations, (4)
differences in the pattern and duration of exposure among contaminants, and (5) the differential
effects of other physical/chemical characteristics of the receiving waters (e.g., organic matter
present in sediment and suspended water). Quantitatively predicting the combined effects of all
these variables on mixture toxicity to any given taxa with confidence is beyond the capabilities
of the available data. However, a qualitative discussion of implications of the available pesticide
mixture effects data involving malathion on the confidence of risk assessment conclusions is
addressed as part of the uncertainty analysis for this effects determination.

28

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Table 2-2. Summary of Available Data That Evaluated Interactive Effects on the Toxicity of Malathion

Chemicals
Tested
(malathion +
chemical named)

Species Tested

Reported Effect

Endpoint Evaluated

Citation

Coumaphos
(Co-Ral)

Japanese Quail and

ring-necked

pheasants

Additive

Mortality

Kreitzer and Spann,
1973

EPN

Japanese Quail and

ring-necked

pheasants

Greater than additive

Mortality

Kreitzer and Spann,
1973

Parathion

Japanese Quail and

ring-necked

pheasants

Additive

Mortality

Kreitzer and Spann,
1973

Trichlorfon

Japanese Quail and

ring-necked

pheasants

Greater than additive

Mortality

Kreitzer and Spann,
1973

Aroclor 1262

Japanese Quail and

ring-necked

pheasants

Additive

Mortality

Kreitzer and Spann,
1973

Parathion

Bluegill

Greater than additive

Mortality

Macek, 1975

Fenthion (Baytex)

Bluegill

Greater than additive

Mortality

Macek, 1975

Carbaryl (Sevin)

Bluegill

Greater than additive

Mortality

Macek, 1975

EPN

Bluegill

Greater than additive

Mortality

Macek, 1975

Ethylan
(Perthane)

Bluegill

Greater than additive

Mortality

Macek, 1975

DDT

Bluegill

Additive

Mortality

Macek, 1975

Toxaphene

Bluegill

Additive

Mortality

Macek, 1975

Copper Sulfate

Rainbow trout

Less than additive

Mortality

Macek, 1975

Diazinon

Coho Salmon

Greater than additive

Acetylcholinesterase
inhibition

Laetz et al., 2009

Chlorpyrifos

Coho Salmon

Greater than additive

Acetylcholinesterase
inhibition

Laetz et al., 2009

Carbaryl

Coho Salmon

Greater than additive

Acetylcholinesterase
inhibition

Laetz et al., 2009

Carbofuran

Coho Salmon

Greater than additive

Acetylcholinesterase
inhibition

Laetz et al., 2009

Atrazine

Midge

Greater than additive

Mortality

Pape-Lindstrom and
Lydy,1997

Endrin

Flagfish

Additive

Growth

Hermanutz et al., 1985

2.3. Previous Assessments

There is a long history of assessments for malathion because malathion has been used as a
pesticide since the 1950s. The following sections summarize the most recent assessments and
those most salient to endangered species issues.

2.3.1. Malathion Registration Eligibility Decision, 2006

In 2006, the Agency completed a screening-level ecological risk assessment in support of the
Reregi strati on Eligibility Decision (RED) for malathion (USEPA 2006a). The RED was finalized
as part of the organophosphate cumulative assessment (USEPA 2006b). The RED assessment

29

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was based on data collected in the laboratory and in the field to characterize the fate and
ecotoxicological effects of malathion. Data sources used in this assessment included: 1)
registrant submissions in support of reregi strati on, 2) publicly available literature on ecological
effects, 3) monitoring data for freshwater streams, lakes, reservoirs, and estuarine areas, 4)
incident reports of adverse effects on aquatic and terrestrial organisms associated with the use of
malathion.

The ecological risk assessment in the RED concluded that use of malathion poses a high risk of
mortality to fish and aquatic invertebrates from acute toxicity. Almost all uses are expected to
pose a high risk of adversely effecting aquatic invertebrate populations, especially in urban
streams and wetlands. High acute risk is also expected to fish and amphibians for uses with
higher application rates or repeated applications. Numerous incidents of fish kills confirm the
acute risk to fish. Use of malathion is generally not expected to pose a high risk of mortality to
terrestrial wildlife (birds, mammals, and reptiles, terrestrial stages of amphibians) although the
acute level of concern (LOC) is exceeded for some uses with high application rates and repeated
applications. Use of malathion poses a risk of impairing reproduction in birds, and may cause
other sublethal effects in wildlife. Although no risk assessment was conducted for beneficial
insects, the RED concluded that use of malathion poses a hazard to bees and other insect
pollinators based on evidence from toxicity studies, field studies, and incidents. Bees may be
harmed from direct exposure, exposure to foliar residues, and exposure to residues on pollen
brought back to the hive.

The ecological risk assessment in the RED concluded that use of malathion could potentially
harm all taxa of threatened and endangered animals. Risk quotients exceeded the level of
concern for threatened and endangered species of fish, aquatic invertebrates, birds, and
mammals.

2.3.2. Organophosphate Cumulative Assessment, and Malathion
Reregistration Eligibility Decision, 2006

Because the Agency had determined that malathion shares a common mechanism of toxicity
with the structurally-related organophosphates insecticides, a cumulative human health risk
assessment for the organophosphate pesticides was necessary before the Agency could make a
final determination of reregistration eligibility of malathion. This cumulative assessment was
finalized in 2006 (USEPA 2006b). The results of the Agency's ecological assessments for
malathion are discussed in the July 2006 final Reregistration Eligibility Decision (RED) (USEPA
2006a).

2.3.3. California Red-legged Frog Endangered Species Assessment

The Agency recently completed an endangered species risk assessment of the potential effects of
malathion and maloxon on the threatened California red-legged frog (Rana aurora draytonii;
CRLF) arising from uses of malathion (USEPA 2007a). Uses included in this 2007 assessment
reflected some post-RED mitigations. This endangered species risk assessment was part of the
Center for Biological Diversity (CBD) vs. EPA et al. (Case No. 02-1580-JSW(JL)) settlement
entered in the Federal District Court for the Northern District of California on October 20, 2006.

-------
The assessment resulted in a determination that the use of pesticide products containing
malathion is likely to adversely affect the CRLF. This determination is based on the potential for
malathion use to both directly and indirectly affect the species and result in modification to
designated critical habitat.

Toxicity values used in this document are in some cases different than those used in the
malathion RED and those used in the current assessment of risk to the DS and CTS. Although
the RED was published in 2006, following completion of the organophosphate cumulative
assessment, the ecological risk assessment was compiled in 1999, prior to the regular
incorporation of open literature ecotoxicological (ECOTOX) data into EFED risk assessments.
Review of the open literature data resulted in a number of lower toxicity endpoints used in the
CRLF assessment. Risk conclusions are similar, in that listed species LOCs are exceeded, but
the risk quotients (RQs) presented in the CRLF assessment are higher than corresponding RQs in
the RED. In this current assessment for the DS and CTS, open literature data have been further
evaluated and toxicity endpoints have been further revised. Some of the toxicity endpoints were
revised higher relative to those used in the CRLF document, and thus some of the RQs have
decreased in this current assessment relative what was reported in the CRLF assessment.

2.3.4. Pacific A nadromous Salmonids Endangered Species Assessment

The Agency completed an endangered species risk assessment of the potential effects of
malathion on 26 listed Evolutionarily Significant Units (ESUs) of Pacific salmon and steelhead
arising from FIFRA regulatory actions regarding use of malathion (USEPA 2004a). This risk
assessment was part of the Washington Toxics Coalition us. EPA (Case No. C01-132C) order
entered in the Federal District Court for the Western District of Washington on July 2, 2002. The
assessment concluded that malathion is toxic to fish as well as to organisms that serve as food for
threatened and endangered Pacific salmon and steelhead. The final conclusion was that the uses
(at that time) of malathion (and its degradate maloxon) may affect 24 of these ESUs.

On November 18, 2008, the National Oceanic Atmospheric Administration National Marine
Fisheries Service (NMFS) issued a final biological opinion on the effect of pesticide products
containing malathion, chlorpyrifos, or diazinon on 28 listed Pacific salmonids (National Marine
Fisheries Service, 2008). This opinion concluded that the effects of registration of pesticide
products that contain malathion or the two other active ingredients is likely to jeopardize the
continued existence of 27 of the 28 species of Pacific salmonids. They concluded that these
pesticides are not likely to jeopardize the continued existence of Ozette Lake Sockeye salmon,
but may adversely affect that species. Furthermore, they concluded that registration of these
products is likely to destroy or adversely modify 25 of the 26 critical habitats that have been
designated for these Pacific salmonids. The only critical habitat that they concluded would not be
adversely modified is that of the Ozette Lake Sockeye salmon. This Biological Opinion is
available on the internet (http://www.nmfs.noaa.gov/pr/pdfs/pesticide biop.pdf).

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2.4. Environmental Fate Properties

Endangered species may be exposed to malathion and its degradates through contamination of
food, water, and air (by suspended particles) which can result from off-target drift, runoff, and
direct application. Increased toxicity may be brought about through oxidation (to maloxon).
Limited data are available on toxic degradates and impurities, but the fate data provided to EFED
for malathion and maloxon was found to be acceptable for performing risk assessment (USEPA
2006) and shows that malathion, typically, will have little persistence in the environment.

Based on registrant submitted data and open literature reports, EFED concludes the primary
routes of dissipation of malathion in surface soils appear to be microbially-mediated soil
metabolism (half-lives measured as <1 to 2.5 days) and hydrolysis (pH 5, 7, and 9 half-lives of
107 days, 6.21 days, and 12 hours, respectively). Malathion monoester, ethyl hydrogen
fumarate, diethyl thiosuccinate, malathion mono- and dicarboxylic acids, demethyl mono- and
di-carboxylic acids, and CO2 are known degradates. Table 2-3 lists the physical-chemical
properties of malathion and maloxon.

Table 2-3. Physical-chemical Properties of Malathion and Maloxon

Property

Malathion (Parent Compound)

Maloxon (Transformation Product)

Value and units

MRID or Source

Value and units

MRID or Source

Molecular Weight

330.3 g/mole

Product Chemistry

314.3 g/mole

MRID 46396601

Chemical Formula

C10H19O6PS2

Product Chemistry

C10H19O7PS

MRID 46396601

Vapor Pressure

4 x 10"5 Torr @ 30°C

Product Chemistry

1.02x 10"4Torr

EPIWeb 4.0
(modified Grain
method)

Henry's Law Constant

1.2 x 10"7 atm-m3/mole
(ci>, 25°C

Estimated1

1.2 x 10"8 atm-m3/mole
25°C

Estimated1

Water Solubility

145 mg/L @ 25°C

Product Chemistry

7500 mg/L
50-100 g/L @ 20°C

NIH NTP Reports
web-site cited in

EPIWeb 4.0
MRID 46396601

Octanol - water partition
coefficient (K0w)

613 (Log Kow = 2.79)
628 (Log Kow = 2.80)

560 (Log Kow = 2.748)

2000 (Log Kow = 3.30)
195 (Log Kow = 2.29)

40119201
158054 and

158062
40944103,
40944104, and
40944108
40966603
EPIWeb 4.0

3.31 (Log Kow = 0.52)

EPIWeb 4.0

Dissociation Constant (pKa
and/or pKb)

13.18/M-hr

EPIWeb 4.0

144.7/M-hr

EPIWeb 4.0

Air-water partition
coefficient (KAw)

2 x 10"7

EPIWeb 4.0

2.2 x 10"8

EPIWeb 4.0

Octanol-air partition
coefficient (K0A)

1.15 x 109

EPIWeb 4.0

1.5 x 108

EPIWeb 4.0

1 Calculated according to USEPA 2002 by: (VP*MW)^-(760*solubility).

Table 2-4 lists the other environmental fate properties of malathion, along with the major and
minor degradates detected in the submitted environmental fate and transport studies.

32

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Table 2-4. Summary of Malathion Environmental Fate Properties

Studv

Value and unit

Major and Minor
Dejjradates

MRI D #

or
Citation

Study
Classification,
Comment

Abiotic Hydrolysis @
25°C

Half-life1 =
107 days, pH 5
6 days, pH 7
0.5 days, pH 9

MCA - major @ pH 7 & 9;

minor @ pH 5
MEF - major @ pH 7 & 9;

minor @ pH 5
DETS - major @ pH 7 & 9
DCA - minor @ pH 7 & 9

40941201

Acceptable

Aqueous photolysis dark

controls:

250 days, pH 4 (non-

sensitized)

219 days, pH 4 (sensitized)

Not measured

41673001

Acceptable

Air Photolysis

Assumed Stable

NA

40969301

Unacceptable

Direct Aqueous
Photolysis

Half-life1 = 97.88 days, pH 4

MCA - not quantified
Several other peaks - not
quantified or confirmed

41673001

Acceptable

Soil Photolysis

Stable (173 days), sandy loam
soil

3 degradates were not
identified

41695501

Supplemental

Aerobic Soil Metabolism3

Half-life1 = 16.3 days, loam

a-MCA - minor
(3-MCA - minor
DCA - major

41721701

Supplemental

Half-life1 =
5.3 days, silty clay
5.1 days, silty loam
4.7 days, sand
4.5 days, silty loam

a-MCA - minor
(3-MCA - major (minor in

sand only)

DCA - major

46769501

Currently being
evaluated

Half-life1 = 25 days, loamy
sand

MCA - minor
DCA - major

47834301

Currently being
evaluated

Anaerobic Soil
Metabolism

Half-life1 < 30 days, loamy
sand

Not quantified

47834301

Currently being
evaluated

Aerobic Aquatic
Metabolism

Half-life1 =

Pond in Macon Co., IL:
1.09 days in water2 pH 8.5
1.09 days in sediment2 Sand,
pH 7.8

1.09 days in total system

MCA - major
DCA - major
dMCA - major
dDCA - minor, but
increasing at study
termination (30 days)

42271601

Supplemental

Anaerobic Aquatic
Metabolism

Half-life1 =

Pond in Macon Co., IL:
2.54 days in water2 pH 8.7
2.54 days in sediment2
Sandy loam, pH 7.8
2.54 days in total system

MCA - major
DCA - major
dMCA - major
dDCA - major

42216301

Supplemental

Soil-water distribution
coefficient (Kd)

Kd =

0.5 L/kg, sandy loam
0.82 L/kg, loam
0.87 L/kg, sand
14.2 L/kg, silty clay

MCA - major
DCA - major

43868601

Acceptable

33

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St u (J v

Value and unit

Major and Minor
Dcjjradatcs

MRID#

or
Citation

Study
Classification,
Comment

Organic-carbon
normalized distribution
coefficient (Koc)

Koc =

151 L/kg, sandy loam
267 L/kg, sandy loam
308 L/kg, sand
176 L/kg, loam
183 L/kg, silt loam

MCA - minor
DCA - minor

41345201

Acceptable

Volatility from Soil
(Laboratory)

<5.1% volatilized by 16 days,
silt loam

NA

42015201

Acceptable

Terrestrial Field
Dissipation

Dissipation Half-life1'2 =
<2 day, Cotton, CA

DCA

41727701
43042402

Acceptable

Dissipation Half-life1'2 =
To rapid to determine, Cotton,
bare ground, GA

DCA

41748901
43042401

Acceptable

Aquatic Field Dissipation

rice paddy, CA

NA

42058401

Unacceptable

rice paddy, MO

NA

42058402

Unacceptable

Bioconcentration Factor
(BCF)- Species Name

Steady State BCF=

23 to 135 L/kg wet wt whole

fish

4.2 to 18 L/kg wet wt edible
tissue

37 to 204 L/kg wet wt
nonedible tissue

MCA - major
DCA - minor
Maloxon - minor
dMalathion - minor
MEF - minor
oxalacetic acid - minor

43106401

43106402
43340301

Acceptable

Abbreviations: DCA = malathion dicarboxylic acid; dDCA = malathion demethyl dicarboxylic acid; DETS =
diethyl thiosuccinate; dMCA = malathion demethyl monocarboxylic acid (a and/or (3 forms); MCA =
malathion monocarboxylic acid (a and/or (3 forms); MEF = monoethyl fumerate; OA = oxalacetic acid; wt
= weight. Chemical structures appear in Appendix Table Dl. Some studies reported a and (3 forms of
malathion monocarboxylic acid or demethyl monocarboxylic acid as total rather than as each chemical
separately.

1	Half-lives were calculated using the single-first order equation and nonlinear regression, unless otherwise

specified.

2	The value may reflect both dissipation and degradation processes.

3	Aerobic soil metabolism half-lives are extremely biphasic with short initial half-lives of less than a day for

the first ~48 hours; followed longer halflives of >10 days.

Hydrolysis: Hydrolysis rates of malathion vary dramatically with pH (107 days at pH 5 to 0.5
days at pH 9). Similarly, maloxon hydrolysis rates also vary dramatically with pH (32 days at pH
5 to 0.16 days at pH 9), but are in general somewhat faster than the analogous (same pH)
hydrolysis rates for malathion.

Aerobic soil Metabolism : Aerobic soil metabolism is the only route of degradation that appears
to result in a faster degradation rate than hydrolysis for malathion. Malathion persistence under
aerobic soil conditions has been examined in several open literature studies which are reviewed
in Table 2-5. Reported half-life values (from field and laboratory studies) vary from hours to 11
days. Persistence is decreased with microbial activity, moisture, and high pH.

34

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Table 2-5. Open Literature Studies Reporting Aerobic Soil Metabolism Degradation Rates

Sou rce

Degradation Rate Value

Comments

Miles and Takashima 1991

t/2 = 8.2 h (laboratory)
t/2 = 2 h (field)

Malathion was mixed with Lihue soil
and incubated at 22°C in lab
experiment. Sterilization decreased
rate by 2-fold.

Walker and Stojanovic 1974

47-95% at 7 days

Malathion was incubated with various
Arthrobacter species. Degradation in
the presence of the 5 most efficient
species was reported.

Walker and Stojanovic 1973

t/2 = ~ 2 days under non-sterile
unfavorable degradation conditions.

In 3 Mississippi soils examined at 25-
26°C, soil microflora were important
in degradation. Slowest degradation
occurred in soils with low nitrogen,
moisture, and carbon content and
increased acidity.

Ca.1F,PA 1996

DT50 = 4.2-6.9 days on sand

Measured at 5 sites under the
conditions of the medfly eradication
program. Each site consisted of 10
aluminum trays containing 500g of
playground sand. Between
applications trays were covered.

Ca.1F.PA 1993

DT50 < 12 h on sand

Application was under controlled
conditions, but temperature was not
noted.

Ca.1F.PA 1993

soil:

38% remaining at 12 hours
15% remaining at 20 days

66% sand, 24% silt, 10% clay, 0.78%
water, pH 6.3. Malathion was applied
under controlled conditions.
Degradation was biphasic.

Kearney el al 1969

75-100% degradation in 1 week

Field persistence

Lichtenstein and Schultz 1964

85% dissipation in 3 days

Conducted under field conditions

Howard 1991

Reported average literature

t/2 = 6 d

In this review, persistence is stated to
vary with moisture content and pH.

USD A

t/2 = 3 days used for modeling

This value was chosen for modeling
malathion in the Boll Weevil
Eradication Program based on a
personal communication with a
previous malathion registrant.

In the three aerobic soil metabolism registrant submitted studies, half-lives are biphasic with
short initial half-lives of less than a day for the first -48 hours; followed by longer half-lives of
>10 days. The first study has been reviewed by the agency, while the last two studies were only
recently submitted and are currently under-going review.

In the first registrant submitted study, [2,3-14C]malathion initially degraded with a calculated
half-life of -0.2 days (based on the first 48 hours of study data) and subsequently degraded with
a half-life of -24 days (based on the study data from 48 hours to study termination at 92 days)
using loam soil (pH 6.1) incubated in the dark at 22 ± 2°C and 75% of field capacity. An
ancillary experiment was conducted to determine the rate of degradation of malathion in sterile
soil. At 4 days post-treatment, malathion comprised close to 100% of the applied radioactivity in

-------
sterile soil (97.84% of the extractable radioactivity). The difference between half lives of the
sterile and non-sterile treatments indicates that microorganisms are important in the rapid
degradation of malathion in soil under acidic aerobic conditions.

Numerous degradates or impurities were identified in the soil extracts and are identified as
follows as a percent of applied radioactivity: dicarboxylic acid of malathion (18.7 - 36.7%), the
P-monocarboxylic acid of malathion (2.8 - 7.3%), the a-monocarboxylic acid of malathion (1.9 -
2.5%>), and maloxon (0.6 - 1.8%). However, the variation of maloxon concentrations with time
appears to indicate that it occurs as an impurity (maloxon is present at the beginning of this study
and declines over time) rather than a degradate (which would be expected to form over the
course of the study) (MRIDs 41721701 and 43166301).

Two additional aerobic soil metabolism studies were recently submitted to the agency, and are
currently under review.

Anaerobic Aquatic Metabolism: An open literature study (Bourquin 1977) and the registrant's
study suggest that malathion persistence in anaerobic environments is short; however, due to the
high pH in the registrant's study a quantitative assessment of the degradation and degradation
products could not be performed.

In the registrant submitted anaerobic aquatic metabolism study, [2,3-14C]- and technical grade-
malathion added to a sandy loam soil degraded with a half-life of approximately 2.5 days in
sediment (pH 7.8) and water (pH 8.7). This study provides useful information, but hydrolysis
was probably the main route of degradation in the study since the pH of the system was in the
basic range which favors hydrolysis. Although most of the residues remained in the water phase
(less than 20% of the applied radioactivity was associated with the soil at any sampling interval),
the degradation products were similar in both sediment and water phases. The degradation
products at maximum concentrations in the water phase were the monocarboxylic acid of
malathion (MCA, 28% at Day 4), demethyl monocarboxylic acid (21% at Day 7), dicarboxylic
acid (21 % at Day 14) and the demethyl dicarboxylic acid metabolite (39% at Day 45). The
degradation products at maximum concentrations in the sediment were the monocarboxylic acid
of malathion (4.5% at 6 hours), demethyl monocarboxylic acid (8.1% at Day 45), and
dicarboxylic acid (5.2% at Day 4). The EFED calculated half-life for malathion monocarboxylic
acid was 11 days.

Aerobic Aquatic Metabolism: USGS monitoring studies (Kratzer 1998, Domagalski, 2000) show
detections of malathion in large rural and urban streams. Many open literature studies have been
conducted on the fate and persistence of malathion in the aquatic environment. Reported
degradation rates vary and are likely to be significantly increased by biodegradation and pH.
Eichelberger and Lichtenberg (1971) found 75% and 90% degradation in river water in one and
two weeks, respectively. Guerrant et al (1970) found malathion half lives in pond, lake, river and
other natural waters varied from 0.5 to 10 days and was dependent on pH. Other studies are
summarized in Mulla et al (1981) and Howard (1991).

Registrant submitted studies were conducted under alkaline conditions which favor hydrolysis.
Thus, degradation rate and products may not be representative of acidic aquatic conditions. In the

36

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registrant submitted aerobic aquatic metabolism study, a mixture of [2,3-14C]- and technical
grade-malathion added to a sandy loam soil rapidly degraded in the aerobic aquatic environment
with half-lives of approximately 1.09 days in the water phase (pH 7.8) and 2.55 days in sediment
(pH 8.5). As mentioned previously, hydrolysis was probably the main route of degradation in the
study since the pH of the system was in the basic range and hydrolysis occurs most rapidly at pH
9. Major degradates in water and soil were similar: mono- and dicarboxylic acids of malathion,
demethyl monoacid and demethyl diacid, while in sediment no demethyl diacid was detected.
The EFED calculated half-life for malathion monocarboxylic acid was 3 days.

Terrestrial field dissipation: Data from open literature and registrant-submitted field dissipation
studies indicate that malathion dissipates rapidly when applied in the field. Open literature
studies provide varying rates of terrestrial dissipation. Mulla etal (1981) summarizes
degradation results from several field studies including: no residues after 6 months (Roberts et al
1962), and 85% degradation in 3 days and 97% in 8 days (Lichtenstein and Schulz 1964). The
fastest route of terrestrial field dissipation is generally accepted to be microbial degradation.

In a registrant submitted field dissipation study using a rate of 1.16 lb ai/A, malathion or
maloxon residues were detected at <10 |ig/kg in the 0-6" layer in cotton/bare ground sites in GA.
Due to the sampling depth it is not possible to determine how much malathion remained at the
soil surface relative to that which moved through the first six inches. Residues detected in the
plots in the 6-12" layer after the 2nd, 3rd, 4th, and 5th treatments averaged 35, 37, 5.6, and 9.4
|ig/kg, respectively. Malathion was detected in the 12-18 inch soil depth at 16 |ig/kg in one
replicate soil sample; however, the detection was attributed to contamination. The detection of
malathion below six inches along with the low Kd values reported for malathion make it feasible
that leaching below 12 inches may have occurred in the field dissipation studies. The terrestrial
field dissipation half-life could not be determined due to the rapid dissipation of malathion,
although it is probably <1 day (MRID 41748901, 43042401, 43166301).

In a field dissipation study located in California, malathion was applied at a maximum rate of
1.16 lb ai/A once a week for 6 weeks. The resulting dissipation half-life was <0.2 days. In certain
instances, malathion was detected below the 12 inch soil depth. No degradates were detected
(MRID 41727701, 43042402, 43166301).

Aquatic field dissipation:

In the registrant aquatic field dissipation study located in Missouri, malathion was applied at a
maximum rate of 0.58 lb ai/A in three weekly applications to a flooded rice paddy (soil pH 6.1,
water pH not stated). Malathion residues detected in water samples collected after the first and
second application dissipated to below the detection limit (10 |ig/L) in samples taken prior to the
second and third applications. In water samples collected one day after the last application,
malathion concentrations averaged 17 |ig/L and had decreased to 10 |ig/L by the second
sampling day. Maloxon residues were <10 |ig/L at all sampling dates.

The data indicate a very rapid dissipation of malathion in water, probably <1 day. An accurate
half-life could not be determined because of the rapid dissipation (MRID 42058402, 43166301).

-------
A second aquatic field dissipation study performed in California was considered invalid because
it seems that only 1-2% of the intended amount of malathion was applied (MRID 42058401,
43166301).

Accumulation in Fish. Aquatic bioconcentration factors ranging from 7.36 (lake trout), 29.3
(coho salmon), 869 (white shrimp), to 959 (brown shrimp) are summarized in Howard (1991).

The registrant submitted study shows [14C]malathion residues did not significantly accumulate in
bluegill sunfish exposed to 0.99 |ig/L [14C]malathion in a flow-through system for 28 days.
Average concentrations of malathion were 3.9 to 18 |ig/kg in the edible portions of fish, 21 to
130 |ig/kg for whole fish, and 34 to 200 |ig/kg in the non-edible tissue. [14C]malathion residue
equivalents in the edible fish tissue during depuration ranged from 18 |ig/kg at the start to 4.8
|ig/kg by day 14. Whole fish concentrations decreased from 110 to 4.5 |ig/kg and non-edible fish
concentrations decreased from 150 to 5.8 |ig/kg after day 14. Approximately 73, 96, and 96% of
the radioactivity depurated by day 28 from the edible, whole, and non-edible portions of fish,
respectively.

The only residue detected in fish tissue at >10% of total radioactive residues (TRR) was
malathion monocarboxylic acid (MCA) in concentrations of 33.3-35.9% (44.8-61.2 |ig/kg) of
TRR. Up to 22 other components were present in levels of 0.1 to 5.7% (0.1 to 7.7 |ig/kg) and
included malathion dicarboxylic acid (DCA), maloxon, desmethyl malathion,
monoethylfumarate, and oxalacetic acid. Maloxon was present in concentrations <2.7 |ig/kg;
while parent malathion was present in concentrations of 0.2 |ig/kg at the end of the depuration
period.

Maximum BCFs, as a function of total radioactive residues present, ranged from 4.2 to 18, 23 to
135, and 37 to 204 for edible, whole fish, and non-edible, respectively (MRID 43106401,
43106402, 43340301).

Table 2-6 lists the other environmental fate properties of maloxon, along with the major and
minor degradates detected in the submitted environmental fate and transport studies. Maloxon
only differs structurally from malathion in the substitution of oxygen for sulfur at the double
bond with phosphorus. Because both chemicals are very similar in form, both degrade into
similar chemicals with the exception of the oxygen/sulfur substitution.

Table 2-6. Summary of Maloxon Environmental Fate Properties

Studv

Value and unit

Major and Minor
Degradates

MRID#

or
Citation

Study
Classifieation,
Comment

Abiotic Hydrolysis @
25°C

Half-life1 =
32 days, pH 5
9 days, pH 7
0.16 days, pH 9

DEMS - major @ pH 9
DEF - major @ pH 9;

minor @ pH 5 & 7
DMM - major @ pH 5 & 7
MA - major @ pH 7 & 9
DSD - major @ pH 9;

minor @ pH 5 & 7
Other - major @ pH 7 & 9;
minor @ pH 5

46396601

Acceptable

1 Half-lives were calculated using the single-first order equation.

38

-------
DEMS = Diethyl mercaptosuccinate; DEF = Diethyl fumarate; DMM = Desmethyl maloxon; MA = a & (3
monoacids; DSD = Disulfide dimer; Other = regions of the chromatograms not associated with known
compounds (no individual "other" peaks exceeded 7.9% of applied radioactivity).

The aerobic half-life of maloxon has been reported as three and seven days in basic and acidic
soils, respectively (Paschal and Neville 1976). This longer half-life relative to malathion is
proposed to be a result of maloxon's biocidal effect on soil microbes which contribute to
malathion's degradation.

2.4.1. Environmental Transport Mechanisms

Potential transport mechanisms include pesticide runoff to surface water, spray drift, and
secondary drift of volatilized or soil-bound residues leading to deposition onto nearby or more
distant ecosystems (>1000 ft). Runoff and spray drift are expected to be the major routes of
exposure for malathion.

Data suggest that important routes of dissipation of malathion from soil are leaching and surface
runoff. Malathion and its degradates, in general, are soluble and do not adsorb strongly to soils.

Acceptable adsorption/desorption data on parent malathion indicate that it is mobile to
moderately mobile in all soils tested (based on the FAO classification system, Kocs range from
151-308 L/kg; FAO 2000). Acceptable terrestrial field dissipation data indicate rapid dissipation
(T1/2 = <2 days). One detection of malathion below 12 inches was found in a terrestrial field
dissipation study, indicating leaching as a likely route of dissipation (MRID 41727701).

Similarly, column leaching studies demonstrated that malathion and its degradates, malathion
mono- and dicarboxylic acids are very mobile in soil (MRID 43868601). Data presented to the
Agency and in the "Pesticides and Groundwater Database" (USEPA 1992) demonstrate that
malathion has the potential to leach to ground water. Malathion has been detected in ground
water in three states (California, Mississippi, and Virginia) at levels ranging from 0.03 to
6.17 |ig/L. Based on these data and the low Kd values, it is clear that malathion has the potential
to contaminate ground water.

Although little or no maloxon production is observed in registrant submitted aquatic studies,
maloxon has been detected in surface waters and the potential for maloxon runoff may be
heightened relative to malathion because it is expected to have higher solubility. EFED is not
aware of reports of maloxon ground water contamination. However, malathion has contaminated
ground water in several states and has the potential to contaminate surface water through runoff.
The increased polarity of maloxon due to the substitution of oxygen for sulfur increases the
expected potential of this chemical to be mobile in soil.

Under many circumstances malathion degrades rapidly to compounds of lower toxicity, usually
through microbial metabolism and hydrolysis. However, in urban areas (e.g., aerial and ground
application for mosquito control), it is likely that malathion will contact dry, microbially
inactive, and low organic content surfaces such as concrete, asphalt, dry soil, roofing material,
and glass. It is expected that maloxon production will be increased on these surfaces as
malathion is exposed to air for extended periods until it is washed away by rain. This is
supported by maloxon monitoring data in urban streams after malathion treatments to urban

-------
areas showing similar or higher levels of maloxon than malathion in some instances (CaEPA,
1981). CaEPA has published two studies measuring maloxon production on dry soil (CaEPA
1993) and steel sheets (CaEPA 1996). Both of these studies showed higher maloxon production
than registrant submitted studies, but maximal levels of maloxon production were not achieved.
On the steel surface, a rainfall event removed most of the malathion after only 2 days. On the dry
soil, maloxon production did not decrease by the time the study was terminated at 22 days.

CaEPA has published a study describing maloxon production on low organic content soil (0.6%)
with a moisture content less than 1% (CaEPA 1993) showing higher maloxon production than
registrant submitted studies using soils with higher organic (2-2.7%) and moisture (75% of water
holding capacity, capacity not stated) content. Based on the CaEPA data, it appears that maloxon
production is favored on dry soils and thus may represent a higher risk scenario for maloxon
production and runoff.

Leaching/adsorption/desorption: The short soil persistence of malathion reduces the risk of
leaching to ground water; however, it has been detected in ground water in three states (USEPA
1992). Demethyl and carboxylic acid degradates are expected to be highly mobile particularly in
alkaline soils.

Based on batch equilibrium (adsorption/desorption) studies, unaged [14C]malathion was
determined to be very mobile in sandy loam, sand, loam, and silt loam soils, with Freundlich Kads
values of 0.83 - 2.47 L/kg and Koc values from 151-308 L/kg. Adsorption was correlated with
organic carbon content. Values for 1/n for Kads were clustered in the range of 0.904 - 0.978
(MRID 41345201).

Maloxon was not detected in any leachate or soil extracts in concentrations >0.12% (>6 |ig/L) of
applied radioactivity (MRID 43868601, 41345201, 43166301)

Laboratory volatility: Three different malathion formulations [Ready To Use (RTU), Ultra Low
Volume (ULV), and Emulsifiable Concentrate (EC)] added to a silt loam soil did not undergo
any appreciable volatilization, when measured under different soil moisture regimes or air flow
rates. No more than 5.1% of the applied radioactivity volatilized during the 16 days of the study
(MRID 42015201).

Spray Drift/Long-range Transport: No registrant-submitted spray drift studies were reviewed. A
study conducted for the Boll Weevil Eradication Program at Pennsylvania State University
(1993) examined malathion drift under conditions of boll weevil control (1 lb/A =112 mg/m2)
with an ultra-low volume (ULV) formulation. Deposition up to 21.0, 11.5, 2.9, and 0.7% of that
applied was observed at 100, 200, 500, and 1000 meters downwind, respectively. Due to the size
of the particles generated, the ULV formulation is expected to produce the highest levels of drift.

A number of studies have documented atmospheric transport and re-deposition of pesticides
from the Central Valley to the Sierra Nevada Mountains (Fellers et al., 2004; LeNoir et al., 1999;
McConnell et al., 1998; Sparling et al., 2001). Prevailing winds blow across the Central Valley
eastward to the Sierra Nevada Mountains, transporting airborne industrial and agricultural
pollutants into the Sierra Nevada ecosystems, where they are deposited in rain and snow.

40

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McConnell etal. (1998) detected malathion in rain and snow samples collected from the Sierra
Navada Mountains at 500 m elevation near the entrance of the Sequoia National Park, at 1920 m
in the Sequoia National Park, and at 2,200m at Ward Creek, west of Lake Tahoe. Measured
concentrations ranged from <0.046 to 24 ng/L. No malathion was detected in the surface water
samples taken in this study. LeNoir et al. (1999) detected malathion in three air samples taken at
200 m and 533 m in Sequoia National Park. Concentrations in these samples ranged from 0.15
to 0.29 ng/m3. They also detected malathion in water samples taken from a transect that ran
from 200 m to 2,040 m at concentrations ranging from 66 to 83 ng/L. These results indicate that
prevailing winds blowing from the Central Valley may transport and re-deposit malathion in
higher elevations of the Sierra Nevada Mountains. This atmospheric transport may result in
exposure to critical habitat segments of the California tiger salamander that are located east of
the Central Valley. However, the California tiger salamander occurs in the foothills that lie
between the Central Valley and the Sierra Nevada Mountains, not in the Sierra Nevada
Mountains themselves. Therefore, the amount of atmospheric deposition that occurs in these
foothill regions west of the high elevation mountain regions where studies were conducted is
uncertain. It should be noted that besides atmospheric transport and re-deposition, exposure to
these critical habitat could also occur from spray drift from nearby agricultural uses, as well as
from residential and mosquito abatement uses occurring within the critical habitat.

Other studies have detected malathion in rainwater and air in urban areas within the Central
Valley. Majewski et al. (2005) monitored pesticides in rainwater collected near Modesto,
California between 2001 and 2004. They report a mean and maximum concentration of
malathion of 0.031 and 0.383 |ig/L, respectively, with a detection frequency of 43%. Majewski
and Baston (2002) report on pesticides in air samples taken near Sacramento, California in 1996
and 1997. They detected malathion but at relatively low frequency (0.0 - 10.8%). Mean air
concentrations were 1.13-2.89 ng/m3 and maximum concentrations were 1.13-3.77 ng/m3.

The magnitude of transport via secondary drift depends on malathion's ability to be mobilized
into air and its eventual removal through wet and dry deposition of gases/particles and
photochemical reactions in the atmosphere. Therefore, physicochemical properties of malathion
that describe its potential to enter the air from water or soil (e.g., Henry's Law constant and
vapor pressure), pesticide use data, modeled estimated concentrations in water and air, and
available air monitoring data from the Central Valley and the Sierra Nevada were considered in
evaluating the potential for atmospheric transport of malathion to locations where it could impact
the California tiger salamander.

In general, deposition of drifting or volatilized pesticides is expected to be greatest close to the
site of application. The computer model(s) of spray drift AgDRIFT and AGDISP were used to
determine potential exposures to aquatic and terrestrial organisms via spray drift. It should be
noted that these models do not predict deposition of volatilized fractions of applied pesticide and
its long-range transport.

2.4.2. Mechanism of Action

Malathion's mode of action is through acetylcholinesterase (AChE) inhibition which disrupts
nervous system function. AChE is an enzyme which cleaves the neurotransmitter acetylcholine

-------
that resides within nervous system junctions. Inhibiting this enzyme leads to accumulation of the
neurotransmitter thus causing signals in the nervous system to persist longer than normal.

Typical symptoms for exposure to pesticides which act in this manner are defecation, urination,
lacrimation, muscular twitching and weakness, and halted respiration.

Malathion, along with other phosphorodithioate insecticides (those containing two sulfur atoms
bonded to phosphorus) must be oxidized before they have inhibitory potency and toxicity.
Oxidation occurs via cytochrome p450 and results in the conversion of the P=S group in
malathion to P=0 forming its oxon, maloxon (Murphy etal 1968). This alteration of the
phosphate group enables the molecule to covalently bind AChE resulting in long lasting
inhibition of the enzyme. Maloxon binds to AChE by mimicking the structure of enzyme's
natural substrate, acetylcholine. The similarity between the size, shape, and properties of
maloxon and the neurotransmitter allow it to "fit" in the acetylcholine binding site on the
enzyme. Altering the structure of maloxon or malathion reduces the ability of the oxon to bind
AChE resulting in detoxification of the molecule.

Detoxification reactions may be a result of enzyme or chemical action on the molecule. It occurs
very rapidly in mammals given pure malathion resulting in a very less acute toxicity [LD50 in rats
is 12,500 mg/kg (Fukuto 1983)]. Important detoxification steps occur through nonspecific
esterase enzymes which are capable of cleaving malathion to less toxic degradates. Common
detoxification reactions for malathion (and maloxon) are ester hydrolysis, demethylation, and
phosphorothiolate ester hydrolysis. When one or more of these detoxification steps are blocked
by another chemical the toxicity of malathion is increased and the added chemical is considered
to synergize malathion toxicity. Chemicals which increase the rate of malathion's conversion to
maloxon may also be synergists.

Because organophosphate insecticides are inhibitors of esterases (most specifically AChE) they
possess the ability to block detoxification enzymes. Several organophosphate impurities that
have historically been present in technical malathion are known to synergize malathion toxicity
probably through blocking malathion detoxification. The toxicity of several malathion impurities
alone is also very high (e.g., the LD50 of 0,0,S-trimethyl phosphorothioate in rats is 15 mg/kg,
or 833 times more toxic than pure malathion) and cause delayed toxicity suggesting a mode of
action other than AChE inhibition. Impurities can be produced through improper storage of
malathion as evidenced by a 35% increase in the acute toxicity of technical malathion stored at
40°C for 6 months (Fukuto 1983).

2.4.3. Use Characterization

Analysis of labeled use information is the critical first step in evaluating the federal action. The
current labels for malathion (at the time this report was written) represented the FIFRA
regulatory action; therefore, labeled use and application rates specified on the label formed the
basis of this assessment. The assessment of use information was critical to the development of
the action area and selection of appropriate modeling scenarios and inputs.

Malathion is one of the most widely used insecticides in the U. S. for residential as well as
agricultural pest control. It is used throughout the state of California. Historically, the

-------
predominant agricultural use was cotton for the Boll Weevil Eradication Program, but it is
currently applied to a large number of other agricultural commodities, including various
vegetable, grain, fruit, and nut crops, as well as stored grains. It is also used extensively in non-
agricultural settings for residential insect control and for adult mosquito control by municipal
vector control programs. Most malathion products are formulated as an emulsifiable concentrate
(EC) spray, an ultralow-volume (ULV) concentrate, or a dust. A few products are formulated as
a powder or wetable powder.

Because of the large numbers of use sites for malathion (Table 2-7), the uses have been grouped
by similar application characteristics (application rates, number of applications per year,
minimum retreatment intervals, and aquatic exposure modeling scenario).

Table 2-7. Malathion Uses, Application Information, and Modeling Scenarios Used in Exposure
Assessment1

Scenario Group. Label Crop/Site

Maximum
Application

Rates2
(Lbs. ai/A)

Applications per

Crop Cycle
(Minimum Days
before Re-
treatment)

PRZM Scenario and
Meteorological Station

Agricultural Uses (spray drift buffers of 25 ft for ground applications and 50 ft for air)

1. Alfalfa, Clover, Lespedeza, Lupine, Trefoil, and
Vetch

Air: 1.56
ULV: 0.61
Ground: 1.56

5(14)
2(14)
5(14)

C AalfalfaW irrigOPCe
ntral valley, CA
(W93193)

2. Macadamia Nut (Bushnut)

Ground: 0.94
Airblast: 0.94

6(7)
6(7)

C AalmondW irrigSTD
Central valley, CA ~
San Joaquin county
(W23232)

3 and 4. Pecan, Walnut (English/Black), and
Chestnut

Ground: 2.5
Airblast: 2.5

3(7)
3(7)

C AalmondW irrigSTD
Central valley, CA ~
San Joaquin county
(W23232)

6. Date (dust)

Air: 4.25
Ground: 4.25

5(7)
5(7)

CAalmondWirrigSTD
Central valley, CA ~
San Joaquin county
(W23232)

8. Avocado

Ground: 4.7

2(30)

CAAvocadoRLF
San Diego County
(W23188)

9. Citrus, Citrus Hybrids other than Tangelo,
Grapefruit, Kumquat, Lemon, Lime, Orange,
Tangelo, and Tangerines

Air: 7.5
ULV: 0.175
Ground: 7.5
Airblast: 7.5

3 (30)
3(7)
3 (30)
3 (30)

C AcitrusW irrigSTD
Central valley, CA ~
Fresno County
(W23155)

10. Amaranth - Chinese, Broccoli (Unspecified,
Chinese, and Raab), Cabbage (Unspecified and
Chinese), Canola\Rape, Cauliflower, Collards, Corn
Salad, Dock (Sorrel), Horseradish, Kale, Kohlrabi,
Mustard, Mustard Cabbage (Gai Choy/Pak-Choi), and
Purslane (Garden and Winter)

Air: 1.25
Ground: 1.25

6(7)
6(7)

CAColeCropRLF
Santa Maria Valley
Area, CA; (W23234)

11. Corn (Unspecified, Field, Pop, and Sweet)

Air: 1.0
ULV: 0.61
Ground: 1.0

2(5)
2(5)
2(5)

CAcornOP

Stanislaus/San Joaquin
Counties (W23232)

43

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Scenario Group. Label Crop/Site

Maximum
Application

Rates2
(Lbs. ai/A)

Applications per

Crop Cycle
(Minimum Days
before Re-
treatment)

PRZM Scenario and
Meteorological Station

12. Cotton

Air: 2.5
ULV: 1.22
Ground: 2.5

3(7)
3(7)
3(7)

CAcottonWirrigSTD
Fresno County, CA
(W93193)

13. Hops

Air: 0.63
Ground: 0.63
Airblast: 0.63

3(7)
3(7)
3(7)

ORhopsSTD
Marion Co., OR
(W24232)

15. Apricot

Ground: 1.5
Airblast: 1.5

2(7)
2(7)

CAfruitWirrigSTD
Fresno County, CA
(W93193)

16. Nectarine and Peach

Ground: 3
Airblast: 3

3(7)
3(7)

CAfruitWirrigSTD
Fresno County, CA
(W93193)

17. Cherry

Air: 1.75
ULV: 1.22
Ground: 1.75
Airblast: 1.75

4(3)
6(7)
4(3)
4(3)

CAfruitWirrigSTD
Fresno County, CA
(W93193)

18. Fig

Ground: 2
Airblast: 2

2(5)
2(5)

CAfruitWirrigSTD
Fresno County, CA
(W93193)

19. Pear

Ground: 1.25
Airblast: 1.25

2(7)
2(7)

CAfruitWirrigSTD
Fresno County, CA
(W93193)

20 and 21. Guava, Mango, and Papaya

Ground: 1.25
Airblast: 1.25

13(3)
13(3)

CAfruitWirrigSTD
Fresno County, CA
(W93193)

22. Garlic and Leek

Air: 1.56
Ground: 2

3(7)
3(6)

CAGarlicRLF
Fresno County, CA
(W23188)

23. Grapes

Ground: 1.88
Airblast: 1.88

2(14)
2(14)

CAgrapesWirrigSTD
Fresno County, CA
(W93193)

24. Mushrooms

Ground: 1.7

4(3)

CAfruitWirrigSTD
Fresno County, CA
(W93193). (See
justification below.)

26. Brussel Sprouts and Dandelion

Air: 1.25
Ground: 1.25

2(7)
2(7)

CAlettuceSTD
Monterey County; CA
(W23273)

27. Swiss Chard, Chervil, Endive (Escarole), Lettuce,
Head Lettuce, Leaf Lettuce (Black Seeded Simpson,
Salad Bowl, Etc.), Orach (Mountain Spinach),
Parsley, Roquette (Arrugula), Salsify, and Spinach

Air: 1.88
Ground: 1.88

2(5)
2(5)

CAlettuceSTD
Monterey County; CA
(W23273)

29. Eggplant

Air: 1.56
Ground: 1.56

5(5)
5(5)

C AtomatoW irrigSTD
San Joaquin County,
CA (W93193).

30. Pumpkin

Air: 1
Ground: 1

2(7)
2(7)

CAMelonsRLF
Fresno, Kern, Kings,
Madera, and Merced
Counties, CA
(W93193)

44

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Scenario Group. Label Crop/Site

Maximum
Application

Rates2
(Lbs. ai/A)

Applications per

Crop Cycle
(Minimum Days
before Re-
treatment)

PRZM Scenario and
Meteorological Station

31. Cucumber, Cucurbit Vegetables, Melons -
Unspecified, Cantaloupe, Honeydew, Musk, Water,
and Winter (Casaba/Crenshaw/Honeydew/Persian),
and Squash (All Or Unspecified)

Air: 1.75
Ground: 1.75

3(7)
3(7)

CAMelonsRLF
Fresno, Kern, Kings,
Madera, and Merced
Counties, CA
(W93193)

32. Onion (Unspecified and Green), Radish, and
Shallot

Air: 1.56
Ground: 1.56

2(7)
2(7)

CAonionWirrigSTD
Kern County, CA
(W23155)

33 and 36. White/Irish Potato and Sweet Potato

Air: 1.56
Ground: 1.56

2(7)
2(7)

CAPotatoRLF
Kern County, CA
(W23155)

34 and 35. Turnip, Parsnip, and Rutabaga

Air: 1.25
Ground: 1.25

3(7)
3(7)

CAPotatoRLF
Kern County, CA
(W23155)

37. Bluegrass, Canarygrass, Grass
Forage/Fodder/Hay, Pastures, Peas (Including Vines),
Rangeland, and Sudangrass

Air: 1.25
ULV: 0.92
Ground: 1.25

1
1
1

CArangelandhayRLF
San Francisco Bay
Area, CA (W23232)

40. Beets and Peas (Unspecified and Field)

Air: 1

Ground: 1.25

2(7)
3(7)

CARowCropRLF
Santa Maria Valley
Area, CA (W23234)

41. Carrot (Including Tops), Celtuce, Fennel, and
Pepper

Air: 1.56
Ground: 1.56

2(5)
2(5)

CARowCropRLF
Santa Maria Valley
Area, CA (W23234)

42. Beans, Beans - Dried-Type, Beans - Succulent
(Lima), and Beans - Succulent (Snap)

ULV: 0.61

2(7)

CARowCropRLF
Santa Maria Valley
Area, CA (W23234)

43. Celery

Air: 1.5
Ground: 1.5

2(7)
2(7)

CARowCropRLF
Santa Maria Valley
Area, CA (W23234)

44. Asparagus

Air: 1.25
Ground: 1.25

2(7)
2(7)

CARowCropRLF
Santa Maria Valley
Area, CA (W23234)

46. Strawberry

Air: 2
Ground: 2

4(7)
4(7)

CAStrawberry-
noplasticRLF
Santa Maria Valley
Area, CA (W23234)

48. Tomato

Air: 1.56
Ground: 1.56

4(5)
4(5)

C AtomatoW irrigSTD
San Joaquin County,
CA (W93193)

49. Okra

Air: 1.2
Ground: 1.2

5(7)
5(7)

C AtomatoW irrigSTD
San Joaquin County,
CA (W93193)

51. Sorghum

Air: 1
ULV: 0.61
Ground: 1

2(7)
2(7)
2(7)

CAWheatRLF
Kings County, CA
(W93193)

52. Barley, Cereal Grains, Oats, Rye, and Wheat

Air: 1.25
ULV: 0.61
Ground: 1.25

2(7)
2(7)
2(7)

CAWheatRLF
Kings County, CA
(W93193)

45

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Scenario Group. Label Crop/Site

Maximum
Application

Rates2
(Lbs. ai/A)

Applications per

Crop Cycle
(Minimum Days
before Re-
treatment)

PRZM Scenario and
Meteorological Station

53,54,56. Gooseberry, Blackberry, Boysenberry,
Dewberry, Loganberry, Raspberry (Black - Red),
Caneberries, and Currant

Air: 1.25
Ground: 2
Airblast: 2

3(7)
3(7)
3(7)

CAWineGrapesRLF
Sonoma County, CA
(W23234)

55. Blueberry

Ground: 1.25
ULV: 0.77

3(5)
3(10)

CAWineGrapesRLF
Sonoma County, CA
(W23234)

57. Passion Fruit (Granadilla)

Ground: 1

8(7)

CAWineGrapesRLF
Sonoma County, CA
(W23234)

58. Mint and Spearmint

Air: 0.94
Ground: 0.94

3(7)
3(7)

ORmintSTD
Marion County, OR
(W24232)

59. Rice and Wild Rice

Air: 1.25
ULV: 0.61
Ground: 1.25

2(7)
2(7)
2(7)

Rice Guidance3

61. Water Cress

Air: 1.25
Ground: 1.25

5(3)
5(3)

Rice Guidance3

Non-agricultural Uses

Cull Piles and agricultural Structures and
Equipment. Cull Piles, Agricultural/Farm
Structures/Buildings and Equipment,
Commercial/Institutional/Industrial
Premises/Equipment (Outdoor), and Meat Processing
Plant Premises (Nonfood Contact)

Drench: 298.7

1

CAcitrusWirrigSTD
Central valley, CA ~
Fresno County
(W23155)

Fence rows/hedge rows.

Ground: 10.6

1

CArightofwayRLF
Central/Coastal, CA
(W23234).

Forestry. Christmas Tree Plantations, Pine (Seed
Orchard), and Slash Pine (Forest)

Air: 3.2
ULV: 0.9375
Ground: 3.2
Airblast: 3.2

2(7)
2(7)
2(7)
2(7)

CAForestryRLF
Shasta County, CA
(W24283)

Nursery. Outdoor Nursery, Outdoor Premises,
Ornamental and/or Shade Trees, Ornamental
Herbaceous Plants, Ornamental Lawns and Turf,
Ornamental Non-flowering Plants, Ornamental
Woody Shrubs and Vines, and Urban Areas

Air: 2.5
Ground: 2.5

2(10)
2(10)

CAnurserySTD
San Diego, CA
(W23188)

Rights-of-way. Uncultivated agricultural areas,
Nonagricultural Rights-of-way/Fencerows, and
Nonagricultural Uncultivated Areas/Soils

Air: 1

ULV: 0.9281
Ground: 1
Airblast: 1

1
1
1
1

CArightofwayRLF
CAImperviousRLF
Central/Coastal. CA
(W23234).

Public Health and Mosquito and Medfly Control.

Nonagricultural Areas (Public Health Use), Urban
Areas, Wide Area/General Outdoor Treatment (Public
Health Use), Intermittently Flooded Areas/Water,
Lakes/Ponds/Reservoirs (with Human or Wildlife
Use), Lakes/Ponds/Reservoirs (without Human or
Wildlife Use), Polluted Water, and
Swamps/Marshes/Wetlands/Stagnant Water

Air: 0.5078
ULV: 0.23

1
1

CAImperviousRLF
San Francisco Bay
Area, CA (W23234)

46

-------
Scenario Group. Label Crop/Site

Maximum
Application

Rates2
(Lbs. ai/A)

Applications per

Crop Cycle
(Minimum Days
before Re-
treatment)

PRZM Scenario and
Meteorological Station

Residential and Refuse/Solid Waste.

Household/Domestic Dwellings (perimeter around
dwelling), Refuse/Solid Waste Containers (Garbage
Cans), and Refuse/Solid Waste Sites (Outdoor)

Ground: 10.6

CAresidentialRLF
CAImperviousRLF
San Francisco Bay
Area, CA (W23234)

Turf. Golf Course Turf (Bermudagrass)

Air: 1.25
ULV: 0.92
Ground: 1.25

1
1
1

CATurfRLF San
Francisco Bay Area,
CA (W23234)

1 Uses assessed based on memorandum from Pesticide Re-evaluation Division (PRD) dated 1/25/2010.

2 Air, ULV, Ground and Airblast refers to aerial, ultra-low volume, ground, and airblast application methods.

3 http://www.epa.gov/oppefedl/models/water/rice_tier_i.htm

Uses that will no longer remain registered after implementation of the 2006 RED and are
therefore not considered in this assessment are: almond; filbert (hazelnut); millet (foxtail) and
sunflower; manure; apple and quince; plum and prune; peppermint; cowpea/blackeyed pea;
peanuts; safflower; anise; and sugar beets (incl. tops).

In June 2009, the Product Registration Division (PRD, previously SRRD) required all malathion
registrants to amend their product labels to reflect mitigation specified in the May 2009 revised
malathion RED. Registrants have since submitted revised labels or voluntary cancellation
requests for the majority of malathion product labels. The revised labels are currently being
reviewed by the Registration Division. Revisions to malathion product labeling are expected to
be substantially complete by December 2010. Because the existing labels are currently being
revised according to a legally binding agreement between the registrant and U.S. EPA, the
maximum per application rate, minimum re-application interval, and maximum number of
applications for each use (use application characteristics) were taken from those listed in the final
revision of the 2006 RED, as defined in Appendix Table D2, rather than from the current labels
at the time this document was written. All future labels (after December of 2010 and once
previously labeled stock has been sold) should conform to the specifications given in Appendix
B. Appendix Table D2 presents the same use specifications as given in Appendix B with the
exception that the uses have been grouped by similar application rates, number of applications,
re-treatment interval, and aquatic modeling scenario.

Some malathion products specify application rates on a per crop cycle basis (not on a per year
basis). Information from BEAD indicates that many crops can be grown more than one
time/year in California (U.S. EPA 2007b). Since standard PRZM scenarios only consist of one
crop per year, applications to only one crop per year were modeled. The crops that may be grown
multiple times in a calendar year that can be treated by malathion include Alfalfa, Clover,
Lespedeza, Trefoil, Vetch, and Turf. If malathion is applied for multiple cropping cycles within a
year, EECs presented in this assessment may underpredict exposures. Because malathion
displays little persistence in the environment (aerobic soil metabolism and terrestrial field
dissipation half-lives from <1 to 2 days), any build up of malathion over succeeding crop cycles
would be minimal. Any under-prediction of exposure is also likely to be minimal. For all other

-------
labeled uses, it was assumed that a maximum seasonal application specified was equivalent to a
maximum annual application.

According to the United States Geological Survey's (USGS) national pesticide usage data (based
on information from 1999 to 2004), an average of 5 million lbs of malathion is applied nationally
to agricultural use sites in the U.S. (non-agricultural uses are not included) (Figure 2-1). Cotton
has the greatest use of malathion nationally claiming over 80% of total annual usage.

2002 estimated annual agricultural use

Crops

Total

Percent

pounds applied

national use

cotton

4040673

80.66

alfalfa hay

227896

4.55

other hay

163467

3.26

cherries

77751

1.55

strawberries

74506

1.49

lettuce

55741

1.11

citrus fruit

42287

0.84

blueberries

40960

0.82

wheat for grain

36399

0.73

walnuts

36145

0.72

Average annual use of
active Ingredient
(pounds per square mile of agricultural
land in county)

~	no estimated use

~	0.001 to 0.01

~	0.011 to 0.06

~	0.061 to 0.208

~	0.209 to 1.135
¦	>=1.136

Figure 2-1. Malathion use in total pounds per county

(from http://\\atcr.usgs.go\/na\\qa/pnsp/usagc/maps/sho\\_map.php'.,ycar=()2&map=m6()33)1

The Agency's Biological and Economic Analysis Division (BEAD) provided an analysis of both
national- and county-level usage information (USEPA 2009) using state-level usage data
obtained from USDA-NASS2, Doane (www.doane.com; the full dataset is not provided due to its

1	The pesticide use maps available from this site show the average annual pesticide use intensity expressed as
average weight (in pounds) of a pesticide applied to each square mile of agricultural land in a county. The area of
each map is based on state-level estimates of pesticide use rates for individual crops that were compiled by the
CropLife Foundation, Crop Protection Research Institute based on information collected during 1999 through 2004
and on 2002 Census of Agriculture county crop acreage. The maps do not represent a specific year, but rather show
typical use patterns over the five year period 1999 through 2004.

2	United States Depart of Agriculture (USDA), National Agricultural Statistics Service (NASS) Chemical Use
Reports provide summary pesticide usage statistics for select agricultural use sites by chemical, crop and state. See
http://www.pestmanagement.info/nass/app usage.cfm.

48

-------
proprietary nature) and the California's Department of Pesticide Regulation Pesticide Use
Reporting (CDPR PUR) database3. CDPR PUR is considered a more comprehensive source of
usage data than USDA-NASS or EPA proprietary databases, and thus the usage data reported for
malathion by county in this California-specific assessment were generated using CDPR PUR
data. Nine years (1999-2007) of usage data were included in this analysis. Data from CDPR
PUR were obtained for every agricultural pesticide application made on every use site at the
section level (approximately one square mile) of the public land survey system.4 BEAD
summarized these data to the county level by site, pesticide, and unit treated. Calculating
county-level usage involved summarizing across all applications made within a section and then
across all sections within a county for each use site and for each pesticide. The county level
usage data that were calculated include: average annual pounds applied, average annual area
treated, and average and maximum application rate across all nine years. The units of area
treated are also provided where available.

A summary of malathion usage for all California use sites is provided below in Table 2-8.

Table 2-8. Summary of California Department of Pesticide Registration (CDPR) Pesticide Use

Reporting (PUR) Data from 1999 to 2007 for Currently

legistered Malathion Uses

Site Name

Average
Annual Pounds
Applied

Average Application
Rate
(lbs a.i./A)

Maximum
Application Rate
(lbs a.i./A)

Alfalfa

130,616

1.21

17.23

Almond

410

2.07

11.92

Apple

72

2.17

49.06

Apricot

5

2.88

6.13

Arrugula

16

1.79

7.67

Asparagus

848

1.18

1.92

Avocado

1,310

0.25

19.74

Barley

985

1.11

1.71

Bean, Dried

2,991

1.28

2.62

Bean, Succulent

1,498

1.34

6.39

Bean, Unspecified

341

1.42

14.72

Beet

154

1.95

8.18

Bermudagrass

4,434

1.12

4.58

Blackberry

1,229

3.43

16.35

Blueberry

102

1.86

2.55

Bok Choy

602

1.87

11.52

Broccoli

6,651

1.85

8.03

Brussels Sprout

71

1.38

2.43

Cabbage

2,015

1.87

12.27

Canola (Rape)

432

2.03

2.90

3	The California Department of Pesticide Regulation's Pesticide Use Reporting database provides a census of
pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/purmain.htm.

4	Most pesticide applications to parks, golf courses, cemeteries, rangeland, pastures, and along roadside and railroad
rights of way, and postharvest treatments of agricultural commodities are reported in the database. The primary
exceptions to the reporting requirement are home-and-garden use and most industrial and institutional uses
(http://www.cdpr.ca.gov/docs/pur/purmain.htni).

49

-------


Average

Average Application

Maximum

Site Name

Annual Pounds
Applied

Rate
(lbs a.i./A)

Application Rate
(lbs a.i./A)

Cantaloupe

401

7.36

87.47

Carrot

2,316

1.63

4.19

Cauliflower

776

1.60

2.60

Celery

14,744

1.44

15.06

Cherimoya

0.03

0.24

0.24

Cherry

498

5.13

37.01

Chervil

0.85

1.92

1.92

Chicory

0.39

2.06

2.06

Chinese Cabbage (Nappa)

2,304

1.99

30.99

Chinese Greens

69

1.69

2.47

Chive

1.59

1.09

1.53

Christmas Tree

90

1.71

15.33

Citrus

197

2.51

40.88

Clover

93

2.21

3.91

Cole Crop

0.43

1.44

1.44

Collard

93

1.88

5.12

Commodity Fumigation

4.43

39.91

39.91

Corn (Forage - Fodder)

318

1.05

2.79

Corn, Human Consumption

906

0.96

6.39

Cotton

3,779

1.26

11.27

Cucumber

458

2.12

28.81

Daikon

0.11

0.53

0.99

Dandelion Green

0.18

1.15

1.28

Date

8,241

2.88

37.50

Eggplant

43

1.65

32.80

Endive (Escarole)

487

1.65

2.86

Fennel

20

1.79

2.10

Fig

949

2.06

2.56

Forage Hay/Silage

2,467

1.30

3.07

Gai Choy

5.55

1.73

4.09

Gai Lon

363

1.86

5.33

Garlic

1,425

1.89

9.81

Grape

2,071

2.41

25.56

Grape, Wine

4,326

2.07

40.89

Grapefruit

264

0.76

76.82

Grass, Seed

8.22

1.23

1.50

Herb, Spice

0.06

1.68

1.68

Kale

950

1.88

11.52

Kiwi

0.08

0.34

0.34

Kohlrabi

12

1.30

11.24

Kumquat

33

3.14

63.60

Landscape Maintenance

1.21

1.38

2.47

Leek

44

1.75

3.84

50

-------


Average

Average Application

Maximum

Site Name

Annual Pounds

Rate

Application Rate



Applied

(lbs a.i./A)

(lbs a.i./A)

Lemon

3,249

5.31

81.77

Lettuce, Head

32,919

1.69

17.03

Lettuce, Leaf

17,638

1.66

21.12

Lime

11

0.36

11.52

Livestock

7.69

0.55

0.63

Mango

0.91

0.27

0.36

Melon

37

2.25

19.88

Mint

123

0.99

9.00

Mizuna

10

2.16

2.40

Mushroom

0.36

2.08

2.08

Mustard

216

1.52

10.22

Nectarine

102

6.43

32.71

N-Outdr Flower

512

1.44

32.71

N-Outdr Plants In Containers

5,157

2.44

65.41

N-Outdr Transplants

539

1.68

50.08

Nuts

3.19

0.97

1.00

Oat

226

1.14

1.62

Oat (Forage - Fodder)

148

1.18

1.92

Okra

45

1.35

1.54

Olive

3.16

1.93

1.93

Onion, Dry

4,847

1.51

16.35

Onion, Green

1,600

1.73

16.35

Orange

22,106

2.58

83.08

Parsley

18

1.39

8.18

Parsnip

42

1.84

1.94

Pastureland

192

1.10

2.04

Peach

45

3.26

12.34

Pear

103

5.74

37.01

Peas

1,404

0.82

24.36

Pecan

26

5.89

9.69

Pepper, Fruiting

700

1.17

10.06

Pepper, Spice

53

2.97

38.41

Plum

12

7.14

37.01

Pomegranate

0.05

0.08

0.08

Potato

195

1.88

3.08

Prune

132

3.55

9.69

Pumpkin

1,325

1.38

2.50

Quince

1.33

0.75

0.75

Radish

104

1.46

16.10

Rangeland

30

1.86

14.97

Rappini

20

2.22

2.57

Raspberry

1,947

1.40

24.53

Regulatory Pest Control

3,421

12.46

95.39

51

-------


Average

Average Application

Maximum

Site Name

Annual Pounds
Applied

Rate
(lbs a.i./A)

Application Rate
(lbs a.i./A)

Research Commodity

0.82

0.37

2.72

Rice

729

1.32

1.75

Rice, Wild

2,124

1.48

11.84

Rights Of Way

0.39

0.60

1.24

Rutabaga

2.27

2.04

2.04

Ryegrass

4.27

1.16

1.16

Safflower

585

0.91

1.44

Shallot

15

2.05

2.05

Sorghum (Forage - Fodder)

51

1.17

1.47

Sorghum/Milo

37

2.40

4.22

Spinach

1,079

1.54

12.78

Squash

490

1.49

11.97

Squash, Summer

473

2.05

96.29

Squash, Winter

82

2.12

8.01

Squash, Zucchini

35

1.62

2.04

Strawberry

76,046

1.86

68.75

Structural Pest Control

6.28

1.94

1.94

Sudangrass

19

1.35

1.92

Sugarbeet

3,298

1.51

28.48

Sunflower

2.99

0.67

2.40

Sweet Potato

218

2.42

14.31

Swiss Chard

206

1.65

4.09

Tangelo

224

3.30

13.63

Tangerine

4,326

4.29

27.23

Tomatillo

11

1.04

2.00

Tomato

640

1.51

9.79

Tomato, Processing

2,674

1.14

9.99

Tropical/Sub tropical Fruit

5.31

0.28

2.47

Turf/Sod

0.12

0.15

0.15

Turnip

161

1.52

16.36

Turnip (Forage - Fodder)

0.31

1.24

1.24

Uncultivated Ag

41

1.42

10.04

Uncultivated Non-Ag

36

1.33

2.04

Vegetable

5.00

2.08

3.84

Vegetables, Leafy

6.54

1.58

1.92

Walnut

26,005

3.82

61.46

Watercress

362

1.03

13.63

Watermelon

427

2.90

29.16

Wheat

3,055

1.05

2.83

Wheat (Forage - Fodder)

389

1.06

1.25

Regulatory Pest Control

2,368

0.60

0.64

Commodity Fumigation

68





Fumigation, Other

71





52

-------
Site Name

Average
Annual Pounds
Applied

Average Application
Rate
(lbs a.i./A)

Maximum
Application Rate
(lbs a.i./A)

Landscape Maintenance

18,156

Public Health

14,433

Regulatory Pest Control

30,308

Rights Of Way

504

Structural Pest Control

31,914

1- Based on data supplied by BEAD (U.S. EPA 2009).

2.5. Assessed Species

Table 2-9 provides a summary of the current distribution, habitat requirements, and life history
parameters for the listed species being assessed. More detailed life-history and distribution
information can be found in Attachment 3.

The DS was listed as threatened on March 5, 1993 (58 FR 12854) by the USFWS (USFWS,
2007). The current range of the DS is shown in Figure 2-2. DS are mainly found in the Suisun
Bay and the Sacramento-San Joaquin estuary near San Francisco Bay. During spawning DS
migrate upstream into freshwater rivers, sloughs, and tributaries that drain into the estuary.

The CTS is listed as three Distinct Population Segments (DPSs): the Sonoma County DPS
(CTS-SC), the Santa Barbara County DPS (CTS-SB), and the Central California DPS (CTS-CC).
This assessment considers exposure from uses of malathion to each DPS separately as they
occupy different geographic areas; however, the natural history and toxic response to malathion
is assumed to be similar for individuals of each of the three DPSs. Thus, the main difference
among the three DPS's in the assessment was in the spatial analysis of the co-occurrences of
habitat of each DPS and uses of malathion. The CTS-SB and CTS-SC were downlisted from
endangered to threatened in 2004 by the USFWS, however, the downlisting was vacated by the
U.S. District Court. Therefore, CTS-SB and CTS-SC are currently listed as endangered while
the CTS-CC is listed as threatened. CTS utilize vernal pools, semi-permanent ponds, and
permanent ponds (including constructed stock ponds), and surrounding grassland and oak
savannah communities in central California. They inhabit valley-foothill habitats up to
approximately 3000 ft (California DFG, 2005). The aquatic environment is essential for
breeding and reproduction and mammal burrows are also important habitat for estivation. The
CTS-CC occurs in isolated segments of the Coastal Range and foothills of the Sierra Nevada
mountains that surround the Central Valley of California (Fig 2-3). The CTS-SC and CTS-SB
inhabit Coastal Range habitats that are located entirely within Sonoma County and Santa Barbara
County, respectively (Fig 2-3).

-------
Table 2-9. Summary of Current Distribution, Habitat Requirements, and Life

history Information for the Assessed Listed Species1

Assessed Species

Size

Current Range

Habitat Type

Designated
Critical
Habitat?

Reproductive
Cvclc

Diet

California Tiger
Salamander (CTS)

(Ambvstoma
californiense)

50i

CTS-SC are primarily found
on the Santa Rosa Plain in
Sonoma County.

CTS-CC occupies the Bay
Area (central and southern
Alameda, Santa Clara,
western Stanislaus, western
Merced, and the majority of
San Benito Counties), Central
Valley (Yolo, Sacramento,
Solano, eastern Contra Costa,
northeast Alameda, San
Joaquin, Stanislaus, Merced,
and northwestern Madera
Counties), southern San
Joaquin Valley (portions of
Madera, central Fresno, and
northern Tulare and Kings
Counties), and the Central
Coast Range (southern Santa
Cruz, Monterey, northern San
Luis Obispo, and portions of
western San Benito, Fresno,
and Kern Counties).

CTS-SB are found in Santa
Barbara County.	

Freshwater pools or ponds
(natural or man-made, vernal
pools, ranch stock ponds,
other fishless ponds);
Grassland or oak savannah
communities, in low foothill
regions; Small mammal
burrows

Yes

Emerge from burrows and
breed: fall and winter

rains

Eggs: laid in pond Dec. -

Feb., hatch: after 10 to 14
days

Larval stage: 3-6 months,

until the ponds dry out,
metamorphose late spring
or early summer, migrate
to small mammal burrows

Aquatic Phase: algae,
snails, zooplankton,
small crustaceans, and
aquatic larvae and
invertebrates, smaller
tadpoles of Pacific tree
frogs, CRLF, toads;
Terrestrial Phase:
terrestrial invertebrates,
insects, frogs, and
worms

Delta Smelt (DS)

(Hvpomesus
transpacificus)

Up to 120
mm in
length

Suisun Bay and the
Sacramento-San Joaquin
estuary (known as the Delta)
near San Francisco Bay, CA

The species is adapted to
living in fresh and brackish
water. They typically occupy
estuarine areas with salinities
below 2 parts per thousand
(although they have been
found in areas up to 18ppt).
They live along the	

Yes

They spawn in fresh or
slightly brackish water
upstream of the mixing
zone. Spawning season
usually takes place from
late March through mid-
May, although it may
occur from late winter

They primarily
planktonic copepods,
cladocerans,
amphipods, and insect
larvae. Larvae feed on
phytoplankton;
juveniles feed on
zooplankton.	

54

-------
Assessed Species

Size

Current Range

Habitat Type

Designated
Critieal
Habitat?

Reproductive
Cvcle

Diet







freshwater edge of the mixing
zone (saltwater-freshwater
interface).



(Dec.) to early summer
(July-August). Eggs
hatch in 9 - 14 days.



1	For more detailed information on the distribution, habitat requirements, and life history information of the assessed listed species, see Attachment 2.

2	Oviparous = eggs hatch within the female's body and young are born live.

3	No data on juvenile CCR body weights are available at this time. As a surrogate for CCR juveniles, data on captive 21-day king rails were averaged for the
juvenile body weight. King rails make an appropriate proxy for the CCR in the absence of information. The birds were once considered the same species by
taxonomists, are members of the same genus (Rallus), and occasionally interbreed where habitats overlap.

55

-------
Delta Smelt Habitat

Stanislaus

10/2009

Marin

Map created by US EPA on 10/6/2009. Projection: Albers Equal
Area Conic USQS, North American Datum of 1983 (NAD 1983).

River data from ESRI (2004), county boundaries from ESRI (2002),
water bodiesfrom NHDPIus (2006).

Delta Smelt section information obtained from Case No. 07-2794-JCS.
Critical habitat data obtained from http:/crithab.tV^'s.gov/.



' Sitter

Sonoma

f	

Legend

Delta smelt critical habitat
Delta smelt occurrence sections
NHD water bodies
Streams and Rivers

CAcounties

Figure 2-2. Critical habitat and occurrence sections of the delta smelt identified in Case No. 07-
2794-JCS.

56

-------
Son oni a
County
DPS



t

n

o

*

p
r*



>

o

-p



*k
t *

Legend

CATiger Salamander CH
OA Tiger Salamander sections
Counties

i Kilometers
0.9 182736

1:1,934,159

Santa
Barbara
DPS

<2



Map Created by USEPA on 2/5/2010. Projection: Alters Equal
Area Conic USGS, North American Datum 1983.

Compiled from ESRI county boundaries and streams (2002).
CTS occurrence section data from Case No. 07-2794-JCS,
critical habitat data from http://crithab.fws.gov.



Figure 2-3. Critical Habitat and Occurrence Sections of the California Tiger Salamander
(Central California DPS, Sonoma County DPS, and Santa Barbara DPS) identified in Case No.
07-2794-JCS. Habitat sections occurring in Sonoma County and Santa Barbara County comprise
the Sonoma County DPS and Santa Barbara DPS, respectively. All other habitat and critical
habitat segments shown are part of the Central California DPS.

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2.6. Designated Critical Habitat

Critical habitat has been designated for the DS and CTS. Risk to critical habitat is evaluated
separately from risk to effects on the species. 'Critical habitat' is defined in the ESA as the
geographic area occupied by the species at the time of the listing where the physical and
biological features necessary for the conservation of the species exist, and there is a need for
special management to protect the listed species. It may also include areas outside the occupied
area at the time of listing if such areas are 'essential to the conservation of the species. Critical
habitat designations identify, to the extent known using the best scientific and commercial data
available, habitat areas that provide essential life cycle needs of the species or areas that contain
certain primary constituent elements (PCEs) (as defined in 50 CFR 414.12(b)). Table 2-10
describes the PCEs for the critical habitats designated for the DS and CTS.

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Table 2-10. Designated Critical Habitat PCEs for the DS and CTS1

Species

PCEs

Reference

California tiger
salamander

Standing bodies of fresh water, including natural and man-made (e.g.,
stock) ponds, vernal pools, and dune ponds, and other ephemeral or
permanent water bodies that typically become inundated during winter
rains and hold water for a sufficient length of time (i.e., 12 weeks)
necessary for the species to complete the aquatic (egg and larval)
portion of its life cycle2

FR Vol. 69 No. 226 CTS,
68584, 2004

Barrier-free uplands adjacent to breeding ponds that contain small
mammal burrows. Small mammals are essential in creating the
underground habitat that juvenile and adult California tiger
salamanders depend upon for food, shelter, and protection from the
elements and predation

Upland areas between breeding locations (PCE 1) and areas with small
mammal burrows (PCE 2) that allow for dispersal among such sites

Delta Smelt

Spawning Habitat—shallow, fresh or slightly brackish backwater
sloughs and edgewaters to ensure egg hatching and larval viability.
Spawning areas also must provide suitable water quality (i.e., low
"concentrations of pollutants) and substrates for egg attachment (e.g.,
submerged tree roots and branches and emergent vegetation).

59 FR 65256 65279, 1994

Larval and Juvenile Transport—Sacramento and San Joaquin Rivers
and their tributary channels must be protected from physical
disturbance and flow disruption. Adequate river flow_is necessary to
transport larvae from upstream spawning areas to rearing habitat in
Suisun Bay. Suitable water quality must be provided so that
maturation is not impaired by pollutant concentrations.

Rearing Habitat—Maintenance of the 2 ppt isohaline and suitable
water quality (low concentrations of pollutants) within the Estuary is
necessary to provide delta smelt larvae and juveniles a shallow
protective, food-rich environment in which to mature to adulthood.

Adult Migration— Unrestricted access to suitable spawning habitat in
a period that may extend from December to July. Adequate flow and
suitable water quality.may need to be maintained to attract migrating
adults in the Sacramento and San Joaquin River channels and their
associated tributaries. These areas also should be protected from
physical disturbance and flow disruption during migratory periods.

1	These PCEs are in addition to more general requirements for habitat areas that provide essential life cycle needs of
the species such as, space for individual and population growth and for normal behavior; food, water, air, light,
minerals, or other nutritional or physiological requirements; cover or shelter; sites for breeding, reproduction,
rearing (or development) of offspring; and habitats that are protected from disturbance or are representative of the
historic geographical and ecological distributions of a species.

2	PCEs that are abiotic, including, physical-chemical water quality parameters such as salinity, pH, and hardness are
not evaluated because these processes are not biologically mediated and, therefore, are not relevant to the endpoints
included in this assessment.

More detail on the designated critical habitat applicable to this assessment can be found in
Attachment 2. Activities that may destroy or adversely modify critical habitat are those that alter
the PCEs and jeopardize the continued existence of the species. Evaluation of actions related to
use of malathion that may alter the PCEs of the designated critical habitat for the DS and CTS
form the basis of the critical habitat impact analysis.

As previously noted in Section 2.1, the Agency believes that the analysis of direct and indirect
effects to listed species provides the basis for an analysis of potential effects on the designated

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critical habitat. Because malathion is expected to directly impact living organisms within the
action area, critical habitat analysis for malathion is limited in a practical sense to those PCEs of
critical habitat that are biological or that can be reasonably linked to biologically mediated
processes.

2.7. Action Area and LAA Effects Determination Area

2.7.1.	Action Area

The action area is used to identify areas that could be affected by the Federal action. The Federal
action is the authorization or registration of pesticide use or uses as described on the label(s) of
pesticide products containing a particular active ingredient. The action area is defined by the
Endangered Species Act as, "all areas to be affected directly or indirectly by the Federal action
and not merely the immediate area involved in the action" (50 CFR §402.2). Based on an
analysis of the Federal action, the action area is defined by the actual and potential use of the
pesticide and areas where that use could result in effects. Specific measures of ecological effect
for the assessed species that define the action area include any direct and indirect toxic effect to
the assessed species and any potential modification of its critical habitat, including reduction in
survival, growth, and fecundity as well as the full suite of sublethal effects available in the
effects literature.

It was recognized that the overall action area for the national registration of malathion was likely
to encompass considerable portions of the United States based on the large array of agricultural
and non-agricultural uses. However, the scope of this assessment limited consideration of the
overall action area to those portions that may be applicable to the protection of the DS and CTS
and their designated critical habitat within the state of California. For this assessment, the entire
state of California was considered the action area. Because federal registrations of malathion
include several residential uses for insect control, as well as forestry uses, the Agency believes
that use of malathion could potentially occur in all areas of the state. The Agency therefore did
not restrict the action area spatially based on co-occurrence with specific agricultural crops, as
has been done for other pesticides. Defining the action area as the entire state ensures that the
initial area of consideration encompasses all areas where the pesticide may be used now and in
the future, including the potential for off-site transport via spray drift and downstream dilution
that could influence the San Francisco Bay Species. Additionally, the concept of a state-wide
action area takes into account the potential for direct and indirect effects and any potential
modification to critical habitat based on ecological effect measures associated with reduction in
survival, growth, and reproduction, as well as the full suite of sublethal effects available in the
effects literature. The state-wide action area does not imply that direct and/or indirect effects
and/or critical habitat modification are expected to or are likely to occur over the full extent of
the action area, but rather to identify all areas that may potentially be affected by the action.

2.7.2.	LAA Effects Determination Area

A stepwise approach was used to define the Likely to Adversely Affect (LAA) Effects
Determination Area. An LAA effects determination applies to those areas where it is expected

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that the pesticide's use will directly or indirectly affect the species and/or modify its designated
critical habitat using EFED's standard assessment procedures (see Attachment I) and effects
endpoints related to survival, growth, and reproduction. This is the area where the "Potential
Area of LAA Effects" (initial area of concern + drift distance or downstream dilution distance)
overlaps with the range and/or designated critical habitat for the species being assessed. The first
step in defining the LAA Effects Determination Area was to understand the federal action. The
federal action was defined by the currently labeled uses for malathion. An analysis of labeled
uses and review of available product labels was completed. Registrations like emergency
exemptions which are restricted to states other than California were excluded from this
assessment. In addition, a distinction was made between food use crops and those that are non-
food/non-agricultural uses. For those uses relevant to the assessed species, the analysis indicated
that, for malathion, there were a wide range of agricultural, residential, and forestry uses
(summarized in Section 2.4.3. Following a determination of the assessed uses, an evaluation of
the potential "footprint" of malathion use patterns {i.e., the area where pesticide application may
occur) was determined. As discussed previously, the footprint for the use of malathion was
considered to be the entire state of California.

Once the initial area of concern is defined, the next step typically is to define the potential
boundaries of the Potential Area of LAA Effects by determining the extent of offsite transport
via spray drift and runoff, and defining the additional areas beyond the footprint where exposure
to the pesticide is predicted to exceed the listed species LOCs. The AgDRIFT model (Version
2.01 was used to define how far from the initial area of concern an effect to a given species may
be expected via spray drift {e.g., the drift distance). The spray drift analysis for malathion uses
the most sensitive endpoint of acute toxicity to terrestrial invertebrates. Further detail on the
spray drift analysis is provided in Section 5.2.4.a.

In addition to the buffered area from the spray drift analysis, the Potential Area of LAA Effects
area also typically considers the downstream extent of predicted pesticide concentrations that
would exceed the LOC based on downstream dilution analysis. However, due to the widespread
use of malathion across multiple land cover classes, this analysis was not performed.

2.8. Assessment Endpoints and Measures of Ecological Effect

2.8.1. Assessment Endpoints

A complete discussion of all the toxicity data available for this risk assessment, including
resulting measures of ecological effect selected for each taxonomic group of concern, is included
in Section 4 of this document. Table 2-11 identifies the taxa used to assess the potential for
direct and indirect effects from the uses of malathion for the two listed species assessed. The
specific assessment endpoints used to assess the potential for direct and indirect effects to each
listed species are provided in Table 2-12. For more information on the assessment endpoints,
see Attachment 1.

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Table 2-11. Taxa Used in the Analyses of Direct and Indirect Effects for the Assessed Listed
Species 								i	

Listed Species

Birds

Mammals

Terr.
Plants

Terr.
Inverts.

FW
Fish

FW
Inverts.

Estuarine/
•Marine
Fish

Estuarine/
Marine
Inverts.

Aquatic
Plants

California
tiger

salamander
(aquatic larval
stages)

N/A

N/A

N/A

N/A

Direct1

Indirect
(prey)

N/A

N/A

Indirect
(food and
habitat)

California
tiger

salamander
(terrestrial
adult stage)

Direct

Indirect
(prey and
habitat)

Indirect
(habitat)

Indirect
(prey)

Indirect
(prey)

Indirect
(prey)

N/A

N/A

N/A

Delta smelt

N/A

N/A

Indirect
(habitat)

N/A

Direct2

Indirect
(prey)

Direct1

Indirect
(prey)

Indirect
(food/
habitat)

Abbreviations: n/a = Not applicable; Terr. = Terrestrial; Invert. = Invertebrate; FW = Freshwater

1	Toxicity data for frog tadpoles were also considered, but the assessment of direct effects was based on data for
freshwater fish because they were more sensitive to malathion than the tadpoles.

2	The most sensitive fish species was selected across freshwater and estuarine/marine test species because the delta
smelt may be found in freshwater or brackish environments. In this case, the toxicity of a freshwater species (the
rainbow trout) was used because it was the most sensitive.

Table 2-12. Taxa and Assessment Endpoints Used to Evaluate the Potential for Use of
Malathion to Result in Direct and Indirect Effects to the Assessed Listed Species or Modification
of Critical Habitat

Taxa Used

Assessed Listed
Species

Assessment Endpoints

Measures of Ecological Effects

Freshwater Fish

Direct Effect -

Survival, growth, and
reproduction of
individuals via direct
effects

Freshwater fish 96-hr LC50 and
chronic NOAEC

-Delta Smelt*

Indirect Effect (orev)

Survival, growth, and
reproduction of
individuals via indirect
effects on aquatic food
supply (i.e., fish and
aquatic-phase amphibians)

-California Tiger
Salamander

Aquatic-Phase
Amphibians

Direct Effect -

Survival, growth, and
reproduction of
individuals via direct
effects

Tadpole 48- or 96-hr LC50

-California Tiger
Salamander

Freshwater Invertebrates

Indirect Effect (orev)

Survival, growth, and
reproduction of
individuals via indirect
effects on aquatic food
supply

Freshwater crustacean 48- to 96-hr
LC50 and chronic NOAEC

- CA Tiger Salamander
-Delta Smelt

Estuarine/Marine Fish

Direct Effect -

Survival, growth, and
reproduction of
individuals via direct
effects

Estuarine/marine fish 96-hr LC50 and
chronic NOAEC

- Delta Smelt*

Estuarine/Marine

Direct Effect

Survival, growth, and

Estuarine/marine crustacean or

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Taxa Used

Assessed Listed
Species

Assessment Endpoints

Mcasu res of Ecological Effects

Invertebrates

-Delta Smelt (if more
sensitive)

reproduction of
individuals via indirect
effects on aquatic food.

mollusk 48- to 96-hr LC50 and
chronic NOAEC

Aquatic Plants
(freshwater/marine)

Indirect Effect
(food/habitat)
-CA Tiger Salamander
-Delta Smelt

Survival, growth, and
reproduction of
individuals or
modification of critical
habitat/habitat via indirect
effects on habitat, cover,
food supply, and/or
primary productivity

Aquatic vascular plant (Lemna) IC50
(at least 14 days) and aquatic algal
IC5o (at least 5 days)

Birds

Direct Effect

-CA Tiger Salamander

Survival, growth, and
reproduction of
individuals via direct
effects

Avian acute oral 14-D LD50,
subacute dietary LC50, and avian
reproduction chronic NOAEL

Mammals

Indirect Effect
(orcy/habitat from
burrows/rearine sites)
-CA Tiger Salamander

Survival, growth, and
reproduction of
individuals or
modification of critical
habitat/habitat via indirect
effects on terrestrial prey
and burrows/rearing sites

Laboratory rat acute LD50
chronic NOAEL

8. Terrestrial
Invertebrates

Indirect Effect (orcy)
-CA Tiger Salamander

Survival, growth, and
reproduction of
individuals via indirect
effects on terrestrial prey
(terrestrial invertebrates)

Honey bee acute contact LD50

9. Terrestrial Plants

Indirect Effect
(food/habitat) (non-
oblisate relationship)
=CA Tiger Salamander
-Delta Smelt

Survival, growth, and
reproduction of
individuals or
modification of critical
habitat/habitat via indirect
effects on food and habitat
(i.e., riparian and upland
vegetation)

(No measurements are available on
the toxicity of malathion to terrestrial
plants.)

Abbreviations: SF=San Francisco

* The most sensitive fish species across freshwater and estuarine/marine environments is used to assess effects for
these species because they may be found in freshwater or estuarine/marine environments.

** Birds are used as a surrogate for terrestrial-phase amphibians and reptiles.

2.8.2. Assessment Endpoints for Designated Critical Habitat

As previously discussed, designated critical habitat is assessed to evaluate actions related to the
use of malathion that may alter the PCEs of the assessed species' designated critical habitat.
PCEs for the assessed species were previously described in Section 2.6. Actions that may
modify critical habitat are those that alter the PCEs and jeopardize the continued existence of the
assessed species. Therefore, these actions are identified as assessment endpoints. It should be
noted that evaluation of PCEs as assessment endpoints is limited to those of a biological nature
{i.e., the biological resource requirements for the listed species associated with the critical
habitat) and those for which malathion effects data are available.

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Assessment endpoints used to evaluate potential for direct and indirect effects are equivalent to
the assessment endpoints used to evaluate potential effects to designated critical habitat. If a
potential for direct or indirect effects is found, then there is also a potential for effects to critical
habitat. Some components of these PCEs are associated with physical abiotic features (e.g.,
presence and/or depth of a water body, or distance between two sites), which are not expected to
be measurably altered by use of pesticides.

2.9. Conceptual Model

2.9.1.	Risk Hypotheses

Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in
assessment endpoints) and may be based on theory and logic, empirical data, mathematical
models, or probability models (USEPA, 1998). For this assessment, the risk is stressor-linked,
where the stressor is the release of malathion to the environment. The following risk hypotheses
are presumed in this assessment:

The labeled use of malathion within the action area may:

•	directly affect DS and CTS by causing mortality or by adversely affecting growth or
fecundity;

•	indirectly affect DS and CTS and/or modify their designated critical habitat by reducing
or changing the composition of food supply;

•	indirectly affect DS and CTS and/or modify their designated critical habitat by reducing
or changing the composition of the aquatic plant community in the species' current range,
thus affecting primary productivity and/or cover;

•	indirectly affect CTS and/or modify their designated critical habitat by reducing or
changing terrestrial habitat in their current range (via reduction in small burrowing
mammals leading to reduction in underground refugia/cover);

•	indirectly affect DS and CTS and/or modify their designated critical habitat by reducing
or changing the composition of the terrestrial plant community in the species' current
range;

•	indirectly affect DS and CTS and/or modify their designated critical habitat by reducing
or changing aquatic habitat in their current range (via modification of water quality
parameters, habitat morphology, and/or sedimentation).

2.9.2.	Diagram

The conceptual model is a graphic representation of the structure of the risk assessment. It
specifies the malathion release mechanisms, biological receptor types, and effects endpoints of
potential concern. The conceptual models for aquatic and terrestrial organisms are shown in
Figure 2-4 and 2-5, respectively. The diagram for aquatic organisms is relevant to the DS and
the aquatic phase of the CTS, whereas the diagram for terrestrial organisms is relevant to

64

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terrestrial stages of the CTS. Although the conceptual models for direct/indirect effects and
modification of designated critical habitat PCEs are shown on the same diagrams, the potential
for direct/indirect effects and modification of PCEs will be evaluated separately in this
assessment.

Figure 2-4. Conceptual model depicting stressors, exposure pathways, and potential effects to
aquatic organisms from the use of malathion.

Dotted lines indicate exposure pathways that have a low likelihood of contributing to ecological risk.

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Stressor

Source

Pesticide applied to use site

Direct
application

Exposure Media
& Receptors

-| Spray drift |-

Terrestrial
inverts

Attribute
Change

Irrigation
~ water"*

Leaching to
Groundwater

¦ Dermal uptake/lngestion*

Terrestrial plants

grasses/forbs, fruit, seeds
(trees, shrubs)

| Runoff 1

*~1 J.

Atmospheric
transport

Soil

¦ Root uptake/contact

.Wet/dry deposition-

~Ingestion

• Ingestion

Ingestion

)— Ingestion-^-

Terrestrial
vertebrates

Individual
organisms

Reduced survival
Reduced growth
Reduced reproduction

Terrestrial
Vertebrates

Food chain

Reduction in prey and food
Modification of PCEs
related to prey availability

Habitat integrity

Reduction in primary productivity
Reduced cover
Community change
Modification of PCEs related
to habitat

Figure 2-5. Conceptual model depicting stressors, exposure pathways, and potential effects to
terrestrial organisms from the use of malathion.

Dotted lines indicate exposure pathways that have a low likelihood of contributing to ecological risk.

2.10. Analysis Plan

In order to address the risk hypothesis, the potential for direct and indirect effects to the assessed
species, prey items, and habitat is estimated based on a taxon-level approach. In the following
sections, the use, environmental fate, and ecological effects of malathion are characterized and
integrated to assess the risks. This is accomplished using a risk quotient (ratio of exposure
concentration to effects concentration) approach. Although risk is often defined as the likelihood
and magnitude of adverse ecological effects, the risk quotient-based approach does not provide a
quantitative estimate of likelihood and/or magnitude of an adverse effect. However, as outlined
in the Overview Document (USEPA, 2004), the likelihood of effects to individual organisms
from particular uses of malathion is estimated using the probit dose-response slope and either the
level of concern (discussed below) or actual calculated risk quotient value.

Descriptions of routine procedures for evaluating risk to the San Francisco Bay Species are
provided in Attachment 1.

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2.10.1. Measures of Exposure

The environmental fate properties of malathion along with available monitoring data indicated
that runoff and spray drift are the principle transport mechanisms of malathion to the aquatic and
terrestrial habitats. In this assessment, transport of malathion through runoff and spray drift were
considered in deriving quantitative estimates of malathion exposure to the California tiger
salamander and delta smelt, their prey, and habitats. Several studies have documented long
range transport of pesticides from the Central Valley of California easterly into the Sierra
Nevada Mountains (Fellers et al., 2004; LeNoir et al., 1999; McConnell et al., 1998; Sparling et
al., 2001). These studies are discussed in Section 2.4.1. Long-range transport thus may be a
significant mechanism of exposure for populations of the CTS-Central DPS which in
mountainous areas east of the Central Valley. This exposure was not considered in the
quantitative risk assessment, but was considered qualitatively in the characterization of risk for
the CTS (see Section 5.2.2). Long range transport is not expected to be a significant route of
exposure for the DS which is restricted to streams and rivers of the Central Valley and San
Francisco Bay Estuary.

Measures of exposure were based on aquatic and terrestrial models that predict estimated
environmental concentrations (EECs) of malathion using maximum labeled application rates and
methods of application. The models used to predict aquatic EECs are the Pesticide Root Zone
Model coupled with the Exposure Analysis Model System (PRZM/EXAMS) and EFED's tier 1
rice model (http://www.epa.gov/oppefedl/models/water/rice_tier_i.htm). Because spray drift
buffers are required for agricultural applications of malathion, AgDrift was used to model the
spray drift fraction contributed directly to the PRZM/EXAMS standard pond. The models used
to predict terrestrial EECs on food items were Terrestrial Residue Exposure (T-REX) and
Terrestrial Herpetofaunal Exposure Residue Program Simulation (T-HERPS). These models are
parameterized using relevant reviewed registrant-submitted environmental fate data. More
information on these models is available in Attachment 1.

2.10.2. Measures of Effect

Data identified in Section 2.8 are used as measures of effect for direct and indirect effects. Data
were obtained from registrant submitted studies or from literature studies identified by
ECOTOX. More information on the ECOTOXicology (ECOTOX) database and how
toxicological data is used in assessments is available in Attachment 1.

2.10.2.a. Integration of Exposure and Effects

Risk characterization is the integration of exposure and ecological effects characterization to
determine the potential ecological risk from agricultural and non-agricultural uses of malathion,
and the likelihood of direct and indirect effects to the assessed species in aquatic and terrestrial
habitats. The exposure and toxicity effects data are integrated in order to evaluate the risks of
adverse ecological effects on non-target species. The risk quotient (RQ) method is used to
compare exposure and measured toxicity values. EECs are divided by acute and chronic toxicity
values. The resulting RQs are then compared to the Agency's levels of concern (LOCs)

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(USEPA, 2004) (see Appendix C). More information on standard assessment procedures is
available in Attachment 1.

2.10.3. Data Gaps

The Agency has sufficient information for malathion and maloxon for the purposes of this
assessment. However, lack of the following information and data results in uncertainties in this
assessment: malathion aerobic aquatic metabolism under acidic conditions; maloxon production
on dry, microbially-inactive surfaces; maloxon metabolism and leaching/adsorption/desorption;
and maloxon effects on birds and aquatic animals.

3. Exposure Assessment

Most malathion products are formulated as a liquid, emulsifiable concentrate (EC), ultralow-
volume (ULV) concentrate, or dust. A few products are formulated as a powder or wetable
powder. Equipment used for application of malathion commonly includes low and high
volume ground sprayers, airblast sprayers, sprayers mounted on fixed-winged aircraft and
helicopters, chemigation equipment, mist blowers, ULV fog generators, and hand-held
sprayers. Risks from ground, airblast, aerial and ultra-low volume (ULV) applications are
considered in this assessment because they are expected to result in the highest off-target
levels of malathion due to generally higher spray drift levels. ULV applications tend to use
lower volumes applied in finer sprays than applications via ground boom, airblast, and non-
ULV aerial applications and thus have a higher potential for off-target movement via spray
drift.

3.1. Label Application Rates and Intervals

Malathion labels are currently being brought into compliance with the 2006 malathion RED.
Appendix A of the 2006 RED specifies the maximum per application rates, minimum re-
application intervals, and maximum number of applications that can be made to each use.

The RED stipulated usage characteristics are used rather than the current labels for two
reasons. First as stated previously, all labels are currently being brought into compliance with
the 2006 RED specifications. Second, the labels as they exist before being brought into
compliance with the 2006 RED often did not specify the maximum number of applications or
minimum re-treatment intervals.

Malathion is registered on many agricultural crops, including various grains, vegetables,
fruits, and nuts, as well as cotton. It also has many nonagricultural uses, including residential
uses and public health uses, such as mosquito control. Uses included in this assessment are
listed in Section 2.4.3. Maximum label use rates and restrictions on the maximum number of
application and minimum intervals between applications are provided for all uses in
California in Appendix B.

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3.2. Aquatic Exposure Assessment

3.2.1. Modeling Approach

The aquatic EECs (Estimated Environmental Concentrations) were calculated for all uses except
rice, wild rice, water cress, and public health (adult mosquito control) using the EPA Tier II
PRZM (Pesticide Root Zone Model) and EXAMS (Exposure Analysis Modeling System) with
the EFED Standard Pond environment. PRZM was used to simulate pesticide transport as a
result of runoff and erosion from an agricultural field, and EXAMS estimated environmental fate
and transport of pesticides in surface water. The most recent PRZM/EXAMS linkage program
(PE5, PE Version 5, dated Nov. 15, 2006) was used to pass data, parameter settings, and results
between the two programs. Use-specific management practices for all of the assessed uses of
malathion were used for modeling, including application rates, number of applications per year,
application intervals, and the first application date for each use (Table 2-7).

PRZM/EXAMS EECs can vary greatly with application date(s). In California, EECs predicted
in the standard pond will be almost exclusively due to spray drift if applications occur during the
summer when little runoff occurs. Because malathion degrades and dissipates relatively quickly
(terrestrial field dissipation half-lives can be less than 2 days), most of the applied malathion will
gone by the time the rains become more substantial in the fall. In winter and other times of the
year when rainfall is more common, EECs will be due to both spray drift and runoff.

In order to select the application dates that represent the maximum potential exposure from dates
when malathion is likely to be applied, the multi-run function of the PE shell was used to
calculate 90th percentile EECs for each potential application date (or set of application dates for
uses that allow multiple applications). This distribution of EECs across application dates was
compared to the distribution of dates when malathion was recorded in the PUR data to find the
highest EECs that occur on a date when malathion is expected to be used in California.

Because the PUR data consists of the mass of active ingredient pesticide applied during each
application, the PUR data is aggregated for each modeled use or modeled group of uses. For
example, only aerial applications to date are summed for all malathion applications to date for
each January first from the years 1990 to 2008 in the PUR data set as the first step in determining
the distribution of malathion use on dates, while the aerial applications to alfalfa, clover,
lespedeza, lupine, grain lupine, trefoil, and vetch use group is done similar to date with the
exception that applications to any of the uses in this use group that occur on January first are
summed across all years. These daily sums are divided by the number of years to estimate an
average mass applied on that day of the year (data from February 29th can be omitted). A 15-day
moving average (centered on the 8th day) is used to smooth interpolate the daily averages over
the course of a year. It is this daily estimate for the 15-day moving average that is used to
determine if malathion is used in California on that day (moving average > 0) or not (moving
average = 0).

As an example, Figure 3-1 compares the variation of EECs across application dates for ground
applications to pecan for the dates that malathion is applied as ground applications to pecan in
California, according to the 1990-2008 PUR data set. The vast majority of ground malathion

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applications to pecans occurs in the dry summer months when EECs are relatively low because
little runoff occurs. However, some applications do occur outside of the summer when EECs are
higher because runoff is more frequent. Based on the method used in this document, the highest
peak EEC that occurs when malathion is applied according to the PUR is 34.9 |ig/L on January
7th, while the 21-day EEC of 12.1 |ig/L and 60-day EEC of 4.6 |ig/L both occur on January 5th
(when only 1.5 lbs are applied per day). Similar graphs for all of the use groups modeled in this
document are available in Appendix D Figure Dl.

Month

Figure 3-1. Variation in 90th percentile peak, 21-day average, and 60-day EECs across first
application dates for ground application to pecan compared to a 15-day moving average of
pounds of malathion applied per day. (Based on CDPR PUR data from years 1990 through
2008.)

Using the highest EECs from the time of the year when malathion is applied is a reasonable way
to characterize the maximum potential aquatic exposure to malathion. However, there is the
potential for the highest EEC to be atypical relative to the other times when malathion is applied
to a use site. The question of how typical is it for malathion to be applied for each use at times
when it is expected that EECs will exceed the levels of concern (LOCs) is addressed in the
Section 6.1.1 of the document by calculating the percentage of the pounds of malathion applied
in California on application dates that are expected to result in EECs exceeding the agencies
LOCs versus the total pounds of malathion applied in California on all dates.

In two cases (macadamia nut and hops), no PUR data were available. Therefore, EECs used in
the analysis were set to the highest EEC from anytime during the year (not just when malathion
was applied). Similarly the percentage of malathion applications that exceeded the LOCs was
based on the number of days when application of malathion would be expected to result in EECs
that exceed the agencies LOCs versus the total number of days in a year (Table 6-1).

-------
Mushrooms

Malathion is used to control various fly species that are attracted to mushrooms and the compost
material in which mushrooms are grown (called "casing"). Typically, mushrooms are grown
indoors in facilities where carbon dioxide and moisture levels can be controlled. Because the
malathion is applied to the casing material inside of a structure, malathion applications to
mushroom casing do not result in a direct exposure to environmental receptors. However, the
mushroom casing material must be periodically replaced as it degrades over time and becomes
less productive. The left-over casing material is typically applied to agricultural fields to increase
soil fertility and water holding capacity of soils with limited water holding capacity (e.g., sandy
soils).

EFED does not have a standard scenario for assessing mushroom use. Because of the similarity
in maximum single application rate to cherries (1.7 lbs/A for mushrooms and 1.75 lbs/A for
cherries), number of uses (both 4) and retreatment intervals (both 3 days), ground applications to
cherries could be used as a surrogate scenario for providing an upper bound of exposure for
mushrooms. Ground applications to cherries assume a one percent spray drift exposure which
may not be applicable to land application of mushroom casings. Also all of the applications of
malathion to mushroom casings would have occurred some time before the casing material was
land applied. Because mushroom casing material is wet, pH adjusted to near neutral, and likely
has large populations of bacteria, it is likely that much of the malathion would be degraded due
to hydrolysis and metabolism before it was land applied. Finally, mushroom casings are
approximately 6 inches deep and, therefore, would likely be spread over a larger area assuming
that the casing material would be spread to a depth considerably less than 6 inches. Therefore,
assuming the malathion concentration is homogeneous throughout the casing material being
spread, would result in a lower application rate than for cherries (e.g., if it is spread on the land
to a 2 inch depth, the malathion application rate would be 2 inches/6 inches or 1/3 of the
application rate to the original casing material).

Additionally, it should be noted that Table 2-8 indicates that only 0.36 pounds of malathion are
applied to mushrooms per year in California. Dividing by the average application of 2.08 lbs.
ai/A (also in Table 2-8) indicates that approximately 0.17 acres of mushrooms are treated per
year with malathion according to the CDPR PUR data.

Cull Piles and Agricultural Structures and Equipment

Three uses of malathion (Cull Piles, Grain/cereal/flour bins (empty), and Grain/cereal/flour
elevators (empty)) are grouped together for assessment. Of the three uses, cull piles has the
highest application rate by far. For cull piles, malathion is applied as a drench at a maximum
single application rate of 298.7 lbs/A (6.857 lb/1000 ft2). A scenario for cull piles was created
that is expected to serve as surrogate scenario and provide conservative estimates of exposure for
the other uses in this group of malathion uses. This scenario assumes the cull piles occur within
the standard PRZM watershed, which drains to the standard EXAMS pond.

Because cull piles as well as the other uses in this group are likely to cover only a small portion
of the watershed area, a method was devised which takes advantage of the linear relationship

-------
between application rate and EEC as well as an assumed linear relationship between the amount
of watershed treated and EEC. Therefore for cull piles, a reference scenario based on a single
application of 1 lbs/A over the entire 10 acre standard PRZM watershed was used to generate
preliminary EECs (1 in 10 year peak EEC = 3.04 |ig/L, 21-day average EEC = 0.72 |ig/L, and
60-day average EEC = 0.26 |ig/L) that then was adjusted to the actual application rate and an
assumption of the area the cull pile occupies in the watershed. (The reason for creating the
reference scenario was the concern that the EECs might be constrained by the solubility limit of
malathion (145 mg/L) if the application rate was applied over the entire watershed.) The
equations used to extrapolate the cull pile scenario EECs from the reference scenario appear
below and are presented graphically in Figure 3-2.

3.04p,g/L ^ 2981b/Ax AreaCullPilesft2
EEC^ -	43,560ft2/Ax10A	= 0,020S^,

0-72 p,g/L ^ 2981b/A x AreaCullPilesft2

EEC21 day = "b/A			= 0.00049-^ x AreaCullPllJt2

21 -day	43,560ft /A X 10A	ft2

0.26 l+g/L x 2981b/A x AreaCullPilesft2	/r

EEC,o day = "b/A	-	= 0.00018^ x AreaCullpnJt2

60-dcy	43,560ft /A x 10A	ft2

100
^ 10

u

UJ

W 1
=

zz

3 o.i
§

0.01

100	1000	10000

Area of Cull Pile (ft2)

Figure 3-2. Variation in estimated environmental concentration (EEC) of malathion and area of
cull piles in the standard PRZM watershed.

For the purpose of estimating risk quotients later in this report, it was assumed that there was one
cull pile in each of the 10 acres of the PRZM watershed and each cull piles occupied 100 ft2 (10

72

-------
ft x 10 ft) or 1000 ft2 over the entire watershed. Solving for 1000 ft2 results in 1 in 10 year EECs
of 2.08 |ig/L (peak), 0.49 |ig/L (average 21-day), and 0.18 |ig/L (average 60-day).

Fence rows/hedge rows

For fence/hedge rows, malathion is applied as a ground application at a maximum single
application rate of 10.62 lbs/A (0.24 Lb/1000 ft2). Because fence/hedge rows would not cover
the entire watershed area, a method was devised to take advantage of the linear relationship
between application rate and EEC as well as an assumed linear relationship between the amount
of watershed treated and EEC. Similar to cull piles, a reference scenario based on a single
application of 1 lbs/A over the entire 10 acre standard PRZM watershed was used to generate
preliminary EECs (1 in 10 year peak EEC = 32.3 |ig/L, 21-day average EEC = 8.3 |ig/L, and 60-
day average EEC = 2.96 |ig/L) that then was adjusted to the actual application rate and an
assumption of the area the fence/hedge row occupies in the watershed. The equations used to
extrapolate the fence/hedgerow scenario EECs from the reference scenario appear below and are
presented graphically in Figure 3-3.

32.35 ng/L x |0 62|b/A x Area ft2

EEC -		= 0 00079-^^ x Area ft2

Peak	43,560ft2/A x 10A	'	ft2	FemeRow

8.30 p,g/L ^ 10 621b/A x AreaF „ ft2	,,

EEC21 dqy = "b/A			= 0.000202 X AreaFenceRJt2

21-day	43,560ft /A X 10A	ft2

2.96 p,g/L ^ 10 621b/A x AreaPenceRowft2

EEC60 d = llb/A			= 0.0000722^^xAreap R ft2

eo-dcy	43,560ft /A x 10A	ft2

73

-------
s

0.001

100	1000	10000

Area in F ence Row (ft2)

Figure 3-3. Variation in estimated environmental concentration (EEC) of malathion and area of
fence row in the standard PRZM watershed.

For the purpose of estimating risk quotients later in this report, it was assumed that a fence row
or hedge row is 10 ft wide and there is 100 ft of fence row or hedge in the 10-acre PRZM
watershed. Therefore, 1000 ft2 of the entire watershed was assumed to be covered by fence or
hedge row. Solving for 1000 ft2 results in 1 in 10 year EECs of 0.79 |ig/L (peak), 0.20 |ig/L
(average 21-day), and 0.072 |ig/L (average 60-day).

Rights-of-way

Three uses of malathion (Agricultural, uncultivated areas, Nonagricultural Rights-of-
way/Fencerows, and Nonagri cultural Uncultivated Areas/Soils) are grouped together for
assessment under the category of "rights-of-way". For additional information on this scenario,
see Attachment IV (Supplemental Information on the California Right-of-Way Scenario) and the
scenario description in Table 2-7.

Aquatic Agricultural Uses

For the aquatic agriculture uses of rice, wild rice, and water cress, aquatic EECs were estimated
using the tier 1 rice model, which assumes direct application to water. This model assumes no

degradation of malathion. The only pesticide removal process is partitioning to the sediment.
This screening model is a single equation as presented below:

0.00105 + 0.00013^

74

-------
and, if appropriate:

Kd - 0.01 Koc

where:

Cw = water concentration [jug/L]

mai' = mass applied per unit area [kg/ha]

Kd = water-sediment partitioning coefficient [L/kg]

Koc = organic carbon partitioning coefficient [L/kg]

Adult Mosquito Control Use

Aquatic EECs for public health use were estimated by using the AGDISP model to estimate the
maximum deposition rate from aerial ULV applications. The predicted maximum deposition
rate was assumed to occur on the EFED Standard Pond, and the residues were assumed to be
distributed evenly throughout the volume of the pond. Aquatic exposure was modeled for
residues of the parent compound, malathion, only. Residues of the toxic degradation product,
maloxon, were not considered because the amount of formation of maloxon and many of the
environmental fate characteristics of maloxon are unknown at this time.

Malathion is used to control adult mosquitoes in residential and recreational areas such as, but
not limited to parks, campsites, woodlands, athletic fields, golf courses, garden playgrounds,
recreational areas, etc. Some of these use sites could involve exposure to various types of water
bodies. Mosquito adulticides are more efficacious if they come into contact with insects in
flight. For that reason, mosquito abatement using malathion (as well as other mosquito
adulticides) is typically applied via aerial or ground spray methods with very fine droplets or
mists, to prevent immediate deposition of the pesticide. This type of application is called an ultra
low volume application. The AGricultural DISPersal model (AGDISP v. 8.13) is used to
calculate of spray drift and deposition from ULV applications. This model estimates the
deposition of the pesticide from a treated area to water bodies using a sub-routine "Deposition
Assessment" in the toolbox of AGDISP.

For aerial ULV spraying of malathion to control adult mosquitoes, most of the labels available
for malathion have very few specifications on various parameters that may affect the exposure to
adjacent bodies of water. The sample label selected for modeling was malathion ULV (EPA Reg.
No. 19713-288). It contains 96.5% malathion and 3.5% other ingredients. The maximum
application rate is 0.232 lb a.i./A. Only aerial mosquito adulticide use was modeled because the
exposure value would be higher due to undiluted use of malathion as compared to diluted
malathion used in ground application. According to the label, the spray equipment must be
adjusted to produce Dvo.s of 50 to 60 |im (half of the volume is contained in droplets smaller than
50 to 60 |im). The altitude or boom height is not specified in the label. Therefore, two heights
(75 ft and 100 ft) above the ground were selected for modeling based on common practice of
adulticide application. Since there is no specification for wind speed in the label, 10 and 15 mph
were simulated for this assessment.

-------
Malathion 60 Micn)infl 75 ft at 10 mph
Deposition

Distance (ft)

AGDISP Malatliion_60m@75ft_10mph.acj 8.13 08-06-2010 10:21:43

Figure 3-4. Deposition curve for a malathion application at a release height of 75 ft and a Dyo.s of
60 |im and wind speed of 10 mph

The spray material is undiluted malathion with specific gravity of 1.23 kg/L and no evaporation
rate was also assumed. The spray volume was 0.0234 gal/A (obtained from the label (3.0 oz/A).
Generally, the remaining input parameters in AGDISP were kept at their default value (unless
otherwise specified). The model assumes that the field of application is on a flat, treeless
landscape, and, therefore, in most cases it will provide a conservative estimate. Also, the volume
and droplet size used for the simulation are beyond the AGDISP's recommended values.
Uncertainty associated with each of these individual components adds to the overall uncertainty
of the modeled outputs. Labels do not specify a maximum number of applications per year. One
application was simulated to provide acute exposure of malathion. This value was also used to
calculate upper bound chronic risk. PRZM/EXAMS simulated exposures suggest that the
chronic EEC values are always lower than the acute exposure EECs (Table 5.1). Therefore,
chronic exposure values from adulticide applications are presumed to be lower than the
estimated acute values, the acute exposure value is expected to be protective for assessing
chronic risk. Various input parameters for AGDISP simulation are listed in Table 3-2. A sample
deposition curve is depicted in Figure 3-2. In order to obtain maximum deposition of malathion
in a water body (i.e. EPA pond) and terrestrial environment (point estimate), deposition
assessment tool of AGDISP was used. Table 3-3 shows estimated acute concentrations in pond
and the deposition rate in the terrestrial environment.

Table 3-2. Input Parameters Used in AGDISP Modeling for Adult Mosquito Control Use of

Vlalathion

Parameter

Value

Aircraft type

Air tractor AT-401, fixed wing

Swath width

60 ft

Wing semispan

24.5 ft

Swath displacement

Oft

Propeller rpm

2000, propeller rad. 4.5 ft

Fixed wing

1 engine

-------
Parameter

Value

Flight lines

20

Flight speed

120 mph

Boom height

75 ft and 100 ft

Number of nozzles

42

Vortex decay rate

1.25 mph

Aircraft drag coefficient

0.1

Propeller efficiency

0.8

Ambient pressure

29.91 inHg

Planform area

294 ft2

Nozzle spacing (even)

0.78 ft

Wind speed

10 and 15 mph

Wind direction

90°, perpendicular to flight path

Surface roughness

0.0075 ft

Canopy roughness

0.07 ft (grass)

Stability

Overcast

Relative humidity

50%

Temperature

65°F

Droplet type

User defined

Dvo.i

24.5urn (Dv05= 50 urn) and 33.6|im (Dv05= 60 |im)

Dv0.5

50.1 |iiii (Dv0 5= 50 |iiii) and 60.1 |im (Dv05= 60 |im)

Dv0.9

84.6 |im (Dv0 5 = 50 |im) and 94.5j.un (Dv0 5 = 60 |im)

Relative span

1.2 (Dv0 5= 50 |im) and 1.01 (Dv0.5= 60 |im)

<141 nm

99.8 % (Dv0 5= 50 |im) and 99.6 (Dv0.5= 60 |im)

Spray material

Oil

Specific gravity

1.23

Active fraction

0.96

Nonvolatile fraction

1.00

Spray volume

0.0234 gal/A

Evaporation rate

Not applicable

Buffer zone

Not applicable

Aauatic Exposure
Downwind water body width
Average depth

208.7 m
6.6 ft ~ 2 m

Terrestrial exposure

Point Estimate

Table 3-3. Deposition of Malathion in Water Body and Terrestrial Environment from Various
Aerial Application Scenarios 	

Wind speed

Release



Maximum

Deposition



(mph)

Height

Aquatie (pond)

Terrestrial (point)



(ft)

Cone.

(Hg/L)

(lbs/A





Dv().5 = 50

Dv().5 = 60

Dv().5 = 50

Dv().5 = 60

10

75

0.79

1.061

0.058

0.0791



100

0.52

0.65

0.038

0.055

15

75

0.44

0.63

0.032

0.046



100

0.23

0.36

0.017

0.026

1 = Bolded values were used in the risk assessment

Residential and Refuse/Solid Waste

Three uses of malathion (Household/Domestic Dwellings (perimeter around dwelling),
Refuse/Solid Waste Containers (Garbage Cans), and Refuse/Solid Waste Sites (Outdoor)) are

77

-------
grouped together for assessment. For all of these residential and refuse/solid waste uses,
malathion is applied as a drench at a maximum single application rate of 10.62 lbs/A (0.24
Lb/1000 ft2). A scenario for residential and refuse/solid waste uses was created that assumes the
refuse/solid waste sites and containers (trash cans) occur within the standard PRZM watershed,
which drains to the standard EXAMS pond.

Because trash cans as well as the other uses in this group are not likely to cover the entire
watershed, a method was devised which takes advantage of the linear relationship between
application rate and EEC as well as an assumed linear relationship between the amount of
watershed treated and EEC. Similar to cull piles and fence/hedge rows, a reference scenario
based on a single application of 1 lbs/A over the entire 10 acre standard PRZM watershed was
used to generate preliminary EECs (1 in 10 year peak EEC = 140.6 |ig/L, 21-day average EEC =
28.7 |ig/L, and 60-day average EEC = 10.3 |ig/L) that then was adjusted to the actual application
rate and an assumption of the area the trash bins occupy in the watershed. The equations used to
extrapolate the trash bin scenario EECs from the reference scenario appear below and are
presented graphically in Figure 3-5.

140.6 p,g/L ^ i o,621b/A x AreaT hBi ft2

J7J7Q =	1 lb/A		 q QQ343 x Area ft2

Peak	43,560ft2/A x 10A	' ft2	TrashBua

28.7 p,g/L ^ i o,621b/A x AreaT hBj ft2	,,

EEC21 = "b/A			= 0.000701 ^-x AreaTmshBlJt2

-day	43,560ft /A x 10A	ft2

' Q,,^fL x 10.621b/A x AreaTrashBlJ\2	,,

EEC,, , = llb/A			= 0.00025x AreaT ft2

-day	43,560ft /A x 10A	ft2

78

-------
100 -r

0.01 H 1 1 1— 1 1 1—

100 1000 10000

Area of Trash Bins (ft2)

Figure 3-5. Variation in estimated environmental concentration (EEC) of malathion and area of
trash bins in the standard PRZM watershed.

For the purpose of estimating risk quotients later in this report, it was assumed that there was one
trash bin site that was treated with malathion in each of the 10 acres of the PRZM watershed and
each trash bin site occupied 100 ft2 (10 ft x 10 ft) or 1000 ft2 over the entire watershed. Solving
for 1000 ft2 results in 1 in 10 year EECs of 3.43 |ig/L (peak), 0.70 |ig/L (average 21-day), and
0.25 |ig/L (average 60-day).

3.2.2. Aquatic Exposure Modeling Results

The aquatic EECs for the various scenarios and application practices of malathion in California
are listed in Table 3-4. The example output from PRZM-EXAMS is provided in Appendix D.
In these scenarios, EECs varied were dependant on application method, application rate, number
of application applied per year, the interval between applications, and the soil characteristics.
Also, EECs were very dependant on the date of first application. Malathion degrades rapidly in
soil. Therefore, aquatic exposure from runoff is much greater when a large rainfall event is
predicted to occur soon after application. In California, rainfall occurs mainly during the winter
months, whereas the summer months are very dry. Since the PRZM model uses historical
meteorological data from the region to predict runoff, applications made during the winter
months have much more runoff, and thus greater aquatic exposure, than applications made

during the summer. The EECs shown in Table 3-4 are the maximum of the set of EECs
produced for all possible dates of the first day of application, with the restriction that the first day
of application must fall within the period which malathion is typically used on the given crop.
Thus, if all other factors were equal, crops for which malathion is typically applied during winter
months have greater EECs than those for which malathion is only applied during the summer.

-------
Appendix D presents graphs showing the relationship between malathion use, seasons,
rainfall for various uses.

80

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Table 3-4. Aquatic EECs (jig/L) for Malathion Uses in California

. . Maximum Max. No. Min.

EECs (ng/L)

Scenario

Method1

Application
Rate (lbs/A)

Apps. per
Crop Cycle

Rctrcatmcnt
Interval (days)

Peak EEC

21-day

EEC

60-dav
EEC

1. Alfalfa, Clover, Lespedeza, Lupine, Grain Lupine,
Trefoil, and Vetch

A

1.56

5

14

22.5

7.77

4.87

ULV

0.61

2

14

8.17

2.85

1.11

G

1.56

5

14

15.5

4.64

2.13

2. Macadamia Nut (Bushnut)

G

0.94

6

7

16.0

5.42

2.38

AB

0.94

6

7

15.6

5.26

2.28

3. Pecan and Walnut (English/Black)

G

2.5

3

7

34.9

12.1

4.61

AB

2.5

3

7

33.0

11.2

4.21

6. Date

A

4.25

5

7

62.2

25.1

13.3

G

4.25

5

7

52.3

19.2

9.22

8. Avocado

G

4.7

2

30

59.3

12.6

4.77

9. Citrus Hybrids Other Than Tangelo, Grapefruit,
Kumquat, Lemon, Lime, Orange, Tangelo, and
Tangerines

A

7.5

3

30

50.1

13.1

8.35

ULV

0.175

3

7

2.66

1.31

0.533

G

7.5

3

30

23.1

5.44

2.37

AB

7.5

3

30

22.1

5.11

2.15

10. Broccoli, Broccoli Raab, Cabbage, Chinese
Amaranth, Chinese Broccoli, Chinese Cabbage,
Canola\Rape, Cauliflower, Cole Crops, Collards, Corn
Salad, Dock (Sorrel), Horseradish, Kale, Kohlrabi,
Leafy Vegetables, Mustard, Mustard Cabbage (Gai
Choy/ Pak-Choi), and Garden and Winter Purslane

A

1.25

6

7

37.6

14.9

7.62

G

1.25

6

7

32.6

11.0

4.73

11. Corn (Silage and Unspecified), Field, Pop, and
Sweet Corn, Millet (Foxtail), and Sunflower

A

1

2

5

33.7

10.4

3.78

ULV

0.61

2

5

23.3

7.87

2.85

G

1

2

5

22.3

6.46

2.37

12. Cotton (Unspecified)

A

2.5

3

7

37.3

14.5

5.76

ULV

1.22

3

7

26.0

11.3

4.50

G

2.5

3

7

23.8

7.26

2.68

13. Hops

A

0.63

3

7

14.6

5.46

2.20

G

0.63

3

7

11.4

3.73

1.41

AB

0.63

3

7

11.1

3.57

1.32

15. Apricot

G

1.5

2

7

10.7

3.2

1.17

AB

1.5

2

7

10.1

2.9

1.04

16. Nectarine and Peach

G

3

3

7

25.3

7.71

2.92

AB

3

3

7

24.0

6.69

2.56

81

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Appl.
Method1

Maximum

Max. No.

Min.

EECs (ug/L)

Scenario

Application
Rate (lbs/A)

Apps. per
Crop Cycle

Rctrcatmcnt
Interval (days)

Peak EEC

21-dav

EEC

60-dav
EEC



A

1.75

4

3

16.7

7.01

2.51

17. Cherry

ULV

1.22

6

7

15.4

7.35

4.74

G

1.75

4

3

19.8

6.27

2.38



AB

1.75

4

3

18.5

5.69

2.07

18. Fig

G

2

2

5

17.0

4.83

1.79

AB

2

2

5

16.0

4.50

1.62

19. Pear

G

1.25

2

7

10.1

2.85

1.07

AB

1.25

2

7

9.5

2.67

0.964

20. Guava, Mango, and Papaya

G

1.25

13

3

22.2

6.75

3.11

AB

1.25

13

3

21.5

6.34

2.85

22. Garlic and Leek

A

1.56

3

7

34.2

10.8

4.08

G

2

3

7

41.8

9.63

3.73

23. Grapes

G

1.88

2

14

12.8

3.68

1.39

AB

1.88

2

14

11.8

3.31

1.24

26. Brussels Sprouts and Dandelion

A

1.25

2

7

52.0

15.4

5.73

G

1.25

2

7

46.9

13.4

4.96

27. Chervil, Chrysanthemum - Garland, Endive

A

1.88

2

5

83.1

24.2

8.84

(Escarole), Lettuce, Head and Leaf Lettuce, Orach















(Mountain Spinach), Parsley, Roquette (Arrugula),
Salsify, Spinach, and Swiss Chard

G

1.88

2

5

74.4

21.2

7.68

29. Eggplant

A

1.56

5

5

25.6

11.6

4.95

G

1.56

5

5

42.2

12.0

4.46

30. Pumpkin

A

1

2

7

8.30

2.42

0.869

G

1

2

7

5.65

1.19

0.437

31. Cantaloupe, Honey dew, Musk, Water, and Winter

A

1.75

3

7

49.7

17.7

6.74

Melons (Casaba/Crenshaw/Honeydew/Persian),
Chayote, Cucumber, Melons, and Squash (All or

G

1.75

3

7

42.9

12.9

4.71

Unspecified, Summer, and Winter (Hubbard))















32. Onion, Onions (Green), Radish, and Shallot

A

1.56

2

7

15.9

5.23

1.94

G

1.56

2

7

8.4

1.90

0.699

33. White/Irish Potato

A

1.56

2

7

12.7

4.35

1.60

G

1.56

2

7

20.3

4.65

1.70

34. Turnip (Greens and Root)

A

1.25

3

7

23.2

7.30

2.81

G

1.25

3

7

16.3

3.87

1.41

37. Bermudagrass, Bluegrass, Canarygrass, Grass

A

1.25

1

NA

16.6

4.57

1.64

82

-------


Appl.
Method1

Maximum

Max. No.

Min.

EECs (ug/L)

Scenario

Application
Rate (lbs/A)

Apps. per
Crop Cycle

Rctrcatmcnt
Interval (days)

Peak EEC

21-dav

EEC

60-dav
EEC

Forage/Fodder/Hay, Pastures, Peas (Including Vines),

ULV

0.92

1

NA

17.1

4.60

1.65

Rangeland, Sudangrass, and Timothy

G

1.25

1

NA

19.2

5.94

2.14

40. Beets, Beets (Unspecified), Cowpea/Blackeyed

A

2.5

2

7

18.3

5.25

1.91

Pea, Cowpeas, Field Peas, and Peas (Unspecified)

G

2.5

3

7

20.1

4.64

1.72

41. Carrot (Including Tops), Celtuce, Fennel, Peanuts,

A

2

2

5

32.4

8.61

3.12

Peanuts (Unspecified), and Pepper

G

2

2

5

25.1

5.27

1.93

42. Beans and Dried-Type and Succulent (Lima and
Snap) Beans

ULV

0.61

2

7

12.0

4.32

1.61

43. Celery

A

1.5

2

7

27.5

7.87

2.87

G

1.5

2

7

22.2

4.58

1.66

44. Asparagus and Safflower (Unspecified)

A

1.25

2

7

22.9

6.56

2.39

G

1.25

2

7

16.0

3.82

1.38

46. Strawberry

A

2

4

7

89.8

31.0

13.0

G

2

4

7

84.6

26.1

10.2

48. Tomato

A

1.56

4

5

45.6

17.1

6.90

G

1.56

4

5

37.1

11.9

4.52

49. Okra

A

1.2

5

7

12.6

4.15

2.27

G

1.2

5

7

9.5

2.22

0.982



A

1

2

7

9.3

2.53

0.930

51. Sorghum and Sorghum Silage

ULV

0.61

2

7

8.8

2.65

0.964



G

1

2

7

11.6

3.91

1.44



A

1.25

2

7

33.4

10.4

3.88

52. Barley, Cereal Grains, Oats, Rye, and Wheat

ULV

0.61

2

7

19.6

6.52

2.41



G

1.25

2

7

28.2

8.29

3.01



A

1.25

3

7

13.5

5.56

2.11

53. Gooseberry

G

2

3

7

35.7

10.3

3.83



AB

2

3

7

35.0

9.86

3.60



ULV

0.77

3

10

8.87

3.63

1.80

55. Blueberry

G

1.25

3

5

9.88

2.61

1.01



AB

1.25

3

5

9.01

2.39

0.865

57. Passion Fruit (Granadilla)

G

1

8

7

0.827

0.401

0.363

AB

1

8

7

0.614

0.284

0.257

58. Mint and Spearmint

A

0.94

3

7

8.30

3.60

1.36

G

0.94

3

7

19.7

6.15

2.32

83

-------
. . Maximum Max. No. Min.

EECs (ug/L)

Scenario

Method1

Application
Rate (lbs/A)

Apps. per
Crop Cycle

Rctrcatmcnt
Interval (days)

Peak EEC

21-dav

EEC

60-dav
EEC

59. Rice and Wild Rice

A

1.25

2

7

1120

1120

1120

ULV

0.61

2

7

548

548

548

G

1.25

2

7

1120

1120

1120

61. Water Cress

A

1.25

5

3

1120

1120

1120

G

1.25

5

3

1120

1120

1120

Non-Agricultural Uses

Cull Piles and Agricultural Structures and Equipment.
Cull Piles, Grain/cereal/flour bins (empty), and
Grain/cereal/flour elevators (empty)

Drench

298.7

1

NA

2.08

0.491

0.176

Fence rows/hedge rows

Drench

10.6

1

NA

0.789

0.202

0.0722

Forestry. Christmas Tree Plantations, Pine (Seed
Orchard), and Slash Pine (Forest)

A

3.2

2

7

60.0

19.8

7.18

ULV

0.9375

2

7

19.9

7.12

2.60

G

3.2

2

7

51.5

13.4

4.84

AB

3.2

2

7

50.1

12.7

4.55

Nursery. Ornamental and/or Shade Trees, Ornamental
Herbaceous Plants, Ornamental Non-flowering Plants,
and Ornamental Woody Shrubs and Vines

A

2.5

2

10

59.2

16.7

6.05

G

2.5

2

10

53.2

12.2

4.39

AB

2.5

2

10

53.0

12.4

4.45

Public Health and Mosquito and Medfly Control. Wide
Area/General Outdoor Treatment (Public Health Use),
Intermittently Flooded Areas/Water, and
Swamps/Marshes/Wetlands/Stagnant Water

ULV

0.23

1

NA

1.06

1.06

1.06

Residential and Refuse/Solid Waste.
Household/Domestic Dwellings (perimeter around
dwelling), Refuse/Solid Waste Containers (Garbage
Cans), and Refuse/Solid Waste Sites (Outdoors)

Drench

10.6

1

NA

3.43

0.701

0.250

Rights-of-way. Agricultural, uncultivated areas,
Nonagricultural Rights-of-way/Fencerows, and
Nonagricultural Uncultivated Areas/Soils

A

1

1

NA

24.0

8.84

3.93

ULV

0.9281

1

NA

7.31

2.76

1.07

G

1

1

NA

5.436

2.08

0.777

AB

1

1

NA

5.494

2.10

0.785

Turf. Golf Course Turf (Bermudagrass)

A

1.25

1

NA

10.3

2.87

1.02

ULV

0.92

1

NA

12.2

3.22

1.15

G

1.25

1

NA

5.69

1.53

0.547

1 A = aerial spray, G = ground spray, AB = air blast, ULV = ultra-low volume.

84

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3.2.3. Existing Monitoring Data

A critical step in the process of characterizing EECs is comparing the modeled estimates with
available surface water monitoring data. Surface water monitoring data are presented from four
monitoring programs. Two programs, California Department of Pesticide Regulation (CaDPR)
and U.S. Geological Survey's National Water Quality Assessment (NAWQA), analyzed surface
water samples for malathion in California, but were not targeted to malathion applications (non-
targeted). Non-targeted monitoring programs are not designed to sample specifically in the
vicinity of malathion applications and sampling is not timed to coincide specifically with
malathion applications. These programs provide information about typical or average malathion
concentrations and the general distribution of concentrations over the region, time period, and
population of sites sampled. The PRZM/EXAMS EECs should, in general, be higher than non-
targeted monitoring values with only the upper end of the distribution of non-targeted malathion
concentration values approaching the PRZM/EXAMS EECs.

The other two USDA programs, the Boll Weevil Eradication Program (BWEP) and the
Mediterranean fruit fly (medfly) control effort, are specifically designed to research the effects of
malathion applications (targeted monitoring). Because targeted monitoring specifically samples
water bodies expected to be most impacted by the malathion application being monitored, the
after application samples should produce environmental concentrations that are much closer to
corresponding PRZM/EXAMS EECs.

In the sections that follow, the ranges of the PRZM/EXAMS EECs are compared to non-targeted
and targeted monitoring.

3.2.3.a. Non-targeted Monitoring

An evaluation of the surface water monitoring data was conducted to assess the occurrence of
malathion and maloxon in California. Surface water data were obtained from the California
Department of Pesticide Regulation (CaDPR) surface water database,
(http://www.cdpr.ca.gov/docs/sw/surfdata.htm). U.S. Geological Survey's National Water
Quality Assessment (NAWQA) data warehouse (http://water.usgs.gov/nawqa/data.htmn. and
CaDPR and NAWQA publications. Maximum site concentrations from these data sets were
compared with PRZM/EXAMS EECs. Because these surface water sampling programs are not
targeted to malathion use areas and were not collected at sites similar to the standard EXAMS
pond (which is designed to present a high EEC scenario), these sampling programs are not
expected to produce concentrations as high as the PRZM/EXAMS EECs. However, any
agreement or disagreement can aid in characterizing the uncertainty of the PRZM/EXAMS
malathion EECs.

Frequency distributions of maximum site malathion concentrations are shown in Figure 3-3. At
many sites, all samples collected were below the level of quantitation ("< LOQ" - gray left-most
bars in each graph of Figure 3-3). The maximum reported concentration of malathion in the
CaDPR data set is 6.00 |ig/L from the Colusa Basin Drain #5 in Colusa County, CA, and
1.35 |ig/L from Warm Creek Near San Bernardino (site 11060400) in San Bernardino, CA, for
the USGS NAWQA data set. Note that these maximums were from locations that are slightly

-------
outside the range of the DS and CTS. The highest concentration found inside the range was 0.63
|ig/L from Arcade Creek. However, the interpretation of these data sets is complicated because
the LOQ varied between samples and over time. The maximum LOQs were 1 and 0.15 |ig/L for
the CaDPR and NAWQA data sets, respectively. Therefore, additional sites may have had actual
concentrations approaching these LOQs in the samples that were collected that are listed as
< LOQ. A total of 9 (CaDPR and NAWQA) sites had measured maximum concentrations in
excess of 1 |ig/L (the highest LOQ). Malathion concentrations specific to the habitat of the DS
is further discussed in Section 5.2.1.a.

CO 1000

£
On

E
s

100

Malathion Concentration (fig/L)

Figure 3-2. Frequency distributions of (a) maximum site malathion concentrations for California
Department of Pesticide Regulation (CaDPR) and (b) U.S. Geological Survey's National Water
Quality Assessment (NAWQA) data sets.

The only maloxon concentration measured above the detection limit in either the CaDPR or
NAWQA data sets is 0.06 |ig/L from the Alamo River at All American Canal in Imperial
County, CA (from the CaDPR data set). The detection limits for maloxon varied from 0.05 to
0.2 |ig/L for the CaDPR data set and from 0.008 to 0.09 |ig/L for the NAWQA data set.

3.2.3.b. Targeted Monitoring

Boll Weevil Eradication Program: Malathion is water soluble and therefore has the potential to
be dissolved in rain water and transported in runoff water from application sites. The Boll
Weevil Eradication Program (BWEP) has monitored malathion in runoff, standing (ponded), and
moving surface water.

Malathion in runoff. Levels of malathion in runoff water have been examined mostly using
automatic runoff sampling equipment which consists of collection bottles with funnels recessed
in the ground at sites where runoff is expected. The amount of malathion in runoff is expected to
be affected by numerous variables including the soil type, half-life on the particular soil, the
amount of time between application and precipitation, the amount of precipitation, and
vegetation. Table 9 shows runoff monitoring data from five treated cotton fields in the Boll
Weevil program close to bodies of water. Sampling was performed close to the field (10-25 feet)
and farther from the field (40-135 feet from the field). In most cases, malathion concentrations
were lower when the interval between application and rainfall was longer and/or distance from
the field was farther. These observations are expected since increasing the time interval since

-------
application allows for more degradation to occur and longer runoff travel distances allow
malathion to penetrate soil and adsorb to soil particles before reaching surface water.

Table 3-1. Field Monitored Runoff1 from the Cotton Boll Weevil Control Program





Field Runoff Malathion Concentration (ug/L)



Time from Applieation to

Closer to Field

Farther from Field

Field Number

Rain (Days)

(Distanee in Feet)

(Distanee in Feet)

1806-502

1

9.3 (20')

1.9(110')



3

7.5 (20')

3.5 (110')



6

>0.3 (20')

>0.3 (110')

1806-504

1

70 (20')

33 (40')



6

0.48 (20')

nd (40')

2025-187

2

0.42 (10')

0.53 (70')

2027-468

1

63 (15')

nd (135')



5

nd (15')

-

2100-200

18

4.2 (25')

3.8 (50')

502

3

1.1 (20')

nd (110')



7

0.5 (20')

nd (110')

504

1

10.9 (20')

nd (40')



3

41.8 (20')

15.6 (40')



7

146 (20')

93.5 (40')

7806

?

0.9 (0')

0.5 (45')



6

1.7 (0')

1.1 (45')



14

<0.3 (0')

0.3 (45')

325

2

8.54(15')

0.82 (60')



9

35.8(15')

16.2 (60')

Malathion levels were measured in runoff water from cotton fields after rain events. Two sets of measurements
were made, one closer to the field and one farther from the field. Adapted from Environmental Monitoring Report:
1997 Southeast Boll Weevil Eradication Program Sensitive Sites (USDA 1997a) and Environmental Monitoring
Report: 1996 Southeast Boll Weevil Eradication Program (USDA 1996)
nd = none detected.

- = not sampled.

? = not recorded.

Spray drift contributions to standing water bodies: In monitoring projects, the stability of
malathion in still water has been examined. A half-acre pond surrounded by cotton fields with a
25 foot buffer was monitored for malathion (USDA 1993). Pesticide drift was determined to be
the most important mechanism of contamination of the pond. Residue levels in the pond were
lower before treatment (<0.1-0.44 |ig/L) and higher immediately after malathion application
(<0.33-91.4 |ig/L). In most cases malathion in the pond degraded to <0.33 |ig/L within 7 days.
Runoff was only a minor contributor of residue to the pond but only two rainfalls occurred
during the sampling period. The malathion in the runoff samples collected were 9.75 and 76.3
|ig/L one day after the first and last treatments, respectively. Other natural bodies of water within
treatment areas, but not intentionally receiving direct spray, showed no detectable levels of
malathion 3-27 days after applications ceased (USDA 1995).

Spray drift contributions to moving water bodies: The Boll Weevil Eradication Program also
assessed spray drift contributions to moving water bodies (Tables 10, 11, and 12). Wide buffer
strips (125-700 feet) with high vegetation appeared to reduce malathion drift to sensitive areas to
levels below detection while narrower and lower buffer afforded less protection (Table 12). With

87

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aerial applications, 8 of 19 applications lead to higher aquatic malathion concentrations, whereas
only 1 of 10 ground applications resulted in higher malathion levels. Aerial applications are
more prone to drift than ground applications. Malathion levels in the streams, rivers, and canals
increased after nearby treatments and then decreased rapidly. The lower concentrations measured
over time are likely due to dilution and in-stream degradation.

Table 3-2. Southeast Boll Weevil Eradication Program Monitoring Data of Spray Drift to
Adjacent Moving Water (USDA 1993)a.		

Application Treatment Number

Downstream Malathion Concentration

Site: Comments

(Aerial /
Ground)

(Days since Last
Treatment)

jijj/L (Minutes
Before Treatment)

jijj/L (Minutes
After Treatment)

McCall's Creek: The

creek was separated
from the field (13.3
acre) by a continuous
600-700' buffer of 30-
60' trees.

Aerial

1(?)

nd

nd

Aerial

2(8)

nd

nd

Aerial

3(6)

nd

nd

Aerial

4(7)

nd

nd

Aerial

5(7)

16.1 (60)

nd

North River: The field
(8.3 acre) is separated
from the river by a
continuous buffer of
mature hardwoods and
moderately dense
understory
approximately 125'
deep.

Ground

1(?)

-

nd

Ground

2(5)

nd

nd

Ground

3(7)

nd

nd

Ground

4(6)

<0.33 (45)

<0.33 (45)

Ground

5(6)

<0.33 (0)

<0.33 (0-120)

Aerial

6(10)

1.54 (45)

1.44 (60)

Aerial

7(6)

<0.33 (0)

<0.33 (0-120)

Aerial

8(7)

1.77 (60)

1.46 (0)

Aerial

9(10)

0.42 (45)

0.55 (45)

Pursley Creek: The

field (95.3 acre) was
separated from the
creek by 100' of mature
hardwoods with a
dense understory.

Aerial

1(?)

nd

3.54 (135)

Aerial

2(7)

nd

0.39 (120)

Aerial

3(7)

nd

1.03 (30)

Aerial

4(7)

nd

<0.33 (75-120)

Aerial

5(7)

6.63 (30)

3.80 (120)

Aerial

6(6)

nd

3.35 (150)

Stewart Creek: The

field (19.2 acre) was
separated from the
creek by a 25' buffer of
low -lying kudzu
vegetation.

Ground

1(?)

nd

nd

Ground

2(8)

<0.33 (60)

nd

Aerial

3(7)

nd

7.69 (60)

Aerial

4(5)

nd

3.16(75)

Ground

5(7)

0.52

<0.33 (0-240)

Ground

6(4)

0.51

10.89(15)

Ground

7(5)

<0.33

<0.33 (15, 105, 135-250)

Aerial

8(6)

1.01

4.52 (60)

Aerial

9(12)

<0.33

3.49 (105)

a Malathion levels in moving water adjacent to cotton fields were measured before and after treatment.

Measurements were made downstream from the field every 15 minutes from one hour before until 2-3.25 hours after
application. Application was made when wind was not blowing directly over the water.

? = not recorded.

88

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Table 3-3. Texas Lower Rio Grande Valley Boll Weevil Eradication Program Monitoring Data
of Spray Drift to Adjacent Moving Water (USDA 1995a)a	



Downstream Malathion Concentration

Site/Com mcnts

Aerial/
Ground

T rcat-
mcnt #

jig/L (Minutes
Before Treatment)

jijj/L (Minutes
After Treatment)

#204060311/

Canal 200' from treated field.

?

1

0.324 (15)

0.297 (15)

?

2

4.89(15)

7.26 (30)

#2144070704 Canal 40' from
treated field

?

1

6.38 (30)

11.4 (0)

?

2

2.27 (45)

1.87 (0)

#212080704/ Canal 150' from
treated field

?

1

4.81 (45)

4.15 (30,120)

?

2

2.4 (30)

4.37 (120)

?

3

5.92 (45)

4.21 (0)

aMalathion levels in moving water adjacent to cotton fields were measured before and after treatment.

Measurements were made downstream from the field every 15 minutes from one hour before until 2-3.25 hours after
application. Application was made when wind was not blowing directly over the water.

? = not recorded.

Table 3-4. Southern Rolling Plains Boll Weevil Eradication Program Monitoring Data of Spray
Drift to Adjacent Moving Water (USDA 1994-5)a	



Peak Downstream Malathion Concentration

Site/Comments

Method of
Application

T reat-
mcnt #

|xg/L (Minutes
Before Treatment)

jijj/L (Minutes
After Treatment)

Concho County Stream
(10303-1408)
Samples collected 0.25 miles
downstream

Hi-Boy

1

0.849 (15)

6.95 (105)

Mist blower

2

0.695 (45)

86.9 (225)

Mist blower

3

0.273 (45)

0.503 (210)

Concho River
(10708-2707)
Samples collected 0.25 miles
downstream

Mist blower

1

0.676 (15)

0.813 (0)

Mist blower

2

0.871 (60)

0.589 (150)

Mist blower

3

2.24 (60)

7.45 (15)

aMalathion levels in moving water adjacent to cotton fields were measured before and after treatment.
Measurements were made downstream from the field every 15 minutes from one hour before until 2-3.25 hours
after application. Application was made when wind was not blowing directly over the water.

Monitoring data suggests that urban malathion use poses the highest risk of contaminating
surface water. However, use data are not available to correlate with monitoring data to determine
which particular uses have the greatest impact. Total usage and use rates in specific cities are
also unavailable. Targeted urban monitoring and preliminary fate experiments suggest that
malathion contacting anthropogenic surfaces is likely to convert to the oxon and has a high
runoff potential (CDPR 1981).

Mediterranean fruit fly (medfly) control effort: Malathion concentrations in water in and around
urban medfly treatment areas in California and Florida have been measured. Although a risk
assessment of malathion use for medfly control is not included in this document (these generally
fall under section 18 local need uses), the monitoring studies associated with this use provide
information on malathion fate and transport in residential settings. In urban areas not involved in
medfly control measures, malathion can be found in runoff water at higher levels than
agricultural areas. A monitoring report by United States Geological Survey showed that higher
residues are found in urban areas. In this analysis of 11 urban streams (604 samples) and 37

89

-------
agricultural streams (1530 samples) malathion concentrations were higher in the urban
tributaries.

It is likely that proposed residential uses will result in aquatic contamination. Residential
malathion uses include outdoor home and garden, public park, and commercial use as well as
residential mosquito control. Home use formulations may be applied as a "... spray to lower
foundation of house, patios and garbage cans ... along fences; to firewood piles; and other
infested areas" (Ortho Malathion 50 Plus Insect Spray label). Malathion on the surfaces
described on this label is likely to persist longer and be more available for runoff than malathion
on soil. Fyfanon ULV formulation is applied at 0.2 - 0.23 lbs/A aerially at 150 mph over
residential areas for mosquito control. In addition to covering anthropogenic surfaces it is likely
that moderate sized bodies of water receive direct spray during normal aerial mosquito control
use. In medfly treatments, malathion is mixed with a bait mixture and applied aerially at nearly
the same rate as in mosquito control but with large buffers (up to 200 feet). Medfly applications
in residential areas provide useful information on the fate and transport of malathion in these
settings, but it is very likely that the smaller particles produced from the ULV formulation used
in mosquito control results in more drift than the baited mixture for medfly. Thus, medfly
monitoring data of drift will be expected to underestimate drift from ULV mosquito use.

In medfly control efforts larger bodies of water are "flagged" to avoid direct malathion
treatment. Thus, contaminated water bodies presumably received insecticide residues by drift
and runoff. On average, reservoirs in the treatment area which were flagged to avoid direct spray
contained 0.16 |ig/L before treatments and 2.59 |ig/L immediately after treatment (Table 14). All
waters in and around the treatment area, whether protected or not, showed increased malathion
levels immediately after treatment. In general, applications were performed approximately
weekly with no noted aggregate accumulation of malathion in water.

Rainwater runoff in California medfly treatment area contributed greatly to malathion levels in a
stream passing through the treatment area. After precipitation, inflow into the treatment area
contained less than 1 |ig/L while downstream water contained up to 203 |ig/L malathion.
Maxima in 1990 and 1981 were 44.1 and 583 |ig/L, respectively (CaEPA1996).

Table 3-5. Malathion Levels in Bodies of Water in Relation to Medfly Control Sprayinga



T reat-

Days

Malathion (jug

/L)

Maloxon (ilg/L)



since















mcnt

Last

No. of

Before

After

No. of

Before

After

Site

No.

Spray

Samples

(Std. Err.)

(Std. Err.)

Samples

(Std. Err.)

(Std. Err.)



1

*

14

*

4.94 (2.71)

*

*

*



2

9

6-16

0.20 (0.05)

18.66 (5.81)

1

*

18.0 (*)

Unprotected1

3

11

13-15

1.50(1.17)

9.78 (2.47)

*

*

*

natural waters

4

7

14-15

.48 (.13)

95.4 (53.2)

1-2

0.64 (*)

1.9 (0.20)



5

7

13-14

.66 (.12)

4.97 (1.05)

4-5

.19(0.046)

.63 (.17)



6

7

11-12

.57 (.20)

23.4(11.6)

1-4

.90 (*)

.35 (.10)

Average

-

8.2

-

.68 (.33)

26.19 (12.8)

-

-

-

Protected2

1

*

20

.091 (.058)

.33 (.078)

*

*

*

natural waters

2

9

20

.12 (.07)

.56 (.10)

*

*

*



3

11

19-20

.056 (.028)

.90 (.15)

*

*

*



4

7

14-15

.12 (.07)

1.25 (.22)

*

*

*



5

7

20-22

.040 (.019)

2.10 (.41)

1

*

.40 (*)

90

-------
l)a j s

Malalhion dlg/l.)

Maloxon (llg/L)

Silo

1 real-

IIH'II (

No.

SI 1100
l.asl
Spra\

No. of
Samples

ISelore
(Sid. I'.rr.)

Aller
(Sul. I'.rr.)

No. of
Samples

Ik-lore
(SKI. I'.IT.)

Aller
(Sul. I'.rr.)

6

7

15-19

.053 (.040)

.39 (.089)

2

*

.45 (.25)

Average

-

8.2

-

.080 (.048)

.92 (.17)

-

-

-

Flagged
reservoirs

2

9

2

.18 (.03)

.75 (.65)

1

*

2.7 (*)

3

11

2

*

.50 (.10)

*

*

*

4

7

19-20

.033 (.024)

8.39(3.81)

2

*

.92 (.29)

5

7

10-12

.51 (.30)

1.90 (.94)

*

*

*

6

7

8

.075 (.062)

1.42 (.41)

1

•1 (*)

.83 (*)

Average

-

8.2

-

.16 (.083)

2.59 (1.18)

-

-

-

Reservoirs
outside
treatment area

2

9

2

.05 (.05)

.34 (.07)

*

*

*

3

11

2-4

.10 (.10)

1.0 (.55)

*

*

*

4

7

10

.03 (.03)

.30 (.16)

*

*

*

5

7

10

.036 (.024)

.14 (.058)

1

1.3 (*)

*

6

7

8-10

.18 (.074)

.21 (.087)

*

*

*

Average

-

8.2

-

.079 (.056)

.40 (.19)

-

-

-

a Malathion was measured immediately before and after spraying a bait formulation at ~0.17 lbs ai/A from an
altitude of 300 feet. This data was adapted from A Characterization of Sequential Aerial Malathion Applications in
the Santa Clara Vallev of California (CaEPA 1981).

1	Unflagged and within the treatment area.

2	Flagged to avoid treatment or outside the treatment area.

* No data.

Table 3-6. Malathion Level in 29 Ponds in Florida Exposed to Direct (Unprotected Aquatic
Sites) or Indirect (Protected Aquatic Sites) Malathion Spray in Medfly Controla	



Before Application

After Application



Number of

Average

St. Dev.

Number of

Average

St. Dev.

site

Samples

(Hg/L)

(Hg/L)

Samples

(ua/L)

(Ug/L)

Unprotected Aquatic Sites

Fairgrounds

8

0.06

0.07

9

1.20

1.54

Palm river

9

0.78

0.72

7

3.97

3.24

Ragen Park

6

14.12

14.17

7

35.75

27.50

University Square Mall

7

0.04

0.07

7

3.77

3.67

Pond Lake

6

4.11

4.35

10

9.25

11.78

Bloomingdale Area

9

0.81

0.71

9

6.12

7.22

Carrolwood

7

1.05

2.01

6

4.77

3.75

Town and Country

6

1.10

1.15

5

6.88

3.07

McDill Site

5

0.12

0.06

4

5.20

2.33

Brandon Town Center

5

3.50

1.86

8

65.71

149.18

Lowry Zoo

7

0.14

0.22

6

1.55

1.86

Sun 'n Fun

8

0.09

0.07

10

7.28

15.48

Hamilton Creek

6

0.61

0.41

7

10.74

19.51

Eagle Lake

7

1.60

2.29

7

13.99

10.39

91

-------
site

Before Application

After Application

Number of
Samples

Average

(ue/L)

St. Dev.
(Utl/L)

Number of
Samples

Average
(UH/L)

St. Dev.
(U2/L)

Protected Aquatic Sites

Moore's lake

0.36

0.78

0.76

1.66

Lake Weeks

0.69

0.67

4.85

4.08

Lake Valrico

0.03

0.06

2.84

6.71

Lake Kathy

0.43

0.91

5.91

9.15

Lake Walden

0.21

0.14

2.21

2.37

Alafia River

0.13

0.17

1.93

4.06

Hillsborough River

0.35

0.39

5.02

9.13

Piatt Lake

0.08

0.85

0.15

Lake Magdalene

0.08

0.80

0.20

Lake Carroll

0.31

0.16

1.65

0.55

Crystal Lake

0.02

0.05

0.46

0.74

Lake Horney

0.03

0.06

3.47

3.86

Banana Lake

0.21

0.33

2.48

3.97

Crews Lake

0.23

0.19

0.82

0.96

a Samples were collected within 18 hours of approximately weekly treatments of 0.15 lbs/A. Unprotected bodies of
water were ~0.1 miles in length and may have received runoff from surrounding watersheds. Protected waters were
rivers or larger lakes. Statistically, values below the detection limit (0.1 |ig/L) were treated as 0 |ig/L and values
below limit of quantitation (0.3 |ig/L) were treated as 0.15 |ig/L. The data was adapted from the Environmental
Monitoring Report: Cooperative Medflv Project Florida (USDA 1997b).

Residential settings are expected to be composed of numerous surfaces which may be physically
and biologically impervious to malathion. The relative quantities and effects of adsorption and
degradation on concrete, roofing, metal, and plastics is unknown in the residential settings where
malathion may be sprayed for medfly and mosquito control. Monitoring results suggest that the
residential surfaces increase availability of malathion for runoff, probably due to lack of
microbial activity which decreases metabolism, less water content which decreases hydrolysis,
and little adsorption. Although the application rate for mosquito control is low relative to
agricultural use (0.20 - 0.6 lbs/A for aerial mosquito control versus 0.175 - 27.47 lbs/A for
agricultural pest control), application over wide areas may be concentrated in storm drain
systems along with malathion from home and garden and commercial site use.

The concentration factor appears to be greater in residential settings when comparing residential
and agricultural runoff. This is consistent with the results of several USGS and USDA
monitoring studies. Preliminary monitoring results for malathion in surface water (USGS 1997)
show malathion was detected above 0.01 |ig/L with a 2.61% frequency in agricultural streams
while in urban streams the frequency was 20.86%. The USDA monitoring studies for boll
weevil control show an average runoff concentration of 15.5 |ig/L (Table 11) while average
downstream creek concentrations in the urban Santa Clara Valley of central California were 177
|ig/L during 1981 malathion spraying for medfly.

The highest levels of aquatic maloxon found in a search of available data were a result of medfly
control efforts in California (CaDFG 1982). The following table is derived from the monitoring
study during the malathion spraying in the Santa Clara Valley. Samples were taken 2-3.5 hours
after the first rainfall six days after the last application. These runoff concentrations are much
higher than agricultural runoff levels.

-------
Table 3-7. Malathion and Maloxon Concentrations in Creeks after Malathion Applications in the
Santa Clara Valley	



.\\er.iiic ( <>iiiTiilr;iliuii (Sid. I)e\.)

Siimpliii^ Locution

Miiliilliion (llli/l.)

Miiloxon

Adobe Creek

50' Upstream

449 (17.7)

164 (33.2)

Drain

583 (40.3)

328 (18.4)

100' Downstream

361 (20.5)

169 (-)

Stevens Creek

50' Upstream

159 (-)

68.0 (-)

Drain

434 (73.5)

147 (4.2)

150' Downstream

156 (23.3)

68.0 (-)

Guadalupe Creek, Site 1

50' Upstream

1.9 (0.2)

0.8 (0.3)

Drain

142 (-)

147 (4.2)

150' Downstream

23.5 (2.1)

22.0 (-)

Guadalupe Creek, Site 2

50' Upstream

137 (25.4)

212 (9.2)

Drain

188(12.0)

250 (8.5)

150' Downstream

169 (6.4)

231 (8.5)

Fate data for malathion clearly show that its major routes of degradation are through aerobic
microbial metabolism and hydrolysis. Both of these routes are expected to be lower on inert, dry
surfaces; thus malathion persistence would be expected to be increased. Malathion persistence on
steel plates is extended relative to soil with only 15% lost in two days (CaEPA 1996) compared
to several soils on which 50% can be degraded in 8 hours. Slowed malathion hydrolysis and
metabolism is likely to result in increased maloxon levels via abiotic oxidation. On the steel plate
study mentioned previously, maloxon accounted for 5% of the degradates, significantly higher
than the maximum of 1.8% on soil reported by the registrant.

3.2.3.C. Atmospheric Monitoring Data

An evaluation of air monitoring data was conducted to assess the occurrence of malathion and
maloxon. Air monitoring data were obtained from the California Department of Pesticide
Regulation (Segawa, et al, 2003 and Kollman 2002). A review of the air monitoring data
indicates that malathion was detected in trace quantities in an air monitoring study in Lompoc
City, Santa Barbara County (Segawa, et al, 2003). Air concentrations of malathion were 7.6
ng/m3 for the highest one day average, 1.01 ng/m3 for the highest 3 day average, 0.54 ng/m3 for
the highest 18 day average concentration. Air concentrations of malathion were not reported in
the California Pesticide Air Monitoring Results: 1986-2000 (Kollman 2002). Additionally, air
monitoring data for the malathion degradation products was not found.

3.3. Terrestrial Animal Exposure Assessment

3.3.1. Exposure to Residues in Terrestrial Food Items

T-REX (version 1.4.1) was used to calculate dietary and dose-based exposure of malathion for
birds (surrogate for terrestrial-phase amphibians and reptiles) and mammals. T-REX simulates
exposure level for a 1-year period following one or multiple spray applications of malathion. T-
HERPS (version 1.1) was then used to refine the EECs for amphibians and reptiles when risk
quotients from T-REX exceeded the Agency's LOCs. The EECs estimated by T-REX and T-

93

-------
HERPS are applicable to all outdoor uses of malathion, including ground and aerial spraying and
ULV applications. Terrestrial EECs were derived for 17 model scenarios to represent the range
of uses of malathion. These scenarios were selected to assess risk for the most widespread uses
and to reflect uses associated with extreme high- and low-end exposure. By including the high-
and low-end scenarios, the scenarios are designed to reflect the full range of terrestrial exposure
expected for all uses of malathion.

For aerial ULV spraying of malathion for control adult mosquitoes, AGDISP was used to predict
deposition on the terrestrial surfaces. The deposition Assessment tool of AGDISP was used for
malathion mass deposition based on point estimate rather than an area basis. The input and
output were described in Section 3.2.2.b.

T-REX and T-HERPS estimate the peak residues that are expected to occur on wildlife food
items following repeated applications of the pesticide. To calculate this, the models require an
estimated half-life for the rate of dissipation of residues on the food item. This half-life was
estimated based on the 37 foliar persistence half-lives published in Willis and McDowell (1987)
for application of various malathion formulations on various agricultural crops. Half-life values
ranged from 0.3 to 10.9 days. All but one of the half-life values were estimated based on total
residues. One value based on dislodgable residues (6.1 days) was included in the analysis. The
90th percentile on these 37 values (6.1 days) was used as the estimate in both models. Other use
specific input values include number of applications and application rate. All input values used
in T-Rex and T-HERPS are provided in Table 3-8. An example of output from T-REX and T-
HERPS are available in Appendix E.

Table 3-8. Input Parameters for Foliar Applications Used to Derive Terrestrial EECs for

Malathion with T-REX and T-HERPS

Use (Application method)

Application

Rate
(lbs a.i./A)

Number of
Applications

Application
Interval

Foliar Dissipation Half-Life

Agricultural Uses

Citrus

7.5

n/a

6.1 days

Citrus (ULV)

0.175

6.1 days

Cotton, chestnut, and walnut

2.5

6.1 days

Pecan

2.5

6.1 days

Strawberry

2.0

6.1 days

Caneberry group

2.0

6.1 days

Mushroom

1.7

6.1 days

Papaya

1.25

6.1 days

Mango

0.9375

6.1 days

Rice, barley, broccoli, carrot,
pear, et al.

1.25

6.1 days

Alfalfa

1.25

6.1 days

Field corn, wheat, oats, sorghum,
melons, peas, et al.

1.0

6.1 days

Field corn, wheat, oats, sorghum,
and beans (ULV)

0.61

6.1 days

Pastures (ULV)

0.92

n/a

6.1 days

-------
Use (Application method)

Application

Rate
(lbs a.i./A)

Number of
Applications

Application
Interval

Foliar Dissipation Half-Life

Non-Agricultural Uses

Cull Pile

299

1

n/a

6.1 days

Fence / hedge row, domestic
dwelling (perimeter), and
refuse/solid waste site

10.6

1

n/a

6.1 days

Adult mosquito control

0.23

0.079a

26

6.1 days

n/a = Not applicable

a Predicted maximum deposition rate from aerial ULV application at the maximum application rate of 0.23 lb ai/A

3.3.1.a. Dietary Exposure to Mammals, Birds, and Amphibians
Derived Using T-REX

T-REX was used to assess direct and indirect effects on the terrestrial phase of the CTS based on
dietary exposure to malathion. T-REX calculates EECs of malathion for various terrestrial food
items, including grass, broadleaf plants, insects, and fruits/seeds. Predicted upper-bound EECs
were derived (Table 3-9) and used to calculate risk quotients. As a first-tier screen for direct
effects to the CTS, risk quotients were calculated for small birds (a surrogate for amphibians)
consuming short grass. In addition, to assess indirect effects, risk quotients were calculated for
small birds and mammals that feed on short grass. Small mammals are important because they
are a prey item of the CTS, as well as because they create burrows which are an important
habitat element for the CTS. Small birds were assessed as a surrogate for terrestrial amphibians,
which are also prey of the CTS. The prey items were assumed to consume short grass because
this is the dietary item predicted to have the highest residues of malathion.

Table 3-9. Upper-bound Kenaga Nomogram EECs for Dietary- and Dose-based Exposures of
Birds and Mammals Derived Using T-REX for Malathion		

Use Scenario

EECs for CTS and
Other Amphibians
(small birds consuming short grass)

EECs for Mammals
(small mammals consuming short

grass)

Dicta rv-bascd
EEC (mg/kg-dict)

Dose-based EEC
(mg/kg-bw)

Dietary-based

EEC
(mg/kg-dict)

Dosc-bascd EEC
(mg/kg-bw)

Agricultural Uses

Citrus

1800

2050

1800

1720

Citrus (ULV)

43.4

93.5

43.4

41.4

Cotton, chestnut, and walnut

993

1130

993

947

Pecan

871

992

871

830

Strawberry

839

955

839

800

Caneberry group

697

793

697

664

Mushroom

831

947

831

763

Papaya

971

1110

971

925

Mango

410

467

410

391

Rice, barley, broccoli, carrots, pears,
et al.

435

496

435

415

Alfalfa

361

411

361

344

Field corn, wheat, oats, sorghum,
melons, peas, et al.

348

397

348

332

95

-------


EECs for CTS and

EECs for Mammals



Other Amphibians

(small mammals consuming short

Use Scenario

(small birds consuming short grass)

grass)





Dicta ry-bascd

EEC
(mg/kg-dict)





Dicta rv-bascd

Dosc-bascd EEC

Dosc-bascd EEC



EEC (mg/kg-dict)

(mg/kg-bw)

(mg/kg-bw)

Field corn, wheat, oats, sorghum, and
beans (ULV)

212

242

212

203

Pastures (ULV)

221

251

221

211

Non-Agricultural Uses

Cull Pile

71,700

81,600

71,700

68,300

Fence / hedge row, domestic dwelling
(perimeter), and refuse/solid waste

2,550

2,900

2,550

2,430

site









Adult mosquito control

23.8

27.1

23.8

22.7

3.3.2. Exposure to Terrestrial Invertebrates

T-REX was also used to calculate EECs for terrestrial invertebrates exposed to malathion.
Available acute contact toxicity data for bees exposed to malathion (in units of |ig a.i./bee), were
converted to |ig a.i./g (of bee) by multiplying by 1 bee/0.128 g. Dietary-based EECs calculated
by T-REX for small and large insects (units of a.i./g) were used to bound an estimate of exposure
to terrestrial invertebrates. Table 3-10 provides EECs predicted for small insects. The EECs
were then compared to the adjusted acute contact toxicity data for bees in order to derive RQs.
An example output from T-REX v. 1.4.1 is available in Appendix E.

96

-------
Table 3-10. Summary EECs for Terrestrial Insects (Surrogate for Terrestrial Arthropods)

Derived Using T-REX ver.

1.4.1.

Use

Rate

Number of

Appl. Interval

Small inseet EEC

(m« ai/kjj)

Audi.

(days)

(mjj/kjj-bw)

A

»ricultural Uses

Citrus

7.5

1

n/a

1012

Citrus (ULV)

0.175

3

30

24.4

Cotton, chestnut, and walnut

2.5

3

7

559

Pecan

2.5

2

7

490

Strawberry

2.0

4

7

472

Caneberry group

2.0

3

7

392

Mushroom

1.7

3

4

468

Papaya

1.25

8

3

546

Mango

0.9375

10

4

231

Rice, barley, broccoli, carrots,
pears, et al.1

1.25

2

7

245

Alfalfa

1.25

2

14

203

Field corn, wheat, oats, sorghum,
melons, peas, et al.

1.0

2

7

196

Field corn, wheat, oats, sorghum,
and beans (ULV)

0.61

2

7

120

Pastures (ULV)

0.92

1

n/a

124



Non

¦Agricultural Uses



Cull Pile

299

1

n/a

40,300

Fence / hedge row, domestic









dwelling (perimeter), and
refuse/solid waste site

10.6

1

n/a

1430

Adult mosquito control

0.23

23

7

13.4

1 See Appendix B for a complete list of uses that fit this use scenario.

3.3.2.a. Dietary Exposure to Amphibians and Reptiles Derived Using T-
HERPS

Birds were used as surrogate species for terrestrial-phase CTS. Terrestrial-phase amphibians and
reptiles are poikilotherms indicating that their body temperature varies with environmental
temperature. Birds are homeotherms indicating that their temperature is regulated, constant, and
largely independent of environmental temperatures). As a consequence, the caloric requirements
of terrestrial-phase amphibians and reptiles are markedly lower than birds. Therefore, on a daily
dietary intake basis, birds consume more food than terrestrial-phase amphibians. This can be
seen when comparing the caloric requirements for free living iguanid lizards (used in this case as
a surrogate for terrestrial phase amphibians) to song birds (USEPA, 1993):

iguanid FMR (kcal/day) = 0.0535 (bw g)0'7"

passerine FMR (kcal/day) = 2.123 (bw g)0'749

With relatively comparable slopes to the allometric functions, one can see that, given a
comparable body weight, the free-living metabolic rate (FMR) of birds can be 40 times higher
than reptiles, though the requirement differences narrow with high body weights.

97

-------
Because the existing risk assessment process is driven by the dietary route of exposure, a finding
of safety for birds, with their much higher feeding rates and, therefore, higher potential dietary
exposure is reasoned to be protective of terrestrial-phase amphibians. For this not to be the case,
terrestrial-phase amphibians would have to be 40 times more sensitive than birds for the
differences in dietary uptake to be negated. However, existing dietary toxicity studies in
terrestrial-phase amphibians for malathion are lacking. To quantify the potential differences in
food intake between birds and terrestrial-phase CTS, food intake equations for the iguanid lizard
were used to replace the food intake equation in T-REX for birds, and additional food items of
the CTS were evaluated. These functions were encompassed in a model called T-HERPS. T-
HERPS is available at: http://www.epa.gov/oppefedl/models/terrestrial/index.htm. EECs
calculated using T-HERPS are shown in this Section and potential risk is further discussed in the
risk characterization.

Table 3-11 show the EECs calculated using T-HERPS for the CTS and used in this risk
assessment. Young CTS in the terrestrial phase consume predominantly arthropods, whereas
larger adult CTS also consume frogs and small mammals. EECs generated by T-HERPS that are
applicable to the CTS are thus small (2 g) amphibians consuming small and large insects, and
medium (20 g) amphibians consuming small and large insects, small herbivorous and
insectivorous mammals, and amphibians. For juvenile CTS, EECs used in this assessment were
for consumption of small insects because the model assumes higher residues on small insects
than on large insects. Likewise, for adult CTS, EECs used in this assessment were for
consumption of herbivorous small mammals because that is the dietary item of adults that has the
greatest predicted residues in this model. Results using these EECs thus would be protective of
CTS which consume all other dietary items.

Table 3-11. Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based Exposures of
Amphibians and Reptiles Derived Using T-HERPS for Malathion

EECs for Juvenile CTS Consuming

EECs for Adult CTS Consuming

Small

Insects

Herbivorous Mammals

Use Scenario

Dictarv-bascd

Dose-based EEC

Dictarv-bascd

EEC
(mg/kg-dict)

Dose-based EEC

EEC (mg/kg-dict)

(mg/kg-bw)

Agricultural Uses

Citrus

1010

32.1

1810

1200

Citrus (ULV)

24.4

0.78

43.6

29.1

Cotton, chestnut, and walnut

559

17.7

997

664

Pecan

490

15.6

874

583

Strawberry

472

15.0

842

651

Caneberry group

447

14.2

797

532

Mushroom

468

14.8

834

556

Papaya

546

17.3

974

649

Mango

343

10.9

612

408

Rice, barley, broccoli, carrots, pears,
et al.

245

7.77

437

291

Alfalfa

203

6.45

363

242

Field corn, wheat, oats, sorghum,
melons, peas, et al.

196

6.22

350

233

Field corn, wheat, oats, sorghum,
and beans (ULV)

120

3.79

213

142

-------
Use Scenario

EECs for Juvenile CTS Consuming
Small Insects

EECs for Adult CTS Consuming
Herbivorous Mammals

Dictarv-bascd
EEC (mj^kg-dict)

Dose-based EEC
(mg/kg-bw)

Dictarv-bascd

EEC
(mg/kg-dict)

Dosc-bascd EEC
(mg/kg-bw)

Pastures (ULV)

124

3.94

221

148

Non-Agricultural Uses

Cull Pile

40,400

1280

72,000

48,000

Fence/hedge row, domestic dwelling
(perimeter), refuse/solid waste site

1430

45.4

2550

1700

3.4. Terrestrial Plant Exposure Assessment

No exposure assessment was conducted for terrestrial plants. No terrestrial plant toxicity data
have been submitted to the Agency that can be used to compare to predicted exposure levels to
conduct a quantitative risk assessment for terrestrial plants. Evidence from the open literature
and the long history of use on a wide variety of plants indicate that malathion does not cause
adverse effects on the plants (see Section 4.3.4). Therefore a quantitative risk assessment on
terrestrial plants was not conducted.

4. Effects Assessment

As described in the Agency's Overview Document (USEPA, 2004), the most sensitive endpoint
for each taxon was used for risk estimation. For this assessment, evaluated taxa included
freshwater fish, amphibians (frog tadpoles), freshwater invertebrates, estuarine/marine fish,
estuarine/marine invertebrates, aquatic plants, birds, mammals, terrestrial invertebrates, and
terrestrial plants. Acute (short-term) and chronic (long-term) toxicity information were
characterized based on registrant-submitted studies and a comprehensive review of the open
literature on malathion.

This assessment evaluated the potential for malathion to directly or indirectly affect DS and CTS
or modify their designated critical habitat. Assessment endpoints for the effects determination
for each assessed species included direct toxic effects on the survival, reproduction, and growth,
as well as indirect effects, such as reduction of the prey base or modification of its habitat. In
addition, potential modification of critical habitat was assessed by evaluating effects to the PCEs,
which are components of the critical habitat areas that provide essential life cycle needs of each
assessed species. Direct effects to the DS and to the aquatic stages of the CTS were based on
available toxicity data for fish. Available acute toxicity data for frog tadpoles were also
considered for the assessment of aquatic stages of the CTS, but were not used in the quantitative
risk calculations. Direct effects for the terrestrial stage of the CTS were based on avian toxicity
data, given that birds are generally used as a surrogate for terrestrial-phase amphibians.

4.1. Ecotoxicity Study Data Sources

Toxicity endpoints were established based on data generated from guideline studies submitted by
the registrant, and from open literature studies that meet the criteria for inclusion into the
ECOTOX database maintained by EPA/Office of Research and Development (ORD) (USEPA,

-------
2004). Ecotoxicity data used in this risk assessment are summarized in Appendix I. Toxicity
data on mammals were obtained from the data review conducted by the Health Effects Division
and published in the Registration Eligibility Decision Document (RED) for Malathion. The
chapter of this RED that presents these toxicity data are given in Appendix J. Open literature
data presented in this assessment were obtained from a previous assessment for the California
red-legged frog (USEPA, 2007a), a search of the ECOTOX database conducted in October 2008,
as well as an update search conducted in February 2010. In order to be included in the ECOTOX
database, papers must meet the following minimum criteria:

(1)	the toxic effects are related to single chemical exposure;

(2)	the toxic effects are on an aquatic or terrestrial plant or animal species;

(3)	biological effect are on live, whole organisms;

(4)	a concurrent environmental chemical concentration/dose or application rate is
reported; and

(5)	duration of exposure was explicitly reported.

Open literature toxicity data for other 'target' insect species (not including bees, butterflies,
beetles, and non-insect invertebrates including soil arthropods and worms), which include
efficacy studies, are not currently considered in deriving the most sensitive endpoint for
terrestrial insects. Efficacy studies do not typically provide endpoint values that are useful for
risk assessment (e.g., NOAEC, EC50, etc.), but rather are intended to identify a dose that
maximizes a particular effect (e.g., EC100). Therefore, efficacy data and non-efficacy
toxicological target insect data were not included in the ECOTOX open literature summary table
provided in Appendix I. For the purposes of this assessment, 'target' insect species are defined
as all terrestrial insects with the exception of bees, butterflies, beetles, and non-insect
invertebrates (i.e., soil arthropods, worms, etc.) which were included in the ECOTOX data
presented in Appendix I. The list of citations including toxicological and/or efficacy data on
target insect species not considered in this assessment is provided in Appendix H

Data that passed the ECOTOX screen were evaluated along with the registrant-submitted data,
and were incorporated qualitatively or quantitatively into this endangered species assessment.
Effects data in the open literature were used when they were more conservative than the
registrant-submitted data. In general, the degree to which open literature data were
quantitatively or qualitatively characterized for the effects determination was dependent on
whether the information was relevant to the assessment endpoints (i.e., survival, reproduction,
and growth). For example, endpoints such as behavior modifications were qualitatively
evaluated, because quantitative relationships between modifications and reduction in species
survival, reproduction, and/or growth are not available. Although the effects determination
relied on endpoints that are relevant to the assessment endpoints of survival, growth, or
reproduction, it is important to note that the full suite of sublethal endpoints potentially available
in the effects literature (regardless of their significance to the assessment endpoints) were
considered, as they were relevant to the understanding of the area with potential effects, as
defined for the action area.

Citations of all open literature not considered as part of this assessment because they were either
rejected by the ECOTOX screen or accepted by ECOTOX but not used (e.g., the endpoint is less

100

-------
sensitive) are included in Appendix H. Appendix H also includes a rationale for rejection of
those studies that did not pass the ECOTOX screen and those that were not evaluated as part of
this endangered species risk assessment.

In addition to registrant-submitted and open literature toxicity information, ecological incident
data were reviewed and used to refine the characterization of potential ecological effects
associated with exposure to malathion. Available aquatic and terrestrial incident data associated
with malathion are summarized in Section 4.5 and presented in detail in Appendix G.

4.2. Toxicity of Malathion to Aquatic Organisms

Table 4-1 summarizes the most sensitive aquatic toxicity endpoints, based on an evaluation of
both the submitted studies and the open literature. A brief summary of submitted and open
literature data considered relevant to this ecological risk assessment for the DS and CTS is
presented below. Additional information is provided in Sections 4.2.1 through 4.2.5. All
endpoints are expressed in terms of the active ingredient (a.i.) unless otherwise specified.

Table 4-1. Aquatic Toxicity Profile for Malathion

Assessment
Endpoint

Acute/
Chronic

Species

% AI

Toxicity Value
(95 % Confidence
Interval)

Citation
MRIDor
ECOTOX1

Comment

Freshwater fish
(surrogate for
aquatic-phase
amphibians)

Acute

Rainbow trout

(Oncorhynchus
mykiss)

96-hr LC50 = 33
(22 - 39) (ig/L

Slope = 4.45 (2.22 -
6.68)

Animal Biology
Laboratory, 1968
MRID 48078003

This study was
conducted at the
Animal Biology
Laboratory of the
USD A. The Agency
determined it was
acceptable for
quantitative risk
assessment. The acute
toxicity category is
very highly toxic.

Chronic

Flagfish

(Jordanella
floridae)

Tech.

LOAEC= 11 ugai/L
NOAEC = 8.6 (ig/L

Eco ref. 000995
(Hermanutz, 1978)

Study was found to be
acceptable for
quantitative risk
assessment.

Freshwater
invertebrates

Acute

Water flea

(Simocephalus
serrulatus)

48-hr EC50= 0.59
(0.46 - 0.77) (ig/L

Slope = 5.45 (2.78-
8.12)

MRID 40098001
(Mayer and
Ellersick, 1986)

Study was conducted
by the Columbia
national Fisheries
Research Laboratories,
US Fish and Wildlife
Service. This study
was found to be
acceptable for
quantitative risk
assessment. The acute
toxicity category is
very highly toxic.

Chronic

Water flea

(Simocephalus
serrulatus)

Estimated NOAEC =
0.035 ng/L

The chronic NOAEC
for freshwater
invertebrates was
derived based on the

101

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Assessment
Endpoint

Acute/
Chronic

Species

% AI

Toxicity Value
(95 % Confidence
Interval)

Citation
MRIDor
ECOTOX1

Comment













ACR for daphnia (see
Section 4.2.2.b.)

Estuarine/
marine fish

Acute

Sheepshead
minnow

(Cyprinodon
variegatus)

94

96-hr LC50= 33
(14-63) (ig/L
(Slope not
determined)

MRID 41174301
(Bowman, 1989)

Study was found to
be acceptable for
quantitative risk
assessment. The acute
toxicity category is
very highly toxic.

Chronic

Bluehead wrasse
(Thalassoma
bifasciatum)



Estimated NOAEC
= 17.3 ng/L



The chronic NOAEC
for the

estuarine/marine fish
was derived based on
the ACR for rainbow
trout (see section
4.2.3.b)

Estuarine/

marine

invertebrates

Acute

Mysid

(Americamysis
bahia)

94

96-hr EC50= 2.2
(1.5-2.6) (ig/L
(Slope not
determined)

MRID 41474501
(Forbis, 1990)

Data are from an
acceptable study
submitted by the
registrant. The acute
toxicity category is
very highly toxic.

Chronic

N/A



Estimated NOAEC
= 0.013 ng/L



The chronic NOAEC
for estuarine/marine
invertebrates was
derived based on the
ACR for daphnia (see
Section 4.2.4.b)

Aquatic plants

Non-
Vascular

Green algae

Pseudokirchneriell
a subcapitata

100

48-hr EC50 = 2400
(1500-3600) (ig/L
Slope = 3.58
NOAEC = 500 ug/L

Eco ref. 085816
(Yeh and Chen,
2006)

Study was found to be
acceptable for
quantitative risk
assessment.

Vascular

Duckmeat

Spirodela
polyrhiza

96.26

NOAEC= 9,630
Hg/L

Eco ref. 054278
(Sinhae/a/., 1995)

Study was found to be
not acceptable for
qualitative use in risk
assessment. However,
it does provide
adequate information to
conclude that aquatic
plants in the duckweed
family are less sensitive
to malathion than green
algae. In the
Registration Review
Problem Formulation,
this paper was
incorrectly cited as Eco
ref. 009184

1 Eco ref numbers refer to the reference numbers used in the ECOTOX database.

Toxicity to fish and aquatic invertebrates was categorized using the system shown in Table 4.2
(USEPA, 2004). Toxicity categories for aquatic plants have not been defined.

102

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Table 4-2. Categories of Acute Toxicity for Fish and Aquatic Invertebrates

LCso (mjj/L)

Toxicity Category

<0.1

Very highly toxic

>0.1-1

Highly toxic

>1-10

Moderately toxic

> 10 - 100

Slightly toxic

> 100

Practically nontoxic

4.2.1. Toxicity to Freshwater Fish and Aquatic-Phase Amphibians

4.2.1.a. Freshwater Fish: Acute Exposure (Mortality) Studies

Table 4-3 summarizes acute toxicity data on the effects of malathion to freshwater fish and
amphibians. Freshwater fish toxicity data for malathion were obtained from studies conducted at
two federal government laboratories, the Columbia National Fisheries Research Laboratory
(Mayer and Ellersieck, 1986) and from the former USEPA Animal Biology Laboratory. To date,
no other freshwater fish toxicity data submitted by pesticide registrants on the toxicity of
malathion has been found to be acceptable for use in this risk assessment. Two freshwater fish
acute toxicity studies conducted in 2001 are currently being evaluated by the Agency.
Preliminary results from these studies, shown in Table 4-3, indicate that neither provides the
lowest acute toxicity endpoint for freshwater fish and, therefore, were not applicable for use in
the screening-level risk assessment. Many studies from the open literature, identified through
the ECOTOX literature search, also provided toxicity data on the acute effects of malathion to
freshwater fish. None of the acute freshwater studies from the open literature are included in
Table 4-3 because they did not provide the lowest toxicity endpoint for freshwater fish. Open
literature data obtained in a 2007 ECOTOX literature search was previously described in the
Agency's assessment for the California red-legged frog (USEPA, 2007a). For amphibians, acute
toxicity data were obtained from studies conducted at the Columbia National Fisheries Research
Laboratory (Mayer and Ellersieck, 1986) and from the open literature. All acute amphibian data
obtained by the Agency are shown in Table 4-3.

In the CRLF assessment, the lowest acute toxicity 96-hr LC50 of 4.1 |ig/L for the rainbow trout
(Oncorhynchus mykiss, Soap Lake strain) (MRID 40098001, Mayer and Ellersieck, 1986) was
used as the endpoint to evaluate direct and indirect effects to freshwater fish and aquatic-phase
amphibians. Further review of this endpoint showed that it is inconsistent with other acute
toxicity data for the rainbow trout, as well as with data for other salmonid species. Figure 4-1
shows a histogram of the 18 96-hr LC50 values obtained for trout. The value of 4.1 |ig/L
(converted to the log value of 0.61) clearly appears as an outlier among the other trout data
which ranged from 34 to 280 |ig/L. In addition, the 4.1 |ig/L LC50 value is approximately five
times lower than the chronic NOAEC values of 21 |ig/L obtained from a fish early life-stage
study with rainbow trout (MRID 41422401). Furthermore, in the Biological Opinion on the
effect of pesticide products containing malathion, chlorpyrifos, or diazinon on 28 listed Pacific
salmonids, the National Oceanic Atmospheric Administration National Marine Fisheries Service
(NMFS) did not incorporate the value of 4.1 |ig/L into their analysis, citing "experimental flaws"
(National Marine Fisheries Service, 2008). Given the uncertainties associated with the 4.1 |ig/L

103

-------
LC50 value, this value was not chosen as the acute endpoint for use in the quantitative risk
assessment freshwater fish and aquatic-phase amphibians.

Mayer and Ellersieck (1986) report the result for a study testing the toxicity of malathion to
bluegill sunfish that yielded a 96-hr LC50 of 20 |ig/L. However, this study was conducted with
very warm water at 29.4° C (84.9° F). The test temperature was much greater than that
recommended by the test guidelines (20-24° C, 68.0-75.2° C). The warm water would have
resulted in reduced dissolved oxygen and may have stressed the test organisms. Another test
reported in Mayer and Ellersieck (1986) that conducted with the same species, pH, and hardness
but at a temperature of 24° C yielded a higher 96-hr LC50 of 40 |ig/L. Therefore, the results from
the test the very warm water temperature was not considered in this analysis.

The next two lowest reported 96-hr LC50 values among studies conducted at the Agency's
recommended test temperature were 30 |ig/L for the bluegill sunfish (MRID 40098001, Mayer
and Ellersieck, 1986) and 32.8 |ig/L reported for the rainbow trout (USEPA, 1968). Because the
raw data could not obtained to validate the results of the bluegill sunfish study reported in Mayer
and Ellersieck (1986), and because these two values were very similar and would yield
essentially equivalent risk quotients, the Agency decided to use the more certain value of 32.8
|ig/L from the acceptable rainbow trout study in the quantitative risk assessment. This rainbow
trout 96-hr LC50 was lower than any of the reported 96-hr LC50 values for amphibians (tadpoles)
in acceptable studies. Therefore, this value of 32.8 |ig/L was selected as the acute endpoint for
quantitative risk assessment of direct and indirect effects to the CTS. However, since this value
was not less than the 96-hr LC50 for most sensitive marine/estuarine fish tests (bluehead wrasse,
Thalassoma bifaciatum, LC50 = 27 |ig/L), the lower value of 27 |ig/L was selected for the DS, a
species that inhabits both fresh and brackish water.

104

-------
6

5

3

2

o +J	l,	t	t	^	M	M	M	l,

1	2	3	4	5	6	7	8

Log (LC50)

Figure 4.1. Distribution of values reported for the acute toxicity of malathion to trout. The bar
on the far left represents a 96-hr LC50 value of 4.1 |ig/L that was obtained in one of the 18
available 96-hr LC50 studies with trout. This value was considered and outlier and was not used
for the lowest value in the quantitative risk assessment.

The lowest acute toxicity endpoint obtained for aquatic stages of amphibians was a 96-hr LC50 of
0.59 |ig/L for the Indian frog Rana hexadcictyla (Khangarot et al., 1985; Eco ref. 011521).
However, the Agency found this study to be unacceptable for quantitative risk assessment
because too little information was available on the testing methods and apparatus, exposure
concentrations were not provided, and several deviations from the Agency's test guidelines were
observed. The value was also inconsistently low compared to all other available acute toxicity
data on amphibians. No other reported amphibian LC50 was lower than the lowest LC50 value for
freshwater fish. Excluding this value, the range of endpoints for the aquatic-stage amphibians of
170 to 19,200 |ig/L was well above the lowest acute endpoint for the freshwater fish; therefore,
the lowest 96-hr LC50 value for freshwater fish (32.8 |ig/L) was used to qualitatively assess
direct effects to the aquatic-phase CTS.

105

-------
Table 4-3. Freshwater Fish and Amphibian Acute Toxicity Studies OPP Data and ECOTOX
Studies Meeting Minimum Quality for Database and OPP		

Species Tested

%
ai

96-hr LCso (Confidence
Limits) in jig ai/L

Reference
MRID or
ECOTOX

Classification

Freshwater fish

Black bullhead catfish

95

11,700
(9,600-14,100)

40098001

Supplemental

Bluegill sunfish

95

20
(16-25)

40098001

Supplemental

Bluegill sunfish

95

30
(10-88)

40098001

Supplemental

Bluegill sunfish

95

40
(32-50)

40098001

Supplemental

Bluegill sunfish

95

55
(50-60)

40098001

Supplemental

Bluegill sunfish

95

103
(87-122)

40098001

Supplemental

Bluegill sunfish

96.9

48
(29-107)

47540304

Acceptable

Brown trout

95

101
(84-115)

40098001

Supplemental

Channel catfish

95

7620
(5820-9970)

40098001

Supplemental

Coho salmon

95

170
(160-180)

40098001

Supplemental

Common Carp

95

6,590
(4920-8820)

40098001

Supplemental

Cutthroat trout

95

174
(112-269)

40098001

Supplemental

Fathead minnow

95

8,650
(6450-11500)

40098001

Supplemental

Goldfish

95

10,700
(8,340-13,800)

40098001

Supplemental

Green sunfish

95

146 (90-234)

40098001

Supplemental

Lake trout

95

76
(47-123)

40098001

Supplemental

Largemouth bass

95

250
(229-310)

40098001

Supplemental

Rainbow trout

95

4.1
(2.2-7.4)

40098001

Supplemental

Rainbow trout

95

32.8*
(21.7-40.0)

Animal Biol
Lab,1968
48078003

Acceptable

Rainbow trout

96.9

170
(90-460)

47540302

Supplemental

Red-ear sunfish

95

62
(58-67)

40098001

Supplemental

Tilapia

95

2000

40098001

Supplemental

Walleye

95

64
(59-70)

40098001

Supplemental

Yellow perch

95

263
(205-338)

40098001

Supplemental

106

-------
Species Tested

%
ai

96-hr LCso (Confidence
Limits) in jig ai/L

Reference
M.RI.D or
ECOTOX

Classification

Amphibians

African clawed frog

Xenopus laevis

>90

9,810-10,900

Eco ref. 066506

Qualitative

Fowler's toad

Bufo woodhousei
fowleri

95

420
(90-980)

MRID 40098001
& 00084757
(Mayer and
Ellersieck, 1986)

Supplemental

Rana hexadactyla

50

0.59
(0.43-0.78)

Khangarot et al.,

1985
Eco ref. 011521

Qualitative

Striped northern chorus
frog

Pseudacris triseriata

95

200
(90-270)

40098001
(Mayer and
Ellersieck, 1986)

Supplemental

Tiger frog, Indian
bullfrog

Rana tigrina

100

170

Eco ref. 061878
(Abbasi and
Soni, 1991)

Qualitative

Western chorus frog

Pseudacris triseriata
triseria

Tech.

320
(180-680)

Eco ref. 002891
(Sanders, 1970)

Qualitative

Yellow-legged frog

(Rana boylii)



2,140

Eco ref. 092498
(Sparling and
Fellers, 2006)

Qualitative

* Endpoint used for quantitative assessment of risk.

In addition to the acute toxicity data presented in Table 4-3, Relyea (2004a, Eco ref 072798, and
2004b, Eco ref 086767) provides toxicity data on the effects of 16-day exposure of a formulated
product of malathion (50.6 % AI) to larvae of several frog species. Data for the endpoint of
mortality are presented in Table 4-4. Estimates of 16-day LC50 values which were provided in
Relyea 2004a ranged from 633 |ig/L for the wood frog to 2,990 |ig/L for the American toad.
These results were comparable to or higher than 96-hr LC50 values reported for other frog
species (Table 4-3). None of these formulated product endpoints were lower than the lowest 96-
hr LC50 obtained in other studies with amphibians, or lower than the lowest 96-hr LC50 value for
freshwater fish.

Table 4-4. Sixteen-Day Mortality Data for Exposure of Frogs to Formulated Product of
Malathion (50.6 % AI).					

Species Tested

16 dav

LCS0
HZ ai/L

NOAEC
fig ai/L

LOAEC
fig ai/L

ECOTOX
Reference

Classification

American toad

(Bufo americanus)

2,990

506

2,530

Eco ref 072798

Qualitative

American toad

(Bufo americanus)

--

1,000

2,000

Eco ref 086767

Qualitative

Bullfrog

(Rana catesbeiana)

759

--

50.6

Eco ref 072798

Qualitative

Bullfrog

(Rana catesbeiana)

--

1,000

2,000

Eco ref 086767

Qualitative

Gray tree frog

(Hyla versicolor)

2,090a
l,010b

506

2,530

Eco ref 072798

Qualitative

107

-------
Species Tested

16 (lav

LCS0
HZ ai/L

NOAEC
fig ai/L

LOAEC
fig ai/L

ECOTOX
Reference

Classification

Gray tree frog

(Hyla versicolor)

2,000

Eco ref 086767

Qualitative

Green frog

(Rana clamitans)

1,850

506

2,530

Eco ref 072798

Qualitative

Green frog

(Rana clamitans)

2,000

Eco ref 086767

Qualitative

Leopard frog

(Rana pipiens)

1,210

506

2,530

Eco ref 072798

Qualitative

Leopard frog

(Rana pipiens)

2,000

Eco ref 086767

Qualitative

Wood frog

(Rana sylvatica)

633

506

2,530

Eco ref 072798

Qualitative

a This value is for measurement of toxicity without stress from predatory cues,
b This value is for measurement of toxicity with stress from predatory cues.

Table 4-5 provides a summary of the available toxicity data of maloxon for fish and aquatic-
phase amphibians obtained from the open literature. Based on this information, the acute
malaxon endpoints for fish and amphibians range from 23 to 1600 |ig/L. The amphibian data for
the yellow-legged frog (Rana boylii) indicates that the oxon degredation product is
approximately 89.9 times more toxic than parent malathion (Sparling and Fellers, 2007; Eco ref
092498). However, this relationship is uncertain because the toxicity tests with malathion
conducted by Sparling and Fellers (2007) yielded poor data for estimation of the LCso- Both the
malathion and maloxon studies were conducted with only 4 test concentrations and the span of
concentrations was not enough to produce a the full range of responses, as is needed for accurate
estimation of the LC50. In the malathion test, no concentration yielded less than 44% mortality,
and in the maloxon test, no concentration yielded greater than 55% mortality. The other studies
which provide data on the acute toxicity of maloxon were also judged to be inadequate for
quantitative risk assessment. The tests with maloxon reported by both Tsuda et al. (1997) and
Gantberg et al. (1989) were conducted with an exposure duration of only 48-hrs, whereas our
test guidelines require 96-hr exposure duration. Furthermore, these papers did not report
mortality data, thus the reported LC50 estimates could not be verified. As previously discussed,
because of the lack of acceptable data on the toxicity and environmental fate of maloxon, the
aquatic risks of exposure to maloxon was assessed only qualitatively.

Table 4-5. Aquatic Organism Maloxon Toxicity Studies (from ECOTOX Studies Meeting

Minimum Quality for

database and OPP

Species Tested

% a.i.

Duration
H.ou rs

LCS0 fig/L

Reference IV1RID or
ECOTOX

Classification

African clawed frog

Xenopus laevis.

900

Snawder and Chamber, 1989
Eco ref. 066506

Qualitative

Yellow-legged frog Rana
boylii

23.8

Sparling and Fellers, 2007
Eco ref. 092498

Qualitative

Medaka

Oryzias latipes

>95

280

Tsuda etal. 1997
Eco ref. 018398

Qualitative

Carp

Cyprinus carpio

1600

Gantberg et al., 1989
Eco ref. 000086

Qualitative

Perch

Perca fluviatilis

150

Gantberg et al., 1989
Eco ref. 000086

Qualitative

108

-------
Species Tested

% a.i.

Duration
Hou rs

LCS0 Jig/L

Reference MRID or
ECOTOX

Classification

Roach

Rutilus rulitus

1100

Gantberg et al., 1989
Eco ref. 000086

Qualitative

Two studies with bluegill sunfish have been submitted that measures the toxicity to of two other
degradation products of malathion, malathion monocarboxilic acid and malathion dicarboxylic
acid (Table 4-6). Note that these results are reported in mg/L. Results from these studies
indicate that both of these degradation products are over lOOOx less toxic to freshwater fish than
the parent compound, malathion.

Table 4-6. Studies Measuring the 96-hr Toxicity of Two Degradation Products of Malathion to
Freshwater Fish

Reference

Test Material /

Duration

MRID or

Test Species

(Hours)

LCso in mj{ ai/L

ECOTOX

Classification

Malathion dicarboxylic acid
Bluegill sunfish (Lepomis
macrochirus)

98.8

>87

47540306

Supplemental

Malathion monocarboxylic
acid (a and (3 mixture)
Bluegill sunfish {Lepomis
macrochirus)

92.2

77
(51-151)

47540309

Acceptable

4.2.1.b. Freshwater Fish: Chronic Exposure (Growth/Reproduction)
Studies

Table 4-7 summarizes the available toxicity data on the effects of chronic exposure of malathion
to freshwater fish. Data on chronic fish toxicity were obtained from an acceptable study
submitted by the registrant (MRID 41422401) and from the open literature. While the rainbow
trout was the most sensitive freshwater fish tested based on acute data, the lowest chronic
endpoint was obtained for the flagfish (,Jordanella floridae). The chronic NOAEC obtained for
this species was 8.6 |ig/L (Hermanutz, 1978). For this species, the LOAEC was 10.9 |ig/L based
on decreased growth and 27.4 |ig/L based on decreased survival of first-generation fish. This
value was used in the quantitative risk assessment for direct and indirect chronic effects to
freshwater fish. Because no chronic aquatic-phase amphibian data were available, and acute
toxicity data indicated that freshwater fish are more sensitive to malathion than aquatic-phase
amphibians, this chronic freshwater fish endpoint was also used to quantitatively risk assessment
for direct and indirect chronic effects to aquatic-phase amphibians.

109

-------
Table 4-7. Freshwater Fish Chronic Exposure Toxicity Data (Growth, Survival, and
Reproduction Endpoints) i

Species

%
ai

Duration

(Days)

LOAEC

(Utl/L)

NOAEC

(Utl/L)

Reference MRID
or ECOTOX

Classification

Rainbow trout

MRID 41422401

Acceptable

Flagfish

(Jordanella floridae)

tech

110

8.6

Eco ref. 000995
(Hermanutz.,
1978)

Quantitative

Fathead minnow

tech

158

350

N.D.

D234663

Qualitative

Snakehead catfish

100

500

Eco ref. 014673

Qualitative

Medaka

99.8

798.4

199.6

Eco ref. 059285

Qualitative

Nile tilapia

100

168

500

Eco ref. 092183

Qualitative

4.2.1.c. Freshwater Fish: Sublethal Effects and Additional Open
Literature Information

Appendix I presents available results of freshwater fish toxicity studies, including those which
showed sublethal endpoints that cannot be directly related to the assessment endpoints of
survival, growth, and reproduction. Sublethal effects observed in these studies include
biochemical, behavioral, hematological, and immunological effects. In general, these additional
sublethal endpoints were at concentrations higher than the endpoint which was used in the
chronic risk assessment for fish and aquatic-phase amphibians (8.6 |ig/L), which was based on
growth effects. In only two cases were reported results for non-assessment endpoints lower
concentrations. In the walking catfish (Clarias batrachus), 16-day exposure to malathion was
reported to affect biochemical markers of thyroid function at concentrations as low as 3.5 |ig/L
(Sinha et al, 1992, Eco ref 089093). Drummond and Olson (1974) reported that a 10-day
exposure to malathion affected the cough response In brook trout at concentrations as low as 6.9
|ig/L (Eco ref 086858). These results cannot be quantitatively related to the growth,
reproduction, or survival of fish, and thus were not used in the quantitative risk assessment.

4.2.2. Toxicity to Freshwater Invertebrates

4.2.2.a. Freshwater Invertebrates: Acute Exposure Studies

Table 4-8 provides available acute toxicity data of malathion to freshwater invertebrates. These
data were obtained from studies submitted to the Agency by pesticide registrants, studies
conducted at the Columbia National Fisheries Research Laboratory (Mayer and Ellersieck,
1986), and from studies published in the open literature sources which yielded a 48-hr or 96-hr
EC50 value of 1.0 |ig/L or less. Among the lowest acute toxicity endpoints reported for
freshwater invertebrates are 0.098 |ig/L (Rawash et al., 1975, Eco ref. 005539) and 0.67 |ig/L
(MRID 47540303), both from studies with the water flea (Daphnia magna). Rawash et al.
(1975) was classified as "invalid" because the study lacked controls and replication, and the
paper lacked adequate description of the experimental methods. MRID 47540303 was classified
as "invalid" because contamination with an unknown substance was observed in the control.
Therefore, data from both of these studies are unacceptable for quantitative or qualitative risk
assessment. Mayer and Ellersieck (1986) reported a 96-hr EC50 value of 0.5 |ig/L for the scud,
but analytical results could not be verified because the raw data from this experiment were not

110

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available. Furthermore, no confidence intervals were reported for this value, adding to the
uncertainty of this value. The next lowest EC50 value is the 48-hr EC50 of 0.59 |ig/L for the
water flea, Simocephalus serrulatus (MRID 40098001). This study was classified as
supplemental because a non-preferred test species was used and the study was conducted at a
temperature of 10°C, which is colder than that recommended by our test guidelines (20°C).
Nevertheless, the Agency judged this study to be acceptable for use in quantitative risk
assessment. This value was selected as a reasonable low-end value for use in the quantitative
risk assessment for indirect effects (effects on food abundance) to the DS and CTS.

In a previous risk assessment conducted for effects of malathion to the California red-legged frog
(USEPA, 2007a), the Agency based the acute risk assessment for aquatic invertebrates on an
endpoint of 0.01 |ig/L which was reported for a freshwater water flea (Miona macrocopa) by
Wong et al. (1995, Eco ref 016371). However, further scrutiny of this study revealed that this
result was actually for an effect of chronic exposure to malathion on survival, specifically a
reduction in the median time to death. This result is therefore not appropriate to assess acute
toxicity risk, which is based on the acute EC50.

Table 4-8. Freshwater Invertebrate Acute Toxicity Studies from OPP Data and ECOTOX
Studies Meeting Minimum Quality for Database and OPP			

Species Tested

%
ai

Duration
(Hours)

EQo in jig/L
(95% confidence
interval)

Reference
MRID or
ECOTOX

Classification

Caddisfly, Hydropsyche sp.

95

48

5.0
(2.9-8.6)

40098001

Supplemental

Caddisfly, Limnephalus sp.

95

48

1.3
(0.77-2.0)

40098001

Supplemental

Crayfish,Orconectes nais

95

96

180
(140-230)

40098001

Supplemental

Damselfly, Lestes congener

95

48

10

(6.5-15.0)

40098001

Supplemental

Glass shrimp, Palaemonetes
kadiakensis

95

96

12
(N.R.)

40098001

Supplemental

Scud, Gammarus fasciatus

95

96

0.5 (flow-through)
(N.R.)

40098001

Supplemental

Scud, Gammarus fasciatus

95

96

0.76 (static)
(0.63-0.92)

40098001

Supplemental

Scud, Gammarus fasciatus

95

96

0.90 (static)
(0.64-1.26)

40098001

Supplemental

Scud, Gammarus lacustris

tech

48

1.8
(1.3-2.4)

05009242

Acceptable

Seed Shrimp, Cypridopsis
vidua

95

48

47
(32-69)

40098001

Acceptable

Snipefly, Atherix variegata

95

48

385
(245-602)

40098001

Supplemental

Sowbug, Asellus brevicaudus

95

96

3000
(1500-8500)

40098001

Supplemental

Stonefly, Claasenia sabulosa

95

49

2.8
(1.4-4.3)

40098001

Supplemental

Stonefly, Isoperla sp.

95

48

0.70
(0.47-0.90)

40098001

Supplemental

111

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Species Tested

%
ai

Du ration
(Hours)

EQo in ixjj/Lj
(95% confidence
interval)

Reference
MRID or
ECOTOX

Classification

Stonefly, Pteronarcella badia

1.1
(0.78-1.5)

40098001

Supplemental

Water flea, Daphnia magna

1.0
(0.7-1.4)

40098001

Acceptable

Water flea, Daphnia magna

2.2
(1.9-2.5)

41029701

Acceptable

Water flea, Daphnia magna

Rawash et al.,

1975
Eco ref. 005539

Invalid

Water flea, Daphnia magna

96.9

47540303

Invalid

Water flea, Daphnia pulex

1.8
(1.4-2.4)

40098001

Acceptable

Water flea, Simocephalus
serrulatus

0.59*
(0.46-0.77)

40098001

Supplemental

*Endpoint used for quantitative assessment of risks.

No data are available on the oxon metabolite of malathion, maloxon, to freshwater invertebrates.
Data on fish and amphibians indicate that maloxon is more toxic to than malathion (see section
4.2.1.a). A similar relationship in toxicity is expected for aquatic invertebrates. Two studies
with the water flea (Daphnia magna) have been submitted that measures the toxicity of two other
degradation products of malathion, malathion monocarboxilic acid and malathion dicarboxylic
acid (Table 4-9). Both of these tests were classified as supplemental because the test was
conducted with only one replicate chamber per test level, and the report lacked details about the
health of the brood culture and did not provide required measurements of some water quality
parameters. The studies nevertheless provide an approximate estimation of toxicity of these
degredation products. Note that the results presented in Table 4-9 are expressed as mg/L, rather
than |ig/L as in other tables. These results indicate that both of these degradation products are
over lOOOx less toxic to freshwater invertebrates than the parent compound, malathion. No acute
freshwater invertebrate data were available on the toxicity of formulated products of malathion.

Table 4-9. Studies with the Water Flea (Daphnia magna) Measuring the 48-hr Toxicity of
Degradation Products of Malathion to Freshwater Invertebrates

lesl Material

»/
/o

Duration
(Hours)

l'.( in m*i/l.

Reference
MRID or
I'.COTOX

( lassificalion

Malathion dicarboxylic acid

98.8

66.9
(48.1 -93.0)

47540305

Supplemental

Malathion monocarboxylic acid
(a and (3 mixture)

92.2

3.1
(1.7-7.0)

47540310

Supplemental

4.2.2.b. Freshwater Invertebrates: Chronic Exposure Studies

Table 4-10 presents available chronic exposure effects endpoints for freshwater invertebrates.
There are limited chronic effects studies for malathion. A life-cycle study with Daphnia magna
yielded chronic NOAEC and LOAEC values of 0.060 |ig/L and 0.10 |ig/L, respectively (MRID
41718401). These chronic endpoints were based on a 16.5% reduction in number of young
produced per day observed at the 0.10 |ig/L exposure level. Because acute toxicity data indicates

112

-------
that the water flea Simocephalus serrulatus is more sensitive than Daphnia magna, a chronic
endpoint was estimated for that species using the acute-to-chronic ratio (ACR) method. The
ACR calculated based on data for Daphnia magna is 1.0/0.06 or 16.7. The estimated chronic
NOAEC for Simocephalus serrulatus is therefore 0.59/16.7 or 0.035 |ig/L. This value was used
as the endpoint for quantitative assessing the chronic risk of malathion to aquatic invertebrates.

Table 4-10. Freshwater Invertebrate Chronic Exposure Toxicity Studies from OPP Data and
ECOTOX Studies Meeting Minimum Quality for Database and OPP

Reference

Duration

NOAEC

MRID or

Species Tested

(Days)

(Ug/L)

LOAEC (u
-------
No submitted data on the chronic toxicity of malathion to estuarine/marine fish are available. A
search of the ECOTOX database yielded only one study that provided information on the chronic
toxicity of malathion to a marine/estuarine fish and used experimental methods comparable to
the EPA test guideline. This study was an unpublished Ph.D. dissertation that reported acute and
chronic toxicity of malathion to red drum (Sciaenops ocellatus) larvae (ECOTOX Ref. No.
081672, Alvarez, 2005). According to this report, malathion did not cause any significant effects
on the growth rate, behavior, or respiration rates in either of the two test concentrations (1.0 and
10 |ig/L, nominal). The measured day-0 concentration of the higher test concentration was 7.4
|ig/L. The study therefore established a NOAEC value for the Red drum at 7.4 |ig/L, but a
LOAEC value was not determined.

Given that a chronic LOAEC has not been established for marine/estuarine fish, and it is unclear
whether the red drum is sensitive to malathion, a chronic effect NOAEC value endpoint was
estimated for the bluehead wrasse based on acute and chronic toxicity data for freshwater fish.
The NOAEC was estimated for the bluehead wrasse, the most sensitive marine/estuarine fish
based on acute toxicity data, using the acute-to-chronic ratio (ACR) calculated based on rainbow
trout data. For the rainbow trout, the LC50 obtained in a study that was found to be acceptable
for quantitative risk assessment was 32.8 |ig/L (Animal Biology Laboratory, 1968). The chronic
NOAEC was for the rainbow trout was 21 |ig/L (41422401). The ACR was thus 1.56. The
bluehead wrasse 96-hr LC50 value (27 |ig/L, Eco ref 000628) was divided by this ratio to yield an
estimated marine/estuarine fish NOAEC value of 17.3 |ig/L. This estimated NOAEC was used
for the quantitative risk assessment to evaluate direct and indirect chronic effects to the DS.
Characterization of the predicted ACR and resulting NOAEC based on consideration of the full
range of acute rainbow trout data is provided as part of the Risk Description.

4.2.4. Toxicity to Estuarine/Marine Invertebrates

4.2.4.a. Estuarine/Marine Invertebrates: Acute Exposure Studies

Table 4-12 gives results of studies of the acute toxicity of malathion to estuarine and marine
invertebrates which were submitted by pesticide registrants or obtained from studies conducted
at the EPA's Environmental Research Laboratory (MRID 40228401, Mayer, 1986). Table 4-12
also reports results from one study published in the open literature that reported acute toxicity of
malathion to a saltwater amphipod, Gammaruspalustris (Leight and Van Dolah, 1999, Eco ref.
051439). Results of this study are presented because they are essentially equivalent to the lowest
acute endpoint obtained from EPA laboratory or registrant submitted studies. Another study in
the open literature reported a lower LC50 of 1.2 |ig/L for the Dungeness crab, Cancer magister
(Caldwell, 1977, Eco ref. 006793). However, this study is classified as invalid, meaning the
results are not suitable for quantitative or qualitative assessment of risk. This conclusion was
based on a lack of negative controls, the reporting of nominal concentrations without indication
if they were corrected for percent active ingredient, and the lack of availability of raw data. All
other results from other published studies on acute toxicity to marine/estuarine invertebrates
were higher (indicating less toxicity) and therefore are not reported here, but are presented in
Appendix I. No additional information on the toxicity of maloxon or formulations of malathion
to estuarine/marine invertebrates was available.

114

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The lowest acute toxicity endpoint obtained for estuarine/marine invertebrates is the 96-hr LC50
value of 2.2 |ig/L for the mysid (Mysidopsis bahia) (MRID 41474501). This toxicity value was
used in the quantitative risk assessment for indirect effects (effects on food abundance) to the
DS.

Table 4-12. Studies Measuring the 96-hr Toxicity of Malathion to Marine and Estuarine
Invertebrates

Test Species

%
ai

Du ration
(Hours)

ECS0 orLCgo
in tig ai/L

Reference MRID
or ECOTOX

Classification

Blue Crab, Callinectes
sapidus

48 hr

LC50 > 1000

MRID 40228401

Supplemental

Eastern oyster, Crassostrea
virginica

96 hr

lc50> 1000

MRID 40228401

Supplemental

Eastern oyster, Crassostrea
virginica

96 hr

EC5o= 2960
(N.R.)

MRID 42249901

Acceptable

Gammarid amphipod

Gammarus palustris

Tech.

96 hr

LC5o = 2.29
(1.74-3.03)

Eco ref 051439

Quantitative

Mysid, Mysidopsis bahia

96 hr

LCS0=2.2*
(1.5-2.6)

MRID 41474501

Acceptable

Pink shrimp, Penaeus
duorarum

48 hr

LC50= 280
(N.R.)

MRID 40228401

Supplemental

*Endpoint used for quantitative assessment of risks.

4.2.4.b. Estuarine/Marine Invertebrates: Chronic Exposure Studies

No submitted or open literature data on the chronic toxicity of malathion to estuarine/marine
invertebrates were available. Therefore, a chronic NOAEC value was estimated using the ACR
method based available acute and chronic toxicity data for the water flea (Daphnia magna). The
water flea 48-hr EC50 value (0.59 |ig/L) and NOAEC value (0.060 |ig/L) yielded an ACR of
16.7. The mysid 96-hr LC50 value of 2.2 |ig/L was divided by this ratio to yield an estimated
estuarine/marine invertebrate NOAEC of 0.13 |ig/L.

This estimated NOAEC was used for the quantitative risk assessment to evaluate direct and
indirect chronic effects to the DS. Characterization of the predicted ACR and resulting NOAEC
based on consideration of the full range of acute water flea data is provided as part of the Risk
Description.

4.2.5. Toxicity to Aquatic Plants

Aquatic plant toxicity studies are used as one of the measures of effect to evaluate whether
malathion may affect primary production. Aquatic plants may also serve as dietary items of the
DS and the larval stages of the CTS. In addition, freshwater vascular and non-vascular plant data
are used to evaluate a number of the PCEs associated with the critical habitat impact analysis.

Pesticide registrants have submitted no data to the Agency on the toxicity of malathion to aquatic
plants. Table 4-13 summarizes available aquatic plant effects data obtained from the open
literature. For unicellular aquatic plants, the lowest EC50 and NOAEC obtained were 2.32 mg/L

115

-------
and 0.50 mg/L, respectively. For vascular plants, there is no established EC50; however, the
NOAEC value was established at 24.1 mg/L based on no significant difference in biomass and
fond number when compared to the control. The results from the study with green algae (Eco.
ref 085816) were used quantitatively in the risk assessment, whereas the NOAEC reported for
duckmeat (Eco ref. 054278) was used qualitatively as an indication that aquatic vascular plants
are likely less sensitive to malathion than algae.

Table 4-3-13. Aquatic Plant Toxicity Studies from OPP Data and ECOTOX Studies Meeting

Minimum Quality

or Database and OPP

Species Tested

%
ai

Duration

(Days)

ECS0
(mg ai/L)

NOEAC
(mg ai/L)

Reference
MRID or
ECOTOX

Classification

Blue-green algae

Anabaena flosaquae

73.6

Eco ref. 061937
(Piri and Ordog,
1999)

Qualitative

Green algae

Scenedesmus
obstusiusculus

31.6

Eco ref. 061937
(Piri and Ordog,
1999)

Qualitative

Green algae

Dunaliella tertiolecta

17.9

Eco ref.066270
(McFetters et al,
1983)

Qualitative

Green algae

Pseudokirchneriella

subcapitata

100

2.4*
(1.5-3.6)

1.2*

Eco ref. 085816
(Yeh and Chen,
2006)

Quantitative

Duckmeat

Spirodela polyrhiza

96.26

24.1

Eco ref. 054278
(Sinha, Rai, and
Chandra, 1995)

Qualitative

*Endpoint used for quantitative assessment of risks.

4.3. Toxicity of Malathion to Terrestrial Organisms

Table 4-14 summarizes the most sensitive terrestrial toxicity endpoints, based on an evaluation
of both the submitted studies and the open literature. A brief summary of submitted and open
literature data considered relevant to this ecological risk assessment for the DS and CTS is
presented below. Additional information is provided in Appendix GI. All endpoints are
expressed in terms of the active ingredient (a.i.) unless otherwise specified

Table 4-14. Terrestrial Toxicity Profile for Malathion

Assessment
Endpoint

Acute/
Chronic

Species

Toxicity Value Used
in Risk Assessment
(95% confidence
interval)

Citation
MRID/ ECOTOX
reference No.

Comment

Birds

(surrogate for

terrestrial-

phase

amphibians
and reptiles)

Acute
Oral

Ring-necked
pheasant

(Phasianus
colchicus)

14-day LD50 = 167
(120-231) mg/kg-bw

Slope NA

MRID 00160000
(Hudson etal. 1984)

Data was generated by
the US Fish and Wildlife
Service and considered
acceptable for
quantitative risk
assessment.

Acute
Dietary

Japanese quail

Coturnix japonica

8-day LC5 o = 2128
(1780-2546) mg/kg-

MRID 00062189,
Eco ref. 035214,

This study was classified
as supplemental.

116

-------
Assessment
Endpoint

Aeute/
Chronic

Species

Toxicity Value Used
in Risk Assessment
(95% confidence
interval)

Citation
MR ID/ ECOTOX
reference No.

Comment

diet

Slope 3.62

Heath et al., 1972

Chronic

Northern
bobwhite

Colinus
virginianaus

NOAEC = 110
mg/kg-diet
I.OAF.I. = 350
mg/kg-diet

MRID 43501501

The results are based on
observation of regressed
ovaries at the 350 mg/kg
level. Data are from an
acceptable study
submitted by the
registrant.

Mammals

Acute

Laboratory rat

(Rattus
norvegicus)

LD5o= 852 (607-
1196) mg ai/kg-bw

MRID 42045401

This study was classified
as guideline. The test
was with Clean Crop 8E,
79.5% AI.

Chronic

Laboratory rat

(Rattus
norvegicus)

NOAEL = 1700 mg/kg-
diet

LOAEL = 5000 mg/kg-
diet

MRID 41583401

The results are based on
a reduction of body
weight of F1 and F2
pups. This study was
found to be acceptable
for quantitative risk
assessment.

Terrestrial
invertebrates

Acute
Contact

Honey bee

(Apis melliferra)

LD50 = 0.20 ng/bee

MRID 05001991
(Stevenson, 1978)

This study was found to
be acceptable for
quantitative risk
assessment.

Terrestrial
plants

No data are available for
quantitative risk
assessment of terrestrial
plants.

NA: not applicable; ND = not determined; bw = body weight

Acute toxicity to terrestrial animals is categorized using the classification system shown in Table
4-15 (USEPA, 2004). Toxicity categories for terrestrial plants have not been defined.

Table 4-15. Categories of Acute Toxicity for Avian and Mammalian Studies

Toxicity Category

Oral LD5„

Dietary LC50

Very highly toxic

<10 mg/kg

< 50 mg/kg-diet

Highly toxic

10-50 mg/kg

50 - 500 mg/kg-diet

Moderately toxic

51 - 500 mg/kg

501 - 1000 mg/kg-diet

Slightly toxic

501 - 2000 mg/kg

1001 - 5000 mg/kg-diet

Practically non-toxic

> 2000 mg/kg

> 5000 mg/kg-diet

4.3.1. Toxicity to Birds, Reptiles, and Terrestrial-Phase Amphibians

A summary of acute and chronic bird and terrestrial-phase amphibian data, including data
published in the open literature, is provided below in Sections 4.3.1.a and 4.3.1.b. As specified

117

-------
in the Overview Document, the Agency uses birds as a surrogate for terrestrial-phase amphibians
when toxicity data for that taxon are not available (USEPA, 2004).

4.3.1.a. Birds: Acute Exposure (Mortality) Studies

Data on the acute toxicity of malathion to birds were obtained from Hudson et al. (1984), Hill el
al, 1975, and other open literature papers. Results of avian oral acute tests with malathion are
tabulated in Table 4-17. The most sensitive species tested was the ring-necked pheasant
(Phasianus colchicus). The LD50 obtained for this species, 167 mg/kg-bw, was used in this
assessment for quantitative risk estimations to terrestrial-phase amphibians including the CTS.

Table 4-17. Avian Acute Oral Toxicity Studies from OPP Data and ECOTOX Studies Meeting
Vlinimum Quality for Database and OPP

Species

%
Al

LD5„ (mg/kg-bw)
(95% confidence interval)

MRID or ECOTOX

Classification

Mallard duck

(Anas

platyrhynchos)

14-day LD50 = 1485
(1020-2150)

MRID 00160000
(Hudson etal. 1984)

Acceptable

Ring-necked
pheasant
(Phasianus
colchicus)

14-day LDS0 = 167*
(120-231)

MRID 00160000

(Hudson etal. 1984)

Acceptable

Horned lark

(Eremophila
alpestris)

14-day LD50 = 403
(247-658)

MRID 00160000
(Hudson etal. 1984)

Supplemental

Sharp-tailed
grouse

(Tympanuchus
phasianellus)

tech

LD50 ~ 220
(171-240)

Crabtree, D.G., 1965, Denver
Wildlife Res. Center, USFWS as
cited in RED

Supplemental

Bantam chicken

97.7

LD5o = 524.8

ECOTOX ref. 036916

Supplemental

*Endpoint used for quantitative assessment of risks.

Data from subacute avian studies with dietary exposure were also used to assess the risk of
malathion to terrestrial-phase amphibians. Subacute dietary toxicity data were obtained from
studies conducted at the US Fish and Wildlife Service (Heath et al., 1972; Hill et al., 1975; Hill
and Camardese, 1986). These data are tabulated in Table 4-18. The lowest subacute dietary
LC50 reported is 2128 mg/kg-diet. This value was used in the quantitative risk assessment for
acute risk to terrestrial-phase amphibians.

Table 4-18. Avian Subacute Dietary Toxicity Studies from OPP data and ECOTOX Studies
VIeeting Minimum Quality for Database and OPP

Species

%
ai

LCso (mg/kg-diet)
(CL's, when available)

Reference
MRID or ECOTOX

Classification

Ring-necked pheasant

Phasianus colchicus

8-day LC50 = 2639
(2220-3098)

MRID 00022923
Hill etal., 1975

Acceptable

Northern bobwhite

Colinus virginianaus

8-day LC50 = 3497
(2959-4011)

MRID 00022923
Hill etal., 1975

Acceptable

Japanese quail

8-day LC50 = 2962

MRID 00022923

Supplemental

118

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LCso (mg/kg-diet)

Reference

Species

(CL's, when available)

MR.I.D or ECOTOX

Classification

Coturnix japonica

(2453-3656)

Hilletal., 1975

Japanese quail
Coturnix japonica

100

8-day LCS0 = 2128*
(1780-2546)

MRID 00062189
Eco ref. 035214
Heath et al., 1972

Supplemental

MRID 40910905

Japanese quail

Coturnix japonica

8-day LC50 = 2968
(2240-3932)

Eco ref. 050181
Hill and Camardese,
1986

Supplemental

Mallard

Anus plytyrhynchos

8-day LC50> 5000

MRID 00022923
Hilletal., 1975

Acceptable

*Endpoint used for quantitative assessment of risks.

Avian toxicity data on maloxon and formulations of malathion are not available.

4.3.1.b. Birds: Chronic Exposure (Growth, Reproduction) Studies

Available avian reproduction laboratory study results are tabulated in Table 4-19. At food
exposure concentrations of 350 mg/kg-diet, 4 of 15 female bobwhite quail exposed to malathion
for 21 weeks displayed regressed ovaries and abnormally enlarged/flaccid gizzards. A reduction
in the proportion of eggs hatched per eggs set also was observed at 350 mg/kg-diet. The
NOAEC established in this study was 110 mg/kg-diet. This was the NOAEC reported from a
fully acceptable study for chronic effects to birds, and was the value used in the quantitative risk
assessment for chronic effects to birds and reptiles.

Table 4-19. Avian Reproduction Studies from OPP Data and ECOTOX Studies Meeting
Minimum Quality for Database and OPP

Species

%
ai

LOAEC mg/kg-diet
Effected Parameters

NOAEC
mg/kg-diet

MRID

Classification

Northern
bobwhite

Colinus
virginianaus

96.4

21-wk LOAEC = 350 — regressed ovaries
and enlarged/flaccid gizzards,

21-wk LOAEC = 1200 - reduction in
proportion of eggs hatches per eggs set.

110*

MRID
43501501

Acceptable

Mallard

94.0

20-wk LOAEC =2400
Growth and viability

1200

MRID
42782101

Acceptable

Bantam

100

56-day LOAEC not determined for growth,
weight, or egg production

>100a

Eco ref.
038417

Qualitative

*Endpoint used for quantitative assessment of risks.

a. No adverse effects were observed in any of the concentrations tested.

Available supplemental data obtained from the ECOTOX database provided information on the
reproductive effects of malathion to the bantam chicken (a domesticated chicken). The Agency
categorized these data as "qualitative" for ecological risk assessment because they were for
effects to a domesticated species. The lowest NOAEC for reproduction effects and chick growth
in one study is 100 mg/kg-diet, the highest exposure level tested. An additional study with the
same species and malathion at similar purity provided both a NOAEC and LOAEC for growth
(475 mg/kg-diet and 237.5 mg/kg-diet) and a NOAEC for egg production (475 mg/kg-diet).

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When taken together, these studies suggest that effects on growth and egg production for this
species are not expected until exposure levels reach or exceed 475 mg/kg-diet in the bantam
chicken. Therefore, the 100 mg/kg-diet NOAEC value is considered to be an artifact of dose
selection rather than a true threshold for effects in the species.

4.3.2. Toxicity to Mammals

A summary of acute and chronic mammalian data, including data published in the open
literature, is provided below in Sections 4.3.2.a and 4.3.2.b. A more complete analysis of
toxicity data to mammals is available in Appendix J, which is a copy of the Health Effects
Division (HED) chapter prepared in support of the reregi strati on eligibility decision completed in
2002, the most recently completed HED chapter for malathion.

4.3.2.a. Mammals: Acute Exposure (Mortality) Studies

Table 4-20 presents the available acute mammalian toxicity endpoints obtained from the Office
of Pesticide Program's Health Effects Division (HED) and the open literature. The rat LD50 of
1036 mg/kg-bw reported by Boyd and Tanikella (1969) was the lowest acute endpoint; however,
the Agency determined that the results from this study are not acceptable for quantitative use in
risk assessment because the experimental design was not adequately described, the mortality data
were not provided, and the statistical calculations were uncertain and incomplete. The next
lowest LD50 value in an acceptable mammal acute toxicity study was 1072 mg/kg-bw, or 852 mg
ai/kg-bw, from an acceptable study submitted by the registrant (MRID 42045401). This study
was conducted with the product Clean Crop Malathion 8E ® (Registration Number 34704-
00452). This value will be used was used in the risk assessment to evaluate indirect effects to
the CTS related to acute toxic effects of malathion to mammals.

Table 4-20. Summary of Acute Toxicity Data of Malathion to Mammals

Species

Test Material
(Rejj. Number)

% AI

LD50

(mg ai/kg-bw)

MRID, Citation

Classification

Norway Rat
(Rattus norvegicus)

TGAI

97.4

5400 (M)
5700 (F)

MRID 00159876

Acceptable

Norway Rat
(Rattus norvegicus)

TGAI

1310 (M)
1550 (F)

MRID 00144490

Guideline

Norway Rat
(Rattus norvegicus)

TGAI

1036

Eco ref. 108637
(Boyd and Tanikella,
1969)

Qualitative

Norway Rat
(Rattus norvegicus)

TGAI

2880 (M)
(2660-3110)

Dauterman and Main,
1966

Qualitative

Norway Rat
(Rattus norvegicus)

Fyfanon 57
(04878-0005)

96.5

3281

(2606-3957)

MRID 40247202

Guideline

Norway Rat
(.Rattus
norvegicus)

Clean Crop 8E
(34704-00452)

79.5

852

(607-1196)

MRID 42045401

Guideline

Norway Rat
(Rattus norvegicus)

Malathion 8 EC
(66330-00248)

80.75

2870 (M)
1360 (F)

MRID 43072404

Acceptable

*Endpoint used for quantitative assessment of risks.

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Two studies submitted to the Agency indicate that malathion has relatively low acute toxicity to
mammals when exposed through dermal and inhalation routes. The acute dermal LD50 for
malathion was found to be greater than 2000 mg/kg (MRID 00159877). The acute inhalation
LC50 was determined to be greater than 5.2 mg/L (MRID 00159878).

Malathion degrades and is metabolically transformed into the oxon derivative, maloxon, which is
more toxic than the parent compound. No data on the acute toxicity of maloxon have been
submitted by the registrant. Two studies in the open literature provide acute oral LD50 estimates
for maloxon (Table 4-20). However, the Agency's review of these studies determined that they
should not be used qualitatively in this risk assessment because of uncertainty of the purity of the
test compounds and lack of information provided on the test methods. Both of these determined
the acute oral LD50 of malathion as well. The reported malathion LD50 was 2880 mg/kg-bw in
Dauterman and Main (1966), and 1942 mg/kg-bw in Chiu et al. (1968). These resulting
estimated ratio of the malathion LD50 divided by the maloxon LD50 (i.e., the number of times
more toxic maloxon is to rats relative to malathion) is 18.2 based on data from Dauterman and
Main (1966), and 7.99 based on data from Chiu et al. (1968).

Table 4-21. Reported Acute Oral Toxicity of Maloxon to IV

ammals

Species

Test Material1

L.Dso (mg/kg-bw)

MRID, Citation

Classification

Norway Rat
(Rattus norvegicus)

Carbethoxy
malaoxon

158 (142- 175)

Dauterman and
Main, 1966

Qualitative

Norway Rat
(Rattus norvegicus)

Succinate malaoxon

243 (218-280)

Chiu et al., 1968

Qualitative

1 The exact descriptions of the test material as presented in the paper are provided. The Agency believes both of
these test materials are equivalent to the form of maloxon that would form in the environment.

4.3.2.b. Mammals: Chronic Exposure (Growth, Reproduction) Studies

Table 4-21 presents the available chronic mammalian toxicity endpoints obtained from HED and
the open literature that relates exposure to malathion to adverse growth and reproductive effects.
The rat NOAEC of 1700 mg/kg-diet was the lowest chronic endpoint reported (MRID
41583401). This value was used in the risk assessment to evaluate indirect effects to the CTS
related to chronic toxic effects of malathion to mammals.

Table 4-21. Malat

lion Chronic Mammalian Toxicity Data

Species

% Al

NOAEC
(mg/kg-dict)

LOAEC (mg/kg-dict)
Effected Parameters

Reference

MRID or ECOTOX

Classification

Rat

Tech

Not determined

4000

reduced pup survival and 9-week
body weight

Eco ref. 104601
(Kalow and Marton,
1961)

Qualitative

Rat

94.0

1700*

5000

Reduced pup body weight

MRID 41583401

Acceptable

*Endpoint used for quantitative assessment of risks.

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4.3.3. Toxicity to Terrestrial Invertebrates

4.3.3.a. Terrestrial Invertebrates: Acute Exposure (Mortality) Studies

Table 4-22 tabulates available data on the effects of malathion on nontarget terrestrial
invertebrates. Data were obtained from registrant submitted bee toxicity studies and from studies
in the ECOTOX open literature query. Many of the studies listed in ECOTOX did not provide a
quantitative estimate of the level of effect beyond a listing of near zero or near 100 percent.

These studies have not been included in the following list as they do not provide endpoints useful
for quantitative risk assessment. The most sensitive acute contact LD50 value obtained from a
reliable source is 0.20 |ig/bee for the honey bee (Apis mellifera) (MRID 05004151, Stevenson,
1968). This value will be used in the quantitative assessment of acute effects of malathion to
nontarget insects.

Table 4-22. Non-Target Insect Acute Contact Toxicity Studies from OPP data and ECOTOX

Studies Meeting Minimum Qua

ity for Database and OPP

Species

% AI

LD;o (juji ai/animal)

Reference
MRID or
ECOTOX

Classification

Honey bee
Apis mellifera

Tech

48 HR LDS0 = 0.20*

MRID 05001991
(Stevenson, 1978)

Acceptable

Honey bee

Apis mellifera

Tech

96 HR LD50 = 0.709
Slope = 8.04

MRID 0001999

Acceptable

Honey bee

Apis mellifera

Tech

LD50 = 0.24a
Slope = 8.3a

MRID 05004151
(Stevenson 1968)

Acceptable

Honey bee

Apis mellifera

100

72 hr LD5o= 0.46

MRID 05008990
(Johansen et al.,
1963)

Acceptable

Alfalfa leafcutter bee

Megachile rotundata

100

72-hr LD50 =0.23

MRID 05008990
(Johansen et al.,
1963)

Acceptable

*Endpoint used for quantitative assessment of risks.

a Results are weighted means of mean values reported for two tests conducted in 196 4 and 3 tests conducted in
1965. The duration of observation was not reported.

Johansen, C., Jaycox, E. R., and Hutt, R. (1963) determined the acute oral toxicity of technical
grade malathion to the honey bee. The acute oral LD50 was found to be 0.38 |ig/bee (MRID
05004151) and 0.76 |ig/bee (MRID 05001991).

Aikins and Wright (1985) studied the acute toxicity of malathion to various larval stages of the
cabbage moth (Mamestra brassicae). Twenty-four hour LD50 values, expressed in terms of |ig
per g of insect, ranged from 3.7 to 12.7 |ig/g for topical application, 3.3 to 5.9 |ig/g for
application by injection, and 102 to 245 |ig/g for application in food (Table 4-23). Note that
these values are not directly comparable to those in Table 4-22 because the units are different.

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Table 4.23. Acute 24-hr LD50 Values for the Instars of the Cabbage Moth (Mamestra brassicae)
Exposed to Mahilhion by Three Types of Applications (from Aikins and Wiiuhl. 1985)

l.;ir\;ic InMiir

24-hr l.lh,,
(u ii/*i in see ()

•)5V'i. C.l.

Slope (±s.e.)

Topical Application

Second

3.7

0.9-9.5

0.8 (±0.1)

Third

7.3

2.6-16.9

1.0 (±0.1)

Fourth

11.3

2.4-38.3

1.1 (±0.2)

Fifth

10.2

2.3-29.2

1.0 (±0.2)

Sixth

12.7

3.7-39.1

0.7 (±0.1)

Application by Injection

Fourth

3.3

1.2-7.4

0.7 (±0.1)

Fifth

5.0

0.9-18.6

0.7 (±0.2)

Sixth

5.9

2.1-14.7

0.8 (±0.1)

Application by Diet

Fifth

102

89-135

2.0 (±0.4)

Sixth

245

214-387

0.9 (±0.2)

In 1989, the Malathion Registration Task Force submitted data on the toxicity of Cythion 57%
EC to the honey bee (MRID 41208001). Cythion 57% EC is a formulated product containing
57%) malathion, 30% xylene, and 13% inactive ingredients. (This formulation is no longer
registered for use in the United States.) The formulated product was applied to alfalfa at a rate of
40 gal/acre, or 1.6 lb ai/acre. The alfalfa was aged and weathered in the field for selected periods
under ambient outdoor conditions. The alfalfa was then chopped and placed in bee test
chambers. Approximately 450 bees were introduced to the test chambers and monitored for
mortality for 24 hours. This study found that residues on alfalfa caused mortality to honey bees
when the alfalfa had been aged for 8 hours, but did not cause significant mortality when residues
had been aged for 24 hours. The study concluded that application of this formulated product on
alfalfa is highly toxic to honey bees for between 8 and 24 hours after application.

Martinez and Phenkowski (ECOTOX ref. 37837) reported immersion contact LC50 values (2
second immersion, 24 hour post exposure observation) for three insect species. The LC50 values
for the potato leafhopper (Empoasca fabae), tarnished plant bug (Lygus lineolaris), and the
predatory nabid (Reduviolus americoferus) were reported to be 41.32, 68.08, and 273.13 mg/1,
respectively.

Panda and Sahu (ECOTOX ref. 52962) reported 96 hour LC50 values for the field earthworm
(.Drawidawillsi) ranging from 15.1 to 18.8 mg/kg-soil. The same authors (ECOTOX ref. 89517)
reported a reduction in the population of the same earthworm species relative to controls
(measures at 60 days post application in laboratory colonies) at a malathion soil concentration of
2.2 mg/kg.

4.3.4. Toxicity to Terrestrial Plants

The risk assessment process relies predominantly on effects endpoints associated with seedling
emergence, growth, and plant viability. There are no submitted registrant data for malathion and
terrestrial plants. However, Brown et al. (1987) provides data on the phytotoxic effects of

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malathion to terrestrial plants that is comparable to the Agency's vegetative vigor tier-1 test
guideline (850.4150). This study evaluated the use of malathion in "chemical exclusion" studies,
that is ecological experiments in which a chemical is applied to exclude insect herbivores from
experimental plots of natural vegetation. Five native herbaceous plant species (Capsella bursa-
pastoris, Chenopodium album, Raphanus raphanistrum, Lotus corniculatus, and Plantago
lanceolata) were grown from seeds in a greenhouse and then tested. Fifteen seedlings in
individual pots were sprayed with Malathion-60 (60% malathion w/v) at a rate of 0.126 g ai/m2
(1.41 lb ai.A), and fifteen control seedlings were treated with an equal volume of water. To
compare plant growth, plant height and number of leaves were measured in all species. Biomass
of plants harvested at the end of the growing season was also measured. The study found no
significant difference between treated and control plants in any of these endpoints. The study
authors concluded that the application of malathion showed no significant effects on the
vegetation.

Efficacy tests, which evaluate the performance of malathion on protecting crops from insect
damage, in some cases also provide data on effects of yield. This yield data provides
information on the effects of malathion treatment to plants. Efficacy studies that tested
application of malathion on wheat (rate 1.25 lb ai/A), field peas (rate 1.00 lb ai/A), and birdsfoot
trefoil (rate 1.25 lb ai/A) found no significant difference between the plant yield in treated plots
compared to untreated control plots (Beauerfeind and Wilde, 1993; Thompson and Sanderson,
1977; Peterson et al. 1992). Other efficacy tests on small grain (rate 1.0 lb ai/A) and cabbage
(rate 0.89 lb ai/A) found significantly increased yields of plants in treated plots compared to
control plots, presumably because of reduction of herbivorous insect pests (Noetzel, 1994, Azad
Thukur and Deka, 1997,). These results indicate that exposure of malathion at rates between
0.89 and 1.25 lb ai/A do not cause toxic effects to terrestrial plants.

Finally, Allen and Snipes (1995) studied the interaction of foliar insecticides and the herbicide
pyrithiobac when applied to greenhouse-grown cotton. As a control, the study included an
evaluation of the effects of malathion applied alone. Endpoints measured were 14-day shoot wet
weight and 14-day visually estimated plant injury. This test found that a foliar application
malathion of 1.16 lb ai/A had no significant effect on treated cotton plants when compared to
untreated control plants.

These studies provide evidence that malathion does not cause significant phytotoxic affects to
both monocot and dicot terrestrial plants. This conclusion is further supported by the fact that
malathion has been used for many years on a very wide variety of herbaceous and woody plants
for protection from pests. The popularity of its use indicates that it is either nontoxic to plants at
the use rates, or that any toxicity is minor and less than beneficial effects provided by protection
from herbivorous insects. Exposure to natural vegetation off the treatment site, resulting from
spray drift and runoff, would be only a fraction of the rate of the target plants that are treated
directly. Since malathion has little or no adverse effects on the target plants, it is not predicted to
have significant adverse effects to vegetation in the habitat of the DS or the CTS.

Finally, Lichtenstein et al. (1962) reports statistically significant (P<0.01) reductions in corn root
length in seedlings grown for 21-days in a pure quartz sand matrix treated with 30 mg/kg
malathion. However, this root length reduction did not translate into any adverse effect in above

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ground growth of the plants or reduction in root or shoot dry weight. Given the extreme growing
conditions in pure quartz sand and the lack of frank effects on plant growth this study was judged
not to demonstrate biologically relevant effects of malathion to monocot plants that would be
manifested under field conditions.

4.4. Toxicity of Chemical Mixtures

As previously discussed, the results of available toxicity data for mixtures of malathion with
other pesticides are presented in Appendix A. According to the available data, studies that
tested the combined effects of malathion together with other pesticides have produced various
results. When chemicals are present in the environment in combination with malathion, the
toxicity of malathion may be increased, offset by other environmental factors, or even reduced
by the presence of antagonistic contaminants if they are also present in the mixture. The variety
of chemical interactions presented in the available data set suggest that the toxic effect of
malathion, in combination with other pesticides used in the environment, can be a function of
many factors including but not necessarily limited to: (1) the exposed species, (2) the co-
contaminants in the mixture, (3) the ratio of malathion and co-contaminant concentrations, (4)
differences in the pattern and duration of exposure among contaminants, and (5) the differential
effects of other physical/chemical characteristics of the receiving waters (e.g. organic matter
present in sediment and suspended water). Quantitatively predicting the combined effects of all
these variables on mixture toxicity to any given taxa with confidence is beyond the capabilities
of the available data. Studies that have evaluated the toxicity of the combination of malathion
and other pesticides are summarized in Table 2-1 of Section 2.2.2. Appendix H also lists studies
in the open literature that evaluated the toxicity of chemical mixtures of malathion.

4.5. Incident Database Review

A review of the Ecological Incident Information System (EIIS, version 2.1), the 'Aggregate
Incident Reports' (v. 1.0) database, and the Avian Monitoring Information System (AIMS) for
ecological incidents involving malathion was completed on February 22, 2010. The EIIS
database contains data on pesticide-related incidents occurring through August 2009. The AIMS
database contains data on pesticide-related avian incidents occurring through approximately
August 2005. The results of this review for terrestrial, plant, and aquatic incidents are discussed
below in Sections 4.5.1 through 4.5.3. A complete list of the incidents involving malathion is
included as Appendix G.

Incidents recorded in these three databases include only reports which have been investigated,
linked to one or more pesticide active ingredient, and reported to the Office of Pesticide
Programs. We believe that these incidents represent only a fraction of the total number of
incidents that have occurred. Incidents in this system are categorized by certainty, which
indicates the Agency's judgment on the probability that malathion was the cause of the observed
effects.

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4.5.1. Aquatic Animal Incidents

Table 4-23 summarizes incidents reported in the EIIS database in which adverse effects to
aquatic organisms were linked to use of malathion. The certainty level, which the Agency
assigns to each incident, describes the level of certainty that malathion was the cause of the
observed effects. Excluding incidents associated with misuses and those with a certainty level
less than "possible," there were 23 incidents in which aquatic animals were killed. All of these
incidents involved mortality of fish. One incident also involved death of blue crabs and one
incident involved the death of an alligator. Aquatic incidents occurred in both freshwater and
saltwater habitats. Incidents were associated with both agricultural uses and mosquito control
uses of malathion. For both of these use types, there were numerous incidents with a high
certainty level ("probable" or "highly probable"), providing strong evidence that both
agricultural and mosquito control uses of malathion can sometimes result in mortality of fish and
other aquatic organisms. There were 6 additional aquatic incidents with a certainty level of at
least "possible" that were associated with known misuses of malathion.

Table 4-23. Summary of Aquatic Animal Incidents Associated with Malathion Use, by Certainty

Certainty

Incident
Type

Use Type

All
(excluding
unlikely)

Unlikely

Possible

Probable

Highly
Probable

Aquatic
(excluding

Agricultural
sites

10(9)

misuse)

Mosquito
control

Unknown

All

24 (23)

Aquatic
(misuse

Agricultural
sites

3(2)

only)

Mosquito
control

Unknown/other

All

7(6)

In 1999, the population of the American lobster (Homarus americanus) in Long Island Sound
suffered a severe mortality event, causing devastating economic damage to the regional lobster
fishery. This die-off occurred following extensive aerial spraying of pesticides for vector control
in the summer of 1999, which was undertaken in response to a widespread outbreak of West Nile
Virus that was occurring at that time in the Northeast. Malathion had been applied in New York.
Two pyrethroids (resmethrin and sumithrin) and methoprene were applied in both New York and
Connecticut. Extensive research was undertaken after this event to identify the cause and to
determine the role of exposure to these pesticides, if any, in the mortality event. The research
ultimately concluded that an outbreak of a parasitic amoebae, Neoparamoebapemaquidensis,
was the proximal cause of the lobster mortality, but that multiple other stressors, including
pesticide exposure, may have contributed to the die-off by physiologically weakening the
lobsters, making their immune response too weak to fend off the disease (Pearce and Balcom,
2005). The findings of the numerous research projects on this topic and the potential
contribution of malathion in the causation of this event is currently being investigated.

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The query of the Aggregate Incident Reports database identified an additional four incidents
linked to malathion use. According to the reporting rule for FIFRA Section 6(a)2, these
incidents were reported to the Agency by pesticide registrants as aggregated counts of minor
fish/wildlife incidents (W-B). Because details about these incidents were not reported, no
information was available on the use site, the certainty level, or on the types of organisms that
were involved. The Agency does not know if these minor incidents involved effects to fish or
terrestrial wildlife; however, based on other reported incidents, they are more likely to involve
aquatic organisms than terrestrial wildlife.

4.5.2. Terrestrial Animal Incidents

Table 4-13 summarizes incidents reported in the EIIS database in which adverse effects to
terrestrial animals were linked to use of malathion. Eight incidents of bee kills were associated
with malathion use. For three incidents, the Agency assigned certainty level of "probable" or
"highly probable." The bee incidents were associated with use of malathion on cherries (3
incidents), alfalfa (1 incident), cotton (1 incident), and unknown use sites (2 incidents). These
incidents provide evidence that agricultural use of malathion can harm nontarget insects. No bee
kill incidents were associated with mosquito control use.

Table 4-13. Summary of Terrestrial Animal Incidents Associated with Malathion Use, by
Certainty

Cerlainlv

Incident Type

Use Type

All

Unlikely

Possible

Probable

Highly
Probable

Bees

Agricultural
sites

Unknown

All

Wildlife

Mosquito
control

Unknown

All

Only two incidents associated with malathion use involved mortality of wildlife. For both these
incidents, the certainty level was "possible." In both cases, wildlife was exposed to one or more
pesticide, other than malathion, which is highly toxic to wildlife. In one incident involving
mortality of 10 fox squirrels, the squirrels also were exposed to zinc phosphide, a rodenticide
which frequently causes mortality of nontarget mammals. In the other terrestrial wildlife
incident in which 17 western sandpipers were killed, the birds also were exposed to temephos, an
insecticide that is much more toxic to birds than does malathion. It is uncertain how much
exposure to malathion contributed to these mortalities.

A query of the AIMS database identified two additional bird kill incidents that were linked to
exposure to malathion; however, in both cases the probable cause of death was diazinon
exposure. The AIMS Event IDs for these two additional incidents are 190 and 254. These
incidents were entered in EIIS as B0000-400-51 and B0000-400-82, respectively, but malathion
was not recorded in the EIIS as a possible cause of death. In both cases, residue analysis of the

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carcass revealed very large amounts of diazinon and only trace amounts of malathion.
Considering this, and the fact that diazinon is much more toxic to birds than is malathion, the
malathion exposure likely had little if any role in causing the bird mortality in both incidents.

4.5.3. Plant Incidents

Table 4-14 summarizes incidents reported in the EIIS database in which adverse effects to plants
were linked to use of malathion. Four incidents of plant damage have been associated with the
use of malathion. One of these was assigned a certainty of "unlikely" and the other three were
assigned a certainty of "possible." Of the three incidents with a certainty of "possible," two
involved exposure to other pesticides, making the determination of cause uncertain. The third
"possible" incident was a complaint from a homeowner that use of a product containing
malathion damaged ornamental roses; however, this allegation was not verified.

Table 4-14. Summary of Plant Incidents Associated with Malathion Use, by Certainty

Ccrtaintv

Incident

Use Type

All

Highly
Probable

Type

(excluding
unlikely)

Unlikely

Possible

Probable

Plants

Agricultural
use

2(1)

Homeowner
use

Unknown

All

4(3)

The query of the Aggregate Incident Reports database identified an additional 216 minor plant
damage incidents linked to malathion use. According to the reporting rule for FIFRA Section
6(a)2, these incidents were classified as minor plant damage incidents (P-B) and were reported
only as aggregated counts. Because details about these incidents were not reported, no
information was available to determine the certainty level. Most of the incidents were associated
with use of malathion products sold for residential uses. Homeowners frequently issue
complaints to pesticide registrants that pesticide products caused damage to ornamental plants,
but these complaints are usually not investigated and thus the cause of the reported plant damage
is seldom determined.

4.6. Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern

The Agency uses the probit dose response relationship as a tool for providing additional
information on the potential for acute direct effects to individual listed species and aquatic
animals that may indirectly affect the listed species of concern (USEPA, 2004). As part of the
risk characterization, an interpretation of acute RQs for listed species is discussed. This
interpretation is presented in terms of the chance of an individual event {i.e., mortality or
immobilization) should exposure at the EEC actually occur for a species with sensitivity to
malathion on par with the acute toxicity endpoint selected for RQ calculation. To accomplish
this interpretation, the Agency uses the slope of the dose response relationship available from the
toxicity study used to establish the acute toxicity measures of effect for each taxonomic group

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that is relevant to this assessment. The individual effects probability associated with the acute
RQ is based on the mean estimate of the slope and an assumption of a probit dose response
relationship. In addition to a single effects probability estimate based on the mean, upper and
lower estimates of the effects probability are also provided to account for variance in the slope, if
available.

Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1
(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP, Environmental
Fate and Effects Division (June 22, 2004). The model allows for such calculations by entering
the mean slope estimate (and the 95% confidence bounds of that estimate) as the slope parameter
for the spreadsheet. In addition, the acute RQ is entered as the desired threshold.

5. Risk Characterization

Risk characterization is the integration of the exposure and effects characterizations. Risk
characterization is used to determine the potential for direct and/or indirect effects to the DS and
CTS or for modification to their designated critical habitat from the use of malathion in CA. The
risk characterization provides an estimation (Section 5.1) and a description (Section 5.2) of the
likelihood of adverse effects; articulates risk assessment assumptions, limitations, and
uncertainties; and synthesizes an overall conclusion regarding the likelihood of adverse effects to
the assessed species or their designated critical habitat {i.e., "no effect," "likely to adversely
affect," or "may affect, but not likely to adversely affect"). In the risk estimation section, risk
quotients are calculated using standard EFED procedures and models. In the risk description
section, additional analyses may be conducted to help characterize the potential for risk.

5.1. Risk Estimation

Risk is estimated by calculating the ratio of exposure to toxicity. This ratio is the risk quotient
(RQ), which is then compared to pre-established acute and chronic levels of concern (LOCs) for
each category evaluated (Appendix C). For acute exposures to the aquatic animals, as well as
terrestrial invertebrates, the LOC is 0.05. For acute exposures to the birds, mammals, reptiles,
and terrestrial-phase amphibians the LOC is 0.1. The LOC for chronic exposures to animals, as
well as acute exposures to plants is 1.0.

Acute and chronic risks to aquatic organisms are estimated by calculating the ratio of exposure to
toxicity. Exposure values were l-in-10 year aquatic EECs (Table 3-) based on the label-
recommended malathion use scenarios summarized in Appendix D. Toxicity values were
appropriate aquatic toxicity endpoint from Table 4-1. Acute and chronic risks to terrestrial
animals are based on estimated residues on terrestrial food items predicted for malathion uses
(Table 3-6 through 3-8) and the appropriate toxicity endpoint from Table 4-14.

5.1.1. Exposures in the Aquatic Habitat

5.1.1.a. Freshwater Fish and Aquatic-phase Amphibians

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Acute risk to fish and aquatic-phase amphibians is based on 1 in 10 year peak EECs in the
standard pond and the lowest acute toxicity value for freshwater fish. Chronic risk is based on
the 1 in 10 year 60-day EECs and the lowest chronic toxicity value for freshwater fish. Risk
quotients for freshwater fish are shown in Table 5-1. Acute RQs ranged from 0.02 to 2.72 for
non-aquatic agricultural uses, 16.6 to 34.0 for aquatic agricultural uses (rice, wild rice, and water
cress), and 0.02 to 1.82 for nonagricultural uses. The acute RQ exceeded the LOC for acute risk
for all use sites except passion fruit and ULV application citrus, ULV wide area application (e.g.
adult mosquito control), cull piles, and fence rows. Due to the rapid degradation of malathion,
chronic RQs generally were lower than acute RQs. They ranged from 0.02 to 1.52 for non-
aquatic agricultural uses, 63.7 to 130 for aquatic agricultural uses, and 0.01 to 0.83 for
nonagricultural uses.

Table 5-1. Acute and Chronic RQs for Freshwater Fish. Risk quotients that exceed the LOC are
shown in bold. The acute LOC is 0.5 for the acute effects and 1.0 for chronic effects.

i:i.( s

Risk Quo(ion(

Scenario

Application
Method

Peak

r.r.c

60-dsij

r.r.c'

Acnlc

Chronic

1. Alfalfa, Clover, Lespedeza, Lupine, Grain
Lupine, Trefoil, and Vetch

4.9

0.68

-------
i:i:< s

Risk Quo!ion(

Scenario

Application
Method

Pciik

i:i.(

Wl-chij

r.r.r

Acule

('limine

16. Nectarine and Peach

25.3

2.9

0.77

0.34

24.0

2.6

0.73

0.30

17. Cherry

16.7

2.5

0.50

0.29

ULV

15.4

4.7

0.47

0.55

19.8

2.4

0.60

0.28

18.5

2.1

0.56

0.24

18. Fig

17.0

1.8

0.52

0.21

16.0

1.6

0.48

0.19

19. Pear

10.1

1.1

0.31

0.12

9.5

1.0

0.29

0.11

20. Guava, Mango, and Papaya

22.2

3.1

0.67

0.36

21.5

2.8

0.65

0.33

22. Garlic and Leek

34.2

4.1

1.04

0.47

41.8

3.7

1.27

0.43

23. Grapes

12.8

1.4

0.39

0.16

11.8

1.2

0.36

0.14

26. Brussels Sprouts and Dandelion

52.0

5.7

1.58

0.67

46.9

5.0

1.42

0.58

27. Chervil, Chrysanthemum - Garland, Endive
(Escarole), Lettuce, Head and Leaf Lettuce, Orach
(Mountain Spinach), Parsley, Roquette (Arrugula),
Salsify, Spinach, and Swiss Chard

83.1

8.8

2.52

1.03

74.4

7.7

2.25

0.89

29. Eggplant

25.6

5.0

0.78

0.58

42.2

4.5

1.28

0.52

30. Pumpkin

8.3

0.9

0.25

0.10

5.7

0.4

0.17

0.05

31. Cantaloupe, Honeydew, Musk, Water, and
Winter Melons

(Casaba/Crenshaw/Honeydew/Persian), Chayote,
Cucumber, Melons, and Squash (All or
Unspecified, Summer, and Winter (Hubbard))

49.7

6.7

1.50

0.78

42.9

4.7

1.30

0.55

32. Onion, Onions (Green), Radish, and Shallot

15.9

1.9

0.48

0.23

8.4

0.7

0.25

0.08

33. White/Irish Potato

12.7

1.6

0.38

0.19

20.3

1.7

0.62

0.20

34. Turnip (Greens and Root)

23.2

2.8

0.70

0.33

16.3

1.4

0.49

0.16

37. Bermudagrass, Bluegrass, Canarygrass, Grass
Forage/Fodder/Hay, Pastures, Peas (Including
Vines), Rangeland, Sudangrass, and Timothy

16.6

1.6

0.50

0.19

ULV

17.1

1.6

0.52

0.19

19.2

2.1

0.58

0.25

40. Beets, Beets (Unspecified), Cowpea/Blackeyed
Pea, Cowpeas, Field Peas, and Peas (Unspecified)

18.3

1.9

0.56

0.22

20.1

1.7

0.61

0.20

41. Carrot (Including Tops), Celtuce, Fennel,
Peanuts, Peanuts (Unspecified), and Pepper

32.4

3.1

0.98

0.36

25.1

1.9

0.76

0.22

42. Beans and Dried-Type and Succulent (Lima
and Snap) Beans

ULV

12.0

1.6

0.37

0.19

43. Celery

27.5

2.9

0.83

0.33

22.2

1.7

0.67

0.19

131

-------
i:i:< s

Risk Quo(ion(

Scenario

Application
Method

Peak
l.l.(

Wl-chij

r.r.r

Aeule

('limine

44. Asparagus and Safflower (Unspecified)

22.9

2.4

0.69

0.28

16.0

1.4

0.49

0.16

46. Strawberry

89.8

13.0

2.72

1.52

84.6

10.2

2.56

1.18

48. Tomato

45.6

6.9

1.38

0.80

37.1

4.5

1.12

0.53

49. Okra

12.6

2.3

0.38

0.26

9.5

1.0

0.29

0.11

51. Sorghum and Sorghum Silage

9.3

0.9

0.28

0.11

ULV

8.8

1.0

0.27

0.11

11.6

1.4

0.35

0.17

52. Barley, Cereal Grains, Oats, Rye, and Wheat

33.4

3.9

1.01

0.45

ULV

19.6

2.4

0.59

0.28

28.2

3.0

0.86

0.35

53. Gooseberry

13.5

2.1

0.41

0.25

35.7

3.8

1.08

0.45

35.0

3.6

1.06

0.42

55. Blueberry

ULV

8.9

1.8

0.27

0.21

9.9

1.0

0.30

0.12

9.0

0.9

0.27

0.10

57. Passion Fruit (Granadilla)

0.8

0.4

0.03

0.04

0.6

0.3

0.02

0.03

58. Mint and Spearmint

8.3

1.4

0.25

0.16

19.7

2.3

0.60

0.27

59. Rice and Wild Rice

1123.3

34.04

130.62

ULV

548.2

16.61

63.74

1123.3

34.04

130.62

61. Water Cress

1123.3

34.04

130.62

1123.3

34.04

130.62

Cull Piles, Agricultural/Farm Structures/Buildings
and Equipment,

Commercial/Institutional/Industrial
Premises/Equipment (Outdoor), Meat Processing
Plant Premises (Nonfood Contact), and
Nonagricultural Outdoor Buildings/Structures

Drench

2.1

0.2

0.06

0.02

Fence Rows

Drench

0.8

0.1

0.02

0.01

Forestry. Christmas Tree Plantations, Pine (Seed
Orchard), and Slash Pine (Forest)

60.0

7.2

1.82

0.83

ULV

19.9

2.6

0.60

0.30

51.5

4.8

1.56

0.56

50.1

4.5

1.52

0.53

Nursery. Nursery Stock

59.2

6.0

1.79

0.70

53.2

4.4

1.61

0.51

53.0

4.4

1.61

0.52

Public Health (Adult Mosquito Control) and
Medfly Control. Nonagricultural Areas (Public
Health Use), Urban Areas, and Wide Area/General
Outdoor Treatment

ULV

1.06

1.06a

0.03

0.12

Residential

Drench

3.43

0.25

0.10

0.03

132

-------

( s

Risk Quo!ion(

Application

Peak

Wl-chij

r.r.r

Scenario

Method

l.l.(

Aeule

('limine

Rights-of-Way. Fencerows/Hedgerows,

24.0

3.9

0.73

0.46

Nonagricultural Rights-of-

ULV

7.3

1.1

0.22

0.12

Way/Fencerows/Hedgerows, and Nonagricultural

5.4

0.8

0.16

0.09

Uncultivated Areas/Soils

5.5

0.8

0.17

0.09

10.3

1.0

0.31

0.12

ULV

12.2

1.1

0.37

0.13

Turf. Golf Course Turf (Bermudagrass)

5.7

0.5

0.17

0.06

a. A prediction of the chronic aquatic EEC for wide area aerial ULV applications was not possible. The acute EEC
was used as a protective estimate of the chronic EEC because the chronic EEC is expected to be smaller.

Based on these results, use of malathion has the potential to directly affect the DS and CTS.
Additionally, since the acute RQs exceed the LOC for most uses, malathion use has the potential
to indirectly affect the DS and CTS because it may affect fish and amphibian prey used by these
species.

5.1.l.b. Freshwater Invertebrates

Acute risk to freshwater invertebrates is based on 1 in 10 year peak EECs in the standard pond
and the lowest acute toxicity value for freshwater invertebrates. Chronic risk is based on 1 in 10
year 21-day EECs and the lowest chronic toxicity value for freshwater invertebrates. Risk
quotients for freshwater fish are shown in Table 5-2. Acute RQs ranged from 1.04 to 152 for
non-aquatic agricultural uses, 929 to 1900 for aquatic agricultural uses (rice, wild rice, and water
cress), and 1.34 to 102 for nonagricultural uses. Chronic RQs ranged from 8.11 to 866 for non-
aquatic agricultural uses, 15,600 to 32,100 for aquatic agricultural uses, and 5.78 to 564 for
nonagri cultural uses. Both acute and chronic RQs exceeded the LOC for all uses.

Table 5-2. Summary of Acute and Chronic RQs for Aquatic Invertebrates. Risk quotients that
exceed the LOC are shown in bold. The acute LOC is 0.1 for the acute effects and 1.0 for
chronic effects.

i:i:cs

I'l'cshuakT iii\ erich rales

Scenario

\pplicalioii
Method

ivak i:i:c

:i-da>
i:i:r

\cule

Chrome

22.5

7.8

38.2

222.0

1. Alfalfa, Clover, Lespedeza, Lupine, Grain

ULV

8.2

2.8

13.9

81.3

Lupine, Trefoil, and Vetch

15.5

4.6

26.3

132.5

16.0

5.4

27.0

154.9

2. Macadamia Nut (Bushnut)

15.6

5.3

26.4

150.4

34.9

12.1

59.2

345.1

3. Pecan and Walnut (English/Black)

33.0

11.2

55.9

321.2

62.2

25.1

105.4

717.7

6. Date

52.3

19.2

88.7

548.3

8. Avocado

59.3

12.6

100.4

359.6

9. Citrus Hybrids Other Than Tangelo,

50.1

13.1

84.9

372.9

Grapefruit, Kumquat, Lemon, Lime, Orange,

ULV

2.7

1.3

4.5

37.4

133

-------

i:i:cs

l ieshwalei' m\ cileh rales

\pplicnlioii

:i-da\

Scenario

MciIkhI

ivak i:i:c

i:i:c

\cule

Chronic

Tangelo, and Tangerines

23.1

5.4

39.1

155.3

22.1

5.1

37.5

146.0

10. Broccoli, Broccoli Raab, Cabbage,

37.6

14.9

63.7

425.3

Chinese Amaranth, Chinese Broccoli, Chinese

Cabbage, CanolaVRape, Cauliflower, Cole
Crops, Collards, Corn Salad, Dock (Sorrel),

Horseradish, Kale, Kohlrabi, Leafy

Vegetables, Mustard, Mustard Cabbage (Gai
Choy/ Pak-Choi), and Garden and Winter

Purslane

32.6

11.0

55.2

313.4

11. Corn (Silage and Unspecified), Field, Pop,

33.7

10.4

57.1

296.4

and Sweet Corn, Millet (Foxtail), and

ULV

23.3

7.9

39.5

224.8

Sunflower

22.3

6.5

37.7

184.7

37.3

14.5

63.3

413.9

ULV

26.0

11.3

44.1

321.7

12. Cotton (Unspecified)

23.8

7.3

40.4

207.3

14.6

5.5

24.8

156.1

11.4

3.7

19.4

106.6

13. Hops

11.1

3.6

18.9

101.9

10.7

3.2

18.1

92.5

15. Apricot

10.1

2.9

17.2

82.9

25.3

7.7

42.9

220.4

16. Nectarine and Peach

24.0

6.8

40.7

194.0

16.7

7.0

28.2

200.2

ULV

15.4

7.3

26.0

210.0

19.8

6.3

33.5

179.3

17. Cherry

18.5

5.7

31.4

162.5

17.0

4.8

28.9

138.1

18. Fig

16.0

4.5

27.1

128.5

10.1

2.9

17.1

81.6

19. Pear

9.5

2.7

16.1

76.3

22.2

6.7

37.6

192.8

20. Guava, Mango, and Papaya

21.5

6.3

36.5

181.1

34.2

10.8

58.0

309.9

22. Garlic and Leek

41.8

9.6

70.9

275.3

12.8

3.7

21.6

105.1

23. Grapes

11.8

3.3

20.1

94.7

52.0

15.4

88.1

440.9

26. Brussels Sprouts and Dandelion

46.9

13.4

79.5

382.4

27. Chervil, Chrysanthemum - Garland,

83.1

24.2

140.8

691.2

Endive (Escarole), Lettuce, Head and Leaf

Lettuce, Orach (Mountain Spinach), Parsley,
Roquette (Arrugula), Salsify, Spinach, and
Swiss Chard

74.4

21.2

126.0

605.2

25.6

11.6

43.4

331.1

29. Eggplant

42.2

12.0

71.4

341.5

8.3

2.4

14.1

69.1

30. Pumpkin

5.7

1.2

9.58

34.0

134

-------

i:i

( s

l ieshwalei' m\ cileh rales

\pplicnlioii

:i-da\

Scenario

MciIkhI

peak i:i:r

i:i:c

\cule

Chronic

31. Cantaloupe, Honeydew, Musk, Water, and

49.7

17.7

84.2

505.9

Winter Melons

(Casaba/Crenshaw/Honeydew/Persian),
Chayote, Cucumber, Melons, and Squash (All
or Unspecified, Summer, and Winter
(Hubbard))

42.9

12.9

72.7

368.4

32. Onion, Onions (Green), Radish, and

15.9

5.2

27.0

149.4

Shallot

8.4

1.9

14.3

54.4

12.7

4.4

21.5

124.3

33. White/Irish Potato

20.3

4.6

34.5

132.8

23.2

7.3

39.3

208.5

34. Turnip (Greens and Root)

16.3

3.9

27.6

110.5

37. Bermudagrass, Bluegrass, Canarygrass,

16.6

4.6

28.1

130.6

Grass Forage/Fodder/Hay, Pastures, Peas

ULV

17.1

4.6

28.9

131.4

(Including Vines), Rangeland, Sudangrass,
and Timothy

19.2

5.9

32.5

169.8

40. Beets, Beets (Unspecified),

18.3

5.2

31.0

149.9

Cowpea/Blackeyed Pea, Cowpeas, Field Peas,
and Peas (Unspecified)

20.1

4.6

34.0

132.5

41. Carrot (Including Tops), Celtuce, Fennel,

32.4

8.6

54.9

245.9

Peanuts, Peanuts (Unspecified), and Pepper

25.1

5.3

42.6

150.5

42. Beans and Dried-Type and Succulent

(Lima and Snap) Beans

ULV

12.0

4.3

20.4

123.5

27.5

7.9

46.6

224.9

43. Celery

22.2

4.6

37.6

131.0

22.9

6.6

38.8

187.4

44. Asparagus and Safflower (Unspecified)

16.0

3.8

27.2

109.2

89.8

31.0

152.2

886.0

46. Strawberry

84.6

26.1

143.3

746.1

45.6

17.1

77.3

487.8

48. Tomato

37.1

11.9

62.9

340.2

12.6

4.1

21.4

118.5

49. Okra

9.5

2.2

16.1

63.3

9.3

2.5

15.8

72.4

ULV

8.8

2.7

14.9

75.8

51. Sorghum and Sorghum Silage

11.6

3.9

19.7

111.8

33.4

10.4

56.6

298.0

52. Barley, Cereal Grains, Oats, Rye, and

ULV

19.6

6.5

33.3

186.2

Wheat

28.2

8.3

47.8

236.8

13.5

5.5

22.9

156.1

35.7

10.3

60.6

294.1

53. Gooseberry

35.0

9.9

59.3

281.7

ULV

8.9

3.6

15.0

103.7

9.9

2.6

16.8

74.7

55. Blueberry

9.0

2.4

15.3

68.4

0.8

0.4

1.40

11.5

57. Passion Fruit (Granadilla)

0.6

0.3

1.04

8.11

58. Mint and Spearmint

8.3

3.6

14.1

102.9

135

-------
i:i:cs

I reshwaler m\ eflehrales

Scenario

\pplicalioii
Melliod

ivak i:i:r

:i-da>

i:i:c

\cuic

Chrome

19.7

6.1

33.4

175.7

59. Rice and Wild Rice

1123.3

1903.9

32095.0

ULV

548.2

929.1

15662.4

1123.3

1903.9

32095.0

61. Water Cress

1123.3

1903.9

32095.0

1123.3

1903.9

32095.0

Cull Piles, Agricultural/Farm
Structures/Buildings and Equipment,
Commercial/Institutional/Industrial
Premises/Equipment (Outdoor), Meat
Processing Plant Premises (Nonfood Contact),
and Nonagricultural Outdoor
Buildings/Structures

Drench

2.1

0.5

3.53

14.0

Fence Rows

Drench

0.8

0.2

1.34

5.78

Forestry. Christmas Tree Plantations, Pine
(Seed Orchard), and Slash Pine (Forest)

60.0

19.8

101.6

564.3

ULV

19.9

7.1

33.7

203.5

51.5

13.4

87.2

382.5

50.1

12.7

84.9

362.3

Nursery. Nursery Stock

59.2

16.7

100.3

476.1

53.2

12.2

90.1

348.9

53.0

12.4

89.8

353.1

Public Health (Adult Mosquito Control) and
Medfly Control. Nonagricultural Areas
(Public Health Use), Urban Areas, and Wide
Area/General Outdoor Treatment

ULV

1.06

1.80

30.3

Residential

Drench

3.43

0.701

5.81

20.0

Rights-of-Way. Fencerows/Hedgerows,
Nonagricultural Rights-of-
Way/Fencerows/Hedgerows, and
Nonagricultural Uncultivated Areas/Soils

24.0

8.8

40.6

252.5

ULV

7.3

2.8

12.4

78.9

5.4

2.1

9.21

59.3

5.5

2.1

9.31

59.9

Turf. Golf Course Turf (Bermudagrass)

10.3

2.9

17.4

81.9

ULV

12.2

3.2

20.7

92.0

5.7

1.5

9.64

43.7

Based on these results, use of malathion use has the potential to indirectly affect the DS and CTS
because it may affect freshwater invertebrate prey used by these species.

5.1.I.e. Estuarine/Marine Fish

Acute risk to fish is based on 1 in 10 year peak EECs in the standard pond and the lowest acute
toxicity value for freshwater fish. Chronic risk is based on the 1 in 10 year 60-day EECs and the
lowest chronic toxicity value for freshwater fish. Risk quotients for freshwater fish are shown in
Table 5-3. Acute RQs ranged from 0.02 to 2.72 for non-aquatic agricultural uses, 16.6 to 34.0
for aquatic agricultural uses (rice, wild rice, and water cress), and 0.02 to 1.82 for nonagricultural

136

-------
uses. The acute RQ exceeded the LOC for acute risk for all use sites except passion fruit and
ULV application citrus, cull piles, and fence rows. Due to the rapid degradation of malathion,
chronic RQs generally were lower than acute RQs. They ranged from 0.01 to 0.77 for non-
aquatic agricultural uses, 31.7 to 64.9 for aquatic agricultural uses, and <0.01 to 0.41 for
nonagricultural uses.

Table 5-3. Summary of RQs for Estuarine/Marine Fish. Risk quotients that exceed the LOC are
shown in bold. The acute LOC is 0.05 for the acute effects and 1.0 for chronic effects.

i:i:cs

1 !sliiariiic marine lisli

\pplicalimi

(>n-da\

Scenario

Melliod

ivak i:i:c

i:i:c

\cnle

( limine

22.5

4.y

0.68

0.28

1. Alfalfa, Clover, Lespedeza, Lupine, Grain

ULV

8.2

l.l

0.25

0.06

Lupine, Trefoil, and Vetch

15.5

2.1

0.47

0.12

16.0

2.4

0.48

0.14

2. Macadamia Nut (Bushnut)

15.6

2.3

0.47

0.13

34.9

4.6

1.06

0.27

3. Pecan and Walnut (English/Black)

33.0

4.2

1.00

0.24

62.2

13.3

1.88

0.77

6. Date

52.3

9.2

1.59

0.53

8. Avocado

59.3

4.8

1.80

0.28

50.1

8.3

1.52

0.48

9. Citrus Hybrids Other Than Tangelo,

ULV

2.7

0.5

0.08

0.03

Grapefruit, Kumquat, Lemon, Lime, Orange,

23.1

2.4

0.70

0.14

Tangelo, and Tangerines

22.1

2.1

0.67

0.12

10. Broccoli, Broccoli Raab, Cabbage, Chinese

37.6

7.6

1.14

0.44

Amaranth, Chinese Broccoli, Chinese Cabbage,

CanolaVRape, Cauliflower, Cole Crops,
Collards, Corn Salad, Dock (Sorrel),

Horseradish, Kale, Kohlrabi, Leafy Vegetables,

Mustard, Mustard Cabbage (Gai Choy/ Pak-
Choi), and Garden and Winter Purslane

32.6

4.7

0.99

0.27

11. Corn (Silage and Unspecified), Field, Pop,

33.7

3.8

1.02

0.22

and Sweet Corn, Millet (Foxtail), and

ULV

23.3

2.9

0.71

0.16

Sunflower

22.3

2.4

0.67

0.14

37.3

5.8

1.13

0.33

ULV

26.0

4.5

0.79

0.26

12. Cotton (Unspecified)

23.8

2.7

0.72

0.15

14.6

2.2

0.44

0.13

11.4

1.4

0.35

0.08

13. Hops

11.1

1.3

0.34

0.08

10.7

1.2

0.32

0.07

15. Apricot

10.1

1.0

0.31

0.06

25.3

2.9

0.77

0.17

16. Nectarine and Peach

24.0

2.6

0.73

0.15

16.7

2.5

0.50

0.14

ULV

15.4

4.7

0.47

0.27

19.8

2.4

0.60

0.14

17. Cherry

18.5

2.1

0.56

0.12

18. Fig

17.0

1.8

0.52

0.10

137

-------

16.0

1.6

0.48

0.09

19. Pear

10.1

1.1

0.31

0.06

9.5

1.0

0.29

0.06

20. Guava, Mango, and Papaya

22.2

3.1

0.67

0.18

21.5

2.8

0.65

0.16

22. Garlic and Leek

34.2

4.1

1.04

0.24

41.8

3.7

1.27

0.22

23. Grapes

12.8

1.4

0.39

0.08

11.8

1.2

0.36

0.07

26. Brussels Sprouts and Dandelion

52.0

5.7

1.58

0.33

46.9

5.0

1.42

0.29

27. Chervil, Chrysanthemum - Garland, Endive
(Escarole), Lettuce, Head and Leaf Lettuce,
Orach (Mountain Spinach), Parsley, Roquette
(Arrugula), Salsify, Spinach, and Swiss Chard

83.1

8.8

2.52

0.51

74.4

7.7

2.25

0.44

29. Eggplant

25.6

5.0

0.78

0.29

42.2

4.5

1.28

0.26

30. Pumpkin

8.3

0.9

0.25

0.05

5.7

0.4

0.17

0.03

31. Cantaloupe, Honey dew, Musk, Water, and
Winter Melons

(Casaba/Crenshaw/Honey dew/Persian),
Chayote, Cucumber, Melons, and Squash (All
or Unspecified, Summer, and Winter
(Hubbard))

49.7

6.7

1.50

0.39

42.9

4.7

1.30

0.27

32. Onion, Onions (Green), Radish, and Shallot

15.9

1.9

0.48

0.11

8.4

0.7

0.25

0.04

33. White/Irish Potato

12.7

1.6

0.38

0.09

20.3

1.7

0.62

0.10

34. Turnip (Greens and Root)

23.2

2.8

0.70

0.16

16.3

1.4

0.49

0.08

37. Bermudagrass, Bluegrass, Canarygrass,
Grass Forage/Fodder/Hay, Pastures, Peas
(Including Vines), Rangeland, Sudangrass, and
Timothy

16.6

1.6

0.50

0.09

ULV

17.1

1.6

0.52

0.10

19.2

2.1

0.58

0.12

40. Beets, Beets (Unspecified),
Cowpea/Blackeyed Pea, Cowpeas, Field Peas,
and Peas (Unspecified)

18.3

1.9

0.56

0.11

20.1

1.7

0.61

0.10

41. Carrot (Including Tops), Celtuce, Fennel,
Peanuts, Peanuts (Unspecified), and Pepper

32.4

3.1

0.98

0.18

25.1

1.9

0.76

0.11

42. Beans and Dried-Type and Succulent (Lima
and Snap) Beans

ULV

12.0

1.6

0.37

0.09

43. Celery

27.5

2.9

0.83

0.17

22.2

1.7

0.67

0.10

44. Asparagus and Safflower (Unspecified)

22.9

2.4

0.69

0.14

16.0

1.4

0.49

0.08

46. Strawberry

89.8

13.0

2.72

0.75

84.6

10.2

2.56

0.59

48. Tomato

45.6

6.9

1.38

0.40

37.1

4.5

1.12

0.26

49. Okra

12.6

2.3

0.38

0.13

9.5

1.0

0.29

0.06

138

-------

9.3

0.9

0.28

0.05

ULV

8.8

1.0

0.27

0.06

51. Sorghum and Sorghum Silage

11.6

1.4

0.35

0.08

33.4

3.9

1.01

0.22

52. Barley, Cereal Grains, Oats, Rye, and

ULV

19.6

2.4

0.59

0.14

Wheat

28.2

3.0

0.86

0.17

13.5

2.1

0.41

0.12

35.7

3.8

1.08

0.22

53. Gooseberry

35.0

3.6

1.06

0.21

ULV

8.9

1.8

0.27

0.10

9.9

1.0

0.30

0.06

55. Blueberry

9.0

0.9

0.27

0.05

0.8

0.4

0.03

0.02

57. Passion Fruit (Granadilla)

0.6

0.3

0.02

0.01

8.3

1.4

0.25

0.08

58. Mint and Spearmint

19.7

2.3

0.60

0.13

1123.3

34.04

64.93

ULV

548.2

16.61

31.69

59. Rice and Wild Rice

1123.3

34.04

64.93

1123.3

34.04

64.93

61. Water Cress

1123.3

34.04

64.93

Cull Piles, Agricultural/Farm
Structures/Buildings and Equipment,
Commercial/Institutional/Industrial

Premises/Equipment (Outdoor), Meat
Processing Plant Premises (Nonfood Contact),
and Nonagricultural Outdoor
Buildings/Structures

Drench

2.1

0.2

0.06

0.01

Fence Rows

Drench

0.8

0.1

0.02

<0.01

60.0

7.2

1.82

0.41

ULV

19.9

2.6

0.60

0.15

Forestry. Christmas Tree Plantations, Pine

51.5

4.8

1.56

0.28

(Seed Orchard), and Slash Pine (Forest)

50.1

4.5

1.52

0.26

59.2

6.0

1.79

0.35

53.2

4.4

1.61

0.25

Nursery. Nursery Stock

53.0

4.4

1.61

0.26

Public Health (Adult Mosquito Control) and
Medfly Control. Nonagricultural Areas (Public
Health Use), Urban Areas, and Wide

Area/General Outdoor Treatment

ULV

1.06

1.06a

0.03

0.06

Residential

Drench

3.43

0.25

0.10

0.01

Rights-of-Way. Fencerows/Hedgerows,
Nonagricultural Rights-of-

24.0

3.9

0.73

0.23

ULV

7.3

1.1

0.22

0.06

Way/Fencerows/Hedgerows, and

5.4

0.8

0.16

0.04

Nonagricultural Uncultivated Areas/Soils

5.5

0.8

0.17

0.05

10.3

1.0

0.31

0.06

ULV

12.2

1.1

0.37

0.07

Turf. Golf Course Turf (Bermudagrass)

5.7

0.5

0.17

0.03

139

-------
Based on these results, use of malathion has the potential to directly affect the DS. Additionally,
since the acute RQs exceed the LOC for most uses, malathion use has the potential to indirectly
affect DS because it may affect estuarine fish prey used by this species.

5.1.l.d. Estuarine/Marine Invertebrates

Acute risk to freshwater invertebrates is based on 1 in 10 year peak EECs in the standard pond
and the lowest acute toxicity value for freshwater invertebrates. Chronic risk is based on 1 in 10
year 21-day EECs and the lowest chronic toxicity value for freshwater invertebrates. Risk
quotients for freshwater fish are shown in Table 5-4. Acute RQs ranged from 0.28 to 40.8 for
non-aquatic agricultural uses, 249 to 510 for aquatic agricultural uses (rice, wild rice, and water
cress), and 0.36 to 27.3 for nonagricultural uses. Chronic RQs ranged from 21.8 to 2390 for non-
aquatic agricultural uses, 42,200 to 86,400 for aquatic agricultural uses, and 15.6 to 1520 for
nonagri cultural uses. Both acute and chronic RQs exceeded the LOC for all uses.

Table 5-4. Summary of Acute and Chronic RQs for Estuarine/Marine Invertebrates. Risk
quotients that exceed the LOC are shown in bold. The acute LOC is 0.1 for the acute effects and
1.0 for chronic effects.

I'lsliiiirinc/ murine

( s

in\crlcl>r;ilcs

Application

IV;ik

2l-d;i\

Scenario

Method

i:i.(

Anile

Chronic

22.5

7.8

10.2

597.8

1. Alfalfa, Clover, Lespedeza, Lupine, Grain

ULV

8.2

2.8

3.72

218.9

Lupine, Trefoil, and Vetch

15.5

4.6

7.05

356.7

16.0

5.4

7.25

416.9

2. Macadamia Nut (Bushnut)

15.6

5.3

7.09

404.8

34.9

12.1

15.8

929.0

3. Pecan and Walnut (English/Black)

33.0

11.2

15.0

864.8

62.2

25.1

28.3

1932.2

6. Date

52.3

19.2

23.8

1476.2

8. Avocado

59.3

12.6

26.9

968.1

50.1

13.1

22.8

1003.8

9. Citrus Hybrids Other Than Tangelo,

ULV

2.7

1.3

1.21

100.6

Grapefruit, Kumquat, Lemon, Lime, Orange,

23.1

5.4

10.5

418.2

Tangelo, and Tangerines

22.1

5.1

10.1

393.2

10. Broccoli, Broccoli Raab, Cabbage,

37.6

14.9

17.1

1144.9

Chinese Amaranth, Chinese Broccoli,

Chinese Cabbage, Canola\Rape, Cauliflower,
Cole Crops, Collards, Corn Salad, Dock

(Sorrel), Horseradish, Kale, Kohlrabi, Leafy

Vegetables, Mustard, Mustard Cabbage (Gai
Choy/ Pak-Choi), and Garden and Winter
Purslane

32.6

11.0

14.8

843.8

11. Corn (Silage and Unspecified), Field,

33.7

10.4

15.3

798.0

Pop, and Sweet Corn, Millet (Foxtail), and

ULV

23.3

7.9

10.6

605.1

Sunflower

22.3

6.5

10.1

497.2

37.3

14.5

17.0

1114.2

ULV

26.0

11.3

11.8

866.2

12. Cotton (Unspecified)

23.8

7.3

10.8

558.2

140

-------

I'lsliiiirinc/ murine

( s

in\crlcl>r;ilcs

Application

IV;ik

2l-d;i\

Scenario

Method

i:i.(

Acnlc

Chronic

14.6

5.5

6.66

420.2

11.4

3.7

5.20

287.0

13. Hops

11.1

3.6

5.06

274.3

10.7

3.2

4.86

249.0

15. Apricot

10.1

2.9

4.61

223.3

25.3

7.7

11.5

593.4

16. Nectarine and Peach

24.0

6.8

10.9

522.2

16.7

7.0

7.57

539.1

ULV

15.4

7.3

6.98

565.3

19.8

6.3

8.98

482.6

17. Cherry

18.5

5.7

8.42

437.5

17.0

4.8

7.75

371.9

18. Fig

16.0

4.5

7.27

346.1

10.1

2.9

4.58

219.6

19. Pear

9.5

2.7

4.31

205.5

22.2

6.7

10.1

519.0

20. Guava, Mango, and Papaya

21.5

6.3

9.78

487.7

34.2

10.8

15.6

834.2

22. Garlic and Leek

41.8

9.6

19.0

741.1

12.8

3.7

5.80

282.9

23. Grapes

11.8

3.3

5.38

255.0

52.0

15.4

23.6

1187.1

26. Brussels Sprouts and Dandelion

46.9

13.4

21.3

1029.4

27. Chervil, Chrysanthemum - Garland,

83.1

24.2

37.8

1861.0

Endive (Escarole), Lettuce, Head and Leaf

Lettuce, Orach (Mountain Spinach), Parsley,
Roquette (Arrugula), Salsify, Spinach, and
Swiss Chard

74.4

21.2

33.8

1629.5

25.6

11.6

891.5

29. Eggplant

42.2

12.0

19.2

919.3

8.3

2.4

3.77

186.0

30. Pumpkin

5.7

1.2

2.57

91.4

31. Cantaloupe, Honey dew, Musk, Water,

49.7

17.7

22.6

1362.1

and Winter Melons

(Casaba/Crenshaw/Honeydew/Persian),
Chayote, Cucumber, Melons, and Squash

(All or Unspecified, Summer, and Winter

(Hubbard))

42.9

12.9

19.5

991.8

32. Onion, Onions (Green), Radish, and

15.9

5.2

7.24

402.3

Shallot

8.4

1.9

3.82

146.5

12.7

4.4

5.76

334.7

33. White/Irish Potato

20.3

4.6

9.24

357.5

23.2

7.3

10.5

561.3

34. Turnip (Greens and Root)

16.3

3.9

7.40

297.4

37. Bermudagrass, Bluegrass, Canarygrass,

16.6

4.6

7.53

351.7

Grass Forage/Fodder/Hay, Pastures, Peas

ULV

17.1

4.6

7.75

353.7

(Including Vines), Rangeland, Sudangrass,
and Timothy

19.2

5.9

8.72

457.2

141

-------

I'lsliiiirinc/ murine

1.1

( s

in\crlcl>r;ilcs

Application

IV;ik

2l-d;i\

Scenario

Method

i:i.(

Acnlc

Chronic

40. Beets, Beets (Unspecified),

18.3

5.2

8.33

403.7

Cowpea/Blackeyed Pea, Cowpeas, Field
Peas, and Peas (Unspecified)

20.1

4.6

9.12

356.6

41. Carrot (Including Tops), Celtuce, Fennel,

32.4

8.6

14.7

662.0

Peanuts, Peanuts (Unspecified), and Pepper

25.1

5.3

11.4

405.3

42. Beans and Dried-Type and Succulent

(Lima and Snap) Beans

ULV

12.0

4.3

5.48

332.5

27.5

7.9

12.5

605.5

43. Celery

22.2

4.6

10.1

352.7

22.9

6.6

10.4

504.6

44. Asparagus and Safflower (Unspecified)

16.0

3.8

7.29

293.9

89.8

31.0

40.8

2385.5

46. Strawberry

84.6

26.1

38.4

2008.8

45.6

17.1

20.7

1313.3

48. Tomato

37.1

11.9

16.9

915.8

12.6

4.1

5.73

319.0

49. Okra

9.5

2.2

4.32

170.4

9.3

2.5

4.23

194.9

ULV

8.8

2.7

4.00

204.1

51. Sorghum and Sorghum Silage

11.6

3.9

5.28

301.1

33.4

10.4

15.2

802.3

52. Barley, Cereal Grains, Oats, Rye, and

ULV

19.6

6.5

8.92

501.3

Wheat

28.2

8.3

12.8

637.6

13.5

5.5

6.15

420.3

35.7

10.3

16.2

791.9

53. Gooseberry

35.0

9.9

15.9

758.5

ULV

8.9

3.6

4.03

279.1

9.9

2.6

4.49

201.1

55. Blueberry

9.0

2.4

4.09

184.0

0.8

0.4

0.38

30.8

57. Passion Fruit (Granadilla)

0.6

0.3

0.28

21.8

8.3

3.6

3.77

276.9

58. Mint and Spearmint

19.7

6.1

8.97

473.0

1123.3

510.6

86409.6

ULV

548.2

249.2

42167.9

59. Rice and Wild Rice

1123.3

510.6

86409.6

1123.3

510.6

86409.6

61. Water Cress

1123.3

510.6

86409.6

Cull Piles, Agricultural/Farm
Structures/Buildings and Equipment,
Commercial/Institutional/Industrial

Premises/Equipment (Outdoor), Meat
Processing Plant Premises (Nonfood
Contact), and Nonagricultural Outdoor
Buildings/Structures

Drench

2.1

0.5

0.95

37.8

Fence Rows

Drench

0.8

0.2

0.36

15.6

Forestry. Christmas Tree Plantations, Pine

60.0

19.8

27.3

1519.3

(Seed Orchard), and Slash Pine (Forest)

ULV

19.9

7.1

9.03

547.9

142

-------
i:i.( s

I'lsliiiirinc/ murine
in\cr(cl)r;Kcs

SiTiiiirio

Application
Method

IV;ik

i:i.(

2 l-d;t\

i:i.(

Acute

Chronic

51.5

13.4

23.4

1029.8

50.1

12.7

22.8

975.5

Nursery. Nursery Stock

59.2

16.7

26.9

1281.8

53.2

12.2

24.2

939.5

53.0

12.4

24.1

950.7

Public Health and Medfly Control.
Nonagricultural Areas (Public Health Use),
Urban Areas, and Wide Area/General
Outdoor Treatment (Public Health Use)

ULV

1.06

1.06a

0.48

81.5

Residential

Drench

3.43

0.70

1.56

53.9

Rights-of-Way. Fencerows/Hedgerows,
Nonagricultural Rights-of-
Way/Fencerows/Hedgerows, and
Nonagricultural Uncultivated Areas/Soils

24.0

8.8

10.9

679.7

ULV

7.3

2.8

3.32

212.4

5.4

2.1

2.47

159.7

5.5

2.1

2.50

161.4

Turf. Golf Course Turf (Bermudagrass)

10.3

2.9

4.67

220.6

ULV

12.2

3.2

5.54

247.6

5.7

1.5

2.59

117.7

Based on these results, use of malathion use has the potential to indirectly affect the DS because
it may affect estuarine invertebrate prey used by these species.

5.1.I.e. Aquatic Plants

Risk to aquatic plants is based on 1 in 10 year peak EECs in the standard pond and the lowest
acute toxicity value. Risk quotients are shown in Table 5-3. Aquatic plant RQs were calculated
based on toxicity data for non-vascular aquatic plants because no acceptable data were available
for vascular aquatic plants. However, supplemental data did show that vascular aquatic plants
are less sensitive to malathion than nonvascular aquatic plants. Therefore, these RQs are
assumed to be protective for all aquatic plants, including vascular ones. Aquatic plants RQs
ranged from <0.01 to 0.04 for non-aquatic agricultural uses, 0.23 to 0.47 for aquatic agricultural
uses (rice, wild rice, and water cress), and <0.01 to 0.02 for nonagricultural uses. None of the
RQs exceeded the LOC for any of the uses of malathion.

Table 5-3 Summary of Acute RQs for Aquatic Plants

Scciiiirio

Application
Method

iv;ik r.r.c

Risk Quotient

1. Alfalfa, Clover, Lespedeza, Lupine, Grain Lupine,
Trefoil, and Vetch

22.5

0.01

ULV

8.2

<0.01

15.5

0.01

2. Macadamia Nut (Bushnut)

16.0

0.01

15.6

0.01

3. Pecan and Walnut (English/Black)

34.9

0.01

143

-------

33.0

0.01

6. Date

62.2

0.03

52.3

0.02

8. Avocado

59.3

0.02

9. Citrus Hybrids Other Than Tangelo, Grapefruit,
Kumquat, Lemon, Lime, Orange, Tangelo, and
Tangerines

50.1

0.02

ULV

2.7

<0.01

23.1

0.01

22.1

0.01

10. Broccoli, Broccoli Raab, Cabbage, Chinese
Amaranth, Chinese Broccoli, Chinese Cabbage,
Canola\Rape, Cauliflower, Cole Crops, Collards, Corn
Salad, Dock (Sorrel), Horseradish, Kale, Kohlrabi, Leafy
Vegetables, Mustard, Mustard Cabbage (Gai Choy/ Pak-
Choi), and Garden and Winter Purslane

37.6

0.02

32.6

0.01

11. Corn (Silage and Unspecified), Field, Pop, and Sweet
Corn, Millet (Foxtail), and Sunflower

33.7

0.01

ULV

23.3

0.01

22.3

0.01

12. Cotton (Unspecified)

37.3

0.02

ULV

26.0

0.01

23.8

0.01

13. Hops

14.6

0.01

11.4

<0.01

11.1

<0.01

15. Apricot

10.7

<0.01

10.1

<0.01

16. Nectarine and Peach

25.3

0.01

24.0

0.01

17. Cherry

16.7

0.01

ULV

15.4

0.01

19.8

0.01

18.5

0.01

18. Fig

17.0

0.01

16.0

0.01

19. Pear

10.1

<0.01

9.5

<0.01

20. Guava, Mango, and Papaya

22.2

0.01

21.5

0.01

22. Garlic and Leek

34.2

0.01

41.8

0.02

23. Grapes

12.8

0.01

11.8

<0.01

26. Brussels Sprouts and Dandelion

52.0

0.02

46.9

0.02

27. Chervil, Chrysanthemum - Garland, Endive
(Escarole), Lettuce, Head and Leaf Lettuce, Orach
(Mountain Spinach), Parsley, Roquette (Arrugula),
Salsify, Spinach, and Swiss Chard

83.1

0.03

74.4

0.03

144

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29. Eggplant

25.6

0.01

42.2

0.02

30. Pumpkin

8.3

<0.01

5.7

<0.01

31. Cantaloupe, Honey dew, Musk, Water, and Winter
Melons (Casaba/Crenshaw/Honeydew/Persian), Chayote,
Cucumber, Melons, and Squash (All or Unspecified,
Summer, and Winter (Hubbard))

49.7

0.02

42.9

0.02

32. Onion, Onions (Green), Radish, and Shallot

15.9

0.01

8.4

<0.01

33. White/Irish Potato

12.7

0.01

20.3

0.01

34. Turnip (Greens and Root)

23.2

0.01

16.3

0.01

37. Bermudagrass, Bluegrass, Canarygrass, Grass
Forage/Fodder/Hay, Pastures, Peas (Including Vines),
Rangeland, Sudangrass, and Timothy

16.6

0.01

ULV

17.1

0.01

19.2

0.01

40. Beets, Beets (Unspecified), Cowpea/Blackeyed Pea,
Cowpeas, Field Peas, and Peas (Unspecified)

18.3

0.01

20.1

0.01

41. Carrot (Including Tops), Celtuce, Fennel, Peanuts,
Peanuts (Unspecified), and Pepper

32.4

0.01

25.1

0.01

42. Beans and Dried-Type and Succulent (Lima and
Snap) Beans

ULV

12.0

0.01

43. Celery

27.5

0.01

22.2

0.01

44. Asparagus and Safflower (Unspecified)

22.9

0.01

16.0

0.01

46. Strawberry

89.8

0.04

84.6

0.04

48. Tomato

45.6

0.02

37.1

0.02

49. Okra

12.6

0.01

9.5

<0.01

51. Sorghum and Sorghum Silage

9.3

<0.01

ULV

8.8

<0.01

11.6

<0.01

52. Barley, Cereal Grains, Oats, Rye, and Wheat

33.4

0.01

ULV

19.6

0.01

28.2

0.01

53. Gooseberry

13.5

0.01

35.7

0.01

35.0

0.01

55. Blueberry

ULV

8.9

<0.01

9.9

<0.01

9.0

<0.01

57. Passion Fruit (Granadilla)

0.8

<0.01

145

-------

0.6

<0.01

58. Mint and Spearmint

8.3

<0.01

19.7

0.01

59. Rice and Wild Rice

1123.3

0.47

ULV

548.2

0.23

1123.3

0.47

61. Water Cress

1123.3

0.47

1123.3

0.47

Cull Piles, Agricultural/Farm Structures/Buildings and
Equipment, Commercial/Institutional/Industrial
Premises/Equipment (Outdoor), Meat Processing Plant
Premises (Nonfood Contact), and Nonagricultural
Outdoor Buildings/Structures

Drench

2.1

<0.01

Fence Rows

Drench

0.8

<0.01

Forestry. Christmas Tree Plantations, Pine (Seed
Orchard), and Slash Pine (Forest)

60.0

0.02

ULV

19.9

0.01

51.5

0.02

50.1

0.02

Nursery. Nursery Stock

59.2

0.02

53.2

0.02

53.0

0.02

Public Health (Adult Mosquito Control) and Medfly
Control. Nonagricultural Areas (Public Health Use),
Urban Areas, and Wide Area/General Outdoor Treatment

ULV

1.06

<0.01

Residential

Drench

3.43

<0.01

Rights-of-Way. Fencerows/Hedgerows, Nonagricultural
Rights-of-Way/Fencerows/Hedgerows, and
Nonagricultural Uncultivated Areas/Soils

24.0

0.01

ULV

7.3

<0.01

5.4

<0.01

5.5

<0.01

Turf. Golf Course Turf (Bermudagrass)

10.3

<0.01

ULV

12.2

0.01

5.7

<0.01

Based on these results, use of malathion as described does not have the potential to indirectly
affect the DS and CTS through adverse effects on aquatic plants which are used as food by these
species.

5.1.2. Exposures in the Terrestrial Habitat

5.1.2.a. Birds (surrogates for Terrestrial-phase Amphibians) and
Mammals

As previously discussed in Section 3.3, potential direct effects to terrestrial species were based
on foliar and ULV applications of malathion. We used the T-REX model to calculate acute and
chronic risk quotients (RQs) for birds, which serve as surrogates for terrestrial-phase amphibians,
and separate RQs for mammals. Acute and chronic RQs were calculated based on acute and

146

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chronic toxicity data for the most sensitive bird and mammal species for which data were
available. For terrestrial-phase amphibians, T-REX was used as a screening tool to determine if a
refined assessment with T-HERPS was necessary. For this screen, the most protective RQs were
calculated by assuming a small bird (surrogate for amphibians) consuming short grass. This
serves as a screen for both direct and indirect effects to the CTS. For mammals, RQs were
calculated for small (15 g) herbivorous mammal feeding on short grass. This represents the most
sensitive mammal species that, if impacted, could cause indirect effects to the CTS.

Acute and chronic RQs derived using T-REX for the CTS, other amphibians, and mammals are
shown in Table 5-4. For all uses assessed, the acute RQ exceed the LOC for direct effects to
amphibians. In addition, the chronic RQ exceeded the LOC for amphibians for all uses except
ULV applications on citrus and ULV application for adult mosquito control. Because all uses
fail to pass this risk screen, refined RQs were derived for amphibians using T-HERPS (see
below).

For mammals, the chronic dose-based RQs exceeded the LOC for all uses except for ULV
applications on citrus and ULV use for adult mosquito control. Therefore, all uses except the
citrus ULV use are predicted to potentially affect the CTS indirectly through effects on small
mammals. The citrus ULV use of malathion had the lowest maximum application rate of all
uses, 0.175 lb ai/A. Adult mosquito control also had low exposure to terrestrial animals because
only a small fraction of the applied material is predicted to deposit on the surface. We predict
that the terrestrial exposure for these two uses is small enough to not result in adverse effects to
small mammals. Uses with the highest use rates, including use on cotton, nuts, and citrus (non
ULV) also had acute RQs that exceeded the LOC for acute risk, thereby predicting potentially
acute toxic effects as well as chronic effects for these uses.

Table 5-4. Acute and Chronic RQs Derived Using T-REX for Malathion and Birds and
Amphibians. Risk quotients that exceed the LOC are shown in bold. The acute LOC is 0.1 for
the CTS (direct effect) and 0.5 for other amphibians and mammals; the chronic LOC is 1.0 for all
species.

RQs for CTS and other

Amphibians

RQs for Small Mammals

(Direct and Indirect Effects)

(Indirect Effects)

Chronic

Acute

Chronic

Use, Formulation, Type of

Acute (Dose-

(Dietary

(Dose-

(Dietary
Based)"1

Chronic

Application

Based)1

Based)2

Based)3

(Dose Based)"1

Agricultural Uses

Citrus

21.92

16.36

0.92

1.06

9.19

Citrus (ULV)

0.53

0.39

0.02

0.03

0.22

Cotton, chestnut, and walnut

12.09

9.03

0.51

0.58

5.07

Pecan

10.60

7.92

0.44

0.51

4.44

Strawberry

10.21

7.62

0.43

0.49

4.28

Caneberry group

8.48

6.33

0.35

0.41

3.56

Mushroom

10.12

7.56

0.42

0.49

4.24

Papaya

11.82

8.82

0.49

0.57

4.95

Mango

4.99

3.73

0.21

0.24

2.09

Rice, barley, broccoli, carrots, pears,

5.30

3.96

0.22

0.26

2.22

et al.

Alfalfa

4.40

3.28

0.18

0.21

1.84

147

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Use, Formulation, Type of
Applieation

RQs for CTS and other
Amphibians
(Direct and Indirect Effects)

RQs for Small Mammals
(Indirect Effects)

Acute (Dose-
Based)1

Chronic
(Dietary
Based)2

Acute
(Dose-
Based)3

Chronic
(Dietary
Based)1

Chronic
(Dose Based)"1

Field corn, wheat, oats, sorghum,
melons, peas, et al.

4.24

3.17

0.18

0.20

1.78

Field corn, wheat, oats, sorghum, and
beans (ULV)

2.59

1.93

0.11

0.12

1.08

Pastures (ULV)

2.69

2.01

0.11

0.13

1.13

Non-Agricultural Uses

Cull piles

872.79

651.69

36.50

42.17

365.85

Fence/hedge row, domestic dwelling
(perimeter), and refuse/solid waste
site

31.04

23.18

1.30

1.50

13.01

Adult mosquito control

0.29

0.22

0.01

0.12

1 Based on dose-based EEC and ring-necked pheasant acute oral LD50 of 167 mg/kg-bw.

2Based on dietary-based EEC and northern bobwhite quail chronic NOAEC of 110 mg/kg-diet.

3Based on dose-based EEC and rat acute oral LD50 of 852 mg/kg-bw.

4Based on dietary-based EEC and rat chronic NOAEL of 1700 mg/kg-diet.

5Based on dose-based EEC and rat chronic NOAEL of 1700 mg/kg-diet.

T-HERPS was used to derive refined RQs for amphibians. These RQs were used to assess both
direct and indirect effects to the CTS. Effects on amphibians could indirectly affect the CTS
because small frogs are a prey item of this species. RQs were derived for both juvenile and adult
salamanders. Juvenile (but post-metamorphosis) salamanders were assumed to be 2 g and to
feed on small insects. Small insects are predicted to have greater pesticide residues than large
insects. RQs derived with this same scenario were also used to assess the risk of effects on small
frogs, a prey item of adult CTS. For direct effects to the CTS, salamanders were assumed to be
20 g and feeding on herbivorous small mammals. Herbivorous small mammals were chosen
because this is the food type that is predicted to have the greatest pesticide residues.

RQs derived for the CTS using T-HERPS are given in Table 5-7. All uses of malathion yielded
at least one RQ that exceed the LOC. For ULV use on citrus and ULV use for adult mosquito
control, only the acute dose-based RQ exceeded the LOC (0.1). For all other uses, RQs met or
exceeded the LOC for both acute and chronic risk to adult salamanders, as well as chronic risk to
juvenile salamanders. Uses with higher application rates (>1.0 lb ai/A) also yielded an acute RQ
that exceeded the LOC for juvenile salamanders consuming small insects. Thus, all uses of
malathion are predicted to potentially cause adverse direct and indirect effects to the CTS
through toxicity to amphibians. This risk conclusion is less certain for citrus ULV use than for
other uses.

Table 5-5. Acute and Chronic RQs for Amphibians Derived Using T-HERPS. Risk quotients
that exceed the LOC are shown in bold. The acute LOC is 0.1 and the chronic LOC is 1.0.

Use, Formulation, Type of
Application

RQs for Juvenile CTS and Small Frogs
Consuming Small Insects

RQs for Adult CTS Consuming
Herbivorous Mammals

Acute (Dose-
Based)1

Acute
(Dietary-
based)2

Chronic
(Dietary
Based)3

Acute (Dose-
Based)1

Acute
(Dietary-
Based)2

Chronic
(Dietary
Based)3

Agricultural Uses

148

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Use, Formulation, Type of
Application

RQs for Juvenile CTS and Small Frogs
Consuming Small Insects

RQs for Adult CTS Consuming
Herbivorous Mammals

Acute (Dose-
Based)1

Acute
(Dietary-
based)2

Chronic
(Dietary
Based f

Acute (Dose-
Based)1

Acute
(Dietary-
Based)2

Chronic
(Dietary
Based)5

Citrus

0.23

0.48

9.20

8.2

0.85

16.42

Citrus (ULV)

0.01

0.22

0.20

0.02

0.40

Cotton, chestnut, and walnut

0.13

0.26

5.08

4.51

0.47

9.06

Pecan

0.11

0.23

4.45

3.95

0.41

7.95

Strawberry

0.11

0.22

4.29

3.81

0.40

7.65

Caneberry group

0.10

0.21

4.06

3.61

0.37

7.25

Mushroom

0.11

0.22

4.25

3.77

0.39

7.59

Papaya

0.13

0.26

4.96

4.41

0.46

8.86

Mango

0.08

0.16

3.12

2.77

0.29

5.56

Rice, barley, broccoli,
carrots, pears, et al.

0.06

0.12

2.23

1.98

0.21

3.97

Alfalfa

0.05

0.10

1.85

1.64

0.17

3.30

Field corn, wheat, oats,
sorghum, melons, peas, et
al.

0.05

0.09

1.78

1.58

0.16

3.18

Field corn, wheat, oats,
sorghum, and beans (ULV)

0.03

0.06

1.09

0.96

0.10

1.94

Pastures (ULV)

0.03

0.06

1.1

1.0

0.10

2.0

Non-Agricultural Uses

Cull piles

9.36

19.0

367

325

33.9

655

Fence/hedge row, domestic
dwelling (perimeter), and
refuse/solid waste site

0.33

0.67

13.0

11.5

1.20

23.2

Adult mosquito control

<0.01

0.01

0.12

0.11

0.01

0.22

1 Based on dose-based EEC and ring-necked pheasant acute oral LD50 of 167 mg/kg-bw.

2Based on dietary-based EEC and Japanese quail subacute LC50 of 2128 mg/kg-diet.

3Based on dietary-based EEC and northern bobwhite quail chronic NOAEC of 110 mg/kg-diet.

5.1.2.b. Terrestrial Invertebrates

Because insects are a prey item of the CTS, adverse effects on insects may indirectly affect the
CTS. Risk of malathion to terrestrial invertebrates was assessed using data for acute contact
toxicity to the honey bee. The lowest measured acute contact LD50 from an acceptable study,
which was 0.20 |ig a.i./bee, was used to calculate risk quotients (MRID 05001991). After
multiplying this value by the conversion factor of 1 bee/0.000128 g, this endpoint becomes 1560
|ig ai/kg, or 1.56 mg ai/kg. RQs were then calculated by dividing the EECs calculated by T-
REX for small insects by this LD50 endpoint. Small insects were chosen because they are
predicted to have greater residues on a per bodyweight basis than large insects.

149

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Table 5-6. Summary of RQs for Terrestrial Invertebrates. Risk quotients that exceed the LOC of
0.1 are shown in bold.

Use

Small insect EEC (mg/kg-bw)

Small Insect RQ*

Agricultural Uses

Citrus

1012

649

Citrus (ULV)

24.4

15.6

Cotton, chestnut, and walnut

559

358

Pecan

490

314

Strawberry

472

302

Caneberry group

392

251

Mushroom

468

300

Papaya

546

350

Mango

231

148

Rice, barley, broccoli, carrots, pears,
et al.

245

157

Alfalfa

203

130

Field corn, wheat, oats, sorghum,
melons, peas, et al.

196

126

Field corn, wheat, oats, sorghum, and
beans (ULV)

120

76.9

Pastures (ULV)

124

79.5

Non-Agricultural Uses

Cull Piles

40,300

25,800

Fence / hedge row, domestic
dwelling (perimeter), and refuse/solid
waste site

1430

917

Adult mosquito control

13.4

8.59

LOC exceedances (RQ > 0.05) are bolded.

All uses of malathion are predicted to potentially cause indirect effect the CTS by adversely
affecting the insects on which it relies for food. Since the RQs are much greater than 1 for all
uses, the certainty of this conclusion is high.

150

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5.I.2.C. Terrestrial Plants

Adverse effects on terrestrial plants may have indirect effects on the DS and CTS by way of
habitat degradation. Generally, for indirect effects, potential effects on terrestrial vegetation are
assessed using RQs from terrestrial plant seedling emergence and vegetative vigor EC25 data as a
screen. In the case of malathion, toxicity data not are available from which one can derive EC25
or NOAEC values for assessment endpoints related to growth and reproduction. Therefore, no
quantitative risk assessment for terrestrial plants was conducted in this assessment. As described
in Section 4.3.4, however, several studies are available from open literature studies which
evaluate effects of direct application of malathion at typical application rates (0.89 - 1.41 lb
ai/A) to various plant species. In all of these studies, the direct application of malathion either
resulted in no observable adverse effects, or in some cases, result in enhanced biomass relative to
control plants, presumable because of the protection it provides from herbivorous insects.
Nontarget plants outside of the treated area of course would receive much less exposure that
plants which are directly treated. These results indicate that malathion has little phytotoxicity
and is unlikely to result in significant adverse effects to terrestrial plants at environmentally
relevant exposure levels.

5.1.3. Primary Constituent Elements of Designated Critical Habitat

For malathion use, the assessment endpoints for designated critical habitat PCEs involve the
same endpoints as those being assessed relative to the potential for direct and indirect effects to
the listed species. Therefore, the effects determinations for direct and indirect effects are used as
the basis of the effects determination for potential modification to designated critical habitat.

5.2. Risk Description

The risk description synthesizes overall conclusions regarding the likelihood of adverse impacts
leading to an effects determination (i.e., "no effect," "may affect, but not likely to adversely
affect," or "likely to adversely affect") for the assessed species and the potential for modification
of their designated critical habitat. If the RQs presented in the Risk Estimation (Section 5.1)
show no direct or indirect effects for the assessed species, and no modification to PCEs of the
designated critical habitat, a "no effect" determination is made, based on malathion's use within
the action area. However, if LOCs for direct or indirect effect are exceeded or effects may
modify the PCEs of the critical habitat, the Agency concludes a preliminary "may affect"
determination for the FIFRA regulatory action regarding malathion.

A summary of the risk estimation results are provided in Table 5-7 for direct and indirect effects
to the listed species assessed here and in Table 5-8 for the PCEs of their designated critical
habitat. For the DS, a preliminary "may effect" determination is concluded based on predicted
potential direct effects of malathion uses as well as potential indirect effects manifested by way
of adverse effects to freshwater and estuarine fish, freshwater and estuarine invertebrates, and
terrestrial invertebrates (which may have aquatic life-stages). For the CTS, a preliminary "may
effect" determination is concluded based on predicted potential direct effects of malathion uses
as well as potential indirect effects manifested by way of adverse effects to freshwater fish,
freshwater invertebrates, terrestrial invertebrates, terrestrial-phase amphibians, small mammals.

151

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Table 5-7. Risk Estimation Summary for Malathion - Direct and Indirect Effects

Taxa

LOC Exceeded

Description of Results of Risk
Estimation

Assessed Species Potentially
Affected

Freshwater Fish and
Aquatic-phase
Amphibians

Yes

RQ for acute toxicity exceeds the
LOC for all uses except passion fruit
and ULV application on citrus and
kumquat. RQ for chronic toxicity
also exceeds the LOC for some uses

Direct Effects: DS. CTS
Indirect Effects: DS. CTS

Freshwater
Invertebrates

Yes

Both acute and chronic RQs exceed
the LOCs for all uses.

Indirect Effects: DS. CTS

Estuarine/Marine
Fish

Yes

RQ for acute toxicity exceeds the
LOC for all uses except passion fruit
and ULV application on citrus and
kumquat. RQ for chronic toxicity
also exceeds the LOC for rice, wild
rice, water cress, mosquito control,
and several nonagricultural uses.

Direct Effects: DS
Indirect Effects: DS

Estuarine/Marine
Invertebrates

Yes

Both acute and chronic RQs exceed
the LOCs for all uses.

Indirect Effects: DS

Vascular Aquatic
Plants

Acute and chronic RQs are below
the LOC for all uses.

Indirect Effects: none

Non-Vascular
Aquatic Plants

Acute and chronic RQs are below
the LOC for all uses.

Direct Effects: none

Terrestrial-Phase
Amphibians

Yes

RQ for acute toxicity exceeds the
LOC for all uses and RQ for chronic
toxicity exceeds the LOC for all
uses except ULV application on
citrus and kumquat

Direct Effects: CTS
Indirect Effects: CTS

Mammals

Yes

Both acute and chronic RQs exceed
the LOCs for all uses except ULV
application on citrus and kumquat.

Indirect Effects: CTS

Terrestrial
Invertebrates

Yes

Acute toxicity (all uses)

Direct/Indirect Effects:
DS and CTS

Terrestrial Plants -
Monocots

Terrestrial Plants -
Dicots

Table 5-8. Risk Estimation Summary for Malathion - Effects to Designated Critical Habitat
(PCEs)

Taxa

LOC Exceeded

Description of Results of Risk
Estimation

Species Associated with a
Designated Critical Habitat
that May Be Modified by the
Assessed Action

Freshwater Fish

Yes

Risk to water quality.

Freshwater
Invertebrates

Yes

Risk to water quality.

Estuarine/Marine
Fish

Yes

Risk to water quality.

152

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Taxa

LOC Exceeded

Description of Results of Risk
Estimation

Species Associated with a
Designated Critical Habitat
that May Be Modified by the
Assessed Action

Estuarine/Marine
Invertebrates

Yes

Risk to water quality.

Vascular Aquatic
Plants

Non-Vascular
Aquatic Plants

Mammals

Yes

Both acute and chronic RQs exceed
the LOCs for all uses except ULV
application on citrus and kumquat.

CTS

Terrestrial Plants -
Monocots

Terrestrial Plants -
Dicots

Following a "may affect" determination, additional information was considered to refine the
potential for exposure at the predicted levels based on the life history characteristics {i.e., habitat
range, feeding preferences, etc) of the assessed species. Based on the best available
information, the Agency used the refined evaluation to distinguish those actions that "may affect,
but are not likely to adversely affect" from those actions that are "likely to adversely affect" the
DT and CTS and their designated critical habitat.

The criteria used to make determinations that the effects of an action are "not likely to adversely
affect" the assessed species or modify its designated critical habitat include the following:

• Significance of Effect: Insignificant effects are those that cannot be meaningfully
measured, detected, or evaluated in the context of a level of effect where "take" occurs
for even a single individual. "Take" in this context means to harass or harm, defined as
the following:

¦ Harm includes significant habitat modification or degradation that results in
death or injury to listed species by significantly impairing behavioral patterns
such as breeding, feeding, or sheltering.

¦ Harass is defined as actions that create the likelihood of injury to listed species
to such an extent as to significantly disrupt normal behavior patterns which
include, but are not limited to, breeding, feeding, or sheltering.

• Likelihood of the Effect Occurring: Discountable effects are those that are extremely
unlikely to occur.

• Adverse Nature of Effect: Effects that are wholly beneficial without any adverse effects
are not considered adverse.

A description of the risk and effects determination for each of the established assessment
endpoints for the assessed species and their designated critical habitat is provided in Section
5.2.1 for the DS and in Section 5.2.2 for the CTS. The discussion of effects determination
follows a similar pattern for both species. Each starts with a discussion of the potential for direct
effects, followed by a discussion of the potential for indirect effects. Since both species have

153

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designated critical habitat, the section will end with a discussion on the potential for modification
to the critical habitat from the use of malathion. Finally, a discussion of any potential overlap
between areas of concern and the species (including any designated critical habitat) is presented
in the spatial analysis section.

5.2.1. Delta Smelt

5.2.1.a. Direct Effects

Risk quotient analysis indicate that all uses of malathion except for passion fruit, fence
rows/hedge rows, and ULV application for adult mosquito control potentially could adversely
effect freshwater and saltwater fish, and thus could have direct adverse effects on the DS (Table
5.1 and 5-3). Since this risk assessment was based on predicted exposure of malathion to a 1-
acre farm pond, considerable uncertainty exists in applying these results to predict risk in the
large rivers and Suisun Bay where the fish lives outside of spawning periods. In these habitats, it
is possible that dilution would result in much lower malathion concentrations, and thus lower
risk to the DS. This has been corroborated by surface water monitoring (see discussion below).
During spawning, however, DS migrate up into shallow freshwater tributaries, soughs, and
drains to reproduce and lay eggs. The aquatic exposure predictions based on the farm pond
scenarios would be much more appropriate for these aquatic habitats. Furthermore, the eggs and
larval stages of the DS would be present in the low-volume habitats with greatest concentration,
and these are generally the life stages with the greatest sensitivity to pesticides. Thus, we
conclude that many uses of malathion could potentially adversely affect adult DS during periods
of spawning, as well as the egg and larval stages.

This conclusion is supported by evidence from ecological incident data. Twenty-three incidents
of mortality of fish and aquatic organisms have been linked to exposure of malathion. Several of
these incidents have been linked to agricultural use of malathion, and several other have been
linked to adult mosquito control use. For both agricultural uses and mosquito control uses, many
of the incidents were given a certainty of probably or highly-probable for malathion being the
cause of the mortality. Numerous incidents of fish kills have been reported for both agricultural
and nonagricultural uses of malathion, many of which were conclusively linked to exposure to
malathion (Table 4-23). Thus, incident data support that both agricultural and urban uses of
malathion have the potential to cause direct adverse effects to the DS.

Findings of recent surface water monitoring programs provide additional information on the
potential of malathion to cause direct effects to the DS. Table 5-12 summarizes detections of
malathion from surface water monitoring in the basins of the Sacramento River and San Joaquin
River in and near the DS habitat. Monitoring data show that malathion was seldom detected in
the main channels of these rivers, as well as the large tributaries of the Merced River and
Tuolumne River, and was never detected above 0.025 |ig/L. In the Yolo Bypass, which receives
overflow water from the Sacramento River during times of high flow, malathion detections were
more frequent (25%), but measured concentrations did not exceed 0.015 |ig/L. In contrast,
detections of malathion were frequent and maximum concentrations were much higher in the
smaller tributaries, sloughs, and agricultural drains. The highest malathion detection frequencies
and concentrations were observed in Arcade Creek near Knights Landing, California, where the

154

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malathion detection frequency was 53.3% and the maximum concentration was 0.63 |ig/L
(Domagalski, 2000). This small stream mainly drains areas with predominantly urban land use
(Domagalski, 2000). Contamination was only slightly lower in Salt Slough in 1993, when the
malathion detection frequency was 23% and the maximum concentration was 0.39 |ig/L (Panshin
et al. 1998). Salt Slough drains mainly agricultural lands, and receives both sub-surface drainage
and surface irrigation return flows (Panshin et al., 1998). A peak concentration of 0.11 |ig/L was
observed in the Orestimba River in the 2002 (Starner et al., 2005). During the time of the
sampling (July - September), this stream would contain predominantly irrigation return flow
from agricultural lands (Panshin et al., 1998). These data indicate that both urban and
agricultural uses of malathion contribute to contamination of surface water, and that
concentrations of malathion are greatest in small streams, sloughs, and agricultural drains.

Higher concentrations of malathion were detected outside range of the DS. Sampling in the
Colusa Basin Drain, conducted by the California Department of Pesticide Regulations in 1996,
detected malathion concentrations as high as 6.0 |ig/L (Gorder el aL, 1996). The sampling site
with the highest malathion detections was near the city of Colusa in Colusa County,
approximately 50 miles north of the northernmost reaches of the designated critical habitat of the
DS. The Colusa Basin Drain receives water largely from intensive rice production in the area,
and the malathion peak concentration occurred just after discharge of water from a rice field that
was treated with malathion just one day prior. This observation represents a high-end exposure
level for malathion that may occur in a drain receiving water from rice production. How
representative this drain is to ones inhabited by the DS, however, is uncertain.

Pulses of elevated insecticide concentrations flow down the Sacramento River and San Joaquin
River into the Suisun Bay following large rainfall events that occur in the region during the
winter. In winter, the primary source of these residues is believed to be spraying of insecticides,
including malathion, on dormant fruit and nut trees (Kuivila and Foe, 1995; Kuivila and Hladik,
2008). Kuivila and Hladik (2008) attributed the detection of malathion in creeks and streams in
the spring largely to malathion applications on alfalfa, and detections in the summer largely to
applications on almonds and walnuts. In contrast, contamination of malathion in streams that
drain predominantly urban areas occurs year-round and is attributed to various residential and
commercial uses of malathion.

In small freshwater tributaries and sloughs within the range of the DS, monitoring studies found
malathion concentrations up to approximately 0.63|ig/L (Table 5-12). The toxicity assessment
endpoint for acute toxicity of malathion was 33 |ig/L for both freshwater and saltwater fish
(Table 4-1.) The margin of safety between the maximum measured concentrations and median
lethal level for fish is 52.3. A peak concentration of 6.00 |ig/L was measured in the Colusa
Basin Drain (Gorder et al. 1996), which is approximately 50 miles to the north of the northern
reaches of the DS. Then the acute toxicity endpoint is compared to this value, the margin of
safety is only 5.5. While these results do not indicate that malathion exposure would likely to
cause mortality to DS, they do not dismiss the risk conclusion based on the RQ analysis. The
assessment endpoint of malathion for chronic effects, including reproductive effects, is 8.6 to
freshwater fish (Table 4-1). The margin of safety between maximum measured concentration
and the chronic NOAEC is 21.5 when compared to the peak concentration in the range of the
DS, or only 1.4 when compared to the peak concentration measured in the Colusa Basin Drain.

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Thus, monitoring data do not confirm that exposure to malathion would cause direct acute or
chronic effects to the DS; however, the margin of safety is not great enough to discount the
possibility of direct effects. All of the available surface water monitoring data are from general
monitoring programs that did not target malathion. Thus, sampling times were not timed to
target periods when malathion concentrations were expected to peak. Furthermore, the duration
of peak concentrations may be very short compared to the sampling interval of these studies.
Therefore, these monitoring studies could have easily missed the peak malathion concentrations.
The RQ analyses, on the other hand, were based on modeled concentrations designed to
represent a reasonable upper bound of malathion concentrations that would be predicted in these
habitats.

Monitoring data indicate that portions of the DS habitat would be contaminated quite frequently
with malathion concentrations that are non-negligible but below acute and chronic thresholds.
Malathion is an organophosphate insecticide whose mode of action in fish is disruption of nerve
function through inhibition of acetylcholinesterase. Numerous other organophosphorous and
carbamate insecticides with this same mode of action were also detected in these waters,
including chlorpyrifos, diazinon, and methidathion, and carbofuran (see review in Kuivila and
Hladik, 2008). The effects of the malathion on inhibition of acetylchonesterase would likely be
at least additive, and in some cases may be synergistic, to the effects of these other insecticides
present in the water (see Section 2.2.2). Bioassays with whole water samples have shown that
the combination of these insecticides occasionally reach levels that are toxic to the water flea,
Ceriodaphnia dubia (Werner et al. 2000) Thus, even at subtoxic levels, malathion contamination
would contribute to the overall degradation of water quality in the habitat of the DS.

The potential for DS to be exposed to the oxon derivative of malathion, maloxon, as well as the
parent compound, adds uncertainty to the assessment of potential direct effects to the DS.

Current information on maloxon formation is very limited, but there appears to be a potential for
low levels of maloxon to be present in surface water. Information on the toxicity of maloxon is
also uncertain, but current data suggest that it may be between 4.1 and 90 times more acutely
toxic to aquatic vertebrates than malathion. Thus, any presence of maloxan would elevate
toxicity above that predicted in this assessment, thereby increasing the likelihood of direct effects
to the DS. See Section 6.1.4 for more information on this uncertainty.

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Table 5-12. Summary of Surface Water Monitoring in the Sacramento River and San Joaquin River Basins in and near the Habitat of

theDS

Siimpliii^ Silo

Years

M;i\.
(ttnc.

(,u "/I •

Min.
Cone.

(.uji/h1

Modiiin
Cone.

(,u "/I •

Doled ion

l'lT(|IK'IH\\

I.ODor I.OU

Uel'erenee

Colusa Basin Drain at Rd. 99E
near Knights Landing

1996-1998

0.054

0.0055

33.3%

0.005 (LOR)

Domagalski 2000

Arcade Creek near Del Paso
Heights

1996-1998

0.63

0.012

0.013

53.3%

0.005 (LOR)

Domagalski 2000

Sacramento River at
Sacramento

1991-1992

0.019 (LOD)

MacCoy et al., 1995

1992-1994

0.035 (LOD)

MacCoy et al., 1995

Sacramento River at Freeport

1996-1998

e0.004

5.3%

0.005 (LOR)

Domagalski 2000

Yolo Bypass at Interstate 80

1996-1998

0.015

25%

0.005 (LOR)

Domagalski 2000

San Joaquin River near
Vernalis

1991-1992

0.031 (LOD)

MacCoy et al., 1995

1992-1994

0.044 (LOD)

MacCoy et al., 1995

2002

0.012 (LOD)
0.05 (LOR)

Starner et al. 2005

San Joaquin River near
Vernalis

1993

0.025

14%

0.005 (LOD)

Panshinetal. 1998

Tuolumne River at Shiloh

2002

0.012 (LOD)
0.05 (LOR)

Starner et al. 2005

Orestimba Creek at River Road
near Crows Landing

1993

0.006

2.1%

0.005 (LOD)

Panshinetal. 1998

2002

0.111

7.1%

0.012 (LOD)
0.05 (LOR)

Starner et al. 2005

Merced River at River Road
near Newman

1993

0.009

2.5%

0.005 (LOD)

Panshinetal. 1998

Salt Slough at Highway 165
near Stevinson

1993

0.39

23%

0.005 (LOD)

Panshinetal. 1998

2002

0.012 (LOD)
0.05 (LOR)

Starner et al. 2005

Id signifies less than reporting limit; nr signifies data were not reported.

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5.2.1.b. Indirect Effects

i. Potential Loss of Prey

The DS feeds on small fish and aquatic invertebrates. Thus, toxic effect on either fish or
invertebrates could reduce the availability of prey and result in indirect effects on the DS. As
discussed in the previous section, RQ analysis showed that most uses of malathion are predicted
to potentially cause adverse acute effects on fish (Table 5-1 and 5-3). This conclusion is
supported by the numerous incidents of fish kills that have been linked to both agricultural and
nonagricultural uses of malathion (Table 4-23). For indirect effects mediated through effects on
invertebrate prey, the risk quotient analysis indicates that all uses of malathion have the potential
to cause both acute and chronic toxic effect to both freshwater and saltwater invertebrates (Table
5-2 and 5-4). Risk of sublethal effects from chronic exposure appears to be especially high, for
which risk was indicated for all uses, most RQ for most uses exceeding 100 and for some uses
exceeding 1000. Thus, we conclude that the use of malathion has a high potential to cause
indirect effects on the DS through reduction of fish and invertebrate prey. As with direct effects,
indirect risks are expected to be greatest in the shallow freshwater habitats that the DS use for
spawning and reproduction.

Direct and indirect risks to the DS can also be evaluated by comparing monitoring data for
malathion with acute and chronic toxicity values. Table 5-12 summarizes detections of
malathion from recent surface water monitoring in the basins of the Sacramento River and San
Joaquin River in and near the DS habitat. As was discussed in the previous section, surface
water sampling in the basins has found that malathion concentrations are highest in small
streams, sloughs, and drains where the predominant land use of the watershed is either urban or
agricultural (Domagalski 2000, Panshin et al. 1998, and Starner et al. 2005). The highest
measure concentration of malathion within the range of the DS was 0.63 |ig/L, which was
measured in Arcade Creek, a small urban stream (Domagalski 2000). In small streams and
sloughs that drain predominantly agricultural lands, peak concentrations were 0.39 |ig/L in Salt
Slough, a tributary of the San Joaquin River (Panshin et al. 1998) and 0.11 |ig/L in Orestimba
Creek (Starner et al. 2005). The assessment endpoint for the threshold of acute toxicity to
freshwater invertebrates is 0.59 |ig/L. Thus, monitoring results indicate that malathion
concentrations occasionally approach or exceed the levels toxic to freshwater invertebrates.
Considering that the monitoring programs were not targeted to capture peak malathion
concentrations, and the water sampling associated with these studies were spatially and
temporally limited, it is likely that peak malathion concentrations occasionally reach levels
higher than observed in these studies. Sampling from the Colusa Basin Drain in Colusa County,
approximately 50 miles north of the northernmost reaches of the designated critical habitat of the
DS, detected malathion concentrations as high as 6.0 |ig/L (Gorder el al., 1996). Thus, it is
likely that malathion concentrations in both primarily agricultural and primarily urban water
bodies will occasionally exceed acute toxicity threshold of aquatic invertebrates.

Concerning chronic effects, measured peak concentrations of malathion were well above the
predicted NOAEC that was derived for freshwater invertebrates using the acute-to-chronic ratio
method. Measured peak concentrations also exceed both the NOAEC (0.06 |ig/L) and the
LOAEC (0.10 |ig/L) for reproductive effects measured in a life-cycle study with the water flea,

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Daphnia magna (MRID 41718401). Uncertainty exists in this comparison because the duration
of exposure to malathion at or above toxic levels in the streams may not be comparable to the
duration of exposure in the laboratory study. Nevertheless, these findings support the quotient-
based risk assessment that agricultural and urban uses of malathion may cause chronic as well as
acute toxic effects on the invertebrate prey of the DS.

Monitoring data found that detections of malathion were much less frequent, and peak
concentrations were much lower, in the main channel of the Sacramento River and San Joaquin
Rivers (Domagalski 2000, MacCoy et al. 1995, Panshin et al. 1998). The highest peak malathion
concentration observed was 0.025 |ig/L in the San Joaquin River (Panshin et al. 1998) and
approximately 0.004 |ig/L in the Sacramento River (Domagalski 2000). These peaks
concentrations are over one order of magnitude less than the acute toxicity assessment endpoint
for freshwater invertebrates (0.59 |ig/L). They are also less than the NOAEC measured for
Daphnia magna (0.06 |ig/L), although the peak concentration observed in the San Joaquin River
exceeds the chronic NOAEC predicted for freshwater invertebrates using the acute-to-chronic
ratio method (0.035 |ig/L). Detection frequencies of malathion were 0-5.3 % in monitoring
studies in the lower Sacramento River (MacCoy et al. 1995, Domagalski 2000) and 14% in the
lower San Joaquin (Panshin et al. 1998), compared to up to 53.3% and 33.3% in small urban and
agricultural streams, respectively. In all, the monitoring data suggest that malathion
concentrations are likely to be relatively low in the main channel of the lower Sacramento and
San Joaquin Rivers, as well as in the Suisan Bay. Therefore, malathion would be less likely to
adversely affect invertebrate prey in these areas which comprise the main range of DS outside of
spawning. However, as noted previously, several other organophosphate and carbamate
insecticides were detected in the lower reaches of these rivers, and while malathion may not
frequently reach toxic levels on its own, it may contribute to a combined accumulative toxicity
that could have significant toxic effects on invertebrate prey.

Kuivila and Foe (1995) conducted bioassays with the water flea (Ceriodaphnia dubia) using
water sampled from the lower Sacramento River and San Joaquin River, and found that the river
water caused 100% mortality during peaks of insecticide concentrations associated with the
pulses of insecticides moving past the sampling sites. However, they did not detect any
malathion in any of the samples they collected from either river, and thus did not attribute the
toxicity to the water flea to malathion. They determined that the elevated diazinon
concentrations in the water were sufficient to explain most of the toxicity. Other dormant spray
insecticides, including methidathion and chlorpyrifos, were also present in elevated
concentrations and likely also significantly contributed to the toxicity of the water. They
attributed the lack of malathion in detectable concentrations to the lower use compared to other
insecticides and the rapid degradation it undergoes in soil. Thus, these studies show that
insecticides concentrations sometimes reach levels that are toxic to the invertebrate prey of the
DS in waters of the Suisun Bay and large rivers that make up non-breeding habitat of the DS;
however, little of the toxicity in these areas can be attributed to malathion.

Werner et al. (2000) sampled water from numerous sites in the Sacramento/San Joaquin River
Delta between 1993 and 1995, conducted water monitoring for pesticides, and evaluated water
samples for toxicity to the water flea (Ceriodaphnia dubia). Toxicity testing with the water flea
included evaluation of both mortality and reproduction impairment. Unlike the studies discussed

159

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above, this study included many monitoring sites at back soughs and small upland streams where
monitoring indicates pesticide concentrations are greatest. They found that a sizable percent
(16.6%) of the samples taken from back sloughs were toxic to C. dubia, whereas toxicity
occurred less frequently in main-stem rivers (6.9%) and rarely in the main channel of the
Sacramento River and San Joaquin River. Toxicity identification evaluations conducted on some
of the toxic water samples identified chlorpyrifos and diazinon as the primary toxicants at most
of the sampling sites. Malathion was identified as a significant contributor to total toxicity in
water from only two sites, Ulatis Creek and French Camp Slough. Both of these sites were back
sloughs or small upland drainages that receive drainage from agricultural areas. Ulatis Creek
also receives drainage from urban areas. Water samples from Ulatis Creek caused over 50%
mortality to C. dubia in March, May, July, and September, November, and December; and
samples from French Camp Slough caused mortality of 50% or more in March and September.
Water samples from these sites also caused significant reproductive impairment to C. dubia.

This paper concluded that malathion was identified as a significant but relatively minor
contributor to toxicity in the tributaries of the Sacramento/San Joaquin River Delta. The highest
malathion concentration measured was 0.061 |ig/L. This level is considerably less than the acute
and chronic assessment endpoint for freshwater fish (33 |ig/L and 8.6 |ig/L, respectively). It is
approximately 10-fold less than the acute assessment endpoint for freshwater invertebrates (0.70
|ig/L), However, it exceeds the chronic NOAEC estimated for sensitive freshwater invertebrates
using the acute-to-chronic method (0.035 |ig/L). Compared to the chronic toxicity endpoints
measured for the water flea (Daphnia magna, MRID 41718401), it is approximately equal to the
NOAEC (0.06 |ig/L) and less than the LOAEC (0.1 |ig/L) by a factor of 0.61.

Considered together, both agricultural uses and urban uses appear to contribute to occasional
poor water quality that occasionally may result in loss of aquatic invertebrate prey in the habitat
of the DS, primarily in the small streams, sloughs, and drains that the fish inhabits during
spawning. The monitoring data show that malathion concentrations in these areas approach or
exceed toxic levels only for short periods during short-term peaks, while remaining well below
toxic levels at other times (Domagalski 2000, Starner et al. 2005). This observation agrees with
the known environmental fate properties of malathion which suggest that it will not be persistent
in soil or water. Thus high levels of water contamination would likely be limited to rainfall
events that occur shortly after application of malathion, and cause runoff before the soil residues
have time to degrade significantly. Nevertheless, these findings indicate that malathion
concentrations alone may occasionally be toxic to invertebrate prey of the DS in parts of its
range, as well as significantly contribute to the overall toxicity of mixtures of organophosphate
and carbamate insecticides that known to contaminate these waters

ii. Potential Modification of Habitat

Aquatic plants serve several important functions in aquatic ecosystems. Non-vascular aquatic
plants are primary producers and provide the autochthonous energy base for aquatic ecosystems.
Vascular plants provide structure, rather than energy, to the system, as attachment sites for many
aquatic invertebrates, and refugia for juvenile organisms, such as fish and frogs. Emergent
plants help reduce sediment loading and provide stability to nearshore areas and lower stream

160

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banks. In addition, vascular aquatic plants are important as attachment sites for egg masses of
aquatic species.

Toxicity testing has found that malathion has low toxicity to aquatic plants. Risk quotients for
all uses of malathion were well below 1. For nonaquatic agricultural uses and nonagricultural
uses, RQs were never greater than 0.04. For aquatic agricultural uses, RQs were as high as 0.47,
but the exposure estimates for these uses are for peak concentrations on the flooded field and are
likely to be much greater than what would occur in off-site aquatic habitats. Peak concentrations
in offsite receiving waters would be much less because of the rapid degradation that malathion
would undergo while the water is held on the field, and because of the dilution that would occur
when the released water mixes with uncontaminated water. We therefore consider the risk of
indirect effects to the DS from malathion causing adverse effects on aquatic plants to be
insignificant and discountable.

Terrestrial plants serve several important habitat-related functions for the listed assessed species.
In addition to providing habitat and cover for invertebrate and vertebrate prey items of the listed
assessed species, terrestrial vegetation also provides shelter and cover from predators while
foraging. Upland vegetation including grassland and woodlands provides cover during dispersal.
Riparian vegetation helps to maintain the integrity of aquatic systems by providing bank and
thermal stability, serving as a buffer to filter out sediment, nutrients, and contaminants before
they reach the watershed, and serving as an energy source.

Despite widespread use, malathion has not been observed to be phytotoxic to the wide variety of
crop and ornamental plants to which it is directly applied. As discussed in Section 4.3.4, plant
field tests have found that application of malathion at typical use rates either do not have
significant effects on the growth of plants, or have significant beneficial effects due to control of
plant pests. Vegetation in the habitat of the DS would be exposed from drift and runoff from
treated sites. This exposure would be at rates much less than the target plants that are directly
treated. Therefore, exposure of plants to malathion in the DS habitat is not expected to result in
any significant damage to vegetation.

5.2.1.c. Modification of Designated Critical Habitat

The PCEs for the DS state that suitable water quality must be maintained in the habitat used by
all life-stages of the smelt. This includes the Sacramento River and San Joaquin River channels
and their tributary channels that the DS inhabits as larvae and juveniles (PCE 2) and migrates
into as adults during spawning periods (PCE 4). It also includes the bays of the Sacramento and
San Joaquin Estuary where the adult smelt occurs outside of spawning (PCE 3). As described in
Section 5.2.1.a, urban and agricultural uses of malathion are predicted to cause occasional
contamination of the tributaries of the Sacramento River and San Joaquin River that could
potentially be toxic to the larvae and juvenile traveling down the channels, as well as the adult
fish migrating up the channels during spawning. Thus, malathion use may significantly degrade
the water quality in these sections of the critical habitat. Due to dilution with less contaminated
water, malathion levels are expected to generally remain below levels that would be directly
toxic to the DS in the main channels of the lower Sacramento River and San Joaquin River, as
well as the Suisan Bay. However, even in these areas, some malathion contamination will occur,

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and their toxicity would add to that of the other organophosphate and carbamate insecticides that
are known to be present in these waters, including chlorpyrifos, diazinon, and carbofuran. Thus,
malathion residues may significantly contribute to deterioration of water quality in these areas
even though may not reach toxic levels by themselves.

Availability of fish and aquatic invertebrates is also an important requirement of the habitat of
the DS because the species depends on these taxa for food. As discussed in Section 5.2.1.b.i, all
uses of malathion are predicted to potential cause mortality to aquatic invertebrates, and most
uses are also predicted to potential cause mortality to fish, especially in the shallow freshwater
habitats used during spawning. Therefore, use of malathion may degrade the critical habitat of
the DS by reducing prey abundance.

5.2.1.d. Spatial Extent of Potential Effects

When LOCs are exceeded, the Agency typically does analysis to determine the spatial extent of
potential "likely to adverse affect" (LAA) where effects may occur in relation to the treated site.
In this assessment, however, the use "footprint" of the use of malathion was considered to be the
entire state of California. All uses of malathion result in an LAA determination because of the
potential for direct and/or chronic effects. Uses include a very wide range of agricultural crops,
fruit and nut trees, forestry, commercial, and residential uses. Since uses are expected in all land
use categories (agricultural crops, orchards, forests, rangeland, and urban areas), the spatial
extent of effects is not limited by the location of uses. Any place where the DS occurs, or that is
part of its critical habitat, is considered to be part of the LAA area.

5.2.1.e. Spray Drift

In order to determine aquatic habitats of concern due to malathion exposures through spray drift,
it is necessary to estimate the distance that spray applications can drift from the treated area and
still be present at concentrations that exceed levels of concern. While we assume that malathion
can potentially be applied anywhere in the state, these calculations may be useful to determine
necessary buffers from local use sites that would be needed to protect aquatic habitats from spray
drift.

For the flowable uses, a quantitative analysis of spray drift distances was completed using
AgDRIFT (v. 2.01) using default inputs for ground applications (i.e., high boom, ASAE droplet
size distribution = Very Fine to Fine, 90th data percentile) and aerial applications (i.e., ASAE
Very Fine to Fine). Winds speed was set at 10 mph. EECs for loading by drift only were
calculated assuming 5% spray drift for aerial applications and 1% spray drift for ground
applications. Drift was assumed to deposit and uniformly dilute into a water body 3-meter deep.
Indirect risk to the DS was assessed based on the acute toxicity endpoint for freshwater
invertebrates (EC50 = 0.59 |ig/L). Results of this analysis are shown in Table 5-13. The distance
a water body must be from the treated site for spray drift to not result in risk that exceeds the
LOC ranges from 0 ft (adjacent) to >1000 feet, depending on the method of application and the

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application rate. This analysis assumes that loading occurs from a single application to a single
use site, with no contributions occurring from other potential use sites.

Table 5-13. Maximum Distance from Edge of Field at which the Spray Drift Deposition from
Malathion Applications are Predicted to Result in an Aquatic Risk Quotient that Exceeds the

LOC

Use

Use Rate

Application
Method1

Freshwater
Invert. RQ

Distance for Exceed
LOC (Feet)

Agricultural Uses

Citrus

7.5

5.835

>1000

1.169

Adjacent

Pecan, chestnut, and walnut

2.5

1.945

>1000

0.390

Adjacent

Cotton

2.5

1.945

>1000

0.390

Adjacent

Strawberry, caneberry group

2.0

1.556

>1000

0.312

Adjacent

Pears, papaya, and guava.

1.25

0.972

623

0.195

Adjacent

Alfalfa, rice, barley, broccoli,
carrots, et al.

1.25

0.972

623

0.195

Adjacent

Field corn, wheat, oats,
sorghum, melons, peas, et al.

1.0

0.778

436

0.156

Adjacent

Mango

0.9375

0.729

387

0.146

Adjacent

Non-A

gricultural Uses

Fence / hedge row, domestic
dwelling (perimeter), and
refuse/solid waste site

10.6

1.653

1 "A" signifies Aerial, "AB" signifies airblast, "G" signifies ground spray.

5.2.1 f. Downstream Dilution Analysis

Typically, the downstream dilution model is used to determine the extent of exposure in streams
and rivers where the EEC could potentially be above levels that would exceed the most sensitive
LOC. For this assessment, however, the use of malathion is not limited to certain land use
classes, but may be used throughout the state. The entire range of the DS is considered to be
within the potential area of use of malathion. Therefore, analysis of downstream dilution was
not necessary for defining the overlap of the potential area of LAA with the habitat and
occurrence of the DS.

5.2.1.g. Overlap of Potential Areas of LAA Effect and Habitat and
Occurrence of the Delta Smelt

As stated above, the LAA determinations for the DS is defined as the entire area of the
occurrence of the DS and its critical habitat, as depicted in Fig. 2-2. Malathion may be used

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throughout the entire state of California, and therefore the use area does not spatially limit the
extent of the potential adverse effects to the DS.

5.2.2. California Tiger Salamander

5.2.2.a. Direct Effects

Both aquatic and terrestrial RQs were evaluated to assess direct effects to the CTS. Aquatic RQs
were based on toxicity assessment endpoints for freshwater fish (surrogate for aquatic stages of
amphibians) and predicted water concentrations in a modeled farm pond. They were used to
predict possible effects on the eggs and aquatic larval stages of the CTS, as well for terrestrial
juvenile and adult stages for times when individuals in these stages are submerged in water.
Terrestrial RQs were based on toxicity assessment endpoints for birds (surrogate for terrestrial
stages of amphibians) and exposure to malathion predicted from dietary exposure.

Aquatic-Phase

Eggs and aquatic larvae stages of the CTS occur primarily in shallow vernal pools. These small
water bodies may receive a large percentage of their water runoff and drainage from surrounding
agricultural and urban areas with malathion use, with little dilution from untreated areas. Also,
the impact of spray drift deposition to these shallow stagnant water bodies would be relatively
high compared to deeper water bodies. Thus, the relatively high (protective) aquatic EECs
predicted by the PRISM and EXAMS models, which predict concentrations for a 1-acre farm
pond, are expected to be more appropriate for assessing aquatic exposure to the CTS than
concentrations measured in streams and rivers from monitoring studies.

Toxicity data for freshwater fish was used to assess risk to aquatic stages of the CTS. Freshwater
fish RQs are shown in Table 5-1. The RQ for acute toxicity exceeded the endangered species
LOC (0.05) for all uses of malathion except passion fruit and aerial ULV applications for public
health use (e.g., adult mosquito control). For approximately half the uses of malathion, the acute
RQ also exceeded the LOC for nonendangered species (0.5). For 32 agricultural uses and 9
nonagricultural uses, the RQ exceeds 1.0, indicating that the predicted peak concentration
exceeds the median lethal dose for sensitive species. Thus, assuming the acute toxicity levels
measured for fish are representative of larvae of the CTS, there is a high likelihood that at least
some of the uses of malathion could cause direct adverse effects to this species by way of acute
toxicity.

Chronic RQs exceeded the LOC (1.0) less frequently. This is likely because malathion residues
are not persistent in water and thus chronic EECs were considerably less than peak EECs.

Chronic RQs exceeded the LOC for 10 agricultural uses and 1 nonagri cultural use.

Data are not available on the toxicity of malathion to any species of salamander larvae.

However, limited data are available on the acute toxicity of malathion to larvae stages of frogs
(i.e., tadpoles). Reported acute toxicity data for frog tadpoles range widely from 0.59 |ig/L for
the Indian frog (Rana hexadactyla) to 19,200 |ig/L for the yellow-legged frog (Rana boylii).

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Thus, it is uncertain how the toxicity of malathion to frog tadpoles relate to the toxicity to young
rainbow trout, the species of the assessment endpoint used to calculate the acute RQs. The
lowest acute toxicity endpoint obtained, 0.59 |ig/L for the Indian frog Rana hexadactyla
(Khangarot et al., 1985; Eco ref. 011521), was judged to be unacceptable for quantitative risk
assessment because too little information was available on the testing methods and apparatus,
exposure concentrations were not provided, and several deviations from the Agency's test
guidelines were observed. Excluding this value, the range of endpoints for the aquatic-stage
amphibians is 170 to 19,200 |ig/L, indicating that the toxicity to frog tadpoles is less than that to
the rainbow trout. All of these studies, however, had deficiencies and were not judged to be
acceptable for quantitative risk assessment. Peak EECs (Table 3-2) were greater than the lowest
frog toxicity endpoint estimate of 0.59 |ig/L for all uses, but were greater than the other frog
toxicity estimates for all uses except for aquatic agriculture. In conclusion, the toxicity data for
amphibian species is too variable and uncertain to draw conclusions of the effects of malathion
to aquatic stages of the CTS.

Sparling and Fellers (2007) found that the oxon of malathion, maloxon, is approximately 90
times more toxic to tadpoles of the yellow-legged frog (Rana boylii) than is malathion. Maloxon
may form on the dry surface of plants and then could be washed into ponds by rainfall. In
addition, maloxon has been found to occur in significant quantities in rainwater (Vogel et al.,
2008) and fog (Schomburg et al., 1991) in California. Thus, malathion may be deposited into
ponds by precipitation. Any exposure to maloxon would likely increase the toxicity to eggs and
larvae of the CTS above that which we predicted for exposure to malathion alone. This increases
the certainty in our conclusion that use of malathion may cause direct adverse effects to aquatic
stages of the CTS. See Section 6.1.4 for more information about the uncertainties concerning
maloxon fate and toxicity.

Terrestrial-Phase

RQs were calculated for terrestrial amphibians (using birds as a surrogate) to assess the risk of
malathion exposure to terrestrial stages of the CTS. Screening-level RQs were first calculated
using the T-Rex model. The acute RQs derived with T-REX exceeded the acute LOC for all
uses (Table 5-7). For most uses, the chronic RQ exceeded the chronic LOC as well. Therefore,
the T-HERPS model was used to derive more refined RQs for the CTS. For juveniles, refined
RQs were calculated for salamanders consuming small insects. For adults, refined RQs were
calculated for salamanders consuming herbivorous small mammals. A diet of small mammals
was selected because this food item is predicted to contain the greatest residues of malathion.
Refined RQs from T-HERPS are presented in Table 5-8.

Greater risk was predicted for adult salamanders feeding on herbivorous small mammals than for
the juvenile salamanders feeding on insects. For adults, acute RQs derived from dose-based
calculations exceeded the LOC for listed species (0.1) for all uses. Use of malathion ultra-low
volume (ULV) products had lower RQs than other agricultural uses because of the lower
application rates used for ULV applications. The RQ for adult mosquito control was also lower
because only a small fraction of the aerial ULV application was predicted to deposit on the
surface and expose terrestrial organisms. For ULV applications on citrus and kumquats, and for
adult mosquito control, the acute RQ exceeded the LOC for listed species (0.1) but not the LOC

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for non-listed species (0.5). Acute RQs derived from dietary-based calculations exceeded the
listed species LOC for listed species (0.1) for all uses except ULV application on citrus and
kumquats, and ULV application for adult mosquito control. The only use with a dietary-based
RQ that exceeded 0.5 was non-ULV use on citrus and kumquats, for which the RQ was 0.85.
For chronic risk, dietary-based RQs exceeded the LOC of 1.0 for all uses except ULV use on
citrus and kumquats, for which the chronic RQ was 0.40, and ULV application for adult
mosquito control, for which the chronic RQ was 0.22.

The terrestrial exposure modeling was less conservative for juvenile salamanders consuming
small insects, and thus yielded lower RQs. Acute RQs exceeded 0.1, the LOC for listed species,
for uses with higher use rates (e.g., non-ULV citrus, cotton, nuts, and berries), but not for uses
with lower use rates (e.g., grains, melons, beans, and pastures). None of the acute RQs for
juveniles exceeded 0.5, the LOC for nonendangered species. Chronic RQs were also lower in
the assessment for juveniles, but all still exceeded the LOC of 1.0 except for ULV application on
citrus and kumquats, which had a chronic RQ of 0.22, and for ULV application for adult
mosquito control, which had a chronic RQ of 0.12.

Taken together, the RQ analysis for adult CTS indicate that all uses of malathion in California
have the potential to cause direct adverse effects to terrestrial-phase CTS, although this
conclusion is less certain for ULV applications to citrus and kumquats, and ULV application for
adult mosquito control. It should be noted however, that use of non-ULV malathion products on
citrus and kumquats yielded the highest RQs of any use. It should also be noted that even the
ULV use on citrus and kumquats and the ULV use for adult mosquito control had aquatic risk
quotients that indicate potential adverse effects on aquatic stages of the CTS.

Incident data confirm that malathion may cause direct effects to aquatic stages of the CTS.
Twenty-three incidents of mortality of fish and aquatic organisms have been linked to exposure
of malathion. Several of these incidents have been linked to agricultural use of malathion, and
several other have been linked to adult mosquito control use. For both agricultural uses and
mosquito control uses, many of the incidents were given a certainty of probably or highly-
probable for malathion being the cause of the mortality. Thus, incident data supports the
conclusion of risk to aquatic stages of the CTS from both agricultural uses and the mosquito-
control use. In contrast, incident data do not confirm that use of malathion poses a risk to
terrestrial adult stages of the CTS. Only four incidents of adverse effects to terrestrial vertebrates
have been linked with exposure to malathion. In all four cases, simultaneous exposure to another
more toxic pesticide occurred which was more likely the cause of the observed effects.

Several studies have shown that long range transport of pesticides used from intensive
agricultural areas of the Central Valley of California contaminate aquatic habitats of amphibians
living in the Sierra Nevada Mountains that lie to the east of the use areas (e.g., McConnell et al.
1998, LeNoir et al. 1999, Fellers et al. 2004). The range of the CTS does not extend into high
mountain regions of the Sierra Nevada, but portions of the central DPS does include areas in the
Sierra Nevada foothills with elevations up to approximately 610 meters (USFWS 2009). In the
summer of 1997, LeNoir et al. (1999) detected malathion in air sampled at 200 m and 533 m, and
detected malathion in surface water at sites ranging from 118 to 2042 m. Surface water
concentrations of malathion sampled at elevations within the range used by the CTS (118-488 m)

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ranged from 64.97 to 83 ng/L. In 1996, McConnell et al. (1998) measured malathion in rain and
snow from Ash Mountain (elevation 500 m) at concentrations as high as 24 ng/L. malathion
concentration measured in both of these studies were less than the assessment endpoint for direct
effects to the CTS for acute toxicity (LC50 = 33 |ig/L) and chronic toxicity (NOAEC = 8.6 |ig/L).
Thus, while malathion concentrations may reach levels that are toxic by themselves, they add to
the toxicity of other organophosphate insecticides that were also detected in these waters, such as
chlorpyrifos and diazinon (McConnell et al. 1998, LeNoir et al. 1999, Fellers et al. 2004), and
could significantly contribute to poor water quality conditions for this species.

The Sonoma County DPS and Santa Barbara County DPS do not occur in the Sierra Nevada
mountains or foothills, but do occur in the Coastal Range that lies between the Central Valley
and the Pacific Ocean. Some segments of the Central DPS also occur in the Coastal Range.
CTS in these areas occur at elevations up to 1067 m (USFWS 2009). Since the prevailing winds
which cause most of the precipitation on mountains areas are from the east, precipitation in the
Coastal Range would not be subject to long range transport of pesticides used in the Central
Valley, but would be subject to long range transport from agricultural areas lying between the
Coastal Range and the Pacific Ocean.

5.2.2.b. Indirect Effects

i. Potential Loss of Prey

The CTS consumes a wide variety of dietary items throughout its life cycle, including terrestrial
and aquatic invertebrates, fish, worms, terrestrial arthropods, amphibians, small mammals, and
algae. Thus, to assess indirect effects through potential loss of food items, RQs were calculated
for freshwater invertebrates, freshwater fish, aquatic plants (algae), terrestrial invertebrates,
amphibians, and small mammals.

RQs for aquatic invertebrates, shown in Table 5-2, can be used to evaluate the potential for
malathion use to cause adverse effects on the abundance of zooplankton and aquatic arthropods
and mollusks that larval stages of the CTS depend on for food. For all uses, the acute RQ
exceeded the LOC for both listed species (0.05) and for nonlisted species (0.5). The RQs for all
uses except passion fruit also exceeded 1.0, indicating that peak concentrations are expected to
exceed the median lethal dose of aquatic invertebrates. RQs for chronic risks were even greater
than those for acute risk, with RQs for most uses exceeding 100, and for some uses exceeding
1000. This fact indicates that the extreme sensitivity of aquatic invertebrates to sublethal toxicity
by malathion outweighed the relatively low persistence of the chemical in water. All chronic
RQs exceeded the LOC (1.0), and the RQ for many uses, both agricultural and nonagricultural,
exceeded 100. Therefore, the use of malathion is likely to cause adverse effects to the aquatic
prey of the CTS.

As discussed above, several studies have shown that long range transport of pesticides used from
intensive agricultural areas of the Central Valley of California contaminate aquatic habitats of
amphibians in the Sierra Nevada Mountains (e.g., McConnell et al. 1998, LeNoir et al. 1999,
Fellers et al. 2004). LeNoir et al (1999) detected malathion in air sampled at 200 m and 533 m,
and detected malathion in surface water at sites ranging from 118 to 2042 m. Surface water

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concentrations of malathion sampled at elevations within the range used by the CTS (118-488 m)
ranged from 64.97 to 83 ng/L. In 1996, McConnell et al. (1998) measured malathion in rain and
snow from Ash Mountain (elevation 500 m) at concentrations as high as 24 ng/L. Malathion
concentration measured in both of these studies were less than the acute toxicity assessment for
freshwater invertebrates (LC50 = 700 ng/L) by only a factor of 10 and exceeded the assessment
endpoint for chronic toxicity (NOAEC = 35 ng/L). Thus, it appears that long-range transport of
malathion, with deposition into aquatic habitats from precipitation potentially may cause
reduction in the abundance of invertebrate prey in portions of the CTS habitat located in the
foothills of the Sierra Nevada. While not investigated in these studies, it is also possible that
areas of the CTS range in the Coastal Range could likewise be affected from long range transport
and deposition of malathion from agricultural areas lying between the Coastal Range and Pacific
Ocean. Toxic effects of malathion on aquatic amphibians would be additive with those of other
organophosphate insecticides known to be deposited by rainwater, including chlorpyrifos and
diazinon (McConnell et al. 1998, LeNoir et al. 1999, Fellers et al. 2004), thereby creating even
greater combined toxicity to aquatic invertebrates.

Being that malathion is an insecticide, it would be expected to also cause adverse effects on
terrestrial invertebrate prey of the CTS. RQs calculated for terrestrial invertebrates (Table 5-9)
did indeed show this to be the case. For various uses of malathion, terrestrial invertebrate RQs
ranged from 76.5 to 648. Thus, all uses of malathion are predicted to have the potential to
adversely affect the abundance of invertebrate prey of the CTS.

Adult CTS may also feed on small mammals and other amphibians. RQs for these prey items are
shown in Table 5-7. For amphibians, RQs for acute toxicity exceeded the LOC for nonlisted
species (0.50) for all uses of malathion. RQs for chronic toxicity also exceeded the LOC (1.0)
for all uses except for ULV application on citrus and kumquats. As discussed above, all uses of
malathion are predicted to potentially cause adverse effects on aquatic stages of amphibians,
which of course could also lead to impacts on the abundance of the adult terrestrial stages. For
mammal prey, acute RQs were lower and exceeded the nonendangered LOC only for crops with
higher use rates (e.g. citrus, cotton, and walnuts). However, the dosed-based chronic RQs
exceeded the chronic LOC (1.0) for all uses except ULV application on citrus and kumquats.

In summary, risk assessments based on RQs indicate that all uses of malathion have the potential
to adversely affect prey items of the CTS, including aquatic invertebrates, terrestrial
invertebrates, fish, and amphibians. All uses except ULV use on citrus and kumquats are also
predicted to cause potential adverse effects on small mammal prey.

ii. Potential Modification of Habitat

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Toxicity testing has found that malathion has low toxicity to aquatic plants. Risk quotients for
all uses of malathion were well below 1. For nonaquatic agricultural uses and nonagricultural
uses, RQs were never greater than 0.04. For aquatic agricultural uses, RQs were as high as 0.47,
but the exposure estimates for these uses are for peak concentrations on the flooded field and are
likely to be much greater than what would occur in off-site aquatic habitats. Peak concentrations
in offsite receiving waters would be much less because of the rapid degradation that malathion
would undergo while the water is held on the field, and because of the dilution that would occur
when the released water mixes with uncontaminated water. We therefore consider the risk of
indirect effects to the CTS from malathion causing adverse effects on aquatic plants to be
insignificant and discountable.

Small mammals play an important roll in the survival of the CTS. CTS depend on the burrows
of small mammals for underground refugia. CTS use the borrows for shelter, protection from
predators, and feeding habitat. Thus, in reduction in the abundance of small mammals would
potentially adversely affect the habitat of the CTS by reducing the availability of burrows.

Despite widespread use, malathion has not been observed to be phytotoxic to the wide variety of
crop and ornamental plants to which it is directly applied. As discussed in Section 4.3.4, efficacy
studies have found that application of malathion at typical use rates either do not have significant
effects on the growth of plants, or have significant beneficial effects due to control of plant pests.
Vegetation in the habitat of the CTS would be exposed from drift and runoff from treated sites.
This exposure would be at rates much less than the target plants that are directly treated.
Therefore, exposure of plants to malathion in the CTS habitat is not expected to result in any
significant damage to vegetation.

5.2.3. Modification of Designated Critical Habitat

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Primary constituent element (PCE) 2 states that there must be "barrier-free uplands adjacent to
breeding ponds that contain small mammals" because "small mammals are essential in creating
the underground habitat that juvenile and adult CTS depend upon for protection from the
elements and predation." RQs for small mammals, shown in Table 5-4, indicate that all uses of
malathion in California have the potential to cause adverse effects to small mammals. Acute RQ
calculated based on oral dose exceeded the listed species LOC (0.1) for all uses. Acute RQs
calculated based on dietary dose also exceeded the LOC for all uses except ULV applications on
citrus and kumquats, and ULV application for adult mosquito control. For chronic risk, RQs
exceeded the LOC for all uses except ULV applications on citrus and kumquats, and ULV
application for adult mosquito control. In conclusion, the RQ analysis indicates that all uses
have the potential to cause adverse effects to critical habitat of the CTS by causing acute and
chronic effects to small mammals that the species depends upon for creation of underground
refugia. As for direct effects to the CTS, risk to mammals is lower for ULV use on citrus and
kumquats, and ULV use for adult mosquito control, making the conclusion of potential effects to
mammals less certain for these uses than for the other uses.

Availability of terrestrial and aquatic invertebrates, amphibians, and small mammals is also an
important requirement of the habitat of the CTS because the species depends on these taxa for
food. As discussed in Section 5.2.2.b.i, all uses of malathion are predicted to potential cause
mortality to aquatic and terrestrial invertebrates, as well as small terrestrial vertebrate prey (e.g.
small mammals and frogs). Therefore, use of malathion may degrade the critical habitat of the
CTS by reducing prey abundance.

5.2.4. Spatial Extent of Potential Effects

When LOCs are exceeded, the Agency typically does analysis to determine the spatial extent of
potential "likely to adverse affect" (LAA) where effects may occur in relation to the treated site.
In this assessment, however, the use "footprint" of the use of malathion was considered to be the
entire state of California. All uses of malathion result in an LAA determination because of the
potential for direct and/or chronic effects. Uses include a very wide range of agricultural crops,
fruit and nut trees, forestry, commercial, and residential uses. Since uses are expected in all land
use categories (agricultural crops, orchards, forests, rangeland, and urban areas), the spatial
extent of effects is not limited by the location of uses. Any place where the CTS occurs, or that
is part of its critical habitat, is considered to be part of the LAA area.

5.2.4.a. Spray Drift

To further characterize the terrestrial risk the use of malathion, the Agency has estimated the
maximum distance from the edge of the treatment area at which spray drift from malathion uses
would result in terrestrial deposition at a rate that would still exceed levels of concern (LOC).
Analysis was conducted using both the LOC for acute risk to terrestrial organisms (0.5) and the
LOC for potential adverse effects to endangered species (0.1). For the flowable uses, a
quantitative analysis of spray drift distances was completed using AgDRIFT (v. 2.01) using
default inputs for ground applications {i.e., high boom, ASAE droplet size distribution = Very
Fine to Fine, 90th data percentile) and aerial applications {i.e., ASAE Very Fine to Fine).

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Calculations were based on toxicity to for terrestrial invertebrates, as measured by the honeybee
acute contact tests, because this was the most sensitive taxa to malathion. Analysis of all uses
was based on a single application. Analysis was only conducted for non-ULV applications.

For aerial applications, the distance at which spray drift deposition would exceed both LOCs for
the CTS exceeded 1000 ft, the maximum distance predicted by the AgDrift model, for all
agricultural uses for which aerial application is permitted. Distances for uses with ground and air
blast applications are shown in Table 5-14. For ground applications, the distance for exceeding
the endangered species LOC exceeds 1000 ft for all agricultural and nonagricultural uses. The
distance for exceeding the LOC for acute risk also exceeded 1000 ft for the nonagri cultural uses
assessed, and range from 374 ft to 725 ft for agricultural uses. The distances were much shorter
for uses with air blast application. For these uses, distances ranged from 52 ft (mango) to 348 ft
(citrus) for exceeding the endangered species LOC, and from 7 ft to 82 ft for exceeding the acute
risk LOC.

Table 5-14. Maximum Distance from Edge of Field at which the Spray Drift Deposition from
Ground Applications Are Predicted to Result in a Risk Quotient for the CTS that Exceeds the

LOC

Application
Method1

Small Insect
RQ

Distance for Exceed LOC (Feet)

Use

Use Rate

Acute Risk LOC
(0.5)

Endangered Species
LOC (0.1)

Agricultural Uses

Citrus

7.5

649

348

Pecan, chestnut, and walnut

2.5

216

135

Cotton

2.5

216

725

> 1000

Strawberry, caneberry group

2.0

173

623

> 1000

Pears, papaya, and guava.

1.25

108

Alfalfa, rice, barley, broccoli,
carrots, et al.

1.25

108

443

> 1000

Field corn, wheat, oats,

1.0

86.5

374

> 1000

sorghum, melons, peas, et al.

Mango

0.9375

81.1

Non-Agricultural Uses

Fence / hedge row, domestic

dwelling (perimeter), and
refuse/solid waste site

10.6

917

> 1000

1 "AB" signifies airblast, "G" signifies ground spray.

For the aquatic stages of the CTS, the spray drift distances would be identical to those calculated
for the DS. These distances are provided in Table 5-13.

5.2.4.b. Downstream Dilution Analysis

Typically, the downstream dilution model is used to determine the extent of exposure in streams
and rivers where the EEC could potentially be above levels that would exceed the most sensitive
LOC. For this assessment, however, the use of malathion is not limited to certain land use
classes, but may be used throughout the state. The entire range of the CTS is considered to be
within the potential area of use of malathion. Therefore, analysis of downstream dilution was

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not necessary for defining the overlap of the potential area of LAA with the habitat and
occurrence of the CTS

5.2.4.C. Overlap of Potential Areas of LAA Effect and Habitat and
Occurrence of the DS and CTS

As stated above, the Limit of Area Affect (LAA) for effects on survival, growth, and
reproduction for the DS is defined as the entire habitat of the DS and its critical habitat, as
depicted in Fig. 2-3. Because malathion is used in areas of all land uses throughout the entire
state, no spatial restrictions were imposed based on use.

5.3. Effects Determinations

5.3.1. Assessed Species

This risk assessment clearly indicates that even with the mitigation measures imposed by the
Malathion RED (USEPA 2006), use of malathion in California has a potential to cause adverse
effects to both the DS and the CTS. Adverse effects may be manifested by both direct acute and
chronic toxicity to the species themselves, as well as indirect effects on prey items and habitat
requirements.

The DS is subject to contamination of malathion because it inhabits water that drains areas of
intensive agricultural and urban land uses. Intensive agricultural areas of the Central Valley are
drained by tributaries which flow into the Sacramento River, San Joaquin River, and the San
Francisco Estuary. Malathion is used on many crops in this area, including cotton, grains,
alfalfa, vegetables, fruits, and nuts. Malathion is also used extensively by homeowners, property
owners, and public health agencies in urban areas near the DS habitat, including Sacramento,
Stockton, and Modesto. Surface water monitoring data have found that potentially harmful
concentrations of malathion occasionally occur in back tributaries that drain agricultural and/or
urban areas. This contamination may cause direct toxic effects to the eggs and larvae that
migrate down these tributaries, as well as the adults that migrate into these tributaries during
spawning. The predicted risk of direct toxic effects to the DS is supported by numerous fish kills
that have been linked with high certainty to exposure to malathion. The DS potentially could
also be adversely impacted by indirect effects of malathion on prey abundance. Malathion is
predicted to reach levels which may be toxic to prey of the DS, especially to aquatic arthropods
which have been shown to be very sensitive to malathion. Toxicity to malathion could be
exasperated by exposure to the oxon degradation product maloxon, which has been shown to be
up to 90 times more toxic than the parent compound. The amount of exposure to maloxon in
water inhabited by the DS is currently largely unknown, but any exposure would increase the
risk beyond what was predicted in this assessment based on exposure to malathion alone.
Residues of malathion and potentially maloxon that enter the San Francisco Estuary by flowing
down the Sacramento River and San Joaquin River, and by deposition of spray drift by aerial
applications, would add to the toxicity of the numerous other organophosphate and carbamate

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insecticides that are known to occur in these water, and would thereby contribute to the overall
water quality degradation caused by pesticides in the waters inhabited by the DS.

The listing of the CTS is comprised of three DPS, the Central California DPS, the Sonoma
County DPS, and the Santa Barbara DPS. The use of malathion in California is so widespread
that it could not be restricted spatially. Since the potential area of effects comprise all areas of
California, all of the three DPSs are entirely within the potential area of effects, and all three
were assessed together. Thus, the following discussion of the CTS applies to all three DPSs.

Considering the numerous widespread agricultural and residential uses of malathion, all
segments of the CTS population could be potentially subjected to exposure to malathion. The
vernal ponds and pools where the species lays its eggs and where the aquatic larval stages live
could be contaminated by spray drift, from runoff from agricultural and urban areas, and from
deposition in rainwater. Contamination levels could be relatively high in these small shallow
water bodies where there would be little dilution of contaminated inflows and spray drift
deposition. The quantitative risk assessment found that almost all uses of malathion could
potentially cause direct adverse effect to the eggs and larvae of the CTS living in these habitats.
In addition, the residue levels of malathion in these habitats are predicted to potentially exceed
the toxicity level of many of the invertebrate prey species of the CTS. Malathion exposure could
cause reduction in the abundance of zooplankton and aquatic arthropods in these ponds, thereby
limiting the food supply of the larvae. The direct and indirect effects on the eggs and larvae of
the CTS could result in reduced recruitment of breeding adult.

The terrestrial stages of the CTS may also be adversely affected by use of malathion. The
quantitative risk assessment found that all uses of malathion could potentially contaminate food
items of the CTS enough to cause direct acute and/or chronic effects to the juvenile and adult
salamanders. The risk assessment did not take into account exposure through dermal absorption
or drinking water, but additional exposure through these sources of exposure potentially could
increase risk above that predicted by the risk assessment. In addition to direct effects, all uses of
malathion are predicted to potentially adversely affect terrestrial invertebrates that comprise a
large portion of the diet of terrestrial-phase CTS. Many uses are also predicted to potentially
cause acute or chronic effects on small terrestrial vertebrates that are also consumed by the CTS.
This could potentially reduce the abundance of food for the terrestrial-phase salamanders.

Finally, many uses of malathion could potential affect small mammals. This could adversely
impact the critical habitat of this species because the terrestrial-phase CTS depend on burrows
created by small mammals for food, shelter and protection from predators.

In conclusion, the Agency makes a "may affect" and "likely to adversely affect" determination
for the DS and for all DPSs of the CTS, as well as a habitat modification determination for their
designated critical habitat of these species, based on the potential for direct and indirect effects
and effects to the PCEs of critical habitat.

5.3.2. Addressing the Risk Hypotheses

In order to conclude this risk assessment, it is necessary to evaluate the risk hypotheses defined
in Section 2.9.1. Based on the conclusions of this assessment, several of the risk hypotheses

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cannot be rejected. For direct effects of malathion to the DS and CTS, none of the risk
hypothesis could be rejected. For indirect effects and/or modification of critical habitat, only the
hypotheses related to alterations of aquatic and terrestrial plant communities could be rejected.
Hypotheses related to other indirect effects and/or modification of critical habitat (i.e., adverse
effects on water quality, prey availability, and availability of small mammal burrows) could not
be rejected. Considered in total, the failures to reject stated hypotheses represent concerns in
terms of direct and indirect effects of malathion on the DS and CTS, as well as potential
modification of critical habitat.

Specifically, the assessment failed to reject that the labeled use of malathion within the action
area may:

• directly affect DS and CTS by causing mortality or by adversely affecting growth or
fecundity;

• indirectly affect DS and CTS and/or modify their designated critical habitat by reducing
or changing the composition of food supply;

• indirectly affect DS and CTS and/or modify their designated critical habitat by reducing
or changing aquatic habitat in their current range (via modification of water quality
parameters, habitat morphology, and/or sedimentation);

• indirectly affect CTS and/or modify their designated critical habitat by reducing or
changing terrestrial habitat in their current range (via reduction in small burrowing
mammals leading to reduction in underground refugia/cover).

However, the assessment did reject the hypotheses that labeled use of malathion within the
action area may:

• indirectly affect DS and CTS and/or modify their designated critical habitat by reducing
or changing the composition of the aquatic plant community in the species' current range,
thus affecting primary productivity and/or cover;

• indirectly affect DS and CTS and/or modify their designated critical habitat by reducing
or changing the composition of the terrestrial plant community in the species' current
range.

6. Uncertainties

Uncertainties that apply to most assessments completed for the San Francisco Bay Species
Litigation are discussed in Attachment 1. This section describes additional uncertainties specific
to this assessment.

6.1. Exposure Assessment Uncertainties

6.1.1. Aquatic Exposure Modeling of Malathion

174

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Because malathion degrades rapidly in the pH-neutral conditions modeled in the aquatic
exposure assessment, the amount of malathion that is transported from treated fields to aquatic
environments via runoff will depend strongly on how soon after application a major rainfall
event occurs. In central and southern California, rainfall is highly seasonal, with almost all of
the annual rainfall occurring during the winter months. Together, these factors make model
predictions of malathion concentrations highly dependant on the dates chosen for the
applications, which in turn depend on the date chosen for the first application. Because of the
greater rainfall, setting the date of first application during the fall or winter would generate much
higher EECs than setting it in the spring or summer. Analysis of the CDPR-PUR data indicated
that many of the uses of malathion occur primarily in the summer, but some lower level of use
occurred in winter also (see Appendix D). To account for the high variability related to date of
first application, the multi-run function of the PE shell was used to calculate 90th percentile EECs
for each potential application date (or set of application dates for uses that allow multiple
applications). This distribution of EECs across application dates was compared to the
distribution of dates when malathion use was recorded in the PUR data. The data were limited to
application dates that were within the period when the CDPR-PUR data showed it was used in
California. The scenario with the application date that predicted the highest EEC was then used
in the assessment.

Using the highest EECs from the time of the year when malathion is applied is a reasonable way
to characterize the maximum potential aquatic exposure to malathion. However there is the
potential for the highest EEC to be atypical relative to the other times when malathion is applied
to a use site. The question of how typical is it for malathion to be applied for each use at times
when it is expected that EECs will exceed the agencies levels of concern (LOCs) is addressed by
summing the pounds of malathion applied in California on application dates that are expected to
result in EECs that exceed the agencies LOCs divided by the total pounds of malathion applied
in California times 100 (Table 6-1).

175

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Table 6-1. Percentage of Pesticide Expected to be Applied on Application Dates when EECs Are Expected to Exceed Agency Levels
of Concern (LOCs) for the Aquatic Impacts of Legal Uses of Malathion in California

Expected Percentage of Pesticide Mass Applied

(%) in California

Maximum

Freshwater

Esluarinc/Marinc

Aquatic

Application

Freshwater fish

invertebrates

fish

invertebrates

plants

Rales'

Acute

Chronic

Acute

Chronic

Acute

Chronic

Acute

Chronic

2400

Scenario Group. Label Crop/Site

(Lbs. ai/A)

33 u«/L

8.6 (.ig/L

0.59 ug/L

.035jig/L

33 )ig/L

17.3 ug/L

2.2 ug/L

.013 ug/L

Ug/L

Agricultural Uses (spray drift buffers of 25 ft for ground applications and 50 ft for air)

1. Alfalfa, Clover, Lespedeza, Lupine, Trefoil,
and Vetch

Air: 1.56
ULV: 0.61

100
100

0
0

100
100

0
0

Ground: 1.56

100

2. Macadamia Nut (Bushnut)

Ground: 0.94
Airblast: 0.94

56
54

0
0

100
100

56
54

0
0

100
100

0
0

3 and 4. Pecan, Walnut (English/Black), and

Ground: 2.5

100

Chestnut

Airblast: 2.5

100

6. Date (dust)

Air: 4.25

100

Ground: 4.25

100

8. Avocado

Ground: 4.7

100

9. Citrus, Citrus Hybrids other than Tangelo,
Grapefruit, Kumquat, Lemon, Lime, Orange,
Tangelo, and Tangerines

Air: 7.5
ULV: 0.175
Ground: 7.5
Airblast: 7.5

100
100
100
100

0
0
0
0

100
100
100
100

0
0
0
0

10. Amaranth - Chinese, Broccoli (Unspecified,

Chinese, and Raab), Cabbage (Unspecified and

Chinese), CanolaVRape, Cauliflower, Collards,
Corn Salad, Dock (Sorrel), Horseradish, Kale,
Kohlrabi, Mustard, Mustard Cabbage (Gai

Air: 1.25
Ground: 1.25

100
59

0
0

100
100

100
59

100
100

0
0

Choy/Pak-Choi), and Purslane (Garden and

Winter)

Air: 1.0

100

11. Corn (Unspecified, Field, Pop, and Sweet)

ULV: 0.61

100

Ground: 1.0

100

Air: 2.5

100

12. Cotton

ULV: 1.22

100

Ground: 2.5

100

Air: 0.63

100

13. Hops

Ground: 0.63

100

Airblast: 0.63

100

176

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Expected Percentage of Pesticide Mass Applied

(%) in California

Maximum

Freshwater

Estuarinc/Marinc

Aquatic

Application

Freshwater fish

invertebrates

fish

invertebrates

plants

Rales'

Acute

Chronic

Acute

Chronic

Acute

Chronic

Acute

Chronic

2400

Scenario Group. Label Crop/Site

(Lbs. ai/A)

33 |ig/L

8.6 m>/L

0.59 jig/L

.035jig/L

33 |ig/L

17.3 u^/L

2.2 Wg/L

.013 ug/L

US/L

15. Apricot

Ground: 1.5

100

Airblast: 1.5

100

16. Nectarine and Peach

Ground: 3

100

Airblast: 3

100

Air: 1.75

100

17. Cherry

ULV: 1.22

100

Ground: 1.75

100

Airblast: 1.75

100

18. Fig

Ground: 2

100

Airblast: 2

100

19. Pear

Ground: 1.25

100

Airblast: 1.25

100

20 and 21. Guava, Mango, and Papaya

Ground: 1.25
Airblast: 1.25

41
38

0
0

100
100

41
38

100
100

0
0

22. Garlic and Leek

Air: 1.56

100

Ground: 2

100

23. Grapes

Ground: 1.88

100

Airblast: 1.88

100

26. Brussel Sprouts and Dandelion

Air: 1.25
Ground: 1.25

100
33

0
0

100
100

100
33

100
100

0
0

27. Swiss Chard, Chervil, Endive (Escarole),

Lettuce, Head Lettuce, Leaf Lettuce (Black
Seeded Simpson, Salad Bowl, Etc.), Orach
(Mountain Spinach), Parsley, Roquette
(Arrugula), Salsify, and Spinach

Air: 1.88
Ground: 1.88

100
36

0
0

100
100

100
36

100
100

0
0

29. Eggplant

Air: 1.56

100

Ground: 1.56

100

30. Pumpkin

Air: 1

100

Ground: 1

100

31. Cucumber, Cucurbit Vegetables, Melons -

Unspecified, Cantaloupe, Honeydew, Musk,
Water, and Winter

(Casaba/Crenshaw/Honeydew/Persian), and
Squash (All Or Unspecified)

Air: 1.75

100

Ground: 1.75

100

177

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Expected Percentage of Pesticide Mass Applied

(%) in California

Maximum

Freshwater

Estuarinc/Marinc

Aquatic

Application

Freshwater fish

invertebrates

fish

invertebrates

plants

Rales'

Acute

Chronic

Acute

Chronic

Acute

Chronic

Acute

Chronic

2400

Scenario Group. Label Crop/Site

(Lbs. ai/A)

33 |ig/L

8.6 m>/L

0.59 jig/L

.035jig/L

33 |ig/L

17.3 u^/L

2.2 Wg/L

.013 ug/L

US/L

32. Onion (Unspecified and Green), Radish, and

Air: 1.56

100

Shallot

Ground: 1.56

100

33 and 36. White/Irish Potato and Sweet Potato

Air: 1.56
Ground: 1.56

100
15

0
0

100
100

100
15

100
100

0
0

34 and 35. Turnip, Parsnip, and Rutabaga

Air: 1.25
Ground: 1.25

100

0
0

100
100

100

100
100

0
0

37. Bluegrass, Canarygrass, Grass

Air: 1.25

100

Forage/Fodder/Hay, Pastures, Peas (Including

ULV: 0.92

100

Vines), Rangeland, and Sudangrass

Ground: 1.25

100

40. Beets and Peas (Unspecified and Field)

Air: 1

Ground: 1.25

100
32

0
0

100
100

100
32

100
100

0
0

41. Carrot (Including Tops), Celtuce, Fennel, and

Air: 1.56

100

Pepper

Ground: 1.56

100

42. Beans, Beans - Dried-Type, Beans - Succulent
(Lima), and Beans - Succulent (Snap)

ULV: 0.61

100

43. Celery

Air: 1.5

100

Ground: 1.5

100

44. Asparagus

Air: 1.25

100

Ground: 1.25

100

46. Strawberry

Air: 2

100

Ground: 2

100

48. Tomato

Air: 1.56

100

Ground: 1.56

100

49. Okra

Air: 1.2

100

Ground: 1.2

100

Air: 1

100

51. Sorghum

ULV: 0.61

100

Ground: 1

100

Air: 1.25

100

52. Barley, Cereal Grains, Oats, Rye, and Wheat

ULV: 0.61

100

Ground: 1.25

100

53, 54, 56. Gooseberry, Blackberry, Boysenberry,

Air: 1.25

100

Dewberry, Loganberry, Raspberry (Black - Red),

Ground: 2

100

Caneberries, and Currant

Airblast: 2

100

178

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Expected Percentage of Pesticide Mass Applied

(%) in California

Maximum

Freshwater

Estuarinc/Marinc

Aquatic

Application

Freshwater fish

invertebrates

fish

invertebrates

plants

Rales'

Acute

Chronic

Acute

Chronic

Acute

Chronic

Acute

Chronic

2400

Scenario Group. Label Crop/Site

(Lbs. ai/A)

33 ug/L

8.6 ng/L

0.59 ng/L

,035ng/L

33 |ig/L

17.3 ug/L

2.2 ug/L

.013 ug/L

US/L

ULV: 0.77

100

55. Blueberry

Ground: 1.25

100

Airblast: 1.25

100

57. Passion Fruit (Granadilla)

Ground: 1

100

Airblast: 1

100

58. Mint and Spearmint

Air: 0.94

100

Ground: 0.94

100

Air: 1.25

100

59. Rice and Wild Rice

ULV: 0.61

100

Ground: 1.25

100

Air: 1.25

100

61. Water Cress

Ground: 1.25

100

Non-agricultural Uses

Cull Piles and agricultural Structures and

Equipment. Cull Piles, Agricultural/Farm

Structures/Buildings and Equipment,

Drench: 298.7

100

Commercial/Institutional/Industrial

Premises/Equipment (Outdoor), and Meat

Processing Plant Premises (Nonfood Contact)

Fence rows/hedge rows.

Ground: 10.6

100

Air: 3.2

100

Forestry. Christmas Tree Plantations, Pine (Seed

ULV: 0.9375

100

Orchard), and Slash Pine (Forest)

Ground: 3.2

100

Airblast: 3.2

100

Nursery. Outdoor Nursery, Outdoor Premises,

Ornamental and/or Shade Trees, Ornamental

Air: 2.5

100

Herbaceous Plants, Ornamental Lawns and Turf,

Ground: 2.5

100

Ornamental Non-flowering Plants, Ornamental

Airblast: 2.5

100

Woodv Shrubs and Vines, and Urban Areas

Rights-of-way. Uncultivated agricultural areas,

Air: 1

TTT.V 0 9281

Nonagricultural Rights-of-way/Fencerows, and

NA (Scenario can not be run across a distribution of dates.)

Nonagricultural Uncultivated Areas/Soils

Airblast: 1

179

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Expected Percentage of Pesticide Mass Applied

(%) in California

Maximum

Freshwater

Estuarinc/Marine

Aquatic

Application

Freshwater fish

invertebrates

fish

invertebrates

plants

Rales'

Acute

Chronic

Acute

Chronic

Acute

Chronic

Acute

Chronic

2400

Scenario Group. Label Crop/Site

(Lbs. ai/A)

33 |ig/L

8.6 ng/L

0.59 ng/L

,()35|ig/L

33 |ig/L

17.3 ug/L

2.2 ug/L

.013 ug/L

US/L

Public Health and Mosquito and Medfly Control.
Nonagricultural Areas (Public Health Use),
Urban Areas, Wide Area/General Outdoor

Treatment (Public Health Use), Intermittently
Flooded Areas/Water, Lakes/Ponds/Reservoirs

ULV: 0.23

100

(with Human or Wildlife Use),

Lakes/Ponds/Reservoirs (without Human or

Wildlife Use), Polluted Water, and

Swamps/Marshes/Wetlands/Stagnant Water

Residential and Refuse/Solid Waste.

Household/Domestic Dwellings (perimeter
around dwelling), Refuse/Solid Waste Containers

Ground: 10.6

(Garbage Cans), and Refuse/Solid Waste Sites

(Outdoor)

Air: 1.25

100

Turf. Golf Course Turf (Bermudagrass)

ULV: 0.92

100

Ground: 1.25

100

1 Air, ULV, Ground, and Airblast refer to aerial, ultra-low volume, ground, and airblast application methods, respectively.

180

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In two cases (macademia nut and hops), no PUR data were available. Therefore the highest EEC
from anytime during the year was used as the highest EECs (not just when malathion was
applied). Similarly the percentage of malathion applications that exceeded agency LOCs was
estimated by counting the days when application of malathion would be expected to result in
EECs that exceed the agencies LOCs divided by the total number of days in a year times 100.

The PRZM model only accounts for runoff that occurs from rainfall events. Even those
scenarios in which surface irrigation is considered, irrigation is not assumed to generate any
additional runoff. However, in central and southern California, many crops are watered by
surface irrigation. Excess irrigation may drain into aquatic habitat of the CTS and DS, resulting
in contamination even when there is not rainfall. In addition, malathion transported via
groundwater may also enter surface water habitats following irrigation. The model predictions
do not include contribution of aquatic residues from these sources.

The PRZM and EXAMS models account for transport of pesticide residues from treated areas to
aquatic habitats occurring by way of runoff and spray drift, but does not account for additional
contributions from long range transport of the volatilized fraction of malathion in the air.

Several studies have shown that prevailing easterly winds transport pesticides applied in the
Central Valley to the Sierra Nevada Mountains to the east, where the residues are deposited via
dry and wet deposition McConnell et al. 1998, LeNoir et al. 1999). Malathion has been
measured from a few sites in the Sierra Nevada Mountains, but the degree that measurements
from these sites represent concentrations in aquatic habitats used by the CTS is unknown. Some
segments of the CTS lie in the foothills of the Sierra Nevada Mountains, but in areas that are
west of the sampling sites of these studies. In addition, no information is available about the
amount of pesticide deposition or malathion concentrations in aquatic habitats of the Coastal
Range where other segments of the CTS range occur. Because the aquatic exposure modeling
did not account for contribution to aquatic habitats of the CTS from long-range atmospheric
transport of malathion, the RQ that were generated based on model predictions may
underestimate exposure to aquatic phase of the CTS.

The Agency is uncertain how much of the oxon of malathion, maloxon, will be present in aquatic
habitats. Maloxon appears to either not form or degrade very rapidly in moist soil and in water.
Field dissipation studies did not detect any maloxon in water or soil (MRIDs 41748901,
43042402, 41748901, and 43042401). On the other hand, maloxon appears to form on dry
surfaces (CDPR 1981). Therefore, maloxon theoretically could form on leaves (if they remain
sufficiently dry) and rain could wash off the residues and cause them to be transported to aquatic
habitats via runoff. The Agency does not currently have sufficient information on the
environmental fate of maloxon to model this process. Maloxon also has been detected in
California in rainwater (Vogel et al. 2008) and fog (Schomburg et al. 1991), which indicates
some maloxon residues are likely deposited into water bodies from precipitation. The amount of
deposition from precipitation is currently uncertain. Because of these uncertainties, predictions
of maloxon concentrations in aquatic habitats were not attempted.

181

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Not accounting for added toxicity from exposure to maloxon and, for the CTS, additional
exposure to malathion and maloxon from long -range atmospheric transport, could have made
the RQs calculated in this assessment underprotective for predicting the potential for adverse
effects. However, even without these additional risk factors being considered, all uses of
malathion were determined to cause potential adverse effects to both the DS and CTS.
Accounting for these additional risk factors could only make these determinations more certain.
The only potential effect on the risk determination from including these factors would be that the
few uses for which no direct effects were determined (passion fruit and ULV applications on
citrus, and ULV applications for adult mosquito control) may also result in direct adverse effect
to this species. It is noted however, that a LAA determination for the DS was made even for
these uses based on indirect effects and impact on critical habitat. All uses already have been
determined to have the potential to cause direct as well as indirect effects to the CTS.

Three of the uses (cull piles, hedge/fence rows, and residential and refuse/solid waste) would not
be expected to result in treatment of the entire upstream watershed which PRZM models. These
uses were modeled by adjusting the EECs generated from a reference scenario to account for
differences in application rate and spatial extent of treatment. Essentially, this results in a
spatially homogeneous application scenario being used to model a spatially variable application.
For cull piles, an important source of uncertainty is the location of the cull piles within the
watershed. The cull piles will likely produce higher EECs in runoff if the cull piles are located in
drainage ways rather than ridge tops. Similarly, fence/hedge rows will likely produce higher
EECs in runoff if the fence/hedge rows cross or are located along drainage ways; and lower
EECs the further the fence/hedge row is away from the drainage way. For trash bins, a site may
be located just upstream of a storm drain that leads directly to a pond occupied by the CTS or
stream with DS. Therefore, there is the potential for malathion to runoff the application site with
little or no rain occurring and the diluting effects that that rain might provide. However,
PRZM/EXAMS modeling does not account for such within watershed spatial variation.

6.1.2. Exposure in Estuarine/marine Environments

Uncertainties regarding dilution and chemical transformations in estuaries

PRZM-EXAMS modeled EECs are intended to represent exposure of aquatic organisms in
relatively small ponds and low-order streams. Therefore it is likely that EECs generated from
the PRZM-EXAMS model will over-estimate potential concentrations in larger receiving water
bodies such as estuaries and coastal marine areas because chemicals in runoff water (or spray
drift, etc.) should be diluted by a much larger volume of water than would be found in the
standard EXAMS pond. However, as chemical constituents in water draining from freshwater
streams encounter brackish or other near-marine-associated conditions, there is potential for
important chemical transformations to occur. Many chemical compounds can undergo changes
in mobility, toxicity, or persistence when changes in pH, Eh (redox potential), salinity, dissolved
oxygen (DO) content, or temperature are encountered. For example, desorption and re-
mobilization of some chemicals from sediments can occur with changes in salinity (Jordan et al.,
2008; Means, 1995; Swarzenski et al., 2003), changes in pH (Wood and Baptista 1993), Eh
changes (Velde and Church, 1999; Wood and Baptista, 1993), and other factors. Thus, although
chemicals in discharging rivers may be diluted by large volumes of water within receiving

182

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estuaries, the hydrochemistry of the marine-influenced water may negate some of the attenuating
impact of the greater water volume; for example, the effect of dilution may be confounded by
changes in chemical mobility (and/or bioavailability) in brackish water. In addition, freshwater
contributions from discharging streams and rivers do not instantaneously mix with more saline
water bodies. In these settings, water will commonly remain highly stratified, with fresh water
lying atop denser, heavier saline water - meaning that exposure to concentrations found in
discharging stream water may propagate some distance beyond the outflow point of the stream
(especially near the water surface). Therefore, it is not assumed that discharging water will be
rapidly diluted by the entire water volume within an estuary or other coastal aquatic
environment. PRZM-EXAMS model results should be considered consistent with
concentrations that might be found near the head of an estuary unless there is specific
information - such as monitoring data - to indicate otherwise. Conditions nearer to the mouth of
a bay or estuary, however, may be closer to a marine-type system, and thus more subject to the
notable buffering, mixing, and diluting capacities of an open marine environment. Conversely,
tidal effects (pressure waves) can propagate much further upstream than the actual estuarine
water, so discharging river water may become temporarily partially impounded near the mouth
(discharge point) of a channel, and resistant to mixing until tidal forces are reversed.

The Agency does not currently have sufficient information regarding the hydrology and
hydrochemistry of estuarine aquatic habitats to develop alternate scenarios for assessed listed
species that inhabit these types of ecosystems. The Agency acknowledges that there are unique
brackish and estuarine habitats that may not be accurately captured by PRZM-EXAMS modeling
results, and may, therefore, under- or over-estimate exposure, depending on the aforementioned
variables.

6.1.3. Modeled Versus Monitoring Concentrations

In order to account for uncertainties associated with modeling, available monitoring data were
compared to PRZM/EXAMS estimates of peak EECs for the different uses. As discussed in
Section 5.2.1, several data values were available from the USGS NAWQA program the
California Department of Pesticide Regulation (CDPR) for malathion concentrations measured in
surface waters receiving runoff from agricultural and urban areas near the San Francisco Estuary.
The specific use patterns (e.g., application rates and timing, crops) associated with the
agricultural areas are unknown, however, they are assumed to be representative of potential
malathion use areas. The maximum malathion concentration detected in surface water
monitoring was 6 |ig/L (see Section 3.2.4.a). The maximum peak EEC predicted by
PRZM/EXAMS was 89.8 |ig/L for non-aquatic agricultural uses, 1120 |ig/L for aquatic
agricultural uses, and 60.0 for non-agricultural uses. Part of the reason for the difference is that
all of the surface water was done in lotic ecosystems (streams and rivers) whereas the modeling
was done for a static pond. In lotic ecosystems, runoff from contaminated sources is generally
diluted with considerable quantity of water from uncontaminated sources. In the standard pond,
however, 100% of the water in the pond was assumed to have drained from land treated with
malathion. The use in the quantitative risk assessment of EECs modeled for a static pond
probably make the results protective of all or most aquatic habitats, but probably overestimate
exposure to organisms living in lotic ecosystems. The DS lives in streams and rivers, and in
inland bays that receive water from streams and rivers. Therefore, the EECs modeled for a static

183

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pond probably overestimates exposure for this species. That is why in Section 5.2.2, the
quantitative risk assessment was supplemented with comparisons of toxicity levels of various
species with measured concentrations from water monitoring programs. The aquatic stages of
the CTS, on the other hand, live in small vernal ponds and pools. These habitats are likely to be
represented much better by the static pond scenario used in the PRZM/EXAMS models. In fact,
malathion concentrations in these habitats may be even greater than predicted by the EECs
because the ponds and pools may be shallower than the 1 acre, 2 m deep pond used for our
modeling scenarios. Shallower water bodies would have greater surface area relative to the
volume, and therefore would receive greater input from spray drift per unit volume compared to
deeper water bodies. Unfortunately, no monitoring data in small ponds or pools were available
to compare with the modeled EECs.

6.1.4. Maloxon formation, environmental fate, and toxicity

Malathion can convert to the oxon derivative, maloxon, through environmental degradation
processes as well as by metabolic processes by animals and microbes. As has been found with
other oxons of organophosphorous pesticides, maloxon has been shown to be more toxic to
terrestrial and aquatic animals than the parent product. Based on data available on acute toxicity
of malathion and maloxon for the same species, estimated maloxon to malathion ratio of 96-hr
LC50 values for aquatic vertebrates has been range from 4.1 and 89.9 (Table 6-2). In order to be
protective, the maximum ratio of 92.9 was assumed in this risk assessment.

Table 6-2. Within Species Comparisons of Ma

athion and Maloxon Acute Toxicity

Species Tested

Malathion LQo jn^/L
(Reference)

Maloxon LC50 fig/L
(Reference)

Ratio of Malathion to
Maloxon Toxicitv

Carp

Cyprinus carpio

6590-23180
(MRID 40098001, Eco
ref. 089874 and 014861)

1600
(Eco ref 000086)

4.1-14.5

Medaka

Oryzias latipes

1800
(Eco ref 0183 98)

280

(Eco ref 0183 98)

48.5

Yellow-legged frog Rana
boylii

2140
(Eco ref 092498)

23.8
(Eco ref 092498)

89.9

The quantitative risk assessments of direct and indirect effects to the DS and CTS were based on
the parent compound, but the potential additional toxicity resulting from maloxon exposure,
assuming additive toxicity of malathion and maloxon, was evaluated qualitatively in the risk
characterization. This assessment was based on estimated maloxon toxicity of the most sensitive
test species, which was calculated by dividing the acute LC50 for malathion by the malathion-to-
maloxon ratio of 89.9.

The same approach was used to estimate the toxicity of maloxon to terrestrial animals. Maloxon
toxicity data were not available for birds, but data on acute toxicity of maloxon to the laboratory
rat was provided by a study published in the open literature. The acute oral LD50 of malathion
and maloxon to the laboratory rat was determined to be 2880 and 158 mg/kg-bw, respectively
(Dauterman and Main, 1966). The malathion-to-maloxon ratio for terrestrial organisms was
therefore 18.2. This ratio was used to estimate the acute oral maloxon LD50 for the most
sensitive bird test species, which was then used in a qualitative assessment of the potential risk

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additional risk of maloxon exposure to the CTS, assuming additive toxicity of malathion and
maloxon.

In terrestrial ecosystems, the formation of maloxon is likely to depend strongly on moisture
levels on treated surfaces, which in turn would be dependent on irrigation method used.

Irrigation techniques in Central California includes surface irrigation, micro-irrigation (drip,
bubbler, microspray, etc.), and traditional above ground sprinkler. When surface or micro-
irrigation techniques are used, the vegetation would not be wetted. In addition, vegetation would
not be wetted by rainfall very often because of the dry climate of the region. Malathion would
likely be more persistent under such conditions because of the lack of hydrolysis and the lack of
wash-off Therefore, the half-life of terrestrial residues may be somewhat longer than in the
published literature studies that yielded data estimating foliar persistence (Wellis and McDowell,
1987). Those studies were all conducted in eastern and southern states where rainfall is greater.
Thus, on sites where surface or micro-irrigation techniques are used, terrestrial residues may be
more persistent than assumed in the T-REX and T-HERPS models, resulting in greater peak
concentrations after repeated applications, and higher risk than predicted.

6.2. Effects Assessment Uncertainties

6.2.1. Data Gaps and Uncertainties

Data are not available to adequately assess the toxicity of malathion to plants. The Agency is
aware of no data that indicates malathion will significantly effect the growth and reproduction of
plants at environmentally relevant exposure levels. In addition, acceptable data for aquatic
plants were only available for nonvascular plants. One study was available on the toxicity or
malathion to a vascular aquatic plant (Sinha, Rai, and Chandra, 1995), but upon review by the
Agency the study was found to be unacceptable for use in quantitative risk assessment.

6.2.2. Use of Surrogate Species Effects Data

Guideline toxicity tests and open literature data on malathion are limited for aquatic-phase
amphibian. Available data were only for acute toxicity to frogs, which may be more or less
sensitive than salamanders. Furthermore, all available acute toxicity data for frogs were
classified as supplemental or as appropriate for only qualitative use. In addition, no data are
available on the chronic effects of malathion to aquatic-phase amphibians. Therefore, freshwater
fish are used as surrogate species for aquatic-phase amphibians and the CTS. Data available
from the open literature on malathion toxicity to aquatic-phase amphibians yielded highly
variable results (Table 4-3). The majority of the results indicated that amphibians were
considerably less sensitive than the rainbow trout. Six out of seven studies estimated 96-hr LC50
studies that were greater than that estimated for the rainbow trout and used in this assessment (33
|ig/L), These studies indicated that that acute toxicity is endpoints for aquatic-phase amphibians
are 5.2 to 330 times less sensitive than freshwater fish. One study, however, estimated an LC50
of 0.50 |ig/L (Khangarot et al., 1985), which was indicates toxicity 56 times greater than the
rainbow trout. We did not have enough confidence with this result to use it in our assessment
because too little information was available on the testing methods and apparatus used, exposure
concentrations were not provided, and several deviations from the Agency's test guidelines were

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observed. On the whole, the data for amphibians suggest that the endpoint we used based on
freshwater fish toxicity are likely to be protective of potential direct effects to aquatic-phase
amphibians including the CTS. The Agency's LOCs for listed species are intentionally set low
in part to account for possible differences in sensitivity between surrogate species and the species
being protected. Conservative estimates made in the screening level risk assessment would also
compensate for these uncertainties.

6.2.3. Sublethal Effects

In this risk assessment, risk from acute exposure was based on mortality as the assessment
endpoint. Organisms may also suffer adverse sublethal effects from acute exposure levels less
than those which produce mortality. For chronic exposure, risk was assessed based sublethal
effects, but limited to those effects that could be directly related to the assessment endpoints of
survival, growth, and reproduction of organisms. Chronic exposure may produce some sublethal
effects which were not considered in this assessment because they could not be readily
extrapolated to effects on the assessment endpoints. To the extent to which sublethal effects are
not considered in this assessment, the potential direct and indirect effects of malathion on listed
species may be underestimated.

7. Risk Conclusions

In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the information
presented in this endangered species risk assessment represents the best data currently available
to assess the potential risks of malathion to the DS and the CTS, and their designated critical
habitat.

Based on the best available information, the Agency makes a Likely to Adversely Affect (LAA)
determination for the DS and for all three DPSs of the CTS (CTS-CC, CTS-SB, and CTS-SC).
Additionally, the Agency has determined that there is potential for modification of the designated
critical habitat for the DS and CTS from the use of the chemical. Given the LAA determination
and the potential modification of designated critical habitat for the DS and CTS, a description of
the baseline status and cumulative effects is provided in Attachment 3.

A summary of the risk conclusions and effects determinations for the DS and CTS and their
critical habitat, given the uncertainties discussed in Section 6 and Attachment 1, is presented in
Table 7-1 and Table 7-2. Use specific effects determinations are provided in Table 7-3.

Table 7-1. Effects Determination Summary for Effects of Malathion on the DS and CTS

Species

Effects
Determination

Basis for Determination

Potential for Direct Effects

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Species

Effects
Determination

Basis for Determination

Delta Smelt

(Hypomesus
transpacificus)

Likely to
Adversely Affect
(LAA)

Aquatic-phase (Eggs, Larvae, and Adults):

Potential for Indirect Effects

Aquatic prey items, aquatic habitat, cover and/or primary productivity

Exposure from uses of malathion is expected to occur throughout the
entire range of the DS. Risk quotients exceed the Agency LOCs for taxa
that comprise the prey of the DS. Toxicological data indicate that use of
malathion is likely to reduce abundance of prey of the DS. Mortality was
observed in the water flea (a freshwater crustacean) and the mysid (an
estuarine/marine crustacean) with acute exposure to malathion at
concentrations much less than less than one-tenth the malathion EEC, and
reproductive impairment was predicted in the water flea (a freshwater
crustacean) and the mysid (an estuarine/marine crustacean) with chronic
exposure to malathion at concentrations much less than the chronic EEC,
as well as less than some malathion concentrations from surface water
samples taken within the range of the DS.

California Tiger
Salamander
(Ambystoma
californiense),
including Central,
Santa Barbara, and
Sonoma County
distinct population
segments

Likely to
adversely affect
(LAA)

Potential for Direct Effects

Aquatic-phase (Eggs, Larvae, and Adults):

Aquatic exposure from uses of malathion is expected to occur throughout
the entire range of the CTS, including all DPSs. Risk quotients exceed the
Agency LOCs for listed species. Mortality was observed in the rainbow
trout (a freshwater fish, surrogate for freshwater amphibians) with acute
exposure to malathion at concentrations less than less than one-twentieth
the malathion EEC, and reproductive impairment was observed in the
flagfish (a freshwater fish, surrogate for freshwater amphibians) with
acute exposure to malathion at concentrations less than less than the
chronic malathion EEC.

Terrestrial-phase (Juveniles and Adults) :

Terrestrial exposure from uses of malathion is expected to occur
throughout the entire range of the CTS, including all DPSs. Risk
quotients exceed the Agency LOCs for listed species. Mortality was
predicted for CTS (based on acute toxicity data for the ring-neck pheasant
and Japanese quail, surrogates for the CTS) at dietary concentrations less
than one-tenth the acute EEC, and reproduction impairment was predicted
for CTS (based on reproduction toxicity data for the northern bobwhite) at
dietary concentrations less than the chronic EEC.

Potential for Indirect

Aquatic prey items, aquatic habitat, cover and/or primary productivity

Aquatic exposure from uses of malathion is expected to occur throughout
the entire range of the CTS, including all DPSs. Risk quotients exceed the

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Species

Effects
Determination

Basis for Determination

Agency LOCs for taxa that comprise the prey of the CTS. Toxicological
data indicate that use of malathion is likely to reduce abundance of prey of
the CTS. Mortality was observed in the water flea (a freshwater
crustacean) with acute exposure to malathion at concentrations much less
than less than one-tenth the malathion EEC, and reproductive impairment
was predicted in the water flea (a freshwater crustacean) with chronic
exposure to malathion at concentrations much less than the chronic EEC.

Terrestrial prey items, riparian habitat

Terrestrial exposure from uses of malathion is expected to occur
throughout the entire range of the CTS, including all DPSs. Risk
quotients exceed the Agency LOCs for taxa that comprise the prey of the
CTS. Mortality was observed in the honey bee and the rat (surrogates for
terrestrial prey of the CTS) at concentrations less than one-tenth the acute
EEC, and reproduction impairment was observed in the rat at
concentrations less than the chronic EEC.

Table 7-2. Effects Determination Summary for the Critical Habitat Impact Analysis

Designated Critical
Habitat for:

Effects
Determination

Basis for Determination

Delta Smelt

(Hypomesus
transpacificus)

Habitat
Modification

Use of malathion has the potential to cause degradation of water quality in
the estuarine and freshwater habitats used by the DS.

California Tiger
Salamander
(Ambystoma
californiense),
including Central,
Santa Barbara, and

Sonoma County
distinct population
segments

Habitat
Modification

Use of malathion has the potential to cause acute and chronic effects to
small mammals, thereby potentially reducing the availability of burrows
on which the CTS depends for underground refugia.

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Table 7-3. Malathion Use-Specific Risk Summary for Delta Smelt and California Tiger
Salamander

Species HITccts

Critical llahilal

Potential lor I'.ITects

1 SC(5)

Determination

Modification

Direct

Indirect

Delta Smelt

All uses except passion
fruit, ULV application on
citrus, and ULV

LAA

Yes

Acute toxicity (all uses)
and chronic toxicity

Acute and chronic
toxicity, reduced prey
abundance, and

application for adult
mosquito control

(some uses)

degradation of water
quality

Passion fruit, ULV
application on citrus, and
ULV application for adult
mosquito control

Acute and chronic

LAA

Yes

None

toxicity, reduced prey
abundance, and
degradation of water
quality

California Tiger Salamander

All uses except ULV
application on citrus, and
ULV application for adult
mosquito control

LAA

Yes

Acute toxicity and
chronic toxicity

Acute toxicity to insects,
chronic toxicity to
mammals, acute toxicity
to mammals (some uses),
reduced prey abundance,
and reduction of mammal
burrows

ULV application on
citrus, and ULV
application for adult
mosquito control

LAA

Yes

Acute toxicity

Acute toxicity to insects
and reduced prey
abundance

Abbreviations: n/A= Not applicable; NE = No effect; NLAA = May affect, but not likely to adversely affect; LAA
= Likely to adversely affect

Based on the conclusions of this assessment, a formal consultation with the U. S. Fish and
Wildlife Service under Section 7 of the Endangered Species Act should be initiated.

When evaluating the significance of this risk assessment's direct/indirect and adverse habitat
modification effects determinations, it is important to note that pesticide exposures and predicted
risks to the species and its resources {i.e., food and habitat) are not expected to be uniform across
the action area. In fact, given the assumptions of drift and downstream transport {i.e., attenuation
with distance), pesticide exposure and associated risks to the species and its resources are
expected to decrease with increasing distance away from the treated field or site of application.
Evaluation of the implication of this non-uniform distribution of risk to the species would require
information and assessment techniques that are not currently available. Examples of such
information and methodology required for this type of analysis would include the following:

• Enhanced information on the density and distribution of DS and CTS life stages
within the action area and/or applicable designated critical habitat. This
information would allow for quantitative extrapolation of the present risk
assessment's predictions of individual effects to the proportion of the population
extant within geographical areas where those effects are predicted. Furthermore,
such population information would allow for a more comprehensive evaluation of

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the significance of potential resource impairment to individuals of the assessed
species.

• Quantitative information on prey base requirements for the assessed species.
While existing information provides a preliminary picture of the types of food
sources utilized by the assessed species, it does not establish minimal
requirements to sustain healthy individuals at varying life stages. Such
information could be used to establish biologically relevant thresholds of effects
on the prey base, and ultimately establish geographical limits to those effects.

This information could be used together with the density data discussed above to
characterize the likelihood of adverse effects to individuals.

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9. MRID List

Environmental Fate Studies

MRID 40941201 Teeter, D. (1988) Malathion (AC 6,601): Hydrolysis: Lab. Rept. No. PD-M 25-
59. Unpublished study prepared by American Cyanamid Co. 66 p.

MRID 40969301. Miller, G. (1988) Vapor Phase Photolysis of Malathion: Laboratory Report
No. PD-M-25-60. Unpublished study prepared by American Cyanamid Co. 17 p.

MRID 41345201. Blumhorst, M. (1989) Adsorption/Desorption Studies-Batch Equilibrium for
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MRID 41673001 Carpenter, M. (1990) Determination of the Photolysis Rate of (Carbon 14)-
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MRID 41695501. Dykes, J.; Kabler, K.; Allen, B. (1990) Determination of the Photolysis Rate
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MRID 41721701. Blumhorst, M. (1990) Aerobic Soil Metabolism Study of Malathion: Lab

Project Number: 135-004. Unpublished study prepared by EPL Bio-Analytical Services,
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196

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MRID 41727701. Rice, F.; Jacobson, B.; Lochhaas, C. (1990) Terrestrial Field Dissipation For
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MRID 41748901. Rice, F.; Jacobson, B.; Lochhaas, C. (1990) Terrestrial Field Dissipation for
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MRID 42015201. Spare, W.; Cutchin, W. (1991) The Volatilization of Malathion from Soil (A
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MRID 42058401. Judy, D.; Jacobson, B.; Lochhaas, C. (1991) Combined Aquatic Sediment
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MRID 42058402. Judy, D.; Jacobson, B.; Lochhaas, C. (1991) Combined Aquatic Sediment
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MRID 42216301. Blumhorst, M. (1991) Anaerobic Aquatic Metabolism Study of Malathion:
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MRID 42271601. Blumhorst, M. (1991) Aerobic Aquatic Metabolism Study of Malathion: Lab
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MRID 43042401. Jacobson, B. (1992) Supplement to: Terrestrial Field Dissipation for

Malathion in Cotton: Final Report: Lab Project Number: 38005: FS-890106. Unpublished
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MRID 43042402. Jacobson, B. (1992) Supplement to: Terrestrial Field Dissipation for

Malathion in Cotton: Lab Project Number: 38003: FA-890210. Unpublished study
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MRID 43106401. Forbis, A.; Leak, T. (1994) Uptake Depuration, and Bioconcentration of

(carbon 14)-Malathion by Bluegill Sunfish (Lepomis macrochirus) under Flow-Through
Test Conditions: Lab Project Number: 40542: XBL-92151. Unpublished study prepared
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MRID 43106402. Forbis, A.; Leak, T. (1994) Raw Data Report for: Uptake Depuration, and
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MRID 43166301. Severn, D. (1993) Overview of the Environmental Behavior of Malathion and
Response to EPA's Reviews of Malathion Environmental Fate Studies: Lab Project
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MRID 43340301. Kammerer, R.; Robinson, R. (1994) Procedure for Flow-Through Bluegill
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197

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MRID 43868601. Nixon, W. (1995) Column Leaching of (carbon 14)-Malathion in Four Soil
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MRID 46396601. Shepler, K. (2004) Hydrolysis of [(Carbon 14)] Malaoxon at pH 5, 7 and 9.

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MRID 46769501. Knoch, E. (2001) Malathion: Aerobic Soil Metabolism. Project Number:

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MRID 47834301. Saxena, A. (1998) Aerobic and Aerobic/Anaerobic Soil Metabolism of
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198

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Ecotoxicity Studies

MRID 00001999. Atkins, L., Jr.; Anderson, L.D. (1967) Toxicity of Pesticides and Other

Agricultural Chemicals to Honey Bees: Laboratory Studies. (Unpublished study received
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MRID 00022923. Hill, E.F.; Heath, R.G.; Spann, J.W.; et al. (1975) Lethal Dietary Toxicities of
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MRID 00062189. Heath, R.G.; Spann, J.W.; Hill, E.F.; et al. (1972) Comparative Dietary

Toxicities of Pesticides to Birds. By U.S. Fish and Wildlife Service, Patuxent Wildlife
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MRID 00144490. Rosenfeld, G. (1984) Acute Oral Toxicity Study in Rats: Malathion: Study
1124A. Unpublished study prepared by Cosmopolitan Safety Evaluation, Inc. 33 p.

MRID 00156311. Wellborn, T. (1971) Toxicity of some compounds to striped bass fingerlings.
The Progresive Fish Culturist: 32-36.

MRID 00159876. Kynoch, S. (1986) Acute Oral Toxicity to Rats of Malathion (Fyfanon)

Technical: 851341D/CHV 33/AC. Unpublished study prepared by Huntingdon Research
Centre Ltd. 16 p.

MRID 00159877. Kynoch, S. (1986) Acute Dermal Toxicity to Rats of Malathion (Fyfanon)

Technical: 851330D/CHV 34/AC. Unpublished study prepared by Huntingdon Research
Centre Ltd. 10 p.

MRID 00159878. Jackson, G.; Hardy, C.; Gopinath, G.; et al. (1986) Fyfanon (Malathion)
96/98% Technical: Acute Inhalation Toxicity Study in Rats 4-hour Exposure: CHV
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MRID 00160000 Hudson, R.; Tucker, R.; Haegele, M. (1984) Handbook of toxicity of pesticides
to wildlife: Second edition. US Fish and Wildlife Service: Resource Publication 153. 91
P-

MRID 05001991. Stevenson, J.H. (1978) The acute toxicity of unformulated pesticides to
worker honey bees. (Apis mellifera). Plant Pathology 27(l):38-40.

MRID 05004151 (00162751) Stevenson, J.H. (1968) Laboratory studies on the acute contact and
oral toxicities of insecticides to honeybees. Ann. appl. Biol. 61(3):467-472.

MRID 05008990. Johansen, C.; Jaycox, E.R.; Hutt, R. (1963) The Effect of Pesticides on the
Alfalfa Leafcutting Bee, Megachile rotundata. Pullman, Wash.: Washington State
University Agricultural Research Station.

MRID 05009242. Sanders, H.O. (1969) Toxicity of Pesticides to the Crustacean Gammarus

lacustris. Washington, D.C.: U.S. Bureau of Sport Fisheries and Wildlife. (U.S. Bureau of
Sport Fisheries and Wildlife technical paper 25)

MRID 40098001. Mayer, F.; Ellersieck, M. (1986) Manual of Acute Toxicity: Interpretation and
Data Base for 410 Chemicals and 66 Species of Freshwater Animals. US Fish & Wildlife
Service, Resource Publication 160. 579 p.

MRID 40228401. Mayer, F.L., 1986. Acute toxicity handbook of chemicals to estuarine
organisms. USEPA, Environmental Research Lab., Gulf Breeze, FL. EPA/600/X-
86/231. 275 pp

199

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MRID 40247202. Kynoch, S. (1986) Acute Oral Toxicity to Rats of Malathion (Fyfanon) 57:
Study No. 851340D/CHV 33/AC. Unpublished study prepared by Huntingdon Research
Centre Ltd. 21 p.

MRID 40910905. Hill, E.; Camardese, M. (1986) Lethal Dietary Toxicities of Environmental
Contaminants and Pesticides to Coturnix. USD A, FWS Technical Report 2. Washington,
D C. 3 p.

MRID 41029701. Burgess, D. (1989) Acute Flow-through Toxicity of Cythion 57% EC to
Daphnia magna: Report No. 37394. Unpublished study prepared by Analytical Bio-
Chemistry Labs Inc. 197 p.

MR TP 41174301. Bowman, J. (1989) Acute Flow-Through Toxicity of Cythion Technical to
Sheepshead Minnow (Cyprinodon variegatus): Report No. 37397. Unpublished study
prepared by Analytical Bio-chemistry Laboratories, Inc. 205 p.

MRID 41208001. Hoxter, K.; Jaber, M. (1989) Cythion Insecticide (6601 57% EC): Honey Bee
Toxicity of Residues of Foliage: Report No. 130-145. Unpublished study prepared by
Wildlife International Ltd. 55 p

MRID 41252101. Bowman, J. (1989) Acute Flow-Through Toxicity of Cythion 57% to

Sheepshead Minow (Cyprinodon variegatus): Report No. 37396. Unpublished study
prepared by Analytical Bio-Chemistry Laboratories, Inc. 245 p.

MRID 41422401. Cohle, P. (1989) Early Life Stage Toxicity of Cythion to Rainbow Trout
(Oncorhynchus mykiss) in a Flow-through System: Lab Report Number: 37400.
Unpublished study prepared by Analytical Bio-Chemistry Laboratories, Inc. 1068 p.

MRID 41474501. Forbis, A. (1990) Acute Flow-through Toxicity of Cythion Technical to
Mysid Shrimp (Mysidopsis bahia): Lab Project Number: 38414. Unpublished study
prepared by Analytical Bio-chemistry Laboratories, Inc. 184 p.

MRID 41583401. Schroeder, R. (1990) A Two-generation (Two-litters) Reproduction Study

with AC 6,601 to Rats: Laboratory Report No.: 87-3243. Unpublished study prepared by
Bio/dynamics, Inc. 2025 p.

MRID 41718401. Blakemore, G.; Burgess, D. (1990) Chronic Toxicity of Cythion to Daphnia
magna Under Flow-through Test Conditions: Lab Project Number: 37399. Unpublished
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MRID 42045401. Robbins, G. (1991) Acute Oral Toxicity in Rats: Clean Crop Malathion 8E
Insecticide: Lab Project Number: A3131. Unpublished study prepared by Cosmopolitan
Safety Evaluation, Inc. 27 p.

MRID 42249901. Wade, B.; Wisk, J. (1992) Effect of Cythion Insecticide 57 Percent EC on
New Shell Growth in the Eastern Oyster under Flow-through Conditions: Lab Project
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MRID 42782101. Pederson, C.; Fletcher, D. (1993) AC 6,601 Technnical: Toxicity and

Reproduction Study in Mallard Ducks: Lab Project Number: 90 DR 39. Unpublished
study prepared by Bio-Life Assocs. 223 p.

MRID 43072404. Kuhn, J. (1993) Acute Oral Toxicity Study in Rats: Malathion 8EC: Lab
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MRID 43501501. Beavers, J.; Haberlein, D.; Mitchell, L.; et al. (1995) Malathion: A One-

generation Reproduction Study with the Northern Bobwhite (Colinus virginianus): Lab
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220 p

200

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MRID 47540302. Gries, T.; Purghart, V. (2001) Malathion Technical: Acute Toxicity Test with
Rainbow Trout (Oncorhynchus mykiss) Under Flow-Through Conditions. Project
Number: 1005/018/108, 306/FYF. Unpublished study prepared by Springborn
Laboratories (Europe) Ag. 54 p.

MRID 47540303. Gries, T.; Purghart, V. (2001) Malathion Technical: Acute Immobilisation
Test with Daphnids (Daphnia magna) under Flow-Through Conditions: Final Report.
Project Number: 1005/018/115, 310/FYF. Unpublished study prepared by Springborn
Laboratories (Europe) Ag. 62 p

MRID 47540304. Gries, T.; Purghart, V. (2001) Malathion Technical: Acute Toxicity Test with
Bluegill Sunfish (Lepomis macrochirus) Under Flow-Through Conditions: Final Report.
Project Number: 314/FYF, 1005/018/105. Unpublished study prepared by Springborn
Laboratories (Europe) Ag. 58 p.

MRID 47540305. Gries, T.; Purghart, V. (2001) Malathion Dicarboxylic Acid: Acute

Immobilisation Test with Daphnids (Daphnia magna) Under Flow-Through Conditions:
Final Report. Project Number: 313/FYF, 1005/020/115. Unpublished study prepared by
Springborn Laboratories (Europe) Ag. 58 p.

MRID 47540306. Gries, T.; Purghart, V. (2001) Malathion Dicarboxylic Acid: Acute Toxicity
Test with BlueGill Sunfish (Lepomis macrochirus) Under Flow-Through Conditions:
Final Report. Project Number: 315/FYF, 1005/020/105. Unpublished study prepared by
Springborn Laboratories (Europe) Ag. 55 p.

MRID 47540309. Gries, T.; Purghart, V. (2001) Malathion Monocarboxylic Acid (alpha and
beta mixture): Acute Toxicity Test with Bluegill Sunfish (Lepomis macrochirus) under
Flow-Through Conditions: Final Report. Project Number: 1005/019/105, 317/FYF.
Unpublished study prepared by Springborn Laboratories (Europe) Ag. 57 p.

MRID 47540310. Gries, T.; Purghart, V. (2001) Malathion Monocarboxylic Acid (alpha and
beta mixture): Acute Immobilisation Test with daphnids (Daphnia magna) Under Flow-
Through Conditions: Final Report. Project Number: 318/FYF, 1005/019/115.
Unpublished study prepared by Springborn Laboratories (Europe) Ag. 59 p.

MRID 48078003. Anonymous (1968) Malathion Technical Toxicity to Rainbow Trout; Test
Number 105. Project Number: MB/69. Unpublished study prepared by Animal Biology
Laboratory. 13 p.

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