PR0^°
Risks of Methyl Parathion Use to Federally
Threatened California Red-legged Frog
(Rana aurora draytonii)
Pesticide Effects Determination
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
February 20, 2008
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Primary Authors
Paige D. Doelling, Ph.D., Fisheries Biologist
Stephen P.Wente, Ph.D., Biologist
Secondary Review/Certification
Thomas Steeger, Ph.D., Senior Science Advisor
Branch Chief, Environmental Risk Assessment Branch 1
Nancy Andrews, Ph.D.
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Table of Contents
1.0 Executive Summary 8
2.0 Problem Formulation 13
2.1 Purpose 13
2.2 Scope 15
2.3 Previous Assessments 16
2.4 Stressor Source and Distribution 16
2.4.1 Environmental Fate Properties 17
2.4.2 Environmental Transport Mechanisms 18
2.4.3 Mechanism of Action 19
2.4.4 Use Characterization 19
2.5 Assessed Species 23
2.5.1 Distribution 23
2.5.1.1 Recovery Units 24
2.5.1.2 Core Areas 24
2.5.1.3 Designated Critical Habitat 25
2.5.1.4 Other Known Occurrences from the CNDBB 25
2.5.2 Reproduction 27
2.5.3 Diet 27
2.5.4 Habitat 28
2.6 Action Area 29
2.7 Assessment Endpoints and Measures of Ecological Effect 38
2.7.1. Assessment Endpoints for the CRLF 38
2.8 Conceptual Model 40
2.8.1 Risk Hypotheses 40
2.8.2 Diagrams 41
2.9 Analysis Plan 45
3.0 Exposure Assessment 46
3.1 Label Application Rates and Intervals 46
3.2 Aquatic Exposure Modeling 47
3.3 Monitoring Data 51
3.3.1 Surface Water Monitoring Data 51
3.3.1.1 Summary of Individual samples 51
3.3.1.2 Summary by Sites 52
3.3.2 Ground Water Monitoring Data 54
3.3.3 Long-range Transport 54
3.3.3.1 Air Monitoring 55
3.2.3.2 Rainwater monitoring 57
3.3.3.3 Long-range Transport Summary 60
3.4 Terrestrial Exposure 61
3.4.1 Bird and Mammal Exposure (TREX) 61
3.4.2 Terrestrial Invertebrate Exposure 62
4.0 Effects Assessment 64
4.1 Aquatic Toxicity Profile 64
4.1.1 Toxicity to Freshwater Fish 65
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4.1.1.1 Acute Exposure (Mortality) Studies 65
4.1.1.2 Chronic Exposure (Growth/Reproduction) Studies 66
4.1.2 Toxicity to Aquatic-Phase Amphibians 66
4.1.2.1 Acute Exposure (Mortality) Studies 66
4.1.2.2 Studies Reporting Sub-lethal Endpoints 67
4.1.3 Toxicity to Freshwater Invertebrates 67
4.1.3.1 Acute Exposure (Mortality) Studies 67
4.1.3.2 Chronic Exposure (Growth/Reproduction) Studies 67
4.1.4 Toxicity to Aquatic Plants 68
4.2 Terrestrial Toxicity Profile 71
4.2.1 Terrestrial Vertebrates (Birds and Mammals) 72
4.2.1.1 Birds 72
4.2.1.2 Mammals 73
4.2.2 Terrestrial Invertebrates 74
4.2.3 Terrestrial Plants 75
4.3 Use of Probit Slope Response Relationship 75
4.4 Incident Database Review 77
5.0 Risk Characterizations 77
5.1 Risk Estimation 77
5.2 Risk Description 80
5.2.1 Direct Effects 80
5.2.1.1 Aquatic Phase 80
5.2.1.2 Terrestrial Phase (Adults and Juveniles) 80
5.2.2 Indirect Effects and Critical Habitat Effects (Reduction in Prey Base).... 80
5.2.2.1 Terrestrial Invertebrates 81
5.2.2.2 Terrestrial-Phase Amphibians 81
5.2.2.3 Aquatic Plants 81
5.2.2.4 Aquatic Invertebrates 81
5.2.2.5 Fish 81
5.2.3 Indirect Effects and Critical Habitat Effects (Habitat Degradation) 81
5.2.3.1 Aquatic Plants (Vascular and Non-vascular) 81
5.2.3.2 Terrestrial Plants 81
5.3 Risk Conclusions 82
6.0 Uncertainties 84
6.1 Exposure Assessment Uncertainties 84
6.1.1 Modeling Assumptions 85
6.1.2 Maximum Use Scenarios 85
6.1.3 Modeling Inputs 85
6.1.4 Aquatic Exposure Estimates 86
6.1.5 Usage Uncertainties 87
6.1.6 Action Area 87
6.2 Effects Assessment Uncertainties 89
6.2.1 Age Class and Sensitivity of Effects Thresholds 89
6.2.2 Use of Surrogate Species Data 89
6.2.3 Extrapolation of Effects 89
6.2.4 Acute LOC Assumptions 90
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6.2.5 Residue Levels Selection
6.2.6 Dietary Intake
6.2.7 Mixtures
6.2.8 Sublethal Effects
6.2.9 Location of Wildlife Species
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References
Appendix A - Fate, Exposure, and Monitoring
Appendix B - Ecological Effects Data
Appendix C - ECOTOX Bibliography
Appendix D - Risk Quotient Method and LOCs
Appendix E - Analysis Summary
Appendix F - Spatial Summary for Methyl Parathion Uses
Appendix G - Product Formulations Containing Multiple Active Ingredients
Attachment 1 - Status and Life History of the California Red-Legged Frog
Attachment 2 - California Red-legged Frog Baseline Status and Cumulative Effects
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Table of Figures
Figure 1 Methyl Parathion Usage in California by Year (Total Applied, 2002-2005).... 22
Figure 2 Methyl Parathion Usage in California by County (Total Applied, 2002-2005) 22
Figure 3 Methyl Parathion Usage in California by Crop (Total Applied, 2002-2005).... 23
Figure 4 California Red-legged Frog Distribution 26
Figure 5. CRLF Reproductive Events by Month *except those that over-winter 27
Figure 6 Land Use Categories in Relation to CRLF Locations 30
Figure 7 Combined Land Use Categories plus Spray Drift Buffer in Relation to CRLF
Locations 31
Figure 8 Extent of Potential Downstream Effects Based on Agricultural Uses 32
Figure 9 Extent of Potential Downstream Effects Based on Orchard Uses 33
Figure 10 Extent of Downstream Effects Based on Rangeland Uses 34
Figure 11 High Usage Counties (CA DPR PUR) in Relation to CRLF Locations (Fresno,
Kings, Kern, and Tulare Counties) 35
Figure 12 High Usage Counties (CA DPR PUR) in Relation to CRLF Locations
(Merced, San Joaquin, and Stanislaus Counties) 36
Figure 13 High Usage Counties (CA DPR PUR) in Relation to CRLF Locations (Butte,
Sutter, and Yuba Counties) 37
Figure 14 Conceptual Model: Direct Effects to Aquatic Phase of the California Red-
Legged Frog 42
Figure 15 Conceptual Model: Direct Effects to the Terrestrial Phase of the California
Red-legged Frog 43
Figure 16 Conceptual model: aquatic component of CRLF critical habitat 44
Figure 17. Conceptual model: terrestrial component of CRLF critical habitat 45
Figure 18 Frequency distribution of maximum surface water methyl parathion
concentrations for each site sampled in the CaDPR (a) and USGS (b) data sets 53
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Table of Tables
Table 1 Effects Determination for Methyl Parathion 11
Table 2. Physical/chemical properties of methyl parathion 17
Table 3 Active Registrations for Methyl Parathion 20
Table 4 Assessment Endpoints and Measures of Ecological Effects 39
Table 5 Application Rates for Modeling 47
Table 6 Input Parameters for Methyl Parathion PRZM Modeling 48
Table 7 Methyl Parathion EECs in the Standard EXAMS Water Body 49
Table 8 Methyl Paraoxon EECs in the Standard EXAMS Water Body 50
Table 9. Aquatic risk quotients (RQs) based the highest observed non-targeted methyl
parathion concentration in surface water 53
Table 10. Number of air masses needed to attain most sensitive toxicity endpoints in the
aquatic toxicity profile for methyl parathion assuming different levels of deposition or
rainfall washout 56
Table 11. Number of air masses needed to attain most sensitive toxicity endpoints in the
aquatic toxicity profile for methyl paraoxon assuming different levels of deposition or
rainfall washout 57
Table 12. One-in-10 year peak estimates of methyl parathion concentrations in aquatic
and terrestrial habitats resulting from deposition of methyl parathion at low (0.194 (J,g/L),
medium (2.77 (J,g/L), and high (22.9 (^g/L) concentration in rain estimates 58
Table 13. Aquatic risk quotients (RQs) solely due to long-range atmospheric transport
and subsequent deposition of methyl parathion in rainwater 59
Table 14. Aquatic risk quotients (RQs) solely due to long-range atmospheric transport
and subsequent deposition of methyl paraoxon in rainwater 60
Table 15 Input Parameters for T-REX 62
Table 16 EECs for Dietary- and Dose-based Exposures 62
Table 17 Terrestrial Invertebrate Exposure 63
Table 18 Aquatic Toxicity Profile for Methyl Parathion 65
Table 19 Aquatic Toxicity Profile for Methyl Paraoxon 69
Table 20 Aquatic Toxicity Profile for Degradate 4-nitrophenol 70
Table 21 Terrestrial Toxicity Profile for Methyl parathion 71
Table 22 Probability of Individual Effects 76
Table 23 Risk Quotients for Direct and Indirect Effects on Aquatic-Phase CRLF 78
Table 24 Risk Quotients for Direct and Indirect Effects on theTerrestrial-Phase CRLF. 79
Table 25 Effects Determination for Methyl Parathion 82
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1.0 Executive Summary
This ecological risk assessment evaluates the potential for the use of the insecticide
methyl parathion (PC#053501) to directly or indirectly affect the California red-legged
frog (Rana aurora draytonii), and/or modify its designated critical habitat. The
California red-legged frog was Federally listed as a threatened species by USFWS
effective June 24, 1996 (USFWS 1996). It is one of two subspecies of the red-legged
frog and is the largest native frog in the western United States (USFWS 2002). Final
critical habitat for the CRLF was designated by USFWS on April 13, 2006 (USFWS
2006; 71 FR 19244-19346). The frog is endemic to California and Baja California
(Mexico) and historically inhabited 46 counties in California, including the Central
Valley and both the coastal and interior mountain ranges (USFWS 1996). Its range has
been reduced by approximately 70%, and it currently inhabits 22 counties in California
(USFWS 1996). This assessment is being undertaken consistent with the settlement for
the court case Center for Biological Diversity (CBD) us. EPA et al. (Case No. 02-1580-
JSW(JL)) and in accordance with the U.S. Fish and Wildlife Service (USFWS) and
National Marine Fisheries Service (NMFS) Endangered Species Consultation Handbook
(USFWS/NMFS, 1998) and procedures outlined in the Agency's Overview Document
(U.S. EPA, 2004).
Seven active registrations currently regulate the use of methyl parathion in California.
Current registrations are limited to orchards (walnuts), agricultural crops, and grass used
as hay, pasture, or forage. It is marketed in two formulations: a microencapsulated liquid
formulation, and an emulsifiable concentrate. Methyl parathion can be applied aerially or
by ground boom, and although chemigation is permitted in other locations, it is
prohibited in California. Methyl parathion is a restricted use pesticide, and may only be
used by certified applicators. There are no residential uses.
Based on data reported in the CDPR PUR database, use of methyl parathion in California
has increased in the period (2002-2005) for which data are available. In this period, total
use of approximately 292,000 lbs was reported. In all years, the dominant use was on
walnuts (94% of all applied). The only other uses accounting for >1% of reported were
corn (5%>) and onions (1%). Of the total applied, 75% was used in only 4 counties
(Tulare, San Joaquin, Stanislaus, and Kings), with an additional 7 counties accounting for
another 24% of reported use.
Methyl parathion is an insecticide, acting via acetylcholinesterase inhibition. In general,
it is acutely toxic to animals, and effects are evident soon after exposure. It is toxic via
both ingestion and dermal contact. In cases where it does not cause mortality, sub-lethal
effects include disorientation and behavioral changes that may increase susceptibility to
predation and/or modify parenting patterns (e.g., nest abandonment in birds). Based on
available, acceptable data, methyl parathion is classified as moderately toxic to fish and
very highly toxic to aquatic invertebrates on an acute basis. Based on acute oral and
subacute dietary toxicity test results, it is classified as very highly toxic to birds and
mammals on an acute and subacute exposure basis. It is also classified as highly toxic to
bees on both an oral and contact basis.
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Methyl parathion is mobile to relatively mobile in soil, but degrades rapidly (ti/2 <5 days)
in both soil and water. Photodegradation (ti/2 = 49 hours) is a relatively rapid dissipation
route in aquatic systems, but may be limited due to light attenuation with depth and
turbidity in most natural waters. The major degradation product (>10% of applied) of
methyl parathion is 4-nitrophenol. Methyl paraoxon is a minor (2.1% of applied), toxic
degradate of methyl parathion, formed under oxidizing conditions in water and on leaf
surfaces. The oxon appears to be as toxic to aquatic invertebrates as the parent, although
the data are extremely limited. The transformation product, 4-nitrophenol, appears to be
less toxic than either the parent or methyl paraoxon.
The Henry's Law constant (6.12 x 10"7) value available for methyl parathion would
indicate very limited volatility. However, the concentrations found in air and rainwater
monitoring data may be sufficient to affect aquatic macroinvertebrates (Section 3.3.3).
Estimated environmental concentrations (EECs) for surface water were derived using
PRZM-EXAMS and the Rice Water Quality Model. Peak l-in-10 year EECs for methyl
parathion ranged from 4.2 |j,g/L to 66.8 |_ig/L. Peak l-in-10 year EECs for methyl
paraoxon ranged from 0.09 |j,g/L to 1.40 |_ig/L. Available water monitoring data for
California were analyzed. The highest measured concentration of methyl parathion
(0.524 |J,g/L) was an order of magnitude lower than modeled peak or chronic
concentrations. In the subset of samples analyzed for methyl paraoxon, none had
concentrations above instrument detection limits, which ranged from 0.02-0.05 |_ig/L.
Risk quotients (RQs) were calculated for the three different land use classes evaluated
(orchards, agricultural lands, and rangeland). For the aquatic phase, which considers
effects on frog eggs, larvae, tadpoles, juveniles, and adults, there were no Level of
Concern (LOC) exceedances for the surrogate taxa (fish) representing aquatic-phase
amphibians except for direct applications to water for use on rice. In the evaluation of
aquatic prey items, there were no LOC exceedances for fish/aquatic-phase amphibians
except for use on rice. For aquatic invertebrates, both acute and chronic RQs exceeded
LOCs for all land uses. Acute RQs for the invertebrates ranged from 9.7 to 69 (LOC=
0.05). Chronic RQs ranged from 13 to 35 (LOC=1.0). There were no LOC exceedances
for aquatic plants. Based on the data available, it appears that detrimental effects on
terrestrial plants are unlikely to occur at a distance >30 ft away from the application site,
even at the highest application rate.
Evaluation of potential impacts on the terrestrial- phase CRLF included analysis of direct
effects on the frog itself (juveniles and adults); and evaluation of indirect effects and/or
modification of critical habitat on the terrestrial-phase frogs by a reduction in prey items
(terrestrial invertebrates, small mammals, and frogs) or modification of the terrestrial
plant community supporting the frog population. For all land uses, acute and chronic
RQs for the frog itself exceeded acute and chronic risk LOCs. Acute RQs ranged from
15-88 (LOC=0.1) for direct effects to terrestrial phase CRLF. RQs for all prey items
evaluated also exceeded the acute risk LOCs (RQ range 15-233, LOCs 0.05 for terrestrial
invertebrates, 0.1 for all other organisms). Based on the data available, it appears that
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detrimental effects on terrestrial plants are unlikely to occur at a distance >30 ft away
from the application site, even at the highest application rate.
Organophosphate pesticides, including methyl parathion, have been documented to cause
sublethal effects including disorientation and behavioral modifications. Currently, no
data are available to establish a lower bound for these types of effects relative to methyl
parathion, thus the Agency has not attempted to delineate a zone of effects around the
various land use classes.
After completing the analysis of the effects of methyl parathion on the Federally-listed
threatened California red-legged frog in accordance with methods delineated in the
Overview Document (USEPA 2004), the Agency concludes that the use of methyl
parathion as currently registered may affect, and is likely to adversely affect (LAA) the
California red-legged frog, based on direct effects on juvenile and adult frogs and indirect
effects on both the aquatic and terrestrial prey base. The Agency also concludes these
potential effects on prey base primary constitute elements and therefore, determines
habitat modification (HM) to designated critical habitat. Rationale for each component
assessed is provided in Table 1.
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Table 1 Effects Determination for Methyl Parathion
Assessment
Endpoint
Effects determination
Basis for Determination
Aquatic-Phase CRLF
(Eggs, larvae, tadpoles, juveniles, and adults)3
Direct Effects
1. Survival,
growth, and
reproduction of
CRLF
No effect
(use on rice is an LAA)
No exceedances of acute or chronic LOCs for
surrogate organisms representing the aquatic-
phase CRLF except for use on rice where both
acute and chronic risk LOCs are exceeded.
Indirect Effects and Critical Habitat Effects
2. Reduction or
modification of
aquatic prey
base
May affect
Likely to adversely affect
Modification of critical
habitat
Acute and chronic exceedances for aquatic
invertebrates for all land uses assessed.
Anticipated effects on aquatic prey base.
3. Reduction or
modification of
aquatic plant
community
No effect
No LOC exceedances for aquatic plants.
4. Degradation
of riparian
vegetation
May affect
Not likely to adversely
affect
(Discountable)
Based on available data, detrimental effects of a
sufficient magnitude to cause take of CRLF due
to effects on these plants appear unlikely.
Terrestrial-Phase CRLF
(Juveniles and Adults)
Direct Effects
5. Survival,
growth, and
reproduction of
CRLF
May affect
Likely to adversely affect
Acute and chronic LOC exceedances for both
adults and juveniles based on both T-REX and T-
HERPS estimates for all land use categories.
Indirect Effects and Critical Habitat Effects
6. Reduction or
modification of
terrestrial prey
base
May affect
Likely to adversely affect
Modification of critical
habitat
Acute and chronic LOC exceedances for all prey
categories for all land use categories.
7. Degradation
of riparian and/or
upland
vegetation
May affect
Not likely to adversely
affect
(Discountable)
Based on available data, detrimental effects of a
sufficient magnitude to cause take of CRLF due
to effects on these plants appear unlikely.
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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 CRLF life stages
within specific recovery units and/or designated critical habitat within the
action area. 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 species.
• Quantitative information on prey base requirements for individual aquatic-
and terrestrial-phase frogs. While existing information provides a
preliminary picture of the types of food sources utilized by the frog, 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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2.0 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 (U.S. EPA 1998), the
Services' Endangered Species Consultation Handbook (USFWS/NMFS 1998) and EPA's
methodologies as described in the Overview Document (U.S. EPA 2004) and reviewed
by the U.S. Fish and Wildlife Service and National Marine Fisheries Service
(USFWS/NMFS 2004).
2.1 Purpose
The purpose of this endangered species assessment is to evaluate potential direct and
indirect effects on individuals of the federally threatened California red-legged frog
(Rana aurora draytonii) (CRLF) arising from FIFRA regulatory actions regarding use of
methyl parathion on agricultural crops grown in the state of California. Crops for which
methyl parathion is currently registered include walnuts, corn, onions, rice, and grass (for
forage). This assessment also evaluates whether use on these crops is expected to result
in the degradation of the species' critical habitat. This ecological risk assessment has
been prepared consistent with a settlement agreement in the case Center for Biological
Diversity (CBD) vs. EPA etal. (Case No. 02-1580-JSW(JL)) settlement entered in
Federal District Court for the Northern District of California on October 20, 2006.
In this assessment, direct and indirect effects to the CRLF and potential modification of
its critical habitat are evaluated in accordance with the methods described in the
Agency's Overview Document (U.S. EPA 2004). Screening level methods include use of
standard models such as Pesticide Root Zone Model-Exposure Analysis Model System
(PRZM-EXAMS), Terrestrial Exposure (TREX) model, Terrestrial Plant model
(TerrPlant), AgDrift, and AgDisp, all of which are described at length in the Overview
Document. Additional refinements include a modification of TREX (THERPS) to
evaluate effects on terrestrial-phase frogs, an analysis of the usage data, and a spatial
analysis. Use of such information is consistent with the methodology described in the
Overview Document (U.S. EPA 2004), which specifies that "the assessment process may,
on a case-by-case basis, incorporate additional methods, models, and lines of evidence
that EPA finds technically appropriate for risk management objectives" (Section V, page
31 of U.S. EPA 2004).
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 methyl parathion is based on an action area. The action area is the area
directly or indirectly affected by the federal action, as indicated by the exceedance of
OPP's Levels of Concern (LOCs). It is acknowledged that the action area for a national-
level FIFRA regulatory decision associated with a use of methyl parathion may
potentially involve numerous areas throughout the United States and its Territories.
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However, for the purposes of this assessment, attention will be focused on the section of
the action area, intersecting with 1) locations where CLRF is known to occur1, 2)
currently occupied core areas for the CLRF2, and 3) designated critical habitat.
As part of the "effects determination," one of the following three conclusions will be
reached regarding the potential use of methyl parathion in accordance with current labels:
• "No effect";
• "May affect, but not likely to adversely affect"; or
• "May affect and likely to adversely affect".
Designated critical habitat identifies specific areas that have the physical and biological
features, (known as primary constituent elements or PCEs) essential to the conservation
of the listed species. The PCEs for CRLFs are aquatic and upland areas where suitable
breeding and non-breeding aquatic habitat is located, interspersed with upland foraging
and dispersal habitat.
If the results of initial screening-level assessment methods show no direct or indirect
effects (no LOC exceedances) upon individual CRLFs or upon the PCEs of the species'
designated critical habitat, a "no effect" determination is made for use of methyl
parathion as it relates to this species and its designated critical habitat. If, however, direct
or indirect effects to individual CRLFs are anticipated and/or effects may impact the
PCEs of the CRLF's designated critical habitat, a preliminary "may affect" determination
is made for the FIFRA regulatory action(s) regarding methyl parathion.
If a determination is made that use of methyl parathion within the action area(s)
associated with the CRLF "may affect" this species and/or its designated critical habitat,
additional information is considered to refine the potential for exposure and for effects to
the CRLF and other taxonomic groups upon which these species depend (e.g., aquatic
and terrestrial vertebrates and invertebrates, aquatic plants, riparian vegetation, etc.).
Additional information, including spatial analysis (to determine the geographical
proximity of CRLF habitat and methyl parathion use sites) and further evaluation of the
potential impact of methyl parathion on the PCEs is also used to determine whether
destruction or modification of designated critical habitat may occur. Based on the refined
information, the Agency uses the best available information to distinguish those actions
that "may affect, but are not likely to adversely affect" from those actions that "may
affect and are likely to adversely affect" the CRLF and/or the PCEs of its designated
critical habitat. This information is presented as part of the Risk Characterization in
Section 5 of this document.
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 critical habitat.
Because methyl parathion is expected to directly impact living organisms within the
action area (defined in Section 2.7), critical habitat analysis for methyl parathion is
1 As documented in the California Natural Diversity Database (CNDDB)
2 As described in the recovery plan.
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limited in a practical sense to those PCEs of critical habitat that are biological or that can
be reasonably linked to biologically-mediated processes. Activities that may destroy or
modify critical habitat are those that alter the PCEs and appreciably diminish the value of
the habitat. Evaluation of actions related to use of methyl parathion that may alter the
PCEs of the CRLF's critical habitat form the basis of the critical habitat impact analysis.
Actions that may affect the CRLF's designated critical habitat have been identified by the
Services and are discussed further in Section 2.6.
2.2 Scope
Methyl parathion (CAS Registry # and 298-00-0), is an organophosphate insecticide
currently registered in the U.S. for agricultural uses only, on a relatively small number of
crops. An analysis of usage patterns in California indicates the dominant use is in walnut
orchards. There are no homeowner, public health, or veterinary use registrations at the
time of this assessment. Methyl parathion is formulated in two ways, as an emulsifiable
concentrate, and in a microencapsulated form. Both are applied to crops as a liquid.
Existing data indicate toxicity of the two forms is similar, and the most sensitive
endpoints, regardless of formulation, are used in this assessment. In the environment,
methyl parathion has two degradates that are of toxicological concern; methyl paraoxon,
which has the same mode of action as the parent, and 4-nitrophenol, which acts as a polar
narcotic. These degradates are considered in this assessment. The scope of this
assessment includes exposure and effects modeling for the active ingredient methyl
parathion.
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, they
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
2004).
Methyl parathion has registered products that contain multiple active ingredients.
Analysis of the available open literature and acute oral mammalian LD50 data for multiple
active ingredient products relative to the single active ingredient is provided in Appendix
G. The results of this analysis show that an assessment based on the toxicity of the single
active ingredient of methyl parathion is appropriate. This current registration includes the
active ingredient malathion, also an organophosphate insecticide. As both chemicals
have a similar mode of action, toxicity for this formulation is expected to be additive
(Appendix G).
The end result of the EPA pesticide registration process (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
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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 methyl parathion in accordance with the approved product labels for
California is "the action" being assessed.
Although current registrations for methyl parathion allow for use nationwide, this
ecological risk assessment and effects determination addresses currently registered uses
of methyl parathion in portions of the action area that are reasonably assumed to be
biologically relevant to the CRLF and its designated critical habitat.3
2.3 Previous Assessments
The ecological risk assessment developed for the re-registration of methyl parathion
concluded that acute and chronic effects on birds and mammals, acute effects on bees,
and acute and chronic effects on aquatic invertebrates were likely to occur as a result of
methyl parathion use. The 2004 evaluation of methyl parathion effects on Pacific
salmonids concluded "some methyl parathion uses may affect 9 listed Pacific salmon and
steelhead evolutionarily significant units (ESUs); may affect but are not likely to
adversely affect 12 listed Pacific salmon and steelhead ESUs; and methyl parathion use
will have no effect on the remaining five ESUs." (USEPA 2004a)
2.4 Stressor Source and Distribution
Methyl parathion has specific properties and uses which help delineate when and where
the active ingredient and/or any impurities/degradates may co-occur temporally and
spatially with the CRLF with sufficient intensity (sufficient concentration) to affect the
CRLF. The parent methyl parathion, a highly toxic but minor (2.1% of applied)
degradate, methyl paraoxon, and a major (-10% of applied) but less toxic degradate, 4-
nitrophenol, are included in this risk assessment. Appendix A summarizes fate data
discussed in the RED (USEPA 2006).
The basic physical and chemical properties and structure of methyl parathion are
presented in Table 2. Methyl paraoxon differs structurally from methyl parathion by the
substitution of a double-bonded oxygen to phosphorus in place of the double-bonded
sulfur (identified by red box in chemical structure diagram) and has a slightly lower
molecular weight of 247.19 g/mole. Throughout this assessment many of the properties
of methyl parathion are assumed to apply to methyl paraoxon due to the similarities in
chemical structure. These assumptions are necessary due to the dearth of information on
methyl paraoxon relative to the amount of information available for methyl parathion.
3 Technical labels also exist, which may include crops not listed on end use labels. Technical products are
used to make formulated end use products. Because these technicals cannot be applied directly, use sites
on these labels are not considered at part of the Federal action.
16
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Table 2. Physical/chemical properties of methyl parathion.
Physical/Chemical
Properties
Value/Description
Chemical Structure
Common Name
Methyl Parathion
0
1
CHj
Chemical Name:
0,0-dimethyl O-p-
nitrophenyl
phosphorothioate
CAS No.
298-00-0
PC Code
053501
Molecular formula
C8H10O5NPS
Molecular weight
265 g/mole
Physical state
White crystalline solid
Melting point
35-36 °C
Boiling Point
decomposes rapidly
above 100 degrees °C
Bulk Density
1.358 g/mL at 25 °C
Henry's Law Constant
(20 °C)
6.12 x 10"' atm. mVmole
Solubility (20 °C)
60 mg/l water
2.4.1 Environmental Fate Properties
The environmental fate assessment for methyl parathion is based on acceptable and
supplemental data. Although the weight of evidence from supplemental data and open
literature suggest that methyl paraoxon is not formed in aerobic soil environments, a
common uncertainty in the metabolism studies was the inability to identify all
degradation products of methyl parathion.
The major routes of dissipation for methyl parathion are microbial degradation, aqueous
photolysis, hydrolysis, and partitioning onto soil organic matter. Methyl parathion
degrades rapidly (ti/2 < 5 days) in soil and water through (aerobic and anaerobic)
microbial degradation. It also is expected to photodegrade (ti/2 = 49 hours) in aquatic
environments. Other degradation processes appear to be less important routes of methyl
parathion dissipation. Methyl parathion slowly hydrolyzed (ti/2 = 68 days at pH 5, ti/2 =
40 days at pH 7, ty2 = 33 days at pH 9) in buffer solutions and slowly photodegraded (ti/2
= 61 days) on soil surfaces.
The major (>10% of applied) degradation product of methyl parathion is 4-nitrophenol.
This degradate is formed through the hydrolytic cleavage of nitrophenyl C-O-P bond.
Other minor degradates (<10% of applied) that have been found in laboratory studies
include methyl paraoxon, monodesmethyl parathion, phosphorothioic acid, 0,S-dimethyl
o-(4-nitrophenyl)ester, nitrophenyl phosphoric acid, mono (4-nitrophenyl) ester and CO2.
Of these, only methyl paraoxon is included in EPA Health Effects Division's (HED's)
tolerance expression. Methyl paraoxon has only been detected (2.1% of applied) in an
anaerobic aquatic metabolism study (MRID 41768901). (A later acceptable anaerobic
aquatic metabolism study, MRID 46997601, did not identify methyl paraoxon, but was
unable to characterize several degradates that were <4% of applied.) The oxon is formed
through a desulfonation (P=S to P=0) reaction. It should be noted, however, that the
amount of methyl paraoxon derived by aerobic soil metabolism is not clear at this time.
17
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In addition, analyses for methyl paraoxon in two field dissipation studies (no oxon found)
are questionable because of storage stability issues.
Methyl parathion is mobile to relatively mobile in soil. However, the low persistence of
methyl parathion is expected to limit the extent of off-site movement. Supplemental data
on parent methyl parathion indicate that it is very mobile to somewhat mobile [Kocs =
230-to-670 1/kg] in mineral soils. There is uncertainty in these results since the soils used
in the batch equilibrium experiment were sterilized by autoclaving. Another route of
dissipation is the secondary movement through volatilization of methyl parathion from
soil and leaf surfaces. Although laboratory studies seem to indicate that methyl parathion
volatilization is not a major route of dissipation, methyl parathion has been detected in air
and rain samples across the United States. These detections appear to be correlated to use
on cotton, soybeans, wheat, and tobacco.
Methyl parathion, formulated as an emulsifiable concentrate (EC), dissipated rapidly (<1
day) in a field dissipation study performed in a cotton field in California. Methyl
parathion was not detected below 4 inches.
Acceptable field studies have not been performed using the microencapsulated
formulation Penncap-M.
2.4.2 Environmental Transport Mechanisms
Potential transport mechanisms include pesticide surface water runoff, spray drift, and
secondary drift of volatilized or soil-bound residues leading to deposition onto nearby or
more distant ecosystems. Surface water runoff and spray drift are expected to be the
major routes of exposure for methyl parathion.
A number of studies have documented atmospheric transport and re-deposition of
pesticides from California's Central Valley to the Sierra Nevada Mountains (Fellers et al.,
2004, Sparling et al., 2001, LeNoir et al., 1999, and McConnell et al., 1998). Prevailing
winds blow across the Central Valley eastward to the Sierra Nevada Mountains,
transporting airborne industrial and agricultural pollutants into the Sierra Nevada
ecosystems (Fellers et al., 2004, LeNoir et al., 1999, and McConnell et al., 1998).
Several sections of critical habitat for the CLRF are located east of the Central Valley.
The magnitude of transport via secondary drift depends on the methyl parathion'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 methyl parathion 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 Mountains are considered in evaluating
the potential for atmospheric transport of methyl parathion to locations where it could
impact the CRLF.
In general, deposition of drifting or volatilized pesticides is expected to be greatest close
to the site of application. Computer models of spray drift (AgDRIFT and AGDISP) are
18
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used to determine potential exposures to aquatic and terrestrial organisms. Methyl
parathion is most toxic to terrestrial invertebrates (primarily insects), thus the distance of
potential impact away from the use sites (action area) is determined by the distance
required to fall below the LOC for these organisms.
2.4.3
2.4.3 Mechanism of A ction
Methyl parathion is an acetylcholinesterase (AChE) inhibitor. AChE is the enzyme
responsible for deactivating acetylcholinesterase, the enzyme which modulates the
chemical signals across cholinergic nerve synapses. The specific reaction between the
pesticide and the enzyme results in binding to the active site of the enzyme (a serine
hydroxyl group), leaving the enzyme inactivated (Ecobichon 1996). For
organophosphorus compounds, this reaction is close to irreversible, and normal response
in the organism does not resume until new AChE has been synthesized. Absence of
AChE results in continuous firing of the cholinergic nerve synapses. Typical symptoms
of exposure include loss of coordination, dizziness, tremors, confusion, and depressed
respiration (Kamrin 1997). Sublethal effects in wildlife may be exhibited as changes in
behavior, including reduced predator avoidance, general disorientation, and decreased
parental caretaking. Methyl parathion may affect organism via ingestion, inhalation, or
dermal contact. Effects are transitory in nature, and organisms which survive often
appear to recover. In mammalian systems, methyl parathion is metabolized and is then
excreted by the kidneys. It does not bioaccumulate, and transformation is relatively
rapid. (Kamrin 1997, Hill 1995).
2.4.4 Use Characterization
Based on a search of active registrations (all types) in EPA's data base (OPPIN, 9/20/07,
PDB), and coordination with the Registration Division (RD) and the Special Review and
Re-registration Division (SRRD), 7 active registrations were identified that currently
regulate the use of methyl parathion in California (Table 1). Other restrictions may be
levied at a state, county, or regional level, but those restrictions are not a part of the
federal action, and are not considered in this assessment. One of the registrations is a
formulation intermediate, and has no registered crop uses. Two labels are the subject of
voluntary cancellation requests (VCR) by the registrants, and are included in the
assessment, although their use is anticipated to be phased-out in the near future. Two
formulations exist: a microencapsulated liquid formulation, and an emulsifiable
concentrate.
19
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Table 3 Active Registrations for Methyl Parathion
Registration
Number
(Type)
Label Date
Name
Registrant
Form
Percent
Active
Ingredient
Additional
Active
Ingredients
4581-393
(Section 3)
9/24/07
Penncap-M
Microencapsulated
Insecticide
Cerexagri,
Inc.
Microencapsulated
20.9%
No
4787-33
(Section 3)
Cheminova Methyl
Parathion
Technical
Cheminova
A/S
Formulation
Intermediate
77%
No
4787-48
(Section 3)
8/28/07
Declare
Cheminova
A/S
Emulsifiable
Concentrate
43.4%
No
5905-533
(Section 3)
VCR 9/20/07
4 lb Methyl
Parathion
Helena
Chemical
Co.
Emusifiable
Concentrate
43.4%
No
5905-534
(Section 3)
VCR 3/16/05
Malathion-Methyl
Parathion
Emusifiable Liquid
Helena
Chemical
Co.
Emusifiable
Concentrate
38.44%
Malathion
39.94%
67760-43
(Section 3)
8/28/07
Cheminova Methyl
Parathion 4EC
Cheminova,
Inc.
Emusifiable
Concentrate
43.8%
No
4581-393
(SLNCA000001)
9/24/07
Penncap-M
Microencapsulated
Insecticide
Cerexagri,
Inc.
Microencapsulated
20.9%
No
Methyl parathion can be applied aerially or by ground boom, and although chemigation is
permitted in other locations, it is prohibited in California. It is a restricted use pesticide,
and may only be used by or under the direct supervision of a certified applicator. Current
registrations are limited to agricultural crops, orchards (walnuts only) and grass used as
hay, pasture, or forage. Agricultural crops for which it is registered include: corn, cotton,
legumes (soybeans, dried peas), cereals (wheat, oats, barley, rye, rapeseed), sunflowers,
onions, sugar beets, potatoes, rice, and alfalfa. Because agricultural crops, orchards, and
rangeland (grass used as hay, pasture, or forage) are different land classes in the National
Land Cover Data (NLCD) (http://landcover.usgs.gov/), and their proximity to CRLF
habitat is somewhat different, they have been addressed separately. Application rates for
agricultural crops range from 0.5 pounds of active ingredient per acre (lb a.i/A) for
onions to 3.0 lb a.i/A for cotton, so these two crops are used in the assessment as lower
and upper bound estimates for the agricultural lands.
The Office of Pesticides Programs' Biological and Economic Analysis Division (BEAD)
provides an analysis of both national- and county-level usage information using state-
level usage data obtained from USDA-NASS4, Doane5, and the California's Department
4 United States Department 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.usda.gOv/nass/pubs/estindxl.htm#agchem.
5 (www.doane.com: the full dataset is not provided due to its proprietary nature)
20
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of Pesticide Regulation Pesticide Use Reporting (CDPR PUR) database6. CDPR PUR is
considered a more comprehensive source of usage data than USDA-NASS or proprietary
databases used by EPA, and thus the usage data reported by county in this assessment
were generated using CDPR PUR data. From the CDPR PUR data, BEAD generated
summaries of average and total methyl parathion usage by year, county, and crop for the
years 2002-2005 (the most recent and best available data). Total usage is shown in
Figures 1-3.
Some uses reported in the CDPR PUR database may be different than those considered in
the assessment. The uses considered in this risk assessment represent currently registered
uses according to a review of all current labels by OPP/BEAD and OPP/SRRD. No other
uses are relevant to this assessment. Any reported uses in the CA DPR database that do
not reflect current labeled uses may represent either historic uses that have been canceled,
misreported uses, or cases of misuse. Historic uses, misreported uses, and misuse are not
considered part of the federal action and, therefore, are not considered in this assessment.
Based on data reported in the CDPR PUR database, use of methyl parathion in California
has increased in the period (2002-2005). In this period, total use of approximately
292,000 pounds of active ingredient was reported. Use of approximately 56,000 lbs a.i
was reported in 2002. Total pounds applied ranged from approximately 75,000-83,000
lbs a.i in 2003-2005. In all years, the dominant use was on walnuts (94% of all applied
from 2002-2005). The only other uses accounting for >1% of reported were corn (5%)
and onions (1%). Of the total applied, 75% was used in only 4 counties (Tulare, San
Joaquin, Stanislaus, and Kings), with 7 other counties accounting for an additional 24%
of reported use.
6 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.
21
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Figure 1 Methyl Parathion Usage in California by Year (Total Applied, 2002-2005)
80,000 i
70,000 -
60.000 -
"5 50.000 -
40.000 -
» 30.000 -
20.000 -
10.000 -
III!
Tulare San Stanislaus Kings Butte Fresno Sutter Contra Yuba Merced Kern Others
Joaquin Costa
County
Figure 2 Methyl Parathion Usage in California by County (Total Applied, 2002-2005)
22
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Walnut
Corn Onion
Crop
Others
Figure 3 Methyl Parathion Usage in California by Crop (Total Applied, 2002-2005)
2.5 Assessed Species
The California red-legged frog was federally listed as a threatened species by USFWS
effective June 24, 1996 (USFWS 1996). It is one of two subspecies of the red-legged
frog and is the largest native frog in the western United States (USFWS 2002). Final
critical habitat for the CRLF was designated by USFWS on April 13, 2006 (USFWS
2006; 71 FR 19244-19346). A brief discussion of distribution, reproduction, diet, and
habitat requirements follows, with more detailed information provided in Attachment 1.
2.5.1 Distribution
The frog is endemic to California and Baja California (Mexico) and historically inhabited
46 counties in California, including the Central Valley and both the coastal and interior
mountain ranges (USFWS 1996). Its range has been reduced by approximately 70%, and
it currently inhabits 22 counties in California (USFWS 1996). The species has an
elevational range of near sea level to 1,500 meters (5,200 feet) (Jennings and Hayes
1994); however, nearly all of the known populations have been documented below 1,050
meters (3,500 feet) (USFWS 2002).
Populations currently exist along the northern California coast, northern Transverse
Ranges (USFWS 2002), foothills of the Sierra Nevada (5-6 populations), and in southern
California south of Santa Barbara (two populations) (Fellers 2005a). A total of 243
streams or drainages are believed to be currently occupied by the species, with the
23
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greatest numbers in Monterey, San Luis Obispo, and Santa Barbara counties (USFWS
1996). Occupied drainages or watersheds include all bodies of water that support CRLFs
(i.e., streams, creeks, tributaries, associated natural and artificial ponds, and adjacent
drainages), and habitats through which CRLFs can move {i.e., riparian vegetation,
uplands) (USFWS 2002).
The distribution of CRLFs within California is addressed in this assessment using four
categories of location. Three of these categories were designated by the USFWS in the
recovery plan (recovery units, core areas, and designated critical habitat). The fourth
category is known occurrences as reported in the California Natural Diversity Database
(CNDDB) (Figure 4). Recovery units are large areas defined at the watershed level that
have similar conservation needs and management strategies. The recovery unit is
primarily an administrative designation, and land area within the recovery unit boundary
is not exclusively CRLF habitat. Core areas are smaller areas within the recovery units
that comprise portions of the species' historic and current range and have been
determined by USFWS to be important in the preservation of the species. Designated
critical habitat is generally contained within the core areas, although a number of critical
habitat units are outside the boundaries of core areas, but within the boundaries of the
recovery units. Additional information on CRLF occurrences from the CNDDB is used
to cover the current range of the species not included in core areas and/or designated
critical habitat, but within the recovery units. For purposes of this assessment, designated
critical habitat, currently occupied (post-1985) core areas, and additional known
occurrences of the CRLF from the CNDDB are considered the range of the species.
2.5.1.1 Recovery Units
Eight recovery units have been established by USFWS for the CRLF. These areas are
considered essential to the recovery of the species. The status of the CRLF "may be
considered within the smaller scale of the recovery units, as opposed to the statewide
range" (USFWS 2002). Recovery units reflect areas with similar conservation needs and
population status, and therefore, similar recovery goals. The eight recovery units are
delineated by watershed boundaries defined by US Geological Survey hydrologic units
and are limited to an elevational maximum for the species of 1,500 m above sea level.
2.5.1.2 Core Areas
USFWS has designated 35 core areas in which to focus recovery efforts. The core areas,
which are distributed throughout portions of the historic and current range of the species,
are intended to provide for long-term viability of existing populations and
reestablishment of populations within historic range. These areas were selected because
they: 1) contain existing viable populations; or 2) they contribute to the connectivity of
other habitat areas (USFWS 2002). Core area protection and enhancement are vital for
maintenance and expansion of the CRLF's distribution and population throughout its
range.
24
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2.5.1.3 Designated Critical Habitat
Critical habitat was designated for the CRLF on April 13, 2006 (USFWS 2006; 71 FR
19244-19346). Critical habitat was selected for the species based on areas: 1) that are
occupied by CRLFs; 2) where source populations of CRLFs occur; 3) that provide
connectivity between source populations; and 4) that are ecologically significant.
Designation of critical habitat is based on habitat areas that provide essential life cycle
needs of the species or areas that contain primary constituent elements (PCEs) (as defined
in 50 CFR 414.12(b)) The designated critical habitat areas for the CRLF are considered
to have the following PCEs that justify critical habitat designation (USFWS 2006):
• Aquatic breeding habitat
• Non-breeding aquatic habitat
• Upland habitat
• Dispersal habitat
Critical habitat does not include certain areas where existing management is sufficient for
CRLF protection. For the CRLF, all designated critical habitat units contain all four
PCEs and were occupied by the CRLF at the time of listing.
USFWS has established modification standards for designated critical habitat (USFWS
2006). Activities that may destroy or modify critical habitat are those that alter the PCEs
and appreciably diminish the value of the habitat. For the CRLF specifically, these
include, but are not limited to, the following:
• Alteration of water chemistry or temperature
• Increased sedimentation
• Alteration of channel or pond morphology
• Elimination of upland foraging areas
• Introduction of non-native species
• Degradation of prey base
The critical habitat designation includes a special rule exempting routine ranching
activities associated with livestock ranching from incidental take prohibitions. The
purpose of this exemption is to promote the conservation of rangelands, which could be
beneficial to the CRLF, and to reduce the rate of conversion to other land uses that are
incompatible with CRLF conservation.
2.5.1.4 Other Known Occurrences from the CNDBB
The CNDDB7 provides location and natural history information on species found in
California. It is the best available information for historical and current species location
sightings.
7 See: http://www.dfg.ca.gov/bdb/html/cnddb info.html for additional information on the CNDDB.
25
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Recovery Units
Sierra Nevada Foothills and Central Valley
North Coast Range Foothills and Western
Sacramento River Valley
North Coast and North San Francisco Bay
South and East San Francisco Bay
Central Coast
Diablo Range and Salinas Valley
Northern Transverse Ranges and Tehachapi
Mountains
Southern Transverse and Peninsular Ranges
Legend
| Recovery Unit Boundaries
Currently Occupied Core Areas
| Critical Habitat
| CNDDB Occurence Sections
County Boundaries q 45
I 1 i_
180 Miles
_l
Core Areas
1.
Feather River
19.
Watsonville Slough-Elkhorn Slough
2.
Viiha River- S. Fork Feather River
20.
Carmel River — Santa Lucia
3.
Traverse Creek/ Middle Fork/ American R. Rubicon
21.
Gablan Range
4.
Cosumnes River
22.
Estero Bay
5.
South Fork Calaveras River*
23.
Arroyo Grange River
6.
Tuolumne River*
24.
Santa Maria River - Santa Ynez River
7.
Piney Creek"
25.
Sisquoc River
8.
Cottonwood Creek
26.
Ventura River — Santa Clara River
9.
Putah Creek - Cache Creek*
27.
Santa Monica Bay — Venura Coastal Streams
10.
Lake Berryessa Tributaries
28.
Estrella River
11.
tipper Sonoma Creek
29.
San Gabriel Mountain*
12.
Petaluma Creek — Sonoma Creek
30.
Forks of the Mojave*
13.
Pt. Reyes Peninsula
31.
Santa Ana Mountain*
14.
Belvedere Lagoon
32.
Santa Rosa Plateau
15.
Jameson Canyon — Lower Napa River
33.
San Luis Ray*
16.
East San Francisco Bay
34.
Sweetwater*
17.
Santa Clara Valley
35.
Laguna Mountain*
18.
South San Francisco Bay
* Core areas that were historically occupied by the California red-legged frog are not included in the map
Figure 4 California Red-legged Frog Distribution
26
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2.5.2 Reproduction
CRLFs breed primarily in ponds; however, they may also breed in quiescent streams,
marshes, and lagoons (Fellers 2005a). According to the Recovery Plan (USFWS 2002),
CRLFs breed from November through late April. Peaks in spawning activity vary
geographically; Fellers (2005b) reports peak spawning as early as January in parts of
coastal central California. Eggs are fertilized as they are being laid. Egg masses are
typically attached to emergent vegetation, such as bulrushes (Scirpus spp.) and cattails
(Typha spp.) or roots and twigs, and float on or near the surface of the water (Hayes and
Miyamoto 1984). Egg masses contain approximately 2000 to 6000 eggs ranging in size
between 2 and 2.8 mm (Jennings and Hayes 1994). Embryos hatch 10 to 14 days after
fertilization (Fellers 2005a) depending on water temperature. Egg predation is reported
to be infrequent and most mortality is associated with the larval stage (particularly
through predation by fish); however, predation on eggs by newts has also been reported
(Rathburn 1998). Tadpoles require 11 to 28 weeks to metamorphose into juveniles
(terrestrial-phase), typically between May and September (Jennings and Hayes 1994,
USFWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until
the following year) (Fellers 2005b, USFWS 2002). Males reach sexual maturity at 2
years, and females reach sexual maturity at 3 years of age; adults have been reported to
live 8 to 10 years (USFWS 2002). Figure 5 depicts CRLF annual reproductive timing.
Month
J
F
M
A
M
J
J
A
S
o
N
D
Young
Juveniles:
Tadpoles*
Breeding/Egg
Masses
Adults and 1 1 1 1
Juveniles 1 1 1 1
Figure 5. CRLF Reproductive Events by Month *except those that over-winter.
2.5.3 Diet
Although the diet of CRLF aquatic-phase larvae (tadpoles) has not been studied
specifically, it is assumed that their diet is similar to that of other frog species, with the
aquatic phase feeding exclusively in water and consuming diatoms, algae, and detritus
(USFWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar, 1980)
via mouthparts designed for effective grazing of periphyton (Wassersug, 1984,
Kupferberg et al.\ 1994; Kupferberg, 1997; Altig and McDiarmid, 1999).
Juvenile and adult CRLFs forage in aquatic and terrestrial habitats, and their diet differs
greatly from that of larvae. The main food source for juvenile aquatic- and terrestrial-
phase CRLFs is thought to be aquatic and terrestrial invertebrates found along the
shoreline and on the water surface. Hayes and Tennant (1985) report, based on a study
examining the gut content of 35 juvenile and adult CRLFs, that the species feeds on as
many as 42 different invertebrate taxa, including Arachnida, Amphipoda, Isopoda,
27
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Insecta, and Mollusca. The most commonly observed prey species were larval alderflies
(Sialis cf. californica), pillbugs (Armadilliadrium vulgare), and water striders (Gerris sp).
The preferred prey species, however, was the sowbug (Hayes and Tennant, 1985). This
study suggests that CRLFs forage primarily above water, although the authors note other
data reporting that adults also feed under water, are cannibalistic, and consume fish. For
larger CRLFs, over 50% of the prey mass may consists of vertebrates such as mice, frogs,
and fish, although aquatic and terrestrial invertebrates were the most numerous food
items (Hayes and Tennant 1985). For adults, feeding activity takes place primarily at
night; for juveniles feeding occurs during the day and at night (Hayes and Tennant 1985).
2.5.4 Habitat
CRLFs require aquatic habitat for breeding, but also use other habitat types including
riparian and upland areas throughout their life cycle. CRLF use of their environment
varies; they may complete their entire life cycle in a particular habitat or they may utilize
multiple habitat types. Overall, populations are most likely to exist where multiple
breeding areas are embedded within varying habitats used for dispersal (USFWS 2002).
Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al.
1997). Dense vegetation close to water, shading, and water of moderate depth are habitat
features that appear especially important for CRLF (Hayes and Jennings 1988).
Breeding sites include streams, deep pools, backwaters within streams and creeks, ponds,
marshes, sag ponds (land depressions between fault zones that have filled with water),
dune ponds, and lagoons. Breeding adults have been found near deep (0.7 m) still or slow
moving water surrounded by dense vegetation (USFWS 2002); however, the largest
number of tadpoles have been found in shallower pools (0.26 - 0.5 m) (Reis, 1999). Data
indicate that CRLFs do not frequently inhabit vernal pools, as conditions in these habitats
generally are not suitable (Hayes and Jennings 1988).
CRLFs also frequently breed in artificial impoundments such as stock ponds, although
additional research is needed to identify habitat requirements within artificial ponds
(USFWS 2002). Adult CRLFs use dense, shrubby, or emergent vegetation closely
associated with deep-water pools bordered with cattails and dense stands of overhanging
vegetation (http://www.fws.gov/endangered/features/rl frog/rlfrog.html#where).
In general, dispersal and habitat use depends on climatic conditions, habitat suitability,
and life stage. Adults rely on riparian vegetation for resting, feeding, and dispersal. The
foraging quality of the riparian habitat depends on moisture, composition of the plant
community, and presence of pools and backwater aquatic areas for breeding. CRLFs can
be found living within streams at distances up to 3 km (2 miles) from their breeding site
and have been found up to 30 m (100 feet) from water in dense riparian vegetation for up
to 77 days (USFWS 2002).
During dry periods, the CRLF is rarely found far from water, although it will sometimes
disperse from its breeding habitat to forage and seek other suitable habitat under downed
trees or logs, industrial debris, and agricultural features (UWFWS 2002). According to
Jennings and Hayes (1994), CRLFs also use small mammal burrows and moist leaf litter
as habitat. In addition, CRLFs may also use large cracks in the bottom of dried ponds as
28
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refugia; these cracks may provide moisture for individuals avoiding predation and solar
exposure (Alvarez 2000).
2.6 Action Area
For listed species assessment purposes, the action area is considered to be the area
affected directly or indirectly by the federal action and not merely the immediate area
involved in the action (50 CFR 402.02). In the Overview Document, EPA defined
exceedances of the pre-established OPP levels of concern (LOCs) as effects (USEPA
2004). The initial area of concern is delineated by the registered use sites, or some
reasonable surrogate, such as a land use type. For this assessment, land use type has been
used, with agricultural land use representing agricultural crops, orchard land use
representing use on walnuts, and rangeland representing use on grass for hay, pasture,
and forage. The extent of the action area is determined by the taxa for which LOCs are
exceeded farthest away from the use site. This offset is added to the edge of the merged
use sites and the total area is considered the action area. For methyl parathion, the most
sensitive taxa for spray drift effects are the terrestrial invertebrates (represented in this
assessment by honeybees). For aquatic organisms, the offset is determined by the
distance downstream required for the most sensitive endpoint to drop below the LOC.
The most sensitive taxa for downstream effects are aquatic invertebrates. Because of the
potential for atmospheric transport of methyl parathion, and the low aquatic concentration
(> 0.05 ng/L), that would exceed the endangered species LOC, several analyses
examining methyl parathion movement into surface water from atmospheric transport
alone were conducted (Section 3.2.3) In several of these analyses, risk quotients for
aquatic invertebrates generated solely on the basis of atmospheric input exceeded the
endangered species LOCs, thus for the purpose of this assessment the entire action area is
defined as the state of California. Action areas by land use categories are shown in
relation to CRLF locations in Figures 6-10. Figures 11-13 depict high use counties in
relation to CRLF locations.
It is recognized by the Agency that the overall action area for the national registration of
methyl parathion includes any locations where registered uses might result in ecological
effects. However, the scope of this assessment limits consideration to the areas in which
application of the pesticide may have direct or indirect effects on California red-legged
frog or its designated critical habitat.
29
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Methyl parathion - Initial Area of Concern
Legend
Pasture use
Orchard use
Cultivated crop use
CNDDB occurence sections
| Critical habitat
Core areas
Recovery units
County boundaries
*
i Kilometers
0 20 40 80 120 160
Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Service (NASS, 2002)
Gap Analysis Program Orchard/Vineyard Laridcower (GAP)
National Land Cover Database (NLCD) (MRLC, 2001)
Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Division.
Projection: Albers Equal Area Conic US OS, North American
Datum of 1903 (WD 1983).
Produced: 1/28/2008
Figure 6 Land Use Categories in Relation to CRLF Locations
30
-------
Methyl parathion - Action Area
vlllilf
Legend
All uses with 6600-ft buffer
CNDDB occurence sections
| Critical habitat
Core areas
Recovery units
County boundaries
0 20 40 80 120 16o"°materS
Compiled from California Count/ boundaries (ESRI, 2002), Map created by US Environmental Protection Agency, Office
US DA National Agriculture Statistical Service (NASS, 2002) of Pesticides Programs, Environmental Fate and Effects Division.
Cap Anatysis Program Orchard/Vineyard Laridcower (GAP) Projection: Albers Equal Area Conic USOS, North American
National Land Cover Database (NLCD) (MRLC, 2001) Datum of 1983 (WD 1983).
Produced: 1/28^008
Figure 7 Combined Land Use Categories plus Spray Drift Buffer in Relation to CRLF
Locations
31
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Methyl parathion - Cultivated Crop Downstream Action Area
Legend
Cultivated crap downstream A A
CNDDB occurence sections
| Critical habitat
Core areas
Recovery units
County boundaries
Ł
Kilometers
80 120 160
0 2U 40
Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Service (NASS, 2002)
Gap Analysis Program Orchard/Vineyard Laridctwer (GAP)
National Land Cover Database (NLCD) (MRLC, 2001)
Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Division.
Projection: Albers Equal Area Conic USGS, North American
Datum of 1983 (WD 1983).
Produced: 1/28/2008
Figure 8 Extent of Potential Downstream Effects Based on Agricultural Uses
32
-------
Methyl parathion - Orchard Downstream Action Area
Kilometers
Legend
— Orchard downstream A A
CNDDB occurence sections
| Critical habitat
Core areas
~ Recovery units
County boundaries
Compiled from California County boundaries (ESRI, 2002), Map created by US Environmental Protection Agency, Office
USQA National Agriculture Statistical Service (NASS, 2002) of Pesticides Programs, Environmental Fate and Effects Division.
Gap Analysis Program Orchard; Vineyard Landcover (GAP) Projection: Albers Equal Area Conic USGS, NorthAmerican
National Land Cover Database (NLCD) (MRLC, 2001) Datum of 1983 (NAD 1983).
Produced: 1/28/200S
Figure 9 Extent of Potential Downstream Effects Based on Orchard Uses
33
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Methyl parathion - Pasture Downstream Action Area
Legend
Pasture downstream AA
CNDDB occurence sections
| Critical habitat
Core areas
Recovery units
County boundaries
Kilometers
80 120 160
0 2U 40
Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Service (NASS, 2002)
Gap Analysis Program Ore hard/ Vineyard Laridcower (GAP)
National Land Cover Database (NLCD) (MRLC, 2001)
Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Division.
Projection: Albers Equal Area Conic USGS, North American
Datum of 1983 (WD 1983).
Produced: 1/28/2008
Figure 10 Extent of Downstream Effects Based on Rangeland Uses
34
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./Merced
Methyl parathion - High usage counties (Total applied, 2002-05)
| methylp_walcult_ovlp_union_elevencount
Walnut action area (6600-ft)
methy I p_c u lt_66 0 Oft
] CNDDB occurence sections
| Critical habitat
Core areas
County boundaries
i Kilometers
3 1421 28
Methyl parathion usage
(total applied. 2002-2005)
~ Less than 10,000 lbs Al
~ 10,000-20,000 lbs Al
B More than 20,000 lbs Al
Compiled from California County boundaries (ESRI, 2002), Map created by US Environmental Protection Agency, Office
US DA National Agriculture Statistical Service (NASS, 2002) of Pesticides Programs, Environmental Fate and Effects Division.
Cap Ana lysis Prog ram Ore hard/Vineyard Land cover (GAP) Projection: Albers Equal Area Conic USGS, North American
National Land Cover Database (NLCD) (MRLC, 2001) Datum of 1903 (NAD1 903).
Produced: 1/28/2008
Figure 11 High Usage Counties (CA DPR PUR) in Relation to CRLF Locations (Fresno,
Kings, Kern, and Tulare Counties)
35
-------
Methyl parathion - High usage counties (Total applied, 2002-05)
| methylp_walcult_ovlp_union
Walnut action area (6600-ft)
methy I p_c u tt_66 Q Oft
] CNDDB occurence sections
| Critical habitat
Core areas
County boundaries
elevencount
J
¦ Kilometers
4 8 1216
1
Methyl parathion usage
(total applied. 2002-2005)
Less than 10,000 lbs Al
~ 10,000-20,000 lbs Al
D More than 20,000 lbs Al
San Joaquin
Merced
r
Stanislaus
Compiled from California County boundaries (ESRI, 2002), Map created by US Environmental Protection Agency, Office
US DA National Agriculture Statistical Service (NASS, 2002) of Pesticides Programs, Environmental Fate and Effects Division.
Oap Analysis Prog ram Ore hard/Vineyard Land cover (GAP) Projection: Albers Equal Area Conic USGS, North American
National Land Cover Database (NLCD) (MRLC, 2001) Datum of1903 (NAD1 903).
Produced: 1/28/200B
Figure 12 High Usage Counties (CA DPR PUR) in Relation to CRLF Locations (Merced,
San Joaquin, and Stanislaus Counties)
36
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Methyl parathion - High usage counties (Total applied, 2002-05)
Methyl
(total a|
Kilometers
Butte
| methylp_walcult_ovlp_union_elevencount
Walnut action area (6600-ft)
methy I p_c u tt_66 0 Dft
CNDDB occurence sections
| Critical habitat
Core areas
County boundaries
Slitter
parathion usage
applied. 2002-2005)
Less than 10,000 lbs Al
10,000-20,000 lbs Al
More than 20,000 lbs Al
Compiled from California County boundaries (ESRI, 2002), Map created by US Environmental Protection Agency, Office
US OA National Agriculture Statistical Service (NASS, 2002) of Pesticides Programs, Environmental Fate and Effects Division.
Oap Analysis Prog ram Ore hard/Vineyard Land cover (GAP) Projection: Albers Equal Area Conic USGS, North American
National Land Cover Database (NLCD) (MRLC, 2001) Datum of 1903 (NAD1 903).
Produced: 1/28/2008
Figure 13 High Usage Counties (CA DPR PUR) in Relation to CRLF Locations (Butte,
Sutter, and Yuba Counties)
37
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2.7 Assessment Endpoints and Measures of Ecological Effect
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."8 Selection of the assessment endpoints is based on valued
entities (e.g., CRLF, organisms important in the life cycle of the CRLF, and the PCEs of
its designated critical habitat), the ecosystems potentially at risk (e.g., waterbodies,
riparian vegetation, and upland and dispersal habitats), the migration pathways of methyl
parathion (e.g., runoff, spray drift, etc.), and the routes by which ecological receptors are
exposed to methyl parathion (e.g., direct contact, etc.).
2.7.1. Assessment Endpoints for the CRLF
Assessment endpoints for the CRLF include direct toxic effects on the survival,
reproduction, and growth of the CRLF, as well as indirect effects, such as reduction of
the prey base and/or modification of its habitat. In addition, potential destruction and/or
modification of critical habitat is assessed by evaluating potential effects to PCEs, which
are components of the habitat areas that provide essential life cycle needs of the CRLF.
Each assessment endpoint requires one or more "measures of ecological effect," defined
as changes in the attributes of an assessment endpoint or changes in a surrogate entity or
attribute in response to exposure to a pesticide. Specific measures of ecological effect are
generally evaluated based on acute and chronic toxicity information from registrant-
submitted guideline tests that are performed on a limited number of organisms.
Additional ecological effects data from the open literature are also considered.
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. A summary of the assessment endpoints and
measures of ecological effect selected to characterize potential assessed direct and
indirect CRLF risks associated with exposure to methyl parathion is provided in Table 4.
8 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
38
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Table 4 Assessment Endpoints and Measures of Ecological Effects
Assessment Endpoint
Measures of Ecological Effectsa
Aquatic-Phase CRLF
(Eggs, larvae, tadpoles, juveniles, and adults)3
Direct Effects
1. Survival, growth, and reproduction of CRLF
via direct effects on aquatic phase individuals
1a. Cutthroat trout acute LC50
1 b. Rainbow trout chronic NOAEC
Indirect Effects and Critical Habitat Effects
2. Survival, growth, and reproduction of CRLF
individuals via indirect effects on aquatic prey
food supply (i.e., fish, freshwater invertebrates,
non-vascular plants)
2a. Cutthroat trout acute LC50
2b. Rainbow trout chronic NOAEC
2c. Water flea acute EC50
2d. Water flea chronic NOAEC.
2e. Non-vascular plant (freshwater algae)
acute EC50
3. Survival, growth, and reproduction of CRLF
individuals via indirect effects on habitat, cover,
food supply, and/or primary productivity (i.e.,
aquatic plant community)
3a. Non-vascular plant acute EC50 (freshwater
algae)c
4. Survival, growth, and reproduction of CRLF
individuals via effects to riparian vegetation
Appropriate data not available. Effects to
plants not anticipated based on mode of action.
Terrestrial-Phase CRLF
(Juveniles and adults)
Direct Effects
5. Survival, growth, and reproduction of CRLF
individuals via direct effects on terrestrial phase
adults and juveniles
5a. Bobwhite quail acute oral LD50
5b. Bobwhite quail chronic NOAEC
Indirect Effects and Critical Habitat Effects
6. Survival, growth, and reproduction of CRLF
individuals via effects on terrestrial prey (i.e.,
terrestrial invertebrates, small mammals , and
frogs)
6a. Honey bee acute contact LD50
6b. Rat acute oral LD50
6b. Rat chronic NOAEC
6b. Bobwhite quail acute oral LD50
6b. Bobwhite quail dietary LC50
6b. Bobwhite quail chronic NOAEC
7. Survival, growth, and reproduction of CRLF
individuals via indirect effects on habitat (i.e.,
riparian and upland vegetation)
Appropriate data not available. Effects to
plants not anticipated based on mode of action.
a Adult frogs are no longer in the "aquatic phase" of the amphibian life cycle; however, submerged
adult frogs are considered "aquatic" for the purposes of this assessment because exposure
pathways in the water are considerably different than exposure pathways on land.
Birds are used as surrogates for terrestrial-phase amphibians.
Avascular aquatic plant data not available for methyl parathion, thus data for non-vascular
aquatic plants were used to assess all potential effects on aquatic plants.
9 All registrant-submitted and open literature toxicity data reviewed for this assessment are included in
Appendix B.
39
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Measures of effect and assessment endpoints defined for indirect effects also apply to
critical habitat. Assessment endpoints used for the analysis of designated critical habitat
are based on the modification standard established by USFWS (2006).
Modification to the critical habitat of the CRLF includes, but is not limited to, the
following, as specified by USFWS (2006):
1. Alteration of water chemistry/quality including temperature, turbidity, and
oxygen content necessary for normal growth and viability of juvenile and
adult CRLFs.
2. Alteration of chemical characteristics necessary for normal growth and
viability of juvenile and adult CRLFs.
3. Significant increase in sediment deposition within the stream channel or pond
or disturbance of upland foraging and dispersal habitat.
4. Significant alteration of channel/pond morphology or geometry.
5. Elimination of upland foraging and/or aestivating habitat, as well as dispersal
habitat.
6. Introduction, spread, or augmentation of non-native aquatic species in stream
segments or ponds used by the CRLF.
7. Alteration or elimination of the CRLF's food sources or prey base.
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.
2.8 Conceptual Model
2.8.1 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 (U.S. EPA, 1998). For this assessment, the
risk is stressor-linked, where the stressor is the release of methyl parathion to the
environment. The following risk hypotheses are presumed for this endangered species
assessment:
• Labeled uses of methyl parathion within the action area may directly affect the
CRLF by causing mortality or by adversely affecting growth or fecundity;
• Labeled uses of methyl parathion within the action area may indirectly affect the
CRLF by reducing or changing the composition of food supply;
• Labeled uses of methyl parathion within the action area may indirectly affect the
CRLF and/or modify designated critical habitat by reducing or changing the composition
of the aquatic plant community in the ponds and streams comprising the current range of
the species and designated critical habitat, thus affecting primary productivity and/or
cover;
• Labeled uses of methyl parathion within the action area may indirectly affect the
CRLF and/or modify designated critical habitat by reducing or changing the composition
40
-------
of the terrestrial plant community {i.e., riparian habitat) required to maintain acceptable
water quality and habitat in the ponds and streams comprising the species' current range
and designated critical habitat;
• Labeled uses of methyl parathion within the action area may modify the
designated critical habitat of the CRLF by reducing or changing breeding and non-
breeding aquatic habitat (via modification of water quality parameters, habitat
morphology, and/or sedimentation);
• Labeled uses of methyl parathion within the action area may modify the
designated critical habitat of the CRLF by reducing the food supply required for normal
growth and viability of juvenile and adult CRLFs;
• Labeled uses of methyl parathion within the action area may modify the
designated critical habitat of the CRLF by reducing or changing upland habitat within
200 ft of the edge of the riparian vegetation necessary for shelter, foraging, and predator
avoidance.
• Labeled uses of methyl parathion within the action area may modify the
designated critical habitat of the CRLF by reducing or changing dispersal habitat within
designated units and between occupied locations within 0.7 mi of each other that allow
for movement between sites including both natural and altered sites which do not contain
barriers to dispersal.
• Labeled uses of methyl parathion within the action area may modify the
designated critical habitat of the CRLF by altering chemical characteristics necessary for
normal growth and viability of juvenile and adult CRLFs.
2.8.2 Diagrams
The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies the stressor {i.e., methyl parathion), release mechanisms, biological receptor
types, and effects endpoints of potential concern. The conceptual models for aquatic and
terrestrial phases of the CRLF are shown in Figure 14 and Figure 15 and the conceptual
models for the aquatic and terrestrial PCE components of critical habitat are shown in
Figure 16 and Figure 17.
Exposure routes shown in dashed lines (Figures 14 and 16 only) are not expected to be
significant. Groundwater is not considered quantitatively as an exposure route because
only 1 (0.00737 |ig/L) of 509 filtered groundwater samples had a methyl parathion
concentration above its respective detection limits (detection limits varied from 0.006 to
0.04 |ig/L) and 0 of 246 filtered groundwater samples had a methyl paraoxon
concentration above their respective detection limits (detection limits varied from 0.019
to 0.0299 |ig/L), Ingestion of aquatic animals and plants is not considered quantitatively
as an exposure route because methyl parathion shows little potential to bioaccumulate
therefore; exposure to residues through either plant or animal food was not considered
further.
The conceptual model for direct effects to the aquatic phase of the CRLF's life cycle
from methyl parathion uses is shown in Figure 14. Groundwater transport is considered
quantitatively through PRZM model, but is considered to be a relatively minor source due
to the non-persistence of methyl parathion, even when its mobility in soil is considered.
41
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The operative routes of exposure will be spray drift at the time of application, run-off due
to precipitation within a few days of application, and long-range atmospheric transport.
The conceptual model for indirect effects to the aquatic phase of the CRLF's critical
habitat from methyl parathion uses is depicted in Figure 15. For the same reasons
identified for direct effects, indirect effects are considered likely through depletion of
forage items and suitable cover.
Stressor
Receptors
Attribute
Change
Methyl parathion applied to use site
I
I
Source
Spray drift | | Runoff |
1
r i
r
Exposure
Surface water/
Media
Sediment
I
| Soil \-
Groundwater
Long range
atmospheric
transport
Wet/dry deposition
Uptake/gills
or integument
Uptake/gills
or integument
t^u
Aquatic Animals
Invertebrates
Vertebrates
Uptake/cell,
roots^leaves
Aquatic Plants
Non-vascular
Vascular
Red-legged Frog
Eggs Juveniles
Larvae Adult
Ladpoles
I
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
~
Ingestion
t
Ingestion
Riparian plant
terrestrial
exposure
pathways see
Figure 8
Food chain
Reduction in algae
Reduction in prey
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Figure 14 Conceptual Model: Direct Effects to Aquatic Phase of the California Red-Legged
Frog
Compartments and pathways in dashed lines are considered possible but not of sufficient significance to
warrant quantification in the assessment.
The conceptual model for direct effects to the terrestrial phase of the CRLF's life cycle
from methyl parathion uses is shown in Figure 15. Again, the operative routes of
exposure will be through direct application and spray drift at the time of application.
The conceptual model for indirect effects to the terrestrial phase of the CRLF's critical
habitat from methyl parathion uses is depicted in Figure 16. Indirect effects are primarily
driven by the depletion of forage items and suitable cover.
42
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Stressor
Source
Exposure
Media
Direct
application
Terrestrial
insects
Ingestion
| Amphibians
Methyl parathion applied to use site
-| Spray drift |-
i
Dermal uptake/Ingestion
—a I Runoff I
I I
Terrestrial/riparian plants
grasses/forbs, fruit, seeds
(trees, shrubs)
Root
Soil
uptake ^ |
Wet/dry deposition
Long range
atmospheric
transport
~ Ingestion
-~ Ingestion
tion I
ill
Ingestion
I
Receptors
Red-legged Frog
Juvenile
Adult
Attribute
Change
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Ingestion M 1 Mammals I
_2zr
Food chain
Reduction in prey
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Figure 15 Conceptual Model: Direct Effects to the Terrestrial Phase of the California Red-
legged Frog
43
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Stressor
Receptors
Attribute
Change
Methyl parathion applied to use site
I
I
Source
Spray drift | | Runoff |
1
r i
r
Exposure
Surface water/
Media
Sediment
I
| Soil \-
Groundwater
Long range
atmospheric
transport
Wet/dry deposition
Uptake/gills
or integument
Uptake/gills
or integument
t^u
Aquatic Animals
Invertebrates
Vertebrates
Uptake/cell,
roots^leaves
Aquatic Plants
Non-vascular
Vascular
Red-legged Frog
Eggs Juveniles
Larvae Adult
Ladpoles
I
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Ingestion
t
Ingestion
Riparian plant
terrestrial
exposure
pathways see
Figure 8
Food chain
Reduction in algae
Reduction in prey
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Figure 16 Conceptual model: aquatic component of CRLF critical habitat
Compartments and pathways in dashed lines are considered possible but not of sufficient significance to
warrant quantification in the assessment.
44
-------
Stressor
Source
Exposure
Media
Direct
application
Terrestrial
insects
Ingestion
| Amphibians
Methyl parathion applied to use site
-| Spray drift |-
i
Dermal uptake/Ingestion
—a I Runoff I
I I
Terrestrial/riparian plants
grasses/forbs, fruit, seeds
(trees, shrubs)
Root
Soil
uptake ^ |
Wet/dry deposition
Long range
atmospheric
transport
Ingestion
I
Receptors
Attribute
Change
Red-legged Frog
Juvenile
Adult
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
^•Ingestion
-~ Ingestion j
Ingestion M | Mammals |
Food chain
Reduction in prey
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Figure 17. Conceptual model: terrestrial component of CRLF critical habitat.
2.9 Analysis Plan
The exposure and effects analysis is conducted in accordance with standard methods
described in the Overview document (U.S. EPA 2004). Refinements specific to this
assessment include the use of an amphibian/reptile-specific terrestrial exposure model (T-
HERPS), evaluation of potential effects on terrestrial invertebrates using honey bees as
the surrogate, the use of AgDrift to estimate clearance distances for both plants and
animals, and the use of partitioning-based estimates to consider atmospheric inputs into
water bodies. All refinements have been approved within EFED and are described in the
appropriate section.
Crops for which methyl parathion is currently registered can be spatially represented by
three land use classes: orchards (walnuts), pasture (grass for forage, pasture and hay), and
agricultural land (all other crops). EECs and RQs are presented for each of these land
uses in their respective tables, and for agricultural land, values are presented for crops
with the highest (cotton) and lowest (onion) application rates. EECs presented in the
body of the document are based on multiple applications at the maximum rate in the
shortest interval.
45
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3.0 Exposure Assessment
3.1 Label Application Rates and Intervals
Based on the existing labels, a number of crop groups were modeled for this assessment.
These crop groups included alfalfa, cereals, corn, cotton, grass, legumes, potatoes, rice,
root and tuber vegetables, seeds, and walnuts. A total of 3 land use groupings were
identified: agricultural, rangeland and orchard. While the agricultural land use grouping
includes many different uses, this assessment modeled those uses that represent the
highest and lowest application rates among the agricultural uses. Thus, cotton and onions
serve as surrogates for modeling the highest and lowest agricultural land cover uses,
respectively. For rangeland and orchard land uses, only the maximum application rate is
assessed; hay and walnuts serve as the surrogate crops within each of the two land use
categories. Land uses and representative crops along with their respective use
information are presented in Table 5.
Use of methyl parathion on rice was not considered fully in the assessment of agricultural
crop uses. Because rice is a direct application to water, it will produce estimated
environmental concentrations (EECs) and, therefore, aquatic risks to the CRLF that are
much higher than other uses (Appendix E lists the rice EECs and Risk quotients).
However, according to the California Department of Pesticide Regulation Pesticide Use
Reporting (CDPR PUR) database methyl parathion use on rice totaled 132 lbs. in the
years 2000 through 2005, which is <0.03% of the total methyl parathion applied over this
time period in California (444,819 lbs). Therefore, efforts were focused on the other
agricultural crop uses in California. Because other methyl parathion uses in California
produce sufficient aquatic risks to the CRLF that result in a finding of "likely to
adversely affect", the omission of rice does not materially affect this finding (a fuller
consideration of rice would only have provided additional support for that determination).
For each of these groups, both a single application and the maximum number of multiple
applications were modeled. Detailed label information, modeling parameters (e.g.,
application rates, application intervals, and maximum number of applications, selection
of application dates) and results from all modeling runs are included in Appendix E. The
highest application rate for each crop and the corresponding maximum number of
applications and minimum intervals were used for modeling. In cases where one label
did not specify the number of applications or interval, assumptions were made based on
information contained in other labels. In the many cases, a specific application interval
was not provided, and EFED conservatively assumed 5 days as the application interval.
Table 5 shows modeling parameters and scenarios used for the two crops used as
bounding estimates for the agricultural land, and the crops used for rangeland and orchard
uses.
46
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Table 5 Application Rates for Modeling
Crop Group
Modeled
(Scenario)
Surrogate
For
Max
Rate
Lb
a.i/A
Max # of
Apps/year
Interval
Label
Agricultural Land Use
Cotton
(CA cotton RLF)
Cotton
(Highest
Agricultural
Rate)
3
5
Not specified
(Assume 5
days)
67760-43
5905-533
Root &Tuber
Vegetables
(CA Onion STD)
Onions
(Lowest
Agricultural
Rate)
0.5
6 a
Not specified
(Assume 5 days
5905-533
Rangeland Use
Grass
(CA range/hay RLF)
Hay
Pasture
Forage
0.75
6
Not specified
(Assume 5
days)
5905-533
Orchard Land Use
Tree Nuts
(CA almonds RLF)
Walnuts
2
4
21 days
4581-533
(SLN)
a Rates in label given as per season, and were converted to a yearly rate based on crop cycle
information developed by BEAD (Kaul 2007).
3.2 Aquatic Exposure Modeling
Typically, the Agency conducts modeling using scenarios intended to represent use sites
in areas that are highly vulnerable to either runoff, erosion, or spray drift. Runoff
estimates predicted by the Pesticide Root Zone Model (PRZM) are linked to the
Exposure Analysis Modeling System (EXAMS). For ecological risk assessment, the
Agency relies on a standard water body to receive the edge-of-field runoff estimates. The
standard water body is of fixed geometry and includes the processes of degradation and
sorption expected to occur in ponds, canals, and low-order streams (e.g. first and second
order streams). The water body is static (no outflow). The CLRF inhabits a range of
water bodies, but generally prefers perennial or near perennial waters in order to
complete its lifecycle (Jennings et al., 1997). Generally it inhabits watersheds and
drainages of 4th order or lower streams (Hayes and Jennings 1998).
Environmental fate input parameters for methyl parathion were obtained from the methyl
parathion RED, and registrant-submitted environmental fate studies. Methyl paraoxon
concentrations were estimated as 2.1% of the methyl parathion concentrations based on
anaerobic aquatic metabolism studies conducted under laboratory conditions. As a initial
conservative EEC estimate for 4-nitrophenol (which is several orders of magnitude less
toxic than either the parent methyl parathion or the methyl paraoxon degradate), EECs of
the degradate were assumed to be equivalent to the parent.
47
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Table 6 Input Parameters for Methyl Parathion PRZM Modeling
Parameter
Value
Comments
Source
Molecular Weight (grams/mole)
265
None
RED
Solubility (mg/L)
60
None
RED
Vapor Pressure (torr)
Henry's Constant (atm mJ/mol)
6.12E-7
None
RED
Koc (L/kg)
486
None
MRID 40999001
Aerobic Soil Metabolism Half-life (days)
11.25
3 X 3.75a
MRID 41735901
Aerobic Aquatic Metabolism Half-life (days)
12.3
3X4.1a
MRID 00103361
MRID 00128789
MRID 42069601
Anaerobic Aquatic Metabolism Half-life
(days)
33.3
3X11.1 a
MRID 46997601
Photodegradation in Water (hours)
49
None
MRID 40809701
Hydrolysis Half-life (days)
40 at pH7
None
MRID 0013275
MRID 40784501
Spray Drift Fraction
1%
5%
Ground
Aerial
Default value
a single measured half-life multiplied by 3 in accordance with PRZM/EXAMS input parameter guidance.
48
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Peak l-in-10 year EECs for methyl parathion ranged from 4.2 |j,g/L to 66.8 |_ig/L. The
21-day average EECs ranged from 2.9 |j,g/L to 42.2 |_ig/L, and the 60-day average EECs
ranged from 2.0 |j,g/L to 25.7 |j,g/L
Table 7 Methyl Parathion EECs in the Standard EXAMS Water Body
Crop
(Iba.i/A)
Application
Application
Technique3
1 in 10 year EEC (Mg/L)
Timing
(month/day -
month/day)
Peak
21 day
average
60 day
Average
Agricultural Land Use
Cottonb
6/17-7/6
Ground
23.6
13.4
7.3
(3.0)
9/12-10/1
Aerial
66.8
42.2
25.7
Onions0
5/27 - 6/21
Ground
6.5
4.4
2.3
(0.5)
9/24-10/19
Aerial
15.3
11.5
7.7
Rangeland Use
Grass
1/25-2/19
Ground
30.4
21.3
12.5
(0.75)
4/22-5/17
Aerial
9.4
7.2
4.6
Orchard Land Use
Walnuts
5/27 - 7/29
Ground
4.2
2.9
2.0
(2.0)
6/21 - 8/23
Aerial
9.5
5.8
4.8
a Both aerial and ground applications were modeled. Aerial applications typically result in higher
aquatic EECs (due to greater spray drift), thus the aerial EECs are used as bounding estimates
for each crop group in those cases. For grass, differences in application dates (and thus rainfall)
resulted in higher EECs for ground application, and these higher EECs were used to calculate
risk quotients.
b Used as the "highest" bounding estimate for developing risk quotients
c Used as the "lowest" bounding estimate for developing risk quotients. Although some estimates
for ground applications are lower, the application rate is a function of the crop, not the application
method, thus it is more conservative to use the aerial EECs.
49
-------
Concentrations of methyl paraoxon were estimated based on a formation rate of 2.1% of
total applied. Peak l-in-10 year EECs for methyl paraoxon ranged from 0.09 |j,g/L to
1.40 |J,g/L. The 21-day average EECs ranged from 0.06 |j,g/L to 0.89 ng/L, and the 60-
day average EECs ranged from 0.04 |j,g/L to 0.54 |ag/L.
Table 8 Methyl Paraoxon EECs in the Standard EXAMS Water Body
Crop
(lb ai/A)
Application
Application
Technique3
1 in 10 year EEC (Mg/L)
Timing
(month/day -
month/day)
Peak
21 day
average
60 day
Average
Agricultural Land Use
Cottonb
6/17-7/6
Ground
0.50
0.28
0.15
9/12-10/1
Aerial
1.40
0.89
0.54
Onions0
5/27 - 6/21
Ground
0.14
0.09
0.05
9/24-10/19
Aerial
0.32
0.24
0.16
Rangeland Use
Grass
1/25-2/19
Ground
0.64
0.45
0.26
4/22-5/17
Aerial
0.20
0.15
0.10
Orchard Land Use
Walnuts
5/27 - 7/29
Ground
0.09
0.06
0.04
6/21 - 8/23
Aerial
0.20
0.12
0.10
a Both aerial and ground applications were modeled. Aerial applications typically result in higher
aquatic EECs (due to greater spray drift), thus the aerial EECs are used as bounding estimates
for each crop group in those cases. For grass, differences in application dates (and thus rainfall)
resulted in higher EECs for ground application, and these higher EECs were used to calculate
risk quotients.
b Used as the "highest" bounding estimate for developing risk quotients
c Used as the "lowest" bounding estimate for developing risk quotients. Although some estimates
for ground applications are lower, the application rate is a function of the crop, not the application
method, thus it is more conservative to use the aerial EECs.
50
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3.3 Monitoring Data
Available surface water, ground water, air monitoring, and rainwater data were evaluated
and are summarized below. All of the data summarized in this section were collected in
California with the exception of some of the rainwater data as noted below. Surface and
ground water data were not targeted for monitoring spatial and/or temporal input from
agricultural sites; in other words, the data may not have been collected in close proximity
to when and/or where methyl parathion was applied.
3.3.1 Surface Water Monitoring Data
An evaluation of the surface water monitoring data was conducted to assess the
occurrence of methyl parathion, methyl paraoxon, and 4-nitrophenol in California surface
waters. Surface water data were obtained from the California Department of Pesticide
Regulation (CaDPR) (http://www.cdpr.ca.gov/docs/sw/surfdata.htm) and USGS
NAWQA data warehouse (http://water.usgs.gov/nawqa/data). The CaDPR surface water
data set is a compilation of data from multiple sources and may include some of the
USGS California data.
3.3.1.1 Summary of Individual samples
Methyl parathion. The CaDPR data set contained monitoring data for methyl parathion
from 4477 samples from 219 sites in California (collected between 2/25/1991 and
6/7/2005). Instrument detection limits varied by sample and ranged from 0.005 to 1 |ig/L.
The maximum concentration measured above the instrument detection limit is 0.524
|ig/L. Of the 13 CaDPR surface water samples with methyl parathion concentrations
measured above their respective sample's instrument detection limits, all fell below the
maximum detection limit in the entire data set of 1 |ig/L (75 samples have instrument
detection limits that exceed the maximum above-the-detection-limit sample concentration
of 0.524 |ig/L), The minimum above-the-detection-limit sample concentration measured
was 0.006 |ig/L. Of the 4477 samples in the CaDPR data set, 4466 samples (>99% of
samples) have instrument detection limits that exceed the minimum above-the-detection-
limit sample concentration of 0.006 |ig/L.
This variation in instrument detection limits makes it difficult to conclude much about the
distribution of methyl parathion in surface waters from the CaDPR data set. Considering
only the 75 samples with detection limits of 1 |ig/L, the potential exists that 75 samples
have almost twice the maximum observed above-the-detection-limit concentration in this
data set or that 75 samples have virtually no methyl parathion. Assuming the highest,
lowest, or some mid-range values for these samples can greatly bias interpretations based
on the data set. Therefore, it is important to appreciate the uncertainty caused by variation
in detection limits when interpreting such data, especially in data sets that are
compilations from different data sources with very different instrument detection limits.
The USGS surface water data set contained monitoring data for 5 sample types of methyl
parathion, 2 sample types of methyl paraoxon, and 3 sample types of 4-nitrophenol. The
methyl parathion sample types are filtered surface water samples (158 samples from 82
51
-------
sites in California - USGS sampling dates not readily available), unfiltered surface water
samples (8 samples from 7 sites in California), solids recoverable (none from California),
suspended sediment data (none from California), and bed sediment (none from
California). Of the 2 USGS methyl parathion sample types that had data from California,
only in filtered surface water samples was methyl parathion detected above the
instrument detection limits which ranged from 0.005 to 0.3 |ig/L. Six of the 7 above-
detection-limit filtered surface results are below the maximum detection limit (0.3 |ig/L).
Again, the variation in instrument detection limits makes it difficult to interpret the USGS
filtered surface water data set. All 8 of the USGS unfiltered methyl parathion surface
water samples were below detection limits (instrument detection limits ranged from 0.015
- 0.06 |ig/L).
The highest methyl parathion surface water sample concentration was the same for both
the CaDPR and USGS data sets (0.524 |ig/L). It appears likely that this is the same
sample and is a USGS sample that was compiled into the CaDPR data set. The CaDPR
data set records this sample as being from "Orestimba Creek at River Road (trib. to SJR)"
in Stanislaus County, CA, collected on 6/26/2002. The USGS data set describes this
sample as being from "Orestimba Cr At River Rd Nr Crows Landing Ca" at USGS site
number 11274538 in Stanislaus County, CA.
Methylparaoxon. The CaDPR data set contained monitoring data from 202 samples from
17 sites in California (collected between 3/15/1993 and 8/8/1995) for methyl paraoxon.
There were no samples measured above the instrument detection limits in the CaDPR
methyl paraoxon data set. The instrument detection limit for all CaDPR methyl paraoxon
samples was 0.05 |ig/L.
The only USGS methyl paraoxon sample type is filtered surface water (21 samples from
18 sites in California). All of the filtered methyl paraoxon surface water sample
concentrations fell below the instrument detection limits, which ranged from 0.019 to
0.0299 |ig/L.
4-nitrophenol. Only the USGS data set contained monitoring data for 4-nitrophenol. Of
the 3 types of surface water samples collected (filtered water, unfiltered water, and
suspended sediment), no samples were collected in the state of California.
3.3.1.2 Summary by Sites
Because concentrations are expected to vary greatly over time at each site, concentration
data were summarized (Figure 18) for methyl parathion only from the CaDPR and USGS
(filtered surface water) data sets based on the maximum concentration occurring at each
site. Again, the highest methyl parathion surface water site concentration is likely the
same for both the CaDPR and USGS data sets (0.524 |ig/L) because this USGS sample
was likely also compiled into the CaDPR data set. A similar analysis of methyl parathion
degradation products and other types of methyl parathion surface water samples
(unfiltered, suspended solids, etc.) was not conducted because there were limited data on
the methyl parathion degradation products and other methyl parathion surface water
sample types.
52
-------
CO 1000
a
&
Ph
a
-c
E
206
100
10
0 0 0 0 0 0
O 1
V1 °
1
!B 1000
a
CO
O
E
100
10
75
cy
o
I
00000000
Methyl Parathion Concentration (jug/L)
Figure 18 Frequency distribution of maximum surface water methyl parathion
concentrations for each site sampled in the CaDPR (a) and USGS (b) data sets.
1
Methyl Parathion Concentration (fig/L)
Risk quotients (RQs) were calculated for aquatic effects of methyl parathion for the
highest observed non-targeted methyl parathion concentration (Table 9). This analysis
shows that methyl parathion has been observed in surface water at concentrations that
exceed levels of concern for acute and chronic risks to freshwater aquatic invertebrates.
Table 9. Aquatic risk quotients (RQs) based the highest observed non-targeted methyl
parathion concentration in surface water.
Surface water
Concentration
(pg/L)
Acute Frog
1850 pg/L
Chronic
Frog
10 pg/L
Acute
Invertebrate
0.97 pg/L
Chronic
Invertebrate
0.25 pg/L
Aquatic
Plants
2900 pg/L
0.524
<0.01
0.05
0.54
2.10
<0.01
It is difficult to directly compare non-targeted surface water monitoring data to the
PRZM/EXAMS EECs generated for this assessment because the surface water sites in the
CaDPR and USGS data sets are likely to be dissimilar to the surface water site modeled
in PRZM/EXAMS. The CaDPR and USGS data sets are likely to be representative of
ditches, streams, and rivers (flow-through systems) farther downstream from any
agricultural sites treated with methyl parathion, while the PRZM/EXAMS pond (no
through-flow) is situated directly downstream and downwind of a field treated with
methyl parathion at its maximum application rates and minimum reapplication intervals.
Additionally, PRZM/EXAMs assumes that the entire watershed is planted in the crop and
that 100% of the watershed is treated simultaneously.
The maximum measured methyl parathion concentration (0.524 |Jg/L) in the monitoring
surface water data is one-fourth the minimum 60-day EEC (2.0 |_ig/L, ground application
to walnuts) and less than l/100th the maximum peak EEC (66.8 |_ig/L, aerial application to
cotton) shown in Table 7. Because methyl parathion degrades relatively rapidly in the
environment, its concentration in surface waters would be expected to be lower at the
non-targeted surface water sites relative to the EECs in water bodies directly receiving
runoff from the application site. Therefore at this gross level of analysis, the
concentrations in the surface water monitoring and EECs do not appear to be
inconsistent.
53
-------
Another relatively firm conclusion that can be drawn from the methyl parathion surface
water data from California is that surface water concentrations greater than the maximum
detection limit (1 |ig/L) have been rare at the type of sites sampled in the CaDPR and
USGS data sets. Therefore, the off-site movement of methyl parathion from its use sites
must be limited enough that the types of sites monitored in the USGS and CaDPR data
sets that widespread incidence of concentrations in excess of 1 |ig/L have not been
reported.
3.3.2 Ground Water Monitoring Data
An evaluation of the ground water monitoring data was conducted to assess the
occurrence of methyl parathion, methyl paraoxon, and 4-nitrophenol in California ground
waters. Ground water data were obtained from the USGS NAWQA data warehouse
(http://water.usgs.gov/nawqa/data).
Methyl parathion. There are 3 kinds of sampling matrices for methyl parathion in ground
water represented in the USGS data set - filtered (509 samples from 430 sites in
California), suspended solids (none in California), and unfiltered (none in California). Of
the 509 filtered ground water samples in the USGS data set, only one sample collected in
Riverside, CA (USGS station ID 340033117204001) had a methyl parathion
concentration (0.00737 |ig/L) above its respective detection limit. The individual sample
detection limits ranged from 0.006 to 0.04 |ig/L. Because 133 samples (26%) had
detection limits higher than the sole above-the-detection-limit sample, it is difficult to
conclude much about the distribution of methyl parathion in ground water based on the
USGS data. However based on the USGS data, it does appear that methyl parathion
concentrations exceeding the maximum detection limit in this data set (0.04 |ig/L) have
been rare at the types of sites monitored in the USGS data set.
Methyl paraoxon. There are 2 kinds of methyl parathion in ground water samples in the
USGS data set - filtered (246 samples from 226 sites in California) and suspended solids
(none in California). Of the 246 filtered ground water samples in the USGS data set,
none had a methyl paraoxon concentration above its respective detection limit. The
individual sample detection limits ranged from 0.019 to 0.0299 |ig/L. Because all sample
concentrations were below their respective detection limits, it appears that methyl
paraoxon concentrations exceeding the maximum detection limit in this data set (0.0299
|ig/L) have been rare at the types of sites monitored in the USGS data set.
4-nitrophenol. Only unfiltered ground water samples of 4-nitrophenol occur in the USGS
data set, and none of these were collected in California.
3.3.3 Long-range Transport
Two methods were used to assess potential impacts from long-range transport of methyl
parathion and methyl paraoxon. The first method used air monitoring data from
California to estimate aquatic EECs and effects to aquatic organisms and habitat. The
second method used rainwater monitoring data from several sources to estimate aquatic
54
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and terrestrial EECs and effects to aquatic and terrestrial organisms and habitat. Both
methods have considerable uncertainty associated with their estimates of potential risks.
3.3.3.1 Air Monitoring
An evaluation of air monitoring data was conducted to assess the occurrence of methyl
parathion and methyl paraoxon in air (no air monitoring data for 4-nitrophenol was
found). Kollman (2002) summarizes two California air monitoring studies - an ambient
air quality monitoring study (monitoring air quality at public places some distance from
the site of application) for both methyl parathion and methyl paraoxon and an application
site monitoring study (monitoring air quality near a site of application) for methyl
parathion only. The ambient study of 5 sites (4 near rice fields and 1 control site) was
conducted between 5/12/1986 and 6/12/1986, a time coinciding with methyl parathion
application to rice for the control of tadpole shrimp (Triops longicaudatus). The
maximum air concentrations observed were 30.1 and 7.79 ng/m3 for methyl parathion and
methyl paraoxon, respectively. The application site monitoring study from May of 1989
monitored 6 sites around a rice field before, during, and for 72 hours after application and
found a maximum air concentration of 548 ng/m3 (methyl paraoxon was not monitored in
this study).
The potential impact of methyl parathion and methyl paraoxon air concentrations on
surface water quality was assessed for the standard PRZM/EXAMS water body, which
has a surface area of 1 ha (10,000 m2) and a volume of 2 x 107 L. This analysis attempts
to estimate 1) the mass of methyl parathion and methyl paraoxon in a column of air
(referred to as an "air mass") hovering over the standard EXAMS pond; and 2) the
number of air masses that need to pass over the standard EXAMS pond during a storm
(depositing some fraction of each air mass's contaminants into this pond) in order to
reach the aquatic toxicity endpoints identified in the effects assessment (Section 4). If this
number of air masses is low enough to reasonably pass over the EXAMS pond in a single
rain event, it would indicate that there is potential for long-range transport to affect the
CRLF. If the number of air masses is high, it would indicate that there is little potential
for long-range transport to affect the CRLF.
To estimate the mass of methyl parathion in each air mass, it is assumed that the
application site monitoring concentration extends to a vertical height of 100 m above the
standard pond and ambient air monitoring concentrations apply to 900 m of the air mass
(above 100 m and extending to a vertical height of 1000 m). Therefore, the mass of
methyl parathion in an air mass (MMpthwn) based on the maximum ambient (30.1 ng/m3)
and application site monitoring (548 ng/m3) data in the aforementioned studies would
potentially be:
MMPtuon =(30.1ng/m3 x900mxl04m2 +548ng/m3 xl00mxl04m2)/106ng/mg
= 819mg
This is an estimate of the mass of methyl parathion in a single air mass passing over the
standard PRZM/EXAMS pond, which can be expressed as 819 mg/air mass.
55
-------
To provide some indication whether the potential exists for atmospheric concentrations of
methyl parathion to impact frog populations, the number of air masses (NuntAirMasses)
required to provide enough MMpthwn to reach the relevant ecological endpoints (Endpt) is
calculated using the following equation assuming 100% (full), 50%, and 25% washout.
Endpt(jugfL)
819mg/airmassxl0 z/g/mg TTr
NumAirMasses = 7 M^LxWash0ut
2* X 1L/ .!_/
where: 2 x 107 L is the volume of the standard PRZM/EXAMS pond and WashOut is the
proportion of the MMpthwn deposited in the pond as the air masses pass over the pond
(Table 10).
Table 10. Number of air masses needed to attain most sensitive toxicity endpoints in the
aquatic toxicity profile for methyl parathion assuming different levels of deposition or
rainfall washout.
Washout
Acute Frog
92.5 Mg/L
Chronic
Frog
10 ug/L2
Acute
Invertebrate
0.0485 ug/L1
Chronic
Invertebrate
0.25 ug/L2
Aquatic
Plants
2900 ug/L3
Full
2259
244
1.2
6.1
70,827
50%
4518
488
2.4
12
141,653
25%
9037
977
4.7
24
283,307
1 Acute endpoint x the listed species LOC (0.05).
2 Chronic endpoint x the chronic LOC (1.0).
3 Aquatic plant endpoint x the aquatic plant LOC (1.0).
The number of air masses needed to exceed the acute and chronic invertebrate endpoints
are both relatively low and could potentially occur within a single rain event. (Though,
chronic endpoints are typically compared to 21-day exposures.) Therefore, the air
monitoring analysis seems to indicate that long-range transport of methyl parathion has
the potential to indirectly impact CRLFs through impacts to aquatic invertebrates.
Because no methyl paraoxon monitoring data are available for application site monitoring
concentrations, methyl paraoxon application site air concentration (CAPPsiteOxon) was
estimated as the methyl parathion application site monitoring concentration corrected for
the ratio of the ambient methyl paraoxon concentration to ambient methyl parathion
concentration:
c—=548ng/m5 x =i42ng/m5
Therefore, the mass of methyl paraoxon in a single air mass over the standard
PRZM/EXAMS pond (MMp0xon) based on the maximum ambient methyl paraoxon
monitoring data (7.79 ng/m3) and an estimated maximum application site methyl
paraoxon air concentration (142 ng/m3) would potentially be:
56
-------
Muptuon = (7.79ng/m3 x900mxl04m2 +142ng/m3 x 100m x 104m2)/106ng/mg
= 212mg
The NumAirMasses required to exceed the relevant ecological endpoints for methyl paraoxon
would be:
Endpt{jUgfL)
212mg/airmassxl0 z/g/mg Tir
NumAirMasses = 7 M^LxWash0ut
2* X 1L/ J_/
The number of air masses required to exceed the methyl paraoxon endpoints under
different assumptions of the fraction washed out of the air masses passing over the
standard PRZM/EXAMS pond are recorded in Table 11.
Table 11. Number of air masses needed to attain most sensitive toxicity endpoints in the
aquatic toxicity profile for methyl paraoxon assuming different levels of deposition or
rainfall washout.
Washout
Acute Frog
89 |jg/L1
Chronic
Frog
(No
Endpoint
Identified)
Acute
Invertebrate
0.115 |jg/L1
Chronic
Invertebrate
1 mq/l2
Aquatic
Plants
(No
Endpoint
Identified)
Full
8392
NA
11
94
NA
50%
16784
NA
22
189
NA
25%
33567
NA
43
377
NA
1 Acute endpoint x the listed species LOC (0.05).
2 Chronic endpoint x the chronic LOC (1.0).
Comparing the number of air masses required to exceed the relevant methyl parathion
(Table 10) and methyl paraoxon (Table 11) endpoints, fewer air masses are required to
exceed the methyl parathion endpoints (Table 10). Therefore, methyl paraoxon seems to
contribute little to the long-range air transport risk from methyl parathion applications
according to the air monitoring data analysis.
3.2.3.2 Rainwater monitoring
Three estimates of maximum methyl parathion concentrations in rainwater were obtained
from literature. Majewski et al 2005 (http://pubs.usgs.gov/of/2005/1307/) report a
maximum methyl parathion concentration in rainwater of 0.194 |ig/L from 13 sites
sampled between 2002 and 2004 in the southern central valley of California. However,
the monitoring for this study appears to have occurred during a time of year (mid-
December through early April) when relatively little methyl parathion would be applied.
A second estimate of maximum methyl parathion concentrations in rainwater of 2.77
|ig/L was obtained from Majewski and Capel (1995). This maximum value was obtained
from a review of 130 studies from the U.S. and Canada.
57
-------
A third estimate of maximum methyl parathion concentrations in rainwater of 22.9 |ig/L
was obtained from Coupe et al (2000). This maximum value was obtained from a study
of weekly wet deposition samples at 2 sites in Mississippi collected between April and
September of 1995.
In an attempt to estimate the amount of methyl parathion potentially deposited into
aquatic and terrestrial habitats from rainwater after long-range atmospheric transport, the
3 estimates of maximum methyl parathion concentrations in rainwater were considered in
combination with California-specific precipitation data and runoff estimates from PRZM.
Precipitation and runoff data associated with several California PRZM scenarios were
used to determine l-in-10 year peak runoff and rain events. The scenarios included were:
CA almond, CA lettuce, CA wine grape, CA row crop, CA fruit, CA nursery, and CA
onion. The corresponding meteorological data were from the following locations in
California: Sacramento, Santa Maria, San Francisco, Monterey County, Fresno, San
Diego, and Bakersfield, respectively.
Aquatic environment. To estimate concentrations of methyl parathion in the aquatic
habitat resulting from wet deposition, the daily PRZM-simulated volume of runoff from a
10 ha field is combined with an estimate of daily precipitation volumes over the 1 ha
EXAMS pond. This volume is multiplied by the 3 estimates of maximum methyl
parathion concentration in precipitation (reported above) to create low medium and high
estimates for each use scenario (based on maximum methyl parathion concentrations in
rainwater of 0.194, 2.77, and 22.9 (J,g/L, respectively). The results are daily mass loads of
methyl parathion into the standard EXAMS pond. This mass is then divided by the
volume of water in the standard EXAMS pond (2.0 xlO7 L) to achieve a daily estimate of
methyl parathion concentration in the standard EXAMS pond, which represents the
aquatic habitat. From the daily values, l-in-10 year peak estimates of the concentration of
methyl parathion in the aquatic habitat are determined for each PRZM scenario (Table
12).
Table 12. One-in-10 year peak estimates of methyl parathion concentrations in aquatic and
terrestrial habitats resulting from deposition of methyl parathion at low (0.194 M9/L),
medium (2.77 |jg/L), and high (22.9 |jg/L) concentration in rain estimates.
Concentration in aquatic
habitat (|jg/l_)
Deposition on terrestrial
habitat (lbs a.i./A)
Met Station
Scenario
Low1
Medium
2
High3
Low1
Medium
2
High3
Sacramento
CA almond
0.036
0.516
4.269
0.0001
0.0017
0.0144
Santa Maria
CA lettuce
0.039
0.556
4.595
0.0001
0.0014
0.0113
San
Francisco
CA wine
grape
0.034
0.486
4.018
0.0001
0.0016
0.0129
Monterey Co.
CA row crop
0.031
0.446
3.688
0.0001
0.0017
0.0144
Fresno
CA fruit
0.014
0.202
1.669
0.0001
0.0010
0.0082
San Diego
CA nursery
0.026
0.375
3.098
0.0001
0.0013
0.0106
Bakersfield
CA onion
0.010
0.149
1.229
<0.0001
0.0007
0.0056
1 Based maximum rainwater methyl parathion concentration in Majewski et al 2005
(http://pubs.usgs.gov/of/2005/1307/).
2 Based maximum rainwater methyl parathion concentration in Majewski and Capel (1995).
3 Based maximum rainwater methyl parathion concentration in Coupe et al (2000).
58
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The highest scenario's rainwater EECs based on the low, medium, and high maximum
rainwater estimates are l/100th, 178th, and approximately equal to, respectively, the lowest
peak PRZM/EXAMS generated EEC in Table 7 (4.2 (J,g/L, ground applications to
walnuts). These same rainwater EECs are l/2000th, l/120th, and 1/15th, respectively, the
highest peak PRZM/EXAMS generated EEC in Table 7 (66.8 (J,g/L, aerial applications to
cotton). Because of the large variation in rainwater methyl parathion concentration
estimates, no rainwater methyl parathion contribution to EECs is included in the EECs
reported in Table 7 or in the use scenarios modeled in the remainder of the document.
However, it is important to note that not including any rainwater methyl parathion
contribution could affect the interpretation of methyl parathion's potential to impact
CRLFs for those scenarios that generate relatively lower PRZM/EXAMS' EECs.
Risk quotients (RQs) were calculated for aquatic effects of methyl parathion from the
scenarios that produced the highest and lowest EECs (Table 13). Similar to the air
monitoring analysis, the rainwater monitoring data analysis shows that there is potential
for acute and chronic risk to freshwater aquatic invertebrates and, therefore, the potential
for indirect effects to the CRLF from long-range atmospheric transport of methyl
parathion.
Table 13. Aquatic risk quotients (RQs) solely due to long-range atmospheric transport and
subsequent deposition of methyl parathion in rainwater.
Maximum
Rainwater
Concentration
Acute Frog
1850 |jg/L
Chronic
Frog
10 Mg/L
Acute
Invertebrate
0.97 ug/L
Chronic
Invertebrate
0.25 ug/L
Aquatic
Plants
2900 ug/L
Highest Scenario: CA Lettuce (Sacramento Meteorological Station)
Low (0.194 |jg/L)'
<0.01
<0.01
0.04
0.16
<0.01
Medium (2.77
MQ/L)
<0.01
0.06
0.57
2.22
<0.01
High (22.9 |jg/L)J
<0.01
0.46
4.74
18.38
<0.01
Lowest Scenario: CA Lettuce (Sacramento Meteorological Station)
Low (0.194 |jg/L)'
<0.01
<0.01
0.01
0.04
<0.01
Medium (2.77
MQ/L)
<0.01
0.01
0.15
0.60
<0.01
High (22.9 |jg/L)J
<0.01
0.12
1.27
4.92
<0.01
1 Based maximum rainwater methyl parathion concentration in Majewski el al 2005
(http://pubs.usgs.gov/of/2005/1307/).
2 Based maximum rainwater methyl parathion concentration in Majewski and Capel (1995).
3 Based maximum rainwater methyl parathion concentration in Coupe et al (2000).
Similarly, RQs were calculated for aquatic effects of methyl paraoxon from the scenarios
that produced the highest and lowest methyl parathion EECs (Table 14). Methyl
paraoxon EECs from long-range transport were estimated by assuming the maximum
methyl paraoxon concentration is 2.1% of the deposited methyl parathion EECs (2.1% is
based on the highest fraction of methyl paraoxon observed in any of the fate studies).
This analysis shows that there is little potential for acute and/or chronic risks to
freshwater aquatic invertebrates and, therefore, little potential for indirect effects to the
CRLF from long-range atmospheric transport of methyl paraoxon.
59
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Table 14. Aquatic risk quotients (RQs) solely due to long-range atmospheric transport and
subsequent deposition of methyl paraoxon in rainwater.
Maximum
Rainwater
Concentration
Acute Frog
1780 itglU
Chronic
Frog
(No
Endpoint
Identified)
Acute
Invertebrate
2.3 |jg/L1
Chronic
Invertebrate
1 mq/l2
Aquatic
Plants
(No
Endpoint
Identified)
Highest Scenario: CA Lettuce (Sacramento Meteorological Station)
Low (0.194 |jg/L)'
<0.01
N.A.
<0.01
<0.01
N.A.
Medium (2.77
MQ/L)
<0.01
N.A.
0.01
0.01
N.A.
High (22.9 |jg/L)J
<0.01
N.A.
0.04
0.10
N.A.
Lowest Scenario: CA Lettuce (Sacramento Meteorological Station)
Low (0.194 |jg/L)'
<0.01
N.A.
<0.01
<0.01
N.A.
Medium (2.77
MQ/L)
<0.01
N.A.
<0.01
<0.01
N.A.
High (22.9 |jg/L)J
<0.01
N.A.
0.01
0.03
N.A.
1 Based maximum rainwater methyl parathion concentration in Majewski el al 2005
(http://pubs.usgs.gov/of/2005/1307/).
2 Based maximum rainwater methyl parathion concentration in Majewski and Capel (1995).
3 Based maximum rainwater methyl parathion concentration in Coupe et al (2000).
Terrestrial environment. To estimate deposition of methyl parathion on the terrestrial
habitat resulting from wet deposition, the daily volume of water deposited in precipitation
on 1 acre of land is estimated. This volume is multiplied by the 3 estimates of maximum
methyl parathion concentration in precipitation (reported above) to create low medium
and high estimates for each use scenario (based on maximum methyl parathion
concentrations in rainwater of 0.194, 2.77, and 22.9 (J,g/L, respectively). The results are
mass loads of methyl parathion per acre (converted to units of lbs a.i. /A). From these
daily values, l-in-10 year peak estimates of the deposition of methyl parathion on the
terrestrial habitat are estimated for each PRZM scenario (Table 12).
For terrestrial insects, the acute effects endpoint is 0.28 |ig/bee. Based on this endpoint,
EFED would consider any application rate in excess of 0.0008 lbs a.i./A to have potential
to cause acute terrestrial effects at the endangered species LOC. All of the scenarios in
Table 3 exceed this deposition rate if these scenarios are based on the high maximum
rainfall methyl parathion concentration estimate (22.9 |ig/L), and all of the scenarios
except CA onions exceed this deposition rate if these scenarios are based on the medium
maximum rainfall methyl parathion concentration estimate (2.77 |ig/L). Therefore
according to the rainwater monitoring data analysis, log-range atmospheric transport has
the potential to harm terrestrial insects and, therefore, indirectly harm the CRLF through
depletion of terrestrial insects that serve as forage items for terrestrial-phase CRLF.
3.3.3.3 Long-range Transport Summary
There are several simplifying assumptions associated with both approaches used to
estimate potential effects due solely to atmospheric transport that contribute uncertainty
to the interpretation of this assessment. The air monitoring data analysis assumes the air
monitored is similar in concentration to the air masses passing over the simulated CRLF
aquatic habitat during a rain event. For CRLF habitat near sites of methyl parathion
60
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application, it seems likely that the air concentrations would be relatively well estimated,
but having a rain event of sufficient intensity to strip out much of the methyl parathion
from the air may be rare in the part of California where, and at the time when, methyl
parathion is typically applied. Conversely for CRLF habitat distant from sites of methyl
parathion application, it is likely that the air concentrations would be over-estimated due
to dilution with air of lower methyl parathion concentration. However, having a rain
event of sufficient intensity to strip out much of the methyl parathion from the air may be
more likely in the parts of California away from where, but at the same time as, methyl
parathion is typically applied.
Similarly, the rainwater monitoring data analysis assumes: 1) the concentration of methyl
parathion in the rain event is spatially and temporally homogeneous (e.g., the average
concentration measured over the 10-ha field and 1-ha pond for the entire rain event
equals the measured concentration); 2) the entire mass of methyl parathion contained in
the precipitation runs off of the field or is deposited directly into the pond; 3) there is no
degradation of methyl parathion between the time it leaves the air and the time it reaches
the pond; and 4) the measured maximum precipitation concentrations are representative
of the pesticide concentrations in precipitation at the site and time of the l-in-10 year
rain/runoff event. However, none of the 3 maximum methyl parathion concentration in
rainwater estimates obtained provided satisfactory estimates for maximum methyl
parathion concentrations at the site and time of actual application. The monitoring data
from Majewski et al (2005) was from the time of the year when methyl parathion
applications, typically, do not occur, while the other 2 estimates were not from
California.
Neither of the long-range transport analyses presented suggests that risks to the CRLF
can be dismissed. Although it is difficult at this time to spatially delineate where long-
range transport of methyl parathion may cause effects, it should be assumed that the
impacts of methyl parathion on CRLFs would likely extend beyond the downstream
effects and spray drift impact zones alone.
3.4 Terrestrial Exposure
3.4.1 Bird and Mammal Exposure (TREX)
The Agency estimates exposure of birds and mammals to pesticides using the Terrestrial
Exposure Model (T-REX). T-REX uses the Kenaga nomogram, as modified by Fletcher
et al. (1994) to determine pesticide residues on several categories of food items, then
calculates the potential dose an organism might receive from ingesting contaminated
items using allometric equations. Unless toxicological endpoints for terrestrial
amphibians or reptiles are available, toxicological endpoints for birds are used as a
surrogate. For the frog, exposure via ingestion of contaminated food items is estimated
using the EECs for a small bird (20 g) consuming small insects. For mammalian prey
items, it is estimated for a small mammal consuming short grass. Assumed foliar
dissipation half-life can have a significant impact on exposure estimates, especially for
pesticides re-applied at relatively short intervals. Willis and McDowell (1987) is a
compilation of foliage half-lives for pesticides. In this publication, a total of 10 foliar
61
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half-lives based on total dislodgeable residues are listed, ranging from 0.1-2.3 days. The
most conservative estimate (2.3 days) has been used in the T-REX modeling. T-REX
also incorporates a scaling factor developed by Mineau et al (1996) to improve
interspecies toxicity extrapolation. The publication lists a scaling factor of 1.17 for
parathion (slightly higher than the default value of 1.15). Although the publication does
not specify whether the value is for ethyl parathion or methyl parathion, the more
conservative estimate has been used in modeling
Table 15 Input Parameters for T-REX
Parameter
Value
Source
Percentage active ingredient
100%
Labels, application rate
already adjusted
Number of applications
Cotton 5
Onions 6
Grass 6
Walnuts 4
Labels
Application interval
Cotton 5
Onions 5
Grass 5
Walnuts 21
Labels
Dissipation half-life1
2.3 days
Wilis and McDowell 1987
Mineau scaling factor
1.17
Mineau et al., 1996
Table 16 EECs for Dietary- and Dose-based Exposures
Use
EECs for CRLF
EECs for Prey
(small mammals)
Dietary-based
EEC (ppm)
Dose-based
EEC
(mg/kg-bw)
Dietary-based
EEC (ppm)
Dose-based
EEC
(mg/kg-bw)
Agricultural
Cotton (3 lb a.i/A)
520
592
924
881
Onions (0.5 lb a.i/A)
87
99
154
147
Orchards
Walnuts (2 lb a.i/A)
270
308
481
458
Rangeland
Grass (0.75 lb a.i/AJ
130
148
231
220
3.4.2 Terrestrial Invertebrate Exposure
Exposure of terrestrial invertebrates was estimated using the dietary-based EECs
produced by TREX for the two insect categories (small and large). The value produced
by TREX, mg a.i./kg insect, is equivalent to |LXg a.i./g insect. The methyl parathion
residue for a bee (|ig a.i./bee) was calculated by multiplying the residue concentration by
the assumed weight of a honey bee (0.128 g) to establish a dose per bee. This method
assumes that contact is the relevant route of exposure, rather than ingestion. EECs are
presented based on the TREX estimates for small insects and large insects to address the
range of organisms potentially affected.
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Table 17 Terrestrial Invertebrate Exposure
Application Rate
(lb a.i/A)
Insect Size Category
EECs
(mg a.i/kg insect)
Dose per Bee
(|j.g a.i/bee)
Agricultural Highest
(Cotton 3 lb a.i/A)
Small insects
520
67
Large insects
58
7.4
Agricultural Lowest
(Onions 0.5 lb a.i/A)
Small insects
87
11
Large insects
9.6
1.2
Orchards
(Walnuts 2 lb a.i/A)
Small insects
270
35
Large insects
30
3.9
Pasture
(Grass 0.75 lb a.i/A)
Small insects
130
17
Large insects
14
1.8
63
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4.0 Effects Assessment
Toxicity data were derived from guideline tests and open literature (ECOTOX). Data for
the parent compound used in the RED (USEPA 2006) were re-reviewed. In some cases,
data had been derived from sources which no longer meet data quality criteria for EFED.
Based on the initial database reports from ECOTOX, studies which had similar or lower
endpoints were reviewed. These reviews, along with tables documenting all toxicity data
located, are included in Appendix B.
In general, methyl parathion is acutely toxic to animals, and effects are noted soon after
exposure. It is toxic via both ingestion and dermal contact. In cases where it does not
cause outright mortality, sub-lethal effects include disorientation and behavioral changes
that may increase susceptibility to predation and/or modify parenting patterns (e.g., nest
abandonment in birds). Based on acceptable data, methyl parathion is classified as
moderately toxic to fish and very highly toxic to aquatic invertebrates on an acute
exposure basis. Based on acute oral and subacute dietary toxicity tests, it is classified as
very highly toxic to birds and mammals on an acute oral and subacute dietary exposure
basis. It is also classified as highly toxic to bees on both an oral dose and contact
exposure basis. In many chronic effects evaluations, mortality occurs at the same
concentrations at which reproductive endpoints are noted.
4.1 Aquatic Toxicity Profile
Table 18 shows assessment endpoints used to evaluate effects on the aquatic-phase
CRLF. Data available for methyl paraoxon is shown in Table 19. Toxicity data from the
RED document for 4-nitrophenol (PC 056301; also known as paranitrophenol (EPA
1998a)) is shown in Table 20.
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Table 18 Aquatic Toxicity Profile for Methyl Parathion
Assessment
Endpoint
Surrogate
Species
Toxicity Value Used
Source
Citation
Comments
Direct Effects
Acute Toxicity to
Frog
Cutthroat
trout1
LC50 = 1,850 p.g/L
95% CI =
1,390-2,470 ng/L
MRID
40094602
No comments
Chronic Toxicity to
Frog
Rainbow trout
NOAEC = <10 ng/L
LOAEC = 10 ng/L
MRID
250628
Endpoint fry length
and weight. Fry
survivability affected
at 20 jag/L
Indirect Effects and Critical Habitat Effects (Prey Reduction)
Acute Toxicity to
Aquatic
Invertebrates
Water flea
(C. dubia)
EC50 = 0.97 p.g/L
95% CI = NR
Slope = NR
ECOTOX
56473
C. dubia typically
more sensitive than
D. magna
Chronic Toxicity
to Aquatic
Invertebrates
Water flea
(D. magna)
NOAEC =
0.25 ng/L
LOAEC =
0.55 ng/L
MRID
128790
Growth affected at
0.55 ng/L,
reproduction at 0.89
M-g/i
Indirect Effects and Critical Habitat Effects (Habitat Modification)
Acute Toxicity to
Aquatic Plants
Green algae2
(Scenedesmus
subspicatus)
EC50 = 15,000 ng/L
NOAEC = 8,000 ng/L
ECOTOX
4008
72-hour test (StaticJ
a Adult frogs are no longer in the "aquatic phase" of the amphibian life cycle; however, submerged
adult frogs are considered "aquatic" for the purposes of this assessment because exposure
pathways in the water are considerably different that exposure pathways on land.
Birds are used as surrogates for terrestrial phase amphibians.
1Data for western chorus frog (Pseudacris triseriata), tested at the same laboratory, yielded a 96-
hour LC50 of 3,700 |ag/L. A bluegill LC50 of 3,700 p.g a.i./L was also determined, but material
tested appears to have been a formulation.
2Data for aquatic vascular plants validated for qualitative use only. 96-hour LC50= 18,000 |ag/Lfor
aquatic mosquito fern (Azolla pinnata). Typically, non-vascular plants are more sensitive to
toxicant effects than vascular plants.
4.1.1 Toxicity to Freshwater Fish
4.1.1.1 Acute Exposure (Mortality) Studies
Review of methyl parathion acute toxicity data based on guideline studies of freshwater
fish (Mayer and Ellersieck 1986) and open literature meeting ECOTOX and OPP criteria
resulted in approximately 40 different 96-hr LC50 values, representing over 25 different
species of freshwater fishes. The LC50 values ranged from 1,850 |j,g/L for cutthroat trout
(1Oncorhynchus clarki) (Mayer & Ellersieck 1986) to 12,806 |_ig/L for Western mosquito
fish (Gambusia affinis; ECOTOX 62030). In some cases, such as for cutthroat trout
(1Oncorhynchus clarki), rainbow trout (Oncorhynchus mykiss), bluegill (Lepomis
macrochirus), and fathead minnow (Pimephalespromelas), multiple LC50 values, often
generated by different investigators, were reported. For cutthroat trout, LC50 values
ranged from 1,850-4,880 |j,g/L (n=2, arithmetic mean 3,365 |~ig/L). For rainbow trout,
LC50 values ranged from 2,200-3,700 |j,g/L (n=4, arithmetic mean 2,863 |~ig/L). For
bluegill, LC50 values ranged from 2,434-6,900 |j,g/L (n=3, arithmetic mean 4,570 ng/L).
65
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For fathead minnow, LC50 values ranged from 7,200-8,900 |j,g/L (n=3, arithmetic mean
7,867 ng/L). The most sensitive value (1,850 |_ig/L, cutthroat trout) was used as the acute
toxicity assessment endpoint.
4.1.1.2 Chronic Exposure (Growth/Reproduction) Studies
The most sensitive chronic endpoint was from a registrant-submitted guideline study of
rainbow trout (MRID 250628, also referenced as Bailey 1983 in RED (USEPA 2006)).
This study was conducted on the microencapsulated formulation (Penncap®-M). In the
study, analytical concentrations for both filtered and unfiltered test water samples were
reported. Filtered concentrations were used as the assessment endpoints to ensure the
effects were associated with bioavailable methyl parathion. Effects were noted at the
lowest concentration tested and a definitive NOAEC was not established. The study was
classified by the reviewer as supplemental. Effects noted at the LOAEC of 10 |j,g/L
included reductions in fry length and weight. Fry survivability was affected at 20 |J,g/L.
4.1.2 Toxicity to Aquatic-Phase Amphibians
4.1.2.1 Acute Exposure (Mortality) Studies
No guidelines currently exist for amphibian toxicity studies. However, five studies
evaluating the acute effects {i.e., mortality) of methyl parathion on frogs met the criteria
for inclusion into ECOTOX (E9226, E12043, E52442, E65895, E66399). These studies
were reviewed, and reviews are included in Appendix B. Two studies (E65895, E66399)
were from the same group of researchers, who reported 96-hr LC50s of 4,360 |j,g/L and
4,860 |j,g/L respectively, for tadpoles of the Indian bullfrog {Rana tigrina) tested with
technical methyl parathion. 10. Mayer and Ellersieck (1986) publication contained data
for western chorus frog tadpoles {Psuedacris triseriata). The 96-hr LC50 for this frog
was 3,700 |_ig/L. Indian researchers evaluated the end-product Metacid® 50, a product
marketed in India that also contains some DDT. These authors reported the 96-hr LC50
for Rana tigrina tadpoles as 9,500 |_ig/L. Metacid® 50 is not registerd in the United
States.
Another group of researchers conducted an experiment exposing adult Rana
cyanophlyctis (skipping or skipper frog) to methyl parathion in solution. They
reported 96-hr LC50 values of 4,000 |j,g/L for adult males and of 5,750 |j,g/L for adult
females. The females were larger than the males (~20g as opposed to ~8g). In this study,
authors noted avoidance behavior and "hyperactivity" in exposed frogs.
The limited data available suggest the sensitivity range for tadpoles and adult frogs
exposed in the aquatic phase are similar to fish. Differences in the species sensitivity
distributions of fish and amphibians are not well understood. Because of this fact, EFED
has elected to use most sensitive LC50 for fish (cutthroat trout 1,850 |~ig/L); this value
10 Paper is unclear as to whether value presented is in terms of solution (50% w/w emulsifiable concentrate,
or technical. Reviewer has assumed reporting is in terms of EC, and corrected for percent technical.
66
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appears to be protective for amphibians that, based on available data, do not appear to be
any more sensitive than fish.
4.1.2.2 Studies Reporting Sub-lethal Endpoints
Sub-lethal effects data included evaluation of changes in glycogen reserves of adult Rana
cyanophlyctis (female NOAEC 2,500 |u.g/L11, E52442); increases in nitrogen excretion in
Rana tigrina tadpoles (LOAEC 486 |_ig/L, NOAEC not established, E65895), and
increases in oxygen consumption in Rana cyanophlictis tadpoles (LOAEC 2,500 |_ig/L,
NOAEC not established).
4.1.3 Toxicity to Freshwater Invertebrates
Both registrant-submitted guideline studies and open literature toxicity data were
available for freshwater invertebrates. Data evaluation records (DERs) and/or studies for
endpoints reported in the RED (USEPA 2006) were located and reviewed. In some
cases, reported data were from government laboratory toxicity tests reported in Mayer
and Ellersieck 1986 and/or Johnson and Finlay 1980. If the raw data were available in
EFED files, it was reviewed to confirm acceptability. In cases where the raw data were
not available, and the LC50 values were questionable in comparison to other data for the
same or similar species, the values were not used in the assessment (in accordance with
EFED policy regarding use of such data.)
4.1.3.1 Acute Exposure (Mortality) Studies
Including registrant-submitted guideline studies and data included in ECOTOX,
approximately 30 LC50 values were located for a range of aquatic invertebrates. Test
duration ranged from 24-120 hours. Guideline tests for aquatic invertebrates require a
48-hr exposure, thus data from this exposure time period was considered first in
determining an assessment endpoint. A total of 11 acceptable 48-hr LC50 values for
aquatic invertebrates were located, from 7 different sources, including guideline studies
for both technical methyl parathion and Penncap®-M. In the data set, there were LC50
values for 7 different species. LC50S ranged from 0.97 |_ig/L (Ceriodaphnia dubia (water
flea), E56473) to 40 ng/L (Metapenaeus monoceros (sand shrimp), E3674). Five
separate LC50 values were available for Daphnia magna, one of the most commonly
tested aquatic invertebrates. LC50 values ranged from 5.1-20 |j,g/L (n=5, arithmetic mean
7.6 ng/L.) The most sensitive value (0.97 |_ig/L, Ceriodaphnia dubia) was used as the
assessment endpoint.
4.1.3.2 Chronic Exposure (Growth/Reproduction) Studies
Including registrant-submitted guideline studies and data included in ECOTOX, there
were 3 acceptable 21-day (standard evaluation period) studies. All were conducted with
Daphnia magna. The lowest NOAEC, derived from a registrant-submitted guideline
study (MRID 128790) was 0.25 |_ig/L. Growth was the most sensitive endpoint, affected
11 Paper is unclear as to whether value presented is in terms of solution (50% w/w emulsifiable concentrate,
or technical. Reviewer has assumed reporting is in terms of EC, and corrected for percent technical.
67
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at the LOAEC of 0.55 |_ig/L. In this study, reproductive parameters were affected at 0.89
|_ig/L. Another registrant-submitted guideline test (MRID 4303501) reported a NOAEC
of 0.43 |j,g/L and a LOAEC of 0.85 |_ig/L. Endpoints affected in this study included
survival, weight, and time to first brood. An open literature study (E6449) reported a
NOAEC of 1.2 |j,g/L based on effects on reproduction and mortality (survival) to the test
organisms.
4.1.4 Toxicity to Aquatic Plants
No guideline tests on freshwater aquatic plants were located. ECOTOX located 4 studies
(E4008, E4335, E17302, E71939) reporting EC50s for freshwater plants. Two of these
studies (E4008, E4335) were written by the same group of researchers and included
reported endpoints for a 10-day exposure in an experimental flow-through system as well
as endpoints for a 72-hr static test conducted in accordance with OECD guidelines.
Authors report the 72-hr EC50 for the green alga Scendesmus subspicatus as 15,000 |_ig/L,
and the NOAEC as 8,000 |ag/L. The 72-hr EC50 and NOAEC for another green alga,
Chlamydomonous reinhardi were both reported as >100,000 |_ig/L. The authors noted
that EC50S for all chemical tested were 3-38 times lower in the flow-through system, but
were unclear as to whether this may have been in response to the extended exposure or
somehow associated with the test system itself. Given this uncertainty the most sensitive
values from the static test (S. subspicatus) were used as assessment endpoints. Another
study (E71939, not reviewed) reported EC50S of 19,200 |j,g/L for the blue-green alga
Anabaena inaequalis and of 290,900 |_ig/L for the green alga Chlorella kessleri. Only
one study (E17302), using the endproduct Metacid® 50, a product marketed in India that
also contains some DDT was located for freshwater vascular plants. This study reported
an EC50 of 18,000 |_ig/L for the aquatic mosquito fern (Azollapinnata) Metacid® 50 is
not registerd in the United States..
No guideline toxicity data were available for methyl paraoxon. However, acceptable
acute data for fish and chronic data for aquatic invertebrates were located in open
literature and are presented in Table 19.
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Table 19 Aquatic r
"oxicity Profile for Methyl Paraoxon
Assessment
Endpoint
Surrogate
Species
Toxicity Value Used
Source
Citation
Comments
Direct Effects
Acute Toxicity to
Frog
No appropriate data located
Chronic Toxicity to
Frog
No data located
Indirect Effects and Critical Habitat Effects (Prey Reduction)
Acute Toxicity to
Aquatic
Invertebrate
Water flea
(D. magna)
LC50 =2.3 ng/L
95% CI = 2.2-2.5 ng/L
24 hr exposure
ECOTOX
91481
24-hr exposure for
both acute and
chronic. Chronic
effects noted
following removal to
clean medium.
Chronic effects on
reproduction, size and
population growth
rate.
Chronic Toxicity
to Aquatic
Invertebrate
NOAEC = 1.0 ng/L
LOAEC = 1.5 ng/L
Indirect Effects and Critical Habitat Effects (Habitat Modification)
Acute Toxicity to
Aquatic Plants
(non-vascular)
Acute Toxicity to
Aquatic Plants
(vascular)
No data located
In the freshwater invertebrate study (ECOTOX 91481), the author exposed I), magna
neonates to a 24-hour pulse of technical grade methyl paraoxon, then moved exposed
animals to clean medium and analyzed survival, growth, reproduction, and biochemical
endpoints for the exposed animals. Experimental conditions for the reproductive test
were based on the OECD 1979 guideline for reproductive tests with D. magna. The
author calculated an EC50, based on survival following a 24-hr exposure and 48-hr
recovery (used in assessment as a 24-hr exposure value); this value is 2.3 |j,g/L (95% CI
2.2-2.5). Although this exposure period is less than is typically acceptable (aquatic
invertebrate guideline tests have a 48-hr exposure period), no other data regarding
toxicity of the oxon to aquatic invertebrates were located. A longer exposure period
could possibly lower the EC50 value, although the time-to-death data that are available
from other studies indicate that in most cases death occurs rapidly following exposure to
methyl parathion, and that organisms which survive the first 24 hours of the test often
survive the entire test.
In the 24-hr exposure study with daphnids, the EC50 values decreased slightly with length
of observation of the recovery time, with the an EC50 of 2.1 |j,g/L with a 24-hr exposure
and 7 days of recovery and an EC50 of 2.0 |j,g/L with a 24-hr exposure and 14 days of
recovery. Cholinesterase inhibition was noted at concentrations as low as 0.7 |j,g/L
during day 1 (exposure to methyl paraoxon). Exposure to concentrations >1.0 |j,g/L
resulted in decreased size, and reduced number of offspring. Effects were statistically
69
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significant at 1.5 |_ig/L. These data indicate that the relatively short acute exposure (24
hr) resulted in long-term effects on growth and survival.
Based on data contained in the RED (USEPA 2006), 4-nitrophenol is slightly toxic to fish
and aquatic invertebrates on an acute basis but is several orders of magnitude less toxic
than the parent compound or its oxon intermediate.
Table 20 Aquatic Toxicity Profile for Degradate 4-nitrophenol
Assessment
Endpoint
Surrogate
Species
Toxicity Value Used
Source
Citation
Comments
Direct Effects
Acute Toxicity to
Frog
Rainbow
trout
l_C5o—4,000 (xg/L
MRID
94659
As cited in 4-
nitrophenol RED
(EPA 1998)
Chronic Toxicity to
Frog
No data located
Indirect Effects and Critical Habitat Effects (Prey Reduction)
Acute Toxicity to
Aquatic
Invertebrates
Water flea
LC50—5,000 |xg/L
MRID
94659
As cited in 4-
nitrophenol RED
(EPA 1998)
Chronic Toxicity
to Aquatic
Invertebrates
No data located
Indirect Effects and Critical Habitat Effects (Habitat Modification)
Acute Toxicity to
Plants (non-
vascular)
No data located
Acute Toxicity to
Plants (vascular)
Based on data contained in 4-nitrophenol RED (EPA 1998a; studies not reviewed), it is
moderately toxic to both fish and aquatic invertebrates.
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4.2 Terrestrial Toxicity Profile
Table 21 Terrestrial Toxicity Profile for Methyl parathion
Assessment
Endpoint
Surrogate
Species
Toxicity Value Used
Source
Citation
Comments
Direct Effects
Acute Toxicity to
Frog
Bobwhite
quail
LD50= 9.8 mg/kg bw
(dose)
9.5-10.2 mg/kg
ECOTOX
39539
Pen-reared birds.
Authors also tested
wild-caught birds and
LD50s were statistically
indistinguishable.
Bobwhite
quail
LC50= 28.2 mg/kg
(dietary)
95% CI =
22.1-35.3 mg/kg
MRID
102329
MP Technical,
Penncap-M also tested,
LC50= 33.3 mg/kg bw
Chronic Toxicity to
Frog
Bobwhite
quail
NOAEC= 6.3 mg/kg
diet
LOAEC= 15.5 mg/kg
diet
MRID
41179302
Effects included
treatment related
mortality, reduction in
eggs laid, and survival
of offspring
Indirect Effects and Critical Habitat Effects (Prey Reduction)
Acute Toxicity to
Terrestrial
Invertebrates
Honey bee
(A. mellifera)
(contact)
LD50 = 0.28 |ag/bee
E91623
Authors also tested
Thai honey bee (A.
cerana)
Acute Toxicity to
Mouse
Rat
LD50=4.5 mg/kg bw
(dose)
MRID
000168
Lowest endpoint for
females, males higher
in this test (6 mg/kg)
Acute Toxicity to
Frog
American
kestrel
LD50= 3.1 mg/kg bw
(dose)
95% CI =
2.3-4.2 mg/kg
ECOTOX
38447
Sub-lethal effects
included hypothermia,
inhibited brain and
cholinesterase activity.
Bobwhite
quail
LC50= 28.2 mg/kg
(dietary)
95% CI =
22.1-35.3 mg/kg
MRID
102329
MP Technical,
Penncap-M also tested,
LC50= 33.3 mg/kg bw
Chronic Toxicity
to Terrestrial
Invertebrates
Honey bee
No acceptable data located
Chronic Toxicity to
Mouse
Rat
NOAEC= 5 mg/kg bw
LOAEC= 25 mg/kg
bw
MRID
005588
Changes in maternal
body weight
Chronic Toxicity to
Frog
Bobwhite
quail
NOAEC= 6.3 mg/kg
diet
LOAEC= 15.5 mg/kg
diet
MRID
41179302
Effects included
treatment related
mortality, reduction in
eggs laid, and survival
of offspring
Indirect Effects and Critical Habitat Effects (Habitat Modification)
Acute Toxicity to
Terrestrial Plants
Monocot
NOAEL=0.202 lb ai/A
E89091
Bread wheat
Dicot
NOAEL=0.445 lb ai/A
E91430
Sesame
a Adult frogs are no longer in the "aquatic phase" of the amphibian life cycle; however, submerged
adult frogs are considered "aquatic" for the purposes of this assessment because exposure
pathways in the water are considerably different than exposure pathways on land.
Birds are used as surrogates for terrestrial-phase amphibians.
71
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4.2.1 Terrestrial Vertebrates (Birds and Mammals)
4.2.1.1 Birds
No registrant-submitted guideline studies were located for acute oral dose studies on
birds. Two open literature studies were located by ECOTOX, one investigating sub-
lethal effects on American kestrels (Falco sparverius,ECOTOX 38447, Rattner and
Franson 1984), and one comparing toxicity effects of methyl parathion on pen-reared as
opposed to wild-caught bobwhite quail (Colinus virginianus, ECOTOX 39539, Buerger
et. al 1994). Both studies were reviewed, and author's reported endpoints were
confirmed using the program TOXANAL and data as given in the paper. Reviews with
accompanying statistics are included in Appendix B.
Acute Oral Dose
In the bobwhite study, authors dosed 64 pen-reared birds and 40 wild-caught birds (equal
sexes) with methyl parathion at concentrations ranging from 9.1-11.1 mg/kg. Dose range
was based on a previous range finding test. Controls were maintained for both sets of
birds, and control mortality was zero. The author determined and the reviewer confirmed
LD50 values for the pen-reared birds and wild-caught birds were 9.8 mg/kg (95% CI 9.5-
10.2), and 10.22 mg/kg (95% CI 9.8-10.5), respectively. The groups were statistically
inseparable. Acute symptoms noted during the tests included lethargy, ataxia, diarrhea,
and muscle tremors. The authors also measured brain cholinesterase activity of both the
birds that died, and those who survived (sacrificed at the end of a 14-day observation
period). Brain cholinesterase activity in the birds that died (both groups) was
approximately 25% that of the controls. Birds that survived exhibited decreased brain
cholinesterase activity (approximately 70% that of controls) at the end of the observation
period, indicating that while there is recovery, a period of impairment for birds receiving
non-lethal doses may last days to weeks. The authors did not discuss whether there was
any gender difference in response to the pesticide. The authors concluded there was no
statistically significant difference in response between the pen-reared bobwhites and the
wild-caught bobwhites for any of the parameters they measured.
The study on American kestrel was focused on physiological responses, and the authors
report an estimated LD50 incidental to their main work. The authors did not note the
source of birds; therefore, the previous exposure history to environmental contaminants
in uncertain. Data used by the reviewer to estimate LD50 include data from three
experiments reported in the same paper. It is unclear if author used data from all three
experiments or just one experiment. The LD50 reported by author and confirmed by
reviewer is 3.1 mg/kg bw, which is slightly above the highest dose tested (3.0 mg/kg).
The upper bound for the 95% confidence interval could not be determined. Authors
evaluated the kestrel's ability to thermoregulate following methyl parathion intoxication
and the correlation of this effect with brain and plasma cholinesterase inhibition. Birds
dosed with 2.0-3.0 mg/kg exhibited a drop in body temperature and plasma cholinesterase
within 2 hrs of dosing. For birds that survived, both body temperature and cholinesterase
levels showed recovery within the 10 hr post-dosing monitoring period. Body
temperature declines appeared to be correlated with approximately a 50% reduction in
72
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brain and plasma cholinesterase activity. Plasma cholinesterase activity was inhibited in
the lower dose (0.375 and 1.0 mg/kg) treatment groups as well, but the percent inhibition
was not statistically different from the controls. Authors also tested the effect of
exposure to lowered temperatures (5°C versus 22 °C) in birds treated with 2.25 mg/kg
methyl parathion. The magnitude of the drop in body temperature to birds exposed to
cold temperatures was similar to birds maintained at 22°C, but the consequences were
more severe, with a 60% (3 out of 5) mortality rate in the cold-exposed birds. There was
no mortality in the treated birds maintained at 22°C. The authors did not note weight of
birds used in study; however, the average mass of an American kestrel is approximately
120 g (Yamamoto and Santolo 2000, Smallwood 1987, Bernstein etal., 1979).
Based on the available acute oral toxicity data, methyl parathion is classified as very
highly toxic to birds on an acute oral exposure basis.
Dietary Toxicity
A registrant-submitted study for bobwhite quail was located (MRID 102329
Supplemental). This study evaluated both technical methyl parathion and the Penncap®-
M microencapsulated formulation. The LC50 value for the technical was reported as 28.2
mg/kg diet (95% CI 22.0-35.3 mg/kg diet). The LC50 value for Penncap®-M was
reported as 33.3 mg/kg diet (95% CI 25.1 and 40.9 mg/kg diet). Based on the subacute
dietary toxicity values, methyl parathion is classified as very highly toxic to birds on a
subacute dietary exposure basis. Effects noted for all treated birds included ruffled
feathers, diarrhea, wing droop, and withdrawal.
Chronic (Reproductive) Toxicity
A registrant-submitted guideline study for bobwhite quail, using technical grade methyl
parathion, was located (MRID 41179302 Core). Birds were tested at feed concentrations
(mean-measured) of 2.6, 6.27 and 15.5 mg/kg. Overt signs of toxicity were noted in the
15.5 mg/kg diet treatment group. No treatment-related mortality was noted in the 2.6 or
6.27 mg/kg diet treatment groups. The only statistically significant effects on
reproductive performance were a reduction in egg laid per hen and eggs set per hen in the
15.5 mg/kg diet group. Based on this study, the NOAEC for bobwhite quail is 6.27
mg/kg diet and the LOAEC is 15.5 mg/kg diet.
4.2.1.2 Mammals
Registrant-submitted guideline studies were available for small mammals. These studies
provided the most sensitive endpoint located, and are used as assessment endpoints.
Acute Oral Toxicity
Testing on laboratory mammals (typically rats or mice) is submitted to OPP's Health
Effects Division (HED), where it is reviewed and evaluated for inclusion into the human
health risk assessment. Three studies reporting acute oral LD50 values were located. In
all cases, LD50s for male and female rats were reported separately. One study,
conducted on a material reported as 80% methyl parathion (Accession # 243414),
resulted in a male LD50 of 3.6 mg/kg bw (95% CI 1.6-7.9), and a female LD50 of 23.0
mg/kg (95% CI 13.7-38.6). Another study (cited as document # 000168 in HED
73
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document 005588 (1986)) on a material reported as technical methyl parathion (not
encapsulated) reported a male LD50 of 6-16 mg/kg bw, and a female LD50 of 4.5-24
mg/kg bw. Within experimental variability, these values are essentially the same and
classify methyl parathion as highly toxic to very highly toxic to mammals on an acute
oral exposure basis. Signs of acute toxicity in tested animals included excitability,
twitching, loss of coordination, and convulsions. HED used the value reported in
document #000168 in the human health assessment conducted for the RED (USEPA
2006), thus EFED has opted to use the same value in this ecological risk assessment.
Chronic Toxicity
A two-generation reproduction study was conducted with the Spargue-Dawley strain of
Norway rats (Rattus norvegicus\ MRID 00119087) to which methyl parathion was
administered in the diet at concentrations of 0.5, 5, and 25 mg/kg diet. The parental
(systemic) NOAEL was 5 mg/kg diet and the LOAEL was 25mg/kg diet based on
decreased pre-mating body weight for F1 females and decreased maternal body weight
during lactation in females of both generations. No parental reproductive toxicity was
observed at any dose level, however, the offspring/developmental NOAEL was 5 mg/kg
diet based on decreased pup survival in early lactation and on decreased body weight gain
and increased food consumption in the period immediately following weaning. The
developmental LOAEL was 25 mg/kg diet.
4.2.2 Terrestrial Inverte brates
A study by Atkins et. al (1976), (also referenced as MRID 00022220, Core) established a
48-hr acute contact LD50 of 0.291 |j,g/bee. This study, conducted on the technical,
classifies methyl parathion as highly toxic to bees on an acute contact exposure basis.
One study located by ECOTOX (E91623) evaluated variations in susceptibility to methyl
parathion in honeybees (Apis mellifera) from different colonies. The LD50 for bees from
the most sensitive colony was 0.28 |j,g/bee (95% CI 0.23-0.35 |j,g/bee). The LD50 for
bees from the least sensitive colony was 0.54 |j,g/bee (95% CI 0.41-0.70 |j,g/bee). The
authors also evaluated effect on the Thai honeybee (Apis cerana). Reported LD50 for
these bees was 0.08 |j,g/bee (95% CI 0.06-1.0 |j,g/bee). The authors did not report weight
of any of the bees tested, but Apis cerana are generally smaller than Apis mellifera
(www.beesfordevelopment.org/info/info/species/honev-bee-species.shtmn. Various
strains of Apis cerana also vary in size. Given uncertainty associated with weight of the
smaller bee, and to maintain consistency between CRLF assessments, the Apis mellifera
endpoint was used to calculate RQ values.
The microencapsulated methyl parathion product, Penncap®-M, is similar in size to that
of a pollen grain. It has been associated with a number of hive and colony kills because
the bees transport it back to the hive, where the larvae that feed on stored pollen are
exposed to it. Because of the potential toxicity of microencapsulated pesticides to
honeybees, states have adopted regulations restricting the use of these formulations
(http://dpr.clemson.edu/Acrobat/Bulletin%205%20protecting%20honevbees.pdf).
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4.2.3 Terrestrial Plants
There were no registrant-submitted guideline studies for terrestrial plants, and ECOTOX
located no studies determining an EC25, which is the value typically used to evaluate
potential effects on non-endangered plant species. ECOTOX did locate a number of
studies (not reviewed) that described no observable adverse effects levels (NOAELs) for
crop species. Authors generally evaluated effects in terms of growth (length) or
population (biomass or abundance). For monocotyledonous plants (moncots), there were
12 studies (ECOTOX Reference Numbers E89091, E91471, E91429, E91647, E91672,
E88845, E89090, E91914, E91390, E92124, E91584, E91626) evaluating effects on 4
different crop species (rice, barley, bread wheat, and grass). NOAELs ranged from
0.202-0.981 lb ai/A. For dicotyledonous plants (dicots), there were 2 studies, one on bell
pepper (E91430) and one on sesame (E91627). NOAELs ranged from 0.445-17.84 lb
ai/A.
Given that the application rate of 3.0 lb ai/A is currently registered for up to 5
applications only 5 days apart on dicots (cotton) and the application rate of 0.75 lb ai/A
(grass, representing the more sensitive monocots) is currently registered for up to 6
applications only 5 days apart, it appears unlikely that even deposition of up to 0.75 lb
ai/A has a low likelihood to cause detrimental effects on either monocots or dicots.
4.3 Use of Probit Slope Response Relationship
Generally, available toxicity data provide an LC50 or an EC50. Because the Endangered
Species Act (ESA) requires determination of potential effects at an individual level, this
information must be extrapolated from existing data. The Agency uses the probit dose
response relationship as a tool for deriving the probability of effects on a single
individual (U.S. EPA, 2004). The individual effects probability associated with the acute
RQ is based on the mean estimate of the probit dose response slope and an assumption of
that probit model is appropriate for the data set. In some cases, probit is not the
appropriate model for the data, and the Agency has low confidence in extrapolations from
these types of data sets. Upper and lower-bound estimates of the effects probability are
also provided. The upper and lower bounds of the effects probability are based on
available information on the 95% confidence interval of the slope. 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). Probabilities of individual effects for the various
assessment endpoints are provided in Table 22.
The methyl parathion probit slopes for assessment endpoints used in the analysis and
from other studies reviewed in preparing the analysis ranged from approximately 10 to
40. A steep slope indicates that mortality (from 0% to 100%) occurs over a fairly small
exposure range. Thus, the chance of an individual mortality effect below the LC50 is
correspondingly also low (<1 x 1016). However, the potential for mortality of all
individuals (LC100) exposed at concentrations only slightly above the LC50 is high (not
quantified by IECV 1.1). The model is not used to evaluate the probability of individuals
with sublethal effects.
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In circumstances where a probit dose-response slope is not available, the Agency relies
on a default slope of 4.5 (USEPA 2004).
Table 22 Probability of Individual Effects
Assessment
Endpoint
Surrogate
Species
LC / LD and Slope
Fits Probit
Chance of
Individual
Effect
Aquatic-Phase
(Eggs, larvae, tadpoles, juveniles and adults)
Direct Effects
Acute Toxicity to
Frog
Cutthroat
trout
1,850 ng/L and 14.8
Unknown1
<1 in 1016
Chronic Toxicity
to Frog
Rainbow
trout
Evaluated based on no effects level,
chance of effects evaluation not required
Indirect Effects (Prey Reduction)
Acute Toxicity to
Prey
Water
flea
0.97 |ag/L and 4.5 (default slope)
Unknown1
1 in 4.2x108
Cutthroat
trout
1,850 ng/L and 14.8
Unknown1
<1 in 1016
Chronic Toxicity
to Prey
Water
flea
Evaluated based on no effects level,
chance of effects evaluation not required
Rainbow
trout
Indirect Effects (Habitat Modification)
Acute Toxicity to
Aquatic Plants
Chance of effects evaluation not required
Acute Toxicity to
Terrestrial Plants
Terrestrial-Phase
(Juveniles and adults)
Acute Toxicity to
Frog
Bobwhite
quail
9.8 mg/kg and 12.6 (lower bound)
9.8 mg/kg and 26.8 (slope)
9.8 mg/kg and 41.0 (upper bound)
Yes
<1 in 10'lb
<1 in 1016
<1 in 1016
Chronic Toxicity
to Frog
Bobwhite
quail
Evaluated based on no effects level,
chance of effects evaluation not required
Acute Toxicity to
Prey
Honey
bee
0.28 |ag/bee and 4.5 (default slope)
Unknown1
1 in 4.2x108
Bobwhite
quail
9.8 mg/kg and 12.6 (lower bound)
9.8 mg/kg and 26.8 (slope)
9.8 mg/kg and 41.0 (upper bound)
Yes
<1 in 1010
<1 in 1016
<1 in 1016
Rat
0.28 |ag/bee and 4.5 (default slope)
Unknown1
Bobwhite
quail
Evaluated based on no effects level,
chance of effects evaluation not required
Acute Toxicity to
Terrestrial Plants
Chance of effects evaluation not required
'Raw data not available to calculate
ND Not determined
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4.4 Incident Database Review
A total of 30 aquatic incidents for methyl parathion were listed in the OPP Ecological
Incident Information System (EIIS) database. Of these, 73% occurred in the 1970's, and
only 5 (16%) occurred more recently than 1990. In all cases where the species affected
was reported, it was a fish kill, with the magnitude of the kill generally ranging from
hundreds to thousands of fish. In a number of cases (43%), the legality of the application
was listed as accidental misuse, with most of the other incidents listed as registered use or
legality unknown. In 47% of the cases, certainty was described as probable to highly
probable. Because methyl parathion is highly toxic to aquatic invertebrates, and death of
such organisms is rarely reported unless they are economically important (e.g., a shrimp
fishery), incidents listed in the database may underestimate impact of methyl parathion
on aquatic ecosystems and as such, the absence of more recent incidents should not be
construed as the absence of incidents.
In the terrestrial category, 63 incidents were reported. Effects on plants are listed in the
database separately, but only 2 plant incidents were listed, and one of them described the
species affected as bees, so they have been included in the terrestrial description, bringing
the total number of reported terrestrial incidents to 65. Of these incidents, the majority
(94%) was reported in the time period following 1990, and they were heavily biased
(95%) to reports regarding effects on pollinators (bees). The magnitude of effect was
difficult to compare, as it was sometimes reported in terms of hives, and at other times in
terms of colonies or sites. The likelihood that the incident was associated with a
particular pesticide, i.e., certainty, was classified as "probable" or "highly probable" for
80%) of the reports. Whether the incident resulted from a labeled use of the pesticide, i.e.,
legality of use, was uncertain, with 12% of the reports listing it as unknown. In 5 cases, it
was listed as either accidental or intentional misuse. Only 3 reports listed species other
than bees, and in all cases those were various bird species, with the magnitude of the kill
ranging from 10 to approximately 1500 individuals.
5.0 Risk Characterizations
5.1 Risk Estimation
Risk is estimated by calculating the ratio of the expected environmental concentration
and the appropriate toxicity endpoint. This value is the risk quotient, which is then
compared to pre-established levels of concern for each category evaluated. The RQ
methodology, LOCs, and specific details of the calculations are contained in Appendix D.
The highest EECs (based on maximum application rates) and most sensitive endpoints
are used to determine the screening-level RQ. Using these two values is intended to
result in a conservative estimate of risk. Risk quotients are presented in Table 23
(aquatic-phase CRLF) and Table 24 (terrestrial-phase CRLF). Both tables contain risk
quotients for the three types of land classes affected by use of methyl parathion
(agricultural, orchards, and rangeland). For agricultural uses, which have a range of
maximum rates, RQs for the highest rate (use on cotton) and the lowest rate (use on
onions) are presented. T-HERPS was also run for each of the land uses (results in
77
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Appendix E), and LOC exceedances followed the same pattern as those for the risk
quotients generated by T-REX.
Appendix E indicates for freshwater fish, RQ values are below acute and chronic LOCs
except for use on rice which exceeds the acute and chronic risk LOCs. Appendix E also
indicates that even following a single application of methyl parathion, RQ values for
freshwater invertebrates exceed the acute and chronic risk LOCs across all of the uses
evaluated.
Table 23 Risk Quotients for Direct and Indirect Effects on Aquatic-Phase CRLF.
Assessment Endpoint
Organism or Life Stage
Concentration
Estimate
RQ
LOC
Exceedence
Aquatic-Phase CRLF (Eggs, larvae, tadpoles, juvenile, and adultsf
Direct Effects
Acute Toxicity to Frog
Juveniles, adults
Agricultural (highest)
Agricultural (lowest)
Orchards
<0.05
<0.05
<0.05
No
No
No
Rangeland
<0.05
No
Chronic Toxicity to
Frog
Eggs, larvae, tadpole
Agricultural (highest)
Agricultural (lowest)
Orchards
<1.0
<1.0
<1.0
No
No
No
Rangeland
<1.0
No
Indirect Effects and Critical Habitat Effects
Fish
Agricultural (highest)
Agricultural (lowest)
Orchards
<0.05
<0.05
<0.05
No
No
No
Acute Toxicity to Prey
Rangeland
<0.05
No
Invertebrate
Agricultural (highest)
Agricultural (lowest)
Orchards
69
16
9.8
Yes
Yes
Yes
Rangeland
9.7
Yes
Fish
Agricultural (highest)
Agricultural (lowest)
Orchards
<1.0
<1.0
<1.0
No
No
No
Chronic Toxicity to
Rangeland
<1.0
No
Prey
Invertebrate
Agricultural (highest)
Agricultural (lowest)
Orchards
35
9.5
13
Yes
Yes
Yes
Rangeland
16
Yes
Acute Toxicity to
Aquatic Plants
(Habitat, Food Source)
Green algae
Agricultural (highest)
Agricultural (lowest)
Orchards
Rangeland
<1.0
<1.0
<1.0
<1.0
No
No
No
No
Acute Toxicity to
Terrestrial Plants
Plant
(based on more
Agricultural (highest)
Agricultural (lowest)
Orchards
Rangeland
No effect distance
140 ft
10ft
(Wetland & Upland)
sensitive monocots)
100 ft
20ft
1 LOCs used in this assessment:
Aquatic animals acute risk endangered species 0.05
Aquatic animals chronic risk 1.0
Aquatic plants acute risk 1.0.
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Table 24 Risk Quotients for Direct and Indirect Effects on theTerrestrial-Phase CRLF.
Assessment Endpoint
Organism or Life Stage
Concentration
Estimate
RQ
LOC
Exceedence
Terrestrial-Phase CRLF (Juveniles and adults)
Direct Effects
Acute Toxicity to Frog
Small (20g)
Agricultural (highest)
Agricultural (lowest)
Orchards
88
15
46
Yes
Yes
Yes
Rangeland
22
Yes
Chronic Toxicity to
Frog
All sizes
Agricultural (highest)
Agricultural (lowest)
Orchards
83
14
43
Yes
Yes
Yes
Rangeland
21
Yes
Indirect Effects and Critical Habitat Effects
Terrestrial Invertebrate
Agricultural (highest)
Agricultural (lowest)
Orchards
237
40
123
Yes
Yes
Yes
Rangeland
59
Yes
Acute Toxicity to Prey
Mouse (15 g herbivore)
Agricultural (highest)
Agricultural (lowest)
Orchards
89
15
46
Yes
Yes
Yes
Rangeland
22
Yes
Frog (20 g)
Agricultural (highest)
Agricultural (lowest)
Orchards
88
15
46
Yes
Yes
Yes
Rangeland
22
Yes
Terrestrial Invertebrate
No data for chronic evaluation
Chronic Toxicity to
Prey
Mouse
(herbivore all sizes)
Agricultural (highest)
Agricultural (lowest)
Orchards
Rangeland
9.2
1.5
4.8
2.3
Yes
Yes
Yes
Yes
Frog (all sizes)
Agricultural (highest)
Agricultural (lowest)
Orchards
83
14
43
Yes
Yes
Yes
Rangeland
21
Yes
Acute Toxicity to
Terrestrial Plants
Plant
(based on more
Agricultural (highest)
Agricultural (lowest)
Orchards
Rangeland
No effect distance
140 ft
10ft
(Wetland & Upland)
sensitive monocots)
100 ft
20ft
1 LOCs used in this assessment:
Terrestrial plants acute risk 1.0
Terrestrial vertebrates acute risk endangered species 0.1
Terrestrial invertebrates acute risk endangered species 0.05
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5.2 Risk Description
5.2.1 Direct Effects
Direct effects quantitatively considered in this assessment and used as the basis for the
determination are survival, growth, and reproduction of both the aquatic and terrestrial-
phase CRLF. Sublethal effects reported in some studies, such as disorientation, which
may cause increased susceptibility to predation and/or behavioral modifications affecting
the survival of either adult or juvenile frogs were not quantitatively evaluated. Because a
lower endpoint for these types of effects is not available, the Agency has not attempted to
spatially distinguish a zone of anticipated effects.
5.2.1.1 Aquatic Phase
The aquatic phase considers life stages of the frog that are obligatory aquatic organisms,
including eggs, larvae, and tadpoles. It also considers juveniles and adults, which spend a
portion of their time in water bodies which may receive runoff containing methyl
parathion. No LOCs (acute or chronic risk) were exceeded for surrogate organisms (fish)
representing the aquatic-phase frog except for direct applications to water for use on rice.
The effects determination for this component is no effect except for use on rice where
both acute and chronic risk LOCs are exceeded.
5.2.1.2 Terrestrial Phase (Adults and Juveniles)
For this ecological risk assessment, terrestrial-phase adults are defined as frogs weighing
lOOg or more, based on the evaluation categories available in the T-REX model. Acute
and chronic LOCs are exceeded for all three land uses. Using T-HERPS, acute and
chronic LOCs were exceeded for all three land uses. The effects determination for this
component is may affect, likely to adversely affect.
For this ecological risk assessment, terrestrial-phase juveniles are defined as frogs
weighing 20 g to 99 g, based on the evaluation categories available in the T-REX model.
Acute and chronic risk LOCs are exceeded for all three land uses. Using T-HERPS,
acute and chronic LOCs were also exceeded for all three land uses. The effects
determination for this component is may affect, likely to adversely affect.
5.2.2 Indirect Effects and Critical Habitat Effects (Reduction in Prey Base)
A reduction in prey base may adversely affect the CRLF by reducing its survival, growth,
or reproduction. It is difficult to quantitatively evaluate the effect a reduction in prey
base may have on an individual frog or frogs. However, based on the fact that both acute
and chronic risk LOCs are exceeded for aquatic invertebrates and all terrestrial prey types
in all land use categories evaluated, it is reasonable to assume there may be a measurable
reduction in prey items in areas treated with methyl parathion or adjacent to areas treated
with methyl parathion. The effects determination for this component of the indirect
effects evaluation is may affect, likely to adversely affect. The effects determination for
this component of the critical habitat evaluation is modification of critical habitat.
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5.2.2.1 Terrestrial Invertebrates
Quantitative evaluation of terrestrial invertebrate effects is based on acute data from
honeybees. Acute risk LOCs for all land use categories evaluated are exceeded.
5.2.2.2 Terrestrial-Phase Amphibians
Small amphibians are a portion of the prey base for the CRLF. For this ecological risk
assessment, small amphibians are defined as frogs weighing 20 g to 99 g, based on the
evaluation categories available in the T-REX model. Acute and chronic LOCs are
exceeded for all three land uses. Using T-HERPS, acute and chronic risk LOCs are also
exceeded for all three land uses.
5.2.2.3 Aquatic Plants
Algae and detritus may be consumed by the aquatic-phase CRLF. No LOCs are
exceeded for aquatic plants based on aquatic plant toxicity data for nonvascular plants.
5.2.2.4 Aquatic Invertebrates
Aquatic invertebrates are a portion of the prey base for the CRLF. Acute and chronic risk
LOCs are exceeded for all land uses
5.2.2.5 Fish
Fish are a portion of the prey base for the CRLF. No acute or chronic risk LOCs are
exceeded for fish.
5.2.3 Indirect Effects and Critical Habitat Effects (Habitat Degradation)
Plants, both aquatic and terrestrial, provide cover and foraging locations for adult and
juvenile CRLF. Degradation of plant communities could results in increased exposure to
predators and/or decrease in prey availability. The effects determination for this aquatic
plant component of the indirect effects evaluation is no effect, and for the terrestrial plant
component is may affect, not likely to adversely affect (discountable). The effects
determination for this component of the critical habitat evaluation is no modification of
critical habitat.
5.2.3.1 Aquatic Plants (Vascular and Non-vascular)
Aquatic plants were evaluated based on data available for nonvascular plants, i.e., green
algae. No LOCs were exceeded for any land use category evaluated.
5.2.3.2 Terrestrial Plants
The application rate of 3.0 lb ai/A is currently registered for up to 5 applications only 5
days apart on dicots (e.g., cotton) and the application rate of 0.75 lb ai/A (grass,
representing the more sensitive monocots) is currently registered for up to 6 applications
only 5 days apart, it appears that even deposition of up to 0.75 lb ai/A has a low
likelihood to cause detrimental effects on either monocots or dicots. Even at the highest
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application rate (3 lb ai/A), the deposition associated with aerial spray drift falls below
this level at 30 ft away from the application site.
Based on the data available, it appears that detrimental effects on terrestrial plants of a
sufficient magnitude to cause take of CRLF due to indirect effects on the shelter and
foraging area provided by these plants are extremely unlikely to occur, i.e., discountable,
thus this component of the determination is considered may effect, not likely to adversely
affect..
5.3 Risk Conclusions
After completing the analysis of the effects of methyl parathion on the federally listed
threatened California red-legged frog (Rana aurora draytonii) in accordance with
methods delineated in the Overview document (USEPA 2004), EFED concludes that the
use of methyl parathion (PC#053501) may affect, and is likely to adversely affect the
California red-legged, based on direct effects on juvenile and adult terrestrial-phase frogs
and indirect effects on both the aquatic and terrestrial prey base. EFED also concludes
that these potential effects on prey base constitute habitat modification (HM) to critical
habitat. Rationale for each component assessed is provided in Table 25.
Table 25 Effects Determination for Methyl Parathion
Assessment
Endpoint
Effects determination
Basis for Determination
Aquatic-Phase CRLF
(Eggs, larvae, tadpoles, juveniles, and adults)3
Direct Effects
1. Survival,
growth, and
reproduction of
CRLF
No effect
(use on rice is an LAA)
No exceedances of acute or chronic risk LOCs
for surrogate organisms representing the CRLF
except for use on rice where both acute and
chronic risk LOCs are exceeded.
Indirect Effects and Critical Habitat Effects
2. Reduction or
modification of
aquatic prey
base
May affect
Likely to adversely affect
Modification of critical
habitat
Acute and chronic risk LOC exceedances for
aquatic invertebrates for all land uses assessed.
Anticipated effects on aquatic prey base.
3. Reduction or
modification of
aquatic plant
community
No effect
No LOC exceedances for aquatic plants.
4. Degradation
of riparian
vegetation
May affect
Not likely to adversely
affect
(Discountable)
Based available data detrimental effects of
a sufficient magnitude to cause take of
CRLF due to by these plants appear
unlikely.
Terrestrial-Phase CRLF
(Juveniles and Adults)
Direct Effects
5. Survival,
growth, and
reproduction of
CRLF
May affect
Likely to adversely affect
Acute and chronic risk LOC exceedances for
both adults and juveniles based on both T-REX
and T-HERPS estimates for all land use
categories.
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Indirect Effects and Critical Habitat Effects
6. Reduction or
modification of
terrestrial prey
base
May affect
Likely to adversely affect
Modification of critical
habitat
Acute and chronic risk LOC exceedances for all
prey categories for all land use categories.
7. Degradation
of riparian and/or
upland
vegetation
May affect
Not likely to adversely
affect
(Discountable)
Based available data detrimental effects of
a sufficient magnitude to cause take of
CRLF due to by these plants appear
unlikely.
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.
Attachment 2, which includes information on the baseline status and cumulative effects
for the CRLF, can be used during this consultation to provide background information on
past US Fish and Wildlife Services biological opinions associated with the CRLF.
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 CRLF life stages
within specific recovery units and/or designated critical habitat within the
action area. 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 species.
• Quantitative information on prey base requirements for individual aquatic-
and terrestrial-phase frogs. While existing information provides a
preliminary picture of the types of food sources utilized by the frog, 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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• 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 frogs and potential modification to critical habitat.
6.0 Uncertainties
Risk assessment, by its very nature, is not exact, and requires the risk assessor to make
assumptions regarding a number of parameters, to use data which may or may not
accurately reflects the species of concern, and to use models which are a simplified
representation of complex ecological processes. In this risk assessment, EFED has used
the best available data regarding such important parameters as the life history of the
California red-legged frog, typical environmental conditions in the proximity of frog
habitat, toxicity of methyl parathion, and usage of methyl parathion in the action area.
Frequently, such information is better expressed as ranges rather then points, and when
this is the case, EFED has opted to use the end of range resulting in a conservative
estimate of risk, in order to provide the benefit of doubt to the frog. These uncertainties,
and the directions in which they may bias the risk estimate, are described below.
6.1 Exposure Assessment Uncertainties
Overall, the uncertainties inherent in the exposure assessment tend to result in over-
estimation of exposures. This is apparent when comparing modeling results with
monitoring data. In general, the monitoring data should be considered a lower bound on
exposure, while modeling represents an upper bound.
Differences between modeled EECs and monitoring results are generally attributable to
three sources: 1) simulation modeling estimates are made using maximum label rates,
monitoring data reflects typical use, 2) modeled values represent a small static water
body, the vast majority of monitoring data is for streams and rivers which tend to be less
vulnerable as high concentration tend to be of short duration as they pesticide is carried
downstream more rapidly; 3) simulation modeling represents a small watershed near the
area of application; 4) monitoring data usually represents higher order streams with large
basins and multiple land uses; 5: modeled values are l-in-10 year exceedance values.
Since most monitoring data are from one or two year studies at any one site, it represents
1 in 2 year values.
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6.1.1 Modeling Assumptions
The uncertainties incorporate in the exposure assessment cannot be quantitatively
characterized. However, given the available data and the EFED's reliance on
conservative modeling assumptions, it is expected that the modeling results in an over-
prediction of exposure. Qualitatively, conservative assumptions which may affect
exposure include the following:
• Modeling for each use site assumes that the entire 10-hectare watershed is
taken up by the respective use pattern.
• The assessment assumes all applications have occurred concurrently on
the same day at the exact same application rate.
• The assessment assumes all applications are at maximum labeled rate.
6.1.2 Maximum Use Scenarios
The screening-level risk assessment focuses on characterizing potential ecological risks
resulting from a maximum use scenario, which is determined from label statements of
maximum application rate and number of applications with the shortest time interval
between applications. The frequency at which actual uses approach this maximum use
scenario may be dependant on pesticide resistance, timing of applications, cultural
practices, and market forces.
6.1.3 Modeling Inputs
The standard ecological water body scenario (EXAMS pond) used to calculate potential
aquatic exposure to pesticides is intended to represent conservative estimates, and to
avoid underestimations of the actual exposure. The standard scenario consists of
application to a 10-hectare field bordering a 1-hectare, 2-meter deep (20,000 m3) pond
with no outlet. Exposure estimates generated using the EXAMS pond are intended to
represent a wide variety of vulnerable water bodies that occur at the top of watersheds
including prairie pot holes, playa lakes, wetlands, vernal pools, man-made and natural
ponds, and intermittent and lower order streams. As a group, there are factors that make
these water bodies more or less vulnerable than the EXAMS pond. Static water bodies
that have larger ratios of pesticide-treated drainage area to water body volume would be
expected to have higher peak EECs than the EXAMS pond. These water bodies will be
either smaller in size or have larger drainage areas. Smaller water bodies have limited
storage capacity and thus may overflow and carry pesticide in the discharge, whereas the
EXAMS pond has no discharge. As watershed size increases beyond 10-hectares, it
becomes increasingly unlikely that the entire watershed is planted with a single crop that
is all treated simultaneously with the pesticide. Headwater streams can also have peak
concentrations higher than the EXAMS pond, but they likely persist for only short
periods of time and are then carried and dissipated downstream.
The Agency acknowledges that there are some unique aquatic habitats that are not
accurately captured by this modeling scenario and modeling results may, therefore,
under- or over-estimate exposure, depending on a number of variables. For example,
aquatic-phase CRLFs may inhabit water bodies of different size and depth and/or are
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located adjacent to larger or smaller drainage areas than the EXAMS pond. The Agency
does not currently have sufficient information regarding the hydrology of these aquatic
habitats to develop a specific alternate scenario for the CRLF. CRLFs prefer habitat with
perennial (present year-round) or near-perennial water and do not frequently inhabit
vernal (temporary) pools because conditions in these habitats are generally not suitable
(Hayes and Jennings 1988). Therefore, the EXAMS pond is assumed to be representative
of exposure to aquatic-phase CRLFs. In addition, the Services agree that the existing
EXAMS pond represents the best currently available approach for estimating aquatic
exposure to pesticides (USFWS/NMFS 2004).
6.1.4 Aquatic Exposure Estimates
In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations
that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone
Model is a process or "simulation" model that calculates what happens to a pesticide in a
farmer's field on a day-to-day basis. It considers factors such as rainfall and plant
transpiration of water, as well as how and when the pesticide is applied. It has two major
components: hydrology and chemical transport. Water movement is simulated by the use
of generalized soil parameters, including field capacity, wilting point, and saturation
water content. The chemical transport component can simulate pesticide application on
the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase concentrations in
the soil are estimated by simultaneously considering the processes of pesticide uptake by
plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection,
dispersion, and retardation.
Uncertainties associated with each of these individual components add to the overall
uncertainty of the modeled concentrations. Additionally, model inputs from the
environmental fate degradation studies are chosen to represent the upper confidence
bound on the mean values that are not expected to be exceeded in the environment
approximately 90 percent of the time. Mobility input values are chosen to be
representative of conditions in the environment. The natural variation in soils adds to the
uncertainty of modeled values. Factors such as application date, crop emergence date,
and canopy cover can also affect estimated concentrations, adding to the uncertainty of
modeled values. Factors within the ambient environment such as soil temperatures,
sunlight intensity, antecedent soil moisture, and surface water temperatures can cause
actual aquatic concentrations to differ for the modeled values.
Unlike spray drift, tools are currently not available to evaluate the effectiveness of a
vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is
highly dependent on the condition of the vegetative strip. For example, a well-
established, healthy vegetative setback can be a very effective means of reducing runoff
and erosion from agricultural fields. Alternatively, a setback of poor vegetative quality
or a setback that is channelized can be ineffective at reducing loadings. Until such time
as a quantitative method to estimate the effect of vegetative setbacks on various
conditions on pesticide loadings becomes available, the aquatic exposure predictions are
likely to overestimate exposure where healthy vegetative setbacks exist and
underestimate exposure where poorly developed, channelized, or bare setbacks exist.
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6.1.5 Usage Uncertainties
County-level usage data were obtained from California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database. Four years of data (2002 -
2005) were included in this analysis because statistical methodology for identifying
outliers, in terms of area treated and pounds applied, was provided by CDPR for these
years only. No methodology for removing outliers was provided by CDPR for 2001 and
earlier pesticide data; therefore, this information was not included in the analysis because
it may misrepresent actual usage patterns. CDPR PUR documentation indicates that
errors in the data may include the following: a misplaced decimal; incorrect measures,
area treated, or units; and reports of diluted pesticide concentrations. In addition, it is
possible that the data may contain reports for pesticide uses that have been cancelled.
The CPDR PUR data does not include home owner applied pesticides; therefore,
residential uses are not likely to be reported. As with all pesticide use data, there may be
instances of misuse and misreporting. The Agency made use of the most current,
verifiable information; in cases where there were discrepancies, the most conservative
information was used.
6.1.6 Action Area
An example of an important simplifying assumption that may require future refinement is
the assumption of uniform runoff characteristics throughout a landscape. It is well
documented that runoff characteristics are highly non-uniform and anisotropic, and
become increasingly so as the area under consideration becomes larger. The assumption
made for estimating the aquatic Action Area (based on predicted in-stream dilution) was
that the entire landscape exhibited runoff properties identical to those commonly found in
agricultural lands in this region. However, considering the vastly different runoff
characteristics of: a) undeveloped (especially forested) areas, which exhibit the least
amount of surface runoff but the greatest amount of groundwater recharge; b)
suburban/residential areas, which are dominated by the relationship between
impermeable surfaces (roads, lots) and grassed/other areas (lawns) plus local drainage
management; c) urban areas, that are dominated by managed storm drainage and
impermeable surfaces; and d) agricultural areas dominated by Hortonian and focused
runoff (especially with row crops), a refined assessment should incorporate these
differences for modeled stream flow generation. As the zone around the immediate
(application) target area expands, there will be greater variability in the landscape; in the
context of a risk assessment, the runoff potential that is assumed for the expanding area
will be a crucial variable (since dilution at the outflow point is determined by the size of
the expanding area). Thus, it important to know at least some approximate estimate of
types of land use within that region. Runoff from forested areas ranges from 45 -
2,700% less than from agricultural areas; in most studies, runoff was 2.5 to 7 times higher
in agricultural areas (e.g., Okisaka et al., 1997; Karvonen et al., 1999; McDonald et al.,
2002; Phuong and van Dam 2002). Differences in runoff potential between
urban/sub urban areas and agricultural areas are generally less than between agricultural
and forested areas. In terms of likely runoff potential (other variables - such as
topography and rainfall - being equal), the relationship is generally as follows (going
from lowest to highest runoff potential):
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Three-tiered forest < agroforestry < suburban < row-crop agriculture < urban.
There are, however, other uncertainties that should serve to counteract the effects of the
aforementioned issue. For example, the dilution model considers that 100% of the
agricultural area has the chemical applied, which is almost certainly a gross over-
estimation. Thus, there will be assumed chemical contributions from agricultural areas
that will actually be contributing only runoff water (dilutant); so some contributions to
total contaminant load will really serve to lessen rather than increase aquatic
concentrations. In light of these (and other) confounding factors, Agency believes that
this model gives us the best available estimates under current circumstances.
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6.2 Effects Assessment Uncertainties
6.2.1 Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids, second instar for
amphipods, stoneflies, mayflies, and third instar for midges).
Testing of juveniles may overestimate toxicity at older age classes for pesticide active
ingredients that act directly without metabolic transformation because younger age
classes may not have the enzymatic systems associated with detoxifying xenobiotics. In
so far as the available toxicity data may provide ranges of sensitivity information with
respect to age class, this assessment uses the most sensitive life-stage information as
measures of effect for surrogate aquatic animals, and is therefore, considered as
protective of the California Red Legged Frog.
6.2.2 Use of Surrogate Species Data
Currently, there are no FIFRA guideline toxicity tests for amphibians. Therefore, in
accordance with the Overview Document (U.S. EPA 2004), data for the most sensitive
freshwater fish are used as a surrogate for aquatic-phase amphibians such as the
California red-legged frog. Available open literature information on methyl parathion
toxicity to aquatic-phase amphibians suggests sensitivity of this taxa to methyl parathion
is in the same range as that of freshwater fish. Species sensitivity distribution data for
amphibians indicates the range of sensitivity for organic compounds is similar to that of
freshwater fish (Birge et al., 2000). Therefore, the endpoint based on freshwater fish
ecotoxicity data is assumed to be protective. Extrapolation of the risk conclusions from
the most sensitive tested species to the California red-legged frog is more likely to
overestimate the potential risks than to underestimate the potential risk. Information to
indicate were the California red-legged frog may fall in an amphibian species sensitivity
distribution was not located.
6.2.3 Extrapolation of Effects
Length of exposure and concurrent environmental stressors (e.g., urban expansion,
habitat modification, predators) will likely affect the response of the California red-
legged frog to methyl parathion. Because of the complexity of an organism's response to
multiple stressors, the overall "direction" of the response is unknown. Additional
environmental stressors may decrease or increase the sensitivity to the herbicide. Timing,
peak concentration, and duration of exposure are critical in terms of evaluating effects.
These factors will vary both temporally and spatially within the action area. Overall, the
effect of this variability may result in either an overestimation or underestimation of risk
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6.2.4 Acute LOC Assumptions
The risk characterization section of this assessment includes an evaluation of the potential
for individual effects. The individual effects probability associated with the acute RQ is
based on the assumption that the dose-response curve fits a probit model. It uses the
mean estimate of the slope and the LC50 to estimate the probability of individual effects.
6.2.5 Residue Levels Selection
The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide
residues in wildlife dietary items. These residue assumptions are believed to reflect a
realistic upper-bound residue estimate, although the degree to which this assumption
reflects a specific percentile estimate is difficult to quantify. It is important to note that
the field measurement efforts used to develop the Fletcher estimates of exposure involve
highly varied sampling techniques. It is entirely possible that much of these data reflect
residues averaged over entire above ground plants in the case of grass and forage
sampling.
6.2.6 Dietary Intake
It was assumed that ingestion of food items in the field occurs at rates commensurate
with those in the laboratory. Although the screening assessment process adjusts dry-
weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food
intake estimates, it does not allow for gross energy differences. Direct comparison of a
laboratory dietary concentration- based effects threshold to a fresh-weight pesticide
residue estimate would result in an underestimation of field exposure by food
consumption by a factor of 1.25 - 2.5 for most food items.
Differences in assimilative efficiency between laboratory and wild diets suggest that
current screening assessment methods do not account for a potentially important aspect of
food requirements. Depending upon species and dietary matrix, bird assimilation of wild
diet energy ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85%
(U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is
formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for
underestimation of exposure may exist by assuming that consumption of food in the wild
is comparable with consumption during laboratory testing. In the screening process,
exposure may be underestimated because metabolic rates are not related to food
consumption.
6.2.7 Mixtures
The California red-legged frog and various components of its ecosystem may be exposed
to multiple pesticides, introduced into its environment either via a multiple active
ingredient formulated product, a tank mixture, or transport from independently applied
active ingredients. Multiple pesticides may act in an additive, synergistic, or antagonistic
fashion. Quantifying reasonable environmental exposures and establishing reasonable
corresponding toxicological endpoints for the myriad of possible situations is beyond the
scope of this document, and in some cases, beyond the current state of ecotoxicological
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practice. Mixtures could affect the CLRF in ways not addressed in this assessment.
Exposure to multiple contaminants could make organisms more or less sensitive to the
effects of methyl parathion, thus the directional bias associated with environmental
mixtures is unknown, and may vary on a case-by-case basis.
6.2.8 Sublethal Effects
For an acute risk assessment, the screening risk assessment relies on the acute mortality
endpoint as well as a suite of sublethal responses to the pesticide, as determined by the
testing of species response to chronic exposure conditions and subsequent chronic risk
assessment. Consideration of additional sublethal data in the assessment is exercised on a
case-by-case basis and only after careful consideration of the nature of the sublethal
effect measured and the extent and quality of available data to support establishing a
plausible relationship between the measure of effect (sublethal endpoint) and the
assessment endpoints.
6.2.9 Location of Wildlife Species
For this baseline terrestrial risk assessment, a generic bird or mammal was assumed to
occupy either the treated field or adjacent areas receiving a treatment rate on the field.
Actual habitat requirements of any particular terrestrial species were not considered, and
it was assumed that species occupy, exclusively and permanently, the modeled treatment
area. Spray drift model predictions suggest that this assumption leads to an
overestimation of exposure to species that do not occupy the treated field exclusively and
permanently.
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