&EPA
               United States
               Environmental Protection
               Agency
                        Health Effects Research
                        Laboratory
                        Research Triangle Park NC 27711
tPA 600 1 80-013
February 1980
               Research and Development
           Worker Reentry in
           Florida Citrus
           Pesticides  in the
           Agricultural
           Environment
>
P 600/1
i)-013

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                RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series These nine broad cate-
gories were established to facilitate further development and  application of en-
vironmental technology.  Elimination of traditional grouping  was  consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are-

      1   Environmental  Health Effects Research
      2   Environmental  Protection Technology
      3   Ecological Research
      4   Environmental  Monitoring
      5   Socioeconomic Environmental Studies
      6.  Scientific and Technical Assessment Reports (STAR)
      7   Interagency Energy-Environment Research and  Development
      8   "Special" Reports
      9.  Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL HEALTH EFFECTS RE-
SEARCH series. This series describes projects and studies relating to the toler-
ances of man for unhealthful substances or conditions This work is generally
assessed from a medical viewpoint, including physiological or psychological
studies. In addition to toxicology and other medical specialities, study areas in-
clude biomedical  instrumentation and health research techniques  utilizing ani-
mals — but always with  intended application to human health measures.
 This document is available to the public through the National Technical Informa-
 tion Service, Springfield, Virginia 22161.

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                                        EPA-600/1-80-013
                                        February  1980
     WORKER REENTRY IN FLORIDA CITRUS
PESTICIDES  IN THE AGRICULTURAL ENVIRONMENT
                   by
               H. N. Nigg
          University of Florida
Institute  of Food and Agricultural Sciences
Agricultural Research and Education Center
          Post Office Box 1088
          Lake Alfred, FL  33850
          Grant Number R-804633
             Project Officer


               J. E. Davis
     Environmental Toxicology Division
    Health Effects Research  Laboratory
     Research Triangle Park, NC  27711
   U.S.  ENVIRONMENTAL PROTECTION AGENCY
    OFFICE  OF RESEARCH AND DEVELOPMENT
    HEALTH  EFFECTS RESEARCH LABORATORY
     RESEARCH TRIANGLE PARK, NC  27711
     LIBRARY
     U.S.
          I, S.J,   Q8S17

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                                 DISCLAIMER
     This report has been reviewed by the Field Studies Section, U.S.
Environmental Protection Agency, and approved for publication.  Approval
does not signify that the contents necessarily reflect the views and policies
of the U.S. Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation for use.
                                    ii

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                                  FOREWARD
     The many benefits of our modern, developing, industrial society
are accompanied by certain hazards.  Careful assessment of the relative
risk of existing and new man-made environmental hazards is necessary
for the establishment of sound regulatory policy.  These regulations
serve to enhance the quality of our environment in order to promote the
public health and welfare and the productive capacity of our nation's
population.

     The Health Effects Research Laboratory, Research Triangle Park,
conducts a coordinated environmental health research program in toxi-
cology, epidemiology, and clinical studies using human volunteer subjects.
These studies address problems in air pollution, non-ionizing radiation,
environmental carcinogenesis and the toxicology of pesticides as well as
other chemical pollutants.  The Laboratory participates in the development
and revision of air quality criteria documents on pollutants for which
national ambient air quality standards exist or are proposed, provides the
data for registration of new pesticides or proposed suspension of those
already in use, conducts research on hazardous and toxic materials, and is
primarily responsible for providing the health basis for non-ionizing radia-
tion standards.  Direct support to the regulatory function of the Agency is
provided in the form of expert testimony and preparation of affidavits as
well as expert advice to the Administrator to assure the adequacy of health
care and surveillance of persons having suffered imminent and substantial
endangerment of their health.

     The persistence of pesticide residues and their toxic conversion
products on foliage, soil, and fruit must be considered when one estimates
the period required for safe reentry of workers into orchards after
spraying.   Fruit residues are also necessary to establish the necessary
period between spraying and harvest so that harmful levels of these
materials are eliminated.  This report describes research that resulted
in a weather model which allows one to predict the rate of decay of a
number of organophosphorus pesticides and their toxic conversion products
over a wide range of weather conditions.  Use of this model will allow the
determination of safer reentry and preharvest intervals for these and
similar pesticides than was possible using a simple model of decay with
time.
                                           F. G. Hueter, Ph.D.
                                             Acting Director
                                   Health Effects Research Laboratory

                                     iii

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                                 ABSTRACT

     The environmental behavior of five organophosphate insecticides in
Florida citrus are reported.  The parathion disappearance rate from fruit,
leaf, and soil surfaces was the same.  The potential worker exposure to
parathion was leaf surface > soil surface » fruit surface and a minor com-
ponent in air.  The disappearance of parathion surface residues was accurately
represented with a first-order solar radiation, rainfall, temperature, and
dew model.  Malathion residue in the rind of five varieties of citrus fruit
had a half-life of 8 days and malathion disappearance was accurately described
with weather.

     Dialifor, malathion, oxydemetonmethyl and dioxathion fruit and leaf sur-
face residues exhibited different disappearance rates.  The disappearance
rate, however, was the same on fruit and leaf surfaces for individual com-
pounds.  Based on rates of disappearance under different environmental con-
ditions, environmental sensitivity was oxydemetonmethyl > malathion >
dioxathion > dialifor.  These data suggest that fruit data could be eliminated
from worker safety reentry registration requirements for organophosphate
insecticides.

     Two surface residue techniques were compared.  The vacuum and dislodge-
able residue techniques differed in the amount of particulate matter and
pesticide residue recovered.  Vacuum, dislodgeable and air particulate
numbers and sizes were relatively comparable.  Few particles above 45 |_i were
found on leaf surfaces and in air and relative numbers and sizes were related
to soil particulates.  Airborne transfer of soil particulates to leaf surface
to worker was suggested.  The dislodgeable residue technique for worker
reentry data appeared superior to the vacuum technique.

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                                 CONTENTS

Foreword	<,.„.<,	»	o	iii
Abstract	„	»	 iv
List of Figures	„	„	„	 vi
List of Tables	„...,,	vii
Abbreviations and Symbols„	«	viii
Acknowledgements. „ „......... „. .<>	o	 ix

     I.  Introduction	„ „	  1
    II.  Conclus ions.... o	o	  2
   III.  Recommendations.. „.. „	„	o	  3
    IV.  Experimental Procedures	„....„	„..  4
              Large plot parathion experiment	  4
              Malathion fruit experiment	o ......... „	  7
              Residue  technique experiment	  8
              Small plot experiment	„	„. „	  8
      Vo  Results and Discussion	<,...«	 10
               Large plot parathion experiment	„	 10
                    Fruit and leaf residues	„	 10
                    Cover crop residues	„	„ 14
                    Soil surface residues	„ „	 15
                    Residues in ambient air«	 15
                    Total residues	0 „	 15
               Malathion fruit experiment	 19
               Residue technique experiment.. „	„	 21
               Small plot experiment,,	„	0... 36

References... . „	<,	0 ...».»	 49
Bibliography	 53

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                              LIST OF FIGURES

Number                                                                Page

  1     Weather Model of Emulsif table Concentrate (EC) and
          Wettable Powder (WP) Parathion Disappearance on
          'Valencia1 Orange Leaves and Fruit .......................... 11

  2     Weather Model of Emulsifiable Concentrate (EC) and
          Wettable Powder (WP) Parathion Disappearance on
          the Soil Surface of Astatula Fine Sand Between Trees ........ 17

  3     Parathion in Ambient Air ...................................... 17

  4     Percentage of Parathion and Paraoxon Residues in Air
          on 'Valencia' Orange Leaves, on 'Valencia' Orange Fruit,
          and on the Soil Surface ..................................... 18

  5     Malathion in Fruit Rind ....................................... 19

  6     Small Plot-Gum. Weather Variables vs. Time in Days ............ 37

  7     Ln-Ln Plot of Combined Malathion Fruit and Leaf
          Surface Residues ............................................ 43

  8     Ln-Ln Plot of Combined Dialifor Fruit and Leaf
          Surface Residues ............................................ 43
  9     Ln-Ln Plot of Combined Dioxathion Fruit and Leaf
          Surface Residues ............................................ 44

 10     Ln-Ln Plot of Combined Oxydemetonmethyl Fruit and
          Leaf Surface Residues ....................................... 44

 11     % Malaoxon Residue ............................................ 45
                                    VI

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                              LIST OF TABLES
 Number                                                              Page
 1    Simple Correlation Matrix for WP Parathion Residues and
        Environmental Variables	 12
 2    Simple Correlations for EC Parathion Residues and
        Environmental Variables	 13
 3    Simple Correlations for WP Paraoxon Residues and
        Environmental Variables	 13
 4    Simple Correlations for EC Paraoxon Residues and
        Environmental Variables	 14
 5    Multiple Linear Regression of Parathion and Paraoxon
        Residues and Environmental Variables	 16
 6    Malathion First-Order Residue Behavior in Florida Citrus
        Varieties Base on Time Alone and Time Plus Weather	 20
 7    Variables Used as Base for First-Order Model of
        Malathion Residue Disappearance	 21
 8    Comparison of 0.8 y and 5.0 y Filters with Parathion WP	 22
 9    Comparison of 5.0 p and Glass Fiber Filters with
        Parathion WP	 24
10    Filter Flow Characteristics	 27
11    Comparison of WP and EC Formulations of Parathion	 29
12    Vacuumed Particulates Size Analyses 0.8 y Filter—
        Day 1 Post Application	 31
13    Vacuumed Particulates Size Analyses 5.0 y Filter—
        Day 1 Post Application	 32
14    Filtered Aqueous Samples Particulate Size Analyses
        (0.22 y)—Day 1 Post Application	 34
15    Soil Particulate Distribution in Florida Citrus Soils	 35
16    Small Plot Experiment 1.—Pesticide Residues	 38
17    Small Plot Experiment 2.—Pesticide Residues	 41
18    Small Plot—Fruit and Leaf Surface Residues—
        Coefficient of Variation	 47
19    Conversion of Pesticide Application Rates from
        English to Metric System	 48

                                   vii

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                      LIST OF ABBREVIATIONS AND SYMBOLS

AI           --active ingredient
CAT          --cumulative average temperature
CLW          —cumulative leaf wetness
CR           --cumulative rainfall
CS           --cumulative solar radiation
EC           —emulsifiable concentrate
fpm          --feet per minute
g            —gram(s)
h or hr      --hour(s)
ha           --hectares
HDD          --heating degree days
kHz          --kilohertz
I            --liter
Ib or Ibs    --pound(s)
LW           --leaf wetness (dew)
ia    ?       --micron
l_ig/cm        —micrograms per square centimeter
|j.g/m^        --micrograms per cubic meter
mjH,           --milliliter
ppm          --parts per million
S.D.         --standard deviation
WP           --wettable powder
                                     viii

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                              ACKNOWLEDGEMENTS

     The technical assistance of S. Cabrera, L. Economu, J. Keller, J.
Lawrence, and D. Steele in the field and R. Surrency, M. Swift, J. Towne,
M. Tynes, and R. Woodruff in the laboratory is gratefully acknowledged.
                                   IX

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                                 SECTION I

                               INTRODUCTION

     Recurring harvester organophosphate intoxications in the Western
United States have forced interest in the components of a worker reentry
pesticide illness.  These components have been identified as (1) application
of an organophosphate insecticide; (2) conversion of the organophosphate to
its 'oxon' metabolite; (3) dusty conditions in the field so as to provide
for transfer of the pesticide to the worker; and (4) suitable weather con-
ditions so that high levels of the pesticide persist on the leaf and soil
surfaces.

     The current approach to regulations to protect the worker has been to
establish a worker reentry time.  A worker reentry time is the time workers
must wait after a pesticide application before reentering a treated field.
These times range from 24 to 48 hours nationally and are as much as 60 days
in California where stringent reentry regulations have been set by the
California Department of Agriculture.  The fact that California has recurring
problems, however, does not mean that a problem exists in the rest of the
U.S.  Yet it is agreed that worker safety reentry regulations are necessary
on a national basis to protect farm labor from adverse pesticide exposure.

     Regardless of pesticide applied and a dusty environment, weather
conditions are the key factor in oxon metabolite production and residue
levels on leaf and soil surfaces after a pesticide application.  This study
focused on the poorly understood relationship between weather conditions
and organophosphate residue levels.

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                               SECTION II


                               CONCLUSIONS

1  The rate of disappearance of parathion and paraoxon from leaf,  fruit,
   and soil surfaces was essentially the same.

2  The rates of disappearance of dialifor, malathion, oxydemetonmethyl, or
   dioxathion residues were identical from leaf and fruit surfaces for an
   individual compound.  Different compounds had different dissipation
   rates.

3  The rate of disappearance of EC and WP formulations was the same.  Dif-
   ferences in surface residue levels between EC and WP formulations ap-
   peared  to be the result of initial deposits of pesticide.

4  Weather modeling of residue disappearance from surfaces was 50% more
   accurate as compared to the time model.

5  Weather modeling of malathion fruit residues indicated that prediction
   of food commodity residues may be a valid approach.

6  Recoveries of surface pesticide residues depended on the stringency of
   the method.  For current regulatory purposes, the Gunther dislodgeable
   residue technique produces residues consistent with total possible
   exposure for both the parent and oxon metabolite.

7  The rate of disappearance was the same for leaf, soil, and leaf surfaces
   for parathion and for leaf and fruit surfaces for malathion, oxydemeton-
   methyl, dialifor, and dioxathion.  Fruit surface residue data required
   for registration of pesticides could be eliminated.

8  Potential exposure of fruit pickers to parathion was greatest on the
   leaf surface, less  on the fruit  surface and very  small in air.

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                             SECTION III

                           RECOMMENDATIONS


The effect of individual weather variables on pesticide disappearance
from surfaces should be studied.  Such studies should include individual
effects of temperature, solar radiation, and water and their confounded
effects on pesticide disappearance from surfaces.

A better kinetic model for pesticide behavior should be sought.  This
model should have a firm theoretical foundation based on a physical or
chemical process.

Investigations of the effect of chemical and physical characteristics
such as hydrolysis, vapor pressure, photolysis, diffusion coefficient,
and oxidation on residue behavior should be conducted.

Environmental factors responsible for the production of oxon metabolites
of organophosphate insecticides should be further investigated.

Correlation of surface organophosphate residues, surface dust levels,
and field worker exposure should be sought.  This will allow accurate
prediction of worker exposure.

A systematic modeling approach including all of the above factors should
be taken to provide a rational basis for regulations.

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                                 SECTION IV

                          EXPERIMENTAL PROCEDURES
LARGE PLOT PARATHION EXPERIMENT

     A mature 'Valencia1 grove in excellent horticultural condition owned by
the University of Florida was used for these experiments.  This grove is not
irrigated and is typical of the approximately 400,000 acres (162,000 ha) of
'Valencia' orange groves in Florida.  Parathion emulsifiable concentrate (EC)
and wettable powder (WP) were applied in separate treatments at a rate of
4 Ibs active ingredient (AI)/acre in 750 gal of water* (4.48 kg Al/ha in
285 dkl) with an air-blast sprayer.  Each treatment was replicated four
times in a random block design including four no-spray control blocks.  Two
buffer rows were left unsprayed between each 48-tree replicate.  Three indi-
vidual experiments were carried out using the same plots.  Experiment 1 was
conducted from Jan. 1 to Mar. 1, 1977; experiment 2 from July 12 to Aug. 2,
1977; and experiment 3 from Oct. 1 to Dec. 14, 1977.

     Orange fruit and leaf samples were collected as described by Gunther
et al. (1973), Westlake et al. (1973), and Iwata et al.  (1977) except that
eight fruit per plot were collected.  Random cover crop samples were ob-
tained by carefully clipping leafy portions of the cover crop into glass
leaf-punch bottles.  Plots were sampled on days 1, 3, 5, 7, and then at
weekly intervals until residue levels were below 0.005 |ag/cm  for 2 consec-
utive sampling days.

      Soil samples were collected by vacuum using the method of Spencer et al.
(1975, 1977) except that a 40-mesh screen was used so that at least 10 g of
soil could be obtained.  Five 20 x 20 cm areas were vacuumed per sample.  A
dripline and a middle (between trees) sample was obtained from each plot.
These samples were not random samples in that areas previously sampled were
marked with stakes so that no resampling occurred.

     Mini-personnel samplers (Andersen 2000, Inc., P. 0. Box 7500, Salt Lake
City, UT 84107) were used to obtain dislodged samples by attaching the
sampler to a pole and sweeping the foliage for 5 min.

     Ambient air was sampled for parathion by using Smith-Greenburg impingers
as described by Sherma and Shafik (1975).  Air flow was monitored at the
beginning and end of each 4-hour sample with a Gilmont Model No. F1400
flowmeter (Roger Gilmont, Instr., Great Neck, NY 11021).  Two-hundred m^
 Because of common usage, spray application rates will be given in the
 English system.  Refer to Table 19 for conversion.

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of ethylene glycol was used per impinger.  A prefliter was not used so
ambient air samples represent a combination of the vapor phase and airborne
particulate parathion.  Air samples were taken from 10 a.m. to 2 p.m. each
sampling day.  All other sampling was begun at 9:30 a.m. and ended at
approximately 11:00 a.m. each sampling day.

     Leaf and cover crop samples were processed as described by Gunther et
al. (1974) as modified by Nigg et al. (1977a).  The Sur-Ten solution was
2 mi of a 1:50 dilution of Sur-Ten per 1.0 i  of water.  Fruit were clipped
in the field into 2.5-gal (9.485, ) pickle jars.  Fruit were rolled twice in
the same pickle jar at 70 rpm for 5 min  in 200 mi of Sur-Ten solution to
obtain dislodgeable fruit residues.  Two 40 mi methylene chloride extrac-
tions were used to recover parathion and paraoxon from fruit washes.

     Dust levels on leaf and fruit surfaces were determined by filtering
leaf and fruit washes through preweighed Whatman //I filter paper after
extraction with methylene chloride.  Filters were dried at room temperature,
reweighed, and the dust level calculated in yg/cm^ of surface (Westlake et
al., 1973; Popendorf et al., 1975).

     Soil samples were mixed by hand shaking and a 10-g subsample was
weighed into a 100 mi beaker.  Two mi of water was used to wet the 10 g of
soil;  the beaker was covered with aluminum foil and placed at 4°C.  After
16 to 18 hr, 40 m£ of acetone was added to the beaker and the soil was
sonicated for 30 sec at 15,000 kHz.  The beaker was immediately recovered
with aluminum foil and the sediment allowed to settle for 5 min.  A 20 mi
aliquot was evaporated in a 50 mi volumetric flask under N_ at 50°C almost

to dryness.  After cooling for approximately 5 min, 5 mi of benzene was
added, followed by 40 m£ of 2% sodium sulfate.  The volumetric flask was
capped, shaken vigorously, the layers allowed to separate, and the benzene
layer brought into the neck of the flask with distilled water.  The benzene
layer was removed by pipette to a brown bottle over a few grams of Na SO,.

Benzene used for these extractions and all solvents used in subsequent
extractions were gas chromatographic grade.

     Mini-sampler impinger plates were extracted by rinsing each plate
three times in 10 m£ benzene, evaporating the benzene to 10 m£, and trans-
ferring the benzene to a brown bottle over Na SO,.  The glass fiber filters
were inserted into brown bottles and 10 mi of benzene added to the bottle.

     Ambient air samples were processed by the method of Sherma and Shafik
(1975).  Processed samples were stored for less than 14 days at-20°C prior
to gas-liquid chromatographic (GLC) analysis.

     Recoveries (mean + S.D.) by these methods were:  fortified Sur-Ten
washes, parathion 99 + 3%, paraoxon 94+4%;  fortified soil, parathion
97 + 2%, paraoxon 92 + 2%; fortified ethylene glycol, parathion 100 + 3%,
paraoxon 98 + 2%.

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     Samples were analyzed by GLC with a flame photometric (PPD) phos-
phorous detector on a Tracor 550 GC.  The 0.8 m X 2 mm inside diameter (I.D.)
silylated glass column was packed with 5% SP2100 on 100/120 mesh Gaschrom Q
(GCQ) (Supelco, Inc., Belefonte, PA 16823).  Operating conditions were:
injection port 210°C, column 190°C, detector 170°C, N~ carrier gas flow
60 mil /min.  Selected samples were also chromatographed on a 5% OV-210,
100/120 mesh GCQ column at 170°C for confirmation of identity and quantity
of detected materials.

     After GLC analysis, samples of each type were combined and subjected
to high-performance liquid chromatography (HPLC), thin-layer chromatography
(TLC), column chromatography, and GLC-mass-spectral analyses.  Paraoxon
was confirmed in each combined type sample by its GLC retention time on a
1.5 m X 2mm I.D. glass column packed with 3% SP2100 on 100/120 mesh
Supelcoport at 200°, 30 m£/min helium flow and by comparison of the mass
spectra of peaks eluting at approximately 5 min with that of a known sample
of paraoxon.  Details have been previously described (Nigg et al., 1977,
1978).

     Both sides of the leaf punch were used for calculating residue concen-
tration in yg/cm^.  For fruit areas, the diameter and length measurement of
each fruit were used for an area calculation of an oblate, prolate, or
regular sphere on a Wang 720C computer (Buslig, 1978).  Other statistical
methods, computer programs, the heating-degree day transformation, and the
first-order weather-time model have been previously described (Nigg et al.,
1977 a,b).
                                                        r  9
     The percent total residue calculation used 240 X 10 cm  of leaf surface
area (Gunther et al., 1973; Turrell, 1961; Wilson, 1978) 20.4 x 106cm2 of
                         3
soil surface, and 9,850 m  of air per 48 tree plot.  Total fruit surface
per plot was calculated using actual fruit production times the average
fruit surface area.  These values were:  9.3 x 10"cm^ of fruit surface
                  (\  9                                        67
(exp. 1); 5.9 x 10 cm  of fruit surface  (exp. 2); and 8.6 x 10 cm  of fruit
surface (exp. 3).  These values are based on a 48-tree plot containing
4.9-m tall trees spaced 7.6 m x 7.6 m.  The percentage of the total residue
in each ecosystem component was obtained by calculating the residue in each
component and dividing by the total.  It was assumed that the concentration
of parathion in air was homogeneous.  The average of WP and EC dripline and
middle residue determinations was used as the soil residue value.  Diffusion
kinetics and mass transfer processes were ignored for this calculation.

     Rainfall, temperature, and leaf wetness methods have been reported
(Nigg et al., 1977a).  For total solar incidence, a Matrix MK 1-G solari-
meter (Matrix, Inc., Mesa, AZ  85201) was used.  This solarimeter was
calibrated by triangulation on a clear day assuming 0.8 transmissivity
according to the equation:
                   -2   -1             -2   -1     cscO
           I(cal cm  min  ) = (2 cal cm  min  ) 0.8      sin 0,

where 0 is the solar elevation angle  (Schultze, 1976).  Determinations were
obtained from 11:30 a.m. to 12:45 p.m. EST at 15 min intervals for this
calibration.

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MALATHION FRUIT EXPERIMENT

     A completely randomized design with four replications per treatment
including four unsprayed check blocks was utilized in this study.  Each
experimental plot consisted of one city block.  Within each plot, 3 to 10
trees of each citrus variety were used as source trees for an 8-fruit sample
of grapefruit, lemon, tangerine, Temple, and Valencia1 varieties on each
sample date.  Malathion (2EC) was applied at 1.5 g AI/& with a hydraulic
sprayer at 29 kg/cm^ (ca 38 £/tree).  Three applications were made at 3-week
intervals and samples were taken after the third application.

     Samples were taken on days 1, 3, 5, 7, 14, and 21, frozen at -20°C and
transported frozen to Lake Alfred for analysis.  Samples were stored
approximately 1 month at -10°C prior to analysis.  Dual samples were taken
on days 1, 3, 5, and 7.  One set was washed in a weak soap solution (liquid
IvoryR) to simulate homeowner washing.

     For analysis, fruit were thawed, the rind removed from one-half of each
fruit, and the pulp sliced into a Waring blender.  The pulp was blended for
3 min and a 10-g subsample removed for analysis.  The rind was diced, blended
for 3 min, and a 10-g subsample removed for analysis.  The 10-g subsample
of either rind or pulp was homogenized in 100 m£ of methylene chloride and
15 g of sodium sulfate for 5 min in a Sorvall blending cup in an ice bath.
The blender cup top was loosened upon removal and particulate matter allowed
to settle for 1 min.  A 20 m£ aliquot was evaporated to dryness at 40° under
N  and transferred to brown glass bottles over sodium sulfate in 10 m£ of
benzene.  The mean + S.D.  for recoveries of malathion and malaoxon were
98 + 3% and 94 + 4%, respectively, from fortified pulp and rind homogenates.
No varietal differences in recovery of standard materials were observed.
Extractions were stored at -20°C prior to GLC analysis.

     GLC analyses for malathion and malaoxon were performed on a Tracor
550 GLC with phosphorous flame photometric detection.  Operating conditions
were:  1.8 m x 2 mm I.D. glass column packed with 5% SP2100 on 100/120 mesh
GCQ, N  60 m£/min, detector 200°, injection port 210°, oven 190°.  Quanti-

fication was by comparison with the peak height of standard materials
chromatographed at the same attenuation.  Standards were chromatographed
every fourth injection.  All injections were 5 vSL .  One-hundred nA of each
solvent was evaporated to 1 m& and 5 \iH chromatographed to check for inter-
fering materials.  Standard malathion and malaoxon were provided by American
Cyanamid Co., Princeton, NJ.  The first-order time-based decay model used
was:

                              In  2_   =  _xt                         (1)
                                   o

and the first-order time-weather based decay model was


             In  —   = a    dt + a.  x.dt +	+ a   x  dt        (2)
                 y       o         11              n   n

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where y  = initial pesticide residue, a = coefficient, x..	, x  =

environmental variables and t = ordinary time.  Other statistics and computer
programs have been described (Nigg et al., 1977a, 1978).

RESIDUE TECHNIQUE EXPERIMENT

     Parathion  (0,0-diethyl 0-(4-nitrophenyl) phosphorothioate) was applied
to 12-year-old  'Valencia1 orange trees at 500 psi by hand to four-tree plots
in a four replicate random block design.  Treatments were:  (1) parathion
wettable powder (WP), (2) parathion emulsifiable concentrate (EC), and (3)
no spray (NS).  Rates are given in the appropriate tables in the Results
section.

     Leaves were vacuumed according to the method described by Popendorf
et al. (1975).  In these studies, the vacuum head was redesigned to improve
sampling time and to allow use of the leaves for residue measurements after
vacuuming.  Sixty leaves, carefully picked by the petiole and inserted
individually into the redesigned apparatus constitute a vacuum sample.
After vacuuming, the filter was placed into a petri dish and the vacuum
head and gaskets (except for the rubber gasket) rinsed with hexane into the
dish.  Filters were air-dried in the laboratory (ca 15 min), folded care-
fully and placed into 4-oz brown bottles.  Each petri dish was rinsed twice
with benzene into a 50 m£ volumetric flask.  The volumetric flask was
brought to volume with benzene, and benzene was added to the brown bottle.
Mean +_ S.D. extraction recoveries from dust fortified with parathion and
paraoxon were 98 + 3% for parathion and 92 + 2% for paraoxon.

     For vacuuming leaves, the following 90-mm filters were used:  Millipore
0.8 y with an efficiency of ca 100% in the 0.8 y range  (Megaw and Wiffen,
1963); Millipore 5.0 y with an efficiency of 90+%  (Liu and Lee, 1976) and
a Whatman GF/A  glass fiber filter, effective retention of 1.6 y (Whatman
catalog).

     Forty leaves of each vacuum sample were punched immediately after
vacuuming to be used with the Gunther et al. dislodgeable residue method
(Iwata et al.,  1977).  An unvacuumed 40-leaf punch sample was also taken
from each plot  to obtain a total surface residue level as measured by the
Gunther et al.  method.

     Particulate sizes were determined with a Millipore Model II MC particle
measurement computer (Millipore Corp., Bedford, MA 01730) and for sizes >
5.0 y with a reticle under 400X magnification with phase contrast.  Values
are averages of five lensfields per replicate.  For particulate size
analyses on aqueous samples obtained from the Gunther method and the aqueous
spray tank samples, a Millipore 0.22 y filter was used.  The leaf area of
both sides of each leaf was obtained by using the formula of Turrell  (1961)
and multiplying by two.

SMALL PLOT EXPERIMENT

     Experimental design, application methodology, sampling extraction of

-------
fruit, leaves and soil, and weather monitoring were previously described
(Nigg et al., 1977a, 1978, 1979; page 4 this report).  Dioxathion  (8E)
(2,3-p-dioxanedithion S,S-bis(0,0-diethyl) phosphorodithioate, oxydemeton-
methyl (2L)  (S-[2-(ethylsulfinyl) ethyl] 0,0-dimethyl phosphorothioate,
dialifor (4E) (0,0-diethyl phosphorodithioate S-ester with N-(2-chloro-l-
mercapto-ethyl) phthalimide, and malathion (9.5E)  (0,0-dimethyl phosphoro-
dithioate of diethyl mercaptosuccinate) were applied at a rate of 4 Ibs
Al/acre in 750 gal of water/acre (4.48 kg Al/ha in 285 dkl water).  Both
experiments were carried out on the same plots.  Experiment 1 was conducted
from March 14 to April 11, 1978 and Experiment 2 from July 11 to August 9,
1979.

     Dioxathion, oxydemetonmethyl and dialifor were analyzed at 210°, 190°
and 230°C,  respectively on a 0.8 mx2 mm I.D.  silanized glass column packed
with 10% DC-200 + 1.5% QF-1 on 80/100 mesh Chromosorb W(HP).  This packing
material was a gift of Dr. J. S. Thornton, Mobay Chemical Corp., Kansas
City, MO 64120.  Detection was with a nitrogen-phosphorous detector in a
Hewlett-Packard 5730A gas chromatograph.  Other conditions were:  He, 30
m£/min, injection port 250°, detector 200°.  Malathion was analyzed on a
0.8 m x 2 mm I.D. silanized glass column packed with 5% SP2100 on 100/120
mesh GCQ.  Operating conditions of the Tracer 550 GC were:  column temp-
erature 180°, injection port 210°,  flame-photometric detector 180°, N
40 m& /min.

     Extraction of leaf and fruit washes and soil were as previously
described (page 4, this report).  Oxydemetonmethyl was oxidized to the
sulfone prior to gas chromatography according to the method of Thornton
et al. (1977).

     Analytical standards of dioxathion and dialifor were provided by
Hercules, Inc., Wilmington, DE 19899.  Malathion and malaoxon standards
were provided by American Cyanamid Corp., Princeton, NJ and oxydemeton-
methyl and oxydemetonmethyl sulfone were provided by Mobay Chemical Corp.,
Kansas City, MO 64120.

     The mean + S.D. for recoveries from fortified 40-leaf punch washes
were:  malathion 88.8 + 2.4%; malaoxon 94.6 + 4.5%; dialifor 83.9 + 5.8%;
oxydemetonmethyl 96.9 + 2%; and dioxathion 80 ± 3.3%.  Results are not
corrected for recovery.

-------
                                SECTION V

                         RESULTS AND DISCUSSION
LARGE PLOT PARATHION EXPERIMENT

Fruit and Leaf Residue

     The weather model for parathion disappearance on 'Valencia' orange
leaves and fruit is presented in Fig. 1.  It should be noted in Tables 1
and 2 that the data trends  for fruit and leaves and EC and WP formulations
are not statistically different.  The model of parathion disappearance in
Fig. 1 utilized both EC and WP parathion residue averages of leaves and
fruit residues.  Time is not used in this model and cumulative rainfall
(inches), cumulative solar incidence (cal/cm^), cumulative leaf wetness
(hrs.), and cumulative average temperature (C° days) account for 75.7% of
the variation observed in the residue data.  Time alone accounts for only
55% of the variation observed.  Cumulative average temperature and heating
degree days correlated equally well with parathion residues (Table 1).
For this reason, cumulative average temperature was used in place of heat-
ing-degree-days since they are approximately proportional and the calcu-
lation of cumulative average temperature does not require a computer.

     The weather model presented in Fig. 1 was the best overall model.  No
improvement in variation explained was obtained by including time instead
of one of the environmental variables.  In the overall fruit and leaf
model, cumulative solar incidence appeared to be the most important envi-
ronmental variable with an R = 0.828.  The addition of rainfall yielded a
multiple R of 0.851, cumulative average temperature a multiple R of 0.861,
and cumulative leaf wetness a multiple R of 0.870.

     On the other hand, the paraoxon-environmental variable correlations
in Tables 3 and 4 indicate the importance of cumulative rainfall.  This
is similar to previous weather correlations of paraoxon residues in Florida
citrus  (Nigg et al., 1978).  This result also supports the supposition that
differences in the levels of paraoxon residues between Florida and
California citrus are due to wet conditions in Florida and dry conditions
in California  (Gunther et al., 1977; Nigg et al., 1978).  However, the
reasons for paraoxon residue differences between geographical regions are
blurred because of simultaneous paraoxon production from parathion and
disappearance behavior of paraoxon itself.  The environmental production
and persistance of paraoxon apparently depends on dusty conditions, ozone,
and dry weather (Popendorf and Leffingwell, 1978; Spear et al., 1975, 1978).
The environmental dependence of paraoxon production on plant surfaces is


                                  10

-------
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LEAVES AND FRUIT
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-------





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-------
               TABLE 2.  SIMPLE CORRELATIONS FOR EC  PARATHION
                    RESIDUES AND ENVIRONMENTAL VARIABLES


Leaves
Fruit
Soil-Mid .
Soil-Drip
Time
-0.604h
-0.760
-0.636
-0.280
HDDlb
-0.601
-0.652
-0.777
-0.374
HDD2°
-0.537
-0.484
-0.784
-0.390
CRd
-0.789
-0.694
-0.811
-0.386
CLW6
-0.604
-0.714
-0.758
-0.360
csf
-0.725
-0.837
-0.688
-0.289
CAT8
-0.616
-0.748
-0.697
-0.321
Q
 Time in days.

 HDD1 temp, limits 0°, 37.8° C.


CHDD2 temp, limits 10°, 37.8° C.


 Cum. rainfall (inches).

Q
 Cum. leaf wetness (h) .

f                              -2
 Cum. solar incidence in cal cm
 Cum. avg. temp.

      R >" 0.496, P <" 0.01.
                TABLE 3.  SIMPLE CORRELATIONS FOR WP PARAOXON
                   RESIDUES AND ENVIRONMENTAL VARIABLES


Leaves
Fruit
Soil-Mid.
Soil-Drip
Timea
-0.504h
-0.406
-0.276
-0.485
HDDlb
-0.659
-0.595
-0.479
-0.565
HDD2C
-0.691
-0.665
-0.570
-0.548
CRd
-0.708
-0.803
-0.530
-0.716
CLW£
-0.642
-0.556
-0.435
-0.549
csf
-0.546
-0.435
-0.280
-0.519
CAT8
-0.584
-0.485
-0.376
-0.534
 Time in days.

DHDD1 temp, limits 0°, 37.8° C.

:HDD2 temp, limits 10°, 37.8° C.

 Cum. rainfall (inches).
 Cum. leaf wetness (h).

f                              -2
 Cum. solar incidence in cal cm

g
 Cum. avg. temp.

      R >" 0.496, P <~ 0.01.
                                    13

-------
               TABLE 4.  SIMPLE CORRELATIONS FOR EC PARAOXON
                   RESIDUES AND ENVIRONMENTAL VARIABLES


Leaves
Fruit
Soil-Mid.
Soil-Drip .
Timea
-0.529h
-0.157
-0.449
-0.442
HDDlb
-0.585
-0.176
-0.557
-0.433
HDD 2°
-0.554
-0.200
-0.573
-0.389
CRd
-0.772
-0.574
-0.671
-0.637
CLWG
-0.581
-0.178
-0.553
-0.444
csf
-0.559
-0.342
-0.461
-0.448
CAT8
-0.560
-0.186
-0.508
-0.435
 Time in days.

bHDDl temp, limits 0°, 37.8° C.

CHDD2 temp, limits 10°, 37.8° C.

 Cum. rainfall (inches).
^
 Cum. leaf wetness (h).
f                              -2
 Cum. solar incidence in cal cm
cr
&Cum. avg. temp.

hWhen R ~ 0.496, P <" 0.01.


indicate an additional difference in Florida and California conditions which
may help explain the lack of reports of acute toxic effects for pickers
exposed in Florida citrus.   Differences between Florida and California
regarding actual amounts of particulate matter dislodged during picking
operations await elucidation.

Cover Crop Residues

     Cover crop residues were obtained during experiment 1 (Jan. - Mar. 1977)
after having allowed the native weed and grasses unrestricted growth from
Aug. 1976 to Jan. 1977.  The disappearance of the residue from the cover
crop was more rapid than from any other sample.  Cover crop residues of
WP parathion were about 12.0 ppm on day 1, 1.3 ppm on day 3, and 0.2 ppm on
day 7.  Residues of EC parathion on the cover crop were about 4.0 ppm on
day 1, 0.70 ppm on day 3, and 0.15 ppm on day 7.  No residues of either EC
or WP parathion were detected after day 7 post application.  The half-life
of parathion on the cover crop was about 1 day compared to 1.3 days for air
and 2.0 days for fruit, leaves, and soil surface.  I attribute this obser-
vation to increased hours of foliage wetness as dew condenses from the
ground up and disappears from the top down.  The cover crop was observed
to remain wet long after the tree foliage was dry.
                                     14

-------
      The  speculation  that  fruit  pickers  and  grove  workers  might be exposed
 to residues  on the  cover crop  is not  supported  by  our  residue data nor by
 normal grove practice.  Florida  citrus groves are  regularly disced and mowed
 before picking operations  at  the demand  of pickers to  reduce inconvenience
 and the possibility of  rattlesnake  bite.

 Soil Surface Residues

      Parathion disappearance  from the soil surface between trees,  although
 slightly  slower,  is essentially  at  the same  rate as for  leaves and fruit.
 There was no significant difference in the rate of decay between EC and WP
 formulations on the soil surface and  these data are combined in Fig.  2.
 The overall  weather model  and  simple  correlations  indicate that cumulative
 rainfall  may be important  to disappearance of parathion  on the soil surface
 between trees in Florida  (Tables 1, 2, and 5).  The weather model  accounts
 for about 78% of the  soil  surface parathion  residue data between trees
 whereas time alone  explains only 42%  on  the  data variation.

      Paraoxon residue behavior on the soil surface between trees showed the
 strongest correlation with cumulative rainfall  (-0.530 for WP and  -0.671
 for EC) suggesting  the  importance of  hydrolysis or water solubility for the
 disappearance of paraoxon.  Compared  to  leaf surface paraoxon correlations,
 however,  both the simple and multiple correlations for paraoxon behavior on
 the soil  surface were poor (Tables  3, 4,  and 5).

      Soil surface residue  data for  parathion disappearance at the  dripline
 of the tree  did not fit first-order kinetics for EC parathion,  but were
 approximately first-order  for  WP parathion  (Table  5).  The overall model for
 WP parathion at the tree dripline does not show the dependence on  rainfall
 that was  observed with  the soil  residue  between trees.  Differences in the
 solar and temperature processes  at  the dripline and nonuniform foliage
 channeling of residue runoff  at  application  and during rainstorms  might
 account for  this observation.

 Residues  in  Ambient Air

      The  ambient air  parathion data in Fig.  3 show levels  of about 5.0,
 2.5,  0.5,  and 0.1 yg/nr of parathion  1,  3, 6, and  8 days post-treatment in
 experiments  2 and 3.  There was  no  difference between  WP and EC formulations
 nor between  experiments for parathion levels in air.  The  very low air
 levels of parathion in  the no-spray plots indicate that  the 0.75-acre (0.3 ha)
 plot size used in these experiments may  be adequate for  determination of
 pesticides in air.  No  paraoxon  was detected in any air  sample.

 Total Residues

      Since values did not  differ between experiments,  the  average  percent
total  residue was used in Fig.  4.  It  is  readily apparent in Fig. 4 that the
 leaf surface residue  represents  the greatest potential for worker  exposure.
 For parathion,  the  soil surface  contained half  as  much compared to leaf
 surface of the total  plot  residue hazardous  to  workers,  while fruit and
 ambient air  contained negligible percentages of residue  available  to workers.

                                    15

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                6  .
                 -4-
SOIL SURFACE OF ASTATULA FINE SAND
                         PARATHION
                         EC    WP
                         o  EXP I •
                         D  EXP2 •
                         4  EXP3 »
                         Rz=07759
                           P^OOI
                           32    I     0-1-2    -3   -4
                           X = 2.4735-05346CR-00329LW-O.OOI5 CS +0.005ICAT
Figure  2.   Weather model of emulsifiable concentrate  (EC) and wettable powder
            (WP) parathion disappearance on the soil surface of Astatula fine
            sand between  trees.  Each  point is the  average of four  replicates.
            CS = cumulative solar incidence, cal/cm^  (cumulative daily hrs.)>
            LW = cumulative leaf wetness (cumulative hrs.), CR = cumulative
            rainfall  (inches), CAT = cumulative average temp. (C° days <0).
                                        PARATHION IN  AMBIENT AIR

                                              EXP 2 = CLOSED SYMBOLS

                                              EXP 3 = OPEN SYMBOLS
                                                  •  NO SPRAY f
                                                  • W POWDER o
                                                   A EM. CONC  A
                                      3456
                                       DAY POST TREATMENT
figure 3.  Parathion in ambient  air in yg/
                  m
                                      17

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                                                 PARAOXON
                      10     20
                    DAY POST APPLICATION
10     20     30
 DAY POST APPLICATION
Figure 4.  Percentage of parathion and paraoxon residues in air,  on  'Valencia'
           orange leaves, on  'Valencia1 orange fruit, and on  the  soil surface.


The leaf surface generally contained 90% whereas  the  soil and fruit  con-
tained about 10% each of the  paraoxon residues.   These  results are in sub-
stantial agreement with Westlake et al.   (1973),  Gunther et al.  (1973),  and
Leffingwell et al.  (1975).  Based on these  results, leaf surface  and soil
surface residue determinations may be sufficient  to assess residue levels
of pesticidal chemicals for the protection  of  farmworkers.  Respiratory
exposure from ambient air and exposure to the  hands in  picking operations
would appear to be not significant, agreeing with Gunther et  al. (1973)
and Wolfe et al.  (1975).  These type of data may  become useful when  correla-
tions with actual worker exposure  are  observed.

     If accurately  constructed, models of pesticide behavior  should  have
worldwide application.  While the  slope coefficient multiplying the  weather
variable in the multiple regression equation must remain  constant, the
variable itself may  vary greatly  from  time  to  time or -region  to region.
This can produce  the effect of  altering or  even  completely  reversing the
relative "importance"  of different weather  variables  in different regions
or at different times.

     Monitoring studies  of  residue dissipation on plant parts and on the
soil surface are  currently  required  for  the registration of  pesticides.
Methods  for estimating worker reentry  times both mathematically  (Serat, 1973,
1974, 1978; Serat et al.,  1975)  and with  laboratory animals   (Guthrie et al.,
1974) have been suggested.  The  weather model of parathion disappearance
presented here indicates  that the estimation of  residues on plant parts,
which is critical for the  mathematical approach,  can be done accurately.
This accuracy, however,  can probably be improved by investigation of  the
                                     18

-------
importance of individual processes  to pesticide  disappearance  from plant
parts, i.e., hydrolysis, volatilization, photolysis,  etc.

MALATHION FRUIT EXPERIMENT

     Malaoxon was not found in any  sample.  Only uninterpretable traces of
malathlon were detected in pulp.  This  lack of malathion  in  citrus pulp
agrees with the results of Blinn et al.  (1959).  There  was no  difference
(P> 0.05) between washed and unwashed fruit rind residues and  these data
were combined for statistical purposes.  The lack  of  a  measurable difference
between these paired samples could have been due to sample handling.

     The disappearance of malathion on  and in the  rind  of each variety
tended to show exponential decay (a first-order  process)  (Fig.  5), except
for lemon which showed a poor correlation of -.50  (Table  6).   The half-life
of malathion was about 8 days for all varieties  (Table  6).   This agrees with
half-life of 7 days for malathion degradation behavior  on and  in California
'Valencia' orange calculated from 1 to  14 days post application data
(R = 0.98) (Blinn et al., 1959).  They  reported  a  persistence  behavior half-
life of 32 days for malathion calculated from 21 to 62  day post application
data.  Using Blinn et al. (1959) overall 1 to 62 day  data, a 13.9 day  half-
life is obtained (R = -0.92) which would indicate  that  malathion is about
one-half as persistent in Florida fruit compared to California  fruit.
                       MALATHION  IN FRUIT RIND
                                             -• TEMPLE
                                             -o GRAPEFRUIT
                                             -A VALENCIA
                                             -A LEMON
                                             -* TANGERINE
                                10         15
                            DAY POST APPLICATION
20
Figure 5.  Malathion disappearance in the rind of Florida citrus varieties.
           Points for days 1 to 7 are averages of eight determinations  while
           14 and 21 day points are averages of four determinations.

     Malathion residues reached a level of 8 ppm or less in  the rind  of
Florida citrus within 5 days after application during  the relatively  dry,
cool Florida winter (Nov. - Jan., 1976-77) (avg. temp, in Ft.  Lauderdale:
Nov. 1976, 21.5°C; Dec. 1976, 19.6°C; Jan. 1977, 15.5°C).  Previous organo-
phosphate residue data indicate that malathion residue levels < 8 ppm  would
                                    19

-------
be reached in about 3 days for rind and less than 12 hrs. for pulp under
relatively wet summer conditions (Nigg et al., 1977a, 1978).

     Time-based half-life differences appear to be related to differences
in weather (Nigg et al., 1977a,  b, 1978).  The use of time plus weather is
more accurate for modeling malathion residue decay compared to time alone
(Tables 6, 7).  For example, the correlation of the lemon data is signifi-
cantly improved from an R of -.50 (time alone) to -.88 by modifying the
first-order model base to include weather (Table 6).  As noted by Nigg et al.
(1978), a variety of weather sets is necessary to demonstrate significant
differences between a time model and a time-weather model of first-order
pesticide disappearance.  Previous weather models for the disappearance of
pesticides from leaf surfaces were highly accurate (Nigg et al., 1977a, 1978),
and this approach has been suggested for preharvest intervals in food
commodities (Nigg et al., 1978).  These fruit rind data for malathion indi-
cate that the use of physical factors to predict the residue level on food-
stuffs is a viable scientific approach.

        TABLE 6.  MALATHION FIRST-ORDER RESIDUE BEHAVIOR IN FLORIDA
        CITRUS VARIETIES BASED ON TIME ALONE AND TIME PLUS WEATHER
Variety
   % variation explained (r^ x 100)a
Time alone    Time + HDD + Cum. rainfall    t 1/2 (days)
Temple
Grapefruit
Valencia
Lemon
Tangerine
X
78*
81**
96**
25
94**

86**
93**
98**
78*
98**

7.7
7.7
6.9
8.7b
7.7
7.7
 r = correlation to equation (1) for time alone and to equation (2) for
 time and weather.

 t 1/2 based on 7, 14+21 day data.

*P < 0.05 (Morrison, 1967).

**P < 0.01.
                                   20

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           TABLE 7.  VARIABLES USED AS BASE FOR FIRST-ORDER MODEL
                     OF MALATHION RESIDUE DISAPPEARANCE

Day post treatment
Variable
Cum. time (days)
I 1 1 Z M. 11
1 3 5 7 14 21
         Cum. heating-
           degree days           15    30    41    59   157   294

         Cum. rainfall
           (inches)             .63   .64   .64   .64   .73   .82
RESIDUE TECHNIQUE EXPERIMENT

     The redesigned vacuum head and the use of Turrell's formula allowed two
significant improvements in the foliage vacuum method.  Spray painting leaves
to obtain a leaf area estimate was eliminated so the leaves were available
for further residue analysis.  Both sides of a leaf were vacuumed at once
which reduces the previous 25 min sampling time to 10 min.

     There was no significant difference between the 0.8 y and 5.0 y filters
in the amount of pesticide removed or in the overall trend of both parathion
and paraoxon disappearance (r = 0.992) (Table 8).  The 5.0 y filter and the
glass fiber filters were also highly correlated with one another in the
overall trend of the parathion and paraoxon data (r = 0.959) (Table 9), but
the glass fiber filter differed significantly (5% level or better) from the
5.0 y filter in the amount of WP parathion removed on days 1, 2, and 5 and
in the amount of paraoxon on days 1 and 9.  These residue collection dif-
ferences appear to be related to air flow rate (Table 10) and reach sig-
nificance (5% level or better) with the comparison of the glass fiber and
5.0 y filters (Table 9).  The flow rate of the glass fiber filter is 5,000
fpm compared to 2,250 with the 5.0 y filter.  Comparison of the means with-
out regard to variation showed an approximate doubling of pesticide residue
collected with the glass fiber filter.  Similar trends were evident with the
0.8 y filter and 5.0 y filter comparison (Table 8).  The 0.8 y filter had a
dustless flow rate of 1,600 fpm vs. 2,250 for the 5.0 y filter, apparently
not enough difference to reach statistical significance in the amount of
pesticide removed.  The absolute amount of residue may be less important than
consistent data for researchers working in dusty groves.  The experiments
reported here reflect dust levels on foliage too low for gravimetric analyses,
but with dusty conditions the 5.0 y filter showed the least flow rate change
with increasing dust load and may produce the most consistent data (Table 10).

     The correlation of the EC and WP vacuum data in Table 11 for both para-
oxon and parathion was 0.982.  There was significantly less vacuumable EC
pesticide compared to WP pesticide on day 1, 3, and 8 for both parathion


                                     21

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                  TABLE 8.  (CONTINUED)
Treatment
                        Day 8 post application
Po (Paraoxon)  Pt (Parathion)  Po/Pt
0.8 y filter
Vacuum

Vacuum punch

Total (vac. +
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5.0 u filter

Vacuum

Vacuum punch

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Dislodgeable
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0.014 + 0.005  0.007 + 0.004   2.12


0.017 + 0.005  0.008 + 0.004   2.13
0.20
0.20
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0.029 + 0.004  0.009 + 0.002   3.25


0.032 + 0.005  0.012 + 0.004   2.22


0.10           0.29

0.020 + 0.007  0.006 + 0.003   3.16
                           23

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                 TABLE 9.  (CONTINUED)
 Treatment
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Po (Paraoxon)  Pt (Parathion)  Po/Pt
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Vacuum punch

Total (vac. +
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Glass filter

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Dislodgeable
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0.013 + 0.001   0.007 + 0.002   1.86


0.014 + 0.002   0.008 + 0.002   1.75
0.07
0.13
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0.012 + 0.003   0.010 + 0.002   1.20


0.013 + 0.002   0.013 + 0.002   1.00


0.15            0.15

0.015 + 0.006   0.008 + 0.006   1.88
                          26

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and paraoxon and also for parathion on day 6.  Comparing the EC dislodgeable
and WP dislodgeable data in Table 11 showed significantly more pesticide
removed with the WP formulation on days 3, 6, and 8.  These observations are
consistent with the fact that the WP formulation is a particulate formulation
and these techniques are designed for particulates.  Insofar as the dislodge-
able residue technique and vacuum residue technique relate to fieldworker
exposure, the EC formulation appears safer where the potential for attachment
to environmental particulates is low.

     Vaporization of pesticides from particulates in a high air flow and
inefficient trapping of particulates are serious questions with the vacuum
method and could result in loss of residue for analysis (Miles et al., 1970;
Van Dyk and Visweswariah» 1975).  The total (vacuum + vacuum punch) in Tables
8, 9, and 11 would be significantly smaller than the unvacuumed dislodgeable
total residue if this were the case.  There was no significant difference
between these two totals.  Consequently, under the conditions of these
experiments, there was efficient trapping of particulate matter with residues
attached and no measurable loss of parathion or paraoxon occurred due to the
high air flow.

     There was a possibility that vacuum determinations would have contained
more paraoxon in relation to parathion as compared with the dislodgeable
technique (Iwata et al., 1977), particularly since soils with smaller
particulates can contain higher levels of paraoxon (Adams et al., 1976).
Higher paraoxon-parathion ratios for the vacuum determinations might then
indicate a special character of the residue substrate removed in relation-
ship to paraoxon.  This is the result on day 1 post application (Tables 8, 9,
11).  On every other sampling; day, both the vacuum punch (which is processed
with the dislodgeable technique) and the dislodgeable total residue paraoxon-
parathion ratio is equal to or greater than the vacuum sample.  Thus, the
dislodgeable residue technique fairly assesses the oxon metabolite level.
No explanation is offered for the day 1 post application result.

     Correlations of the data trends of the vacuum residue data with the
Gunther et al. dislodgeable residue technique were 0.756 for paraoxon and
0.994 for parathion with the 0.8 y filter and are 0.982 for paraoxon and
0.999 for parathion with the 5.0 y filter.  The EC vacuum data in Table 9
for both the 5.0 y filter and the glass fiber filter also correlated sig-
nificantly  (5% level or better) with the EC dislodgeable residue data:  5.0 y
filter, 0.729 for paraoxon, and 0.959 for parathion; glass fiber filter
0.824 for paraoxon and 0.999 for parathion.  The WP vacuum and WP dislodgeable
data in Table 10 have a correlation of 0.936 for paraoxon and 0.980 for
parathion.  The EC vacuum and EC dislodgeable data have a correlation of
-0.230 for paraoxon and 0.946 for parathion  (Table 10).  The negative correlation
for  paraoxon with the EC formulation is probably due to no decrease in EC
vacuum paraoxon on day 3 and an apparent increase on day 6.  These high
correlations obtained comparing the vacuum and dislodgeable techniques are in
substantial agreement with the results of Spear et al.  (1977).

     Overall, the particulate analyses showed that the Gunther et al. dis-
lodgeable method removes approximately five times the number of particulates
                                      28

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compared to the vacuum method.  This agrees with the six times dislodgeable/
vacuum comparison by particulate weight in a California study (Popendorf et
al., 1975).  For the 0.8 y filter the EC formulation had an average of 12
particles  (5-200 y) per lensfield.  This was 79% of the total particulate
sample.  The mean particle size was 27 y.  No-spray (NS) values were 42, 79%,
and 24 y respectively and the WP values were 94, 90%, and 27 y respectively
(Table 12).

     With  the 5.0 y filter the EC formulation had 20 particulates  (5-200 y)
per lensfield representing 88% of the total sample, with a mean particle
size of 25 y.  The NS values were 37 particles per lensfield 5-200 y in
size representing 86% of the total sample and a mean particle size of 26 y.
The WP formulation values were 57, 94%, and 26 y.  Values for the air samples
taken in the grove were six particulates (5-45 y) which was 100% of the
sample with a mean particle size of 27 y.  All of"the above samples had about
25 particles < 5 y per lensfield (Table 13).  No particulate analyses were
performed  on the Whatman GF/A glass fiber filter.

     Analyses of the particulate sizes and number using a 0.22 y filter and
the dislodgeable samples resulted in the following:  EC, 260, 88%, 26 y;
NS, 240, 87%, 24 y; WP, 264, 74%, 29 y; WP tank sample diluted 1:100, 418,
60%, 23 y; EC tank sample diluted 1:100, 16, 100%, 23 y, and the grove soil
passing 100 mesh, 125 particles representing 99% of the sample with a mean
particle size of 39 y.  The above samples contained approximately 400
particles  < 5 y per lensfield except for the EC tank sample with 20
particles  < 5 y per lensfield (Table 14).

     The relative numbers of particle sizes from 5 to 45 in 5 y increments
for the vacuum and dislodgeable techniques were the same.  However, the
vacuum technique recovered about 5 to 10% particulates < 5 y when compared
witli the air and dislodgeable samples.  Recent reports stress the importance
of < 1 y particulates in urban aerosols (Natusch and Wallace, 1974) and of
1.5 y in aerosols with a soil derived component (Patterson and Gillette,
1977b).

     All samples in this study were almost devoid of particulates in the
5 to 10 y  range and most had no particulates in the 10 to 15 y range.  In
addition,  only 5% of the particulate matter from the leaf was in the range
of 45 to 200 y.  None of the air samples contained particulates above 45 y.
Thus, the major particulate load is < 45 y on leaves and in air.  Others
report airborne particulate size ranges of < 50 y (Patterson et al., 1976;
Patterson  and Gillette, 1977a, b) and these observations are consistent with
an airborne transfer of soil particulates to the leaf surface.  However,
these data differ from airborne particulate sizes for three California citrus
foliage samples which were reported to average 3.1 y (Popendorf and Spear,
1974).  Analyses of California soils report 5 to 43% (most over 10%)
particulates < 2 y and of 28 to 57% particulates from 2 to 50 y (Adams et
al., 1976; Iwata et al., 1973; Iwata et al., 1975).  Analyses of 16 Florida
citrus soils are strikingly  different.  Florida citrus soils are all classed
as sands with 4.4 + 2.8% 2 to 50 y particulates and 1.8+0.9%<2y parti-
culates (Table 15).  From these soil data it appears that the "potential"
                                     33

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agricultural worker exposure to particulate matter could be at least 10 times
greater in California compared to Florida.

     These data justify the following conclusions:  (1) sample integrity
through manual leaf handling and high air flow pesticide stripping remain
questions with the vacuum technique for pesticides other than parathion.
Consequently, air flow stripping must be assessed for individual pesticides,
(2) both the Gunther et al. dislodgeable technique and vacuum technique are
biased toward estimates of airborne exposure of agricultural workers due
to the transfer mechanics of soil particulates from leaf surface to worker,
(3) the two techniques are highly correlated for both residue and particulate
data trends, and (4) the residue obtained with the dislodgeable technique
appears to be more concentrated on a "per particulate" basis.

     The primary difference between the vacuum and dislodgeable residue
techniques was the amount of pesticide recovered from the leaf surface.  This
difference reflects the stringency of the method used to recover the surface
pesticide residue.  The Gunther et al. dislodgeable residue technique is
consequently more representative of the total potential leaf surface residue
hazard to agricultural workers and should remain the residue technique to
use for worker safety reentry data.  However, actual exposure needs to be
correlated to the potential as determined by this dislodgeable method, in
order to truly assess residue hazard during reentry.

SMALL PLOT EXPERIMENT

     Weather varied appreciably comparing the two experiments.  Cumulative
average temperature (°C) after 29 days was 581.26 (exp. 1) and 840.4 (exp. 2).
Cumulative relative humidity (hr over 90%) was 336.5 (exp. 1) and 472.5
(exp. 2).  Cumulative solar incidence (gm cal cm~^ min  ) was twice as great
in experiment 1 (23,251.9) compared to experiment 2 (10,518.9).  There was no
rainfall in experiment 1 and 12.71 cumulative inches during experiment 2.
Cumulative leaf wetness (hr) was 206.68 (exp. 1) and 371.81 (exp. 2).

     In previous studies, leaf, fruit, and soil surfaces residue disappearance
was correlated with cumulative weather variables (Nigg et al. 1977, 1978,
1979).  In this series of experiments, however, time alone was so similar
to a weather model in explaining residue variation that a time base was used
for these data.  Figure 6 illustrates the difficulty.  Time correlates
extremely well with each of the cumulative weather variables and weather
variables correlate with one another.  It is impossible in this situation to
determine the relative importance of any individual weather variable to
pesticide disappearance in a given experiment.

     There were no differences in the rate of disappearance of any individual
residue from fruit and leaf surfaces.  These data have been combined in Figs.
7 through 10.  Individual residue determinations are in Tables 16 and 17.
Pesticide disappearance has been represented as first-order (Gunther and
Blinn, 1955), first-order-weather (Nigg et al., 1977, 1978, 1979) and dif-
fusion kinetics (Stamper et al., 1979).  The diffusion In-ln representation
of the data  (Stamper et al., 1979) was the best statistically and all of the
 2
R  values of 0.768 to 0.999 are significant at the 0.01 level.  The figures

                                     36

-------
Figure 6.
Cumulative weather variables vs. time in days.  Cumulative average
temperature (°C), cumulative relative humidity (hr over 90%);
Cumulative solar incidence (gm cal cm~2 min"1), cumulative leaf
wetness (hr); cumulative rainfall (inches).  There are no actual
units on the y-axis for comparative purposes.
(7-10) indicate a moderate weather effect, i.e., larger slopes (faster dis-
appearance) in experiment 2 under hot, wet, cloudy conditions.  Based on dif-
ferences in these slopes, oxydemetonmethyl shows the greatest weather effect,
malathion is intermediate and dioxathion and dialifor show a much smaller, but
similar effect of weather on their disappearance.

     The slope of this disappearance should theoretically be 1.5 (Stamper
et al., 1979).  Malathion slopes were very close to this value (1.571, 1.027,
Fig. 7), similar to results obtained for ethion, and parathion in previous
experiments (Stamper et al., 1979).  Oxydemetonmethyl had a slope of 1.328
in experiment 2, but only 0.355 in experiment 1; dialifor and dioxathion
were very similar with slopes of about 0.35 to  0.60.  Disappearance rates of
individual materials were in the order malathion » oxydemetonmethyl >
dialifor  > dioxathion.
                                     37

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TABLE 16.  (CONTINUED)

Day 29
Leaves
Wg/cm


Fruit
pg/cm


Soil
vacuum
(middle)
ppm


Soil
vacuum
(dripline)
ppm


Delnav
Malathion/
MT oxon
MSR
Torak
Delnav
Malathion/
M'oxon
MSR
Torak
Delnav
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M1 oxon
MSR
Torak
Delnav
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M' oxon
MSR
Torak
0.5 +
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+ 1.3
1.2
2.5
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                       o
                       •s.
                       o 2
                                   MALATHION
                                    t, = l day
                                    • EXP I
                                    • EXP II
                                  R* = 0.95I
                                  B = 1.571
Figure 7,
Ln-ln plot of  combined  malathion fruit and leaf surface  residues.
Initial concentration (day 1) of malathion fruit:  0.4+1  yg/cm2
experiment 1,  leaves  0.5 + 0.12 yg/cm2 experiment  1;  fruit  0.0006
+ 0.002 yg/cm2 experiment 2, malathion leaves 0.006 + 0.003 yg/cm2
experiment 2.
                               DIALIFOR
                                  t| = l day
                                  • EXP I
                                  • EXP II
                                                        905
                                                      = 0 440
                       -0.5
                                        L (1/1,)
Figure 8.
Ln-ln plot of combined  dialifor fruit and leaf surface residues.
Initial concentration  (day 1)  of dialifor fruit 1.1 + 0.5 yg/cm2
experiment 1, leaves 0.6  + 0.08 experiment 1; fruit 0.2 + 0.05  yg/
cm2 experiment 2, leaves  0.1 + 0.02 yg/cm2 experiment 2.
                                     43

-------
                             DIOXATHION
                               t, = l  day
                               • EXP I
                               • EXP II
                                                   878
                                                B =0 340
                      -05
                                        Ln( 1 /I,
Figure 9.  Ln-ln plot of  combined  dioxathion fruit and leaf surface residues.
           Initial concentration (day 1)  of dioxathion fruit 0.6 + 0.1 yg/cm
           experiment 1,  leaves  0.3 + 0.003 yg/cm2 experiment 1; fruit 0.06
           to 0.03 yg/cm2 experiment 2,  leaves 0.01 + 0.02 experiment 2.
                        o*-
                             OXYDEMETONMETHYL
                               1, =l day
                               • EXP I
                               • EXP II
                                                     768
                                                 B =0 335
                      -05
                                   I         2
                                        Ln(1/ t ,)
 Figure 10.
Ln-ln plot of combined oxydemetonmethyl fruit and leaf surface
residues.  Initial concentration (day 1) of oxydemetonmethyl fruit
0.5 + 0.03 yg/cm2 experiment  1,  leaves 0.2 + 0.02 yg/cm2 experi-
mentTl; fruit 0.005 + 0.002 yg/cm2 experiment 2; leaves 0.003 +
0.002 yg/cm  experiment  2.
                                      44

-------
     Figure 11 presents the malaoxon data for leaf and fruit surfaces  in
experiment 1 (dry, cool, clear conditions).   Actual residue values  are noted
by each point.  The line is the percent malaoxon residue  (malaoxon/malathion
x 100).  The actual quantity of malaoxon was surprisingly  constant over the
course of this experiment.  In previous experiments an initial  rise  of oxon
metabolite of parathion, carbophenothion and ethion was evident (Nigg  et  al.,
1977, 1978, 1979) followed by a decrease.   Since the parent compound,  malathion,
exhibited a steady disappearance,  the percentage of malaoxon increased (Fig.
11).  A small production of malaoxon during the extraction process might
account for these data, but no malaoxon was detected in malathion-fortified
fruit and leaf washes thus eliminating this possibility.   No malaoxon  was
detected during experiment 2  (wet,  hot, cloudy conditions).  This is similar
to results of previous  experiments (Nigg et al., 1977,  1978, 1979)  and supports
the supposition that hydrolysis is central  to disappearance  of  the oxon
metabolites of the organophosphates (Gunther et al.,  1977, Spencer et  al.
1975).
                         24
                                     % MALAOXON RESIDUE
                                        Expl
                                                 002 fiq /cm2
                                                       002
                            13    8 10   14
                                     T(DAY)
                                               22
                                                      29
 Figure 11.
% malaoxon residue.  (Malaoxon/malathion x 100)
are next to each point in yg/cm  .
                                                               Actual  values
                                       45

-------
     Fruit and leaf surface organophosphate residue data are so similar that
only one type of sample need be taken for worker reentry residue data.  Leaf
samples are much more convenient to process and extract compared to fruit
(Gunther et al., 1977, Iwata et al., 1977) and the variation for both types
of sample is essentially the same (Table 18).   We suggest that fruit samples
be eliminated as a requirement for worker reentry data for the registration
 of organophosphate pesticides.

     The physical and chemical characteristics of individual pesticides
coupled with the effects of environmental conditions on these characteristics
determine disappearance rate.  Theory suggests that the individual diffusion
coefficient or vapor pressure may be the most important physical chemical
characteristics in residue disappearance  (Stamper et al., 1979) and
environmental effects on these chemical characteristics warrant investigation.
                                      46

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TABLE 19.  CONVERSION OF PESTICIDE APPLICATION RATES
           FROM ENGLISH TO METRIC SYSTEM

(A)
English
Pounds
Gallons
Acre
Pounds/acre
To convert from
(B) English to metric,
Metric multiply column A by
Kilograms
Liters
Hectare
Kg/ha
0.454
3.79
0.405
1.12
                         48

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                                REFERENCES

Adams, J. D.,  Y. Iwata, and F. A. Gunther.  1976.  The effect of dust derived
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Blinn, R. C.,  G. E. Carman, W. H. Ewart, and F. A. Gunther.  1959.  Residual
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Calhoun, F. G., V. W. Carlisle, R. E. Caldwell, L. W. Zelazuy, L. C. Hammond,
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Gunther, F. A., J. H. Barkley, and W. E. Westlake.  1974.  Worker environ-
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Gunther, F. A., Y. Iwata , G. E. Carman, and C. A. Smith.  1977.  The citrus
     reentry problem:  Research on its causes and effects, and approaches
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Gunther, F. A., W. E. Westlake, J. H. Barkley, W. Winterlin, and L.
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Guthrie, F. E., J. J. Domanski, A. R. Main, D. G. Sanders, and R. R. Monroe.
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     pesticide-treated fields.  Arch.Environ. Contam. Toxicol.  2:233-242.

Iwata, Y., M.  E. Dusch, W. E. Westlake, and F. A. Gunther.  1975.  Behavior
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     types.  Bull. Environ. Contam. Toxicol.  14:49-56.

Iwata, Y., J.  B. Knaak, R. C. Spear, and R. B. Foster.  1977.  Worker
     reentry into pesticide-treated crops.  I.  Procedure for the determina-
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     Contam. Toxicol.  18:649-655.

Iwata, Y., W.  E. Westlake, and F. A. Gunther.  1973.  Persistence of
     parathion in six California soils under laboratory conditions.
     Arch. Environ. Contam. Toxicol.  1:84-96.
                                    49

-------
Leffingwell, J. T., R. C. Spear, and D. Jenkins.  1975.  The persistence
     of ethion and zolone residues on grape foliage in the central valley
     of California.  Arch. Environ. Contam. Toxicol.  3:40-54.

Liu, B. Y. H., and K. W. Lee.  1976.  Efficiency of membrane and nuclepore
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Megaw, W. J., and R. D. Wiffen.  1963.  The efficiency of membrane filters.
     Int. J. Air Wat. Poll.  7:501-509.

Miles, J. W., L. E. Fetzer, and G. W. Pearce.  1970.  Collection and
     determination of trace quantities of pesticides in air.  Environ. Sci.
     Technol.  4:420-425.

Morrison, D. F.  1967.  Multivariate Statistical Methods,  p. 104.  McGraw-
     Hill, NY.  338 pp.

Natusch, D. F. S., and J. R. Wallace.  1974.  Urban aerosol toxicity:  The
     influence of particle size.  Science  186:695-699.

Nigg, H. N., J. C- Allen, R. F. Brooks, G. J. Edwards, N. P. Thompson,
     R. W. King, and A. H. Blagg.  1977a.  Dislodgeable residues of ethion
     in Florida citrus and relationships to weather variables.  Arch.
     Environ. Contam. Toxicol.  6:257-267.

Nigg, H. N., J. C. Allen, and R. F. Brooks.  1977b.  Weather and pesticide
     residues.  Proc. Int. Soc. Citriculture  2:437-441.

Nigg, H. N., J. C. Allen, R. W. King, N. P. Thompson, G. J. Edwards, and
     R. F. Brooks.  1978.  Dislodgeable residues of parathion and carbo-
     phenothion in Florida citrus:  A weather model.  Bull Environ. Contam.
     Toxicol.  19:578-588.

Nigg, H. N., J. C. Allen, and R. W. King.  1979.  Behavior of parathion
     residues in the Florida'Valencia' orange agroecosystem.  J. Agric.
     Food Chem.  27:578-582.

Patterson, E. M., and D. A. Gillette.  1977a.  Measurements of  visibility
     vs. mass-concentration for airborne soil particles.  Atmospheric
     Environ.  11:193-196.

Patterson, E. M., and D. A. Gillette.  1977b.  Commonalities in measured
     size distributions  for aerosols having a soil-derived component.  J.
     Geophys. Res.  82:2074-2082.

Patterson, E. M., D. A.  Gillette, and  G. W. Grams.  1976.  The  relation
     between visibility  and  the size-number distribution of airborne  soil
     particles.  J. Appl. Meteorol.  15:470-478.

Popendorf, W. J., and J.  I. Leffingwell.   1978.  Natural variations in the
     decay and oxidation of parathion  foliar residues.  J. Agric. Food.

                                    50

-------
     Chem.  26:437-441.

Popendorf, W. J.,  and R. C. Spear.  1974.  Preliminary survey of factors
     affecting the exposure of harvesters to pesticide residues.  Amer.
     Ind. Hyg. Assoc. J.  35:374-380.

Popendorf, W. J.,  R. C. Spear, and S. Selvin.  1975.  Collecting foliar
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Schultze, R. E.  1976.  A physically based method of estimating solar
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Serat, W. F.  1973.  Calculation of a safe reentry time into an orchard
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Serat, W. F., and J. B. Bailey.  1974.  Estimating the relative toxicologic
     potential of each pesticide in a mixture of residues on foliage.
     Bull. Environ. Contam. Toxicol.  12:682-686.

Serat, W. F.  1978.  Estimating a worker entry interval for the carbamate
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Serat, W. F., D. C. Mengle, H. P. Anderson, E. Kahn, and J. B. Bailey.
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Spear, R. C.  1978.  Organophosphate residue poisoning among agricultural
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     Conversion of parathion to paraoxon in foliar residues:  Effects of
     dust level and ozone concentration.  J. Agric. Food Chem.  26:434-436.

Spear, R. C., W. J. Popendorf, J. T. Leffingwell, and D. Jenkins.  1975.
     Parathion residues on citrus foliage.  Decay and composition as related
     to worker hazard.  J. Agric. Food Chem.  23:808-810.

Spear, R. C., W. J. Popendorf, J. T. Leffingwell, T. H. Milby, J. E. Davies,
     and W. F. Spencer.  1977.  Fieldworkers response to weathered residues
     of parathion.  J. Occ. Med.  19:406-410.
                                    51

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Spencer, W. F. , M. M. Cliath, K. R. Davis, R. C. Spear, and W. J.
     Popendorf.  1975.  Persistence of parathion and its oxidation to
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     Environ. Contam. Toxicol.  18:656-662.

Stamper, J. H., H. N. Nigg, and J. C. Allen.  1979.  Organophosphate
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Thornton, J. S., T. J. Olsen, and K, Wagner.  1977.  Determination of
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Westlake, W. E., F. A. Gunther, and G. E. Carman.  1973.  Worker environ-
     ment research:  dioxathion (Delnav^) residues on and in orange fruits
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     sprayed trees.  Arch. Environ. Contam. Toxicol.  1:60-83.

Wolfe, H. R., J. F. Armstrong, D. C. Staiff, S. W. Comer, and W. F. Durham.
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     Environ. Contam. Toxicol.  3:257-267.
                                     52

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                              BIBLIOGRAPHY

Nigg, H. N., N. P. Thompson, J. C. Allen, and R. F. Brooks.  1977.  Worker
     reentry and residues of ethion, parathion, and carbophenothion
     (Trithion) on Florida citrus.  Proc. Fla. State Hort. Soc.  90:19-21.

Nigg, Herbert N., and Jon C. Allen.  1979.  A comparison of time and time-
     weather models for predicting parathion disappearance under California
     conditions.  Environ. Sci. Technol.  13:231-233.

Nigg, Herbert N.  1979.  Comparison of pesticide and particulate recoveries
     with the vacuum and dislodgeable surface pesticide residue techniques.
     Arch. Environ. Contam. Toxicol.  8:369-381.

Nigg, H. N.  James A. Reinert, and G. E. Fitzpatrick.  1979.  Weather-
     dependent residue behavior of malathion in Florida citrus varieties.
     Bull. Environ. Contam. Toxicol.  21:697-702.

Nigg, H. N.,and J. H. Stamper.  1980.  Comparative disappearance of
     dioxathion, malathion, oxydemetonmethyl and dialifor from Florida citrus
     leaf and fruit surfaces.  J. Econ. Entomol.   (Submitted).
                                    53

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TECHNICAL REPORT DATA
IP'ease read Instructions on the re\ erse before completing)
1 REPORT NO.
EPA-600/1-80-013
2.
4. TITLE AND SUBTITLE
Worker Reentry in Florida Citrus Pesticides in
the Agricultural Environment
7 AUTHOR(S)
H.N. Jigg
9 PERFORMING ORGANIZATION NAME AND ADDRESS
University of Florida
Institute of Food and Agricultural Sciences
P.O. Box 1088
Lake Alfred, FL 33850
12. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
February 1980
6. PERFORMING ORGANIZATION CODE
8 PERFORMING ORGANIZATION REPORT MO
10. PROGRAM ELEMENT NO.
1EA615
11. CONTRACT/GRANT NO.
R-804633
13. TYPE OF REPORT AND PERIOD COVERED
14 SPONSORING AGENCY CODE
EPA 600/11
15. SUPPLEMENTARY NOTES
16. ABSTRACT
              The environmental behavior of five organophospate insecticides in
         Florida citrus are reported.  Parathion disappearance rate from fruit, leaf,
         and soil surfaces was the same.  Potential worker exposure to parathion was
         leaf surface^ soil surface» fruit surface and a minor component in air.
         Disappearance of parathion surface residues was accurately represented with a
         first-order solar radiation, rainfall, temperature, and dew model.

              Dialifor, malathion, oxydemetonmethyl, and dioxathion fruit and leaf
         surface residues exhibited different disappearance rates.  The disappearance
         rate, however, was the same on fruit and leaf surfaces for individual
         compounds.   Based on rates of disappearance under different environmental
         conditions, environmental sensitivity was oxydemetonmethyl  malathion
         dioxathion  dialifor.  These data suggest that fruit data could be eliminated
         from worker safety reentry  registration requirements for organophosphate
         insecticides.
              Two surface residue techniques were compared.  Vacuum and dislodgeable
         residue techniques differed in the amount of particulate matter and pesticide
         residue recovered.  Vacuum, dislodgeable and air particulate numbers and sizes
         were relatively comparable.  The dislodgeable residue technique for worker reen
17.
a.
aata appeared superior to tne vacuum tecnnlque.
rr KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Organophosphate insecticide
Citrus workers
Leaf /soil/fruit surfaces
18.
DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
b. IDENTIFIERS/OPEN ENDED TERMS
Parathion
Dialifor
Malathion
Oxydemetonmethyl
Dioxathion
Toxicology
19. SECURITY CLASS (This Report)
UNCLASSIFIED
20 SECURITY CLASS /This page)
UNCLASSIFIED
c. COSATI field/Group
06F,T
21. NO. OF PAGES
63
22. PRICE
EPA Form 2220—1 (Rev. 4-771   PREVIOUS EDITION is OBSOLETE
                                            54

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