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OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

December 12, 2011 

PC Code: 061601 

MEMORANDUM DP Barcode: 392076 

SUBJECT: EFED Registration Review: Preliminary Problem Formulation for Paraquat 

Dichloride 

FROM: Kristina Garber, Senior Biologist 

 James Lin, Environmental Engineer 

Environmental Risk Branch II 

Environmental Fate and Effects Division (7507P) 

 

REVIEWED 

BY: Jean Holmes, DVM, MPH, Risk Assessment Process Leader 

R. David Jones, Ph.D., Senior Agronomist 

THROUGH: Brian Anderson, Chief 

 Environmental Risk Branch II 

 Environmental Fate and Effects Division (7507P) 

 

TO: Molly Clayton, Chemical Review Manager 

 Michael Goodis, Chief 

Risk Management and Implementation Branch III 

Pesticide Re-Evaluation Division (7508P) 

 
Page 2 of 71 

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation (attached) for the ecological risk, environmental fate, endangered species, and 

drinking water assessments to be conducted as part of the registration review of the herbicide, 

paraquat dichloride. The problem formulation draws on information from both open literature 

and studies submitted by the technical registrant in response to data requirements. This 

document is intended to provide an overview of what is currently known regarding the 

environmental fate and ecological effects associated with paraquat dichloride and outlines 

uncertainties, including data gaps. This problem formulation describes the preliminary 

ecological risk hypothesis and the processes that will be used during the completion of drinking 

water and ecological risk assessments in support of registration review for paraquat dichloride. 

This document also identifies information gaps and recommends studies that the Pesticide ReEvaluation Division (PRD) should include in a data call-in (DCI) to address uncertainties 

surrounding the environmental fate and potential ecological effects of paraquat dichloride. 
Page 3 of 71 

 

Preliminary Problem Formulation for the 

Environmental Fate and Ecological Risk, Endangered 

Species, and Drinking Water Assessments in Support 

of the Registration Review of Paraquat Dichloride 

Chemical name: 1,1'-dimethyl-4,4'-bipyridinium dichloride 

PC: 061601 

Prepared by:

Kristina Garber, Senior Biologist 

James Lin, Environmental Engineer 

U. S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division 

Environmental Risk Branch II 

1200 Pennsylvania Ave., NW 

Mail Code 7507P 

Washington, DC 20460

Reviewed by: 

Jean Holmes, DVM, MPH, Risk Assessment Process Leader 

R. David Jones, Ph.D., Senior Agronomist 

Brian Anderson, Branch Chief 

N

N

+

+ 2Cl-
Page 4 of 71 

Table of Contents 

1. Purpose ....................................................................................................................................... 5

2. Nature of Regulatory Action ...................................................................................................... 5

3. Conclusions from Previous Risk Assessments .......................................................................... 5

4. Stressor Source and Distribution ................................................................................................ 6

4.1. Mechanism of Action .......................................................................................................... 6

4.2. Overview of Pesticide Usage .............................................................................................. 6

4.3. Environmental Fate and Transport .................................................................................... 13

Mobility .......................................................................................................................... 14

Degradation ................................................................................................................... 15

Field Dissipation ............................................................................................................ 15

4.4. Monitoring Data ................................................................................................................ 16

4.5. Nature of Stressor ............................................................................................................. 16

5. Receptors.................................................................................................................................. 17

5.1. Effects to Aquatic Organisms ........................................................................................... 17

5.3. Ecological Incidents .......................................................................................................... 19

6. Ecosystems Potentially at Risk .......................................................................................... 22

7. Assessment Endpoints ............................................................................................................. 22

8. Conceptual Model ..................................................................................................................... 22

8.1. Risk Hypothesis ................................................................................................................ 23

8.2. Conceptual Diagram ......................................................................................................... 23

9. Analysis Plan ............................................................................................................................ 25

9.1. Measures of Exposure ....................................................................................................... 26

9.2. Measures of Effect ............................................................................................................ 28

9.3. Integration of Exposure and Effects ................................................................................. 29

9.4. Endangered Species Assessments ..................................................................................... 30

9.5. Drinking Water Assessment ............................................................................................. 31

10. Endocrine Disruptor Screening Program ....................................................................... 31

11. Preliminary Identification of Data Gaps ............................................................................ 32

11.1. Fate .................................................................................................................... 32

11.2. Effects ................................................................................................................ 34

12. References .............................................................................................................................. 41

Appendix A. Ecological Effects Characterization .................................................................... 61

 
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1. Purpose 

The purpose of problem formulation is to provide the foundation for risk assessment. It sets the 

assessment objectives, evaluates the nature of the problem, and provides a plan for analyzing the 

data and characterizing the risk. This problem formulation provides a plan for analyzing data 

relevant to paraquat dichloride and for conducting environmental fate and ecological risk, 

endangered species, and drinking water assessments as part of the registration review of its 

registered uses. Additionally, this problem formulation identifies data gaps, uncertainties, and 

potential assumptions used to address those uncertainties, relative to characterizing the 

ecological risk associated with the registered uses of paraquat dichloride. 

The active ingredient, paraquat dichloride, is generally applied as a flowable solution. As a 

result, paraquat dichloride readily dissociates into its cation, paraquat. Therefore, the following 

discussions involving paraquat dichloride will focus on the paraquat cation as the stressor of 

concern. 

 

2. Nature of Regulatory Action 

The Food Quality Protection Act of 1996 mandated the Environmental Protection Agency (EPA) 

to implement a new program for assessing the risks of pesticides, i.e., registration review 

(http://www.epa.gov/oppsrrd1/registration_review/). All pesticides distributed or sold in the 

United States generally must be registered by EPA. The decision to register a pesticide is based 

on the consideration of scientific data and other factors showing that it will not cause 

unreasonable risks to human health, workers, or the environment when used as directed on 

product labeling. The registration review program is intended to ensure that, as the ability to 

assess risk evolves and as policies and practices change, all registered pesticides continue to 

meet the statutory standard of no unreasonable adverse effects to human health and the 

environment. Changes in science, public policy, and pesticide use practices will occur over time. 

Through the new registration review program, the Agency periodically reevaluates pesticides to 

ensure that as change occurs, products in the marketplace can be used safely. 

As part of the implementation of the new registration review program pursuant to Section 3(g) of 

the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the Agency is beginning its 

evaluation to determine whether paraquat dichloride continues to meet the FIFRA standard for 

registration. This problem formulation for the environmental fate and ecological risk assessment 

chapter in support of the registration review is intended for the initial docket, opening the public 

phase of the review process. 

3. Conclusions from Previous Risk Assessments 

Paraquat has a long regulatory history. A re-registration eligibility decision (RED) was made in 

1997. In the 1997 RED, the Agency requested additional data in order to establish tolerances on 
Page 6 of 71 

taro foliage, corn and soybean aspirated grain fractions, wheat and hay, cotton and gin 

byproducts, and processed grapes, as well as data to confirm that the existing tolerance for field 

corn was adequate to cover the specialized use of paraquat as a harvest aid. The ecological risk 

assessment for the RED concluded that uses of paraquat dichloride pose risks to birds, mammals 

and plants. The maximum single application rate of paraquat was 1.6 lb cation/A. This rate was 

reduced to 1.0 lb cation/A in the RED in order to reduce risks. 

In June 2009, an endangered species risk assessment was completed by EFED to determine the 

Risks of Paraquat Use to Federally Threatened California Red-legged Frog (CRLF; Rana aurora 

draytonii). This assessment considered all registered uses of paraquat that are relevant to the 

state of California. The assessment concluded that paraquat may affect, and is likely to adversely 

affect the CRLF based on the direct effects to the terrestrial-phase CRLF, and indirect effects to 

the aquatic- and terrestrial-phase CRLF. Indirect effects are specifically related to declines in 

prey (algae, amphibians, mammals) and habitat of the frog. 

In July, 2011, EFED completed an ecological risk assessment for the use of paraquat dichloride 

on tropical and subtropical trees (DP 382001). Risk conclusions were similar to previous 

conclusions and included LOC exceedances for plants, aquatic invertebrates, mammals, birds, 

terrestrial-phase amphibians and reptiles. A decision on that action is pending. 

4. Stressor Source and Distribution 

4.1. Mechanism of Action 

Paraquat dichloride is a quaternary ammonium compound widely used for broadleaf weed 

control. It is a fast-acting contact herbicide used to suppress or eradicate a wide spectrum of 

post-emergent weeds. It also functions as a defoliant and desiccant and is most effective on 

growing plants with abundant green tissue. It is highly toxic (EPA toxicity class I) but readily 

immobilized. Paraquat is quickly absorbed by living (especially healthy) plant tissue and 

produces superoxides during photosynthesis, which destroy plant cells. It is less effective on 

dry, drought-stressed, woody, or fully mature plants. 

4.2. Overview of Pesticide Usage 

Two formulated products are commercial available: an emulsifiable concentrate (EC) and a 

liquid (L, only for cotton use). The application equipment include aircraft, ground, and low 

pressure ground sprayer. The application method types include banded and broadcast, or spottreatment sprays and a tree wound treatment. 

The uses considered for this Registration Review are listed in Table 1. Many of the current 

labels do not contain sufficient information to limit maximum annual numbers of applications or 

maximum annual application rates. Note that these applications rates are based on lb paraquat 

dichloride/A. A rate of 1.417 lb/A is equivalent to 1 lb cation/A. 
Page 7 of 71 

Table 1. Currently Registered Uses to be Considered for Registration Review (provided by BEAD)1

Use Site Max App 

Rate / App 

Max # Apps / 

Year or Crop 

Cycle 

Use Group: Forest 

arborvitae (forest/shelterbelt), ash (forest/shelterbelt), elm 

(forest/shelterbelt), 

fir (forest/shelterbelt), forest trees (softwoods, conifers), oak 

(forest/shelterbelt), pine (forest/shelterbelt) 

1.417 lb/ac 5 

forest trees (hardwoods, broadleaf trees) 1.385 lb/ac 5 

use group: terrestrial feed 

alfalfa 1.400 lb/ac 2 

clover 1.388 lb/ac 2 

corn (silage) 0.689 lb/ac 3 

crown vetch, legume vegetables, lespedeza, lupine, sainfoin, trefoil, vetch 1.102 lb/ac 1 

tyfon 1.417 lb/ac 3 

use group: terrestrial food 

acerola (west indies cherry), apple, avocado, banana, beech nut, 

blackberry, blueberry, boysenberry, brazil nut, butternut, calamondin, 

cashew, chestnut, chinquapin, citron (citrus), cocoa, coffee, currant, 

elderberry, fig, filbert (hazelnut), gooseberry, grapefruit, grapes, hickory 

nut, huckleberry, kumquat, lemon, lime, loganberry, macadamia nut 

(bushnut), orange, papaya, pear, pecan, pistachio, prune, pummelo 

(shaddock), raspberry (black, red), walnut (english/black), 1.417 lb/ac 5 

apricot, artichoke, asparagus, beans, succulent (lima), broccoli, cabbage, 

cabbage (chinese), carrot (including tops), cauliflower, chayote, cherry, 

collards, cucumber, eggplant, gherkin, gourds, gourd (wax), chinese, 

groundcherry (strawberry tomato/tomatillo), kiwi fruit, lettuce, melons, 

bitter (balsam pear), melons, cantaloupe, melons, citron, melons, musk, 

melons, water, nectarine, peach, peas (unspecified), pepino (melon pear), 

pepper, pineapple, plum, pumpkin, safflower (unspecified), soybeans 

(unspecified), squash (all or unspecified), sugar beet, sunflower, tomatillo, 

tomato, turnip (greens), 

1.417 lb/ac 3 

beans, succulent (snap), corn (sweet), 1.417 lb/ac NS 

brussels sprouts, vegetables (unspecified), 1.385 lb/ac 3 

catjang (jerusalem/marble pea), lentils, yam, 0.692 lb/ac 2 

crabapple 1.385 lb/ac NS 

endive (escarole) 1.400 lb/ac 3 

garlic, onion, 1.417 lb/ac 1 

ginger 1.385 lb/ac 6 

guar, hops, manioc (cassava), strawberry, 0.692 lb/ac 3 

guava 1.379 lb/ac 4 

kale, kohlrabi 1.385 lb/ac 3 

loquat, mayhaw (hawthorn), plantain, quince, tangelo, 1.385 lb/ac 5 

melons 0.367 lb/ac 2 

mint/peppermint/spearmint 1.049 lb/ac 2 

okra 1.385 lb/ac 1 

olive 1.417 lb/ac 4 

passion fruit (granadilla) 1.379 lb/ac 5 
Page 8 of 71 

Table 1. Currently Registered Uses to be Considered for Registration Review (provided by BEAD)1

peas, pigeon 0.692 lb/ac 1 

pepper (chili type) 0.689 lb/ac NS 

persimmon 1.311 lb/ac 5 

rhubarb 1.417 lb/ac 2 

sage, clary, sugarcane, 1.038 lb/ac 2 

taro 1.102 lb/ac 2 

yautia 0.692 lb/ac 3 

use group: terrestrial food + feed 

agricultural fallow/idleland / conservation reserve 1.417 lb/ac 2 

almond, barley, corn (unspecified), corn, field, corn, pop, corn, sweet, 

cotton (unspecified), rice, small grains (unspecified), sorghum, wheat 1.417 lb/ac NS 

beans, asparagus, beans, broad, beans, dried-type, beans, moth, beans, 

mung, beans, rice, beans, succulent (lima), beans, succulent (snap), beans, 

tepary, beans, urd, cowpea/blackeyed pea, garbanzos (including chick 

peas), guar, lupine, grain, peas, dried-type, peas, southern, potato, 

white/irish 

0.692 lb/ac NS 

peanuts 0.346 lb/ac NS 

peanuts (unspecified) 0.354 lb/ac NS 

vegetables (unspecified) 1.038 lb/ac NS 

use group: terrestrial non food 

agricultural fallow/idleland / conservation reserve, 1.417 lb/ac 3 

airports/landing fields, commercial/institutional/industrial 

premises/equipment (outdoor), deciduous fruit trees (unspecified), grasses 

grown for seed, nonagricultural rights-of-way/fencerows/hedgerows, 

nonagricultural uncultivated areas/soils, orchards (unspecified), ornamental 

and/or shade trees, ornamental herbaceous plants, ornamental woody 

shrubs and vines, 

1.417 lb/ac NS 

alfalfa, guayule (rubber) 1.385 lb/ac NS 

corn (unspecified), nonagricultural areas (public health use), 1.400 lb/ac NS 

pastures 0.692 lb/ac NS 

1 Any registrations or uses registered prior to conduct of the Registration Review risk assessment 

will also be considered. 

Form Code: NS = Not Specified on label, CC = Crop Cycle

A national map showing the estimated poundage of paraquat used in 2002 by county is presented 

in Figure 1. The map is an illustrated estimate of the extent of paraquat use. The map was 

downloaded from the U.S. Geological Survey (USGS), National Water Quality Assessment 

Program (NAWQA) website.1

 The map represents typical agricultural use patterns over a five 

year period from 1999 through 2004. It does not reflect any new registrations, label changes, 

changing use patterns, or mitigation measures that may have occurred between that time and the 

time of this problem formulation. 

 

1 http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=02&map=m1616
Page 9 of 71 

Figure 1. Paraquat Dichloride Use in Pounds Per Square Mile in U.S. Counties 

BEAD’s Screening Level Usage Analysis (SLUA) estimates of the agricultural uses of paraquat 

dichloride (in total pounds active intergradient applied) are listed in Table 2. An estimated of 

over three million pounds of paraquat dichloride are applied per year in the U.S. The top five 

uses are corn (700,000 lb), cotton (700,000 lb), soybeans (300,000 lb), almonds (200,000 lb), and 

grapes (200,000 lb). 

Table 2. Screening Level Usage Analysis for paraquat dichloride 

Percent Crop Ttd. 

Crop Lbs. A.I. Avg. Max. 

Alfalfa 100,000 <1 <2.5 

Almonds 200,000 25 35 

Apples 100,000 20 30 

Apricots 1,000 10 20 

Artichokes 2,000 25 40 

Asparagus 4,000 10 15 

Avocados 1,000 <2.5 5 

Barley 2,000 <1 <2.5 

Beans, Green 1,000 <1 <2.5 

Blueberries 3,000 10 20 

Broccoli <500 <1 <2.5 

Brussels Sprouts <500 N.C. N.C. 

Cabbage 1,000 <2.5 10 
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Caneberries 6,000 45 70 

Cantaloupes 2,000 5 10 

Carrots 1,000 <2.5 <2.5 

Celery <500 <1 <2.5 

Cherries 30,000 20 30 

Chicory <500 N.C N.C. 

Corn 700,000 <2.5 <2.5 

Cotton 700,000 15 25 

Cucumbers 3,000 5 30 

Dry Beans/Peas 10,000 <2.5 5 

Fallow, Summer 40,000 <1 <2.5 

Figs 1,000 N.C N.C. 

Garlic <500 <1 <2.5 

Grapefruit 3,000 <2.5 5 

Grapes 200,000 20 30 

Kiwifruit 2,000 30 30 

Lemons 2,000 <2.5 5 

Lettuce 1,000 <1 <2.5 

Nectarines 4,000 10 25 

Olives 1,000 5 10 

Onions 3,000 5 10 

Oranges 60,000 5 10 

Pasture 50,000 <1 <2.5 

Pastureland 40,000 <1 <2.5 

Peaches 50,000 30 40 

Peanuts 60,000 20 35 

Pears 9,000 10 20 

Peas, Green <500 <1 <2.5 

Pecans 40,000 5 20 

Peppers 6,000 10 20 

Pistachios 50,000 25 40 

Plums 6,000 15 20 

Potatoes 20,000 5 10 

Prunes 20,000 10 25 

Pumpkins 2,000 5 10 

Rice 5,000 <1 <2.5 

Sorghum 20,000 <1 <2.5 

Soybeans 300,000 <1 <2.5 

Spinach 1,000 5 10 
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Squash 2,000 5 15 

Strawberries 4,000 10 25 

Sugar Beets 2,000 <1 <2.5 

Sugarcane 20,000 5 10 

Sunflowers 4,000 <1 <2.5 

Sweet Corn 3,000 <2.5 5 

Tangelos <500 10 15 

Tangerines 1,000 10 15 

Tobacco <500 <1 <2.5 

Tomatoes 20,000 5 15 

Walnuts 50,000 15 20 

Watermelons 2,000 5 5 

Wheat 50,000 <1 <2.5 

All numbers rounded. 

<500 Less than 500 pounds of active ingredient 

<2.5 Less than 2.5 percent of crop treated 

<1 Less than 1 percent of crop treated 

 

Publicly available data from the California Department of Pesticide Regulation (Cal. DPR) was 

used to produce Table 3, which outlines the pounds of paraquat dichloride used in California 

over the three most recent years available (2007 - 2009). 

Table 3. Paraquat dichloride (061601) California DPR Usage Data 

Commodity 

2007 

Pounds 

Applied 

2008 

Pounds 

Applied 

2009 

Pounds 

Applied 

alfalfa (forage - fodder) (alfalfa hay) 133988 163439 193301 

almond 282732 230243 218579 

apple 1962 2747 923 

apricot 762 783 1271 

artichoke (globe) (all or unspec) 10479 4921 8042 

asparagus (spears, ferns, etc.) 772 1087 467 

avocado (all or unspec) 57 99 0 

barley, general 21 135 171 

beans (all or unspec) 30 

beans, dried-type 195 54 439 

beans, succulent (other than lima) 864 648 343 

bermudagrass (forage - fodder) 31 324 

blackberry 4 40 14 

blueberry 3687 1957 2528 

bok choy (wong bok) 9 

boysenberry (boysens) 4 

broccoli 278 234 684 

buildings and structures (non-ag outdoor) 2 

cabbage 24 45 

cantaloupe 103 301 115 
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cardoon (cardoni) 9 

carrots, general 21 95 

cauliflower 22 86 10 

cherry 15751 10363 13721 

chestnut 111 30 2 

chinese cabbage (nappa, won bok, celery cabbage) 77 30 37 

christmas tree plantations 3 

citrus fruits (all or unspec) 37 26 104 

clover (all or unspec) (forage - fodder) 54 24 43 

commercial, institutional or industrial areas 23 34 

commodity fumigation 7 

corn (forage - fodder) 6860 5818 4298 

corn, field, dent (grain crop) 120 90 

corn, human consumption 251 96 707 

cotton, general 163085 118074 85617 

cucumber (pickling, chinese, etc.) 366 259 235 

date 21 

eggplant (oriental eggplant) 154 2 17 

endive (escarole) 2 23 

fig 1553 686 696 

forage - fodder grasses (all or unspec) (hay) 42 8 

garbanzos (including chick peas) 35 

garlic 169 234 112 

grapefruit 40 37 95 

grapes 143968 72349 81990 

grapes, wine 74881 50557 85512 

kiwi fruit 1172 1180 1194 

landscape maintenance 96 129 61 

lemon 1032 680 246 

lettuce, head (all or unspec) 1232 835 986 

lettuce, leaf (all or unspec) 168 384 176 

melons 34 155 1 

mint (all or unspec) 1220 881 1370 

mushrooms 6 

nectarine 6431 8897 7872 

n-outdr container/fld grwn plants 407 400 368 

n-outdr grwn cut flwrs or greens 235 417 179 

n-outdr grwn trnsplnt/prpgtv mtrl 107 274 264 

oats, general 82 

olive (all or unspec) 1793 1748 1943 

onion (dry, spanish, white, yellow, red, etc.) 422 416 482 

onions (green) 30 

orange (all or unspec) 9089 5171 5227 

pastures (all or unspec) 24 5 399 

peach 8477 7957 10747 

pear 502 402 1986 

peas, general 1 8 
Page 13 of 71 

pecan 115 75 88 

peppers (chili type) (flavoring and spice crop) 325 442 506 

peppers (fruiting vegetable), (bell,chili, etc.) 3681 1411 1640 

persimmon 86 66 33 

pimento (pimiento type pepper) 14 

pistachio (pistache nut) 41606 40423 35381 

plum (includes wild plums for human consumption) 7997 8565 9458 

pluot 3 

potato (white, irish, red, russet) 146 19 

prune 12366 8923 9049 

pumpkin 60 34 17 

radicchio 16 

raspberry (all or unspec) 107 17 

research commodity 47 189 182 

rice (all or unspec) 83 7 62 

rights of way 3296 2529 1655 

safflower, general 214 2470 5644 

soil application, preplant-outdoor (seedbeds,etc.) 499 170 750 

sorghum (forage - fodder) (sorgo, etc.) 768 80 38 

sorghum/milo general 530 14 

squash (all or unspec) 39 19 392 

squash (summer) 25 14 1 

strawberry (all or unspec) 738 537 370 

structural pest control 45 54 10 

sugarbeet, general 69 189 

sunflower, general 2900 2069 2528 

tangelo 51 88 

tangerine (mandarin, satsuma, murcott, etc.) 2400 1961 2503 

tomatillo 4 

tomato 1452 672 265 

tomatoes, for processing/canning 5436 6287 8886 

uncultivated agricultural areas (all or unspec) 28875 25255 30618 

uncultivated non-ag areas (all or unspec) 190 458 522 

walnut (english walnut, persian walnut) 34865 28115 27936 

watermelons 921 856 192 

wheat (forage - fodder) 125 937 1139 

wheat, general 883 2555 955 

Grand Total 1026158 831646 875207 

Date Prepared: 02/10/11, Cal DPR Data: http://www.cdpr.ca.gov/docs/pur/purmain.htm, 

Empty cells indicate no available usage. 

4.3. Environmental Fate and Transport 

The primary route of environmental dissipation of paraquat is adsorption to soil clay particles. 

Paraquat does not hydrolyze and is photodegraded very slowly in aqueous solutions. It is 
Page 14 of 71 

resistant to microbial degradation under aerobic and anaerobic conditions. Essentially no 

microbial degradation of paraquat was observed after 180 days of aerobic incubation or after 60 

days of anaerobic incubation following a 30 day aerobic incubation. Environmental fate and 

transport properties of paraquat are summarized in Table 4. 

Table 4. Physical/Chemical Properties and Environmental Fate Parameters of Paraquat. 

Parameter Value Reference

Physical/Chemical Parameters

Molecular mass 257.2 g/mol (C12H14N2Cl2) Calculated 

Vapor pressure (25°C) 1.73 x 10-15 torr MRID 46098802

Henry’s Law constant (25°C) 1.26 x 10 -20 atm – m3

/mole Calculated 

Water solubility (20°C) 464,000 mg/L MRID 46098802 

Log octanol-water partition 

coefficient ( log KOW)

2.44 R. F. Platford, 1983 (Chemosphere, 

vol. 12, pages 1107 - 1110) 

Persistence in Water

Hydrolysis half-life no evidence of degradation at pH 5, 7, 9 Upton, Hendley and Skidmore, 

1985, no MRID. 

Aqueous photolysis half-life Very slow and unquantified. No degradates 

reported , CO2 (0.15%) 

4-carboxyl-1-methylpyridinium (QINA) 

(6%) after 85 weeks 

MRID 40562301 

Reviewed by Jordan, 2/14/1986 

Aerobic aquatic metabolism 

half-life 

No degradates reported. <2 weeks (only 

represents water phase. Did not measure 

amount of paraquat sorbed to the soil) 

MRID 00055093 

Persistence in Soil

Soil photolysis half-life no evidence of degradation No degradates 

reported. 

MRID 146807 

Aerobic soil metabolism halflife 

no evidence of degradation. Did not 

degrade. No degradates reported. 

MRID 41319301 

Anaerobic soil metabolism halflife

Stable. No degradates reported MRID 41319302 

Mobility

Adsorption/Desorption Study Kd-ads (mL/g), 68 – 50,000 (no measureable 

correlation with % OC). No desorption was 

observed during the desorption step. 

Koc- ads / Koc-des (mL/g), 15,473 to 1,000,000

MRID 40762701 

http://www.ermanz.govt.nz/consult

ations/ceir/t.pdf 

Field Dissipation

Terrestrial field dissipation halflife

No degradates reported. Half-life not 

calculated; however, cited reference 

indicates a half-life of > 10 years, no 

leaching potential 

MRID 41293202, 42802101, 

42738701, 42738702, 

42802102 

Mobility 

In laboratory studies with radiolabeled paraquat, no radioactivity volatilized from the soil surface 
Page 15 of 71 

to adsorb to glass or to collect in volatile traps. With low vapor pressure and extremely high 

adsorption coefficients, paraquat would not be expected to volatilize once applied to the soil. 

Low volatilization would be expected for an ionic compound. 

Paraquat dichloride was immobile in silty clay loam, loamy sand, and sand soils. It was not 

possible to determine Freundlich Kads values because no paraquat was detected in the adsorption 

solution at normal application rates. At application rates 50-1000 times the approved field 

application rates, Kads values ranged from 68-50,000. There was no desorption of paraquat from 

any of these soils (MRID 40762701). 

Degradation 

Paraquat dichloride exhibited little or no discernable degradation under any laboratory 

conditions. Paraquat dichloride at 91 ppm did not hydrolyze at pH 5, 7, or 9 when incubated at 

25° or 40° C (Upton et al., 1985). Paraquat dichloride at 28 ppm in sterile pH 7 aqueous solution 

did not photodegrade when continuously irradiated with a xenon arc lamp for 32 days at 25° C. 

Paraquat accounted for 90.2-98.0% of the applied radioactivity throughout the study in the 

irradiated and dark control samples; no degradates were reported. Volatiles were trapped and 

0.15% of the applied radioactivity was recovered as CO2 (MRID 40562301). Paraquat did not 

photodegrade when mixed with a sterile soil solution and exposed to natural sunlight for 85 

weeks (Pack, 1982). 

Paraquat (4.32 ppm) did not degrade in sandy loam soil incubated under aerobic conditions at 

20° C for 180 days. Paraquat comprised 93% of applied radioactivity at 180 days post-treatment. 

There was no volatile radioactivity. No degradates were reported from TLC or HPLC analysis 

(MRID 41319301). In a 1985 study, paraquat was removed from a water column with a 

“resident half-life” of <2 weeks. Soil was not sampled, but presumably contained most or all of 

the paraquat residues (MRID 00055093). 

Paraquat at 4.32 ppm did not degrade in sandy loam soil incubated under anaerobic conditions 

for 60 days following a 30-day aerobic incubation. Paraquat comprised 88.8% of the applied 

radioactivity at 90 days post-treatment. Only 0.29% was recovered in the water phase at 61 days 

post-treatment. No volatile radioactivity was detected. No degradates were reported (MRID 

41319302). 

Field Dissipation 

Paraquat dichloride dissipated very slowly in Delaware on a loamy sand soil planted in soybean. 

Residues decreased from an average of 1.1 mg/kg soil immediately post-treatment to 0.76 mg/kg 

at 86 days, and remained at 0.42-0.51 mg/kg from 296 to 657 days post-treatment. Paraquat did 

not leach below the 0-3.5 inch soil depth. 

Four long-term field dissipation studies were reported with data from: Champaign, IL (MRID 

42802101); Visalia, CA (MRID 42738701); Leland, MS (MRID 42738702); and Pikeville, NC 

(MRID 42802102). Paraquat was applied in three or four single annual applications to plots of 

bare ground, corn, peach trees, soybeans, and cotton. Paraquat did not appreciably degrade at 

any of the four sites. Half-lives were not calculated, but authors cited references for field studies 
Page 16 of 71 

that indicated a paraquat half-life of >10 years. 

Transformation Products 

QINA (4-carboxyl-1-methylpyridinium) is a minor degradate formed in the photodegradation in 

water study. The quantity of QINA present was only 6% of the radioactivity of paraquat after 85 

weeks of natural sunlight irradiation. Due to paraquat degrading very slowly, the minor 

degradate, QINA, does not pose an important environmental concern and will not be evaluated in 

this assessment. The structure is shown below: 

4.4. Monitoring Data 

Any available monitoring data from the registrants and public organizations such as US EPA, 

USGS, Department of Pesticide Regulation (CDPR), and others will be considered in this review 

process. 

4.5. Nature of Stressor 

Paraquat dichloride is generally applied as a flowable solution. As a result, paraquat dichloride is 

already dissociated into its cation, paraquat. Therefore, assessments involving paraquat dichloride 

will focus on the paraquat cation as the stressor of concern. All EECs and toxicity values will be 

reported in terms of the paraquat cation. 

As discussed in the environmental fate and transport characterization above, no major degradates of 

paraquat dichloride were reported in the available environmental fate studies. In general, paraquat is 

stable in the environment. QINA (4-carboxyl-1-methylpyridinium) is a minor degradate (6% of 

radioactivity) formed by paraquat in an aqueous photolysis study. Because QINA was only observed 

in one environmental fate study at minor concentrations, this degradate is not considered a stressor of 

concern. 
Page 17 of 71 

5. Receptors

Consistent with the process described in the Overview Document (USEPA 2004), the risk 

assessment for paraquat dichloride will rely on a surrogate species approach. Toxicological data 

generated from surrogate test species, which are intended to be representative of broad 

taxonomic groups, are used to extrapolate to potential effects on a variety of species (receptors) 

included under these taxonomic groupings. 

 

Acute and chronic toxicity data from studies submitted by pesticide registrants along with the 

available open literature are used to evaluate the potential direct and indirect effects of paraquat 

dichloride on aquatic and terrestrial receptors. These include toxicity data on the technical grade 

active ingredient, degradates, and when available, formulated products (e.g. “Six-Pack” studies). 

The open literature studies are identified using EPA’s ECOTOX database (USEPA 2007d), 

which employs a literature search engine for locating chemical toxicity data for aquatic life, 

terrestrial plants, and wildlife. The evaluation of both sources of data can also provide insight 

into the direct and indirect effects of paraquat on biotic communities from loss of species that are 

sensitive to the chemical and from changes in structure and functional characteristics of the 

affected communities. 

5.1. Effects to Aquatic Organisms 

On an acute exposure basis, paraquat is slightly toxic to aquatic-phase amphibians and fish and 

moderately toxic to freshwater invertebrates. No chronic toxicity studies have been identified for 

fish or aquatic invertebrates exposed to paraquat. Compared to aquatic animals, paraquat is 

orders of magnitude more toxic to aquatic plants. Table 5 includes the most sensitive endpoints 

that may be used for risk assessment purposes (i.e., to derive RQs) to represent the acute effects 

of paraquat on aquatic animals as well as effects of paraquat on aquatic plants. Additional 

toxicity data on paraquat are provided in Appendix A. 

Table 5. Endpoints used to represent acute effects of paraquat on aquatic animals and plants. 

Taxa Species 

(scientific name) 

Measure of 

Effect 

Endpoint Duration

(hours) 

Mean 

conc. (mg 

cation/L) 

Study 

Classification 

Ref. 

(MRID) 

Fish and 

aquatic-phase 

amphibians 

Fowler’s toad 

(Bufo woodhousei 

fowleri) 

mortality LC50 96 15 Supplemental 40098001 

Aquatic 

invertebrates 

Water Flea 

(Daphnia magna) immobility EC50 48 1.3 Supplemental 0014473 

Non-vascular 

plants 

freshwater diatom 

(Navicula 

pelliculosa) 

growth 

EC50

96 

0.00040 

Acceptable 42601006 

NOAEC 0.00016 

Vascular 

plants 

Duckweed 

(Lemna gibba) growth 

EC50

14 d 

0.071 

Acceptable 42601003 

NOAEC 0.011 
Page 18 of 71 

The endpoint from a study where fowler’s toad tadpoles were exposed to technical paraquat may 

be used to represent fish and aquatic-phase amphibians. Available toxicity data with freshwater 

fish exposed to paraquat dichloride in formulated products (see Table A2 of Appendix A) 

suggests that fish may be more sensitive to paraquat than the fowler’s toad.

5.2. Effects to Terrestrial Organisms 

Paraquat is moderately toxic to birds and mammals on an acute exposure basis. For honey bees, 

paraquat is practically non-toxic. In reproduction studies, paraquat did not impact the 

reproduction in rats tested up to 108 mg cation/kg-diet. Paraquat did impact the reproduction of 

mallard ducks at 100 mg cation/kg-diet, resulting in a NOAEC of 30 mg cation/kg-diet for 

reproductive effects (decrease in number of eggs laid, number of normal hatchlings, number of 

14-d old survivors, and % viable embryos/set). In addition, in a study where pheasant eggs were 

sprayed with paraquat dichloride, effects to the number of eggs hatched and number of 28-d old 

survivors were observed at 1.0 lb cation/A, resulting in a NOAEC of 0.5 lb cation/A. Table 6

includes the most sensitive endpoints that may be used for risk assessment purposes (for deriving 

RQs) to represent the acute and chronic effects of paraquat on terrestrial animals. Additional 

information on the toxicity of paraquat to terrestrial animals is provided in Appendix A. 

Table 6. Endpoints used to represent acute and chronic effects of paraquat on terrestrial animals. 

Taxa 

Species 

(common 

name)

Measure of effect Endpoint 

Mean 

Concentration Units Study Classification

Reference 

(MRID)

Birds, 

terrestrialphase 

amphibians 

and reptiles 

Colinus 

virginianus

(northern 

bobwhite ) 

Mortality LD50 124 

mgcation/kgbw 

acceptable 00029001 

Coturnix 

coturnix 

(Japanese quail)

Mortality LC50 698 

mgcation/kgdiet 

supplemental 00022923 

Anas 

platyrhynchos

(mallard Duck)

number of eggs 

laid, number of 

normal hatchlings, 

number of 14-d old 

survivors, and % 

viable embryos/set 

NOAEC 30 

mgcation/kgdiet Acceptable 00110455 

Phasianus 

colchicus 

(pheasant)

Number of eggs 

hatched, number of 

28-d old survivors 

NOAEC 0.5 lb 

cation/A Supplemental 43942605 

Mammals 

Rattus 

norvegicus 

(laboratory rat) 

Mortality LD50 (oral 

dose)

91 

mg 

cation/kgbw Acceptable 00054573 

Mortality 

LC50

(inhalati

on) 

0.001 mg/L acceptable 00046105 

Reproduction 

NOAEL 7.5 

Mg 

cation/kgbw Acceptable 

00126783, 

00149748, 

& 

NOAEC 108 00149749 

Mg 

cation/kgbw 
Page 19 of 71 

Taxa 

Species 

(common 

name)

Measure of effect Endpoint 

Mean 

Concentration Units Study Classification

Reference 

(MRID)

Terrestrial 

invertebrates 

Apis mellifera

(honey bee) Mortality LD50 52 μg 

cation/bee Acceptable 43942603 

Plants are sensitive to this herbicide. When comparing effects of paraquat on seedling emergence 

and vegetative vigor of plants, vegetative vigor is more sensitive. Table 7 includes the most 

sensitive seedling emergence and vegetative vigor endpoints for terrestrial plants exposed to 

paraquat. These values may be used to generate RQs. Additional information on the toxicity of 

paraquat to terrestrial plants is provided in Appendix A. 

Table 7. Endpoints used to represent effects of paraquat on terrestrial plants.

Species NOAEC 

(lb cation/A) 

EC25

(lb cation/A) 

Most sensitive 

parameter Test type MRID 

Zea mays corn 

(monocot) 0.67 >0.67 none Seedling emergence 42639601 

Xanthium sp 

Cocklebur (dicot) 0.37 0.67 Emergence Seedling emergence 42639601 

Corn (monocot) 0.064 0.16 Dry weight Vegetative vigor 42601001 

Cocklebur (dicot) 0.0065 (EC05) 0.014 Dry weight Vegetative vigor 42601001 

5.3. Ecological Incidents 

A review of the Ecological Incident Information System (EIIS, version 2.1), the ‘Aggregate 

Incident Reports’ (v. 1.0) database, and the Avian Incident Monitoring System (AIMS) for 

ecological incidents involving paraquat dichloride (PC code 061601), paraquat (PC code 

061603), and paraquat bis (methyl sulfate) (PC code 061602) was completed on 8/31/2011. 

Although paraquat and paraquat bis (methyl sulfate) are no longer registered for use in the 

United States, like paraquat dichloride, the active ingredient of both of these chemicals is 

paraquat. Therefore, it was assumed that incidents associated with paraquat and paraquat bis 

(methyl sulfate) would be representative of incidents that may occur when paraquat dichloride is 

applied. The incidents reported in each database are summarized below. These incidents will be 

described in more detail in the ecological risk assessment of paraquat dichloride. 
Page 20 of 71 

EIIS 

A review of the EIIS database for ecological incidents involving paraquat and paraquat 

dichloride, which are used interchangeably in the database, was completed on August 31, 2011. 

Reported incidents occurred between 1981 and 2005. The results of this review for terrestrial, 

plant, and aquatic incidents are discussed below. A total of 4 incidents involving paraquat were 

reported, and a total of 26 incidents involving paraquat dichloride were reported. There were no 

incidents reported for paraquat bis (methyl sulfate). 

There were three reported incidents involving terrestrial animals after applications of paraquat 

dichloride. Two incidents were considered to be likely related to paraquat. These are briefly 

described below: 

 The first incident occurred in Virginia in June 1998. In this report, a formulation with a 

registered use on corn resulted in the mortality of 5 Canadian geese. Paraquat dichloride 

was the probable cause of the incident (I008168-001). 

 The second incident occurred in Illinois in June 1998. This report included the death of 

individuals of 4 unknown species of birds after drift/spray exposure. Paraquat was 

identified as the probable cause of the incident (I007334-001). 

There were a total of 4 plant incidents listed for paraquat and 17 incidents for paraquat 

dichloride. These are briefly described below: 

 For the paraquat incidents, plant damage was sustained to three non-target species, 

including: radishes, apples, and ornamentals (I014409-001, I013884-038, and I013884-

014). Mortality of alfalfa was also reported (I014409-024). All 4 incidents were from 

Washington, one from a registered use on peas where ornamentals were affected, and 

paraquat was the probable cause of plant damage; one from a misuse (alfalfa) where 

paraquat was a possible cause of mortality; and, for the other two, the use was of 

undetermined legality, and paraquat was a possible cause of plant damage. All exposures 

occurred from drift, with apples also being exposed from direct spray. 

 Two accidental misuse incidents occurred in an agricultural area in Wisconsin resulting 

in plant damage to alfalfa, ash, and ornamentals (I005660-005), and ash, oats and 

discoloration to alfalfa (I005880-005) from drift exposure. Paraquat was the probable 

cause of these incidents. 

 Three accidental misuse incidents on corn resulted in plant damage to grass (I007371-

033, I007371-034, and I007371-035) on June 17, 1997, and paraquat was the probable 

cause of these incidents. 

 120 acres of a corn field was damaged after a broadcast application of undetermined 

legality occurred May 9, 2000. Paraquat was a possible cause of this incident (I012366-

023). 

 Plant damage to 181 acres of peppermint occurred after registered use May 1, 1996, and 

paraquat was a possible cause of this incident (I013636-029). 

 A paraquat dichloride application of undetermined legality use was the possible cause of 

150 (75% of 200) acres of corn damaged on May 11, 1999 in Alabama (I009573-009). 
Page 21 of 71 

 After a legally-applied application of paraquat dichloride,10 acres of peanuts were 

damaged on June 19, 2001 in North Carolina. Paraquat was a possible cause of this 

incident (I011838-055). 

 Carryover from the broadcast application of paraquat dichloride was the probable cause 

of damage to 1040 acres of corn May 24, 2002 in Illinois (I013554-040). 

 The label-use application of paraquat dichloride was a possible cause of the damage to 60 

acres of pasture grass April 23, 2003 in Georgia (I014034-009). 

 The label-use of paraquat dichloride on peanuts was a possible cause of plant damage to 

5 acres of peanuts in Virginia May 23, 2001 (I012684-010). 

 An application of paraquat dichloride on peanuts of undetermined legality use was a 

possible cause of plant damage to 80 acres of peanuts in Oklahoma (I011838-091) and all 

25 acres in Georgia (I011838-038). 

 A label-use broadcast application of paraquat dichloride to soybeans was a possible cause 

of plant damage to an unknown tree as a result of drift June 27, 1994 in Arkansas 

(I001131-001). 

 It is highly probable that the accidental misuse of paraquat dichloride on soybeans 

resulted in plant damage to unknown amounts of soybeans as the result of drift May 20, 

1997 in Pennsylvania (I007371-008). 

 Intentional misuse of paraquat dichloride by spray application on wheat was the probable 

cause of plant damage to 120 of 184 acres from drift January 26, 2005 in California 

(I016940-005). 

 In June 1998, plant damage was reported on 18 of 103 acres of corn in Illinois from 

drift/spray exposure (I007334-001); paraquat was of probable cause for the incident. 

There were six reported aquatic incidents listed for paraquat dichloride. Incidents where 

paraquat was suspected of being the primary cause are briefly described below: 

 A use of paraquat dichloride of undetermined legality on an agricultural area was a 

possible cause of the mortality of 54 fish (1 largemouth bass, and 53 sunfish) due to 

runoff on June 4, 1981 in Virginia (B0000-502-18). 

 The application of paraquat dichloride on a field was a possible cause of the mortality of 

fish (bass, bluegill, and crappie) in Indiana on June 2, 1997 (I009314-005). 

 An application of paraquat dichloride of undetermined legality was a possible cause of 

the mortality of an unknown amount of bass, bluegill, and crappie to die in Indiana on 

January 1, 1997 (I005805-001). 

 Paraquat dichloride was a possible cause of the 200 bass and bluegills that were found 

dead after an application of paraquat dichloride of undetermined legality on June 3, 1999 

(I008768-007). 

Aggregate Incident Database 

For paraquat dichloride, the aggregate incident database included 82 minor plant incidents, 4 

minor fish and wild life incidents and 3 other non-target incidents that were reported between 

1995 and 2010. For paraquat, there was one minor incident involving other non-target organisms 

that was reported in 2004. There were no incidents reported for paraquat bis (methyl sulfate). 

AIMS 
Page 22 of 71 

Two indicents are reported in the AIMS database. One incident, involving Canadian geese, was 

also reported in EIIS (Incident I008168-001). 

The other incident involved mortalities of several passerines (robins, sparrows, starlings and 

grackles). This incident also involved exposures of birds to carbofuran. The report indicated that 

it was certain that carbofuran was responsible for the mortalities and probable that paraquat was 

responsible. This incident was also captured by EIIS (I005750-001, I004169-026 and I000097-

015). 

6. Ecosystems Potentially at Risk 

The ecosystems potentially at risk are often extensive in scope; therefore, it may not be possible 

to identify specific ecosystems during the development of a nation-wide ecological risk 

assessment. However, in general terms, terrestrial ecosystems potentially at risk could include 

the treated field and immediately adjacent areas that may receive drift or runoff. Areas adjacent 

to the treated field could include cultivated fields, fencerows and hedgerows, meadows, fallow 

fields or grasslands, woodlands, riparian habitats, and other uncultivated areas. 

Aquatic ecosystems potentially at risk include water bodies adjacent to, or downstream from, the 

treated field and might include impounded bodies such as ponds, lakes and reservoirs, or flowing 

waterways such as streams or rivers. For uses in coastal areas, aquatic habitat also includes 

marine ecosystems, including estuaries. 

7. Assessment Endpoints 

Assessment endpoints represent the actual environmental value that is to be protected, defined by 

an ecological entity (species, community, or other entity) and its attribute or characteristics 

(USEPA 1998). For paraquat, the ecological entities include the following: birds, reptiles, 

terrestrial-phase amphibians, mammals, freshwater fish, freshwater aquatic-phase amphibians 

and invertebrates, estuarine/marine fish and invertebrates, terrestrial plants, insects, aquatic 

plants, and algae. The attributes for each of these entities include growth, reproduction, and 

survival. 

8. Conceptual Model 

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must have a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors, and a feasible route of exposure. 
Page 23 of 71 

The conceptual model for paraquat provides a written description and visual representation of the 

predicted relationships between paraquat, potential routes of exposure, and the predicted effects 

for the assessment endpoint. A conceptual model consists of two major components: risk 

hypothesis and a conceptual diagram (USEPA 1998). 

8.1. Risk Hypothesis 

A risk hypothesis describes the predicted relationship among the stressor, exposure, and 

assessment endpoint response along with the rationale for their selection. For paraquat 

dichloride, the following ecological risk hypothesis is being employed for this national-level 

ecological risk assessment: 

Based on use patterns of paraquat dichloride, its fate and transport potential, and the 

sensitivity of non-target aquatic and terrestrial species, paraquat has the potential to 

reduce survival, reproduction, and/or growth in non-target terrestrial and aquatic 

organisms when used in accordance with labels. These non-target organisms include 

Federally-listed threatened and endangered species as well as non-listed species

 

8.2. Conceptual Diagram 

The environmental fate properties of paraquat indicate that runoff and spray drift represent 

potential transport mechanisms of paraquat to aquatic habitats where non-target organisms may 

be exposed. It is expected that non-target terrestrial organisms can be exposed to paraquat 

through consumption of contaminated food items. These transport mechanisms (i.e., sources) are 

depicted in the conceptual models below (Figures 1 and 2) along with the receptors of concern 

and the potential attribute changes in the receptors due to exposures of paraquat. Dotted lines 

represent transport pathways that are assumed to have a low likelihood of occurring and/or of 

contributing to ecological risk. 
Page 24 of 71 

Figure 1. Conceptual model for paraquat effects on terrestrial organisms.

Stressor

Source 

Receptors 

Attribute 

Change 

Paraquat dichloride applied to use site 

Direct 

deposition Spray drift

Birds/terrestrialphase 

amphibians/ 

 reptiles/mammals 

Terrestrial 

insects 

 Individual organisms 

 Reduced survival 

 Reduced growth 

 Reduced reproduction 

Food chain

Reduction in prey 

Effects to PCEs 

related to prey 

availability 

Habitat integrity 

 Reduction in primary productivity 

 Reduced cover 

 Community change 

 Effects to PCEs related to habitat 

Terrestrial/riparian plants

grasses/forbs, fruit, seeds 

(trees, shrubs) 

Runoff

Mammals

/ Birds 

Exposure 

Media 

Soil

Ingestion 

Ingestion 

Ingestion

Ingestion 

Dermal 

Long range 

atmospheric 

transport 

Root 

Wet/dry deposition 

Terrestrialphase 

amphibians 

Ingestion 
Page 25 of 71 

Figure 2. Conceptual model for paraquat effects on aquatic organisms.

9. Analysis Plan 

In order to address the risk hypothesis, the potential for adverse effects on the environment is 

estimated. The use, environmental fate, and ecological effects of paraquat are characterized and 

integrated to assess the risks. This is accomplished using a risk quotient (ratio of exposure 

concentration to effects concentration) approach. Although risk is often defined as the likelihood 

and magnitude of adverse ecological effects, the risk quotient-based approach does not provide a 

quantitative estimate of likelihood and/or magnitude of an adverse effect. However, as outlined 

in the Overview Document (USEPA 2004), the likelihood of effects to individual organisms 

from particular uses of paraquat dichloride is estimated using the probit dose-response slope and 

either the level of concern (discussed below) or actual calculated risk quotient value. 

This analysis plan will be revisited and may be revised depending upon the information 

submitted by the public in response to the opening of the registration review docket for paraquat 

dichloride. 

Stressor

Source 

Receptors 

Attribute 

Change 

Paraquat dichloride applied to use site 

Spray drift 

Fish/aquaticphase amphibians 

 Individual organisms 

 Reduced survival 

 Reduced growth 

 Reduced reproduction 

Food chain

Reduction in algae 

Reduction in prey 

Effects to PCEs 

related to prey 

availability 

Habitat integrity 

 Reduction in primary productivity 

 Reduced cover 

 Community change 

 Effects to PCEs related to habitat 

Surface water/ 

Sediment 

Runoff

 Aquatic Animals

 Invertebrates 

 Vertebrates 

Exposure 

Media 

Uptake/gills 

or integument 

Ingestion Ingestion 

Long range 

atmospheric 

transport 

Wet/dry deposition 

Soil Groundwater

Uptake/gills 

or integument 

Aquatic Plants

 Non-vascular 

 Vascular 

Uptake/cell, 

roots, leaves Riparian plant

terrestrial 

exposure 

pathways see 

Figure 1 
Page 26 of 71 

9.1. Measures of Exposure 

In order to estimate risks of paraquat exposures in aquatic and terrestrial environments, all 

exposure modeling and resulting risk conclusions will be based on maximum application rates 

and methods cited in Section 4.2 and will be estimated for each use of paraquat dichloride. 

Measures of exposure are based on aquatic and terrestrial models that predict estimated 

environmental concentrations (EECs) of paraquat. The models used to predict aquatic EECs are 

the Pesticide Root Zone Model coupled with the Exposure Analysis Modeling System 

(PRZM/EXAMS). The model used to predict terrestrial EECs on food items is the Terrestrial 

Residue Exposure (T-REX). The model used to derive EECs relevant to terrestrial and wetland 

plants is TerrPlant. These models are parameterized using relevant reviewed environmental fate 

data from registrant submissions and the literature; model input values will be consistent with the 

most recent version of the input parameter guidance.2

PRZM (currently version 3.12.2; 5/15/05) and EXAMS (currently version 2.98.04.06; 4/25/05) 

are simulation models coupled with the linkage program shell: PE (PRZM EXAMS Model Shell; 

v5.0; 11/15/06), which incorporates the standard scenarios developed by EFED. The models 

generate daily exposures and calculated 1-in-10 year EECs of paraquat residues of concern that 

may occur in surface water bodies adjacent to application sites. PRZM simulates pesticide fate 

and transport as a result of leaching, direct spray drift, runoff and erosion from an agricultural 

field, and EXAMS estimates environmental fate and transport of pesticides in a surface water 

body for a 30-year period. The combined model is designed to estimate pesticide concentrations 

found in water (standard pond) at the edge of the treated field. As such, it provides high-end 

values of the pesticide concentrations that might be found in ecologically sensitive environments 

following pesticide application. The location of the field is specific to the crop being simulated 

using site-specific information on the soils, weather, cropping, and management factors 

associated with the scenario. The crop/location scenario is intended to represent a high-end 

exposure site on which the crop is normally grown. Based on historical rainfall patterns, the 

receiving water body receives multiple runoff events during the years simulated. Weather and 

agricultural practices are simulated for 30 years so that the 10-year exceedance probability at the 

site can be estimated. The simulation is generated using 30 years of meteorological data, 

encompassing the years from 1961 to 1990. Additional information on these models can be 

found at: http://www.epa.gov/oppefed1/models/water/index.htm. 

The standard scenarios used for ecological pesticide assessments assume application to a 10-

hectare agricultural field that drains into an adjacent 1-hectare water body that is 2 meters deep 

(20,000 m3

 volume) with no outlet. PRZM/EXAMS is used to estimate screening-level exposure 

of aquatic organisms to paraquat. The measure of exposure for aquatic species is the 1-in-10 

year return peak or rolling mean concentration. The 1-in-10 year peak is used for estimating 

acute exposures of direct effects to aquatic organisms. The 1-in-10-year 60-day mean is used for 

assessing chronic exposure to fish and aquatic-phase amphibians. The 1-in-10-year 21-day mean 

is used for assessing chronic exposure to aquatic invertebrates. 

 

2

 Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, Version 

2.1. U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects 

Division. 2009. 
Page 27 of 71 

Exposure estimates for terrestrial animals assumed to be in the target area or in an area exposed 

to spray drift are derived using the T-REX model (version 1.4.1, 10/09/2008). This model 

incorporates the Kenega nomograph, as modified by Fletcher et al. (1994), which is based on a 

large set of field residue data. The upper limit values from the nomograph represent the upper 

bound of residue values from actual field measurements (Hoerger and Kenega 1972). The 

Fletcher et al. (1994) modifications to the Kenega nomograph are based on measured field 

residues from 249 published research papers, including information on 118 species of plants, 121 

pesticides, and 17 chemical classes. 

The Screening Imbibition Program (SIP v.1.0, Released June 15, 2010) was used to calculate an 

upper bound estimate of exposure using paraquat’s solubility (464,000 mg/L), the most sensitive 

acute and chronic avian toxicity endpoints (see Table 6) and the most sensitive acute and chronic 

mammalian toxicity endpoints (see Table 6). Drinking water exposure alone was not determined 

to be a potential pathway of concern for avian or mammalian species on an acute or chronic basis 

(See Appendix B). Although drinking water exposure alone does not appear to be of concern, 

this does not take into account that when aggregated with other exposure pathways (dietary food 

sources, dermal, inhalation) drinking water may contribute to a total exposure that has a potential 

for effects on non-target animals and should be explored further. Because there is a high degree 

of conservatism in the SIP 1.0 exposure estimate, there is limited expectation that use scenarios 

not triggering a SIP 1.0 concern would contribute significantly to aggregate risks from water plus 

diet when a refined water exposure model is incorporated in the actual quantitative risk 

assessment. Detailed information about SIP v.1.0, as well as the tool, can be found on the EPA’s 

website at http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial. 

The Screening Tool for Inhalation Risk (STIR v.1.0, November 19, 2010) was used to calculate 

an upper bound estimate of exposure using paraquat’s vapor pressure and molecular weight for 

vapor phase exposure as well as the maximum application rate and method of application for 

spray drift. STIR incorporates results from several toxicity studies including acute oral and 

inhalation rat toxicity endpoints obtained from the “six-pack” of core studies, which are a series 

of six guideline studies that are submitted to the Registration Division of the Office of Pesticide 

Programs for technical and formulated products of a pesticide (Table 6) as well as the most 

sensitive acute oral avian toxicity endpoint (Table 6). Based on the results of the STIR model, 

inhalation exposure alone was determined to be a potential pathway of concern for avian and 

mammalian species on an acute basis. The inhalation pathway via spray drift is of potential 

significance. This pathway will be explored further by requesting additional toxicity or exposure 

data (non-guideline acute avian inhalation toxicity) that may reduce uncertainty and the 

incorporation of this data into the inhalation risk assessment for birds and mammals. For a 

sample of the output generated by STIR v.1.0, please see Appendix C. Detailed information 

about the STIR v.1.0 tool can be found on the EPA’s website at: 

http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial. 

EECs for terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant (version 

1.2.2, 12/26/2006). This model uses estimates of pesticides in runoff and in spray drift to 

calculate EECs. EECs are based upon solubility, application rate and minimum incorporation 

depth. 
Page 28 of 71 

Available monitoring data will be used to qualitatively characterize exposure and compare with 

modeling results. The Agency is aware of monitoring conducted by Federal and state agencies 

and this route of exposure will be considered in the assessment to the extent that data on paraquat 

are available. 

Two spray drift models, AGDISP and AgDRIFT are used to assess exposures of terrestrial plants 

to paraquat deposited in terrestrial habitats by spray drift. AGDISP (version 8.13; dated 

12/14/2004) (Teske and Curbishley 2003) is used to simulate aerial applications. AgDrift 

(version 2.01; dated 5/24/2001) is used to simulate ground spray and orchard blast applications. 

9.2. Measures of Effect 

Ecological effect data are used as measures of direct and indirect effects to biological receptors. 

Data were obtained from registrant-submitted studies or from literature studies identified by 

ECOTOX. The ECOTOXicology database (ECOTOX) was searched in order to provide more 

ecological effects data to bridge existing data gaps. ECOTOX is a source for locating single 

chemical toxicity data and potential chemical mixture toxicity data for aquatic life, terrestrial 

plants, and wildlife. ECOTOX was created and is maintained by the USEPA, Office of Research 

and Development, and the National Health and Environmental Effects Research Laboratory's 

Mid-Continent Ecology Division (USEPA 2007). 

Information on the potential effects of paraquat on non-target animals is also collected from the 

Ecological Incident Information System (EIIS; USEPA 2007b). The EIIS is a database 

containing adverse effect (typically mortality) reports on non-target organisms where such 

effects have been associated with the use of pesticides. 

Where available, sublethal effects observed in both registrant-submitted and open literature 

studies will be evaluated qualitatively. Such effects have included behavioral changes (e.g., 

lethargy, changes in coloration and olfaction effects). Quantitative assessments of risks, though, 

are limited to those endpoints that can be directly linked to the Agency’s assessment endpoints of 

impaired survival, growth and reproduction. 

The assessment of risk for direct effects to non-target organisms makes the assumption that 

toxicity of paraquat to birds is similar to terrestrial-phase amphibians and reptiles. The same 

assumption is made for fish and aquatic-phase amphibians. 

The acute measures of effect used for animals in this screening-level assessment are the LD50, 

LC50 and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a material, given all at 

once, that is estimated to cause the death of 50% of the test organisms. LC stands for “Lethal 

Concentration” and LC50 is the concentration of a chemical that is estimated to kill 50% of the 

test organisms. EC stands for “Effective Concentration” and the EC50 is the concentration of a 

chemical that is estimated to produce a specific effect in 50% of the test organisms. Endpoints 

for chronic measures of exposure for listed and non-listed animals are the NOAEL/NOAEC and 

NOEC. NOAEL stands for “No Observed-Adverse-Effect-Level” and refers to the highest tested 

dose of a substance that has been reported to have no harmful (adverse) effects on test 

organisms. The NOAEC (i.e., “No-Observed-Adverse-Effect-Concentration”) is the highest test 
Page 29 of 71 

concentration at which none of the observed effects were statistically different from the control. 

The NOEC is the No-Observed-Effects-Concentration. For non-listed plants, only acute 

exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants); for listed 

plants, either the NOAEC or EC05 is used. 

9.3. Integration of Exposure and Effects 

Risk characterization is the integration of exposure and ecological effects characterization to 

determine the potential ecological risk from the use of paraquat on crops listed in Section 4.2

and the likelihood of direct and indirect effects to non-target organisms in aquatic and terrestrial 

habitats. The exposure and toxicity effects data are integrated in order to evaluate the risks of 

adverse ecological effects on non-target species. For the assessment of paraquat risks, the risk 

quotient (RQ) method is used to compare exposure and measured toxicity values. EECs are 

divided by acute and chronic toxicity values. The resulting RQs are then compared to the 

Agency’s LOCs (USEPA 2004; Table 8). These criteria are used to indicate when paraquat’s 

uses, as directed on the label, have the potential to cause adverse direct or indirect effects to nontarget organisms. As noted previously, where data are lacking on the toxicity of paraquat, risk 

will be presumed. 

 

The quantitative assessment of risk will primarily depend on the deterministic point-estimate 

based approach described in the risk assessment. An effort will be made to further qualitatively 

describe risk using probabilistic tools that the Agency has developed. These tools have been 

reviewed by FIFRA Scientific Advisory Panels and have been deemed as appropriate means of 

refining assessments where deterministic approaches have identified risks. 

Table 8. Agency risk quotient (RQ) metrics and levels of concern (LOC) for Federally-listed (listed) 

threatened/endangered and non-listed species per risk class.

Risk Class Risk Description RQ LOC 

Aquatic Animals (fish and invertebrates)

Acute Potential for effects to non-listed animals from 

acute exposures Peak EEC/LC501

 0.5 

Acute Restricted 

Use 

Potential for effects to animals from acute 

exposures. Risks may be mitigated through 

restricted use classification. 

Peak EEC/LC501

 0.1 

Acute Listed 

Species 

Listed species may be potentially affected by 

acute exposures Peak EEC/LC501

 0.05 

Chronic Potential for effects to non-listed and listed 

animals from chronic exposures 

60-day EEC/NOEC (fish) 

1 21-day EEC/NOEC 

(invertebrates) 

Terrestrial Animals (mammals and birds) 

Acute Potential for effects to non-listed animals from 

acute exposures 

EEC2

/LC50 (Dietary) 

0.5 

EEC/LD50 (Dose) 
Page 30 of 71 

Risk Class Risk Description RQ LOC 

Acute Restricted 

Use 

Potential for effects to animals from acute 

exposures. Risks may be mitigated through 

restricted use classification 

EEC2

/LC50 (Dietary) 

0.2 

EEC/LD50 (Dose) 

Acute Listed 

Species 

Listed species may be potentially affected by 

acute exposures 

EEC 2

/LC50 (Dietary) 

0.1 

EEC/LD50 (Dose) 

Chronic Potential for effects to non-listed and listed 

animals from chronic exposures EEC 2

/NOAEC 1 

Plants 

Non-Listed Potential for effects to non-target, non-listed 

plants from exposures EEC/ EC25

1 

Listed Plant Potential for effects to non-target, listed plants 

from exposures 

EEC/ NOEC 

1 

EEC/ EC05

1 LC50 or EC50. 2

 Based on upper bound Kenaga values. 

9.4. Endangered Species Assessments 

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to Federally-listed threatened and/or endangered (listed) species from 

registered uses of paraquat dichloride. This assessment will be conducted in accordance with the 

Overview Document (USEPA 2004), provisions of the ESA, and the Services’ Endangered 

Species Consultation Handbook (USFWS/NMFS 1998). 

The assessment of effects associated with the registration of paraquat dichloride is based on an 

action area. The action area is considered to be the area directly or indirectly affected by the 

federal action, as indicated by the exceedance of Agency LOCs used to evaluate direct or indirect 

effects. The Agency’s approach to defining the action area under the provisions of the Overview 

Document (USEPA 2004) considers the results of the risk assessment process to establish 

boundaries for that action area with the understanding that exposures below the Agency’s 

defined LOCs constitute a no-effect threshold. For the purposes of this assessment, attention will 

be focused on the footprint of the action (i.e., the area where paraquat dichloride application 

occurs), plus all areas where offsite transport may result in potential exposure that exceeds the 

Agency’s LOCs. Specific measures of ecological effect that define the action area for listed 

species include any direct and indirect effects and/or potential modification of its critical habitat, 

including reduction in survival, growth, and reproduction as well as the full suite of sub-lethal 

effects available in the effects literature. Therefore, the action area extends to a point where 

environmental exposures are below any measured lethal or sub-lethal effect threshold for any 

biological entity at the whole organism, organ, tissue, and/or cellular level of organization. In 

situations where it is not possible to determine the threshold for an observed effect, the action 

area is not spatially limited and is assumed to be the entire United States. 
Page 31 of 71 

9.5. Drinking Water Assessment 

In order to bring the drinking water assessment up to date with current data, simulation models 

and guidance, a new drinking water exposure assessment will be conducted to support future 

human health dietary risk assessments of paraquat. The drinking water assessment will 

incorporate model estimates of paraquat in surface water and ground water. Concentrations of 

paraquat in surface waters will be estimated using PRZM/EXAMS (see description above) with 

Index Reservoir as the receiving water body. With paraquat’s high adsorptive properties, the 

regular water treatment process is expected to remove almost all paraqat in the water. EFED is 

requesting the treatability study form the registrant to confirm this property. 

An Estimated Drinking Water Concentration (EDWC) of paraquat in groundwater will be 

estimated using the Tier I aquatic model SCIGROW (Screening Concentration in Ground Water, 

version 2.3; 8/8/2003). SCIGROW is a regression model used as a screening tool to estimate 

pesticide concentrations found in ground water used as drinking water. The output of 

SCIGROW represents the concentrations that might be expected in shallow unconfined aquifers 

under sandy soils, which is representative of the ground water most vulnerable to pesticide 

contamination likely to serve as a drinking water source. 

The drinking water assessment will also include available surface and ground water monitoring 

data with consideration of changes in use patterns that may have occurred. States are encouraged 

to submit monitoring data for review. 

 10. Endocrine Disruptor Screening Program 

As required under FFDCA section 408(p), EPA has developed the Endocrine Disruptor 

Screening Program (EDSP) to determine whether certain substances (including pesticide active 

and other ingredients) may have an effect in humans or wildlife similar to an effect produced by 

a “naturally occurring estrogen, or other such endocrine effects as the Administrator may 

designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, and or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

 

Between October 2009 and February 2010, EPA issued test orders/data call-ins for the first 

group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. 

This list of chemicals was selected based on the potential for human exposure through pathways 

such as food and water, residential activity, and certain post-application agricultural scenarios. 

This list should not be construed as a list of known or likely endocrine disruptors. 

Paraquat is not among the group of 58 pesticide active ingredients receiving EDSP test orders. 

For information on the status of the orders issued under the EDSP for each chemical, please visit 
Page 32 of 71 

our website at http://www.epa.gov/endo/ and click on the "Status of EDSP Orders/DCIs" in the 

Highlights Box. Additional information on the EDSP, including the policies and procedures, the 

list of 67 chemicals, the test guidelines and the Tier 1 screening battery, can also be found at this 

website. 

11. Preliminary Identification of Data Gaps 

11.1. Fate 

Table 9. Available environmental fate data for paraquat and remaining data gaps.

OCSPP 

Guideline 

Data Requirement Submitted Studies 

(MRID) 

Classification Data 

Gap? 

Comments 

835.2120 Hydrolysis No MRID Acceptable No -- 

835.2240 Aqueous photolysis 40562301 Acceptable No -- 

835.2410 Soil photolysis 00146807 Acceptable No -- 

835.4100 Aerobic soil metabolism 41319301 Acceptable No -- 

835.4200 Anaerobic soil metabolism 41319302 Acceptable No -- 

835.4300 Aerobic aquatic metabolism 00055093 Acceptable No -- 

835.4400 Anaerobic aquatic metabolism No data No Yes -- 

835.1230 

835.1240 

Adsorption/ desorption and 

leaching 40762701 Acceptable No -- 

835.6100 Terrestrial field dissipation 

41293202 

Acceptable No -- 

42802101 

42738701 

42738702 

42802102 

835.6200 Aquatic field dissipation No data Waived No No aquatic uses 

850.1730 Fish bioaccumulation No data Waived No 

Log Kow is below 3, 

indicating that 

bioaccumulation of 

paraquat is not 

expected. 

840.1100 Spray Drift - Droplet size 

spectrum No data No Yes -- 

840.1200 Spray Drift – Drift field 

evaluation No data No Yes -- 

Anaerobic Aquatic Metabolism (Guideline 835.4400)

Acceptable data have not been provided to quantify the metabolism of paraquat under anaerobic aquatic 

conditions. According to Code of Federal Regulations 40 (CFR40 2007) Part 158 Subpart D (data 

requirements for pesticides) anaerobic aquatic metabolism are required for pesticides with terrestrial or 
Page 33 of 71 

aquatic uses. Since paraquat uses are classified as terrestrial, anaerobic aquatic metabolism data for 

paraquat should be submitted to fulfill OPPTS Guideline 835.4400. 

Currently there are no acceptable anaerobic aquatic metabolism studies that track the formation and 

decline of paraquat and its degradates. The submitted data will be used to characterize and quantify the 

environmental fate of paraquat and its degradates in aquatic environments. For quantitative exposure 

estimation, these data will be used to confirm the conceptual model of paraquat fate and transport in 

aquatic environments. 

Without these required data, the fate of paraquat cannot be fully characterized and exposure to potentially 

toxic degradates cannot be quantified. The persistence of paraquat and its degradates to which terrestrial 

and aquatic organisms will be exposed to is uncertain. In the absence of acceptable data, conservative 

assumptions will be made regarding the potential for formation of paraquat degradates. Therefore, 

potential for risk to aquatic organisms may be overestimated and the use of paraquat might need to be 

restricted in areas where endangered species could be exposed. The lack of these data will limit the 

flexibility the Agency and registrants have in coming into compliance with the Endangered Species Act 

and could result in use restrictions for paraquat which are unnecessarily severe. 

Drinking Water Treatability (non-guideline study) 

EFED notes that submission of a drinking water treatability study (i.e., Jar Test) would be of 

high value to drinking water assessments. The study is a laboratory bench scale test to mimic the 

processes of chemical addition, coagulation, and sedimentation in a typical water treatment plant. 

This study provides the simplest and most direct method to show that paraquat is removed during 

drinking water treatment. 

Guideline Number: N/A - Special study 

Study Title: Drinking Water Treatability Study 

Rationale for Requiring the Data 

Use of paraquat can result in the presence of this chemical in the drinking water reservoirs 

and rivers by off-target spray drift and runoff. For drinking water exposure assessment, 

EFED will be using the PRZM/EXAMS model’s Index Reservoir scenario to estimate 

exposures in the receiving water body to derive the estimated drinking water concentrations. 

With paraqua dichloride’s high adsorptive properties, the Agency believes that the regular 

water treatment process may remove most of the paraquat from the water. However, EFED 

has no data to confirm this. Since EFED does not have any water treatment studies for 

paraquat quantifying the removal mechanism, the Agency would have to assume in the 

registration review risk assessment that no removal occurs in water treatment. 

A bench scale drinking water treatability study (similar to the Jar Test) is necessary to 

determine how much paraquat dichloride is removed from water during the regular water 

treatment process. These data will be used to refine the expected drinking water exposure 

values. 

Practical Utility of the Data 

How will the data be used? 

The data will be used to assess the removal efficiency of paraquat dichloride in typical 

drinking water treatment facilities through the processes of chemical addition, coagulation 
Page 34 of 71 

and sedimentation. The removal efficiency derived from the bench scale water treatment test 

will be used to refine the expected drinking water exposure assessment. 

How could the data impact the Agency’s future decision-making? 

The Agency will use these data to refine the drinking water exposure risk from paraquat 

dichloride. Without these data, the Agency would have to assume that paraquat dichloride is 

not removed in drinking water treatment facilities. This assumption would lead to high 

drinking water exposure values. These values, if used in a dietary risk assessment, would 

yield risk estimates above the Agency’s level of concern, which would necessitate the 

implementation of mitigation measures such as reduced application rates and cancellation of 

some uses. The lack of these data will limit the flexibility the Agency and registrants have in 

coming into compliance with the Federal Food Drug and Cosmetic Act and the Federal 

Insecticide, Fungicide and Rodenticide Act and could result in use restrictions for this 

chemical that may be unnecessary. 

11.2. Effects 

Although many submissions have been made to provide data on the effects of paraquat to aquatic 

and terrestrial organisms, data gaps still exist. The available ecological effects data submitted for 

paraquat dichloride and the remaining data gaps are summarized in Tables 10, 11 and 13. The 

data gaps are also described below, along with EFED’s rationales for recommending PRD 

required certain studies to fulfill the guideline requirements. 
Page 35 of 71 

Table 10. Available ecological effects data for terrestrial animals exposed to paraquat and remaining data 

gaps. 

Guideline 

# Description MRID Classification Data Gap? Comments 

850.2100 Acute avian oral 

toxicity 

29001 acceptable Yes No toxicity data are available for a 

160000 passerine species. invalid 

none 

Acute avian 

inhalation toxicity none Not applicable Yes 

STIR indicates that inhalation 

exposure may be a concern for 

birds; therefore, acute inhalation 

toxicity ddata for birds should be 

submitted. 

850.2200 Avian dietary 

toxicity 

22923 acceptable 

No 

MRID 22923 included 4 test 

species, including the bobwhite 

quail and the mallard duck. 

MRID 90975 is the same 

submission as MRID 55103. 

55103* invalid 

850.2300 Avian reproduction 

110453 supplemental 

No 

MRIDs 110454 and 110455 are 

currently being re-reviewed by 

EFED; however, available data are 

adequate for risk assessment. 

110454 Under review 

110455 Under review 

43942604 supplemental 

43942605 supplemental 

850.3020 Honeybee acute 

contact toxicity 

36935 acceptable 

No None 

5001991 acceptable 

111488* supplemental 

43942603 acceptable 

850.3030 

Honey bee toxicity 

or residues on 

foliage 

none Not applicable No Study is not required because acute 

contact LD50 is >11 μg a.i./bee. 

850.3040 Field testing for 

pollinators none Not applicable No Study is not required. 

*Formulated product exposure. 

Avian Acute Oral Toxicity with a passerine species (Guideline 850.2100)

The Part 158 data requirements specify that acute avian oral toxicity data be submitted for either 

a mallard duck or bobwhite quail AND a passerine species. These studies are required for TGAI. 

Acceptable data have been submitted for the bobwhite quail exposed to TGAI (MRID 29001); 

however, no acute oral data have been submitted for a passerine species. Therefore, EFED 

recommends that PRD require an avian oral toxicity test (OPPTS Guideline 850.2100) for a 

passerine species exposed to TGAI paraquat dichloride. The registrant will need to submit a 

passerine study protocol for review by the Agency prior to initiation of the passerine study. 

Avian Acute Inhalation toxicity 
Page 36 of 71 

Guideline Number: Non-guideline 

Study Title: Avian inhalation toxicity 

Rationale for Requiring the Data 

Acceptable avian acute toxicity data were submitted for oral exposures of birds to paraquat; 

however, data are not available for inhalation toxicity to birds. An evaluation of inhalation as 

a route of exposure using the Screening Tool for Inhalation Risk (STIR, v. 1.0) suggests that 

inhalation exposure is a pathway of concern for avian wildlife due to drift of the pesticide. In 

addition, paraquat is moderately toxic to avian species on an acute exposure basis, and 

paraquat is highly toxic to mammals on an acute inhalation basis. Therefore, EFED 

recommends that PRD require an acute avian inhalation toxicity test using the most sensitive 

avian species as shown by avian acute oral studies. The study being requested will aid in 

evaluating this pathway of concern for avian taxa. An avian inhalation study protocol must 

be submitted for review and approval by the Agency prior to initiation of this study. 

Practical Utility of the Data 

How will the data be used? 

Acute avian inhalation toxicity data will be used to identify potential risks to birds form 

acute exposure to paraquat. The data will reduce uncertainties associated with the current 

risk assessment for birds and will improve the Agency’s understanding of the potential 

effects of paraquat on terrestrial species. If inhalation acute toxicity data are not submitted 

for birds, then risk to birds from acute inhalation exposure to paraquat will be presumed. If 

acute inhalation toxicity data are not submitted for birds, the method used by STIR will be 

used to estimate an acute inhalation endpoint for birds from the available mammalian 

toxicity data. 

How could the data impact the Agency’s future decision-making? 

If future endangered species risk assessments are performed without these data, the Agency 

would have to assume that paraquat “may affect” listed bird species directly (and listed 

species from other taxa indirectly), and the use of paraquat dichloride and its formulated may 

need to be restricted in areas where listed species could be exposed. The lack of these data 

will limit the flexibility of the Agency and the registrants for compliance with the 

Endangered Species Act and could result in use restrictions for paraquat dichloride that are 

unnecessarily severe. 

Table 11. Available ecological effects data for aquatic animals exposed to paraquat and remaining data gaps. 
Page 37 of 71 

Guideline Description MRID Classification Data 

Gap? 

Comments 

 850.1075 Freshwater fish – 

Acute toxicity 

162736 supplemental 

Yes 

A TGAI study is needed. No 

acceptable studies are available 

for this guideline; formulated 

product endpoints are more 

sensitive than the most 

sensitive TGAI endpoint. 

162737 supplemental 

162738 supplemental 

40098001 supplemental 

 850.1075 Saltwater fish – 

Acute toxicity 40228401* Supplemental Yes TGAI study needed 

 850.1010 

Freshwater 

invertebrates – 

Acute toxicity 

114473 Supplemental 

No 

Although no acceptable studies 

are available for this guideline, 

the results of several 

scientifically valid studies are 

all consistent. Therefore acute 

toxicity of paraquat to aquatic 

invertebrates is not considered 

a data gap. 

162752 Supplemental 

40098001 supplemental 

 850.1025 

850.1035 

Saltwater 

invertebrates – 

Acute toxicity 

40228401* Supplemental Yes 

TGAI studies needed 

 850.1300 

Freshwater 

invertebrate – 

 life cycle test 

none Not applicable Yes 

none 

 850.1350 

Saltwater 

invertebrates – 

life cycle test 

none Not applicable Yes 

none 

 850.1400 Freshwater fish – 

early life stage test none Not applicable Yes none 

 850.1400 Saltwater fish – 

early life stage test none Not applicable Yes none 

850.1735 

Freshwater 

invertebrate – acute 

sediment toxicity 

none Not applicable Yes 

none 

Nonguideline 

Freshwater 

invertebrate – 

chronic sediment 

toxicity 

none Not applicable Yes 

Protocol must be submitted 

prior to study initiation. 

*Formulated product exposure. 

Acute toxicity data for freshwater (warm and cold water species) and estuarine/marine fish 

In order to satisfy guideline 850.1075, toxicity data should be submitted for 3 species of fish: one 

warm freshwater species, one cold, freshwater fish and one saltwater fish exposed to TGAI; 

however, acceptable toxicity data involving freshwater fish exposed to technical paraquat 

dichloride are not available. 

Acute toxicity data are available for warm and cold species of freshwater fish (i.e., bluegill 
Page 38 of 71 

sunfish and rainbow trout, respectively) and saltwater fish (i.e., longnose killifish) exposed to a 

formulated product containing paraquat (Table 12). Available formulated product data suggest 

that paraquat is moderately to slightly toxic to freshwater fish. Data are also available from a 

study involving exposures of fowler’s toad tadpoles to TGAI paraquat dichloride. These data 

suggest that paraquat is slightly toxicity to aquatic-phase amphibians. 

Table 12. 96-h LC50 values for fish and aquatic-phase amphibians exposed to paraquat. All values are 

expressed as paraquat cation. 

Test species (scientific name) Water 

type 

TGAI (T) 

or formula 

(F) 

LC50

(mg 

cation/L) 

MRID Study 

classification 

Longnose killifish (Fundulus similis) SW F >0.72 40228401 supplemental 

Rainbow Trout (Oncorhynchus mykiss) FW F 6.1 162736 supplemental 

Rainbow Trout (Oncorhynchus mykiss) FW F 8.1 162738 supplemental 

Bluegill sunfish (Lepomis macrochirus) FW F 12 40098001 supplemental 

Fowler’s toad (Bufo woodhousei fowleri) FW T 15 40098001 supplemental 

Rainbow Trout (Oncorhynchus mykiss) FW F 16 40098001 supplemental 

Bluegill sunfish (Lepomis macrochirus) FW F 32.7 162737 supplemental 

Channel catfish (Ictalurus punctatus) FW T >100 40098001 supplemental 

In order to fulfill guideline 850.1075, the registrant should submit toxicity data with TGAI 

paraquat dichloride for a two freshwater fish (cold and warm water) and one saltwater fish 

species. These data are necessary because 1) EFED uses endpoints from TGAI studies with 

aquatic organisms to derive RQs that consider both runoff and spray drift transport (the 

formulated product endpoints should be used for spray drift EECs only); 2) available formulated 

product data for fish are more sensitive than TGAI studies that involve other test species; 3) the 

relative toxicity of TGAI paraquat dichloride to formulated products containing paraquat 

dichloride is unknown; 4) incident reports have been identified through EIIS where paraquat was 

related to mortalities of fish, suggesting a concern for acute exposures. 

Acute toxicity data for estuarine/marine invertebrates 

Acute toxicity data are available for brown shrimp and eastern oyster exposed to a formulated 

product containing paraquat (MRID 40228401). In order to fulfill guidelines 850.1025 and 

850.1035 for estuarine/marine invertebrates, data should be submitted for TGAI paraquat 

dichloride. 

Chronic toxicity data for fish and aquatic invertebrates (both freshwater and saltwater) 

At this time, no chronic toxicity data have been submitted for aquatic animals exposed to 

paraquat. According to 40 CFR Part 158, chronic toxicity data with freshwater fish and 

invertebrates (guidelines 850.1300 and 850.1400) are required for all pesticides with terrestrial 

uses. Chronic toxicity data for saltwater fish and invertebrates (guidelines 850.1400 and 

850.1350) are required when “studies of other organisms indicate the reproductive physiology of 
Page 39 of 71 

fish and/or invertebrates may be affected.” Available chronic toxicity data for birds indicate that 

paraquat may have reproductive effects on animals; therefore, EFED recommends that PRD 

require chronic toxicity data for estuarine/marine fish and invertebrates. 

Acute and chronic toxicity data for sediment dwelling invertebrates 

No data are currently available to characterize the acute or chronic toxicity of paraquat to 

sediment dwelling invertebrates. The updated Part 158 data requirements, published in October 

2007, specify that acute and chronic toxicity data for sediment invertebrates are conditionally 

required if the half-life of the pesticide in sediment >10 days in aerobic soil or aquatic 

metabolism studies and if any of the following conditions exist: a) the Kd is ≥50; b) the log Kow

is ≥3 or c) the Koc is ≥1000. Since the half-live of paraquat in soil under aerobic conditions is 

>10 days (41319301) and the Kd is >50 (MRID 40862701), EFED recommends that PRD require 

acute and chronic toxicity data for one species of sediment-dwelling invertebrate for paraquat. 

Paraquat dichloride registrants must submit a study protocol for review by the Agency 

prior to initiation of the chronic toxicity study with sediment dwelling invertebrates. 

Although there is no guideline for the chronic sediment toxicity study, the following methods by 

the USEPA’s Office of Research and Development may be consulted: 

 ORD study method EPA 600/R-099-064: chronic freshwater sediment testing flowthrough 

(Hyalella azteca) 

 ORD study method EPA 600/R-099-064: chronic freshwater sediment testing flowthrough 

(Chironomus dilutus or C. tentans) 

 ORD study method EPA 6001R-0l/020: chronic estuarine/marine sediment testing flowthrough 

(Leptocheirus plumulosus)
Page 40 of 71 

Table 13. Available ecological effects data for plants exposed to paraquat and remaining data gaps. 

Guideline Description MRID Classification Data 

Gap? 

Comments 

 

 850.4100 

Terrestrial Plant 

toxicity: Tier 2 

seedling emergence 

42639601 Supplemental Yes Tier II data are required for 4 

monocot and 6 dicot species. 

Tier I data involving exposures 

at 1 lb cation/A may be 

submitted to fulfill this guideline 

if <25% effects to a test species 

are observed. 

 850.4150 Terrestrial Plant 

toxicity: Tier 2 

vegetative vigor 

42601001 Supplemental Yes Data are required for 6 dicot 

species and 4 monocot species as 

specified in the guideline. 

 850.5400 Aquatic Plant Growth: 

algae 

40228401 Supplemental No none 

42601002 Acceptable 

42601004 Acceptable 

42601005 Acceptable 

42601006 Acceptable 

 850.4400 Aquatic Plant Growth: 

vascular plants 

42601003 Acceptable No none 

Terrestrial plant toxicity – seedling emergence 

According to the 850.4100 guideline, seedling emergence data are required for a total of 10 plant 

species, including 4 monocot and 6 dicot species. The 4 monocot species must be from at least 2 

families. One species of monocots must be corn. The 6 dicot species must be from 4 different 

families, and must include soybean and a root crop. 

Acceptable seedling emergence data are available for 2 monocot species, including: corn and 

purple nutsedge (MRID 42639601). These data are from species from two different families (i.e., 

Poaceae and Cyperaceae). In these studies, no effects were observed at the highest test 

concentration (i.e., 0.67 lb cation/A); however, this application rate is below the highest 

application rate permitted for paraquat (i.e., 1 lb cation/A). Therefore, 850.4100 is not fulfilled 

for monocots. 

Acceptable seedling emergence data are available for 6 species of dicots (family in parentheses), 

including soybean (Fabaceae), beet (Chenopodiaceae), oilseed rape (Brassicaceae), morning 

glory (Convolvulaceae), velvetleaf (Malvaceae) and cocklebur (Asteraceae; MRID 42639601). 

Effects were observed in cocklebur; however, the EC25 was equivalent to the highest application 

rate of the study. This leaves uncertainty in the endpoint for cocklebur, since the EC25 is not 

bound by higher test concentrations. As with the monocots, no effects were observed for 

soybean, beet, oilseed rape, morning glory and velvet leaf at the highest test concentration (i.e., 

0.67 lb cation/A); however, this application rate is below the highest application rate permitted 

for paraquat (i.e., 1 lb cation/A). Therefore, 850.4100 is not fulfilled for dicots. 

In order for the 850.4100 guideline requirement to be fulfilled, EFED recommends that PRD 
Page 41 of 71 

require a test involving 4 monocots and 6 dicots exposed up to the highest single application rate. 

Since no effects were observed in the majority of the test species in MRID 42639601 when 

exposed to 0.67 lb cation/A, it may be possible to fulfill this guideline using a Tier I seedling 

emergence study involving exposures to 1 lb cation/A. If ≥25% effects are observed for any 

species exposed to 1 lb cation/A, a Tier II seedling emergence study must be submitted for that 

species. 

Terrestrial plant toxicity – vegetative vigor 

According to the 850.4150 guideline, vegetative vigor data are required for a total of 10 plant 

species, including 4 monocot and 6 dicot species. The 4 monocot species must be from at least 2 

families. One species of monocots must be corn. The 6 dicot species must be from 4 different 

families, and must include soybean and a root crop. 

Supplemental vegetative vigor data are available for 1 monocot and 6 dicot species (MRID 

42601001). Although these data are scientifically valid, they are uncertain due to guideline 

deviations. Therefore, EFED recommends that PRD require Tier II vegetative vigor data for 6 

dicot and 4 monocot species as indicated in the paragraph above. 

12. References 

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation of the 

EPA food-chain (Kenaga) nomogram, an instrument for estimating pesticide residues on plants. 

Environ. Tox. Chem. 13:1383-1391. 

Hoerger, F. and E. E. Kenaga. 1972. Pesticide Residues on Plants: Correlation of 

Representative Data as a Basis for Estimation of their Magnitude in the Environment. In F. 

Coulston and F. Korte, eds., Environmental Quality and Safety: Chemistry, Toxicology, and 

Technology, Georg Thieme Publ., Stuttgart, West Germany, pp. 9-28. 

USEPA. 1998. Guidelines for Ecological Risk Assessment. Risk Assessment Forum, Office of 

Research and Development, Washington, D.C. EPA/630/R-95/002F. April 1998. 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=30759 

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

Programs. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic 

Substances, Office of Pesticide Programs, Washington DC. January 23, 2004. 

USEPA. 2007. ECOTOXicology Database. Office of Research and Development National 

Health and Environmental Effects Research Laboratory’s (NHEERL’s) Mid-Continent Ecology 

Division (MED). http://cfpub.epa.gov/ecotox/. 

USEPA. 2007b. Ecological Incident Information System. 

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf
Page 42 of 71 

U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS). 1998. 

Endangered Species Consultation Handbook: Procedures for Conducting Consultation and 

Conference Activities Under Section 7 of the Endangered Species Act. Final Draft. March 

1998. 

Environmental Fate Studies: 

161-1 Hydrolysis 

MRID Citation Reference 

67161 Funderburk, H.H., Jr.; Negi, N.S.; Lawrence, J.M. (1966) Photo- chemical 

decomposition of diquat and paraquat. Weeds 14:240- 243. 

(Also~In~unpublished submission received Aug 22, 1977 under 239-1663; 

submitted by Chevron Chemical Co., Richmond, Calif.; CDL:231432-L) 

85678 Harned, W.H.; Lengen, M.R. (1981) The Photolysis of Harvade in Aqueous and 

Soil Environments: Project No. 8031. (Unpublished study received Aug 19, 

1981 under 1F2560; submitted by Uniroyal Chemical, Bethany, Conn.; 

CDL:070240-E) 

114412 Slade, P. (1965) Photochemical degradation of paraquat. Nature 207 

(4996):515-516. (Also In unpublished submission received on unknown date 

under 5G0440; submitted by California Chemical Co., Richmond, CA; 

CDL:092728-A) 

161-2 Photodegradation-water 

MRID Citation Reference 

40562301 Parker, S.; Leahey, J. (1988) Paraquat Aqueous Photolysis at pH 7: Laboratory 

Project ID R0633B. Unpublished study prepared by ICI Plant Protection 

Division. 51 p. 

161-3 Photodegradation-soil 

MRID Citation Reference 

17934 Hance, R.J. (1967) Decomposition of herbicides in the soil by non- biological 

chemical processes. J. Sci. Fd Agric. 18(?/Nov):544- 547. 
Page 43 of 71 

(Also~In~unpublished submission received Aug 20, 1976 under 39445-1; 

submitted by American Carbonyl, Inc., Tenafly, N.J.; CDL:228229-AX) 

67161 Funderburk, H.H., Jr.; Negi, N.S.; Lawrence, J.M. (1966) Photo- chemical 

decomposition of diquat and paraquat. Weeds 14:240- 243. 

(Also~In~unpublished submission received Aug 22, 1977 under 239-1663; 

submitted by Chevron Chemical Co., Richmond, Calif.; CDL:231432-L) 

85678 Harned, W.H.; Lengen, M.R. (1981) The Photolysis of Harvade in Aqueous and 

Soil Environments: Project No. 8031. (Unpublished study received Aug 19, 

1981 under 1F2560; submitted by Uniroyal Chemical, Bethany, Conn.; 

CDL:070240-E) 

108334 Corbin, F. (1967) Influence of pH on the Detoxication of Herbicides in Soil. 

Abstracted from: Weeds 15(4):370-377. (Unpublished study received Nov 4, 

1971 under 1F1042; prepared by North Carolina State Univ., Dept. of Crop 

Science, submitted by Stauffer Chemical Co., Richmond, CA; CDL:091932-L) 

140344 Tucker, B.V.; Pack, D.E. (1965) Paraquat Metabolic Fate--Status Re- port. 

(Unpublished study received Apr 7, 1971 under unknown admin. no.; submitted 

by Chevron Chemical Co., Richmond, Calif.; CDL:180001-C) 

140345 Baldwin, B.C.; Slade, P. (1968) The Fate of Carbon-14 Labelled Par- aquat in 

Soil under Field Conditions: AR 2220 B. (Unpublished study received Apr 7, 

1971 under unknown admin. no.; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180001-D) 

140346 Chevron Chemical Company (1970) The Fate of Carbon 14 Labelled Paraquat 

in Soil under Field Conditions. (Unpublished study received Apr 7, 1971 under 

unknown admin. no.; CD:180001-E) 

140350 Tucker, B.V.; Pack, D.E. (1966) The Metabolism 4-Carboxy-1- 

methylpyridinium Ion in Soil. (Unpublished study received Apr 7, 1971 under 

unknown admin. no.; submitted by Chevron Chemical Co., Richmond, Calif.; 

CDL:180001-M) 

146806 Day, S.; Hemingway, R. (1981) [Carbon-14] Paraquat: Degradation on a Sandy 

Soil Surface in Sunlight: Report Series RJ 0168B. Unpublished study prepared 

by ICI Plant Protection Division. 40 p. 

146807 Pack, D. (1982) Long Term Exposure of [Carbon 14] Paraquat on a Sandy Soil 

to California Sunlight. Unpublished study prepared by Chevron Chemical 

Company. 16 p. 

162-1 Aerobic soil metabolism 

MRID Citation Reference 
Page 44 of 71 

55092 Burns, R.G.; Audus, L.J. (1970) Distribution and breakdown of Paraquat in soil. 

Weed Research 10:49-58. (Also~In~unpublished submission received Apr 7, 

1971 under unknown admin. no.; sub- mitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180000-H) 

91369 Chevron Chemical Company (19??) The Fate of Paraquat in Soils. (Unpublished 

study received Mar 2, 1966 under 6F0483; CDL: 090543-F) 

114414 Chevron Chemical Co. (1967) Name, Chemical Identity and Composition of the 

Pesticide Chemical: (Paraquat). (Compilation; unpub- lished study received Apr 

3, 1967 under 7F0592; CDL:092880-A) 

140345 Baldwin, B.C.; Slade, P. (1968) The Fate of Carbon-14 Labelled Par- aquat in 

Soil under Field Conditions: AR 2220 B. (Unpublished study received Apr 7, 

1971 under unknown admin. no.; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180001-D) 

140346 Chevron Chemical Company (1970) The Fate of Carbon 14 Labelled Paraquat 

in Soil under Field Conditions. (Unpublished study received Apr 7, 1971 under 

unknown admin. no.; CD:180001-E) 

140350 Tucker, B.V.; Pack, D.E. (1966) The Metabolism 4-Carboxy-1- 

methylpyridinium Ion in Soil. (Unpublished study received Apr 7, 1971 under 

unknown admin. no.; submitted by Chevron Chemical Co., Richmond, Calif.; 

CDL:180001-M) 

140355 Anderson, J.R.; Drew, E.A.; Tomlinson, T.E. (1971) Distribution of 

?~Lipomyces starkey~in Some Soils and Its Ability To Degrade Paraquat in Soil 

or Clay Associations: Report No. AR 2236 A. (Unpublished study received Apr 

7, 1971 under unknown admin. no.; prepared by Imperial Chemical Industries, 

Ltd., submitted by Chevron Chemical Co., Richmond, Calif.; CDL:180001-R) 

140356 Anderson, J.R.; Drew, E.A.; Tomlinson, T.E. (1971) Growth Charac- teristics 

of, and Paraquat Degradation by, a Species of~Lipo~?- ?~myces: Report No. 

AR 2238 A. (Unpublished study received Apr 7, 1971 under unknown admin. 

no.; prepared by Imperial Chem- ical Industries, Ltd., submitted by Chevron 

Chemical Co., Rich- mond, Calif.; CDL:18001-S) 

41319301 Vickers, J.; Hurt, A.; Bewick, D. (1989) Paraquat: Degradation in Aerobic Soil: 

Lab Project Number: 88JH386. Unpublished study prepared by ICI 

Agrochemicals. 33 p. 

162-2 Anaerobic soil metabolism 

MRID Citation Reference 

41319302 Vickers, J.; Hurt, A.; Bewick, D. (1989) Paraquat: Degradation in Anaerobic 

Soil: Lab Project Number: 88JH386. Unpublished study prepared by ICI 
Page 45 of 71 

Agrochemicals. 34 p. 

163-1 Leach/adsorp/desorption 

MRID Citation Reference 

17934 Hance, R.J. (1967) Decomposition of herbicides in the soil by non- biological 

chemical processes. J. Sci. Fd Agric. 18(?/Nov):544- 547. 

(Also~In~unpublished submission received Aug 20, 1976 under 39445-1; 

submitted by American Carbonyl, Inc., Tenafly, N.J.; CDL:228229-AX) 

22802 Warnock, R.E.; Leary, J.B. (1978) Paraquat, Atrazine and Bladex- Dissipation 

in Soils. (Unpublished study received Jul 30, 1979 under 201-279; prepared by 

Chevron Chemical Co., submitted by Shell Chemical Co., Washington, D.C.; 

CDL:238889-G) 

25063 Shell Chemical Company (1975) Dissipation of Bladex^(R)I Herbicide and 

Paraquat in Soil following Application of Bladex, Paraquat, or a Tank Mix of 

Bladex and Paraquat: TIR-24-135-74. (Unpub- lished study received Apr 22, 

1976 under 201-279; CDL:224461-F) 

29088 Mangels, G.D. (1979) CL 222,705: Determination of Mobility by Soil ThinLayer Chromatography: Project No. 0414. (Unpublished study received Apr 22, 

1980 under 241-259; submitted by American Cyanamid Co., Princeton, N.J.; 

CDL:099383-E) 

32006 Weissler, M.S.; Prashad, S.; Hill, I.R. (1979) Paraquat: Strong Ad- sorption 

Capacities, Measured by Wheat Bioassay, of Seven Sandy Soils from West 

Germany: Report Series RJ 0097 B. (Unpublished study received May 2, 1980 

under 239-2186; prepared by ICI, sub- mitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:242382-B) 

32045 Reichert, B.L.; Knoll, B.A. (1979) CL 217,300: Determination of Mobility in 

Soil: Project No. 0420. (Unpublished study received Jun 11, 1980 under 241-

260; submitted by American Cyanamid Co., Princeton, N.J.; CDL:099457-C) 

33449 Clinch, R.C.; Middleton, M.R.; Winchester, J.N. (1962) Bipyridylium 

Herbicides: Adsorption of Diquat and Paraquat Salts and Formula- tions by 

Soils: Experimental Report No. PP/E/178. (Unpublished study received Jun 10, 

1963 under 239-1994; prepared by Imperial Chemical Industries, Ltd. in 

cooperation with Plant Protection, Ltd., submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL: 001407-B) 

33837 California Chemical Company (1964) Bio-assay of Extracts from Para- quatTreated Soils with~Lemna minor~?. (Unpublished study re- ceived Oct 14, 1965 

under 239-1994; submitted by Chevron Chemi- cal Co., Richmond, Calif.; 

CDL:001432-C) 
Page 46 of 71 

52390 Gowman, M.A.; Riley, D.; Newby, S.E. (1980) Paraquat and Diquat: LongTerm High-Rate Trial, Frensham, UK. 2. Persistence and Movement in Soil, and 

Glasshouse Bioassays: Report Series RJ 0014 B. (Unpublished study received 

Jun 4, 1980 under 239-2186; prepared by ICI, submitted by Chevron Chemical 

Co., Richmond, Calif.; CDL:242577-B) 

55086 Coats, G.E.; Funderburk, H.H., Jr.; Lawrence, J.M.; et al. (1966) Factors 

affecting persistence and inactivation of Diquat and Paraquat. Weed Research 

6(1):58-66. (Also~In~unpublished sub- mission received Apr 7, 1971 under 

unknown admin. no.; submitted by Chevron Chemical Co., Richmond, Calif.; 

CDL:180000-B) 

55087 Knight, B.A.G.; Denny, P.J. (1970) The interaction of Paraquat with soil: 

Adsorption by an expanding lattice clay mineral. Weed Research 10:40-48. 

(Also~In~unpublished submission received Apr 7, 1971 under unknown admin. 

no.; submitted by Chevron Chemical Co., Richmond, Calif.; CDL:180000-C) 

55088 Knight, B.A.G.; Tomlinson, T.E. (1967) The interaction of Paraquat (1:1'-

Dimethyl 4:4'-dipyridylium dichloride) with mineral soils. Journal of Soil 

Science 18(2):233-243. (Also~In~unpublished submission received Apr 7, 1971 

under unknown admin. no.; sub- mitted by Chevron Chemical Co., Richmond, 

Calif.; CDL:180000-D) 

55089 Tomlinson, T.E.; Knight, B.A.G.; Bastow, A.W.; et al. (1968) Structural factors 

affecting the adsorption of bipyridylium cations by clay minerals. Pages 317-

333,~In~Physico-Chemical and Biophysical Factors Affecting the Activity of 

Pesticides. By ? London, England: Soc. of Chem. Ind. (S.C.I. monograph no. 29; 

also~In~unpublished submission received Apr 7, 1971 under unknown admin. 

no.; submitted by Chevron Chemical Co., Richmond, Calif.; CDL:180000-E) 

55090 Weber, J.B.; Perry, P.W.; Upchurch, R.P. (1965) The influence of temperature 

and time on the adsorption of Paraquat, Diquat, 2,4-D and Prometone by clays, 

charcoal, and an anion-exchange resin. Soil Science Society of America 

Proceedings 29:678-688. (Also~In~unpublished submission received Apr 7, 

1971 under unknown admin. no.; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180000-F) 

55092 Burns, R.G.; Audus, L.J. (1970) Distribution and breakdown of Paraquat in soil. 

Weed Research 10:49-58. (Also~In~unpublished submission received Apr 7, 

1971 under unknown admin. no.; sub- mitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180000-H) 

55093 Coats, G.E.; Funderburk, H.H., Jr.; Lawrence, J.H.; et al. (1964) Persistence of 

Diquat and Paraquat in pools and ponds. Proceed- ings, Southern Weed Control 

Conference 17:308-320. (Also~In~ unpublished submission received Apr 7, 

1971 under unknown admin. no.; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL: 180000-I) 

55097 Austin, W.G.L.; Calderbank, A. (1964) Diquat and Paraquat: Residues in Water 

and Toxicity to Fish and Other Aquatic Fauna: Experi- mental Report No. 
Page 47 of 71 

PP/E/303. (Unpublished study received Apr 7, 1971 under unknown admin. no.; 

prepared by Plant Protection, Ltd., submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180000-M) 

56053 Tucker, B.V. (19??) Lack of Effect of a Polar Hydroxy triazine Com- pound on 

Paraquat Leaching in Soil. (Unpublished study received Jun 19, 1973 under 

1F1014; submitted by Chevron Chemical Co., Richmond, Calif.; CDL:091760-

C) 

64796 Pack, D.E. (1980) Mobility of Naled and Dichlorvos in Soil As De- termined by 

Soil Thin-layer Chromatography: File No. 722.2. (Unpublished study received 

Oct 20, 1980 under 239-1633; submit- ted by Chevron Chemical Co., 

Richmond, Calif.; CDL:243547-A) 

65606 Baldwin, B.C.; Knight, B.A.G. (1967) The Fate of Diquat in Soils: Survey of 

Present Knowledge: TMJ 224. (Unpublished study re- ceived Aug 22, 1977 

under 239-1663; prepared by Imperial Chem- ical Industries Ltd., England, 

submitted by Chevron Chemical Co., Richmond, Calif.; CDL:231430-F) 

65609 Gamar, Y.; Mustafa, M.A. (1975) Adsorption and desorption of di- quat^2tI and 

paraquat^2tI on arid-zone soils. Soil Science 119(4):290-295. 

(Also~In~unpublished submission received Aug 22, 1977 under 239-1663; 

submitted by Chevron Chemical Co., Richmond, Calif.; CDL:231430-I) 

65610 Haque, R.; Lilley, S.; Coshow, W.R. (1970) Mechanism of adsorption of diquat 

and paraquat on Montmorillonite surface. Journal of Colloid and Interface 

Science 33(1):185-188. (Also~In~unpub~ lished submission received Aug 22, 

1977 under 239-1663; submit- ted by Chevron Chemical Co., Richmond, Calif.; 

CDL:231430-J) 

65611 Hayes, M.H.B.; Pick, M.E.; Toms, B.A. (1972) Application of microcalorimetry to the study of interactions between organic chem- icals and soil 

constituents. Science Tools 19:9-12. (Also~In~ unpublished submission 

received Aug 22, 1977 under 239-1663; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL: 231430-K) 

65613 Khan, S.U. (1974) Adsorption of bipyridylium herbicides by humic acid. 

Journal of Environmental Quality 3(3):202-206. (Also ?~In~unpublished 

submission received Aug 22, 1977 under 239- 1663; submitted by Chevron 

Chemical Co., Richmond, Calif.; CDL:231430-M) 

65614 Khan, S.U. (1973) Interaction of bipyridylium herbicides with or- gano-clay 

complex. Journal of Soil Science 24(2):244-248. (Al- so~In~unpublished 

submission received Aug 22, 1977 under 239- 1663; submitted by Chevron 

Chemical Co., Richmond, Calif.; CDL:231430-N) 

65615 Philen, O.D., Jr.; Weed, S.B.; Weber, J.B. (1970) Estimation of surface charge 

density of mica and vermiculite by competitive adsorption of Diquat^2I^+I vs. 

Paraquat^2I^+I. Soil Science Society of America Proceedings 34:527-531. 

(Also~In~unpublished submission received Aug 22, 1977 under 239-1663; 
Page 48 of 71 

submitted by Chevron Chemical Co., Richmond, Calif.; CDL:231430-O) 

65618 Tucker, B.V.; Pack, D.E.; Ospenson, J.N. (1967) Adsorption of bipy- ridylium 

herbicides in soil. Journal of Agricultural and Food Chemistry 15(6):1005-1008. 

(Also~In~unpublished submission re- ceived Aug 22, 1977 under 239-1663; 

submitted by Chevron Chemi- cal Co., Richmond, Calif.; CDL:231430-S) 

65619 Weber, J.B.; Weed, S.B. (1968) Adsorption and desorption of diquat, paraquat, 

and prometone by montomorillanitic and kaolinitic clay minerals. Soil Science 

Society of America Proceedings 32:485- 487. (Also~In~unpublished submission 

received Aug 22, 1977 un- der 239-1663; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:231430-T) 

65621 Weber, J.B.; Perry, P.W.; Upchurch, R.P. (1965) The influence of temperature 

and time on the adsorption of paraquat, diquat, 2,4-D and prometone by clays, 

charcoal, and an anion-exchange resin. Soil Science Society of America 

Proceedins 29(6):678- 688. (Also~In~unpublished submission received Aug 22, 

1977 un- der 239-1663; submitted by Chevron Chemical Co., Richmond, Calif.; 

CDL:231430-V) 

65622 Weed, S.B.; Weber, J.B. (1969) The effect of cation exchange caparity on the 

retention of Diquat 2I+I and Paraquat21+I by three-layer type clay minerals: I. 

Adsorption and release. Soil Science Society of America Proceedings 

33(3):379-382. (Also in unpublished submission received Aug 22, 1977 under 

239-1663; submitted by Chevron Chemical Co., Richmond, Calif.; 

CDL:231430-W) 

65623 Weed, S.B.; Weber, J.B. (1968) The effect of adsorbent charge on the 

competitive adsorption of divalent organic cations by layer- silicate minerals. 

American Mineralogist 53(Mar-Apr):478-490. (Also~In~unpublished 

submission received Aug 22, 1977 under 239- 1663; submitted by Chevron 

Chemical Co., Richmond, Calif.; CDL: 231430-X) 

65624 Best, J.A.; Weber, J.B.; Weed, S.B. (1972) Competive adsorption of 

Diquat^2I^+I, Paraquat^2I^+I, and Ca^2I^+I on organic matter and exchange 

resins. Soil Science 114(6)444-450. (Also~In~unpub- lished submission 

received Aug 22, 1977 under 239-1663; submit- ted by Chevron Chemical Co., 

Richmond, Calif.; CDL:231430-Y) 

68226 Coats, G.E.; Funderburk, H.H., Jr.; Lawrence, J.M.; et al. (1964) Persistence of 

diquat and paraquat in pools and ponds. Pro- ceedings of the Southern Weed 

Control Conference 17:308-320. (Also~In~unpublished submission received 

Aug 22, 1977 under 239- 1663; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL: 231431-J) 

70873 Pack, D.E. (1980) Paraquat, Atrazine and Terbutryn--Dissipation in Soils Alone 

and in Combination: File No. 721.7/R-127. (Unpub- lished study received Mar 

24, 1981 under 239-2186; submitted by Chevron Chemical Co., Richmond, 

Calif.; CDL:244725-A) 
Page 49 of 71 

82259 Spinks, C.A.; Hendley, P.; Arnold, D.J. (1976) PP796--Degradation in Soil 

under Laboratory Conditions: Report Series TMJ 1419 B. (Unpublished study 

received Apr 13, 1977 under PP0796; prepared by Imperial Chemical Industries, 

Ltd., England, submitted by Chevron Chemical Co., Richmond, Calif.; 

CDL:098315-G) 

90396 California Chemical Company (1964) Paraquat Residues in Soil. (Compilation; 

unpublished study received Feb 25, 1965 under 5G0440; CDL:090479-B) 

91369 Chevron Chemical Company (19??) The Fate of Paraquat in Soils. (Unpublished 

study received Mar 2, 1966 under 6F0483; CDL: 090543-F) 

91370 Chevron Chemical Company (1965?) Adsorption of Bipyridylium Herbi- cides 

in Soil. (Unpublished study received Mar 2, 1966 under 6F0483; CDL:090543-

G) 

96972 Pack, D.E. (1977) Soil Mobility of Captan, Folpet and Captafol As Determined 

by Soil Thin-layer Chromatography: File No. 722.0. (Unpublished study 

received May 30, 1978 under 239-2211; sub- mitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:234046-N) 

105942 Leake, C.; Lines, D.; Tiffen, K. (1981) The Leaching of NC 21 314 in Four Soil 

Types Using Soil TLC: METAB/81/40. (Unpublished study received Jul 1, 1982 

under 45639-EX-7; prepared by FBC Ltd., Eng., submitted by BFC Chemicals, 

Inc., Wilmington, DE; CDL:070966-E) 

111528 McCall, H.; Bovey, R.; McCully, M; et al. (1972) Adsorption and desorption of 

picloram, trifluralin, and paraquat by ionic and nonionic exchange resins. Weed 

Science 20(3):250-255. (Also In unpublished submission received Sep 26, 1974 

under 464-323; submitted by Dow Chemical U.S.A., Midland, MI; 

CDL:120317-U) 

113707 Clinch, R.; Middleton, M.; Winchester, J. (1962) Bipyridylium Herbicides: 

Adsorption of Diquat and Paraquat Salts and Formula- tions by Soils: Report 

No. PP/E/178. (Unpublished study re- ceived Aug 1, 1962 under unknown 

admin. no.; submitted by Imperial Chemical Industries Ltd., London, Eng.; 

CDL:121729-A) 

114299 Leake, C.; Somerville, L.; Lines, D.; et al. (1982) The Leaching of Amitraz in 

Four Soil Types Using Soil T.L.C.: METAB/82/16. (Un- published study 

received Sep 8, 1982 under 45639-49; prepared by FBC, Ltd., Eng., submitted 

by BFC Chemicals, Inc., Wilmington, DE; CDL:248318-B) 

116619 Kinne, L.; Reynolds, J.; Froelich, L.; et al. (1982) Soil Mobility of FMC 57020: 

M-4862. (Unpublished study received Oct 1, 1982 under 279-EX-93; submitted 

by FMC Corp., Philadelphia, PA; CDL: 248476-C) 

121311 Hayes, M.; Pick, M.; Toms, B. (1972) Application of microcalor- imetry to the 

study of interactions between organic chemicals and soil constituents. LKB 

Instrument Journal 19:9-12. (Also In unpublished submission received Dec 21, 
Page 50 of 71 

1982 under 239-2247; submitted by Chevron Chemical Co., Richmond, CA; 

CDL:249102-K) 

121313 Philen, O.; Weed, S.; Weber, J. (1970) Estimation of surface charge density of 

mica and vermiculite by competitive adsorption of di- quat vs. paraquat. Soil 

Science Society of America Proceedings 34:527-531. (Also In unpublished 

submission received Dec 21, 1982 under 239-2247; submitted by Chevron 

Chemical Co., Rich- mond, CA; CDL:249102-O) 

121317 Weber, J.; Weed, S. (1968) Adsorption and Desorption of diquat, paraquat, and 

prometone by montmorillonitic and kaolinitic clay minerals. Soil Science 

Society of America Proceedings 32:485- 487. (Also In unpublished submission 

received Dec 21, 1982 under 239-2247; submitted by Chevron Chemical Co., 

Richmond, CA; CDL:249102-T) 

121318 Weed, S.; Weber, J. (1968) The effect of adsorbent charge on the competitive 

adsorption of divalent organic cations by layer-sil- icate minerals. American 

Mineralogist 53(Mar-Apr):478-490. (Also in unpublished submission received 

Dec 21, 1982 under 239-2247; submitted by Chevron Chemical Co., Richmond, 

CA; CDL: 249102-X) 

128974 LaFleur, K. (1979) Sorption of pesticides by model soils and agro- nomic soils: 

Rates and equilibria. Soil Science 127(2):94-101. (Also In unpublished 

submission received Jun 16, 1983 under 464-502; submitted by Dow Chemical 

U.S.A., Midland, MI; CDL: 250517AE) 

135717 Chevron Chemical Co. (1970) Diquat: Residue Tolerance Petition: The Results 

of Tests on the Amount of Residue Remaining, Including a Description of the 

Analytical Methods Used: ?Water, Aquatic Life and Soil|. (Compilation; 

unpublished study received Dec 12, 1970 under 1F1101; CDL:090861-A) 

140075 Chevron Chemical Company (1965) Leaching of Paraquat in Soil. (Unpublished study received Apr 7, 1971 under unknown admin. no.; CDL:180001-

AH) 

140076 Chevron Chemical Company (1971) Effect of Massive Paraquat Soil Treatment 

on Soil Leaching. (Unpublished study received Apr 7, 1971 under unknown 

admin. no.; CDL:180001-AI) 

140346 Chevron Chemical Company (1970) The Fate of Carbon 14 Labelled Paraquat 

in Soil under Field Conditions. (Unpublished study received Apr 7, 1971 under 

unknown admin. no.; CD:180001-E) 

140358 Tucker, B.V. (1969) Paraquat Stability in Soil. (Unpublished study received Apr 

7, 1971 under unknown admin. no.; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180001-V) 

5016652 Helling, C.S. (1971) Pesticide mobility in soils: II_ Applications of soil thinlayer chromatography. Proceedings of the Soil Science Society of America 

35(5):737-743. 
Page 51 of 71 

164-1 Terrestrial field dissipation 

MRID Citation Reference 

23515 Ballantine, L.G.; Herman, M.M.; Coan, R.M.; et al. (1979) Bi- cep^(R)I plus 

Roundup^(R)I or Paraquat and Dual^(R)I/Prin- cep^(R)I plus Roundup or 

Paraquat Tank Mix Soil Dissipation Studies: Report No. ABR-79101. 

(Unpublished study received Dec 10, 1979 under 100-583; prepared in 

cooperation with Chevron Chemical Co. and others, submitted by Ciba-Geigy 

Corp., Greens- boro, N.C.; CDL:241649-A) 

27021 Chevron Chemical Company (1976) Residue Data Sheet: Soil: Test Number T4088 (AG-A 4084 I-IV). (Unpublished study received Dec 10, 1979 under 100-

583; submitted by Ciba-Geigy Corp., Greens- boro, N.C.; CDL:241649-F) 

27022 Chevron Chemical Company (1976) Residue Data Sheet: Soil: Test Number T4089 (AG-A 4085 I-IV). (Unpublished study received Dec 10, 1979 under 100-

583; submitted by Ciba-Geigy Corp., Greens- boro, N.C.; CDL:241649-G) 

27023 Chevron Chemical Company (1978) Residue Data Sheet: Soil: Test Number T4834 (AG-A 6061). (Unpublished study received Dec 10, 1979 under 100-583; 

submitted by Ciba-Geigy Corp., Greensboro, N.C.; CDL:241649-H) 

33836 Chevron Chemical Company (1957) Paraquat Residues in Soil. (Unpub- lished 

study received Oct 14, 1965 under 239-1994; CDL:001432-B) 

52390 Gowman, M.A.; Riley, D.; Newby, S.E. (1980) Paraquat and Diquat: LongTerm High-Rate Trial, Frensham, UK. 2. Persistence and Movement in Soil, and 

Glasshouse Bioassays: Report Series RJ 0014 B. (Unpublished study received 

Jun 4, 1980 under 239-2186; prepared by ICI, submitted by Chevron Chemical 

Co., Richmond, Calif.; CDL:242577-B) 

52394 Tucker, B.V.; Agbakoba, C.S.O. (1978) ?Paraquat Soil Residue Stud- ies|. 

(Unpublished study received Jun 4, 1980 under 239-2186; submitted by 

Chevron Chemical Co., Richmond, Calif.; CDL: 242577-G) 

55091 O'Toole, M.A. (1965) Residual effects of Paraquat on peat soil. Irish Journal of 

Agricultural Research 4(2):231-233. (Also~In~ unpublished submission 

received Apr 7, 1971 under unknown admin. no.; submitted by Chevron 

Chemical Co., Richmond, Calif.; CDL:180000-G) 

55093 Coats, G.E.; Funderburk, H.H., Jr.; Lawrence, J.H.; et al. (1964) Persistence of 

Diquat and Paraquat in pools and ponds. Proceed- ings, Southern Weed Control 

Conference 17:308-320. (Also~In~ unpublished submission received Apr 7, 

1971 under unknown admin. no.; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL: 180000-I) 

55109 Geoghegan, M.J.; Newman, J.F.; Wilkinson, W. (1966) Bipyridylium 

Herbicides--Paraquat, Preliminary Observations on the Effects on Soil 
Page 52 of 71 

Organisms: Central File No. A.126,393. (Unpublished study received Apr 7, 

1971 under unknown admin. no.; prepared by Imperial Chemical Industries, 

Ltd., submitted by Chevron Chemi- cal Co., Richmond, Calif.; CDL:180000-

AB) 

65606 Baldwin, B.C.; Knight, B.A.G. (1967) The Fate of Diquat in Soils: Survey of 

Present Knowledge: TMJ 224. (Unpublished study re- ceived Aug 22, 1977 

under 239-1663; prepared by Imperial Chem- ical Industries Ltd., England, 

submitted by Chevron Chemical Co., Richmond, Calif.; CDL:231430-F) 

73770 Frank, P.A.; Comes, R.D. (19??) Herbicidal residues in pond water and 

hydrosoil. Weeds 15(Jul):210-213. (Also~In~unpublished submission received 

Aug 29, 1979 under 2217-624; submitted by PBI-Gordon Corp., Kansas City, 

Kans.; CDL:240872-P) 

90396 California Chemical Company (1964) Paraquat Residues in Soil. (Compilation; 

unpublished study received Feb 25, 1965 under 5G0440; CDL:090479-B) 

113724 Thompson-Hayward Chemical Co. (1967) Proposed Irrigation Study with Water 

Treated with Dichlobenil. (Compilation; unpublished study received Jan 12, 

1968 under 148-673; CDL:000651-A) 

114414 Chevron Chemical Co. (1967) Name, Chemical Identity and Composition of the 

Pesticide Chemical: (Paraquat). (Compilation; unpub- lished study received Apr 

3, 1967 under 7F0592; CDL:092880-A) 

114443 Whipp, A.; Thompson, R. (1962) Progress Report: Diquat and Paraquat Soil 

Residue Studies. (Unpublished study received Sep 4, 1962 under unknown 

admin. no.; submitted by Chevron Chemical Co., Richmond, CA; CDL:120436-

A) 

118549 Amchem Products, Inc. (1971) Fenac Residue Data--Total Water Treat- ment. 

(Compilation; unpublished study received Jul 7, 1972 under 2F1213; 

CDL:091039-T) 

122696 Newman, J. (1976) Diquat: Biological Effects and Residues in Soil and Crops in 

a High Rate Field Trial on a Loamy Sand: TMJ 1225A. (Unpublished study 

received Dec 21, 1982 under 239-2247; pre- pared by Plant Protection, Ltd., 

Eng., submitted by Chevron Chemical Co., Richmond, CA; CDL:249103-E) 

122704 Coats, G.; Funderburk, H.; Lawrence, J.; et al. (1963) Persistence of Diquat and 

Paraquat in Pools and Ponds. (Unpublished study received Dec 21, 1982 under 

239-2247; prepared by Auburn Univ., Agricultural Experiment Station, 

submitted by Chevron Chemical Co., Richmond, CA; CDL:249104-I) 

140345 Baldwin, B.C.; Slade, P. (1968) The Fate of Carbon-14 Labelled Par- aquat in 

Soil under Field Conditions: AR 2220 B. (Unpublished study received Apr 7, 

1971 under unknown admin. no.; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180001-D) 

140346 Chevron Chemical Company (1970) The Fate of Carbon 14 Labelled Paraquat 
Page 53 of 71 

in Soil under Field Conditions. (Unpublished study received Apr 7, 1971 under 

unknown admin. no.; CD:180001-E) 

140359 Baldwin, B.C.; Slade, P. (1970) Bipyridylium Herbicides: Residues of Paraquat 

in Soil following Field Application of Gramoxone: Report No. AR 2219 B. 

(Unpublished study received Apr 7, 1971 under unknown admin. no.; submitted 

by Chevron Chemical Co., Richmond, Calif.; CDL:180001-W) 

140361 Gratton, R.P. (1970) The Significance of Paraquat Residues from the South 

African Trial PE/G/20 (b): Report Series TMJ 588 B. (Un- published study 

received Apr 7, 1971 under unknown admin. no.; prepared by Plant Protection, 

Ltd., submitted by Chevron Chemi- cal Co., Richmond, Calif.; CDL:18001-Y) 

5013351 Doughty, C.C. (1978) Terbacil phytotoxicity and quackgrass (?~Agropyron 

repens?~) control in highbush blueberries (?~Vaccinium corymbosum?~). Weed 

Science 26(5):448-492. 

41293201 Earl, M.; Anderson, L.; Muir, G. (1989) Paraquat: Field Soil Dissipation under 

In-use Conditions in the USA (Champaign, Illinois) during 1987-89--Analytical 

Report: Lab Project Nos. PP148BD05; RJ0781B; TMR0089B. Unpublished 

study prepared by ICI Agrochemicals, Jealott's Hill Research Station in 

cooperation with ICI Western Research Center. 93 p. 

41293202 Anderson, E.; Muir, G. (1989) Paraquat Short Term Field Soil Dissipation under 

In-use Conditions in the USA (Sussex County, Delaware) during 1987-89: 

Analytical Report: Lab Project Numbers PP148BD04; RJ0776B; TMR0068B. 

Unpublished study prepared by ICI Agrochemicals, Jealott's Hill Research 

Station in cooperation with ICI Americas Western Research Center. 85 p. 

41319303 Anderson, L.; Emburay, G.; Hoag, R.; et al. (1989) Paraquat: Field Soil 

Dissipation Under In-use Conditions in the USA (Leland, Mississippi) During 

1987-1988: Lab Project Number: PP148BD05. Unpublished study prepared by 

ICI Agrochemicals. 122 p. 

41319304 Anderson, L.; Muir, G.; Hoag, R. (1989) Paraquat: Field Dissipation under Inuse Conditions in the USA (Visalia, California) during 1987-89: Lab Project 

Number: PP148BD05. Unpublished study prepared by ICI Agrochemicals. 129 

p. 

41352101 Anderson, L.; Embury, G.; Hoag, R.; et al. (1989) Paraquat: Short Term Field 

Soil Dissipation Under In-use Conditions in the USA (Pullman, Washington) 

during 1987-1989: Lab Project Number: PP148BD04: Report No. RJ0797B. 

Unpublished study prepared by ICI Agrochemicals. 102 p. 

41352102 Anderson, L.; Embury, G.; Hoag, R. et al. (1989) Paraquat: Short Term Field 

Soil Dissipation under In-use Conditions in the USA (Clermont, Florida) During 

1987-1989: Lab Project Number: PP148- BD04: Report No. RJ0794B. 

Unpublished study prepared by ICI Agrochemicals. 91 p. 

164-2 Aquatic field dissipation 
Page 54 of 71 

MRID Citation Reference 

31833 Yeo, R.R. (19??) Dissipation of Diquat and Paraquat and effects on aquatic 

weeds and fish. Weeds ? (? ):42-46. (Also~In~unpub- lished submission 

received Sep 15, 1972 under 1F1101; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:090862-D) 

31853 Austin, W.G.L.; Calderbank, A. (1964) Diquat and Paraquat: Residues in Water 

and Toxicity to Fish and Other Aquatic Fauna: Experimental Report No. 

PP/E/303. (Unpublished study received Sep 15, 1972 under 1F1101; prepared 

by Imperial Chemical Industries, Ltd., submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL: 090862-AC) 

55093 Coats, G.E.; Funderburk, H.H., Jr.; Lawrence, J.H.; et al. (1964) Persistence of 

Diquat and Paraquat in pools and ponds. Proceed- ings, Southern Weed Control 

Conference 17:308-320. (Also~In~ unpublished submission received Apr 7, 

1971 under unknown admin. no.; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL: 180000-I) 

55097 Austin, W.G.L.; Calderbank, A. (1964) Diquat and Paraquat: Residues in Water 

and Toxicity to Fish and Other Aquatic Fauna: Experi- mental Report No. 

PP/E/303. (Unpublished study received Apr 7, 1971 under unknown admin. no.; 

prepared by Plant Protection, Ltd., submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL:180000-M) 

55100 Grzenda, A.R.; Nicholson, H.P.; Cox, W.S. (1966) Persistence of four 

herbicides in pond water. Journal of the American Water Works Association 

58(Mar):326-332. (Also~In~unpublished sub- mission received Apr 7, 1971 

under unknown admin. no.; submitted by Chevron Chemical Co., Richmond, 

Calif.; CDL:180000-P) 

68226 Coats, G.E.; Funderburk, H.H., Jr.; Lawrence, J.M.; et al. (1964) Persistence of 

diquat and paraquat in pools and ponds. Pro- ceedings of the Southern Weed 

Control Conference 17:308-320. (Also~In~unpublished submission received 

Aug 22, 1977 under 239- 1663; submitted by Chevron Chemical Co., 

Richmond, Calif.; CDL: 231431-J) 

68232 Yeo, R.R. (1967) Dissipation of diquat and paraquat and effects on aquatic 

weeds and fish. Weeds 15:42-46. (Also~In~unpublished submission received 

Aug 22, 1977 under 239-1663; submitted by Chevron Chemical Co., Richmond, 

Calif.; CDL:231431-R) 

73770 Frank, P.A.; Comes, R.D. (19??) Herbicidal residues in pond water and 

hydrosoil. Weeds 15(Jul):210-213. (Also~In~unpublished submission received 

Aug 29, 1979 under 2217-624; submitted by PBI-Gordon Corp., Kansas City, 

Kans.; CDL:240872-P) 

113724 Thompson-Hayward Chemical Co. (1967) Proposed Irrigation Study with Water 
Page 55 of 71 

Treated with Dichlobenil. (Compilation; unpublished study received Jan 12, 

1968 under 148-673; CDL:000651-A) 

113733 Thompson-Hayward Chemical Co. (1967) Disappearance of Dichlobenil and 

2,6-Dichlorobenzoic Acid in Water: Report R-649. (Compila- tion; unpublished 

study received Feb 23, 1967 under 148-673; CDL:000655-A) 

116737 3M Co. (1970) ?Residue Analyses of 3MCAP-D and Other Chemicals in 

Various Products|. (Compilation; unpublished study received on unknown date 

under 10556-EX-1; CDL:127733-A) 

118549 Amchem Products, Inc. (1971) Fenac Residue Data--Total Water Treat- ment. 

(Compilation; unpublished study received Jul 7, 1972 under 2F1213; 

CDL:091039-T) 

122704 Coats, G.; Funderburk, H.; Lawrence, J.; et al. (1963) Persistence of Diquat and 

Paraquat in Pools and Ponds. (Unpublished study received Dec 21, 1982 under 

239-2247; prepared by Auburn Univ., Agricultural Experiment Station, 

submitted by Chevron Chemical Co., Richmond, CA; CDL:249104-I) 

135717 Chevron Chemical Co. (1970) Diquat: Residue Tolerance Petition: The Results 

of Tests on the Amount of Residue Remaining, Including a Description of the 

Analytical Methods Used: ?Water, Aquatic Life and Soil|. (Compilation; 

unpublished study received Dec 12, 1970 under 1F1101; CDL:090861-A) 

164-5 Long term soil dissipation 

MRID Citation Reference 

146803 Abell, J. (1984) High Rate Paraquat Soil Residue Trial: Mt. Holly New Jersey. 

Unpublished study prepared by Chevron Chemical Company. 12 p. 

146804 Abell, J. (1984) High Rate Paraquat Soil Residue Trial: Fresno California. 

Unpublished study prepared by Chevron Chemical Company. 13 p. 

146805 Riley, D.; Abell, J. (19??) Long Term Fate and Biological Activity of Bound 

Paraquat Residues in Soil. Unpublished study prepared by Jealotts Hill Research 

Station and Chevron Chemical Co. 16 p. 

42738701 Anderson, L.; Hoag, R.; Anders, C. et al. (1992) Paraquat: Field Soil Dissipation 

under In-Use Conditions in the USA During 1987-91 (Visalia, California): Lab 

Project Number: PP148BD05: RJ1191B. Unpublished study prepared by ICI 

Agrochemicals. 132 p. 

42738702 Anderson, L.; Hoag, R.; Anders, C. et al. (1992) Paraquat: Field Soil Dissipation 

under In-Use Conditions in the USA During 1987-89 (Leland, Mississippi): Lab 

Project Number: PP148BD05: RJ1206B. Unpublished study prepared by ICI 

Agrochemicals. 98 p. 
Page 56 of 71 

42802101 Anderson, L.; Hoag, R.; Safford, J. et al. (1992) Paraquat: Field Soil Dissipation 

under In-Use Conditions in the USA During 1987-91 (Champaign, Ill.): Lab 

Project Number: PP148BD05: RJ1187B. Unpublished study prepared by ICI 

Agrochemicals, Jealott's Hill. 127 p. 

42802102 Anderson, L.; Hoag, R.; Anders, C. et al. (1992) Paraquat: Field Soil Dissipation 

under In-Use Conditions in the USA During 1987-91 (Golddsboro, NC): Lab 

Project Number: PP148BD05: RJ1146B. Unpublished study prepared by ICI 

Agrochemicals, Jealott's Hill. 116 p. 

Ecological Effects Studies: 

850.2100 Avian Single Dose Oral Toxicity 

MRID Citation Reference 

29001 Fink, R.; Beavers, J.B.; Grimes, J.; et al. (1979) Acute Oral LDI50^--Bobwhite 

Quail: Paraquat dichloride Technical Salt (SX- 1142): Project No. 162-121. 

Final Rept. (Unpublished study received Feb 21, 1980 under 239-2422; 

prepared by Wildlife International, Ltd., submitted by Chevron Chemical Co., 

Rich- mond, Calif.; CDL:241819-A) 

0160000 Hudson, R.; Tucker, R.; Haegele, M. (1984) Handbook of toxicity of pesticides 

to wildlife: Second edition. US Fish and Wildlife Service: Resource 

Publication 153. 91 p. Mallard study 

850.2200 Avian Dietary Toxicity 

MRID Citation Reference 

22923 Hill, E.F.; Heath, R.G.; Spann, J.W.; et al. (1975) Lethal Dietary Toxicities of 

Environmental Pollutants to Birds: Special Scientific Report--Wildlife No. 

191. Mallard, Japanese quail, Ring-necked pheasant, and bobwhite quail 

55103 Ives, M. (1965) Report to Imperial Chemical Industries, Limited: Toxicity 

Studies on Pheasants and Wild Mallard Ducks: Paraquat Formulation. 

(Unpublished study received Apr 7, 1971 under unknown admin. no.; prepared 

by Industrial Bio-Test Labora- tories, Inc., submitted by Chevron Chemical 

Co., Richmond, Calif.; CDL:180000-S) 

850.2300 Avian Reproduction 
Page 57 of 71 

MRID Citation Reference 

110452 Leary, J.; Tucker, B. (1981) Assessment of Diet Homogeneity and Stability of 

Paraquat Technical (SX-1305) in Game Bird Ration (Wildlife International Ltd. 

Project 162-136): Chevron File No. 721.11/S-1951. (Unpublished study received 

Aug 18, 1982 under 239-2186; submitted by Chevron Chemical Co., Richmond, 

CA; CDL:248133-A) 

110453 Fink, R.; Beavers, J.; Joiner, G.; et al. (1981) Subacute Feeding-- Reproduction 

Screening Bioassay (Bobwhite Quail): Paraquat Technical (SX-1305): Project 

No. 162-138; S-1994. Final rept. (Unpublished study received Aug 18, 1982 

under 239-2186; pre- pared by Wildlife International Ltd., submitted by Chevron 

Chemical Co., Richmond, CA; CDL:248133-B) 

110454 Fink, R.; Beavers, J.; Joiner, G.; et al. (1982) One-generation Reproduction--

Bobwhite 

Quail: Paraquat Technical (SX-1305): Project No. 162-142. Final rept. 

(Unpublished study received Aug 18, 1982 under 239-2186; prepared by 

Wildlife International Ltd., submitted by Chevron Chemical Co., Richmond, CA; 

CDL: 248133-C) LOEC=215 PPM 

110455 Fink, R.; Beavers, J.; Joiner, G.; et al. (1982) One-generation Reproduction--

Mallard Duck: Paraquat Technical (SX-1305): Project No. 162-145. Final rept. 

(Unpublished study received Aug 18, 1982 under 239-2186; prepared by 

Wildlife International Ltd., submitted by Chevron Chemical Co., Richmond, CA; 

CDL: 248133-D) LOEC= 100 PPM 

43942604 Hakin, B.; Chanter, D. (1988) The Effect of Paraquat on the Hatchability of 

Fertile Mallard Duck Eggs: Lab Project Number: ISN 170/881711: ISN/170. 

Unpublished study prepared by Huntingdon Research Centre, Ltd. 128 p. 

43942605 Roberts, N.; Hakin, B.; Chanter, D. (1989) The Effect of Paraquat on the 

Hatchability of Fertile Pheasant Eggs: Amended Report: Lab Project Number: 

ISN 171/881712: ISN/171. Unpublished study prepared by Huntingdon Research 

Centre, Ltd. 134 p. 

 

 

850.1075 Acute Toxicity to Freshwater Fish 

MRID Citation Reference 

162736 Palmateer, S. (1980) Biological Report of Analysis: [Toxicity Test of 

Paraquat on Rainbow Trout]. Unpublished study prepared by U.S. 
Page 58 of 71 

Environmental Protection Agency, Terrestrial & Aquatic Biology 

Laboratory. 1 p. 

162737 Palmateer, S. (1979) Biological Report of Analysis: [Toxicity Test of 

Paraquat on Bluegills]. Unpublished study prepared by U.S. Environmental 

Protection Agency, Terrestrial & Aquatic Biology Laboratory. 1 p. 

162738 McCann, J. (1977) Biological Report of Analysis: [Toxicity Test of Ortho 

Paraquat CL Concentrate on Rainbow trout]. Unpublished study prepared by 

U.S. Environmental Protection Agency, Animal Biology Laboratory. 1 p. 

40098001 Mayer, F.; Ellersieck, M. (1986) Manual of Acute Toxicity: Inter- pretation 

and Data Base for 410 Chemicals and 66 Species of Freshwater Animals. US 

Fish & Wildlife Service, Resource Pub- lication 160. 579 p. 

Rainbow trout, channel cat, bluegill, 

850.1010 Acute Toxicity to Freshwater Invertebrates 

MRID Citation Reference 

114473 Wheeler, R. (1978) 48 Hour Acute Static Toxicity of Paraquat Dichloride Salt 

(SX957) to 1st Stage Nymph Water Fleas (Daphnia magna Straus). 

(Unpublished study received Sep 15, 1978 under 239-2422; submitted by 

Chevron Chemical Co., Richmond, CA; CDL:235419-A) 

162752 Tompkins, J. (1979) Biological Report of Analysis: [Toxicity of Ortho 

Paraquat to Daphnia magna]. Unpublished study prepared by U.S. 

Environmental Protection Agency, Terrestrial & Aquatic Bio- logy Unit 

Laboratory. 1 p. 

40098001 Mayer, F.; Ellersieck, M. (1986) Manual of Acute Toxicity: Inter- pretation 

and Data Base for 410 Chemicals and 66 Species of Freshwater Animals. US 

Fish & Wildlife Service, Resource Pub- lication 160. 579 p. - Daphnia, 

stonefly nymph and Gammarus faciatus 

850.1075 Acute Exposures to Estuarine/marine fish 

MRID Citation Reference 

40228401 Mayer, F.L. USEPA Gulfbreeze Estuarine Toxicity tests - marine algaes, 

brown shrimp, oyster, longnose killifish 

850.1025/850.1035 Acute Exposures to Estuarine/marine invertebrates 
Page 59 of 71 

MRID Citation Reference 

40228401 Mayer, F.L. USEPA Gulfbreeze Estuarine Toxicity tests - marine algaes, 

brown shrimp, oyster, longnose killifish 

850.4400 Aquatic plant growth – vascular plants 

MRID Citation Reference 

42601003 Smyth, D.; Sankey, S.; Cornish, S.; et al (1992) Paraquat Dichloride: 

Toxicity to the Duckweed Lemna Gibba: Lab Project Number: BL4493/B: 

T168/E (FT10/92). Unpublished study prepared by Imperial Chemical 

Industries PLC. 24 p. 

850.5400 Aquatic plant growth - algae 

MRID Citation Reference 

40228401 Mayer, F.L. USEPA Gulfbreeze Estuarine Toxicity tests - marine algaes, 

brown shrimp, oyster, longnose killifish 

42601002 Smyth, D.; Sankey, S.; Penwell, A. (1992) Paraquat Dichloride: Toxicity to 

the Green Alga Selenastrum capricornutum: Lab Project Number: 

BL4578/B: T168/G (FT11/92). Unpublished study prepared by Imperial 

Chemical Industries PLC. 23 p. 

42601004 Smyth, D.; Sankey, S.; Penwell, A. (1992) Paraquat Dichloride: Toxicity to 

the Marine Alga Skeletonema costatum: Lab Project Number: BL4580/B: 

T168/C (FT08/92). Unpublished study prepared by Imperial Chemical 

Industries PLC. 22 p. 

42601005 Smyth, D.; Sankey, S.; Cornish, S. (1992) Paraquat Dichloride: Toxicity to 

the Blue-green Alga Anabaena flos-aquae: Lab Project Number: BL4579/B: 

T168/B (FT07/92). Unpublished study prepared by Imperial Chemical 

Industries PLC. 26 p. 

42601006 Smyth, D.; Sankey, S.; Cornish, S. (1992) Paraquat Dichloride: Toxicity to 

the Freshwater diatom Navicula pelliculosa: Lab Project Number: 

BL4464/B: T168/D (FT09/92). Unpublished study prepared by Imperial 

Chemical Industries PLC. 22 p. 

850.4150 Vegetative Vigor 
Page 60 of 71 

42601001 Canning, L. and J.S. White. 1992. Paraquat: A Glasshouse Study to 

Evaluate the Effects on Vegetative Vigour of a 300 g ai litre-1 (2.5 lb ai US 

gal-1) Soluble Concentrate Formulation on Terrestrial Non-target Plants. 

Laboratory Project ID No. 92JH088. Conducted by ICI Agrochemicals, 

Jealotts Hill Research Station, Bracknell, Berkshire, UK. Submitted by ICI 

Americas, Inc., Wilmington, DE. EPA MRID No. 426010-01. 

850.4100 Seedling Emergence 

42639601 Canning, L. and J.S. White. 1992. Paraquat: A Glasshouse Study 

to Evaluate the Effects on Seedling Emergence of a 300 g ai litre-1

(2.5 lb ai US gal-1) Soluble Concentrate Formulation on Terrestrial 

Non-target Plants. Laboratory Project ID No. 92JH089. 

Conducted by ICI Agrochemicals, Jealotts Hill Research Station, 

Bracknell, Berkshire, UK. Submitted by ICI Americas Inc., 

Wilmington, DE. EPA MRID No. 426396-01. 

850.3020 Honey bee acute contact 

MRID Citation Reference 

36935 Atkins, E.L.; Greywood, E.A.; Macdonald, R.L. (1975) Toxicity of Pesticides 

and Other Agricultural Chemicals to Honey Bees: Labo- ratory Studies. By 

University of California, Dept. of Entomolo- gy. ?: UC, Cooperative 

Extension. (Leaflet 2287; 

published study.) 

5001991 Stevenson, J.H. (1978) The acute toxicity of unformulated pesticides to worker 

honey bees (?~Apis mellifera~L_). Plant Pathology 27(1):38-40. 

111488 Moffett, J.; Morton, H.; MacDonald, R. (1972) Toxicity of some herbicidal 

sprays to honey bees. Journal of Economic Entomology 65(1):32-36. (Also In 

unpublished submission received Sep 26, 1974 under 464-323; submitted by 

Dow Chemical U.S.A., Midland, MI; CDL:120345-H) 

43942603 Bull, J.; Wilkinson, W. (1987) Paraquat: Acute 5-Day Contact and Oral 

Toxicity to Honey Bees (Apis mellifera): Lab Project Number: RJ0578B: 

PP148CM008. Unpublished study prepared by ICI Plant Protection Division. 

27 p. 

 
Page 61 of 71 

Appendix A. Ecological Effects Characterization 

 

A1. Aquatic Organisms 

On an acute exposure basis, paraquat is slightly toxic to aquatic-phase amphibians and 

fish and moderately toxic to freshwater invertebrates. No chronic toxicity studies have 

been identified for fish or aquatic invertebrates exposed to paraquat. Compared to aquatic 

animals, paraquat is orders of magnitude more toxic to aquatic plants. Table A1 includes 

the most sensitive endpoints that may be used for risk assessment purposes (i.e., to derive 

RQs) to represent the acute effects of paraquat on aquatic animals as well as effects of 

paraquat on aquatic plants. Additional information on the toxicity of paraquat to aquatic 

organisms is provided below.

Table A1. Endpoints used to represent acute effects of paraquat on aquatic animals and plants. 

Taxa Species 

(scientific name) 

Measure of 

Effect 

Endpoint Duration

(hours) 

Mean 

conc. (mg 

cation/L) 

Study 

Classification 

Ref. 

(MRID) 

Fish and 

aquatic-phase 

amphibians 

Fowler’s toad 

(Bufo woodhousei 

fowleri) 

Mortality LC50 96 15 Supplemental 40098001 

Aquatic 

invertebrates 

Water Flea 

(Daphnia magna) Immobility EC50 48 1.3 Supplemental 0014473 

Non-vascular 

plants 

freshwater diatom 

(Navicula 

pelliculosa) 

growth 

EC50

96 

0.00040 

Acceptable 42601006 

NOAEC 0.00016 

Vascular 

plants 

Duckweed 

(Lemna gibba) growth 

EC50

14 d 

0.071 

Acceptable 42601003 

NOAEC 0.011 

Fish and Aquatic-phase Amphibians 

Two acute toxicity studies are available where aquatic vertebrates were exposed to 

technical paraquat dichloride: one for the aquatic-phase amphibian fowler’s toad and the 

other for the channel catfish. These two species exhibited orders of magnitude 

differences in sensitivities to paraquat. The fowler’s toad had a 96-h LC50 of 15 mg 

cation/L. 

In this supplemental study, Daphnia magna exhibited a 48h EC50 value of 1.3 mg 

cation/L (MRID 0014473). Several studies are available where aquatic invertebrates were 

exposed to paraquat through formulated products (Table A2). Based on these data, 

paraquat is classified as moderately toxic (i.e., LC50 is between 1 and 10 mg/L) to 

freshwater invertebrates. 

 
Page 62 of 71 

Table A2. 96-h LC50 values for fish and aquatic-phase amphibians exposed to paraquat. All values 

are expressed as paraquat cation. 

Test species (scientific name) Water 

type 

TGAI (T) 

or formula 

(F) 

LC50

(mg 

cation/L) 

MRID Study 

classification 

Longnose killifish (Fundulus similis) SW F >0.72 40228401 supplemental 

Rainbow Trout (Oncorhynchus mykiss) FW F 6.1 162736 supplemental 

Rainbow Trout (Oncorhynchus mykiss) FW F 8.1 162738 supplemental 

Bluegill sunfish (Lepomis macrochirus) FW F 12 40098001 supplemental 

Fowler’s toad (Bufo woodhousei fowleri) FW T 15 40098001 supplemental 

Rainbow Trout (Oncorhynchus mykiss) FW F 16 40098001 supplemental 

Bluegill sunfish (Lepomis macrochirus) FW F 32.7 162737 supplemental 

Channel catfish (Ictalurus punctatus) FW T >100 40098001 supplemental 

No chronic toxicity studies have been identified for fish exposed to paraquat. 

Invertebrates 

One acute toxicity study is available where aquatic invertebrates were exposed to 

technical paraquat dichloride. In this supplemental study, Daphnia magna exhibited a 

48h EC50 value of 1.3 mg cation/L (MRID 0014473). Several studies are available where 

aquatic invertebrates were exposed to paraquat through formulated products (Table A3). 

Based on these data, paraquat is classified as moderately toxic (i.e., LC50 is between 1 

and 10 mg/L) to freshwater invertebrates. 

Table A3. EC50 values for aquatic invertebrates exposed to paraquat. All values are expressed as 

paraquat cation. 

Test species (scientific name) Water 

type 

TGAI 

(T) or 

formula 

(F) 

Duration 

(days) 

EC50

(mg 

cation/L) 

MRID Study 

classification 

brown shrimp (Penaeus aztecus) SW F 4 >0.72 40228401 supplemental 

eastern oyster (Crassostrea virginica) SW F 4 >0.72 40228401 supplemental 

Waterflea (Daphnia magna) FW T 2 1.3 114473 supplemental 

Waterflea (Daphnia magna) FW F 2 1.7 162752 supplemental 

Waterflea (Daphnia pulex) FW F 2 3.6 40098001 supplemental 

Waterflea (Simocephalus serrulatus) FW F 2 3.8 40098001 supplemental 

Stonefly (Pteronarcys californica) FW F 4 >10 40098001 supplemental 

Scud (Gammarus fasciatus) FW F 4 12 40098001 supplemental 

No chronic toxicity studies have been identified for aquatic invertebrates exposed to 

paraquat. 
Page 63 of 71 

Aquatic plants 

Data are available from registrant-submitted and federal laboratory studies involving 

exposures of aquatic plants to paraquat (Table A4). The freshwater diatom (Navicula 

pelliculosa) was the most sensitive non-vascular plant with a 4d EC50 of 0.40 μg/L and a 

corresponding NOAEC of 0.16 μg/L (MRID 42601006). In a study with the vascular 

plant Lemna gibba, the 14d EC50 was 71 μg/L, with a corresponding NOAEC of 11.5 

μg/L (MRID 42601003). 

Table A4. EC50 values for aquatic plants exposed to paraquat. All values are expressed as paraquat 

cation. 

Test species (common) Duration 

(days) 

EC50

(μg cation/L) 

NOAEC 

(μg cation/L) MRID 

Navicula pelliculosa (Freshwater diatom) 4 0.40 0.16 42601006 

Anabaena flos-aquae (Blue-green algae) 5 11 2.3 42601005 

Lemna gibba (duckweed) 14 71 11 42601003 

Selenastrum capricornutum (green algae) 4 230 58 42601002 

Skeletonema cosatum (Marine diatom) 4 2045 158 42601004 

Isochrysis galbana (hapatophyte algae) 10 3600 NA 40228401 

Phaeodactylum tricornutum (marine 

diatom) 10 7200 NA 40228401 

Dunaliella tertiolecta (green algae) 10 14400 NA 40228401 

Chlorococcum sp. (green algae) 10 36000 NA 40228401 

NA = not available 

A2. Terrestrial Organisms 

Paraquat is moderately toxic to birds and mammals on an acute dose basis and slightly 

toxic to birds on a sub-acute dietary basis. For honey bees, paraquat is practically nontoxic. In reproduction studies, paraquat did not impact the reproduction in rats tested up 

to 108 mg cation/kg-diet. Paraquat did impact the reproduction of mallard ducks at 100 

mg cation/kg-diet, resulting in a NOAEC of 30 mg cation/kg-diet for reproductive 

effects. In addition, in a study where pheasant eggs were sprayed with paraquat 

dichloride, effects to the number of eggs hatched and number of 28-d old survivors were 

observed at 0.72 lb cation/A, resulting in a NOAEC of 0.36 lb cation/A. Table A5 

includes the most sensitive endpoints that may be for risk assessment purposes (for 

deriving RQs) to represent the acute and chronic effects of paraquat on terrestrial 

animals. Additional information on the toxicity of paraquat to terrestrial animals is 

provided below. 

 
Page 64 of 71 

Table A5. Endpoints used to represent acute and chronic effects of paraquat on terrestrial animals. 

Taxa 

Species 

(common 

name)

Measure of effect Endpoint 

Mean 

Concentration Units Study Classification

Reference 

(MRID)

Birds, 

terrestrialphase 

amphibians 

and reptiles 

Colinus 

virginianus

(Bobwhite 

quail) 

Mortality LD50 124 

mgcation/kgbw 

acceptable 00029001 

Coturnix 

coturnix 

(Japanese quail)

Mortality LC50 698 

mgcation/kgdiet 

acceptable 00022923 

Anas 

platyrhynchos

(Mallard Duck)

number of eggs 

laid, number of 

normal hatchlings, 

number of 14-d old 

survivors, and % 

viable embryos/set 

NOAEC 30 

mgcation/kgdiet Acceptable 00110455 

Phasianus 

colchicus 

(pheasant)

Number of eggs 

hatched, number of 

28-d old survivors 

NOAEC 0.5 lb 

cation/A Supplemental 43942605 

Mammals 

Rattus 

norvegicus 

(laboratory rat) 

Mortality LD50 91 

mg 

cation/kgbw Acceptable 00054573 

Reproduction 

NOAEL 7.5 mg/kg-bw 

Acceptable 

00126783, 

00149748, 

& 

NOAEC 108 mg/kg-bw 00149749 

Terrestrial 

invertebrates 

Apis mellifera

(Honey Bee) Mortality LD50 52 μg 

cation/bee Acceptable 43942603 

Plants are sensitive to this herbicide. When comparing effects of paraquat on seedling 

emergence and vegetative vigor of plants, vegetative vigor is more sensitive. Table A6 

include the most sensitive seedling emergence and vegetative vigor endpoints for 

terrestrial plants exposed to paraquat. These values may be used to generate RQs. 

Additional information on the toxicity of paraquat to terrestrial plants is provided below. 

Table A6. Endpoints used to represent effects of paraquat on terrestrial plants.

Species NOAEC 

(lb cation/A) 

EC25

(lb cation/A) 

Most sensitive 

parameter Test type MRID 

Corn (monocot) 0.67 >0.67 none Seedling emergence 42639601 

Cocklebur (dicot) 0.37 0.67 Emergence Seedling emergence 42639601 

Corn (monocot) 0.064 0.16 Dry weight Vegetative vigor 42601001 

Cocklebur (dicot) 0.0065 (EC05) 0.014 Dry weight Vegetative vigor 42601001 

 
Page 65 of 71 

Birds 

In an avian acute oral study with Northern Bobwhite quail exposed to technical paraquat 

dichloride, the LD50 value was 124 (99-148) mg cation/kg-bw. In this test, mortality, 

effects to body weight and lethargy were observed in birds dosed with 115 mg/kg-bw. 

The slope of the dose-response curve was 6.6 (3.5-9.7) (MRID 00029001). 

The most sensitive subacute dietary LC50 value was 698 ppm for the Japanese quail. 

Three additional studies with the same formulated product resulted in 5d LC50 values of 

706 ppm for the northern bobwhite quail, 1057 ppm for the ring-necked pheasant and 

2915 ppm for the mallard duck. This subacute study involved exposures of birds to 

29.1% paraquat dichloride (MRID 22923; Table A7). Paraquat is considered moderately 

toxic to birds on an acute oral and sub-acute dietary basis. 

Table A7. Five-day, dietary LC50 values for birds exposed to paraquat (MRID 22923). All values are 

expressed as paraquat cation. 

Test species (scientific name) 

LC50 (95% Confidence 

Interval) (mg 

cation/kg) 

Slope (sd)* MRID 

Japanese quail (Coturnix cortunix) 698 (593-821) 6.059 (1.307) 22923 

Bobwhite quail (Colinus virginianus) 706 (564-873) 5.022 (1.283) 22923 

Ring-necked pheasant (Phasianus colchicus) 1057 (927-1205) 5.846 (1.973) 22923 

Mallard duck (Anas platyrhynchos) 2915 (2471-3518) 6.765 (1.281) 22923 

Avian reproductive toxicity endpoints were submitted for two species: the northern 

bobwhite quail (MRID 00110454) and the mallard duck (MRID 00110455). 

Reproduction of the northern bobwhite was not affected by paraquat at the highest test 

concentration (i.e., 100 mg cation/kg-diet). At that same concentration, several 

reproductive effects were observed in the mallard duck study, including: number of eggs 

laid, number of normal hatchlings, number of 14-d old survivors, and % viable 

embryos/set. The resulting NOAEC for the mallard duck is 30 mg cation/kg-diet. 

In two non-guideline studies, a formulated product containing paraquat dichloride was 

sprayed onto the eggs of pheasant (MRID 43942605) and mallard ducks (MRID 

43942604). In the pheasant study, a decrease in the number of eggs hatched and the 

number of 28-d old survivors was observed at 1.0 lb cation/A, resulting in a study 

NOAEC of 0.5 lb cation/A. In the mallard study, an application rate of 2.0 lb cation/A 

increased the number of embryonic deaths (at days 13 and 19) as well as the number of 

dead embryos in the shell at day 31. At this concentration, the number of hatchlings and 

number of chicks surviving to 28 d were also decreased. The resulting NOAEC was 1.0 

lb cation/A. 

Mammals 

Paraquat is classified as moderately toxic on an acute oral basis to mammals. This is 

based on an acute oral LD50 value of 91 mg cation/kg-bw (MRID 00054573). 

In an acceptable 3-generation reproduction and fertility study, paraquat was administered 
Page 66 of 71 

to Wistar Derived Rats-Alderley Park Strain (MRIDs 00126783, 00149748, & 

00149749). The study NOAEL was 7.5 mg cation/kg-bw (NOAEC = 108 ppm), which 

was the highest test concentration. No LOAEL was established in this study for endpoints 

related to survival, growth or reproduction of rats. At a lower test concentration (3.75 

mg/kg-bw), an increased incidence of alveolar histiocytes was observed in the parents; 

however, this value is not used for deriving chronic mammalian RQs because the 

relationship of this endpoint to survival, growth or reproduction is unknown. 

Terrestrial Invertebrates 

Several toxicity studies are available involving acute exposures of honey to paraquat, 

including contact and oral doses. The most conservative acute contact and oral 48-h 

LD50s are 52 and 22 μg cation/bee, respectively (Table A8). These data indicate that 

paraquat is practically non-toxic (i.e., >11 μg a.i./bee) to honey bees. Available data 

suggest that formulated paraquat is more toxic compared to the TGAI and that paraquat is 

more toxic as an oral dose compared to a contact dose. 

Table A8. Endpoints from acute toxicity studies involving exposures of honey bees to paraquat or 

paraquat dichloride. Values are expressed as paraquat cation. 

48-h LD50

(μg cation/bee) 

Exposure TGAI (T) or 

Formula (F) MRID 

Study 

Classification 

22 oral F 43942603 Acceptable 

>35 contact T 05001991 Acceptable 

37 oral T 43942603 Acceptable 

52 contact F 43942603 Acceptable 

>104 contact T 43942603 Acceptable 

Several acute contact studies have been conducted with honey bees being exposed to 

technical paraquat (or paraquat dichloride). None of these studies have established 48-h 

LD50 values. In a study from the open literature, exposure of honey bees to technical 

paraquat through dusting to 6.04 μg a.i./bee resulted in 2.74% mortality (MRID 36935). 

In two other honeybee acute contact studies with technical paraquat, the 48h LD50 values 

were > 35 and >104 μg/bee (MRID 05001991 and 43942603, respectively). 

In an acute toxicity study with Gramoxone, a formulated product containing paraquat 

dichloride, the 48-h contact LD50 value was 52 μg a.i./bee (MRID 43942603). This value 

suggests that the toxicity of formulated products containing paraquat may be higher than 

TGAI paraquat, where the 48-h acute contact LD50 from the same study was >104 μg 

a.i./bee. 

In another literature study, caged bees were exposed to a direct application of 4 lb a.i./A 

formulated paraquat. After 2 days, approximately 55% mortality was observed (MRID 

00111488). 

In acute oral studies with honey bees, technical and formulated (Gramoxone) paraquat 

yielded oral 48-h LD50 values of 37 and 22 μg a.i./bee (MRID 43942603). When 
Page 67 of 71 

compared to acute contact values for TGAI and formulated paraquat from the same study 

(i.e., >104 and 52 μg a.i./bee, respectively), these data suggest that paraquat is more toxic 

as an oral dose compared to a contact dose. 

Terrestrial Plants 

Supplemental vegetative vigor data involving paraquat (in a formulated product) are 

available for 1 monocot (corn; Zea mays) as well as 6 dicots, the most sensitive of which 

is cocklebur (Xanthium strumarium). For corn, the EC25 and NOAEC values are 0.16 

(95% CI 0.073–0.36) lbs cation/A, and the NOAEC value was 0.064 lbs cation/A. For 

cocklebur, a NOAEC could not be established; therefore the EC05 is used as the endpoint 

for listed dicots. The EC25 and EC05 values for vegetative vigor effects to cocklebur are 

0.014 (95% CI 0.01–0.019) 0.0065 EC05 (95% CI 0.0040–0.01) lbs cation/A, 

respectively. Other dicot test species included: beet (Beta vulgaris), soybean (Glycine 

max), oilseed rape (Brassica napus), velvetleaf (Abutilon theophrasti) and morning glory 

(Ipomoea hederacea). Although these test species were less sensitive than cocklebur, 

their EC25 values were on the same order of magnitude as cocklebur (MRID 42601001). 

Compared to vegetative vigor, seedling emergence is much less sensitive to paraquat. 

Acceptable seedling emergence data are available for 2 species of monocots [corn and 

purple nutsedge (Cyperus rotundus)] and 6 species of dicots (cocklebur, beet, soybean, 

oilseed rape, velvetleaf and morning glory). The only test species that showed effects was 

cocklebur, with an EC25 of 0.67 lb cation/A based on decreased emergence and a 

NOAEC of 0.34 lb cation/A (LOAEC = 0.67 lb cation/A). For all other test species, no 

effects to emergence or dry weight were observed, resulting in NOAEC values of 0.67 lb 

cation/A for those test species (MRID 42639601) 

 
Page 68 of 71 

Appendix B. Output from SIP v1.0 

Table 1. Inputs 

Parameter Value 

Chemical name paraquat 

Solubility (in water at 25oC; mg/L) 464000 

 

Mammalian LD50 (mg/kg-bw) 91 

Mammalian test species laboratory rat 

Body weight (g) of "other" mammalian 

species 

 

Mammalian NOAEL (mg/kg-bw) 7.5 

Mammalian test species laboratory rat 

Body weight (g) of "other" mammalian 

species 

 

Avian LD50 (mg/kg-bw) 124 

Avian test species mallard duck 

Body weight (g) of "other" avian species 

Mineau scaling factor 1.15 

 

Mallard NOAEC (mg/kg-diet) 30 

Bobwhite quail NOAEC (mg/kg-diet) 

NOAEC (mg/kg-diet) for other bird species 

Body weight (g) of other avian species 

NOAEC (mg/kg-diet) for 2nd other bird 

species 

Body weight (g) of 2nd other avian species 

 

 

Table 2. Mammalian Results 

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 79808.0000 79808.0000 

Adjusted toxicity value (mg/kg-bw) 69.9936 5.7687 

Ratio of exposure to toxicity 1140.2183 13834.6493 

Conclusion* 

Exposure through 

drinking water alone is a 

potential concern for 

mammals 

Exposure through 

drinking water alone is a 

potential concern for 

mammals 

 

Table 3. Avian Results 

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 375840.0000 375840.0000 

Adjusted toxicity value (mg/kg-bw) 64.3840 1.4884 

Ratio of exposure to acute toxicity 5837.4796 252516.6874 
Page 69 of 71 

Conclusion* 

Exposure through 

drinking water alone is a 

potential concern for 

birds 

Exposure through 

drinking water alone is a 

potential concern for 

birds 

 

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. 

Therefore, when aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through 

drinking water may contribute to a total exposure that has potential for effects to non-target animals. 

 
Page 70 of 71 

Appendix C. Output from STIR v1.0 

Welcome to the EFED 

Screening Tool for Inhalation Risk 

This tool is designed to provide the risk assessor with a rapid method for determining the potentia

significance of the inhalation exposure route to birds and mammals in a risk assessment. 

 

Input 

Application and Chemical Information 

Enter Chemical Name paraquat 

Enter Chemical Use agriculture 

Is the Application a Spray? (enter y or n) y 

If Spray What Type (enter ground or air) air 

Enter Chemical Molecular Weight (g/mole) 257.2 

Enter Chemical Vapor Pressure (mmHg) 1.73E-15 

Enter Application Rate (lb a.i./acre) 1 

 

Toxicity Properties 

Bird 

Enter Lowest Bird Oral LD50 (mg/kg bw) 124 

Enter Mineau Scaling Factor 1.15 

Enter Tested Bird Weight (kg) 0.178 

Mammal 

Enter Lowest Rat Oral LD50 (mg/kg bw) 90 

Enter Lowest Rat Inhalation LC50 (mg/L) 0.001 

Duration of Rat Inhalation Study (hrs) 6 

Enter Rat Weight (kg) 0.35 

 

Output 

Results Avian (0.020 kg ) 

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 2.39E-11 

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 3.01E-12 

Adjusted Inhalation LD50 1.15E-02 

Ratio of Vapor Dose to Adjusted Inhalation LD50 2.61E-10 Exposure not Likely Significant 

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 9.61E-02 

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 8.34E+00 Proceed to Refinements 

 

Results Mammalian (0.015 kg ) 

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 2.39E-11 

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 3.78E-12 
Page 71 of 71 

Adjusted Inhalation LD50 8.93E-02 

Ratio of Vapor Dose to Adjusted Inhalation LD50 4.24E-11 Exposure not Likely Significant 

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.21E-01 

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 1.35E+00 Proceed to Refinements