Page 3 of 66

Problem Formulation for the Environmental Fate, Ecological 

Risk, Endangered Species, and Drinking Water Exposure 

Assessments in Support of the Registration Review of 

Mesotrione

2- [4-methylsulfonyl-2-nitrobenzoyl]-l,3-cyclohexanedio 

CAS Registry Number: 104206-82-8

PC Code: 122990

Prepared by:

Michael J. Wagman, Biologist

Iwona L. Maher, Chemist U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch VI

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

William P. Eckel, Senior Science Advisor

Amy Blankinship, Senior Scientist

Mark Corbin, ERB 6 Branch Chief 

June 3, 2014

Office of Chemical Safety 

and Pollution Prevention
Page 4 of 66

Table of Contents

1. Executive summary......................................................................................................5

2. Introduction..................................................................................................................9

3. Use Characterization....................................................................................................9

4. Conclusions from Previous Risk Assessments..........................................................10

4.1. Ecological Risk Assessment ......................................................................................10

4.2. Drinking Water Exposure Assessments............................................................. 11

4.3. Clean Water Act Programs................................................................................. 11

5. Environmental Fate and Transport.............................................................................12

6. Receptors....................................................................................................................15

6.1. Effects to Aquatic Organisms ............................................................................ 16

6.2. Effects to Terrestrial Organisms ........................................................................ 20

6.3. Ecological Incidents........................................................................................... 23

7. Exposure Pathways of Concern .................................................................................25

8. Analysis Plan .............................................................................................................26

8.1. Stressors of Concern........................................................................................... 26

8.2. Measures of Exposure ........................................................................................ 26

8.3. Measures of Effect ............................................................................................. 28

9. Endangered Species Assessments.......................................................................... 28

10. Endocrine Disruptor Screening Program ........................................................... 29

11. Preliminary Identification of Data Gaps ............................................................ 30

11.1. Environmental Fate......................................................................................... 30

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

12. References..................................................................................................................39

Appendix A: Label Use Information for Mesotrione (PC Code 122990) by Use Site 41

Appendix B: Summary Data for Mesotrione Related Incidents................................... 44

Appendix C: SIP Inputs and Outputs.................................................................................65
Page 5 of 66

1. Executive summary

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

problem formulation for the ecological risk, environmental fate, endangered species, and 

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

mesotrione. The problem formulation describes the methods planned to be used during 

the completion of drinking water and ecological risk assessments in support of 

registration review and provides an overview of the environmental fate, ecological 

effects, and potential risks associated with the use of mesotrione as well as uncertainties

unique to the risk assessment of mesotrione. This document also identifies additional 

studies that would be beneficial to the conduct of an ecological risk assessment. Major 

findings include:

The following environmental fate data gaps exist for mesotrione: 

 Environmental Chemistry Methods and Independent Laboratory Validation 

on Soil, Water, and Sediment (OCSPP Guideline 850.6100): The 

environmental chemistry method for mesotrione residues of concern (parent plus 

major degradates) in soil, water, and sediment as well as independent laboratory 

validation of the methods are required to support monitoring for mesotrione 

residues and current and newly submitted environmental fate and ecological 

effects data. This is considered a major data gap.

 Anaerobic soil metabolism for Mesotrione (Guideline 835.4200): No data are 

available for anaerobic soil metabolism. It is expected that mesotrione anaerobic 

soil metabolism is pH dependent hence data for soils with typical pH for 

mesotrione use areas are recommended.

 Aerobic Aquatic Metabolism for Mesotrione (Guideline 835.4300): 

This data for mesotrione are limited to two British natural water-sediment systems 

with experimental pH 7.9 and 6.9.These experimental pHs are higher than those 

of most of the many soils used in the aerobic soil metabolism studies, and we 

might expect longer half-lives at lower aquatic system pHs. In addition, it is not 

certain that the microbial makeup of the British water-sediment systems is similar 

to the one in the US. Therefore, a new study conducted on a US natural-water 

sediment system at a variety of pHs typical for mesotrione use areas is needed. 

Study should be conducted until patterns of decline of parent and patterns of 

formation and decline of transformation products are established. For the purpose 

of modeling a very conservative approach will be taken in selecting the input 

parameters if the data are not available.

 Anaerobic aquatic metabolism for Mesotrione (Guideline 835.4400): 

Currently the data for mesotrione are limited to one flooded Radford U.S. soil 

system with purified water (two radiolabels and pH 6.9 to 7) and the obtained 

half-life is comparable to the aerobic soil metabolism rate, and essentially the 

same as those from the two different aerobic aquatic systems. These results 
Page 6 of 66

indicate that metabolism progresses under suboxic conditions, and may be more 

influenced by pH than lower oxygen content. An additional anaerobic aquatic 

metabolism study is requested to facilitate our understanding of mesotrione 

metabolism under anaerobic aquatic conditions in natural systems in variety of 

pHs. Study should be conducted until patterns of decline of parent and patterns of 

formation and decline of transformation products are established. For the purpose 

of modeling a very conservative approach will be taken in selecting the input 

parameters if the data are not available. 

 Aerobic Soil Metabolism for MNBA (OCSPP Guideline 835.4100): No 

aerobic soil metabolism data are available for MNBA alone and therefore it is 

uncertain if there is concern for exposure from MNBA from mesotrione use. Fate 

data indicate that MNBA would be a major product in many soils in which corn

and other major use sites are grown. The data are needed to alleviate the 

uncertainty associated with the chemical behavior in soil and availability for 

potential transport to surface water and availability for exposure. The aerobic soil 

metabolism study should be conducted at a variety of pHs. 

 Aerobic Aquatic Metabolism for MNBA (OCSPP Guideline 835.4300): The 

Agency has no data on the fate of MBNA under aerobic aquatic conditions. The 

longer MBNA persists in the soil, the greater the opportunity for it to move into 

surface water, where its fate is unknown and where it potentially could impact 

aquatic species. Data from this study would address the uncertainty in regards to 

MNBA behavior in the aquatic environment under aerobic conditions. The study 

should be conducted at a variety of pHs.

 Analytical Methods (OCSPP Guideline 835.6100) with the Storage Stability 

Characteristics for Surface Water Monitoring (MRID 47244503): It is 

requested for the purpose of upgrading an unacceptable Surface Water Monitoring 

study to supplemental because surface water samples were stored for up to 18 

months before analysis. If upgraded, the available surface water data could be 

used for qualitative characterization or even used more quantitatively (chronic 

exposure results) in the risk assessment.

 Drinking Water Treatment Method for MRID 47578301 (OCSPP Guideline 

not Available): Information on the types of treatment that were used in surface 

water samples from the monitoring study (MRID 47244503) to obtain drinking 

water are requested. 

Data are requested for the following mesotrione ecological data gaps:

Estuarine/Marine Invertebrate Acute Toxicity Study using MNBA (OCSPP 

Guideline 850.1035): Mesotrione is significantly more toxic on an acute basis to 

estuarine/marine invertebrates compared to freshwater invertebrates. Data for the 

degradates indicate that they are substantially (~5.3—6.3x) more toxic than parent 

mesotrione to daphnids. If the degradate MNBA is also similarly more toxic to 
Page 7 of 66

mysids than parent mesotrione, our calculations suggest that adverse acute effects 

for estuarine/marine invertebrates could occur at surface water concentrations 

near 1/20th the peak mesotrione EECs calculated in past assessments (USEPA, 

2013; D408583). A preliminary Individual Effect Chance (IEC) analysis 

conducted for this problem formulation indicates that the chance of an adverse 

effect to an individual organism is 0.2% for exposure to parent and may be up to 

4.3% for the metabolites. These calculations suggest a potential for risk to listed 

species of saltwater invertebrates. Since AMBA is usually produced under 

anaerobic conditions, it is not expected that there would be a likely exposure 

pathway for saltwater invertebrates in the water column and therefore, an acute 

mysid toxicity test with this degradate is not requested at this time. However, 

the lack of an acute mysid toxicity study with the degradate MNBA remains a 

major data gap, and this study is requested. In the absence of this information, 

EPA may rely on the differential in the acute daphnid toxicity studies between 

parent mesotrione and the MNBA degradate to calculate an acute mysid endpoint 

for MNBA’s effects to saltwater invertebrates and compare that to expected 

MNBA EECs in the risk assessment. However, it is uncertain whether this 

approach would underestimate or overestimate risk to saltwater invertebrates.

 Estuarine/Marine Invertebrate Chronic Toxicity Study (OCSPP Guideline 

850.1350): Mesotrione has outdoor uses that may result in exposure to 

estuarine/marine invertebrates. Mysids are the most sensitive aquatic animal on an 

acute basis and are significantly (~2 orders of magnitude) more sensitive than 

daphnids. No acceptable chronic data are available for either freshwater or 

saltwater invertebrates, therefore an acute to chronic ratio (ACR) approach cannot 

currently be used. Since the mysid is significantly more acutely sensitive than the 

daphnid, the lack of a chronic saltwater invertebrate study is a major data gap. 

EPA may use acute and chronic estuarine/marine invertebrate data in an ACR 

approach to estimate a chronic freshwater invertebrate endpoint. In the absence 

of these data, risk cannot be precluded for aquatic invertebrates.

 Terrestrial Plant Seedling Emergence Tier II Study (OCSPP Guidelines 

850.4100) with the degradate MNBA on onion, lettuce and cabbage: No data 

are available for the toxicity of the metabolite MNBA to terrestrial plants. Since 

MNBA is a major degradate that forms at a rate up to 60% of parent in aerobic 

soil metabolism studies to which non-target plants may be exposed via runoff, 

these data are needed to evaluate the risk posed to terrestrial plants from runoff 

containing the degradate. Testing should be conducted using the most sensitive 

monocot (onion) and dicot (lettuce and cabbage) species as determined from the 

parent mesotrione seedling emergence data.

 

The following ecological data gaps for mesotrione are also noted, but as new data would 

likely not change the risk assessment, the data are not needed at this time:
Page 8 of 66

 Freshwater Invertebrate Life Cycle (OCSPP Guideline 850.1300): A 

submitted chronic daphnid study was previously deemed Acceptable. However, 

this study (MRID 44505010) had several issues confounding its results (including 

precipitates and extremely acidic conditions in high concentrations and 

inconsistent effects at lower concentrations) which has resulted in its downgrade 

to Supplemental—Qualitative. The lack of an acceptable chronic freshwater 

invertebrate study is a data gap. However, on an acute basis the estuarine/marine 

invertebrate (mysid) was much more sensitive (2-3 orders of magnitude) to 

mesotrione than the freshwater invertebrate (daphnid). Previous assessments 

indicate that maximum expected environmental concentrations are substantially 

lower than acute freshwater invertebrate endpoints and levels of concern were not 

exceeded. Therefore, if a chronic mysid study is available at the time of the risk 

assessment, an acute to chronic ratio (ACR) can be generated from the acute and 

chronic mysid data and applied to the acute daphnid data to estimate a chronic 

daphnid endpoint. 

 Estuarine/Marine Fish Early-Life Stage Toxicity Study (OCSPP Guideline 

850.1400): An estuarine/marine fish early life-stage test using the TGAI has not 

been submitted, since it was not considered to be necessary based on previous risk 

assessments for mesotrione. An ACR approach cannot be used because the 

endpoints in the acute data are nondefinitive. In the absence of these data EPA 

will use the rainbow trout early life stage data as a surrogate for the chronic 

saltwater fish. The utility of an estuarine/marine fish ELS study for the risk 

assessment is considered low at this time, given the predicted difference between 

the exposure estimates from previous assessments and the toxicity estimate 

derived using the freshwater fish ELS study. Therefore, an estuarine/marine fish 

early life stage toxicity test is not requested at this time.

 Acute Avian Oral Toxicity Study—Passerine species (OCSPP Guideline 

850.2100): No data are available for passerine species, which may be more 

sensitive than the tested bobwhite species. However, the LD50 and LC50 data for 

the mallard and bobwhite were all nondefinitive (“greater than”) values, and there 

were no sublethal effects in any acute or subacute avian study. Maximum use 

rates for currently registered uses of mesotrione are expected to result in residues 

in dietary items that are below any levels of concern for birds using the 

nondefinitive acute endpoints. Therefore, a passerine study is not needed at this 

time. However, if there is an expansion of the Experimental Use Permit (EUP) on 

soybeans (which has a maximum annual application rate that is three times other 

currently registered uses) to a broader use pattern or if other new registrations 

with higher application rates are proposed, the lack of passerine data would be 

considered a major data gap.

Major uncertainties:
Page 9 of 66

Major uncertainties are raised by the lack of chronic aquatic invertebrate data for parent 

mesotrione and both terrestrial plant and acute estuarine/marine invertebrate data for 

mesotrione’s major degradate MNBA. Lack of fate data for both parent mesotrione and

MNBA is also a major uncertainty. Given the large number of reported terrestrial plant 

incidents for this chemical, damage to non-target plants from spray drift from mesotrione 

formulations is of particular concern. 

2. Introduction

Mesotrione is a tri-ketone compound used as a systemic pre-emergence and postemergence herbicide for "the selective contact and residual control of broadleaf weeds."

(Callisto label, EPA Reg. No. 100-1131). It is absorbed from the soil by emerging weeds 

and through the foliage of emerged weeds. According to the registrant, it acts by 

inhibiting the enzyme p-hydroxyphenylpyruvate dioxygenase (HPPD), which is 

necessary for carotenoid biosynthesis resulting in photodegradation of the affected plant’s 

chlorophyll by sunlight. Mesotrione is a synthetic analog of leptospermone developed to 

mimic the effects of that natural herbicide produced in some members of the myrtle 

(Myrtaceae) family (Cornes, 2005).

There are currently 27 Section 3 registered products, 14 Section 24c (Special Local 

Need—SLN) registered products and 1 section 5 EUPs for mesotrione. 

EFED evaluated the most recent ecological risk assessments for mesotrione in association 

with the updated toxicity, exposure, and usage information to determine if sufficient data 

are available and if further updates are needed to support registration review. Recent risk 

assessments include a 2013 assessment modifying the uses on corn, sugarcane, grass 

seed, cranberry and grain sorghum (USEPA, 2013a; D408583) and a 2008 Experimental 

Use Permit and New Use assessment on HPPD-tolerant soybeans (USEPA, 2008b; 

D357888). In addition, EFED considered the latest Agency science policies and risk 

assessment methodologies. 

3. Use Characterization

Currently registered uses include asparagus, corn (field corn, field corn for silage, yellow

popcorn, and sweet corn), bush and cane berries (blueberries, lingonberries, black and red

raspberries, and blackberries), cranberries, flax, sod farms, grass for seed, millet (pearl 

and proso), oats, okra, rhubarb, sorghum (sweet and grain), sugarcane, and soybean. 

Registered non-agricultural use sites include: golf courses, lawns, ornamental turf, 

ornamental flowering plants, buildings and recreational areas. For currently registered 

uses, the maximum single application rates range from 0.168 lb a.i./A to 0.25 lb a.i./A 

and seasonal application rates range from 0.188 to 0.5 lb a.i./A. Appendix A provides 

additional label use information for mesotrione, organized by use site. The EUP on 

soybeans has an annual application rate three times higher than any registered application 

rate. The annual EUP rate is 1.5 lbs ai/A and allows for three applications made in 14-d 
Page 10 of 66

interval; i.e. 0.75 lb a.i/A, 0.375 a.i/A, and 0.375 a.i/A, respectively. The highest usage, 

in terms of total pounds applied and total acres treated with mesotrione is on corn with 

approximately 98% of total usage (most usage on field corn, but also substantial usage on 

sweet corn, BEAD Chemical Profile, USEPA 2014). Other use sites with substantial 

usage (average >5% of crop) of mesotrione include blueberries and sorghum (BEAD 

Screening Level Usage Analysis, USEPA, 2013b). 

Mesotrione is applied both pre- and post-emergence and is registered for both ground and 

aerial applications.

4. Conclusions from Previous Risk Assessments

4.1. Ecological Risk Assessment 

The last ecological risk assessment conducted on mesotrione was the 2013 new use 

assessment adding aerial application for corn and sugarcane, increasing the number of 

applications and application rate for grasses grown for seed, adding chemigation for 

cranberry and modifying application timing for use on grain sorghum (USEPA, 2013a). 

This assessment did not include a new assessment for terrestrial animals since the label 

changes did not impact the overall risk conclusions compared to previous assessments as 

the proposed maximum application rates were lower than already assessed rates on 

different use sites. The assessment did evaluate risk to plants and included a spray drift 

analysis to characterize the extent of risk to off-field terrestrial plants from spray drift for 

ground compared with aerial applications. The aquatic assessment was refined using Tier 

II models. Risks of concern were identified for listed and non-listed vascular aquatic 

plants from the sugarcane and cranberry use patterns, for listed vascular aquatic plants 

from the corn use, and for listed and non-listed monocots and dicots from all proposed 

uses. No other taxa were concluded to be at risk. No data gaps were noted in this risk 

assessment. 

In 2008 EFED conducted a combined Section 3 New Use Assessment on Soybeans and a 

Section 5 Experimental Use Permit (USEPA, 2008b) which included an annual 

application rate of 1.5 lbs a.i./A (three times the highest previously registered rate for any 

use site) on soybeans. For the proposed Section 3 use (applied at 0.188 lbs ai/A), the 

proposed application rate was equal to the lowest previously registered rate, and risks of 

concern were identified for all categories of terrestrial plants except for non-listed 

monocots in adjacent dry upland areas exposed to mesotrione in runoff. However, for the 

EUP rate, levels of concern were exceeded for all categories of terrestrial and aquatic 

plants except for non-vascular aquatic plants. Additionally, the Section 5 assessment 

indicated acute risk to listed species of birds (small birds feeding on short grass only) and 

chronic risk (all size classes of birds feeding on short grass or tall grass). 
Page 11 of 66

4.2. Drinking Water Exposure Assessments

The latest surface water exposure modeling for the drinking water exposure assessment

for the EUP in 2008 was based on the Mississippi Soybean scenario. Since then,

Estimated Drinking Water Concentrations (EDWCs) for ground water have been 

simulated using the newly available PRZM-GW model (US EPA, 2014; D415369). The 

total annual rate modeled was 1.5 lbs ai/A/yr (3 apps, 14-d interval, 0.75 lb a.i/A, 0.375 

a.i/A, 0.375 a.i/A, respectively) (USEPA, 2008, D354510). Modeling results are 

presented in Table 1 below.

Table 1. Estimated Drinking Water Concentrations (EDWCs) for Mesotrione

Drinking water 

source (model)

Use

(modeled rate)

1-in-10 year 

acute (μg/L)

1-in-10 year 

chronic (μg/L)

30- year average 

(μg/L)

Surface waterA

(PRZM/EXAMS)

Soybean-EUP

(1.5 lb ai/A) ground 38.1 5.1 2.2

Ground waterB

(PRZM-GW)

Soybean-EUP/WI corn

(1.5 lb ai/A) ground 26.2 18.4 ≤18.4

Ground waterA

(SCI-GROW)

Soybean-EUP

(1.5 lb ai/A) ground 0.54 ≤0.54 ≤0.54

A Source: US EPA, 2008; D354510.

B

 Source: US EPA, 2014, D415369

In addition, the registrant submitted a community water system (CWS) surface water 

monitoring study for mesotrione (MRID 47244503), conducted in the Midwest, primarily 

in Illinois, Indiana, and Ohio. This study indicates that 18% of raw surface water samples 

had detections of mesotrione. The annual average raw water concentration of mesotrione 

was 0.22 pg/L in 2005 and 0.32 pg/L in 2006. The maximum mesotrione concentration 

was 2.4 pg/L in untreated water with detectable residues lasting for at least several weeks. 

This study was deemed unacceptable (upgradable to supplemental upon submittal of

information on the analytical methods and storage stability characteristics since samples 

were stored up to 18 months before analysis). If upgraded, the results of the study can be 

incorporated into mesotrione drinking water assessments for qualitative characterization

or potentially be used more quantitatively (chronic exposure results).

The same monitoring study had no detections of mesotrione in finished water. The 

sampling was conducted at the same time and in the same locations as that for untreated 

water, but there is no information as to the types of treatment that were used in sampled 

systems. Preliminary review of a submitted chlorination study (MRID 47578301) 

indicates that upon addition of chlorine mesotrione is rapidly transformed to the 

degradate MNBA.

4.3. Clean Water Act Programs

Mesotrione is not identified as a cause of impairment for any water bodies listed as 

impaired under section 303(d) of the Clean Water Act. No Total Maximum Daily Load 
Page 12 of 66

(TMDL) criteria have been developed for mesotrione. Aquatic benchmarks have been 

established for mesotrione and are available at 

http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm. Any data 

submitted or otherwise located as part of the registration review process may be used to 

update aquatic life benchmarks if applicable. 

5. Environmental Fate and Transport

This chemical has acidic ionic property (pKa of 3.12; is 40 times more acidic than acetic 

acid) that has a major influence on the behavior of mesotrione in environmental media at 

different pHs. Mesotrione appears to be mobile based on Koc of 16.5 to 390 L/kg, and 

presents limited persistence in soil and aquatic environments. The lower the pH, the 

higher the sorption to soil organic matter. In soil, mesotrione dissipates through aerobic 

metabolism with half-lives ranging from 5.5 days to 32 days that are increasingly rapid in 

acidic environments. The lower the pH, the higher the sorption to soil organic matter and 

the longer the corresponding aerobic soil half-life. Mesotrione major routes of dissipation 

include leaching into the soil profile, runoff into surface water, microbial-mediated 

degradation in soil and water and photodegradation on soil.

In the terrestrial field studies in IL, MS, and NC (MRID 44505205, 44505206, and 

44505207), mesotrione dissipated rather rapidly with half-lives ranging from 2 to14 days 

and did not find any residues below 6 inches. In NC small-scale prospective groundwater 

study, mesotrione and its degradates were detected above the limit of quantitation only in 

soil-pore water at the 3 foot depth. Throughout the 38 months of the study duration, no 

detections of parent or degradates were made at any deeper lysimeters or in ground water. 

These findings are indicative that the parent is not very likely to leach into ground water 

in soil of a moderate to low permeability (MRID 47418901). Because mesotrione has 

properties and characteristics associated with chemicals detected in ground water, this 

study result does not preclude the fact that mesotrione use may result in groundwater 

contamination in areas where soils are very permeable, and the water table is shallow. 

Mesotrione may reach surface water through spray drift during its application and runoff. 

In aquatic environments, mesotrione is stable to hydrolysis and has limited photolysis but 

degrades rapidly through aerobic (half-lives (t1/2) = 3 to 6 days) and anaerobic 

metabolism (t1/2 = 4 days). Based on physicochemical properties, mesotrione is not 

expected to bioconcentrate. Likewise, it is not expected to volatilize from soil. A 

selection of mesotrione environmental fate and transport properties is summarized in 

Table 2 below.

Table 2. Physical Chemical and Environmental Fate Properties of Mesotrione.

Parameter Value Source

Selected Physical/Chemical Parameters

Chemical Structure MRID 44505131 
Page 13 of 66

Table 2. Physical Chemical and Environmental Fate Properties of Mesotrione.

Parameter Value Source

Empirical Formula C14 H13 O7NS D253844

IUAPC Name 2- [4-methylsulfonyl-2-nitrobenzoyl]-l,3-

cyclohexanedio

D253844

CAS Name

CAS No. 104206-82-8 D253844

Molecular Weight 339 g/mole Product Chemistry

Physical state opaque solid DP Barcode D253844

Vapor pressure 4.30 x 10-8torr DP Barcode D263245

Aqueous solubility (25C) 1,600 mg/L DP Barcode D263245

Dissociation constants (pKa ) pKa = 3.12 at 20" C DP Barcode D253844

pH at 25 oC 3.4 (for a 1% by wt. dispersion in water) DP Barcode D253844

Henry’s Law Constant 5.1 x 10-7 Pa-m3/mol DP Barcode: D263245

Log octanol-to-water partition 

coefficient(log POW) at 20" C

log Pow = 0.1 1 in unbuffered water

log Pow = 0.90 in pH 5 buffer

log Pow < -1 at pH 7 and 9 buffered water

DP Barcode D253844

Persistence

Hydrolysis half-life (pH 5, 7, 9) Stable MRID: 44373529

Aqueous photolysis half-life 84 days 

(dark corrected; 12 hr light/12 hr dark 

cycle)

MRID: 44537108

Soil photolysis half-life 29 days MRIDs: 44505128 and

45196005

Aerobic soil metabolism halflife (range in days)5 to 32 days (mean 28.9 days) 

Measured in 17 soils and found to be 

strongly pH correlated

MRID: 44505129

DP Barcode D253844

Anaerobic aquatic metabolism 

half-life (avg. of two 

radiolabels in total system)

4 daysA MRIDs: 44505131 and 

44505132

Aerobic aquatic metabolism 

half-life (total system)

3 days (pH=7.9) and 6 days (pH=6.9) in 

British natural water-sediment systems

MRID: 45196011

Mobility

Adsorption/desorption (Kf-oc 

range)

16.5 to 390 mL/g

Soil mobility was measured in 17 soils and 

found to be strongly pH correlated. 

MRIDs: 44505204

Field Dissipation

Terrestrial Field Dissipation 2 to 14 days (did not find any residues 

below 6 inches soil depth)

MRIDs: 44505207 & 

44505 125, 44505206,

44505205 & 44505126

A- The system was a flooded Radford series silt loam soil under moderately oxidizing to moderately reducing 

(suboxic) conditions.

Mesotrione appears to metabolize to two major degradates MNBA (2-nitro-4-

methylsulfonylbenzoic acid) and AMBA (2-amino-4-methylsulfonylbenzoic acid), in 

addition to C02. MNBA was detected in the aerobic soil metabolism study at up to 60%, 

and AMBA in the anaerobic aquatic metabolism study at up to 60%. MNBA is formed by 
Page 14 of 66

an oxidative process when the cyclohexane ring portion of the mesotrione molecule splits 

away. AMBA is the amine product formed by reduction of the MNBA nitro group. 

AMBA aerobic soil metabolism half-life ranged from 16 to 27 days (MRID 44901714) 

and its only identified metabolite was carbon dioxide. Data were insufficient to 

determine the range of variation of half-life with pH. Under suboxic conditions, half-lives 

for AMBA could not be reliably established from formation and decline curve because of 

study deficiencies (D253844); a crude estimation half-life for AMBA under the existing 

study conditions is 110 days, but may be longer with greater restriction of oxygen.

Because of the acidic nature of MNBA, its sorption is likely to be affected by pH. The 

aerobic soil metabolism half-life of MNBA can only be crudely estimated from the 

available data and are highly uncertain. In at least two aerobic soils, MNBA half-lives 

appeared to be measured in one to several months, but seemed to be much shorter in 

others (D253844). Neither of the degradates were detected at any sampling interval of 

three terrestrial field dissipation studies conducted prior 1997. MNBA was not detected 

in any soil samples in an NC Prospective Ground Water (PGW) study. In the same study, 

AMBA was detected in soil on days 3 through 28, at concentrations 2.4 to 6.4 ppb, with a 

peak at 14 days and return to the LOQ level of 2.0 ppb by 64 days. Mesotrione and both 

degradates were detected in soil-pore water at the 3 foot depth (MRID 47418901). These 

degradates were not included in the previous risk assessments. Their physicochemical 

properties and available environmental fate properties are summaries in Table 3 below.

Their maximum percent formation are presented in Table 4.

Table 3. Selected Physicochemical Properties of MNBA and AMBA

Chemical Name MNBA: 4-(methylsulfony1)-2-nitrobenzoic acid

AMBA: 2-amino-4-(methylsulfonyl)benzoic acid 

CAS No. MNBA: 110964-79-9

AMBA: Not Available

Molecular Mass (g/mol) MNBA: 245.21

AMBA: 215.22

Acid Ionization Constant in

Water (Ka) and pKa

MNBA: 1.6 x (pKa= 1.8)

AMBA: 9.3 x (pKa = 4.0) 

Approximate values calculated from solubility and pH in

unbuffered water given in next row below:

Solubility in water MNBA: 4.0 mg/mL in unbuffered water (final pH 2.0)

 14.2 mg/mL at pH 2.6

 32.4 mg/mL at pH 2.9 Note: 

exceeds buffer capacities at higher pH

AMBA: 0.3 mg/mL in unbuffered water (final pH 3.5)

 1.8 mg/mL at pH 4.7

 23 mg/mL at pH 6.1

Octanol/Water Partition Coefficient 

(Pow)

MNBA: log Pow = -1.3 in unbuffered water

 log Pow = -2.6 in pH 5 buffer

AMBA: log Pow = 0.32 in unbuffered water

 log Pow = -0.30 in pH 5 buffer

Vapor Pressure MNBA: 6.4 x l0-7 Pa (4.8 x 10-9 Torr)

AMBA: 4.7 x 10-7 Pa (3.5 x 10-9 Torr)

Henry's Law Constant (Calculated from 

vapor pressure and solubility above) in 

unbuffered water:

MNBA: 3.9 x 10-8 Pa-m3/mol (3.9 x 10-13 atmm3

/mol)

AMBA: 3.4 x 10-7 Pa-m3/mol (3.4 x 10

-l2 atm-m3

/mol)
Page 15 of 66

Table 3. Selected Physicochemical Properties of MNBA and AMBA

Adsorption/desorption (Kf-oc) MNBA: 3 and 6 mL/g (US soils), 

 less than 20, 6, and 10 mL/g (European soils)

AMBA: 45, 23, 122, 51, and 18 mL/g 

Aerobic soil metabolism half-life AMBA: 16, 27, and 20 days (effect of pH could not be 

determined)

Table 4. Environmental Degradates of Mesotrione. 

Degradate/

Molecular formula Chemical 

Structure

Max Percent Formation in 

%AR (Study) Source/Study MRID

MNBA

4-(methylsulfony1)-2-

nitrobenzoic acid

7.9% (6 d)

6-8%

57.2% (28 d)

27.9% (7 d) US sandy loam

46.8% (7 d) French loam soil

Aerobic Soil Metabolism./44373531

Aerobic Soil Metabolism./45196006

Aerobic Soil Metabolism/44505129

Aerobic Soil Metabolism/44505208

Aerobic Soil Metabolism/44505208

AMBA

2-amino-4-

(methylsulfonyl)benzoic 

acid

9.7% (23 d)

6-8%

ca. 60% (14 d)

4.2% (7 d)

Aerobic Soil Metabolism./44373531

Aerobic Soil Metabolism./45196006

Anaerobic Aquatic Metabolism/44505131

Aerobic Soil Metabolism/44505208

It is important to note that because of specific study shortcomings, their partial nature, the 

existence of several closely related series of studies, and the pH dependence of 

mesotrione and degradates, individual DERs cannot be used in isolation, but must be 

taken in the context of all submitted data (US EPA, 2001; D253844).

6. Receptors

Tables 5 through 10 provide a summary of the aquatic and terrestrial taxonomic groups, 

and the most sensitive surrogate species tested to characterize the potential acute and 

chronic ecological effects of mesotrione and its degradates, AMBA and MNBA. In 

addition, the tables provide a preliminary overview of the potential acute toxicity of 

mesotrione by providing the acute toxicity classifications. 

Much of the aquatic data had issues with precipitates and highly acidic conditions, most 

pronounced in the highest treatments. Based on the available ecotoxicity information, 

mesotrione is practically non-toxic to all freshwater animals and estuarine/marine fish 

and slightly to moderately toxic to estuarine/marine invertebrates. The chronic freshwater 

invertebrate study (MRID 44505010) is being downgraded to supplemental-qualitative 

due to pH, solubility issues, and significant differences in bodyweights even at the lowest 

concentrations (i.e., NOAEC < 97,000 ppb), though it could not be determined from the 

limited data whether these differences were treatment related since only two treatment 
Page 16 of 66

groups had organisms survive to test termination with 46% inhibition at the 97,000 ppb 

treatment group but only 18% inhibition in the 180,000 ppb treatment group. 

Additionally, no chronic data are available for mesotrione’s effects to estuarine/marine 

invertebrates. For aquatic plants, mesotrione was significantly more toxic (two orders of 

magnitude) to vascular plants than to non-vascular plants. 

Mesotrione’s degradates, AMBA and MNBA, were slightly more toxic to freshwater fish 

and invertebrates, though still practically non-toxic, and were somewhat less sensitive to

green algae than parent mesotrione. No degradate data were available for the most 

sensitive aquatic taxa to parent mesotrione, estuarine/marine invertebrates and aquatic 

vascular plants. 

For terrestrial animals, the available data indicate that mesotrione is practically non-toxic 

to all taxa on an acute basis. As expected for an herbicide, mesotrione’s end-use products 

appear particularly toxic to terrestrial plants. Additional detail is included in the 

following tables. No information is available on the toxicity of the major metabolites, 

AMBA and MNBA to terrestrial plants, birds or insects, though the available data 

indicate that these degradates are practically non-toxic to mammals on an acute basis. 

6.1. Effects to Aquatic Organisms

Table 5. Summary of the Most Sensitive Endpoints from Aquatic Animal Toxicity Studies 

for Mesotrione (toxicity endpoints in ppb)

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity 

Value

(all units in 

terms of 

measured 

active 

ingredient)

Acute 

Toxicity 

Classification

Source

(Classification)

Freshwater fish1

Acute

Rainbow Trout

Oncorhynchus 

mykiss

96-Hr LC50 > 

120,000

Practically 

non-toxic

44373510

(Acceptable)

Chronic 

(Early 

LifeStage)

Fathead Minnow

Pimephales 

promelas

32-Day 

NOAEC = 

11,000

LOAEC = 

23,000

(Endpoint: 

length)

N/A 44505011

(Acceptable)

Freshwater 

invertebrates

Acute Waterflea

Daphnia magna

48-Hr EC50 = 

840,000

Practically 

non-toxic

44373511

(Acceptable)

Chronic Waterflea

Daphnia magna

NOAEC < 

97,000

LOAEC = 

97,000

Endpoint: 

Body Weight

N/A

44505010

(Supplemental--

Qualitative)
Page 17 of 66

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity 

Value

(all units in 

terms of 

measured 

active 

ingredient)

Acute 

Toxicity 

Classification

Source

(Classification)

Estuarine/marine 

fish

Acute

Sheepshead 

minnow 

Cyprinodon 

variegates

96-Hr LC50 > 

100,000

NOAEC = 

100,000

Practically 

non-toxic

44505007

(SupplementalQualitative)

Chronic No Data NOAEC = 

11,0002 N/A N/A2

Estuarine/marine 

invertebrates

Acute Mysid Shrimp

Mysidopsis bahia

96-Hr LC50 = 

3,300 

Slope = 1.46

Moderately 

Toxic

44505008

(Acceptable)

Acute Pacific Oyster 

Crassostrea gigas

48-Hr EC50 = 

72,000 Slightly Toxic 44505009(Acceptable)

Chronic No Data No Data N/A N/A

1 Freshwater fish may be surrogates for aquatic-phase amphibians.

2

In the absence of additional data, the freshwater fish chronic NOAEC of 11,000 ppb will be used as a surrogate for the 

saltwater fish chronic endpoint.

Table 6: Summary of Most Sensitive Aquatic Plant Toxicity Data from the Use of Mesotrione, Alone 

and with Adjuvants (toxicity endpoints in ppb)

Surrogate 

Species No Adjuvant1 AgriDex2 Agral 903

VASCULAR Duckweed

Lemna gibba

114-D EC50 = 17.7

 NOAEC = 7.5

EC50 = 6.7

NOAEC = 2.4

EC50 = 7.1

NOAEC=3.8

NONVASCULAR

Green Alga

Selenastrum 

capricornutum

120-Hr EC50 = 1900

NOAEC = 820 No Data No Data

1 The endpoints with no adjuvant were reported in the DERs for duckweed (MRID 44505123) and green algae (MRID 

44505124)

2 The duckweed endpoint with the AgriDex adjuvant was reported in the DER for MRID 46562907.

3 The duckweed endpoint with the Agral 90 adjuvant was reported in the DER for MRID 46562906.

Table 7. Summary of the Most Sensitive Endpoints from the Available Aquatic Toxicity 

Studies for Degradate AMBA (units in ppb)

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(all units in terms 

of measured 

active ingredient)

Acute

Toxicity 

Classification

Source

(Classification)

Freshwater fish1 Acute

Rainbow Trout

Oncorhynchus 

mykiss

96-Hr LC50 = 

150,000

Practically 

non-toxic

44901702

(Acceptable)

Freshwater 

invertebrates Acute Water FleaDaphnia magna

48-Hr EC50 = 

160,000

Practically 

non-toxic

44901704

(Acceptable)
Page 18 of 66

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(all units in terms 

of measured 

active ingredient)

Acute

Toxicity 

Classification

Source

(Classification)

Aquatic plants 

and algae

Nonvascular

Green Algae

Selenastrum 

capricornutum

72-Hr IC50 = 8,900

NOAEC = 3,700 N/A 44901709(Supplemental)

1 Freshwater fish may be surrogates for aquatic-phase amphibians.

Table 8. Summary of the Most Sensitive Endpoints from the Available Aquatic Toxicity 

Studies for Degradate MNBA (units in ppb)

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(all units in terms 

of measured 

active ingredient)

Acute

Toxicity 

Classification

Source

(Classification)

Freshwater fish1 Acute

Rainbow Trout

Oncorhynchus 

mykiss

96-Hr LC50 > 

120,000

Practically 

non-toxic

44901703

(Acceptable)

Freshwater 

invertebrates Acute Water FleaDaphnia magna

48-Hr EC50 = 

134,000

Practically 

non-toxic

44901705

(Acceptable)

Aquatic plants 

and algae2

Nonvascular

Green Algae

Selenastrum 

capricornutum

No Data N/A No Data)

1 Freshwater fish may be surrogates for aquatic-phase amphibians.

Although there are no chronic data for saltwater fish, the test chemical was not any more 

acutely toxic to saltwater fish than freshwater fish and the chronic freshwater fish 

endpoint is several orders of magnitude above the expected environmental concentrations 

from recent assessments. Therefore additional chronic data on saltwater fish would be 

unlikely to add significant value to the risk assessment. In the absence of additional data, 

the chronic freshwater fish endpoint will be used as a surrogate for chronic saltwater fish 

in the risk assessment. The lack of chronic estuarine/marine invertebrate data is a major 

data gap. Since the mysid shrimp data suggests that estuarine/marine invertebrates are

much more (two orders of magnitude) acutely sensitive than freshwater invertebrates, the 

lack of data establishing a definitive chronic freshwater invertebrate NOAEC is not 

considered a major data gap likely to add significant value to the risk assessment. If an 

estuarine/marine invertebrate life cycle study is submitted, than an Acute to Chronic 

Ratio (ACR) will be calculated and applied to the daphnid acute value to generate a new 

chronic daphnid endpoint for the risk assessment. 

As noted above, there were issues with pH in several of the aquatic plant studies. In the 

blue-green algae study (MRID 44505122) the pH of the two highest treatment 

concentrations was very acidic (3.6—4.1) and precipitate was in the highest test 

concentration with no filtration or centrifugation of test samples. This study has been 

downgraded to Supplemental—Qualitative. However, no effects were seen at the 56,000 

ppb treatment level and pH was normal at this dosage. Given the difference between the 

NOAEC and other aquatic plant endpoints (duckweed IC50 of 17.7 ppb) as well as 
Page 19 of 66

maximum EECs in past assessments, the lack of an acceptable blue-green algae is not 

considered a major data gap and a new study is not needed. 

In the available green algae study with parent mesotrione (MRID 44505122), the algae in 

the control and lowest two treatments may have grown to the extent they were at the 

upper bound of the test systems carrying capacity as pH in these groups was very high 

(9.9—10.0). These high pH levels are unlikely to represent actual conditions in the 

environment and may have inhibited performance in these groups which leads to 

uncertainty around the IC50 estimate. This study is also being downgraded to 

Supplemental—Qualitative, however, the NOAEC of 820 ppb seems valid and there is 

still a large difference between this value and either the most sensitive aquatic plant data 

(duckweed IC50 of 17.7 ppb) and the maximum EECs from past assessments. Therefore, 

the lack of an acceptable green algae study is not considered a major data gap and a new 

study is not requested. 

In the freshwater diatom study (MRID 44505121), mesotrione appeared to cause 

progressively increasing stimulation of cell densities with concentration (11—46% 

stimulation compared to controls) except for the very highest concentration of 96,000 ppb 

which experienced a 96% decrease in cell density compared to the control plants. This 

study is being downgraded to Supplemental—Quantitative. The NOAEC of 46,000 ppb 

from this study is considered valid and is significantly higher than other available 

endpoints for aquatic plants. A new study with freshwater diatoms is not requested at this 

time. 

There are no data on the toxicity of the degradates, AMBA and MNBA to the most 

sensitive aquatic taxa to parent mesotrione, estuarine/marine invertebrates and vascular 

aquatic plants. Since mesotrione only metabolizes to AMBA in anaerobic environments, 

the lack of ecotoxicity data for this degradate is not considered a major data gap. In the 

available green algae study with the degradate MNBA (MRID 44901710), the pH in the

control and four lowest treatment doses rose to high basic levels (9.5—10) and declined 

to very acidic levels (<4.5) in the three highest treatment doses. These high and low pH’s 

are unlikely to represent conditions in the environment and are likely to have impacted 

both control performance and each treatment level’s performance. Therefore, there is 

uncertainty around the IC50 and NOAEC endpoints and this study is being downgraded to 

Supplemental—Qualitative. This makes comparison with the green algae study with 

parent mesotrione difficult. However, since this study had similarly high pH’s in the 

control and three lowest concentrations (3,300—10,000 ppm) and there was no inhibition 

in these concentrations, while the green algae study with parent mesotrione had 

significant inhibition at concentrations as low as 1,500 ppm, the lack of data on MNBA’s 

effects to aquatic plants is not considered a major data gap and new data is not requested. 

For aquatic invertebrates, since the MNBA degradate appears to be approximately 6.3x 

more toxic to daphnids than parent mesotrione, the lack of ecotoxicity data for the 

MNBA degradate to estuarine/marine invertebrates is considered a major data gap. If the 

difference in toxicities between parent mesotrione and MNBA (~6.3x) from the daphnid 

studies is applied to the mysid acute LD50 endpoint of 3300 ppb, than an estimated mysid 
Page 20 of 66

LD50 for MNBA would be approximately 524 ppb. When compared to the maximum 

EECs from previous assessments (cranberry use site; USEPA, 2013a, D408583), this 

estimated LD50 value is < 20 times greater; therefore, there is potential for risk to 

endangered species. EFED ran the IEC v1.1 (Individual Effect Chance) model to 

quantify the potential for risk to an individual organism. Using the threshold value of 

0.067 (from the estimated mysid LD50 value for MNBA and the highest peak EEC of 35 

ppb from previous assessments) and a probit dose-response slope of 1.46 (from the mysid 

acute toxicity study with parent mesiotrione), the likelihood of an effect for an individual 

organism is 4.3% (95% CI: 1.2%--12%). The likelihood of an effect for an individual 

organism exposed to mesotrione without MNBA was calculated to be 1-in-508 (0.2%). 

The submission of mysid acute data with the MNBA degradate would enable EFED to 

determine the action area for endangered species determinations. In the absence of this 

data, EFED will use the estimated LD50 value described here (524 ppb) in the risk 

assessment, however it is uncertain whether this approach will under- or over-estimate 

risk. 

Certain adjuvants or formulations may increase the toxicity of mesotrione to plant 

species. Duckweed exposed to either the Agral 90 or AgriDex adjuvants in combination 

with mesotrione was approximately twice as toxic compared to mesotrione alone. The 

endpoints reported in previous assessments for the Agral 90 and AgriDex studies are 

slightly different than what is reported in this problem formulation. Previous assessments 

used the endpoints reported by the study authors in laboratory reports while this problem 

formulation reports endpoints from the relevant DERs (for MRIDs 46562906 & 

46562907) which are slightly lower and will be used in the risk assessment.

6.2. Effects to Terrestrial Organisms

Table 9. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for Mesotrione.

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(all units in 

terms of 

measured active 

ingredient)

Acute 

Toxicity 

Classification

Source

(Classification)

Birds1

Acute

Bobwhite quail

Colinus 

virginianus

14-d LD50 > 2000 

mg/kg

Nominal

Practically 

non-toxic

44373506

(Acceptable)

Sub-acute 

dietary

Bobwhite quail

Colinus 

virginianus

8-D LC50 > 4,770 Practically 

non-toxic

44373507

(Acceptable)

Chronic

Mallard Duck

Anas 

platyrhynchos

22-Wk NOAEC = 

120 ppm

LOAEC = 600 

ppm

Endpoint: Normal 

hatchlings/eggs 

laid

N/A 44505005

(Acceptable)
Page 21 of 66

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(all units in 

terms of 

measured active 

ingredient)

Acute 

Toxicity 

Classification

Source

(Classification)

Mammals

Acute

Oral

Laboratory rat

Rattus 

norvegicus

LD50 > 5,000 

mg/kg

Practically 

non-toxic

44373512

(Acceptable)

Acute 

Inhalation No Data No Data N/A N/A

Chronic

Mouse

Mus musculus

NOAEL = 350 

ppm

LOAEL = 1500

ppm

(71.4 mg/kgbw/day)

Endpoint: Body 

weight in F1 and 

F2 male pups & 

opaque/cloudy 

eyes

N/A 4450534

(Acceptable)

Insects

Acute 

contact

Honeybee

Apis mellifera

48-Hr LD50 > 100 

μg/bee

Practically 

non-toxic

44373528

(Acceptable)

Acute 

Oral

Honeybee

Apis mellifera

48-Hr LD50 > 11 

μg/bee

Practically 

non-toxic

44373528

(Acceptable)

1 Birds are considered a surrogate for terrestrial phase amphibians and reptiles

Table 10. Summary of most sensitive terrestrial plant toxicity data from application 

of mesotrione, alone and with adjuvants.

No Adjuvant1 AgriDex2 Agral 902

Most 

Sensitive 

Species

EC25/

NOAEC 

Most 

Sensitive 

Species

EC25/

NOAEC

(or EC05)

Most 

Sensitive 

Species

EC25/

NOAEC

(or EC05)

Terrestrial Plants – Seedling Emergence (lb a.i./A)

MONOCOT Onion 0.028/

0.017 Onion 0.011/0.006 Onion 0.016/0.0023

DICOT Lettuce 0.0033/

0.0012 Cabbage 0.0032/0.0007 

Cabbage 0.0019/

 0.0005 

Terrestrial Plants – Vegetative Vigor (lb a.i./A)

MONOCOT Onion 0.0009/

0.0001 None3 > 0.0208/0.0208 Onion 0.014/0.00695

DICOT Tomato 0.00023/

0.0001 Lettuce 0.00051/0.000086

Lettuce &

Cucumber

0.0017/

0.000257

1 All of these endpoints with no adjuvant were reported in the initial new use assessment, DP Barcode D253844.

2 These endpoints with adjuvants were reported in DER review memos, either DP Barcode D318274 (MRID 

46562903) or D338942 (MRID 47093501).

3 No monocots exhibited a reduction of 25% for any endpoint analyzed.
Page 22 of 66

The available data indicate that mesotrione is practically non-toxic on an acute basis to 

birds and mammals. There is no data for the effects of mesotrione to passerine birds. 

Passerine bird species can frequently be more sensitive than upland and waterfowl bird 

species. Using T-Rex version 1.5.2 to model mesotrione’s residues on avian dietary 

items, the maximum expected residues for all currently registered uses is less than 1/10th

the bobwhite non-definitive LD50 value. However, the EUP rate on soybeans is over 

three times higher than other registered use rates and would result in dietary residues 

greater than 1/10th the bobwhite acute endpoint. Since neither mortality nor sublethal 

effects were observed in the acute oral test (MRID 44373506), the only mortalities 

occurring in subacute dietary studies (MRIDs 44373507 & 44373508) did not appear to 

be treatment related and expected residues are lower than 1/10th the nondefinitive 

bobwhite acute endpoint, the lack of a passerine study is not considered a major data gap 

and a new study is not requested for the risk assessment. However, if there is an 

expansion of the EUP to a broader use pattern or if application rates change in the future, 

than the lack of passerine data would be considered a major data gap.

Previous EFED assessments used the chronic rat study (MRID 44920801) with a LOAEL 

of 2,000 mg/kg-diet (ppm) based on ossification. However, the most sensitive data 

available to the agency is a two generation study using the mouse (MRID 4450534). At 

low doses (10—350 ppm), this study found tyrosinemia, increased kidney weights and 

increased incidence of occular discharge. EFED does not typically use these endpoints in 

risk assessment as their direct relation to survival, growth and reproduction is uncertain. 

At the highest doses (7,000 ppm), body weight was decreased in F1 generation males and 

females (16-17%) at one week, P generation females during lactation (3--13%), F1 

generation females during gestation (9%) and F1 generation females during lactation (9—

12%). Food consumption was also reduced at this dosage for P generation females (15—

28%) and F1 generation females (10--33%). The average day of preputial separation was 

also reduced (10% or ~ 3 days) in the F2 generation at 7000 ppm. F1 and F2 pup body 

weights were also reduced at 7,000 ppm (6—24% for F1 pups and 9—20% for F2 pups). 

Pup body weights were also significantly reduced for both male (11-14%) and female (9-

14%) for F1 pup weights at 1500 ppm and for male F2 pup weights (8-10%). Pup weights 

at lower treatment levels were also significantly reduced, but with less than 10% 

inhibition. Incidence of opaque or cloudy eyes was elevated in F2 males at both the 7,000 

ppm (30%) and 1500 ppm (13%). Given that significant pup body weights were observed 

across multiple generations and these decreases were > 10% at the 1500 ppm treatment 

level and the elevated occurrence of opaque/cloudy eyes (which may result in decreased 

fitness for the survival, growth and reproduction of mammals in the environment) at the 

same treatment level, EFED will use a NOAEC of 350 ppm and a LOAEC of 1500 ppm 

in the risk assessment.

No acute toxicity data are available for the mouse using either mesotrione or its 

degradates. However, there is no evidence to indicate that the compound has a greater 

acute effect on mice than it does to rats. 
Page 23 of 66

No avian toxicity data are available for mesotrione’s metabolites, MNBA and AMBA. 

However, acute data are available for the degradates’ toxicity to rats (MRIDs 44505015

& 44505016) with both being practically non-toxic (LD50s > 5,000 mg/kg). 

The available data indicate that certain adjuvants can increase the toxicity of mesotrione 

to plant taxa. For vegetative vigor, adjuvants did not appear to increase the toxicity, 

however for effects on seedling emergence the adjuvants did appear to increase the 

toxicity of mesotrione, as much as ~2—2.5x for Agral 90 and AgriDex, respectively, to 

onion seedling emergence. Although no data are available for Typical End-Use Product 

(TEP) effects to vegetative vigor, Syngenta has stated that the amount of adjuvant used in 

the Agral 90 and AgriDex vegetative vigor studies is “proportionally to the product as 

they are recommended and used by commercial applicators” (D338942). EFED raised 

concerns that although the percentage of adjuvant applied is consistent with label rates, 

the diminishing test concentrations were applied in a constant volume of water (USEPA, 

2007). If the adjuvant is used in the formulation to facilitate active ingredient contact 

with leaf surface, such facilitation may have been affected due to the greater relative 

proportion of carrier (water) than the label prescribes. As such uncertainty exists as to 

whether the true extent of toxicity was identified. While a new study is not being 

requested at this time, the uncertainty has been highlighted.

6.3. Ecological Incidents

A preliminary review on April 15, 2014 of the Ecological Incident Information System 

(EIIS, version 2.1.1), which is maintained by the Agency’s Office of Pesticide Programs,

and the Avian Monitoring Information System (AIMS), which is maintained by the 

American Bird Conservancy, indicates a total of 319 reported ecological incidents in the

United States associated with the use of mesotrione (summarized by certainty in Table 

11 with a more thorough listing by date and location in Appendix B). All of the reported 

incidents associated with mesotrione involved damage to terrestrial plants and appear to 

be crop damage. It is unclear how many of the incidents were due to spray drift compared 

to other exposure routes.

All of the mesotrione incidents occurred between 2001 and 2013 (mesotrione was first 

registered by EPA in 2001). The certainty categories1regarding the likelihood that the 

 

1 The Ecological Incident Information System (EIIS) used by EPA to store incident data relies on the following 

certainty indices: 

 Highly Probable: (residues detected in affected organisms and other lines of evidence support cause)

 Probable: (residues were not measured or the measured residues were not sufficient to be considered toxic, 

but pesticide was used in close proximity and would be capable of exerting such an effect)

 Possible: multiple pesticides were used in close proximity and any of them are capable of causing such an 

effect.

 Unlikely: there are no measured residues and the observed effects are not consistent with those caused by 

pesticides used in the area or there was no pesticide use known in the area.

 Unrelated: effects observed in the incident are unrelated to pesticide use.
Page 24 of 66

use of mesotrione caused the 319 incidents ranged from Unlikely (5 incidents, 1.6%), 

Possible (116 incidents, 36.4%), and Probable (198 incidents, 46%). 184 (58%) of the 

incidents were considered to be associated with the legal use of mesotrione, 29 (9%) were 

considered to be misuses (4 of which were identified as accidental misuses), and the 

legality of use was not determined in 101 (32%) of the reported incidents.

In the risk assessment, the incidents will be further evaluated to determine if the reported 

incidents represent current patterns of use for mesotrione. Examples of additional 

considerations are mitigation (e.g., reduced application rates), product cancellations, and 

changes in use patterns that have occurred since the date of the reported incidents.

Table 11. Summary of ecological incidents associated with mesotrione use, by certainty

Incident 

Type Use Type

Certainty

All (excluding 

unlikely) Unlikely Possible Probable Highly Probable

Plants

Agricultural 

Site 

(Misuse)

29 0 4 25 0

Agricultural 

Site 

(Registered 

Use)

184 5 18 166 0

Agricultural 

Site 

(Unknown)

101 0 94 7 0

In addition to the incidents recorded in EIIS and AIMS, additional incidents have been 

reported to the Agency in aggregated incident reports. Pesticide registrants report certain 

types of incidents to the Agency as aggregate counts of incidents occurring per product 

per quarter. Ecological incidents reported in aggregate reports include those categorized 

as ‘minor fish and wildlife’ (W-B), ‘minor plant’ (P-B), and ‘other non-target’ (ONT) 

incidents. ‘Other non-target’ incidents include reports of adverse effects to insects and 

other terrestrial invertebrates. For mesotrione, registrants have reported 1 minor fish and 

wildlife incidents, 748 minor plant incidents, and 0 other non-target incidents. Unless 

additional information on these aggregated incidents becomes available, they will be 

assumed to be representative of registered uses of mesotrione in the risk assessment.
Page 25 of 66

7. Exposure Pathways of Concern

The environmental fate properties and use patterns of mesotrione indicate that direct

spray onto food residues, spray drift, leaching to ground water, and runoff represent 

potential transport mechanisms of mesotrione to aquatic and terrestrial organisms. 

The Screening Tool for Inhalation Risk (STIR v.1.0) is normally used to assess the 

potential for risk to birds and mammals through inhalation exposure. The exposure 

pathways that are assessed by this tool include both droplet inhalation and vapor-phase 

inhalation. STIR, used in the problem formulation phase, is intended to determine if 

exposure is likely and not whether the potential for risk exists. If STIR predicts that 

exposure is likely, additional inhalation data may be necessary to adequately assess risk 

due to the inhalation exposure pathway. However, because no data are currently available 

for mammalian inhalation toxicity, STIR analysis cannot be conducted for mammals 

exposed to mesotrione. However, given the vapor pressure of the chemical and the acute 

oral toxicity data, inhalation is not deemed a likely route of exposure.

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

calculate an upper bound estimate of exposure using mesotrione’s solubility in water 

(1600 mg/L), the most sensitive acute and chronic avian toxicity endpoints (nondefinitive 

bobwhite acute LD50 of >2,000 mg/kg-bw, mallard chronic NOAEC of 120 mg/kg-diet) 

and the most sensitive acute and chronic mammalian toxicity endpoints (nondefinitive 

laboratory rat acute LD50 of >5,000 mg/kg-bw and mouse chronic NOAEL of 10 mg/kgbw). Drinking water exposure alone was not determined to be a potential pathway of 

concern for mammalian species on an acute basis, but was determined to be a potential 

pathway of concern for mammalian species on a chronic basis. For birds, drinking water 

exposure alone was determined to be a potential pathway of concern on both an acute and 

chronic basis. Potential for concern may be less than the screening tool indicates as for 

acute exposures, the avian LD50 used in the screening tool was nondefinitive (i.e. “greater

than”). Additionally, as described in the fate and acute ecotoxicity studies, mesotrione’s 

solubility is variable and may be considerably less than 1600 mg/L depending on 

environmental conditions. Therefore, less of the chemical may be available for uptake in 

drinking water.

These conclusions are for drinking water exposure alone. The results do 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 v1.0, as well as the 

tool, can be found on the EPA’s website at 

http:www.epa.gov/pesticides/science/models_pg.htm#terrestrial.
Page 26 of 66

This pathway will be explored further with the development of SIP v.2.0 in the 

Ecological Risk Assessment for mesotrione. For a sample of the output generated by SIP 

v.1.0, please see Appendix C. 

Non-target terrestrial plants may be exposed to mesotrione residues from spray drift, 

runoff or if residues persist on the field. Aquatic plants may also be exposed via direct 

contact or vascular uptake.

8. Analysis Plan

8.1. Stressors of Concern

8.1.1. Ecological Risk Assessment

The stressor of concern are mesotrione and mesotrione’s major degradates, MNBA and 

AMBA. Due to the limited persistence of mesotrione and similarities in toxicity of the 

parent and the degradates a total toxic residues (TTR) approach is recommended for the 

risk assessment. Because available fate studies may not allow for the TTR half-life 

calculations and there are limited data available for the degradates, at the time of writing 

a risk assessment a decision will be made whether conduct an assessment on the TTR or 

the parent and degradates separately depending on which approach will allow for less 

uncertainty.

8.1.2. Drinking Water 

The drinking water assessments conducted to support future human health risk 

assessments of mesotrione will incorporate modeling of the parent only, mesotrione, in 

surface and ground water. Since the last drinking water assessment was conducted, EFED 

has updated its models (PRZM-EXAMS), the drinking water modeling input parameters, 

and the percent crop area (PCA) guidelines. For all modeling, the input parameters will 

be selected according to the current input guidelines, and where in question a 

conservative approach will be taken in the selection of half-lives. Descriptions of all 

executable versions of current models for drinking water exposure can be obtained from 

the following URL link: http://www.epa.gov/oppefed1/models/water/ 

EFED will consider all ground and surface water monitoring data available to us, and will 

conduct a comprehensive evaluation of the data for the risk assessment. 

8.2. Measures of Exposure 

EFED will use standard available models to evaluate potential exposures to aquatic and 

terrestrial organisms as described at 

http://www.epa.gov/pesticides/science/models_db.htm. 
Page 27 of 66

Available Monitoring Data

Mesotrione was not included in the United States Geological Survey (USGS) National 

Water-Quality Assessment (NAWQA) Program monitoring schedule. 

The registrant, however, submitted monitoring study for mesotrione in surface water 

(MRID 47244503). The study analyzes raw and finished water samples collected from 

2005 - 2007 at Community Water Systems included in the Atrazine Monitoring Program. 

In raw water, the study found mesotrione concentrations of up to 2.4 ppb with primary 

dissipation times of one to several weeks and low levels (≤0.5 ppb) persisting for several 

weeks beyond that. Sampling was conducted in the Midwest, primarily in Illinois, 

Indiana, and Ohio, and in those areas is representative of use on corn, the only registered 

use at the time of sampling. The study was classified as “unacceptable upgradable” at the 

time of evaluation and was not upgraded since then. Upon submittal of an analytical 

methods and storage stability characteristics the study could be upgraded to 

supplemental.

Aquatic Exposure Modeling

The models used to predict aquatic estimated environmental concentrations (EECs) are 

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

(PRZM/EXAMS) and PRZM-Groundwater (PRZM-GW) publically available at: 

http://www.epa.gov/oppefed1/models/water/index.htm. The PRZM/EXAMS Standard 

Pond scenario will be used to estimate the aquatic EECs in surface water. Modeling will 

be conducted for the TTR of mesotrione preferably or the parent and degradates 

separately. All use patterns will be assessed using standard approaches, however, 

applications to rooftops is a non-standard use. Applications to rooftops will be assessed 

with the same method as spot treatments. That is, it is assumed residues are washed off 

by a minimum of 2 mm of water for washoff stipulated in the PRZM model. The treated 

area will be assumed to be 50% and impervious surface scenarios will be used.

Terrestrial Exposure Modeling

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 1.5.2, March 2012). 

This model incorporates the Kenaga 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 95th percentile of residue values from actual field measurements 

(Hoerger and Kenega 1972). The Fletcher et al. (1994) modifications to the Kenaga 

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. 

Instead of a default 35-day foliar dissipation rate, an estimated foliar dissipation half-life 

will be used derived from the available magnitude residue data. Screening level 

calculations have suggested that the drinking water exposure pathway may be a 
Page 28 of 66

significant concern for birds and will be further evaluated at the time of risk assessment 

with SIP v2.0. 

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

(version 1.2.2, December 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 in addition to type of formulation and method of 

application.The Agency is currently developing a replacement model for TerrPlant. If the 

replacement has been approved prior to the initiation of the risk assessment, this new 

model will be used instead. 

Two spray drift models, AgDisp and AgDRIFT, are used to assess exposures of aquatic 

and terrestrial organisms to mesotrione deposited in terrestrial and aquatic habitats by spray 

drift. AgDrift (version 2.1.1; dated 12/29/2011) is the model most commonly used to 

simulate spray drift into terrestrial and aquatic environments from aerial and ground 

applications. AgDisp (version 8.13; dated 12/14/2004) (Teske and Curbishley, 2003) is 

used when a parameter needs to be modeled that is not available in AgDRIFT. Spray drift 

analysis will be an important part of the analysis in defining the potential area of effects 

for endangered species.

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 EFED’s aquatic model input parameter guidance (Version 2.1; 

EFED 2009). 

8.3. Measures of Effect 

Toxicity data presented in Section 6 of this problem formulation will be used to calculate 

risk quotients. Any additional information submitted by the registrant or found in the 

open literature prior to conduct of the risk assessment will also be considered. The open 

literature studies are identified using EPA’s ECOTOXicology database (ECOTOX) 

(USEPA, 2009), 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 pesticides on biotic 

communities from loss of species that are sensitive to the chemicals and from changes in 

structure and functional characteristics of the affected communities.

9. 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 pesticides in registration review. The process for 

evaluating potential risks to listed species is further described at 
Page 29 of 66

http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm. An endangered species 

assessment has not been conducted for mesotrione to date.

10. Endocrine Disruptor Screening Program

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential 

adverse outcomes from exposure to chemicals. Collectively, these studies include acute, 

subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, 

developmental, reproductive, and general or systemic toxicity. These studies include 

endpoints which may be susceptible to endocrine influence, including effects on 

endocrine target organ histopathology, organ weights, estrus cyclicity, sexual maturation, 

fertility, pregnancy rates, reproductive loss, and sex ratios in offspring. For ecological 

hazard assessments, EPA evaluates acute tests and chronic studies that assess growth, 

developmental and reproductive effects in different taxonomic groups. As part of the 

Problem Formulation for Registration Review for mesotrione, EPA reviewed these data 

and selected the most sensitive endpoints for relevant risk assessment scenarios from the 

existing hazard database. However, as required by FFDCA section 408(p), mesotrione is 

subject to the endocrine screening part of the Endocrine Disruptor Screening Program 

(EDSP). 

EPA has developed the 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, 

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. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. 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. A 

second list of chemicals identified for EDSP screening was published on June 14, 20132

and includes some pesticides scheduled for registration review and chemicals found in 

water. Neither of these lists should be construed as a list of known or likely endocrine 

disruptors. 

 

2 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final 

second list of chemicals.
Page 30 of 66

For further information on the status of the EDSP, the policies and procedures, the lists of 

chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our 

website.3

11. Preliminary Identification of Data Gaps 

11.1. Environmental Fate

Table 12 identifies environmental fate studies by MRID that offer data for each guideline 

requirement, as well as study classifications and whether or not further data are needed in 

order to support risk assessment.

Table 12. Submitted Environmental Fate Data for Mesotrione and its Degradates.

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are new

data 

required?

Rationale for Additional Data Need

835.2120 Hydrolysis 44373529 Acceptable No Not Applicable

835.2240 Aqueous 

photolysis 44537108 Acceptable No Not Applicable

835.2410 Soil photolysis

44505128 &

45196005 

(addendum)

Supplemental

upgradable No Not Applicable

835.4100 Aerobic soil 

metabolism

44373530,

44505130,

(44373531 & 

45196006),

44505129,

44505208,

(44901714, 

AMBA)

Acceptable No Not Applicable

835.4200 Anaerobic soil 

metabolism Not Available Not Available Yes

An anaerobic soil metabolism study is 

required for soils under different pH 

conditions characteristic for mesotrione 

use areas.

835.4300 Aerobic aquatic 

metabolism 45196011 PartiallyAcceptable Yes

The study was conducted on two British 

natural water-sediment systems in only

two pHs. The microbial makeup of the

studied system may not be similar to the 

one in the US. A new study conducted 

on US natural-water sediment systems in 

variety of pHs typical in mesotrione use 

area is requested. 

 

3 http://www.epa.gov/endo/
Page 31 of 66

Table 12. Submitted Environmental Fate Data for Mesotrione and its Degradates.

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are new

data 

required?

Rationale for Additional Data Need

835.4400

Anaerobic 

aquatic 

metabolism

44505131 & 

44505132

Partially

Acceptable Yes

The results obtained in this study are 

essentially the same as those from the 

two different aerobic aquatic systems. 

This could suggest that metabolism 

progresses under suboxic conditions, and 

may be more influenced by pH than 

lower oxygen content. Additional study is 

required to verify this assumption.

835.1230

835.1240

Adsorption/ 

desorption 

Leaching 

44505203,

44505204,

44373532,

44505201 

(MNBA)

44505202

(AMBA)

Acceptable No No Applicable

835.6100 Terrestrial field 

dissipation

(44505207 & 

44505125),

44505206,

(44505205 & 

44505126)

Supplemental No Not Applicable

850.1730 Fish 

bioconcentration Not Available None No

Bioconcentration of mesotrione and its

metabolites is not expected based on low 

octanol-to-water partitioning ratios which 

are consistent with low sorptions to soil 

organic matter and relatively high

solubilities in water for these polar, 

acidic compounds. On this basis and their 

relative lack of persistence under aerobic 

conditions (which decreases opportunity 

for prolonged surface exposure), the 

Agency is not requiring any formal study 

of bioconcentration.

835.7100

Small-Scale 

Prospective

Ground Water 

Study

44901718

44901717

46562901

47020001

47106801

47418901

Acceptable No Not Applicable

850.6100

Analytical 

method in soil

44505125, 

44505126, 

44505127 and

44505210

Unacceptable Yes

Inadequacy was noted of soil extraction 

methods for aged soil. As a result the 

extraction and separation of mesotrione 

and degradates/metabolites were not 

reliable and quantitatively efficient. 

Analytical 

method in water 

and sediment.

44901715

44901716 --- Yes

The methods are required to support 

monitoring for mesotrione residues and 

current and newly submitted 

environmental fate and ecological effects 

data.
Page 32 of 66

Table 12. Submitted Environmental Fate Data for Mesotrione and its Degradates.

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are new

data 

required?

Rationale for Additional Data Need

Not 

available

Surface Water 

Monitoring 47244503 Unacceptable upgradable Yes

This study can be upgraded to

supplemental upon submittal of the 

analytical methods and storage stability 

characteristics since samples were stored 

up to 18 months before analysis.

Not 

available

Chlorination of 

River Water 47578301 --- No Only preliminary review is available.

840.1100 Droplet Size 

Spectrum

spray drift task 

force spray drift task force

840.1200 Drift Field 

Evaluation

spray drift task 

force spray drift task force

Environmental Fate Data Gaps

Environmental Chemistry Methods and Associated Independent Laboratory 

Validation: Guideline 850.6100

The environmental chemistry method for mesotrione residues of concern (parent plus 

major degradates) in soil, water, and sediment as well as independent laboratory 

validation of the methods are required to support monitoring for mesotrione residues and 

current and newly submitted environmental fate and ecological effects data. 

Independently validated analytical methods for residues in soil, water, and sediment, and 

plant material (environmental chemistry methods) submitted by the registrant are used to 

evaluate analyses described in submitted environmental fate and ecological effects 

studies. Submitted analytical methods are also used by various federal, state, tribal, and 

local agencies to detect and monitor residues that are or are suspected to be in 

environmental compartments from outdoor uses and accidental releases. Independent 

laboratory validations for submitted analytical methods are necessary to confirm that the 

methods are functional and to confirm the levels of detection and quantitation reported in 

registrant-prepared validations. Presently, the available methods for soil are not reliable 

and of questionable value.

Anaerobic soil metabolism for Mesotrione: Guideline 835.4200

No data are available for anaerobic soil metabolism. It is expected that mesotrione 

anaerobic soil metabolism is pH dependent hence data for soils with typical pHs for 

mesotrione use areas are recommended.

Aerobic Aquatic Metabolism for Mesotrione: Guideline 835.4300

Laboratory data for mesotrione are limited to two British natural water-sediment systems 

with experimental pH 7.9 and 6.9. A longer half-lives at lower aquatic system pHs might 

be expected if the aerobic aquatic metabolism rates are system pH dependent. In addition, 

it is not certain that the microbial makeup of the British water-sediment systems is similar 

to the one in the US. Therefore, a new study conducted on US natural-water sediment 

system at a variety of pHs typical in mesotrione use area is recommended. Study should 
Page 33 of 66

be conducted until patterns of decline of parent and patterns of formation and decline of 

transformation products are established. For the purpose of modeling a very conservative 

approach will be taken in selecting the input parameters if the data are not available.

Anaerobic aquatic metabolism for Mesotrione: Guideline 835.4400

Currently the data for mesotrione are limited to one flooded Radford U.S. soil system 

with purified water (two radiolabels and pH 6.9 to 7) and the obtained half-life is 

comparable to the aerobic soil metabolism rate, and essentially the same as those from 

the two different aerobic aquatic systems. These results indicate that metabolism 

progresses under suboxic conditions, and may be more influenced by pH than lower 

oxygen content. If this is true, an additional study is requested to further understand 

mesotrione metabolism under anaerobic aquatic conditions in natural systems at a variety

of pHs. Study should be conducted until patterns of decline of parent and patterns of 

formation and decline of transformation products are established. For the purpose of 

modeling a very conservative approach will be taken in selecting the input parameters if 

the data are not available.

Aerobic Soil Metabolism for MNBA: Guideline 835.4100

There are no separate aerobic soil metabolism study for MNBA alone, as there was for 

AMBA, thus is not certain if there is concern for exposure from MNBA from mesotrione

use. Fate data indicate that MNBA would be a major product in many soils in which corn 

is grown. (In three of seventeen aerobic soils with more neutral pHs (more desirable for 

growing corn), maximum concentrations of MNBA reached approximately 30, 50, and

60% of the dose.) Even though the registrant attempted to estimate half-lives for MNBA 

from mesotrione metabolism data, EFED concludes that the available data are insufficient 

for the purpose. In at least two soils, MNBA "half-lives" appeared to be one to several 

months, but much shorter in others. The submitted data will alleviate the uncertainty 

associated with the metabolite persistence and uncertainty with its availability in soil for 

potential transport to surface water. Without this data it will be assumed that the 

degradate’s aerobic soil metabolism half-life is three times the most conservative 

estimated half-live obtained from a formation and decline curve.

Aerobic Aquatic Metabolism for MNBA: OCSPP Guideline 835.4300

The Agency has no data on the fate of MBNA under aerobic aquatic conditions. The 

longer MBNA persists in the soil, the greater the opportunity for it to move into surface 

water, where its fate is unknown and where it potentially could impact aquatic species. 

Data from this study would address the uncertainty in regards to MNBA behavior in the 

aquatic environment under aerobic conditions. The study should be conducted at a variety 

of pHs.

Analytical Methods with the Storage Stability Characteristics for Surface Water 

Monitoring (MRID 47244503): Guideline 850.6100

Additional data are requested for the purpose of upgrading the unacceptable Surface 

Water Monitoring study. Surface water samples collected for the monitoring study were 

stored for up to 18 months before analysis. If upgraded, the available surface water data 
Page 34 of 66

could be used for qualitative characterization or used more quantitatively (chronic 

exposure results) in the risk assessment.

Drinking Water Treatment Method for MRID 47578301: Guideline not Available

Information on the types of treatment that were used in surface water samples from the 

monitoring study (MRID 47244503) to obtain drinking water are requested. The surface

monitoring study had no detections of mesotrione in finished water. The sampling was 

conducted at the same time and in the same locations as that for untreated water, but there 

is no information as to the types of treatment that were used to obtain finished water. 

11.2. Effects

Table 13 and Table 14 identify ecological effects studies by MRID that offer data for 

each guideline requirement, as well as study classifications and whether or not further 

data are needed in order to support risk assessment. 

Table 13. Submitted Aquatic Ecological Effects Data for Mesotrione and its Degradates

OCSPP

Guideline

Data 

Requirement

TGAI/

TEP/

Metabolite

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed to 

conduct 

risk 

assessment?

Current Additional Data 

Need

/Notes

850.1010 Freshwater 

invertebrate 

acute toxicity

TGAI 44373511 Acceptable No N/A

AMBA 44901704 Acceptable

MNBA 44901705 Acceptable

850.1025

850.1035

850.1045

850.1055

Saltwater 

invertebrate 

acute toxicity 

TGAI 44505008 Acceptable No 1 MNBA was more toxic than 

parent to freshwater 

invertebrates and saltwater 

invertebrates were much more 

(~2 orders of magnitude) 

acutely sensitive to parent 

mesotrione than freshwater 

invertebrates. An acute mysid 

study with the MNBA 

degradate is required.

TGAI 44505009 Acceptable No

AMBA No Data N/A No

MNBA No Data N/A Yes1

850.1075 Freshwater fish 

acute toxicity 

TGAI 44373510 Acceptable No N/A

TGAI 44373509 Acceptable

AMBA 44901702 Acceptable

MNBA 44901703 Acceptable

850.1075 Saltwater fish acute 

toxicity 

TGAI 44505007 Supplemental—

qualitative2

No 2 None—the study is sufficient 

to indicate the LC50 for 

saltwater fish is greater than 

100 ppm AMBA No Data N/A

MNBA No Data N/A

850.1300 Freshwater 

invertebrate 

TGAI 44505010 Supplemental—

Qualitative3

No3 3 The previously acceptable 

daphnid study was downgraded 
Page 35 of 66

OCSPP

Guideline

Data 

Requirement

TGAI/

TEP/

Metabolite

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed to 

conduct 

risk 

assessment?

Current Additional Data 

Need

/Notes

life cycle AMBA No Data N/A due to issues with solubility, 

pH and inconclusive effects 

data. However, since the 

mysid is much more acutely 

sensitive to mesotrione, a new 

study is not requested. In the 

absence of data, EFED will use 

the mysid acute and chronic 

(see below) data to generate an 

ACR that can be applied to the 

daphnid acute data.

MNBA No Data N/A

850.1350 Saltwater 

invertebrates 

life cycle 

TGAI None N/A Yes4 4 Since the mysid was 

significantly more (~2 orders of 

magnitude) acutely toxic than 

the daphnid, chronic data is 

required. Additionally, the 

results of this study will be 

used to generate an ACR and 

applied to the freshwater 

invertebrate acute endpoints. 

AMBA None N/A No

MNBA None N/A No

850.1400 Freshwater fish 

early-life stage

TGAI 44505011 Acceptable No --

AMBA No Data N/A

MNBA No Data N/A

850.1400 Saltwater fish 

early-life stage 

TGAI No Data N/A No5 5 In the absence of data EPA 

will use the freshwater fish 

ELS study endpoint as a 

conservative surrogate for the 

saltwater fish chronic endpoint.

AMBA No Data N/A

MNBA No Data N/A

850.1500 Fish life cycle TGAI No Data N/A No --

AMBA No Data N/A No

MNBA No Data N/A No

850.4400 Aquatic plant 

Toxicity Test using 

Lemna spp.

TGAI 44505123 Acceptable No 6 Since Lemna is much more 

sensitive (~3 orders of 

magnitude) to mesotrione than 

the green algae, and MNBA 

forms in aerobic conditions, a 

Tier II study with Lemna using 

MNBA is required. 

TEP 46562906 Acceptable No

TEP 46562907 Acceptable No

AMBA No Data N/A No

MNBA No Data N/A Yes6

850.4500 Algal toxicity TGAI 44505120 Acceptable No

TGAI 44505124 Supplemental--

Qualitative

No

TGAI 44505121 Supplemental--

Quantitative

No
Page 36 of 66

OCSPP

Guideline

Data 

Requirement

TGAI/

TEP/

Metabolite

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed to 

conduct 

risk 

assessment?

Current Additional Data 

Need

/Notes

AMBA 44901709 Supplemental--

Quantitative

No

MNBA 44901710 Supplemental--

Qualitative

No

850.4550 Cyanobacteria TGAI 44505122 Supplemental--

Qualitative

No --

AMBA No Data N/A No

MNBA No Data N/A No

Table 14. Submitted Terrestrial Ecological Effects Data for Mesotrione.

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Current Additional 

Data Need

850.2100 Avian oral 

toxicity

44373506 Acceptable No1 1 A passerine acute oral 

study is not required due 

to no mortality or 

sublethal effects in the 

available data and EECs 

are expected to be lower 

than would trigger the 

study request. However, 

if there is an expansion of 

the EUP to a broader use 

pattern, than the lack of 

passerine data would be 

considered a major data 

gap as EECs would be 

high enough to trigger the 

study request.

No Data N/A

850.2200 Avian dietary 

toxicity 

44373507 Acceptable No --

44373508 Acceptable No

850.2300 Avian 

reproduction

44505005 Acceptable No

44505006 Supplemental--

Quantitative

No

850.3020 Honey bee 

acute contact 

toxicity

44373528 Acceptable No --

850.3030 Honey bee 

residue on 

foliage

No Data N/A No --
Page 37 of 66

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Current Additional 

Data Need

850.3040 Field testing 

for 

pollinators

No Data N/A No --

850.4100 Seedling 

Emergence 

and Seedling 

Growth

47093501 Acceptable No 2 Data for cabbage and 

onion were supplemental

3 Data for lettuce and 

cabbage were invalid 

46562902 Supplemental2/

Acceptable

No

46562903 Supplemental/

Invalid3

No

44505119 Acceptable No

N/A N/A Yes4 4 Seedling emergence 

data are required for 

MNBA’s effects. The 

recommended species are 

the most sensitive ones 

from the parent 

mesotrione dataset, onion 

(for monocot species), 

lettuce and cabbage.

850.4150 Vegetative 

Vigor

44505119 Acceptable No --

46592904 Acceptable No

46592905 Acceptable No

Ecological Effects Data Gaps

 Freshwater Invertebrate Life Cycle (OCSPP Guideline 850.1300): A 

submitted chronic daphnid study was previously deemed Acceptable. However, 

this study (MRID 44505010) had several issues confounding its results (including 

precipitates and extremely acidic conditions in high concentrations and 

inconsistent effects at lower concentrations) which has resulted in its downgrade 

to Supplemental—Qualitative. The lack of an acceptable chronic freshwater 

invertebrate study is a data gap. However, on an acute basis the estuarine/marine 

invertebrate (mysid) was much more sensitive (2-3 orders of magnitude) to 

mesotrione than the freshwater invertebrate (daphnid). Previous assessments 

indicate that maximum expected environmental concentrations are substantially 

lower than acute freshwater invertebrate endpoints and levels of concern were not 

exceeded. Therefore, if a chronic mysid study is available at the time of the risk 

assessment, an acute to chronic ratio (ACR) can be generated from the acute and 

chronic mysid data and applied to the acute daphnid data to estimate a chronic 

daphnid endpoint. 

 Saltwater Invertebrate Acute Toxicity Study (OCSPP Guideline 850.1035) 

with the degradates AMBA and MNBA : Mesotrione is significantly more toxic 

on an acute basis to estuarine/marine invertebrates compared to freshwater 
Page 38 of 66

invertebrates. Although data is available for the degradates toxicity to daphnids, 

this may underestimate their toxicity to mysids, especially since the degradates 

were significantly (5-6) times more toxic than parent mesotrione to the daphnid. 

Using the toxicity differential between parent and metabolites described in the 

acute daphnid toxicity studies and applying this differential to the mysid acute 

endpoint with parent mesotrione results in acute endpoints with the degradates 

that are near 1/20th the peak mesotrione EECs calculated in past assessments 

(USEPA, 2013; D408583). A preliminary IEC analysis conducted in this problem 

formulation indicates that the chance of an effect to an individual organism is 

0.2% for exposure to parent and may be up to 4.3% for the metabolites. 

Therefore, there is potential for risk to listed species of saltwater invertebrates. 

However, since AMBA is usually produced under anaerobic conditions, it is not 

expected that there would be a likely exposure pathway for saltwater invertebrates 

in the water column and therefore, an acute mysid toxicity test with this degradate 

is not requested at this time. However, the lack of an acute mysid toxicity study 

with MNBA remains a major data gap, and this study is requested. In the absence 

of this information, EPA may use the differential in the acute daphnid toxicity 

studies between parent mesotrione and the MNBA degradate to calculate an acute 

mysid endpoint for MNBA’s effects to saltwater invertebrates and compare that to 

expected MNBA EECs in the risk assessment. However, it is uncertain whether 

this approach would underestimate or overestimate risk to saltwater invertebrates. 

 Estuarine/Marine Invertebrate Chronic Toxicity Study (OCSPP Guideline 

850.1350): Mesotrione has outdoor uses that may result in exposure to 

estuarine/marine invertebrates. Mysids are the most sensitive aquatic animal on an 

acute basis and are significantly (~2 orders of magnitude) more sensitive than 

daphnids. No acceptable chronic invertebrate data is available for either 

freshwater or saltwater invertebrates, therefore an acute to chronic ratio (ACR) 

approach cannot currently be used. Since the mysid is significantly more acutely 

sensitive than the daphnid, the lack of a chronic saltwater invertebrate study is a 

major data gap and is more significant than the lack of a chronic freshwater 

invertebrate study. Therefore, EPA requests that a chronic estuarine/marine 

invertebrate study be submitted and endpoints from this study may also be used in 

an ACR approach to estimate a chronic freshwater invertebrate endpoint. In the 

absence of this data, risk would not be able to be precluded to estuarine/marine 

invertebrates in the risk assessment.

 Estuarine/Marine Fish Early-Life Stage Toxicity Study (OCSPP Guideline 

850.1400): An estuarine/marine fish early life-stage test using the TGAI has not 

been submitted, since it was not considered to be necessary based on previous risk 

assessments for mesotrione. An ACR approach cannot be used because the 

endpoints in the acute data are nondefinitive. In the absence of data EPA will use 

the rainbow trout early life stage data as a surrogate for the chronic saltwater fish. 

Although according to the data requirement section in 40 CFR Part 158 the lack 

of this study is considered a data gap, the utility of an estuarine/marine fish ELS 

study for the risk assessment is considered low at this time, given the predicted 
Page 39 of 66

difference between the exposure estimates from previous assessments and the 

toxicity estimate derived using the freshwater fish ELS study. Therefore, an

estuarine/marine fish early life stage toxicity test is not requested at this time.

 Acute Avian Oral Toxicity Study (OCSPP Guideline 850.2100): No data are

available for passerine species, which may be more sensitive than the tested 

bobwhite species. However, the LD50 and LC50 data for the mallard and bobwhite 

were all nondefinitive (“greater than”) values, and there were no sublethal effects 

in any acute or subacute avian study. Maximum use rates for currently registered 

uses of mesotrione are expected to result in residues in dietary items that are 

below any levels of concern for birds using the nondefinitive acute endpoints.

Therefore, a passerine study is not requested at this time. However, if there is an 

expansion of the EUP on soybeans (which has a maximum annual application rate 

that is three times other currently registered uses) to a broader use pattern or if 

other new registrations with higher application rates become registered, than the 

lack of passerine data would be considered a major data gap.

 

12. References 

Derek Cornes, 2005. Callisto: a very successful maize herbicide inspired by 

allelochemistry". Fourth World Congress on Alleopathy. The Regional Institute 

Ltd. Retrieved May 26, 2011.

USEPA, 2001. New Chemical Review (Section 3) for the Use on Corn of the Herbicide 

Mesotrione (DP Barcode D253844). May, 2001. USEPA/OPPTS/OPP.

USEPA, 2007a. Section 3 registration for new use of mesotrione on cranberries, flax, 

millet, and bush and cane berries (DP Barcode D325840) and on turf (DP 

Barcodes D333402, D333409, D333414, D333419). January, 2007. 

USEPA/OPPTS/OPP.

USEPA, 2007b. Section 3 registration for new use of mesotrione on asparagus, grass 

grown for seed, oats, okra, rhubarb, sugarcane, and sorghum (DP Barcodes 

D335361 and D335363). November, 2007. USEPA/OPPTS/OPP.

USEPA, 2008a. Tier II Drinking Water Assessment for Mesotrione New Uses on

Soybeans (Experimental Use Permit), Soybeans (Section 3 New Use), and Turf 

(Section 3 New Use). November 25, 2008. USEPA, OPP, EFED, Washington, 

DC.

USEPA, 2008b. Ecological Risk Assessment for Experimental Use Permit (DP Barcode 

34510) and Section 3 New Use (DP Barcode 357888) registrations for use of 

mesotrione on soybeans. December 22, 2008. USEPA/OPPTS/OPP. 

Washington, D.C.
Page 40 of 66

USEPA, 2013a. Environmental Fate and Ecological Risk Assessment for the Section 3 

New Uses of Mesotrione (Callisto Herbicide) (DP Barcode 408583). September 

10, 2013. USEPA/OPPTS/OPP.

USEPA, 2013b. Mesotrione (122990) Screening Level Usage Analysis (SLUA). March 

12, 2013. USEPA/OPPTS/OPP.

USEPA, 2014. Mesotrione: Drinking Water Exposure Assessment for New Use on 

Mesotrione-Tolerant Soybean. (DP Barcode 415369). April, 2014. 

USEPA/OPPTS/OPP.

USEPA, 2014. BEAD Chemical Profile (BCP) for Registration Review: Mesotrione 

(122990). Biological and Economic Analysis Division. Office of Pesticide 

Programs. U.S. Environmental Protection Agency. Arlington, VA. April 9, 

2014.
Appendix A: Label Use Information for Mesotrione (PC Code 122990) by Use Site

Use Site Formulation 

Type

Max Rate (lbs 

a.e./Acre)

Max. 

No. of 

Apps 

per 

Year1

Min. 

App. 

Interval2

Application 

Methods

Comments/

Restrictions Single Annual

Caneberry 

subgroup

Soluble 

Concentrate 0.1875 0.1875 NS 14 Broadcast, Directed Spray

Nonbearing or 

Prebloom

Bushberry 

subgroup

Soluble 

Concentrate 0.1875 0.1875 NS 14 Broadcast, Directed Spray

Nonbearing or 

prebloom

Airports/Landing 

Fields

Emulsifiable 

Concentrate 0.25 0.5 NS 14 Broadcast, Spot Treatment

Aerial Not 

Allowed

Asparagus Soluble 

Concentrate 0.2406 0.2406 NS NS Band Treatment, Broadcast Postharvest

Blueberry Soluble 

Concentrate 0.125 0.125 1 NA Broadcast

Prebloom/

Aerial not 

Allowed

Restricted to 

Maine

Commercial/

Industrial Lawns

Soluble 

Concentrate, 

Emulsifiable 

Concentrate

0.25 0.5 NS NS (14) Broadcast, Spot 

Treatment, Spray

Corn (silage, 

unspecified, 

field, pop & 

sweet)

Soluble 

Concentrate, 

Emulsifiable 

Concentrate, 

Water 

Dispersible 

Granules

0.2406 0.2406 NS NS (14)

Soil Band, Soil, 

Broadcast, 

Burndown, 

Directed Spray, 

Soil Treatment 

(Surface), Spray, 

All have Aerial 

not allowed 

except for label 

Reg. Nos 100-

1131 on corn 

(unspecified) & 

AR130010,

MO130001 & 

MS120006 on 

field corn

Cranberry Soluble 

Concentrate 0.25 0.5 2 14 Broadcast, Chemigation

After bud 

break

Flax Soluble 

Concentrate 0.1875 0.1875 1 NA Broadcast Preemergence

Golf Course Turf

Emulsifiable 

Concentrate, 

Soluble 

0.25 0.5 NS 14 Broadcast, Spot 

treatment, Spray

Aerial not 

allowed except 

for EPA Reg. 

No. 100-1265
Concentrate, 

Granular

Grasses grown 

for Seed

Soluble 

Concentrate 0.1875 0.2813 NS NS Broadcast

Millet (pearl) Soluble 

Concentrate 0.1875 0.1875 NA NA Broadcast Preemergence

Oats Soluble 

Concentrate 0.1875 0.1875

1 NA Broadcast

Okra Soluble 

Concentrate 0.1875 0.1875

1 NA

Directed spray, 

soil band 

treatment

Postemergence 

use has a lower 

rate (0.938 lbs 

ai/A)

Ornamental 

Herbaceous 

Plants

Emulsifiable 

Concentrate, 

Soluble 

Concentrate

0.125 NS NS NS Broadcast

Only registered 

in North 

Carolina and 

Minnesota 

(lower rate in 

MN)

Ornamental 

Lawns and Turf

Emulsifiable 

Concentrate 0.25 0.5 NS NS (14) Broadcast, Spot Treatment

Aerial Not 

Allowed

Ornamental Sod 

Farm

Emulsifiable 

Concentrate, 

Granular

0.25 0.5 NS (2) NS (14) Broadcast, Spot 

Treatment

Aerial Not 

Allowed except 

for label Reg. 

No. 100-1265

Recreation Area 

Lawns

Soluble 

Concentrate, 

Granular

0.2493 0.495 NS (2) NS (14) Broadcast, Spray

Aerial Not 

Allowed except 

for label Reg. 

No. 100-1265

Recreation 

Areas

Emulsifiable 

Concentrate 0.25 0.5 NS NS (14) Broadcast, Spot Treatment

Aerial Not 

Allowed

Residential 

Lawns

Emulsifiable 

Concentrate, 

Soluble 

Concentrate, 

Branular

0.25 0.5 NS NS (14) Broadcast, Spot 

Treatment, Spray

Aerial Not 

Allowed except 

for label Reg. 

No. 538-317 & 

100-1265

Rhubarb Soluble 

Concentrate 0.1875 NS NS (1) NS Broadcast Dormant, Preemergence 

Sorghum

Emulsifiable 

Concentrate, 

Soluble 

Concentrate

0.2 NS (0.2) NS (1) NS

Broadcast, Soil 

treatment 

(surface), Directed 

Spray

Aerial Not 

Allowed except

for label Reg. 

No. 100-1131

Soybeans Soluble 

Concentrate 0.1875 0.1875 NS NS Broadcast Preemergence

Sugarcane Soluble 

Concentrate, 0.2406 0.3344 NS (2) 14 Broadcast, Spray, Directed Spray
NS = Not Specified

NA = Not Applicable

1 NS (#) = Some labels did not state the maximum number of applications per year. The # in parentheses is the maximum for the labels which did 

provide a number.

2 NS (#) = Some labels did not state the minimum interval between applications. The # in parentheses represents the minimum for those 

labels which did provide a number.

Emulsifiable 

Concentrate
Appendix B: Summary Data for Mesotrione Related Incidents

EIIS Pesticide Summary Report: General Information

Mesotrione (122990)

Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable.

Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), U=Unknown.
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

PLANTS

Agricultural area

I021485-019 Adair IA 2 M Post-Broadcast 60.0 acres

I013554-015 6/29/2002 La Porte IN 3 M SC Broadcast 113 acres

I018035-085 5/17/2006 Jackson IN 3 RU Broadcast 126 acres

I020283-057 11/1/2007 MN 2 UN F Broadcast 120 acres

I020283-061 11/1/2007 IL 2 UN F Broadcast 240 acres

I020283-058 11/1/2007 MN 2 UN F Broadcast 300 acres

I020283-059 11/1/2007 MN 2 UN F Broadcast 10 acres

I020283-069 11/1/2007 MN 2 UN F 6 acres

I020283-085 11/1/2007 MN 2 UN F 30 acres

I020283-052 11/1/2007 NE 2 UN F Broadcast 73 acres

I020283-060 11/1/2007 MN 2 UN F Broadcast 22 acres

I020283-047 11/1/2007 MN 2 UN F Broadcast 30 acres

I020283-051 11/1/2007 NE 2 UN F Broadcast 49 acres

I020283-090 11/1/2007 IA 2 UN F Broadcast 250 acres

I020283-009 11/1/2007 MS 3 UN F Broadcast 10 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I020283-015 11/1/2007 WI 2 UN F Broadcast 22 acres

I020283-067 11/1/2007 IL 2 UN F Broadcast 80 acres

I020283-136 11/1/2007 IA 3 UN F Broadcast 3575 acres

I020283-062 11/1/2007 IL 2 UN F Broadcast 300 acres

I020283-049 11/1/2007 MN 2 UN F Broadcast 280 acres

I020283-092 11/1/2007 IN 2 UN F Broadcast 40 acres

I021500-015 7/7/2009 Macoupin IL 2 UN Broadcast 90 acres

I022450-007 3/31/2010 Stearns MN 2 UN Broadcast, 

unincorporated

319 acres

I022450-005 6/22/2010 Carver MN 2 UN Broadcast 350 acres

I022450-006 8/17/2010 Wabasha MN 2 UN Broadcast 25 acres

I022450-008 9/24/2010 Stearns MN 2 UN Broadcast, 

unincorporated

400 acres

I022450-003 9/29/2010 Richland ND 2 UN Broadcast 82 acres

Alfalfa

I013554-005 5/13/2002 ADAIR IA 3 RU SC Broadcast All 150 acres

I015713-050 8/18/2004 Grant WI 2 RU Broadcast 73 acres affected

I021500-002 10/5/2009 Grant WA 2 UN Broadcast 125 acres

I022450-015 6/28/2010 McLeod MN 2 UN Broadcast 37 acres

Apple

I013554-006 6/14/2002 Van Buren MI 2 UN SC Broadcast 5400 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I014597-028 5/26/2003 Kalamazoo MI 3 M F Spray

Bean

Bean, dry

52 acres

I013554-013 7/24/2002 Wadena MN 3 M SC Broadcast 66 acres

Berry, blackberry

I023444-003 6/29/2011 Washington OR 2 UN N/R Band 100% of 14 acres

Corb, field

I015713-009 6/1/2004 Peoria IL 2 RU Broadcast 185 acres

Corn

I013554-020 6/11/2002 Gage NE 2 MA SC Broadcast 120 acres

I015713-037 8/2/2004 Steuben IN 3 RU Broadcast 70 acres

I015713-013 8/10/2004 Boone NE 2 RU Broadcast 12 acres affected

I015713-018 9/22/2004 Effingham IL 2 RU Broadcast 136 acres

I015713-061 10/22/2004 IN 2 RU Broadcast 55 acres affected

I016296-001 5/16/2005 Knox IN 2 UN Spray Small

I016813-001 6/4/2005 Grundy IL 1 RU RTU Spray 80 acres corn

I016928-001 6/27/2005 NE 1 RU RTU Spray 75 acres

I016906-001 7/15/2005 Tippecanoe IN 1 RU RTU Spray 100 acres

I016903-007 7/21/2005 IL 2 RU RTU Broadcast 70 acres popcorn

I016905-001 7/27/2005 Hendricks IN 1 RU RTU Spray 65 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I016941-001 8/9/2005 Wilkin MN 1 RU RTU 187 acres

I018065-070 11/1/2005 Kosciusko IN 3 RU Broadcast 100

I018035-027 5/25/2006 Grundy MO 3 RU Broadcast 70 acres

I018035-052 6/7/2006 Bureau IL 3 RU Broadcast 40 acres

I018035-101 6/7/2006 Bureau IL 3 RU Broadcast 100 acres

I018035-005 6/9/2006 Monroe MI 3 RU Broadcast 4 out of 6 acres

I018035-119 6/23/2006 Whiteside IL 3 RU Broadcast 45 acres

I018035-008 6/23/2006 Whiteside IL 3 RU Broadcast 122 acres

I018035-082 7/11/2006 Cass IL 3 RU Broadcast 85 acres

I018035-127 7/12/2006 Coles IL 3 RU Broadcast 80 acres

I018035-097 7/12/2006 Champaign IL 3 RU Broadcast 80 acres

I018035-100 7/12/2006 Champaign IL 3 RU Broadcast 60 acres

I018035-098 7/12/2006 Coles IL 3 RU Broadcast 40 acres

I018035-016 7/13/2006 Woodford IL 3 RU Broadcast 130 acres

I018035-110 7/13/2006 Ford IL 3 RU Broadcast 59.1 acres

I018035-057 7/13/2006 McLean IL 3 RU Broadcast 125 acres

I018035-049 7/14/2006 Livingston IL 3 RU Broadcast 101 Acres

I018035-109 7/14/2006 Marshall IL 3 RU Broadcast 22 acres

I018035-080 7/17/2006 Champaign IL 3 RU Broadcast 80 acres

I018035-012 7/17/2006 Olmsted MN 3 RU Broadcast 25 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I018035-006 7/17/2006 Olmsted MN 3 RU F Broadcast 105 acres

I018035-117 7/18/2006 Carroll IL 3 RU Broadcast 80.1 acres

I018035-023 7/18/2006 Cumberland IL 3 RU Broadcast 50 acres

I018035-075 7/19/2006 Piatt IL 3 RU Broadcast 80 acres

I018035-056 7/19/2006 Champaign IL 3 RU Broadcast 77 acres

I018035-041 7/21/2006 MI 3 RU Broadcast 50 acres

I018035-087 7/22/2006 Grant WI 3 RU Broadcast 50 acres

I018035-123 7/22/2006 Racine WI 3 RU Broadcast 247 acres

I018035-074 7/22/2006 Fond Du Lac WI 3 RU Broadcast 80 acres

I018035-120 7/24/2006 Grant WI 3 RU Broadcast 34 acres

I018035-046 7/24/2006 Fond Du Lac WI 3 RU Broadcast 60 acres

I018035-035 7/25/2006 Lenawee MI 3 RU Broadcast 50 acres

I018035-090 7/25/2006 St. Joseph IN 3 RU Broadcast 65 acres

I018035-091 7/25/2006 Henry OH 3 RU Broadcast 144 acres

I018035-030 7/25/2006 Fulton OH 3 RU Broadcast 30 acres

I018035-044 7/25/2006 Henry OH 3 RU Broadcast 30 acres

I018035-036 7/25/2006 Wood OH 3 RU Broadcast 33 acres

I018035-068 7/25/2006 St. Joseph IN 3 RU Broadcast 15 acres

I018035-089 7/25/2006 Wood OH 3 RU Broadcast 40 acres

I018035-032 7/26/2006 Porter IN 3 RU Broadcast 50 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I018035-055 7/26/2006 La Porte IN 3 RU Broadcast 50 acres

I018035-104 7/26/2006 La Porte IN 3 RU Broadcast 320 acres

I018035-066 7/26/2006 Henry OH 3 RU Broadcast 269 acres

I018035-096 7/26/2006 Porter IN 3 RU Broadcast 40 acres

I018035-025 7/26/2006 Jasper IN 3 RU Broadcast 75 acres

I018035-053 7/26/2006 Eaton MI 3 RU Broadcast 47 acres

I018035-073 7/27/2006 Livingston IL 3 RU Broadcast 260 acres

I018035-077 7/27/2006 Kosciusko IN 3 RU Broadcast 10 acres

I018035-114 7/28/2006 Kosciusko IN 3 RU Broadcast 300 acres

I018035-121 7/28/2006 La Salle IL 3 RU Broadcast 240 acres

I018035-047 7/28/2006 Kosciusko IN 3 RU Broadcast 200 acres

I018035-099 7/28/2006 La Salle IL 3 RU Broadcast 40 acres

I018035-069 7/28/2006 Kosciusko IN 3 RU Broadcast 300 acres

I018035-017 7/28/2006 Whiteside IL 3 RU Broadcast 32 acres

I018035-116 7/28/2006 Marshall IL 3 RU Broadcast 640 acres

I018035-009 7/28/2006 La Salle IL 3 RU Broadcast 30 out of 100 acres

I018035-015 7/28/2006 Mercer IL 3 RU Broadcast 100 acres

I018035-125 7/28/2006 La Salle IL 3 RU Broadcast 50 acres

I018035-128 7/28/2006 Portage WI 3 RU Broadcast 55 acres

I018035-072 7/28/2006 Kosciusko IN 3 RU Broadcast 30 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I018035-010 7/28/2006 Columbia WI 3 RU Broadcast 45 out of 100 acres

I018035-065 7/28/2006 Livingston IL 3 RU Broadcast 250 acres

I018035-088 7/28/2006 Livingston IL 3 RU Broadcast 165 acres

I018035-084 7/28/2006 Marshall IN 3 RU Broadcast 40 acres

I018035-070 7/28/2006 Kosciusko IN 3 RU Broadcast 65 acres

I018035-107 7/28/2006 Whiteside IL 3 RU Broadcast 280.1 acres

I018035-092 7/28/2006 Kosciusko IN 3 RU Broadcast 600 acres

I018035-083 7/28/2006 Ogle IL 3 RU Broadcast 739 acres

I018035-018 7/31/2006 Whiteside IL 3 RU Broadcast 200 acres

I018035-113 7/31/2006 Ogle IL 3 RU Broadcast 70 acres

I018035-103 7/31/2006 Jo Daviess IL 3 RU Broadcast 73 acres

I018035-061 7/31/2006 Ogle IL 3 RU Broadcast 700 acres

I018035-102 7/31/2006 Stephenson IL 3 RU Broadcast 185 acres

I018035-111 7/31/2006 Edgar IL 3 RU Broadcast 80 acres

I018035-007 7/31/2006 Vermilion IL 3 RU F Broadcast 68 acres

I018035-048 7/31/2006 Livingston IL 3 RU Broadcast 40 acres

I018035-108 7/31/2006 Whiteside IL 3 RU Broadcast 100 acres

I018035-050 7/31/2006 Carroll IL 3 RU Broadcast 257 acres

I018035-051 7/31/2006 Carroll IL 3 RU Broadcast 72 acres

I018035-064 7/31/2006 Whiteside IL 3 RU Broadcast 184 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I018035-067 7/31/2006 Champaign IL 3 RU Broadcast 80 acres

I018035-126 7/31/2006 Champaign IL 3 RU Broadcast 37.5 acres

I018035-112 8/1/2006 Livingston IL 3 RU Broadcast 40 acres

I018035-086 8/1/2006 Washington IA 3 RU Broadcast 1 acre

I018035-081 8/1/2006 Livingston IL 3 RU Broadcast 80 acres

I018035-029 8/1/2006 Kendall IL 3 RU Broadcast 136.1 acres

I018035-093 8/1/2006 Ogle IL 3 RU Broadcast 78 acres

I018035-014 8/1/2006 McLean IL 3 RU Broadcast 40 acres

I018035-042 8/2/2006 Wayne IL 3 RU Broadcast 80 acres

I018035-106 8/2/2006 De Kalb IL 3 RU Broadcast 460.8 acres

I018035-118 8/2/2006 De Kalb IL 3 RU Broadcast 294.6 acres

I018035-054 8/2/2006 De Kalb IL 3 RU Broadcast 144 acres

I018035-059 8/2/2006 La Salle IL 3 RU Broadcast 58 acres

I018035-038 8/3/2006 IL 3 RU Broadcast 30 acres

I018035-011 8/3/2006 Fond Du Lac WI 3 RU Broadcast 75 acres

I018035-062 8/4/2006 Columbia WI 3 RU Broadcast 85 acres

I016903-005 8/8/2006 Grant WI 2 RU RTU Broadcast 27 acres corn seed

I018035-078 8/9/2006 Marshall IN 3 RU Broadcast 200 acres

I018035-040 8/9/2006 Henderson IL 3 RU Broadcast 50 acres

I018035-028 8/9/2006 Kosciusko IN 3 RU Broadcast 32 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I018035-013 8/14/2006 De Kalb IL 3 RU Broadcast 50.0 acres

I018035-076 8/22/2006 St. Charles MO 3 RU Broadcast 40 acres

I018035-063 8/24/2006 Marshall IN 3 RU Broadcast 75 acres

I018035-060 8/24/2006 Marshall IN 3 RU Broadcast 160 acres

I018035-105 8/24/2006 Marshall IN 2 RU Broadcast 60 acres

I018035-115 8/24/2006 Kosciusko IN 3 RU Broadcast 35 acres

I018035-037 8/29/2006 Huron OH 3 RU Broadcast 20 acres

I018035-079 8/30/2006 Fulton OH 3 RU Broadcast 25 acres

I018035-026 8/30/2006 Van Buren MI 3 RU Broadcast 202 acres

I018035-045 8/30/2006 IL 3 RU Broadcast 84 acres

I018035-043 8/30/2006 Kankakee IL 3 RU Broadcast 39 acres

I018035-033 8/30/2006 Kankakee IL 3 RU Broadcast 120 acres

I018035-122 8/30/2006 Hillsdale MI 3 RU Broadcast 24 acres

I018035-034 8/30/2006 Kankakee IL 3 RU Broadcast 93 acres

I018035-039 8/31/2006 Huron OH 3 RU Broadcast 42 acres

I018035-024 8/31/2006 Morgan IL 3 RU Broadcast 10 acres

I018035-031 8/31/2006 Macoupin IL 3 RU Broadcast 15 acres

I018035-071 9/5/2006 Tazewell IL 3 RU Broadcast 80 acres

I018035-124 10/9/2006 Columbia WI 3 RU Broadcast 200 acres

I018035-095 10/9/2006 Dodge WI 3 RU Broadcast 200 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I018035-094 10/9/2006 Rock WI 3 RU Broadcast 50 acres

I018035-058 10/12/2006 Marshall IN 3 RU Broadcast 300 acres

I019130-029 6/10/2007 Louisa IA 2 UN Broadcast 210 acres

I019130-039 6/21/2007 Lee IL 2 UN Broadcast 59.7 acres

I018130-051 7/19/2007 Valley NE 2 UN Broadcast 82 acres

I021500-020 12/2/2008 Madison IN 2 UN Broadcast 48 acres

I021500-010 5/31/2009 Carver MN 2 UN Broadcast 500 acres

I021500-013 6/15/2009 Ogle IL 2 UN Broadcast 18 acres

I021500-014 7/7/2009 Sibley MN 2 UN Broadcast 74 acres

I021500-011 7/17/2009 Holt NE 2 UN Broadcast 100 acres

I022450-014 6/14/2010 Kearney NE 2 UN Broadcast 151acres

I022450-016 10/25/2010 Rush IN 2 UN Broadcast 290 acres

I025458-018 6/21/2013 Mills IA 3 M total garden yellow

field

I015713-027 Delaware IA 3 RU Broadcast 65 acres affected

I015713-066 5/25/2004 Posey IN 2 RU Band 60 acres affected

I015713-065 5/25/2004 Knox IN 2 RU Broadcast 38 acres affected

I015713-067 5/28/2004 Henry IL 2 RU Broadcast 250 acres affected

I015713-010 6/1/2004 Peoria IL 2 RU Broadcast 46 acres affected

I015713-068 6/24/2004 Boone NE 2 RU Broadcast 140 acres affected

Corn,
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I015713-025 6/25/2004 VA 3 RU Broadcast 6 acres

I015713-069 6/30/2004 Henry IL 2 RU Broadcast 260 acres affected

I015713-026 6/30/2004 Delaware IA 3 RU Broadcast 533 acres

I015713-070 7/1/2004 Kalamazoo MI 2 RU Broadcast 75 acres affected

I015713-071 7/2/2004 Kalamazoo MI 2 RU Broadcast 232 acres affected

I015713-072 7/19/2004 MO 2 RU Broadcast 50 acres affected

I015713-073 7/21/2004 Vigo IN 2 RU Broadcast 160 acres affected

I015713-036 7/27/2004 MD 3 RU N/R 24 acres affected

I015713-011 7/30/2004 Sac IA 2 RU Broadcast 75 acres affected

I015713-074 8/2/2004 Johnson IA 2 RU Broadcast 15 acres affected

I015713-016 8/13/2004 Buffalo NE 2 RU Broadcast 50 acres affected

I016908-001 7/8/2005 Jay IN 2 MA RTU Spray 50 acres

I016903-004 7/18/2005 Boone NE 2 RU RTU Broadcast 75 acres of corn

I021500-003 7/2/2009 Bon Homme SD 2 UN Broadcast 78 acres

I022082-038 6/8/2010 Plymouth IA 2 UN Broadcast 100% of 160 acres

sweet

I016903-006 6/25/2005 Mower MN 2 RU RTU Broadcast 230 acres corn

I021500-004 7/16/2009 Freeborn MN 2 UN Broadcast 24 acres

Corn,

N/R

I013554-012 5/27/2002 Dakota MN 3 M SC Broadcast 1572 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I013554-018 6/12/2002 ST JOSEPH MI 3 M SC Broadcast 285 acres

I013554-019 6/19/2002 KANDIYOHI MN 3 M SC Broadcast 37 acres out of 80

I013554-017 6/20/2002 SHERBURNE MN 3 M SC Broadcast 72 acres

I013554-014 6/29/2002 La Porte IN 3 M SC Broadcast 30 acres

I013554-016 6/29/2002 La Porte IN 3 M SC Broadcast 60 acres

I013554-011 7/21/2002 Calhoun IA 3 MA SC Broadcast 144 acres

I013554-021 9/10/2002 La Porte IN 3 MA SC Broadcast 498 acres

I014597-013 4/10/2003 Rock WI 3 M RTU 150 acres

I014597-014 5/1/2003 Kosciusko IN 2 M RTU 80 acres

I014597-012 5/12/2003 Fulton IN 3 M RTU 100 acres

Pea

I013554-009 4/22/2002 Mason IL 3 UN SC Broadcast 156 acres

I014597-030 4/22/2003 Nicollet MN 3 M F Spray 60acres

I014597-029 4/28/2003 Watonwan MN 3 M F Spray 120 acres

I014597-032 5/2/2003 Brown MN 3 M F Spray 30 acres

I014597-033 5/3/2003 Faribault MN 3 M F Spray 38 acres

Potato

I013554-010 7/3/2002 Tama IA 3 UN SC Broadcast 342 acres

Soybean

I013554-007 6/21/2002 Marshall IA 3 RU SC Broadcast 174 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I015713-024 6/18/2004 Holt NE 3 RU Broadcast 180 acres

I015713-030 7/1/2004 MN 3 RU Broadcast 170 acres affected

I015713-031 7/9/2004 Mills IA 3 RU Broadcast 74 acres affected

I015713-032 7/13/2004 Emmet IA 3 RU Broadcast 85 acres affected

I015713-033 7/14/2004 Calhoun IA 3 RU Broadcast 155 acres affected

I015713-034 7/19/2004 Des Moines IA 3 RU Broadcast 90 acres affected

I015713-035 7/26/2004 Otsego MI 3 RU Broadcast 60 acres

I015713-038 8/2/2004 Brown NE 3 RU Broadcast 130 acres affected

I015713-039 8/2/2004 Holt NE 3 RU Broadcast 71.7 acres affected

I015713-014 8/10/2004 Allegan MI 2 RU Broadcast 20 acres affected

I015713-046 8/12/2004 Minnehaha SD 3 RU Broadcast 35 acres affected

I015713-015 8/12/2004 Carver MN 2 RU Broadcast 120 acres affected

I015713-045 8/12/2004 Minnehaha SD 3 RU Broadcast 300 acres affected

I015713-042 8/12/2004 Minnehaha SD 3 RU Broadcast 45 acres affected

I015713-043 8/12/2004 Minnehaha SD 3 RU Broadcast 20 acres affected

I015713-041 8/12/2004 Ingham MI 3 RU Broadcast 60 acres affected

I015713-040 8/12/2004 MI 3 RU Broadcast 80 acres affected

I015713-044 8/12/2004 Minnehaha SD 3 RU Broadcast 200 acres affected

I015713-012 8/13/2004 Poweshiek IA 2 RU Broadcast 32 acres affected

I015713-047 8/16/2004 Cedar IA 3 RU Broadcast 98 acres affected
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I015713-078 8/16/2004 Allamakee IA 3 RU Broadcast 39 acres affected

I015713-076 8/16/2004 Clayton IA 3 RU Broadcast 8 acres

I015713-077 8/16/2004 Clayton IA 3 RU Broadcast 9 acres

I015713-048 8/17/2004 Woodbury IA 3 RU Broadcast 16 acres affected

I015713-049 8/18/2004 Lafayette WI 3 RU Broadcast 63 acres affected

I015713-051 8/18/2004 Iowa WI 3 RU Broadcast 225 acres affected

I015713-052 8/18/2004 Franklin NE 3 RU Broadcast 78 acres affected

I015713-053 8/18/2004 Lac qui Parle MN 3 RU Broadcast 160 acres affected

I015713-017 8/19/2004 Goodhue MN 2 RU Broadcast 69 acres affected

I015713-079 8/19/2004 Fillmore MN 3 RU Broadcast 90 acres affected

I015713-054 8/19/2004 Rock WI 3 RU Broadcast 20 acres affected

I015713-057 8/20/2004 Minnehaha SD 3 RU

Broadcast

75 acres affected

I015713-056 8/20/2004 Minnehaha SD 3 RU Broadcast 55 acres affected

I015713-055 8/20/2004 Fremont IA 3 RU Broadcast 80 acres affected

I015713-059 10/21/2004 Montgomery IA 3 RU Broadcast 200 acres affected

I015713-058 10/21/2004 Mills IA 3 RU Broadcast 185 acres affected

I015713-060 10/21/2004 Montgomery IA 3 RU Broadcast 220 acres affected

I015713-062 10/26/2004 Columbus WI 3 RU Broadcast 54 acres affected

I015713-064 10/26/2004 Dane WI 3 RU Broadcast 13 acres affected

I015713-063 10/26/2004 Columbus WI 3 RU Broadcast 200 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I019130-034 6/14/2007 Lee IL 2 UN Broadcast 69 acres

I019130-037 6/18/2007 McLean IL 3 UN Broadcast 217 acres

I019130-040 6/21/2007 Lee IL 2 UN Broadcast 30 acres

I019130-043 6/26/2007 Wright MN 2 UN Broadcast 65 acres

I019130-044 6/29/2007 Faribault MN 2 UN Broadcast 40 acres

I019130-046 7/3/2007 Adams IA 2 UN Broadcast 438.8 acres

I019130-054 7/25/2007 Otter Tail MN 2 UN Broadcast 55 acres

I019130-055 7/26/2007 Morrison MN 2 UN Broadcast 135 acres

I019130-090 7/26/2007 Livingston IL 2 UN Broadcast 200 acres

I019130-089 7/26/2007 Livingston IL 2 UN Broadcast 200 acres

I019130-088 7/26/2007 McLean IL 2 UN Broadcast 60acres

I019130-064 8/24/2007 Moultrie IL 3 UN Broadcast 63 acres

I019130-085 10/23/2007 Linn IA 2 UN Broadcast 34 acres

I021500-018 11/19/2008 Clinton MI 2 UN Broadcast 500 acres

I021500-017 7/24/2009 Clinton MI 2 UN Broadcast 30 acres

I021500-016 7/24/2009 Shiawassee MI 2 UN Broadcast 40 acres

I021500-006 8/2/2009 Winona MN 2 UN Broadcast 160 acres

I021500-012 9/21/2009 Noble IN 2 UN Broadcast 200 acres

I021500-019 9/21/2009 De Kalb IN 2 UN Broadcast 200 acres

I022450-017 3/31/2010 Otter Tail MN 2 UN Broadcast, 

unincorporated

1,200 acres
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

I013554-008 6/14/2002 Peoria IL 3 UN SC Broadcast

I015285-013 6/28/2004 NC 2 UN

I022450-004 10/19/2010 Washington WI 2 UN Broadcast 3,300 acres

I023444-004 8/6/2011 Le Sueur MN 2 UN N/R Broadcast 100% of 90 acres

Soybeans

I014597-020

I014597-021

I014597-015

I014597-019

I014597-018

I014597-016

I014597-017

I015713-029

I015713-028

I015713-075

Soybena

4/26/2003

5/2/2003

5/13/2003

5/18/2003

5/20/2003

5/30/2003

6/10/2003

7/1/2004

7/7/2004

8/12/2004

Kosciusko 

Marshall 

Dane 

Porter 

Sauk 

Berrien 

Knox 

Brown 

Clay

Minnehaha

IN 3 M SC Spray 145 acres 

IN 3 M SC Spray 80 acres 

WI 3 M SC Spray 1 acre 

IN 3 M SC Spray 100 acres 

WI 3 M SC Spray 28 acres 

MI 3 M SC Spray 50 acres 

IN 3 M SC Spray 78 acres 

NE 3 RU Broadcast 150 acres 

IA 3 RU Broadcast 75 acres 

SD 3 RU Broadcast 20 acres affected

I021500-005 6/22/2009 Dakota MN 2 UN Broadcast 83% of treated

acres

Tree

Unknown

2

Unknown
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

TERRESTRIAL
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

Corn

I023444-032 11/1/2010 Wabash IL 2 UN N/R Broadcast 46% of 120 acres

I023444-030 11/1/2010 Du Page IL 2 UN N/R Broadcast 100% of 45 acres

I023444-031 11/8/2010 ST. CROIX WI 2 UN N/R Broadcast 100% of 141 acres

I023444-029 11/24/2010 Miami IN 2 UN N/R Broadcast 70% of 250 acres

I023444-023 6/6/2011 Posey IN 2 UN N/R Broadcast 100% of 123 acres

I023444-027 6/6/2011 Edwards IL 2 UN N/R Broadcast 50% of 80 acres

I023444-024 6/6/2011 Daviess IN 2 UN N/R Broadcast 100% of 232 acres

I023444-014 6/13/2011 Stark IL 2 UN Broadcast 100% of 30 acres

I023444-016 6/13/2011 Marshall IL 2 UN Broadcast 100% of 1,500 

acres

I023444-013 6/13/2011 Le Sueur MN 2 UN Broadcast 100% of 25 acres

I023444-015 6/13/2011 Marshall IL 2 UN Broadcast 100% of 400 acres

I023444-020 6/14/2011 Gibson IN 2 UN Broadcast 100% of 50 acres

I023444-025 6/14/2011 Daviess IN 2 UN N/R Broadcast 89% of 90 acres

I023444-017 6/28/2011 Peoria IL 2 UN Broadcast 100% of 400 acres

I023444-018 7/25/2011 Fillmore IL 2 UN Broadcast 50% of 100 acres

I023444-028 8/6/2011 Waupaca WI 2 UN N/R Broadcast 50% of 16 acres

I023444-019 8/22/2011 Marion OH 2 UN Broadcast 100% of 33 acres

I023444-033 9/12/2011 Lawrence IL 2 UN N/R Broadcast 91% of 160 acres

I023444-021 10/20/2011 Kosciusko IN 2 UN N/R Broadcast 100 % of 60 acers
Incident # Date County State Certainty Legal. Formul. Appl. Method Total Magnitude

Corn field

I022529-007

Corn, field

I022202-072

Sorghum

6/11/2010

7/5/2010

Shelby

Muskegon

IL 2 RU N/R Post-broadcast 100% of108 acres

MI 2 UN Spray 1.2 acres

I023444-026 7/6/2011 Red Willow NE 2 UN N/R Broadcast 100% of 283 acres

I023444-022 7/28/2011 Nuckolls NE 2 UN N/R Broadcast 54% of 185 acres

Appendix C: SIP Inputs and Outputs

Table 1. Inputs

Parameter Value

Chemical name Mesotrione

Solubility (in water at 25oC; mg/L) 1600

Mammalian LD50 (mg/kg-bw) 5000

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian 

species

Mammalian NOAEL (mg/kg-bw) 10

Mammalian test species other

Body weight (g) of "other" mammalian 

species 35

Avian LD50 (mg/kg-bw) 2000

Avian test species northern bobwhite quail

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 120

Bobwhite quail NOAEC (mg/kg-diet) 3000

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
Enter body weight of 'other' mammalian species for NOAEL.

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 275.2000 275.2000

Adjusted toxicity value (mg/kg-bw) 3845.8028 4.3253

Ratio of exposure to toxicity 0.0716 63.6255

Conclusion*

Drinking water exposure 

alone is NOT 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) 1296.0000 1296.0000

Adjusted toxicity value (mg/kg-bw) 1440.8590 5.9535

Ratio of exposure to acute toxicity 0.8995 217.6868

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.