### -2 of 61- over time and additional metabolism studies would aid characterization and reduce uncertainty.

 Anaerobic Aquatic Metabolism (OCSPP guidelin e # 835.4400) Further data are needed to support risk assessment. Concentrat ions in submitted soil metabolism studies

fluctuated over time and additional metabo lism studies would aid characterization and reduce uncertainty. In the absence of data, it will be assumed that the anaerobic aquatic

metabolism half life is doubl e that of the anaerobic soil metabolism half life.

 Environmental Chemistry Methods and I ndependent Laboratory Validation (OCSPP guideline # 850.6100) This study is requi red to corroborate methods used in

environmental fate studies and to assist in the enforcement of pesticide tolerances.

The available effects data are considered incomp lete for the purposes of risk assessment. The following data gap(s) exist:

 OCSPP 850.2100 – Avian Acute Oral. An avian acute oral toxicity study with a passerine is necessary for risk assessment. Additionally the available avian acute oral study resulted in a LD 50 

### value of 169.2 mg a.i./kg-bw, which classifies metribuzin as moderately toxic to North ern bobwhite quail via the oral route. Therefore additional data are necessary to strengthen the risk assessment for birds via the oral route since the subacute dietary studies via the dietary route do not indicate toxicity from metribuzin exposure. It is reco mmended that a definitive study be conducted; however, a limit test with a higher exposur e concentration (to be determined through consultation with the Agency) may also be acceptable.

 OCSPP 850.2300- Avian Reproduction. An avi an reproduction toxicity study with the Northern bobwhite quail is necessary for risk assessment . The available avianreproduction studies with bobwhite quail and mallard duck indicated no doseresponse effects were observed at any con centrations including the highest test

concentrations tested. However, in the RED, the risk assessment suggests the risk to birds exists based on the toxicity value sele cted from the reproduction studies for use in

the avian risk assessment. But a closer look of the study indicated the test concentrations were not tested high enough or at/above envi ronmentally relevant concentrations, which explain why the LOC exceedance exists when no effects occurred; it is uncertain if there is actually any risks to birds. A new study w ith higher test concentr ations (up to 1,500 mg a.i./kg diet) should address the risk uncerta inty. The recommended test species for the new reproduction study is the Northern bobwh ite quail since acute effects were observed in this species in the avian acute oral toxicity test.

Additional detail on the current data gaps for environmental fate and effects is provided in

Section 8.0.

### -3 of 61- 

# Problem Formulation for the Environmental Fate and Ecological Risk, Endangered Species, and Drinking

Water Assessments in Support of the Registration

Review of Metribuzin

4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4 H )-one CAS Registry Number: 21087-64-9

PC Code: 101101

P

repared by: Stephen Carey, Biologist Andrew Shelby, Physical Scientist U. S. Environmental Protection Agency Office of Pesticide Programs

E nvironmental Fate and Effects Division

E nvironmental Risk Branch I V 1200 Pennsylvania Ave., NW

M

ail Code 7507P Washington, DC 20460 R eviewed by: Stephanie Syslo, Environmental Scientist Brian Kiernan, Biologist William P. Eckel, Acting Branch Chief, ERB 6



### June 27, 2012

### -4 of 61- 1. Purpose

The purpose of this problem formulation is to pr ovide an understanding of what is known about the environmental fate and ecological effects of the registered uses of metribuzin (PC Code 101101) in preparation for conducting environm ental fate and ecologi cal risk, endangered species, and drinking water assessments for its registered uses. Additionally, this problem formulation is intended to identify data gaps, uncertainties, and potential assumptions used to characterize the ecological risk associated with the registered uses of metribuzin.

Metribuzin belongs to the Triazi none group of herbicides and it is applied as a pre-plant and preemergence herbicide with selective activity on gra sses and broad leaf weeds. Its mode of action is inhibition of photosynthesi s via photosystem II.

2. Problem Formulation

2.1. Nature of Regulatory Action

Under the Federal Insecticide, F ungicide, and Rodenticide Act (FIF RA), all pesticid es distributed

or sold in the United States generally must be registered by the Environmental Protection Agency (EPA). As part of determining whether a pesticide can be registered in the U.S., the Agency evaluates its safety to non-target spec ies based on a wide range of environmental and health effects studies. In 1996, FIFRA was amended by the Food Quality Protection Act, and the Agency was mandated to implement a new program for the periodic review of pesticides, i.e

., Registration Review ( http://www.epa.gov/oppsrrd1/registration_review/ ). The Registration Review program is intended to ensure that, as th e ability to assess risk evolves and as policies and practices change, all register ed pesticides continue to meet the statutory standard of no

unreasonable adverse effects to human health and the environment. Changes in science, public policy, and pesticide use practic es occur over time. Through th e Registration Review program, the Agency periodically reevaluates pesticides to make sure that as change occurs, products in the marketplace can be used safely.

As part of the implementation of the Registratio n Review program pursuant to Section 3(g) of the Federal Insecticide, Fungicide and Rodentic ide Act (FIFRA), the Agency is beginning its

evaluation of metribuzin to de termine whether it continues to meet the FIFRA standard for registration. This problem formulation for the environmental fate, ecological risk, endangered species, and drinking water assessment chapter in support of the Registration Review will be posted in the initial docket, which will open the public phase of the review process.

2.2. Previous Risk Assessments

Metribuzin was registered in the United States in 1973 as a pr e-emergent and post-emergent herbicide to selectively control certain broadlea f weeds and grassy weed species in various crop and noncrop areas. The Registration Standard was issued in July 1985. A Reregistration Eligibility Decision (RED) was i ssued in 1998 and concluded that registered uses exceed levels

### -5 of 61- of concern for acute and chronic avian and mamm alian effects, nontarget terrestrial and aquatic plant species, and endangered species. It al so concluded groundwater contamination is a concern. In addition, concentratio ns of metribuzin in ground wa ter have not exceeded the LOC for terrestrial plants, but over th e long term, persistent pesticid es that have leached to ground water will be discharged to su rface-water bodies. Although there is not a concern at the present time, in areas where irrigation water is contamin ated with metribuzin, residues could pose a threat to plants since levels of metribuz in detected in ground water have approached approximately 40% of the concentrat ions which could present a risk.

3. Stressor Source and Distribution

3.1. Mechanism of Action

Metribuzin is an herbicide with selective activ ity on certain grasses and broad leaf weeds.

Metribuzin is a triazinone and i nhibits electron transport in p hotosynthesis via photosystem II. Triazinones are very closely relate d to triazines and are thought to have very similar modes of

action. Triazinones and triazines bind to D-1 proteins forming free radicals that destroy chloroplasts and associated plant tissue.

3.2. Overview of Pesticide Use and Usage

Metribuzin is a pre-emergent and post-emergent herbicide. It is formulated as an emulsifiable concentrate, flowable concentrate, wettabl e powder, water soluble packaging, and water dispersible granules. Applicati on methods for metribuzin includ e ground spray, aerial spray, and chemigation. The application rate varies with th e formulation used, stage of weed growth, and application timing. Table 1 below provides the specific use patterns and provides the PRZM/EXAMS scenarios that may be used to represent each use pattern.

### -6 of 61- Table 1. Registered uses of Metribuzin. Use pattern Maximum single application rate (lb ai/A) Maximum annual application rate (lb ai/A) Application

interval

Soybean 1 1 Pre-emergence

0.625+0.5 1.125 Pre-plant then preemergence
Potato 1 1 NA 1



### Alfalfa/

Sainfoin 1 1 NA

Sugarcane 6 (Hawaii) 8 NS 3 (Louisiana and Texas) NS NS

2 (Florida) 2 NS Lentils/peas 0.375 (preemergence)

0.25 (postemergence) 0.5 Pre-emergence and

post-emergence

Chick peas 0.375 0.375 Pre-emergence Carrots 0.25 0.5 21 days

Tomatoes 1 1 NA

Cereals 0.5 0.5 NA Asparagus 2 2 NACorn 0.375 0.562 Pre-plant and preemergence Perennial

grasses 0.5625 0.5625 NA

Fall seeded

triticale 0.085 0.085 NA

Winter wheat 0.085 0.085 NA

1 NA = Not applicable (single application only)

2 NS = Not specified

### -7 of 61- The Biological and Economic Analysis Division ’s (BEAD) Screening Level Usage Analysis (SLUA; USEPA 2011) shows that the largest aver age amount of metribuzin is applied annually on potatoes, followed by soybeans, sugarcan e, and alfalfa (Table 2).

Table 2. Screening Level Estimates of Agricult ural Uses of Metribuzin (SLUA) Sorted Alphabetically from February 25, 2011. Percent Crop Ttd.

Crop Lbs. A.I. Avg. Max.

1 Alfalfa 200,000 <2.5 <2.5
2 Apples+ <500 <1 <2.5
3 Asparagus 20,000 30 50
4 Barley <500 <1 <2.5
5 Carrots 1,000 <2.5 5
6 Corn 50,000 <1 <2.5
7 Dry Beans/Peas 10,000 <2.5 5
8 Grapes+ <500 <1 <2.5
9 Pasture/Range+ <500 <1 <2.5
10 Peas, Green 1,000 5 10
11 Peppers+ 1,000 <2.5 5
12 Potatoes 400,000 75 85
13 Pumpkins+ <500 <1 <2.5
14 Soybeans 300,000 <2.5 5
15 Squash+ <500 <1 <2.5

16 Strawberries+ <500 <2.5 <2.5
17 Sugarcane 300,000 25 45
18 Sunflowers + 6,000 <1 <2.5
19 Sweet, Corn <500 <1 <2.5
20 Tomatoes 40,000 20 30
21 Wheat 50,000 <1 <2.5

All numbers rounded. <500 Less than 500 pounds of active ingredient <2.5 Less than 2.5 per cent of crop treated

<1 Less than 1 percent of crop treated

+ Crops not known to be listed on active e nd use product registrations or as Section 18 emergency exemptions when this report was run

SLUA data sources include:

### -8 of 61- USDA-NASS (United States Depa rtment of Agriculture's National Agricultural Statistics Service)

Private Pesticide Market Research California DPR (Department of Pesticide Regulation)

Figure 1 represents the national agricultu ral usage pattern of metribuzin in 2002 1 

### . It shows that usage was dispersed around the country but most concentrated in the Midwest and along the Mississippi Delta. Soybeans domin ated the agricultural use patte rns in 2002 accounting for an

estimated 44% of metribuz in usage. Since that time, use on potatoes has become the dominant use pattern though use on soybeans, s ugarcane, and alfalfa remain high.

Figure 1. Metribuzin Use in Total Pounds per County*.

1 The map was downloaded from a U.S. Geological Survey (USGS) , National Water Quality Assess ment Program (NAWQA) website. (http://water.usgs.gov/nawqa/pnsp/usa ge/maps/compound_listing.php?year=02)

### -9 of 61- 3.3. Environmental Fate and Transport

The Agency has reviewed or preliminarily reviewed all available fate data previously submitted by the registrant. All environmental fate data re quirements have been fully satisfied, except for aerobic aquatic metabolism and an aerobic aquatic metabolism.

Aerobic aquatic metabolism and anaerobic aquatic metabolism studies have been submitted but a preliminary review indicates they will not be used to support risk a ssessment because aerobic

and anaerobic conditions were not controlled or demonstrated and replicate data were not provided (MRID 00159423). Submitted aerobi c soil metabolism (MRID 40367602) and anaerobic soil metabolism (MRID 40367603) are su fficient to support risk assessment but

metribuzin concentrations in both studies fluctuated such that sample concentrations early in the study were less than some samples later in th e study. Submission of additional metabolism studies will generally reduce uncertainty in the es timation of metabolism half-lives and allow for

better characterization of the degradation kinetics.

Two terrestrial field dissipation studies have been submitted. One of the studies (MRID 40380901) provided useful information on the dissipa tion of metribuzin residues in the surface layer, but did not account for leaching below 6 inches in the soil profile. Neither terrestrial field dissipation study was fully acceptable: however, a small-scale prospective ground water study has been performed (MRID 45737901). This study accounted for the leaching of metribuzin and its degradates over the seve n years it was conducted.

Table 3 summarizes the submitted environmental fate data for metribuzin.

TABLE 3. General Chemical Properties and Environmental Fate Properties of Metribuzin

Parameter Value Reference (MRID)

/Comment

Physical/Chemical Parameters

CAS Registry Number 21087-64-9 Metribuzin RED

Chemical formula C 8 H 14 N 4 OS Metribuzin RED

Molecular mass 214.3 g/mol Metribuzin RED

SMILES Codes O=C1N(N)C(SC)=NN=C1C(C)(C)C EPISuite 1

Vapor pressure 9.1 x10 -7 torr Foot Print Pesticide Properties

Database 2.

Henry’s Law Constant 3.5*10 -11 atm-m 3 /mol Metribuzin RED

Water solubility (20°C) 1165 mg/L Foot Print Pesticide Properties

Database.

Octanol-water partition coefficient (Log K OW ) 1.65 Foot Print Pesticide Properties

Database.

Dissociation Constant pKa = 0.99 pKb = 13 Foot Print Pesticide Properties

Database.

### -10 of 61- Parameter Value Reference (MRID)

/Comment

Mobility

Freundlich K ads (mL/g), K oc- ads (mL/g

oc ) Metribuzin

1) 0.246 (1/n = 1.08), 46.7 (sand)
0.0182 (1/n = 1.52), 3.14 (sandy loam)
0.221 (1/n = 1.16), 14.5 (silt loam)
0.196 (1/n = 1.06), 17.0 (clay loam)

Metribuzin-DADK

2) 0.70 (1/n = 1.07), 44.7 (sandy loam)
0.15 (1/n = 1.16), 43.1 (sand)
0.29 (1/n = 0.96), 55.6 (clay)
0.95 (1/n = 1.08), 49.6 (silt loam)

Metribuzin-DK

3) 0.47 (1/n = 1.00), 30.0 (sandy loam)
0.13 (1/n = 1.06), 37.4 (sand)
0.19 (1/n = 1.04), 36.4 (clay)
0.51 (1/n = 1.10), 26.6 (silt loam) 1) MRID 42283001

2) MRID 43058502

3) MRID 43058501

Persistence in Water

Hydrolysis half-life (25°C, pH 5, 7, & 9) Stable at pH 5, 7 and 9 MRID 00157530

Aqueous photolysis half-life (26-29 °C, unbuffered pH 6.6) t 1/2 = 4.34 hours MRID 00157529

Persistence in Soil

Aerobic soil metabolism half-life t 1/2 = 106 d (sandy loam; parent) MRID 40367602

Anaerobic soil metabolism half-life t 1/2 = 112 d (sandy loam; parent) MRID 40367603

Soil Photolysis t 1/2 = 2.5 d MRID 00157531

Field Dissipation

Terrestrial field dissipation half-life 1) t 1/2 = 58d silty clay loam)

t 1/2 = 107d sandy loam muck

t 1/2 = 93d clay loam

t 1/2 = 67d sandy clay loam

muck

t 1/2 = 68d sandy clay loam

t 1/2 = 42d loamy sand

t 1/2 = 37d sandy loam

t 1/2 = 9d sandy loam

t 1/2 = 26d sandy loam

t 1/2 = 64d sandy loam

t 1/2 = 12d sand

2) t 1/2 = 40d days sandy loam

t 1/2 = 128d days sandy loam 1) MRID 40380901 2) MRID 42236101



### 1 EPISuite v4.0

2 http://sitem.herts.ac.uk/aeru/footprint/

### -11 of 61- Parent metribuzin is very stable to abiotic hydr olysis and relatively stable to both aerobic and anaerobic soil metabolism (T 1/2 

### s of 106 and 112 days, respectively). Although metribuzin appears to degrade rapidly in the laboratory by direct photolysis in water and on soil (T 1/2 

### s of 4.3 hours 1⁄2 and 2.5 days), only metribuzin that is on the surface of the soil is affected by photolysis. For that reason, persistence in fi eld soil appears to be more aff ected by soil metabolism (aerobic and anaerobic) than by photolysis, with field ha lf-lives of 40-128 days . While the rate of photodegradation is rapid for exposed chemicals, only approximately the top 1mm of soil is actually exposed to sunlight. Once in ground water, metribuzin is expected to persist due to its stability to hydrolysis and the lack of light pene tration. Conversely, resi dues of metribuzin in surface water are not likely to pe rsist in clear, well-mixed, sha llow surface water with good light penetration since parent metribuz in degrades rapidly by aqueous phot olysis with a calculated half life of 4.3 hours. However, if the surface wate r that receives metribuzin runoff contains significant sediments, metribuzin is expected to persist since it is stable to hydrolysis and since light penetration would be limited.

Based on available data, the primary routes of degradation of metribuzin are microbial metabolism and photolytic degradation on soil a nd its major degradates (>10% of applied metribuzin detected) are deaminated metribuzin (DA), and deaminated diketo metribuzin (DADK). The minor degradates are diketo me tribuzin (DK), pentylidene metribuzin, and hexylidene metribuzin. The DA and DK moieties degrade further to DADK as the respective keto group or amino group is removed. While fo rmation and decline can be observed in the review aerobic soil metabolism study for DA and DK, only formation can be observed for DADK. Therefore the persistence of DADK is an uncertainty. The photolytic products were deaminated (DA) metribuzin in water and pentyl idene and hexylidene metribuzin on soil. These compounds will be available for leaching to grou nd water and runoff to surface water in many

use conditions.

Metribuzin and its degradates diketo metribuzin (DK) and d eaminated diketo metribuzin (DADK) are persistent and mobile in soil. Me tribuzin has been found in ground water in 27 states as a result of normal agricultural appl ications done under a wide range of hydrogeological and climatic conditions. The highest metribuz in groundwater detecti on reported through the National Water-Quality Assessment Program (NAWQA) is 2.92 ppb in Virginia. The Metribuzin RED (1998) reports a concentration of 54 ppb in groundwater in Wisconsin but the

source of this data could not be confirmed. Metr ibuzin has been detected in surface water in 38 states with the highest concentration of 6.61 ppb detected in Louisiana. These monitoring

concentrations are derived from non-targeted studies and do not re present the highest metribuzin

residue concentration that can o ccur in the environment. There is a great deal of uncertainty regarding the degree to which these concentrations are representative.

3.4. Bioaccumulation

### -12 of 61- The Log K

ow 

### of metribuzin is 1.65 indicating th e compound has a low potential to

bioaccumulate. Because of this low bioaccumu lation potential, fish bioconcentration study has not been requested.

4. Receptors

Consistent with the process described in th e Overview Document (USEPA 2004), the risk assessment for metribuzin will rely on a surrogate species approach. Toxicological data generated from surrogate test species, which are intended to be representative of broad taxonomic groups, are used to extrapolate the poten tial effects on a variety of species (receptors)

included under these ta xonomic groupings.

Acute and chronic toxicity data from studies submitted by the pest icide registrant, along with the available open literature, will be used to evaluate the potential direct and indirect effects of metribuzin to aquatic and terrestrial receptors. This includes toxicity on the technical grade active ingredient, degradates, and when available, formulated products ( e.g. , “Six-Pack” studies). Open literature studies may be identified th rough EPA’s publically available ECOTOXicology (ECOTOX) database, which employs a literature search engine for locating chemical toxicity data for aquatic and terrestrial plants and wildli fe. The evaluation of both sources of data may also provide insight into the direct and indirect effects of metribuzin usage on biotic communities from loss of species that are sensitive to th e chemical and from ch anges in structure and

functional characteristics of the affected communities.

### -13 of 61- A brief summary of the aquatic and terrestrial toxicity data available for the species most sensitive to metribuzin is pr ovided in Sections 4.1 and 4.2, re spectively. A more complete summary of the available data is presented in Appendix B . In addition, a summary of ecological

incidents associated with metr ibuzin and a description of eco systems potentially at risk are provided in Sections 4.3 and 4.4, respectively. As noted previous ly, data on the formation and decline of metribuzin degradates are minimal, and there are practically no data on the potential toxicity of any degradates ex cept for a chronic aquatic inve rtebrate life cycle study with degradate DADK. In the DADK study, similar chronic effects were observed at levels similar to what was observed in the parent study, making th e degradate DADK equally toxic as the parent. Additionally, the ECOSAR model -a predictive system that estimates aquatic toxicity- indicates that DA, DK, and DADK are potentially similarly toxic as parent metri buzin (Appendix E) and because the toxicity of the degrad ates were estimated to be similar to of the parent’s, additional toxicological data on the de gradates is not required for registration review.

Toxicity to fish and aquatic invertebrates is categorized using the system shown in Table 4 (US EPA, 2004). Toxicity to terrestrial fauna (birds and mammals) is categorized using the system

shown in Table 5 . Toxicity categories for plan ts have not been defined.

Table 4. Categories of Acute T oxicity for Aquatic Animals

LC 50 (ppm) Toxicity Category < 0.1 Very highly toxic > 0.1 - 1 Highly toxic > 1 - 10 Moderately toxic > 10 - 100 Slightly toxic

> 100 Practically nontoxic



### Table 5. Categories of Acute Toxi city for Terrestrial Animals

LD 50 (mg/kg) LC 50 (ppm) Toxicity Category <10 <50 Very highly toxic 10-50 50-500 Highly toxic 51-500 501 - 1000 Moderately toxic 501-2000 1001 - 5000 Slightly toxic

>2000 >5000 Practically nontoxic



### 4.1. Effects to Aquatic Organisms

The most sensitive of the available aquatic toxicity data from registrant-submitted studies are provided in Table 6 . If open literature studies are iden tified through ECOTOX, they will be

reviewed for the risk assessment. Based on the av ailable information, metribuzin is slightly toxic to most aquatic animals yet is moderately toxic to freshwater invertebra tes on an acute exposure
basis. Chronic studies with fr eshwater fish and invertebrates indicate reproductive and growth effects were observed as low as 1.29 mg a.i./L ; however, the NOAEC for growth in the fish study could not be determined due to effects obser ved in all treatment levels (<3.0 mg a.i./L). A review of the comments from the registrant suggests it is unlikel y a new study with lower concentrations to achieve a NOAEC will impact th e risk assessment; thus, a re-examine of the study indicates that the growth NOA EC would have to be 64 times more toxic to result in a LOC exceedance, the reviewer agreed th at it is unlikely and the freshw ater fish early life-stage study does not have to be repeated to achieve a gr owth NOAEC. In addition, the structure-activity

### -14 of 61- relationship (SAR) model, ECOSAR , in Appendix D indicates the estimated chronic values are similar to the values observed in the laboratory studies, it is unlikely a new study will obtain a NOAEC 64 times more toxic that would impact th e risk assessment. In the absence of a NOAEC to assess chronic risk to freshwater fish, the LOAEC will be used as the surrogate. No chronic

studies with estuarine/marine fish and invertebrates were availabl e, acute-to-chronic calculations (ACR) would be used to estimate the LOAEC for estuarine/marine fish and the NOAEC for

estuarine/marine invertebrates. The use of ACR calculations are for assessing whether additional testing are needed from the registrant in absenc e of available data when concerns are raised.

Available data indicate both vascular and nonvascul ar aquatic plants are affected by metribuzin. Based on ECOSAR modeling for the degradate toxicity estimations and an acceptable DADK chronic study with daphnids indi cate that the degradates are as toxic as the parent; thus, the

ECOSAR values will be used to assess risk to aquatic organi sms exposed to the degradates; however, the uncertainty on using the ECOSAR va lues may be reduced with the submission of aquatic toxicity data for the degradates.

### -15 of 61- Table 6. Aquatic Toxicity Profile fo r Metribuzin and its Degradate DADK

Taxonomic Group Species (Common Name) Endpoint (mg a.i./L) Acute

Classification Reference (MRID)

Freshwater Fish Oncorhyncus mykiss (rainbow trout) LC 50 

### =42 Slightly toxic 40098001 (Acceptable)

Oncorhyncus mykiss (rainbow trout) NOAEC<3.0 a



### LOAEC =3.0 -- 42447801 (Acceptable)

Freshwater

Invertebrates Daphnia magna (daphnid shrimp) EC 50 

### =4.2 Moderately toxic 0072083 (Acceptable) Daphnia magna (daphnid shrimp) NOAEC=1.29

LOAEC=2.62 -- 42447802 (Acceptable) Daphnia magna (daphnid shrimp) exposed to DADK, a degradate NOAEC=3.3

LOAEC=5.6 -- 42732501 (Acceptable)

Estuarine/marine

Fish Cyprinodon variegatus (Sheepshead minnow) LC 50 

### =85 Slightly toxic 42094502 (Acceptable)

Acute to Chronic ratio (ACR) ACR

LOAEC= 6.1* -- Not Applicable

Estuarine/marine

Invertebrates Crassostrea virginica (Eastern oyster) LC 50 

### =40.7 Slightly toxic 00106197 (Acceptable)

Acute to Chronic ratio (ACR) ACR

NOAEC=30 b 

### -- Not Applicable

Vascular plants Lemna gibba (duckweed) IC 50 

### =0.13

NOAEC=0.018 -- c 

### 43893501 (Acceptable)

Nonvascular plants Psuedokirchneriella subcapitata (Green algae) IC 50 

### =0.0081

NOAEC=0.0023 -- c 

### 43921001 (Acceptable)

a Memorandum dated April 7, 1994 – A new study with lower test concentrations to determine the NOAEC for growth is not required since the LOAEC was still above ex posure estimates. The maximum use rate was 6 lb a.i./A, with multiple applications allowed up to 16 lb a.i./A, re sulting in a maximum EEC of 183 μg a.i./L. The EEC of 183 μg a.i./L is 16 times less than the LOAEC determined from the study for growth (3000 μg a.i./L) and are 64 times

less than the NOAECs determined for su rvival and hatchability (11,700 μg a.i. /L). Since the NOAEC for growth is uncertain, applying a safety factor of 10 still results in a value (300 μg a.i./L) greater than the EEC.

b Pink shrimp, an estuarine/marine invertebrate (MRID 00106197), was used in the acute-chronic ratio calculation since the species is more similar to daphnid shrimp than Eastern oyster.

c Toxicity categories for plants have not been defined. * The LOAEC from the freshwater fish early life stage (MRID 42447801) was used in the ACR calculation to estimate the LOAEC for chronic toxicity to estuarine/ marine fish because the NO AEC was not available for

calculation.



### 4.2. Effects to Terres trial Organisms

### -16 of 61- Table 7 summarizes the most sensitiv e terrestrial toxicity endpoint s for metribuzin, based on an

evaluation of the submitted data. If open literature studies are identified through ECOTOX, they

will be reviewed for the risk assessment. Metribuz in is classified as moderately toxic to upland game birds based on the available acute oral st udy with the Northern bobwhite quail; however, an acute oral study with a passeri ne species is necessary for risk assessment to strengthen the toxicity classification for birds via the acute oral route. Passerines tend to have greater sensitivity to pesticides than game birds. No effects fr om subacute and chronic exposure to upland game

birds and waterfowls via the diet ary route were observed; however, an uncertainty exists because in the RED, there were LOC exceedances for birds when no effects were observed in the studies. Thus, the test concentrations were not tested high enough or tested at/above environmentally relevant concentrations, a new reproduction stud y at or above the envi ronmentally relevant

concentrations is recommended to address the uncer tainty whether there are actual risks to birds. The recommended species for the new reproducti on study should be the bobwhite quail since acute effects in quails were observed in the avian acute oral study. Metribuz in is classified as slightly toxic to mammals on an acute oral exposure basis, although effects from chronic exposure include reduced body weights and body wei ght gain. Metribuzin is classified as practically nontoxic to honey bees ( Apis mellifera ) on an acute contact exposure basis. As expected with an herbicide, metribuzin ha s adverse effects on terrestrial plants.

In summary, terrestrial data needed:

OCSPP 850.2100 – Avian Acute Oral. An avian ac ute oral toxicity study with a passerine species is necessary for risk assessment. A dditionally the available avian acute oral study with bobwhite quail resulted in a LD 50 

### value of 169.2 mg a.i./kg-bw, which classifies metribuzin as moderately toxic to birds via the oral route. Therefore additional data are necessary to strengthen the risk assessment for bi rds from acute effects since the subacute dietary

studies indicate metribuzin is not toxic to birds via the dietary r oute. It is recommended that a definitive study be conducted; however, a limit test with a higher exposure concentration (to be determined through consultation with the Agency) may also be acceptable.

OCSPP 850.2300- Avian Reproduction. An avian reproduction toxicity study with the Northern bobwhite quail is necessary for risk assessment. The available avian reproduction studies with bobwhite quail and mallard duck indicated no dose-response effects were observed at any concentrations including the highest test concentrations tested. However, in the RED, the risk assessment sugge sts the risk to birds exists base d on the toxicity value selected from the reproduction studies for use in the avian risk assessment. But a closer look at the study

indicated the test concentrations were not tested high enough or at /above environmentally relevant concentrations, which explain why the LOC exceedance exists when no effects occurred; it is uncertain if there is actually any risks to birds. A ne w study with higher test concentrations (up to 1,500 mg a.i./kg diet) should addre ss the risk uncertainty. The recommended test species for the new reproducti on study is the Northern bobwhite quail since acute effects were observed in this species in the avian acute oral toxicity test.

### -17 of 61- Table 7. Terrestrial Toxicity Profile for Metribuzin.

Taxonomic Group Surrogate Species (Common

Name) Endpoint Acute Classification/

Chronic effect Reference (MRID)

Birds Colinus virginianus (Bobwhite quail) LD 50 

### =169.2 mg a.i./kg bw Moderately toxic 00255025 (Acceptable)

LC 50 

### >4000 mg a.i./kg diet Practically nontoxic 00262228 (Acceptable)

Passerine bird No data No data --

Anas platyrhynchos (Mallard duck) NOAEC=368 mg a.i./kg-diet

LOAEC>368 mg a.i./kg-diet No effects observed 43860501 (Acceptable)

Mammals Mus musculus (Laboratory mouse) LD 50 

### =698/711 mg a.i./kg bw (Female/Male) Slightly toxic 00106158 (Health Effects Division)

Laboratory rat NOAEC=30 mg a.i./kg-diet (1.5 mg a.i./kg/day-bw) Body weight and body weight gain 40838401 (Health Effects Division)

Beneficial

Insects Apis mellifera (Honey bee) LD 50 

### =60.4

μ g/bee Practically nontoxic 28772 (Acceptable)

Seedling

emergence Monocot:

Onion

Dicot: Turnip IC 25 

### =0.02

NOAEC=0.014

IC 25 

### =0.008

NOAEC=0.007 -- a 

### 42447803

Vegetative vigor Monocot:

Onion

Dicot: Turnip IC 25 

### =0.017

NOAEC=0.011

IC 25 

### =0.005

NOAEC=0.003 -- 42447803

a 

### toxicity categories not assigned to plants



### 4.3. Incident Database Review

A review of the EIIS database for ecological incidents involving metribuzin was completed on May 24, 2012. 58 total incidents are reported in the database, two aquatic and 56 terrestrial (Appendix B).

The terrestrial incidents reported are for adverse effects to crops, trees, and ornamentals plants. Effects include mortality, plant damage, and disc oloration. The incidents occurred both from direct application and from spray drift. Two a quatic incidents reported we re for fish kills, but

### -18 of 61- involved other herbicides (ala chlor, chlorimuron-methyl, a nd paraquat dichloride) and the

contribution of metribuzin is unknow n. The legality of the applica tion of metribuzin is uncertain

for these incidents.

A search of the Avian Incide nt Monitoring System (AIMS; http://www.abcbirds.org/abcprograms /policy/toxins/aims/aims/index.cfm ), a database administered by the American Bird Conservanc y which contains publicly available data on reported avian incidents involving pesticides did not report any in cidents for metribuzin as of May 24, 2012.

Pesticide registrants report cert ain types of incidents to the Ag ency as aggregate counts of incidents occurring per product per quarter. Forty one aggregated incidents have been reported to the Agency associated with metribuzin. All aggregated incidents are for minor plant damage.

4.4. Ecosystems Potentially at Risk

The ecosystems at risk are often extensive in scop e; therefore, it may not be possible to identify specific ecosystems during the development of a nation-wide ecological risk assessment. However, in general terms, terrestrial ecosystem s potentially at risk could include the treated field and immediately adjacent areas that may r eceive drift or runoff. Areas adjacent to the

treated field could include cultiv ated fields, fencerows and hedgero ws, meadows, fallow fields or grasslands, woodlands, riparian habi tats and other uncultivated areas.

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

treated field and could include impounded bodies such as ponds, lake s and reservoirs, or flowing waterways such as streams or rivers. For uses in coastal areas, aquatic habitat also includes marine ecosystems, including estuaries.

5. Assessment Endpoints

Assessment endpoints are defined as “explicit expressions of the actual envir onmental value that is to be protected.” 2 

### Selection of the assessment endpoi nts is based on valued entities ( e.g., fish, birds), the ecosystems potentially at risk ( e.g., waterbodies, riparian vegetation, and upland habitats), the migration pa thways of metribuzin ( e.g., runoff, drift, etc .), and the routes by which ecological receptors are e xposed to metribuzin ( e.g., direct contact, etc. )

.

Assessment endpoints for metribuzin include dire ct toxic effects on the survival, reproduction, and growth of the receptors, as we ll as indirect effects, such as reduction of the prey base or modification of habitat. Each assessment endpoint requires one or more “measures of ecological effect,” defined as changes in the attributes of an assessment endpoint or changes in a surrogate entity or attribute in response to exposure to a pesticide. Specif ic measures of ecological effect are generally evaluated based on acute and chronic toxicity information from registrantsubmitted guideline tests that are performed on a limited number of organisms. Additional ecological effects data from the open literature will also be considered.

2 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.

### -19 of 61- 6. Conceptual Model

For a pesticide to pose an ecological risk, it mu st reach ecological receptors in biologically significant concentrations. An exposure pathway is the means by which a pesticide moves in the environment from a source to an ecological recepto r. For an ecological pathway to be complete, it must have a source, a release mechanism, an environmental transport medium, a point of exposure for ecological receptors, an d a feasible route of exposure.

The conceptual model for metribuzin provides a written description (ris k hypothesis) and visual representation (conceptual diagram) of the predicted relationships between metribuzin, potential routes of exposure, and the pr edicted effects for the assessmen t endpoint. A conceptual model consists of two major components: risk hypot hesis and a conceptual diagram (USEPA 1998).

Based on the available data (including those from studies with problems, and considering existing data gaps), metribuzin is stable in neutra l, acidic and basic water. Metribuzin is expected to be resistant to biotic degradation under ae robic and anaerobic aquatic conditions; and degrade slowly in soil under aerobic condi tions. On the other hand; metri buzin photodegrades rapidly in clear, shallow surface water. However, direct photolytic degradation of the parent or its degradates in turbid and/or deeper waters will be limited by the attenuation of sunlight.

Metribuzin and its degradates are mobile in all soil conditions. Metribuzin and its degradates can be expected to leach to groundwater, where it is expected to persist in the anaerobic conditions

Metribuzin is not expected to bi oaccumulate in aquatic or terres trial food chains based on its low Log K
ow 

### value.

6.1. Risk Hypothesis

A risk hypothesis describes the predicted re lationship among the stre ssor, exposure, and assessment endpoint response along with the rationa le for their selection. For metribuzin, the following ecological risk hypothesis will be empl oyed for the national-level ecological risk

assessment:

Given the uses of metribuzin and its environmental fate proper ties, there is a likelihood of exposure to non-target terrestrial and aquatic or ganisms. When used in accordance with the label, metribuzin may result in potential adverse effects upon the survival, growth, and reproduction of non-target terrestrial and aquatic organisms.

6.2. Conceptual Diagram

The conceptual model used to depict the potentia l ecological risk associated with the use of metribuzin (the stressor) assumes that as a pestic ide, metribuzin can adversely affect terrestrial

### -20 of 61- and aquatic organisms (the receptors) if environm ental concentrations exceed toxic thresholds as a result of application accord ing to the label directions ( Figures 2 and 3 ). Ecological receptors that may potentially be exposed to metribuzin include terrestrial and semi-aquatic wildlife ( e.g. , mammals, birds, terrestrial-phase amphibians and reptiles), terres trial and semi-aquatic plants, and terrestrial invertebrates ( e.g. , honey bees). Additionally, gi ven the mobility of metribuzin, aquatic organisms ( i.e. , freshwater and estuarine/marine fi sh and invertebrates, aquatic-phase amphibians, and aquatic plants) are potential rece ptors in adjacent water b odies through off-site transport of metribuzin from the application site through runoff, erosion, and spray drift.

Figure 2. Conceptual model for metribuzin exposure to aquatic organisms. Dashed lines indicate route of exposure considered of lower importance for metribuzin. 

### Stressor

Source

Receptors

Attribute Change Pesticide applied to use site

Spray drift

Fish/aquatic-phase amphibians Eggs

Larvae

Juveniles / Adults

Individual organisms

Reduced survival Reduced growth Reduced reproduction Food chain Reduction in algae Reduction in prey Habitat integrity Reduction in primary productivity

Reduced cover Community change Surface water Runoff

Aquatic Animals

Invertebrates

Vertebrates 

### Exposure

Media

Uptake/gills or integument

Ingestion Ingestion Atmospheric

transport

Wet/dry deposition Soil Ground water

Uptake/gills or integument

Aquatic Plants

N on-vascular

Vascular Uptake/cell, roots, leaves Riparian plant

terrestrial

exposure pathways see

Figure 2

### -21 of 61- Figure 3. Conceptual model for metribuzin exposure to terrestrial organisms. Dashed lines indicate route of exposure considered of lower importance for metribuzin.

### -22 of 61- 7. Analysis Plan

In order to address the risk hypot hesis, the potential for adverse effects on the environment will be estimated. The use, environmental fate, a nd ecological effects of metribuzin will be characterized and integrated to assess the risks. This will be accomplished using a risk quotient (ratio of exposure concentration to effects c oncentration) approach. Although risk is often defined as the likelihood and magnitude of advers e ecological effects, the risk quotient-based approach does not provide a quantitative estimate of likelihood and/or magnitude of an adverse effect. However, as outlined in the Overview Document (USEPA 2004), the likelihood of effects to individual organisms from particular uses of metribuzin may be estimated using the probit dose-response slope and either th e level of concern (discussed be low) or the actual calculated risk quotient value.

This analysis plan will be revisited and may be revise d depending upon the information submitted by the public in response to the openi ng of the Registration Review docket for

metribuzin.

7.1. Stressors of Concern

The stressors of concern in the assessment will be metribuzin and its major degradates DAmetribuzin and DADK-metribuzi n. Based on a chronic freshwat er invertebrate study with DADK-metribuzin and ECOSAR modeling indicate th e degradates to be of similar toxicity to the parent; therefore a total toxic residue approach will be applied in the risk assessment. The uncertainty in exposure due to the use of TTR may be reduced with th e submission of aquatic toxicity data for the degradates if the data in dicates the degradates ar e not of toxicological

concern.

In its ecological risk assessments, the Agency does not routinely include an evaluation of mixtures of active ingredients, either those mi xtures of multiple activ e ingredients in product formulations or those in the applicator’s tank. In the case of the product formulations of multiple active ingredients (that is, a regi stered product containing more than one active ingr edient), each active ingredient is subject to an individual risk assessment for regulatory decision regarding the active ingredient on a particular use site. If e ffects data are available for a formulated product containing more than one active ingredient, the da ta may be used qualitatively or quantitatively in accordance with the Agency’s Overview Document and the Services’ Evaluation Memorandum (USEPA, 2004; W illiams and Hogarth, 2004).

7.2. Measures of Exposure

In order to estimate risks of metribuzin expos ures in aquatic and terrestrial environments, exposure modeling will be based on application rates and methods fo r products registered at the time of Registration Review. Measures of expos ure are based on aquatic and terrestrial models that predict estimated environmental concentratio ns (EECs) of metribuzin and degradates of

### -23 of 61- concern. 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_pg.htm

7.3. Measures of Effect

Ecological effects data are used as measures of di rect and indirect effect s to biological receptors. Effects data are obtained from registrant-submitted studies or from literature studies identified by

the ECOTOX database.

The acute measures of effect used fo r animals in this assessment are the LD 50 

### , LC 50 

### and EC 50



### . LD stands for "Lethal Dose", and LD 50 

### is the amount of a material, given all at once, that is

estimated to cause the death of 50% of the test organisms. LC stands for “Lethal Concentration”

and LC 50 

### is the concentration of a chemical that is estimated to kill 50% of the test organisms.

EC stands for “Effective Concentration” and the EC 50 

### is the concentration of a chemical that is estimated to produce a specific effect in 50% of the test organisms. Endpoints for chronic measures of exposure for listed and non-listed animals are the NOAEL/NO AEC. NOAEL stands

for “No Observed-Adverse-Effect-Level” and refers to the highest tested dose of a substance that has been reported to have no harmful (adve rse) effects on test organisms. The NOAEC ( i.e.

, “No-Observed-Adverse-Effect-Concen tration”) is the highest test concentration at which none of

the observed effects were statisti cally different from the control. For non-listed plants, only acute exposures are assessed ( i.e. , IC 25 

### for terrestrial plants and IC 50 

### for aquatic plants); for listed plants either the NOAEC or IC 05 

### is used.

Where available, sublethal effects observed in both registrant-submitted and open literature studies will be evaluated qualitatively. Such effects may include behavioral changes ( e.g. , lethargy and changes in coloration). However, qua ntitative assessments of risks are limited to those endpoints that can be di rectly linked to the Agency’s assessment endpoints of impaired survival, growth and reproduction.

In the absence of taxon-specific da ta, the assessment of risk fo r direct effects to non-target organisms makes the assumption that toxicity of metr ibuzin to birds is similar to terrestrial-phase amphibians and reptiles. The same assumption is ma de for fish and aquatic-phase amphibians. In

the absence of data for either acute or chronic effects, the conservative assumption will be to presume that metribuzin is toxic.

7.4. Integration of Exposure and Effects

Risk characterization is the integration of e xposure and ecological effects characterization to determine the potential ecological risk from the registered uses of metr ibuzin and the likelihood of direct and indirect effects to non-target or ganisms in aquatic and terrestrial habitats. The exposure and toxicity effects data are integrated in order to evaluate the risks of adverse ecological effects on non-target spec ies. For the assessment of metri buzin risks, the risk quotient (RQ) method is used to compare exposure and measured toxicity values. EECs are divided by acute and chronic toxicity values . The resulting RQs are then compared to the Agency’s Levels of Concern (LOCs) (USEPA 2004). Th ese criteria are used to indicate when metribuzin use, as directed on the labels, has the potential to cause a dverse direct or indirect effects to non-target

### -24 of 61- organisms. In addition, incident data from the EIIS will be considered as part of the risk

characterization.

7.5. Deterministic and Probabilistic Assessment Methods

The quantitative assessment of risk will primarily depend on the deterministic point-estimate (RQ) based approach described in the risk assessment. An effo rt will be made to further qualitatively describe risk usi ng probabilistic tools that the Ag ency has developed. These tools have been reviewed by FIFRA Scientific Advisory Panels ( http://www.epa.gov/sc ipoly/sap/index.htm ) and have been deemed as appropriate means of refining assessments where deterministic approach es have identified risk s. Newer tools may be available to assess the routes of exposure ( e.g. TIM and SWAMP models) and will be applied as appropriate in Re gistration Review.

7.6. Endocrine Disruptor Screening Program

As required under FFDCA section 408(p), EP A has developed the Endocrine Disruptor Screening Program (EDSP) to determine whether certain substances (inc luding pesticide active and other ingredients) may have an effect in humans or wildlife si milar 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 ap proach 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 estroge n, androgen, and or thyroid (E, A, or T) hormonal systems. Chemicals that go th rough Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal systems will proceed to the next stag e of the EDSP where EPA will determine which, if any, of th e Tier 2 tests are necessary base d on the available data. Tier 2 testing is designed to identify a ny adverse endocrine related eff ects caused by the substance, and establish a dose-response relationship between the dose and the E, A, or T effect.

Between October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, which contains 58 pesticid e active ingredients and 9 inert ingredients.

This list of chemicals was selected based on th e potential for human exposure through pathways such as food and water, residen tial activity, and certain post-applic ation agricultural scenarios.

This list should not be construed as a lis t of known or likely e ndocrine disruptors.

Metribuzin is among the group of 58 pesticide active ingredients on the initial list to be screened under the EDSP. The Agency will review the EDSP Tier 1 data and any “other scientifically relevant information” submitted in response to test orders. Based on this review the Agency will determine the need for additional testing. For fu rther information on the status of the EDSP, the policies and procedures, the list of 67 chemicals, the test guide lines and the Tier 1 screening battery, please visit our webs ite: http://www.epa.gov/endo/.

7.7. Endangered Species Assessment

### -25 of 61- Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the Agency will evaluate risks to Federally-listed th reatened and/or endangere d (listed) species from registered uses of metribuzin. This assessm ent will be conducted in accordance with the Overview Document (USEPA 2004), provisi ons of the ESA, and the Services’ Endangered Species Consultation Handbook (USFWS/NMFS, 1998).

The assessment of effects associat ed with the registration of me tribuzin is based on an action

area. The action area is considered to be the area directly or indirectly affected by the federal action, as indicated by the exceedance of Agency Le vels of Concern (LOCs) used to evaluate

direct or indirect eff ects. The Agency’s approach to defi ning the action area under the provisions of the Overview Document (USEPA 2004) considers the results of the risk assessment process to
establish boundaries for that action area with the understandi ng that exposures below the Agency’s defined LOCs constitu te a no-effect threshold. For th e purposes of this assessment,

attention will be focused on the footprint of the action ( i.e ., the area where metribuzin application occurs), plus all areas where offsite transport ( i.e ., spray drift, runoff, etc .) may result in potential exposure that exceeds the Agency’s LOCs. Specific m easures of ecological effect that define the action area for listed species include any direct and indi rect effects and/or potential modification of its critical habitat, including reduction in survival, growth, and reproduction as well as the full

suite of sublethal effects availabl e in the effects literature. Theref ore, the action area extends to a point where environmental exposures are below any measured lethal or sublethal effect threshold for any biological entity at the whole organism, organ, tissue, and cellular level of organization. In situations where it is not possible to determin e the threshold for an observed effect, the action area will initially be assumed to include all counties where metribuzin is used in the United

States.

7.8. Drinking Water Assessment

In order to bring the drinking water exposure assessment up to da te with current data, models and simulation model guidance, a new drinking water assessment will be conducted to support future human health dietary risk assessments of metribuzin. The drinking water exposure assessment will be conducted for the maximum labeled use in support of the human health dietary risk assessment. The drinking water assessment will incorporate model estimates of metribuzin in surface water and ground water includi ng any residues that are determined to be of toxicological concern. Concentratio ns of metribuzin and degradate in surface waters (Estimated Drinking Water Concentrations, or EDWCs) will be estimated using PRZM (Version 3.12.2, May 12, 2005), EXAMS (Version 2.98.04.06, Apr. 25, 2005), but using the Index Reservoir

scenario rather than the sta ndard pond used for assessment of exposure in drinking water.

An EDWC of metribuzin in gr ound water will be estimated usi ng EFED’s Tier I aquatic model SCIGROW (Screening Concentrat ion in Ground Water, version 2.3; 8/8/2003). SCIGROW is a regression model used as a scr eening tool to estimate pesticid e concentrations found in ground water used as drinking water. The output of SC IGROW represents the concentrations that might be expected in shallow unconfined aquifers unde r sandy soils, which is representative of the ground water most vulnerable to pesticide contam ination likely to serve as a drinking water source. If a refined drinking wa ter assessment is requested or if considered appropriate at the

### -26 of 61- time of assessment, an appropriate Tier II groundwater model may be used to determine

EDWCs.

7.9. Environmental Monitoring Data

Surface water:

Surface water monitoring data from the Unite d States Geological Survey (USGS) NAWQA program were obtained on May 23, 2012. Of the 14,779 tests for metribuzin, 3,702 (25%)

resulted in detections of metri buzin. Detection concentrations ranged from the lowest LOD of 0.004 μg/L up to 6.61 μg/L detected in th e Tensas River in Louisiana.

Limited surface water monitoring data is available for metribuzin de gradates. Only 2 tests were made in one state (Iowa). The only degradate that was analyzed for was DADK metribuzin; no detections were reported. The extent and magnit ude of metribuzin degrad ates in surface waters is an uncertainty.

Groundwater:

Ground water monitoring data from the United States Geological Survey (USGS) NAWQA program were obtained on May 23, 2012. A total of 13,397 water samples across various sites throughout the US were analyzed for metribuzi n. There were 195 detec tions of metribuzin which ranged from 0.0016 to 3.69 μg/L.

A Prospective Groundwater (PGW) study was conducted near Minden, Nebraska (MRID 45737901). Metribuzin was applied at a rate of 0.816 lb a.i./ac. To tal metribuzin residues were measured in multiple wells at the site thr oughout the duration of the study, with a peak concentrations of 1.64 μg/L occurring 2,210 days after treatment. The study was terminated shortly after these peak detecti ons were recorded because bromid e tracer concentrations were no longer increasing.

8.0. Preliminary Identification of Data Gaps

8.1. Environmental Fate

The available environmental fate and transport da ta are considered incomplete for the purposes of risk assessment. The following data gaps exist:

 Aerobic Aquatic Metabolism (OCSPP guideline # 835.4200) Further data are needed to support risk assessment. Concentrations in submitted soil metabolism studies fluctuated

over time and additional metabolism studies would aid characterization and reduce uncertainty.

### -27 of 61-  Anaerobic Aquatic Metabolism (OCSPP guidelin e # 835.4400) Further data are needed to support risk assessment. Concentrat ions in submitted soil metabolism studies

fluctuated over time and additional metabo lism studies would aid characterization and reduce uncertainty.

 Environmental Chemistry Methods and I ndependent Laboratory Validation (OCSPP guideline # 850.6100) This study is requi red to corroborate methods used in

environmental fate studies and to assist in the enforcement of pesticide tolerances.

Table 8 identifies studies by MRID that offer data for each guideline requirement, as well as study classifications and whether or not furthe r data are needed in order to support risk assessment ( i.e. , whether there is a data gap).

Table 8. Summary of available environmental fate data.

Guideline Study Title MRID /

ACC No. Classification Data Gap? Comments

835.2120 Hydrolysis 00157530 Acceptable No

835.2240 Photodegradation

in Water 00157529 Acceptable No

835.2410 Photodegradation

on Soil 00157531 Acceptable No

835.4100 Aerobic Soil

Metabolism 40367602 Acceptable No

835.4200 Anaerobic Soil

Metabolism 40367603

41555105 Acceptable

In Review No

835.4300 Aerobic Aquatic

Metabolism 159423 In Review Yes Further data are needed to support risk

assessment. Concentrations in submitted soil

metabolism studies fluctuated over time and

additional metabolism studies would aid characterization and reduce uncertainty. In the absence of data, it will be assumed that the aerobic aquatic metabolism half life is double that

of the aerobic soil metabolism half life.

835.4400 Anaerobic Aquatic

Metabolism 159423 In Review Yes F urther data are needed to support risk assessment.

C oncentrations in submitted soil metabolism studies

f luctuated over time and additional metabolism

studies would aid char acterization and reduce

u ncertainty. In the absence of data, it will be

a ssumed that the anaerobic aquatic metabolism half

l ife is double that of the anaerobic soil metabolism

h alf life

835.1240,

835.1230 Mobility - Adsorption / Desorption 1) 42283001

2) 43058502

3) 43058501 Acceptable No

835.6100 Terrestrial Field Dissipation 40380901

42236101 Supplemental

Invalid Yes Terrestrial field dissipation is considered a data gap

b ecause leaching was not accounted but the

p rospective ground water study accounts for

l eaching. Therefore, a new terrestrial field

d issipation study is not being requested at this time.

835.7100 Groundwater monitoring 45737901 In review No

### -28 of 61- 8.2. Ecological Effects

The available ecological effects database for metr ibuzin is incomplete (Tables 9-11). Acute avian oral toxicity data (850.2100) on a passeri ne species and new avian reproduction data (850.2300) with the bobwhite quail are necessary:

 OCSPP 850.2100- Avian Acute Oral. An avian acute oral toxicity study with a passerine is necessary for risk assessment. Additionally the available avian acute oral study resulted in a LD 50 

### value of 169.2 mg a.i./kg-bw which classifies metribuzin as moderately toxic to bobwhite quail via oral exposure. Therefore additional data are necessary to strengthen the risk assessment for birds from acute effects since the subacute dietary studies via the dietary route indicate metribuzin is not

toxic to birds. It is recommended that a definitive study be conducted; however, a limit test with a higher exposure c oncentration (to be determined through consultation with the Agency) may also be acceptable.

 OCSPP 850.2300- Avian Reproduction. An avi an reproduction toxicity study with the Northern bobwhite quail is necessary for risk assessment . The available avianreproduction studies with bobwhite quail and mallard duck indicated no doseresponse effects were observed at any con centrations including the highest test

concentrations tested. However, in the RED, the risk assessment suggests the risk to birds exists based on the toxicity value sele cted from the reproduction studies for use in

the avian risk assessment. But a closer look of the study indicated the test concentrations were not tested high enough or at/above envi ronmentally relevant concentrations, which explain why the LOC exceedance exists when no effects occurred; it is uncertain if there is actually any risks to birds. A new study w ith higher test concentr ations (up to 1,500 mg a.i./kg diet) should address the risk uncerta inty. The recommended test species for the new reproduction study is the Northern bobwh ite quail since acute e ffects were observed in this species in the avian acute oral toxicity test.

### -29 of 61- TABLE 9. Available ecological effects data for t errestrial animals exposed to metribuzin

Guideline Description MRID/

Accession Classification Data Gap? Comments

850.2100 Avian oral toxi city 255025 Acceptable Yes a Avian acute oral toxicity data

are not available for passerines, which are required

under 40 CFR Part 158. Additionally, the available acute oral study classified metribuzin as moderately toxic to upland game birds via the oral route. A passerine study would strengthen the oral route toxicity

classification since available subacute dietary data indicate

metribuzin is not toxic via the dietary route.

There were LOC exceedances in the previous risk assessment for reproductive and growth

risk to birds at concentrations where no reproductive effects

were observed. To address this uncertainty, the test

concentrations in the avian reproduction studies need to be tested high enough or at environmentally relevant

concentrations to better assess

chronic risk to birds. The recommended species is the bobwhite quail. 850.2200 Avian dietary toxicity 262228 Acceptable No 065507 Acceptable

850.2300 Avian reproduction 43926601 Acceptable Yes 43860501 Acceptable

850.3020 Honeybee acute contact toxicity 028772 Acceptable No

a Bold indicates data necessa ry for risk assessment

TABLE 10. Available ecological effects data for aquati c animals exposed to metribuzin and its degradate

DADK.

Guideline Description MRID/

Accession Classification Data Gap? Comments

850.1075 Freshwater fish – Acute toxicity 40098001

255025

090427 Acceptable No

850.1075 Estuarine/marine

fish – Acute toxicity 42094502 Acceptable No

850.1010 Freshwater

invertebrates – Acute toxicity 72083

34016 Acceptable No

### -30 of 61- Guideline Description MRID/

Accession Classification Data Gap? Comments

850.1035

850.1055 Estuarine/marine

invertebrates –Acute toxicity 43851

106197

42094501

47023411 Supplemental Acceptable Acceptable Supplemental No

An ACR will be applied in the

absence of data. 106197 Acceptable No

850.1300 Freshwater

invertebrate – life cycle test 42447802

Acceptable No 42732501 (DADK, a degradate)

850.1350 Estuarine/marine

invertebrates – life cycle test -- -- No a

850.1400 Freshwater fish – early life stage test 42447801 Acceptable No

850.1400 Estuarine/marine

fish – early life stage test -- -- No a

a Conditionally required when 40 CFR 158 criterions are triggered; however, none of the criteria were triggered, data are not required.

TABLE 11. Available ecological effects da ta for plants exposed to metribuzin.

Guideline Description MRID Classification Data Gap? comments

850.4100 Terrestrial Plant toxicity: Tier II seedling emergence 42447803

43208301 Acceptable No

850.4150 Terrestrial Plant toxicity: Tier II vegetative vigor 42447803 Acceptable No

850. 5400 Aquatic Plant Growth: algae 43133601

43867701

43826101

43893502 Acceptable Acceptable Acceptable Supplemental No

850.4400 Aquatic Plant Growth: vascular plants 43893501 Supplemental No



### 9. Other Information Needs

There is specific information that will assist the Agency in refini ng the ecological risk assessment, including any species-specific effect s determinations. The Agency is very much interested in obtaining the following information:

1. confirmation on the following label information

a. frequency of application, applicati on intervals, and maximum number of applications per season

### -31 of 61- b. geographic limitations on use

2. use or potential use distribution ( e.g ., acreage and geographical distribution of relevant crops)

3. use history

4. median and 90 th 

### percentile reported use rates (lbs. a. i./acre) from usage data – national, state, and county

5. application timing (date of first application and application interval s) by crop – national, state, and county

6. More specific definitions of non-agricultu ral use areas

7. sub-county crop location data

8. directly acquired county-level usage da ta (not derived from state level data)

a. maximum reported use rate (lbs. a.i. /acre) from usage data – county

b. percent crop treated – county

c. median and 90 th 

### percentile number of applications – county

d. total pounds per year – county

e. the year the pesticide was last us ed in the county/sub-county area

f. the years in which the pesticide was applied in the county/sub-county area

9. state or local use restrictions

10. ecological incidents (non-target plant damage and avian, fish, reptilian, amphibian and mammalian mortalities) not alr eady reported to the Agency

11. monitoring data

10. References

Open Literature Citations

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger . 1994. Literature review and evaluation of the EPA food-chain (Kenaga) nomogram, an instru ment for estimating pesticide residues on plants. Environ. Tox. Chem. 13:1383-1391.

Hoerger, F., and E.E. Kenaga. 1972. Pesticide residues on plants: Correlation of representative

data as a basis for estimation of thei r magnitude in the environment. In F. Coulston and
F. Korte, eds ., Environmental Quality and Safety: Chemistry, Toxicology, and Technology, Georg Thieme Publ, St uttgart, West Germany, pp. 9-28.

U.S. Fish and Wildlife Service (USFWS) and Na tional Marine Fisheries Service (NMFS). 1998. Endangered Species Consultation Handbook: Procedures for Conducting Consultation

and Conference Activities Under Section 7 of the Endangered Sp ecies Act. Final Draft.

March 1998.

USEPA. 1998. Guidelines for Ecological Risk Asse ssment. Risk Assessment Forum, Office of Research and Development, Washi ngton, D.C. EPA/630/R-95/002F. April 1998. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=30759

### -32 of 61- U.S. EPA. 2002. Refined Estimated Environmenta l Concentrations (EECs) for Metribuzin and its Degradate Desmethylmetribuzin in Surface Water and Groundwater. DP 282196. Washington, D.C. May 1, 2002.

USEPA. 2004. Exposure Analysis Modeling System (EXAMS): User Manual and System

Documentation. EPA/600/R-00/81-023. May 2004. Ecos ystems Research Division. United States Environmental Protection Agency. Available at http://www.epa.gov/ceampubl/swate r/exams/exams29804/EXAMREVG.PDF (Accessed September 2, 2011).

USEPA. 2004. Overview of the Ecological Risk Assessment Process in th e Office of Pesticide Programs. U.S. Environmental Protection Ag ency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Washington DC. January 23, 2004.

USDA, National Agricultural Statistics Service. Citrus Fruits 2011 Su mmary (September 2011). Accessed on March 19, 2012 @ http://usda01.library.cornell.edu/usda/c urrent/CitrFrui/Cit rFrui-09-22-2011.pdf.

USEPA. 2011. Guidance On Using Non-Definitive Endpoints In Evaluating Risk To Listed And Nonlisted Animal Species. Memo from Donald J. Brady, Ph.D., Director, Environmental

Fate and Effects Division. 5/11/2011.

Willis, G.H. and L.L. McDowell. 1987. Pesticide Persistence on Foliage in Reviews of

Environmental Contaminati on and Toxicology. 100:23-73.

Submitted Fate Studies

161-1 Hydrolysis

MRID Citation Reference

66193 Day, E.W.; Sullivan, W.L.; Decker, O.D. (1976) A Hydrolysis Study of the Herbicides Oryzalin and Metribuzin. (Unpublished stud y received Sep 16, 1977 under 1 471-96; submitted by Elanco Products Co., Div. of Eli Lilly and Co., Indianapolis, Inc.; CDL:231825-D)

106169 Mobay Chemical Corp. (1972) Sencor (BAY 94337): Metabolic, Analyt- ical, and Residue Information on Tomatoes. (Comp ilation; un- published study received Apr 25, 1972 under 4F1432; CDL: 093821-A)

145117 Mobay Chemical Corp. (1985) Product Chemistry of Tycor Technical. Unpublished compilation. 71 p.

157530 Morgan, J. (1986) The Hydrolysis of Sencor-5-[carbon 14]: Mobay Report No. 91764. Unpublished study prepared by Mobay Chemical Corp. 11 p.

161-2 Photodegradation-water

MRID Citation Reference

### -33 of 61- 153722 Timme, G.; Scholz, K. (1980) Behaviour in Water: Sencor. Unpublished Mobay report no. 69692 prepared by Bayer AG. 4 p.

153725 Timme, G.; Scholz, K. (1980) Photodegradation [of Sencor in Water and Air]. Unpublished study prepared by Bayer AG. 9 p.

156339 Rosen, J.; Siewierski, M. (1971) Photolysis of 4-Amino-3-methyl- thio-6-phenyl-1,2,4-triazin-5- one (Aglpt). Bulletin of Environ- mental Contamination 6(5):406-408.

157529 Morgan, J. (1986) The Aqueous Photolysis of Sencor-5-[carbon 14]: Mobay Report No. 91763. Unpublished study prepared by Mobay Chemical Corp. 21 p.

161-3 Photodegradation-soil

MRID Citation Reference

30169 Pinney, P.; Miaullis, J.B. (1979) Project 148237 R-33865: Soil Metabolism Studies--Interim Report No. 3. (Unpublished study received Ma r 21, 1980 under 476-EX -96; submitted by Stauffer Chemical Co., Rich mond, Calif.; CDL:242046-C)

45272 Houseworth, L.D.; Tweedy, B.G. (1974) Ph otodecomposition of Sencor: Report No. 39414. (Unpublished study received Mar 7, 1975 under 5F 1559; prepared by Univ . of Missouri, Dept. of Plant Pathology, submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL: 094871-S)

106220 Mobay Chemical Corp. (1976) Supplement No. 2 to Brochure Entitled: Sencor, the Effects on the Environment: Document No. AS77-335. (Com pilation; unpublished study received Feb 28, 1977 under 3125-277; CDL:238058-A)

153666 Murphy, J.; Thornton, J.; Olson, T. (19??) Metabolism and Persis- tence of SENCOR in Soils: Mobay Report No. 44078. Unpublished study prepared by Chemagro. 8 p.

153667 Hyzak, D.; Zimdahl, R. (1974) Rate of degradation of metribuzin and two analogs in soils. Weed Science 22(1):75-79.

153668 Bouchard, D.; Lavy, T.; Marx, D. (1982) Fate of metribuzin, meto- lachlor, and fluometuron in

soil. Weed Science 30:629-632.

153693 Webster, G.; Sama, L.; Macdonald (1978) Nonbiological degradation of the herbicide

metribuzin in Manitoba soils. Bull. Environm. Contam. Toxicol. 20:401-408.

156338 Stegh, R.; Wilmes, R. (1982) Light-Induced Degradation of Agro- chemical Parent Compounds on Silica Gel as a Model for Photode- gradation on Soil: Report No. 1666. Unpublished Mobay report no. 82363 prepared by Bayer AG. 40 p.

157531 Morgan, J. (1986) The Photodecomposition of Sencor-5-[Carbon 14] on Soil: Mobay Report No. 91765. Unpublished study prepared by Mobay Chemical Corp. 26 p.

41555103 Hanlon, C. (1989) Photodegradation of Metribuzin on Soil: Lab Pro- ject Number: 99608. Unpublished study prepared by Mobay Corp., Ag. Chem. Div. 30 p.

161-4 Photodegradation-air

MRID Citation Reference

153725 Timme, G.; Scholz, K. (1980) Photodegradation [of Sencor in Water and Air]. Unpublished study prepared by Bayer AG. 9 p.

### -34 of 61- 162-1 Aerobic soil metabolism

MRID Citation Reference

54367 Sharom, M.; Stephenson, ? (1976) Behavior and fate of Metribuzin. Weed Science 24(2):153- 160. (Submitter report no. 491 27; also in unpublished submi ssion received Aug 14, 1980 under 3125-314; submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL: 243067-T)

153677 Ladlie, J.; Meggitt, W.; Penner, D. (1976) Effect of soil pH on microbial degradation, adsorption, and mobility of metribuz in. Weed Science 24(5):477-481.

161501 Lane, J. (1986 ) Sencor Aged Soil Residue Leaching: Report No. 93110. Unpublished report prepared by Mobay Corporation. 24 p.

40367602 Detra, R.; Lane, J.; Thyssen, M. (1987) Degradation of Sencor in Aerobic Sandy Loam: Rept. No. 94880. Unpublished study prepared by Mobay Corp. 44 p.

41555104 Lenz, M. ; Parker, G. (1989) Degradation of Metribuzin in Aerobic Sandy Loam: Lab Project Number: 99775. Unpublished study pre- pared by Mobay Corp., Ag. Chem. Div. 47 p.

162-2 Anaerobic soil metabolism

MRID Citation Reference

40367603 Detra, R.; Thyssen, M. (1987) Degradation of Sencor in Anaerobic Sandy Loam: Rept. No. 94881. Unpublished study prepared by Mobay Corp. 43 p.

41555105 Lenz, M. ; Parker, G. (1989) Degradation of Metribuzin in Anaerobic Sandy Loam: Lab Project Number: 99774. Unpublished study pre- pared by Mobay Corp., Ag. Chem. Div. 45 p.

162-3 Anaerobic aquatic metab.

MRID Citation Reference

159423 McNamara, F. (1985) The Degradation of Sencor in Aerobic and An- aerobic Aquatic Systems: 90384. Unpublished study prepared by Mobay Chemical Corp. 27 p.

162-4 Aerobic aquatic metab.

MRID Citation Reference

159423 McNamara, F. (1985) The Degradation of Sencor in Aerobic and An- aerobic Aquatic Systems: 90384. Unpublished study prepared by Mobay Chemical Corp. 27 p.

163-1 Leach/adsorp/desorption

MRID Citation Reference

25729 Obrist, J.J.; Thornton, J.S. (1979) Soil Thin-Layer Mobility of Baycor(TM), (R)Baytan, (R)Drydene and Peropal( TM). (Unpublished study received D ec 21, 1979 under 3125-EX-168; prepared in cooperation with Agricultural Consultants, Inc.; submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:099185-M)

29887 Thornton, J.S.; Hurley, J.B.; Obrist, J.J. (1976) Soil Thin-Layer Mo bility of Twenty Four

### -35 of 61- Pesticides (sic) Chemicals: Report No. 51016. (Unpublished study receive d Jan. 28, 1980 under 5F1547; submitted by Mobay Chemical Corp., Pittsburgh, Pa.; CDL: 099216-I)

30169 Pinney, P.; Miaullis, J.B. (1979) Project 148237 R-33865: Soil Metabolism Studies--Interim Report No. 3. (Unpublished study received Ma r 21, 1980 under 476-EX -96; submitted by Stauffer Chemical Co., Rich mond, Calif.; CDL:242046-C)

30654 Monsanto Company (19??) The Soil Dissipation of Glyphosate, Alachlor and Metribuzin Mixtures. (Unpublished study received Jan 16 , 1978 under 524-285; CDL:232680-E)

44979 Ford, J.J. (1979) Herbicide Combination--Soil Dissipation Study In- volving Antor Herbicide

with Three Commercial Herbicid es: RI 47- 003-06. (Unpublished study received May 3, 1979 under 43142-1; submitted by Hercules, Inc., Wilmington, Del.; CDL:098274-L)

45268 Houseworth, L.D.; Tweedy, B. G. (1973) Report on Parent L eaching Studies for ^(R)ISencor: Report No. 37180. (Unpub lished study received Mar 7, 1975 un der 5F1559; prep ared by Univ. of Mis- souri, Dept. of Plant Pathology, submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:094871-N)

45276 Tweedy, B.G.; Houseworth, L.D. (1974) Leaching of Aged Residues of Sencor-3-14C in Sandy Loam Soil: Report No. 40567. (Unpub- lished study received Mar 7, 1975 under 5F1559; prepared by Univ. of Missouri, Dept. of Plant Pathology, submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:094870-D)

45277 Flint, D.R.; Shaw, H.R., II (1974) The Mobility of Sencor Residues in Soil Runoff Water: Report No. 40851. (Unpub lished study received Mar 7, 1975 under 5F1559; prepared in cooperation with Agricultural Consultants Laboratory, submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:094870-H)

54234 United States Borax Research Corporation (1975) Cobex^(R)I plus Sencor^(R)I (or Lexone)-- Degradation in Soil. (Unpublished study received May 27, 1975 under 1624-104; CDL:223287- C)

54367 Sharom, M.; Stephenson, ? (1976) Behavior and fate of Metribuzin. Weed Science 24(2):153- 160. (Submitter report no. 491 27; also in unpublished submi ssion received Aug 14, 1980 under 3125-314; submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL: 243067-T)

54368 Savage, K.E. (1976) Adsorption and mobility of Metribuzin in soil. Weed Science 24(5):525- 528. (Submitter report no. 519 03; also in unpublished submi ssion received Aug 14, 1980 under 3125-314 submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL: 243067-V)

68125 Ciba-Geigy Corporation (1976 ) ?Residue Data|. (Compilation; unpublished study received Oct 12, 1976 under 100-523; CDL:230858-A)

106163 Mobay Chemical Corp. (1969) Bay 94337 Metabolic, Analytical, and Residue Information on Potatoes and Soybeans. (Compilation; unpublished study received Jan 16, 1970 under 0G0940; CDL: 091607-A)

106169 Mobay Chemical Corp. (1972) Sencor (BAY 94337): Metabolic, Analyt- ical, and Residue Information on Tomatoes. (Comp ilation; un- published study received Apr 25, 1972 under 4F1432; CDL: 093821-A)

106216 Horton, W. (1978) Disappearance of Fluchlor alin and Metribuzin in Silt Loam and Sandy Loam Soils. (Unpublished study received Nov 8, 1978 under 7969-46; submitted by BASF Wyandotte Chemical Corp., Parsippany, NJ; CDL:235698-C)

134358 Mobay Chemical Co rp. (1979) ?Efficacy: Sencor|. (Comp ilation; unpublished study received Aug 14, 1980 under 3125-314; CDL: 243066-A)

137540 Obrist, J.; Thorton, J. (1982) Soil Thin-layer Mobility of Bay FCR 1272, Bay Sir 8514, and Bay

### -36 of 61- SSH 0860: 82232. (Unpublished study received Feb 13, 1984 under 3125-351; submitted by Mobay Chemi- cal Corp., Kansas City, MO; CDL:072361-D)

143037 Liu, L.; Cibes-Viade, H. (1972) Absorption of fluometuron, prome- tryne, sencor, and 2,4-D by soils. Journal of Agriculture of University of Puerto Rico p. 286-293.

153668 Bouchard, D.; Lavy, T.; Marx, D. (1982) Fate of metribuzin, meto- lachlor, and fluometuron in

soil. Weed Science 30:629-632.

153673 Jarczyk, H. (1972) Migration of herbicides in different soil types. Pflanzenschutz-Nachrichten 25(1):3-19.

153674 Scott, H.; Phillips, R.; Paetzold, R. (19??) Di ffusion of Herbi- cides in the Adsorbed Phase. Unpublished study prepared by Univ. of Arkansas in cooperation with Univ. of Kentucky. 21 p.

153675 Scott, H. (1975) Movement of Pesticides inthe Soil-water-fertili- zer System: Project No.: A021-ARK. Unpublished study prepared by Water Resources Research Center in cooperation with Univ. of Arkansas. 129 p.

153677 Ladlie, J.; Meggitt, W.; Penner, D. (1976) Effect of soil pH on microbial degradation, adsorption, and mobility of metribuz in. Weed Science 24(5):477-481.

153682 Lafleur, K. (1980) Metribuzin movement in soil columns: Observation and prediction. Soil Science 129(2):107-114.

153683 Lafleur, K. (1979) Sorption of metribuzin by model soils and agro- nomic soils: Rates and equilibria. Soil Science 127(1):51-55.

153685 Schmidt, R. (1973) Calculations on the Herbicidal Activity of Metribuzin in Relation to VariousSoil Properties. Unpublished paper presented at Proc. Eur. Weed Res. Coun. Symp. HerbicidesSoil; 1973, Leverkusen, Germany. 3 p.

153723 Timme, G.; Scholz, K. (1980) Behaviour in Soil [of Sencor]. Unpub- lished study prepared by Bayer AG. 26 p.

159418 Pettygrove, D.; Naylor, D. (1985) Metribuzin degradation kinetics in organically amended soil. Weed Science 33(2):267-270.

42201607 Boesten, J.; Van Der Pas, L. (1988) Modeling adsorption/ desorption kinetics of pesticides in a soil suspension. Soil Science 146(4):221-231.

42283001 Daly, D. (1988) Soil Adsorption/Desorption with ?Carbon 14|-Sencor: Lab Project Number: #36997. Unpublished study prepared by Analytical Bio-Chemistry Laboratories, Inc. 54 p.

43058501 Blumhorst, M.; Halarnkar, P. (1993) Soil Adsorption/Desorption of Metribuzin-DK: Lab Project Number: 122S17: SE182101: 106233. Unpublished study prepared by Bio-Analytical Services, Inc. 58 p.

43058502 Blumhorst, M.; Halarnkar, P. (1993) Soil Adsorption/Desorption of Metribuzin-DADK: LabProject Number: 122S18: SE182102: 106234. Unpublished study prepared by EPL BioAnalytical Services, Inc. 58 p.

163-2 Volatility - lab

MRID Citation Reference

150930 Obrist, J.; Thornton, J. (1976) Soil Thin-lay er Mobility of Various Pesticides: Report No.: 48887. Unpublished study prepared by Mobay Chemical Corporation. 8 p.

153672 Savage, K. (1973) Sencor Mobility [in Soil]: Mobay Report No. 37782. Unpublished study

### -37 of 61- prepared by USDA and Chemagro. 2 p.

153677 Ladlie, J.; Meggitt, W.; Penner, D. (1976) Effect of soil pH on microbial degradation, adsorption, and mobility of metribuz in. Weed Science 24(5):477-481.

163-3 Volatility - field

MRID Citation Reference

153653 Chemagro (1984) SENCOR: Environmental Ch emistry. Unpublished com- pilation. 12 p.

153721 Mobay Chemical Corp. (1978) [Residue Data and Soil Persistence of SENCOR]. Unpublished compilation. 776 p.

164-1 Terrestrial field dissipation

MRID Citation Reference

16613 Ballantine, L.G.; Herman, M.M. (1978) Metol achlor plus Propazine Tank Mix Soil Dissipation: Report No. ABR-78037. Summary of studies 237816-D and 237816-E. (Unpublished study received Mar 16, 1979 under 1 00-604; submitted by Ciba-Geigy Corp., Greens- boro, N.C.; CDL:237816-A)

26872 Moyer, M.; Potts, C.; Devine, J.M.; et al. (1 975) Prowl^(R)I(CL 92,553): Determination of CL92,553 ?N-(1-Ethylpropyl)-3,4-di- methyl-2,6-dinitrobenzenamine| and Sencor ?4-Amino-6-tbutyl-3- (methylthio)-1,2,4-triazin-5-one| in Soil: Report No. C-859. (Unpublished study received Nov 20, 1975 under 6F1704; submitted by American Cyanamid Co., Princeton, N.J.; CDL:094647-H)

26873 Potts, C.R.; Laporta, M.M.; Devine, J.; et al . (1975) Prowl^(R)I (CL 92,553): Determination of CL 92,553 ?N-(1-Ethylpropyl)-3,4- dimethyl-2,6-dinitrobenzenamine| and Sencor ?4-Amino-6- t-butyl- 3-(methylthio)-1,2,4-tr iazin-5(4H)-one| in Soil: Report No. C- 801. (Unpublished study received Nov 20, 1975 under 6F1704; submitted by American Cyanamid Co., Princeton, N.J.; CDL: 094647-I)

27120 Muir, D.C.; Baker, B.E. (1976) Detection of Triazine herbicides and their degradation products

in tile-drain water from fields under intensive co rn (maize) production. Journal of Agricultural and Food Chemistry 24(1):122-125. (Also in unpublished submission received Jul 19, 1978 under 201-403; submitted by Shell Chemical Co., Washington, D.C.; CDL:234475-Q)

54367 Sharom, M.; Stephenson, ? (1976) Behavior and fate of Metribuzin. Weed Science 24(2):153- 160. (Submitter report no. 491 27; also in unpublished submi ssion received Aug 14, 1980 under 3125-314; submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL: 243067-T)

61420 Waggoner, T.B. (1973) Survey of Sencor Residues in Soils from the United States: Report No. 37660. Rev. (Unpublished study re- ceived Sep 13, 1976 under 3125-277; submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:226759-E)

61423 Olson, T.J. (1974) Survey of Sencor Residues in Soils from the United States and Canada--1973: Report No. 41627. (Unpub lished study received Sep 13, 1976 under 3125-277; submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:226759-J)

68125 Ciba-Geigy Corporation (1976 ) ?Residue Data|. (Compilation; unpublished study received Oct 12, 1976 under 100-523; CDL:230858-A)

101533 Danhaus, R.; Lenox, E.; Dubelman, S.; et al. (1982) Dissipation of Alachlor in Field Soils following Preemergent Applications of Lasso ME Alone or in Tank Mix Combinations with

### -38 of 61- Roundup, Atrazine, Dyanap, Metribuzin or Cyanazine: MSL-2109. (Unpub- lished study received May 10, 1982 under 524-344; prepared in cooperation with ABC Laboratories, Inc. and Craven Laboratories, Inc., submitted by Monsanto Co., Washington, DC; CDL:070841-D)

106163 Mobay Chemical Corp. (1969) Bay 94337 Metabolic, Analytical, and Residue Information on Potatoes and Soybeans. (Compilation; unpublished study received Jan 16, 1970 under 0G0940; CDL: 091607-A)

106169 Mobay Chemical Corp. (1972) Sencor (BAY 94337): Metabolic, Analyt- ical, and Residue Information on Tomatoes. (Comp ilation; un- published study received Apr 25, 1972 under 4F1432; CDL: 093821-A)

106206 Mobay Chemical Corp. (1972) Supplement No. 4 to Brochure Entitled: Sencor: The Effects on

the Environment: Document No. AS77-1968. (Compilation; unpub lished study received Dec 5, 1977 under 3125-277; CDL:232432-A)

106805 Devine, J.; Kust, C.; Moyer, M.; et al. (1975) Prowl (CL 92,553): Determination of CL 92,553 ... and Sencor ... in Soil. Indi- ana.: Report No. C-859. (Unpublished study received Nov 14, 1975 under 6F1704; submitted by American Cyanamid Co., Prince- ton, NJ; CDL:097956-E)

106806 Devine, J.; Kust, C.; Potts, C.; et al. (1975) Prowl (CL 92,553): Determination of CL 92,553 ... and Sencor ... in Soil. Kan- sas. 1974: Repo rt No. C-801. (Unpublished study received Nov 14, 1975 under 6F1704; submitted by American Cyanamid Co., Princeton, NJ; CDL:097956-F)

135055 American Cyanamid Co. (1977) Combat (=CL 206,784) Herbicide Residue and Metabolism. (Compilation; unpublished study received Feb 23, 1978 under 241-EX- 89; CDL:096835-A)

152205 Danhaus, R. (1982) Dissipation of Glyphosate in Field Soils follow- ing Minimum Till Application of Roundup Alone or in Tank Mix Combinations with Lasso ME, Atrazine, Dyanap or Metribuzin: Re- port No. MSL-2422. Unpublished study prepared by Monsanto Co. and ABC Laboratories, Inc. 143 p.

153675 Scott, H. (1975) Movement of Pesticides inthe Soil-water-fertili- zer System: Project No.: A021-ARK. Unpublished study prepared by Water Resources Research Center in cooperation with Univ. of Arkansas. 129 p.

153676 Chemagro (1975) [Dissipation in Soil of Sencor 50WP]. Unpublished study. 2 p.

153679 Ladlie, J.; Meggitt, W.; Penner, D. (1976) Role of pH on metribuzin dissipation in field soils. Weed Science 24(5):508-511.

153686 Webster, G. (1975) [Non-biological Degradation of Sencor in Soil]. Unpublished study prepared by Chemagro in cooperation with the Univ. of Manitoba. 9 p.

153691 Mobay Chemical Corp. (1982) [Chemistry Data of Metribuzin and Its Metabolic Behaviour in Soil]. Unpublished compilation. 25 p.

153723 Timme, G.; Scholz, K. (1980) Behaviour in Soil [of Sencor]. Unpub- lished study prepared by Bayer AG. 26 p.

40380901 Delk, J. (1987) Dissipation of Sencor and its Oxidative Metabolites in Field Soil: Laboratory Project ID: SR-8300-87. Unpublished Mobay report no. 95000 prepared by Morse Laboratories Inc. 198 p.

42236101 Grace, T.; Cain, K. (1990) Dissipation of Me tribuzin in California Soils: Lab Project Number: SE830089R01; 100170; ML022101. Unpublished study prepared by Plant Sciences, Inc.; Siemer and Assoc's., Inc. and NET Atlantic, Inc. 3154 p.

### -39 of 61- 164-2 Aquatic field dissipation

MRID Citation Reference

106150 Mobay Chemical Corp. (1971) Supplement to Synopsis of Analytical and Residue Information on Use of Sencor (Bay 94337) with Potatoes and Soybeans: Supplement No. 1. (Compilation; unpub- lished study received Jul 20 , 1971 under 0G0940 ; CDL:091605-A)

164-5 Long term soil dissipation

MRID Citation Reference

153661 Prestel, D.; Weisgerber, I.; Klein, W.; et al. (1978) Accountabil- ity of the Distribution and Metabolism of [Carbon-14]-metribuzin (SENCOR) in Potatoes, Carrots, and Soil under Field Conditions. Unpublished translation of study in Chemosphere (2):137-144 (1976). 12 p.

165-0 Accumulation Studies -- General

MRID Citation Reference

106172 Mobay Chemical Corp. (1972) Sencor: The Effects on the Environment. (Compilation; unpublished study received May 31, 1972 under 2F1274; CDL: 094868-A; 094869)

165-1 Confined rotational crop

MRID Citation Reference

40577701 Naidu, M. (1988) Metribuzin Confined Accumulation Study on Peanuts: Laboratory Project ID AMR-563-86. Unpublished study prepared by Research and Development Division, E. I. du Pont de Nemours and Company, Inc. 47 p.

40838402 Christopher, R.; Lane, J.; Parker, G. (1988) Residues of Metribuzin (Sencor) in Rotational Crops and Soils: Report No. 98324: Project No. SE-052301. Unpublished study prepared by Mobay Corp. 45 p.

41254101 Naidu, M. (1989) Metribuzin Confined Accumulation Study of Peanuts: Supplement No. 1: Laboratory Project ID AMR-563-86. Unpublished study prepared by E.I. du Pont de Nemours and Co., Inc. 16 p.

166-1 Ground water-small prospective

MRID Citation Reference

44757901 Coody, P.; Fisher, J. (1999) A Geographic Groundwater Vulnerability Assessment for Metribuzin (SENCOR): Lab Project Number: 108839. Unpublished study prepared by Bayer Corporation. 40 p.

45737901 Dyer, D. (2002) Progress Report--July, 2002 FOE 5043 (AXIOM)--Small-Scale Prospective Ground-Water Monitoring Study, Corn in Nebraska, 1995: Lab Project Number: F3212402: 200257. Unpublished study prepared by Bayer Corp. 211 p.

Submitted Effects Studies

### -40 of 61- 850.2100 Avian Single Dose Oral Toxicity

MRID Citation Reference

145911 or ACC

255025 Lamb, D.; Jones, R. (1972) Acute Oral Toxicity of Sencor Technical to Bob White Quail and Mallard Ducks: Mobay Report No. 33172. Unpublished study prepared by Mobay Chemical Corp. 6 p.

Accession No.

255025 Schafer, E.W. (1971) Bird Toxicity on Inugan (Bay 79770), Sencor – Bay DIC 1468 (Bay 94337) and Methyl EU paren (Bay 49854). Prepared by Denver Laboratory) Assumed US Fish and Wild life Service) Chemagro Report No.

29741. EPA Accession No. 255025.

Accession No.

255025 Shellenberger, T. (1969) Toxicological Evaluations of Bay 94337 with Fish and Wildlife Report No. 25527. Prepared by Gulf South Research Institute, New Iberia, Louisiana. Submitted to Chemagro Corp., Kansas City, Missouri. EPA

Accession No. 255025.

850.2200 Avian Dietary Toxicity

MRID Citation Reference

65507 Lamb, D.W.; Burke, M.A. (1977) Dietary Toxicity of ~(R)ISencor Technical to Bobwhite Quail and Mallard Ducks : Report No. 51593. (Unpublished study received Apr 13, 1977 under 3125-270; s ubmit- ted by Mobay Chemical Corp., Kansas City, Mo.; CDL:229312-A)

157528 Stubblefield, W. (1986) Subacute Dietary LC50 of Technical Metri- buzin (Sencor) to Bobwhite Quail: Study No. 86-175-01: Mobay Report No. 91757. Unpublished study prepared by Mobay Chemical Corp. 24 p.

Accession No.

262228 see

157528 (1986?) Subacute dietary LC50 of Technical Metribuzin (Sencor®) to Bobwhite Quail. Report No. 91757, March 25, 1986. Study Prepared and Submitted by Mobay Corporation; EPA Accession No. 262228.

850.2300 Avian Reproduction

MRID Citation Reference

43860501 Hancock, G. (1995) Effect of Technical SENCOR on Mallard Reproduction: Lab Project Number: SE740801: 106983. Unpublished study prepared by Bayer Corp. 107 p.

43926601 Hancock, G. (1996) Effect of Technical SENCOR on Northern Bobwhite Reproduction: Lab Project Number: SE741701: 106984. Unpublished study prepared by Bayer Corp. 110 p.

850.2500 Simulated or Actual Field Testing

### -41 of 61- MRID Citation Reference

35931 Findlay, G.M.; Baker, S.R. (1972) Assessing the Environmental Haz- ard of Pesticide Use: Report No. 37553. (Unpublished study re- ceived Mar 7, 1975 under 5F1559; prepared by Univ. of Manitoba, Dept. of Entomology, submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:094871-O)

850.1075 Acute To xicity to Freshwater Fish

MRID Citation Reference

75541 Chambers, H.; Fabacher, D.L. (1974) Acute toxicity of pesticides to channel catfish fingerlings. MAFES Research Highlights 37(2):1. (Also~In~unpublished submission recei ved on unknown date under 538-135; submitted by O.M. Scott & Sons Co., Marysville, Ohio; CDL:221963-A)

78513 Rowehl, E.R. (1969) ?Study on Fish Toxicity Using Dasanit and Various Other Chemicals|: Report No. G-3045; Report No. 26929. (Unpublished study received Jul 31, 1972 under 3125-213; submit- ted by Mobay Chemical Corp., Kansas City, Mo.; CDL:120480-AJ)

90427 McCann, J.A. (1972) ?Sencor 70% WP: Rainbow Trout (?~Salmo gaird~?- ?~neri?~)|: Test No. 462. (U.S. Agricu ltural Research Service, Pesticides Regulation Div., Animal Biology Laboratory; unpub- lished study; CDL:130267-A)

94219 Galletta, W.A. (1969) Fish Toxicity Trial No. 1/69: Report No. G- 2857; 24992. (Unpublished study, including letter dated Jun 6, 1969 from W.M. Zeck to Glenn Brussels, received Mar 25, 1 970 under 3125-235; pr epared by Vero Beach Laboratories, Inc., sub- mitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:007178-C)

114006 Rowehl, E. (1969) Fish Toxicity Trial No. 66/69: Report No. G-3045; 26929. (Unpublished study received May 1, 1973 under unknown admin. no.; prepared by Vero Beach Laboratories, Inc., submitted by Mobay Chemical Corp., Kansas City, MO; CDL:120301-L)

145910 Linn, J.; Denning, D. (1971) Report Summary: [Fish Toxicity to Bay 94337 Technical]: Mobay Report No. 29532. Unpublished study prepared by California Dept. of Fish & Game in cooperation with Chemagro Corp. 3 p.

147251 Hermann (1982) Fish Toxicity: [Metribuzin on Rainbow Trout]: Mobay Agchem No. 80970 . Unpublished study prepared by Bayer AG. 6 p. Rainbow trout study – reviewed by E. Zucker in 1985- Invalid

Accession No.

255025 Chemagro Corp. Report (1970) Bay 94337 Technical Fish Toxicity. Report No. 29532. Prepared by Chem agro Chemical Research Department. EPA Accession

No. 255025.

34713 Tooby, T.E., P.A. Hursey, J.S. Alabaster (1975) The Acute Toxicity of 102 Pesticides and Miscellaneous Substances to Fish. Chemistry and Industry 21(?/Jun): 523-526. (Published Study).

Accession No.

255025 Lamb, D.W., D.J. Roney (1972) April 13, 1972 Acute Toxicity of Sencor to Fish. Report No. 33124. Prepared by Chemagro Division Research and

### -42 of 61- ZUOMET05 on

the DERs Development. EPA No. 255025. Bluegill and Rainbow trout

40098001 Mayer F.L., Ellersieck M.R. (1986) Manual of Acute toxicity: Interpretation

and Date Base for 410 Chemicals and 66 Species of Freshwater Animals. United States Department of the Interior, Fish and Wildlife Services, Publication No. 160. Washington, DC.

33320 Clemens, H.P., K.E. Sneed (1959) Lethal Doses of Several Commercial Chemicals for Fingerling Channel Catfish. Washington, DC. US Fish and Wildlife Service. (Special Scientific Report No. 316; Published Study).

45273 Fabacher, D.L.; Chambers, H. (1973) Acute Toxicity of Three Pes- ticides to Channel Catfish Fingerlings: Report No. 40426. (Un- published study received Mar 7, 1975 under 5F1559; prepared by Mississippi State Univ., Agricultural and Forestry Experiment Station, Dept. of Entomology, submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:094870-A)

850.1010 Acute Toxici ty to Freshwater Invertebrates

MRID Citation Reference

134495 Nelson, D.; Roney, D. (1979) Acute Toxicity of Sencor Technical to Daphnia magna: Report No. 67262. (Unpublished study received Oct 31, 1983 under 3125-277; submitted by Mobay Chemical Corp., Kansas City, MO; CDL:072083-A)

139483 Schneider, P.W., Jr. (1976) 48-Hour LC50 to~Daphnia magna~?: Has- kell Laboratory Report No. 671-76. (Unpublished study received Oct 21, 1976 under 352-382; submitted by E.I. du Pont de Nemours & Co., Wilmington, Del.; CDL:226357-J)

45088223 Ort, M.; Fairchild, J.; Finger, S. (1994) Acute and Chronic Effects of Four Commercial Herbicides on Ceriodaphnia dubia. Archives of Environmental Contamination and Toxicology 27:103-106.

34016 Goodman, N.C. (1978) 48-Hour LC50^2I to~Daphnia magna~?: Report No. 400-78. (Unpublished st udy received Nov 20, 1978 u nder 352- 390; submitted by E.I. du Pont de Nemours & Co., Wilmington, Del.; CDL:236581-K)

72083 Roney, D.J. 1979. Acute Toxicity of Sencor technical to Daphnia magna : Report # 67262. Prepared by Mobay Chemical for Mobay Chemical Corporation, Stilwell, Kansas.

850.1025, 850.1035, 850.1075 Acute Toxicity to Estuarine/Marine Organisms

MRID Citation Reference

106197 Heitmuller, T. (1975) Acute Toxicity of Sencor to Eastern Oysters (Crassostrea virginica), Pink Shrimp (Penaeus duorarum), and Fiddler Crabs (Uca pugilator): (Submitter) 43851. (Unpublished stud y received Aug 19, 1975 under 3125-294; prepared by Bion- omics--EG & G, Inc., submitted by Mobay Chemical Corp., Kansas City, MO; CDL:165011-A)

### -43 of 61- 161502 Surprenant, D. (1986) Acute Toxicity of Sencor to Eastern Oysters (Crassostrea virginica): Study No. 274-1285-6105-504: Report No. BW-86-02-1941. Unpublished study prepared by Springborn Bio- nomics, Inc. 21 p.

161503 Nicholson, R.; Surprenant, D. (1986) Acute Toxicity of Sencor to Sheepshead Minnow (Cyprinodon variegatus): Study No. 274-1285-6105-500: Report No. BW-86-2-1942. Unpublished study prepared by Springborn Bionomics, Inc. 20

p.

42094501 Gagliano, G. (1991) Raw Data Supplement for Acute Toxicity of Senc- or Technical to Eastern Oysters (Crassostr ea virginica): Lab Project Number: 274- 1285-6105-504: 91755-1. Unpublished study prepared by Springborn Bionomics, Inc. 11 p.

42094502 Gagliano, G. (1991) Raw Data Supplement for Acute Toxicity of Senc- or Technical to Sheepshead Minnow (Cyp rindon variegatus): Lab Project Number: 274-1285-6105-500: 91756-1. Unpublished study prepared by Springborn Bionomics, Inc. 13 p.

No MRID on

DER Dionne, Emily, Donald C. Suprenant (19??) Acute Toxicity of Sencor to Eastern Oysters (Crassostrea virginica). Study Performed by Springborn Bionomics, Inc. 790 Main Street, Wareham, Massachusetts 02571 in March 1986 for Mobay Chemical Corporation, Stillwell, Kansas. MRID No. 470234- 011? Toxicology Report No. 728. DP Barcode 166533. Study No. 91755.

See 161503

above Nicholson, Richardson, Donald C. Suprenant (1986?) Acute Toxicity of Sencor to Sheepshead Minnow (Cyprinodon variegates). Study Performed by Springborn Bionomics, Inc. 790 Main Street, Wareham, Massachusetts 02571 in March 1986 for Mobay Chemical Corp oration, Stillwell, Kansas. MRID No. 470234-012? Toxicology Report No. 729. DP Barcode 166533. Study No.

91756.

850.1400/850.1300 Fish Early Life Stage/Aquatic Invertebra te Life Cycle Study

MRID Citation Reference

51483 Marking, L.L. (1969) Letter sent to Thomas H. Schultz dated Sep 4, 1969 ?Toxicity of candidate chemicals to fish: Results of pre- liminary tests|: Report no. 26225. (U.S. Fish and Wildlife Service, Fish Control Laboratories, unpublished study; CDL: 222267-B)

42447801 Gagliano, G.; Roney, D. (1992) Early Life Stage Toxicity of Sencor Technical to the Rainbow Trout (Oncorhynchus mykiss) under Flow-through Conditions: Lab Project Number: 103249: SE842201. Unpublished study prepared by Miles, Inc. 87 p.

42447802 Gagliano, G.; Bowers, L. (1992) Chronic Toxicity of Sencor Technical to the Waterflea (Daphnia magna) under Flow-through Conditions: Lab Project Number: 103248: SE840701. Unpublished study prepared by Miles, Inc. 75 p.

42731201 Gagliano, G.; Bowers, L. (1993) Chronic Toxicity of Sencor Technical to the Waterflea (Daphnia magna) Under Flow-Through Conditions: Lab Project Number: SE840702: 105023. Unpublished study prepared by Miles Inc. 60 p.

42732501 Heimbach, F. (1993) Influence of DADK (Metabolite of Metribuzin) on the Reproduction Rate of Water Fleas: Lab Project Number: E 321 0676-05:

### -44 of 61- HBF/RDM 45: 105035. Unpublished study prepared by Bayer AG Crop Protection Research. 31 p.

43002001 Thornton, J. (1993) Letter Sent to E. Feris dated September 14, 1993: Sencor metribuzin herbicide...: Fish early lif e stage study. Prepared by Miles Inc. Agric. Div. 7 p.

850.1950 Aquatic Field Study

42201600 ICI Americas Inc. (1992) Submission of New Formulation Mesocosm Data To Support Registration of Force 1.5G. Transmittal of 11 studies.

850.4100/850.4150 Seed germination/seedling emergence and vegetative vigor

MRID Citation Reference

42447803 Burge, C. (1992) Tier 2 Seed Germination, Seed Emergence, and Seedling Vigor Nontarget Phytotoxicity Study Us ing Metribuzin: Lab Project Number: 103800: SE201601. Unpublished study prepared by Miles, Inc. 90 p.

43208301 Johns, C. (1994) Tier 2 Seed Germination and Seed Emergence Nontarget Phytotoxicity Study Using Metribuzin: Lab Project Number: SE201602: 106568. Unpublished study prepared by Miles Inc. 44 p.

45227704 Davis, D. (1980) Effects of Herbicides on Submerged Seed Plants: Lab Project Number: A-067-ALA: 14-34-0001-0101. Unpublished study prepared by Auburn University. 10 p.

850.4400/850.5400 Aquatic plant growth

MRID Citation Reference

42438301 Gagliano, G.; Bowers L. (1992) Acute Toxicity of Sencor Technical to the Green Alga (Selenastrum capricornutum): Lab Project Number: SE881401: 103239. Unpublished study prepared by Miles Inc., Agricultural Division. 32 p.

43133601 Gagliano, G.; Orr, W. (1994) Acute Toxicity of SENCOR Technical to the Green Alga (Selenastrum capricornutum): Lab Project Number: SE881402. Unpublished study prepared by Miles, Inc. Sponsor report number: 106417. 33

p.

43826101 Bowers, L. (1995) Acute Toxicity of (carbon 14)-Sencor to the Freshwater Diatom (Navicula pelliculosa): Lab Project Number: 106975: SE881601. Unpublished study prepared by Bayer Corp. 33 p.

43867701 Bowers, L. (1995) Toxicity of (carbon 14)-Sencor to the Marine Diatom, Skeletonema costatum: Lab Project Nu mber: SE881602: 106992. Unpublished study prepared by Bayer Corp. 34 p.

### -45 of 61- 43893501 Boeri, R.; Magazu, J.; Ward, T. (1 995) Toxicity of Sencor to the Duckweed, Lemna gibba G3: (Amended Report): Lab Project Number: 667-MI: 106982. Unpublished study prepared by T. R. Wilbury Labs, Inc. 32 p.

43893502 Boeri, R.; Magazu, J.; Ward, T. (1995) Toxicity of Sencor to the Freshwater Alga, Anabaena flos-aquae: (Amended Report): Lab Project Number: 666-MI: 106974. Unpublished study prepared by T. R. Wilbury Labs, Inc. 31 p.

43921001 Bowers, L. (1996) Toxicity of (carbon 14)-Sencor to the Green Alga Selenastrum capricornutum: Lab Project Number: 107142: SE883501. Unpublished study prepared by Bayer Corp. 32 p.

44016901 Bowers, L. (1996) Data Analysis Correction for the Effect of Sencor Technical on the Growth of Selenastrum capricornutum: Lab Project Number: SE881402: 106417-1. Unpublished study prepared by Bayer Corp. 17 p.

45088212 Fairchild, J.; Ruessler, D.; Haverlan d, P. et al. (1996) Comparative Sensitivity of Selenastrum capricornutum and Lemna minor to Sixteen Herbicides. Archives of Environmental Contamination and Toxicology 32:353-357.

45227708 Fairchild, J.; Ruessler, S.; Carlson, A. (1998) Comparative sensitivity of five species of macrophytes and six species of algae to atrazine, metribuzin, alachlor, and metolachlor. Environmental Toxicology and Chemistry 17(9)1830-1834.

850.3030 Honeybee Acute Toxicity

59460 Atkins, E.L. (1975) Letter Sent to Charles A. Hanson Dated Sep. 30, 1975. Laboratory Tests on Pesticides Tested for Comparative Honey Bee Toxicity. (Unpublished Study Receive d Aug. 19, 1976 under 8 340-EX-3; Prepared by Univ. of California – Riverside, Citrus Research Center and Agricultural Experiment Station, Dept. of Entomo logy, Submitted by American Hoechst Corp., Somerville, NJ; CDL: 095253-AJ).

28772 Atkins, E.L., Greywood, E.A., Macdonald, R.L. (1973) Toxicity of Pesticides and other Agricultural Chemicals to Hone y Bees; Laboratory Studies. Rev. by Univ. of California-Riverside, Dept. of Entomology. Riverside, Calif.; UC, Agricultural Extension Service. (Als o In Unpublished Submission Received Apr. 2, 1980 under 464-556; Submitted by Dow Chemical U.S.A. Midland, Mich.; CDL: 242149-Z).

Non Guideline Selections

42317100 Monsanto Co. (1992) Submission of an incident report under FIFRA 6(a)(2) status involving Canopy and Freedom herbicides. Transmittal of 1 study.

42347000 North Carolina Cooperative Extension Service (1992) Submission of FIFRA 6(a)2 data for Metalaxyl, Alachlor, Tri azines, Nitrate- Nitr ogen, Metolachlor,

and Metribuzin adverse effects. Trans- mittal of 1 study.

42775101 Gould, T. (1993) A Review of the Plant Metabolism of Metribuzin: Supplemental Information : Lab Project Number: 105166. Unpublished study prepared by Miles Inc. Agriculture Division. 26 p.

43544701 Fairchild, J.; Carlson, A. (1994) An Aquatic Risk Assessment of Four Herbicides Using Six Species of Al gae and Five Species of Aquatic Macrophytes. Unpublished study prepared by U. S. Fish and Wildlife Service and U. S. EPA. 9 p.

### -46 of 61- 43571600 Miles, Inc. (1995) Submission of Effects on Microorganisms and Plants Data in Support of FIFRA 6(a)(2) For Metribuzin. Transmittal of 1 Study.

43598610 Johnson, E. (1993) The Effects of Representative Groundwater Pesticides on Reproduction and in utero Development of Experimental Animals: Lab Project Number: 311U-4349-16: 356/311U--3698. Unpublished study prepared by Ciba-Geigy Corp. 19 p.

43633401 Heindel, J.; Chapin, R.; Gulati, D. et al. (1993) Assessment of the reproductive and developmental toxicity of pesticide/ fertilizer mixtures based on confirmed pesticide contamination in California and Iowa groundwater. Fundamental and Applied Toxicology 22:605-621. (Maybe human health related)

45020003 Davies, P.; Cook, L.; Barton, J. (1994) Triazine Herbicide Contamination of Tasmanian Streams: Sources, Concentrations and Effects on Biota.

Freshwater Res. 45:209-226.

45020007 Krieger, K.; Baker, D.; Kramer, J. (1988) Effects of Herbicides on Stream Aufwuchs Productivity and Nutrient Uptake. Archives of Environmental Contamination and Toxicology 17:299-306

.
47543509 Krieger, K.; Baker, D.; Kramer, J. (1988) Effects of Herbicides on Stream Aufwuchs Productivity and Nutrient Uptake . Arch. Environ. Contam.

Toxicol. 17: 299-306.

45255 Chemagro Corporation (1975) Supplement to Synopsis of the Effects of Sencor on the Environment. Summary of Studies 094871-C through 094871-F, 094871-I through 094871-O, 094871-Q through 094871-S. (Supplement no. 1; Unpublished Study Received Mar. 7, 19 75 under 5F1559; Submitted by Mobay Chemical Corp., Kansas City, MO., CDL:094871-A).

Accession No.

255025 Shellenberger, T. (1969) Toxicological Evaluations of Bay 94337 with Fish and Wildlife Report No. 25527. Prepared by Gulf South Research Institute, New Iberia, Louisiana. Submitted to Chemagro Corp., Kansas City, Missouri. EPA

Accession No. 255025.

106172 Mobay Chemical Corp. (1972) Sencor: The Effects on the Environment. (Compilation; unpublished study r eceived May 31, 1972 under 2F1274; CDL:094868-A; 094869)

### -47 of 61- Appendix A. Summary of available effects studies

A brief summary of submitted data considered relevant to the ecological risk assessment for the Registration Review is presented below.

Toxicity of Metribuzin to Aquatic Organisms

Toxicity to Fish

A summary of acute and chronic freshw ater fish data is provided below.

Freshwater Fish: Acute Exposure (Mortality) Studies
Submitted guideline studies provide insight into the potential acute effects of metribuzin on freshwater fish. Studies (MRIDs 255025 a nd 40098001; Acceptable) w ith bluegill sunfish, ( Lepomis macrochirus ), resulted in LC 50 

### s of 75.96, 92 and 131.1 mg a.i./L. Studies (MRIDs 40098001, 090427 and 255025; Acceptable), with rainbow trout ( Onchorhynchus mykiss ; formerly Salmo gairdneri ), resulted in LC 50 

### s of 42, 76.77, 99 and 147 mg a.i./L. For a protective assessment, the LC 50 

### of 42 mg a.i./L will be used for RQ calculation. Metribuzin is categorized as slightly toxic to practically nontoxic to freshwater fish on an acute exposure basis.

Freshwater Fish: Chronic Exposure (Early Life Stage and Re production) Studies
A guideline early life stage (ELS) study is availabl e for evaluation of poten tial chronic effects of

metribuzin on freshwater fish. The rainbow trout study (MRID 42447801) resulted in a NOAEC of <3.0 mg a.i./L and the LOAEC is 3.0 mg a.i./L. No NOAEC was achieved in this study due to effects on growth at all levels tested. Based on the highest 56-day a quatic EEC from the RED assessment (0.12 mg a.i./L), and using the lowest concentration tested as the LOAEC value, the ratio (RQ-value) is 0.04, well below the chronic LOC of 1.0. Therefore, based on the available information, risk to listed freshwat er fish from chronic exposure to metribuzin is not expected. A request for new data to establish a definitive endpoint is not recommended at this time, it is unlikely a new study with lower concentrations to achieve a NOAEC will impact the risk

assessment.

Estuarine/marine Fish: Acute exposure
One study evaluating the toxicity of metribuzin to estuarine/marine fish is available (MRID 42094502; Acceptable). The 96h LC 50 

### for sheepshead minnow ( Cyprinodon variegatus ) is 85 mg a.i./L; therefore metribuzin is classified as slightly toxic to estuarine/marine fish.

Estuarine/marine Fish: Chronic Exposure (E arly Life Stage and Reproduction) Studies

There are no data on the effect of chronic exposure to metribuz in to estuarine/marine fish. In lieu of asking for this study, an acute to chronic ration (ACR) will be used in the risk assessment.

Toxicity to Aquatic Invertebrates

Freshwater Invertebrates: Acute Exposure (Mortality) Studies
Two guideline studies with Daphnia magna (MRIDs 34016 and 72083; Acceptable) the EC 50 

### s were 4.2 and 98.5 mg a.i./L. For a protective assessment, the EC 50 

### of 4.2 mg a.i./L will be used

### -48 of 61- for RQ calculation. Metribuzin is categorized as moderately to slightly toxic to freshwater invertebrates on an acute exposure basis.

Freshwater Invertebrates: Chronic Exposure (Reproduction) Studies
A guideline study evaluating potential chronic e ffects to aquatic inve rtebrates (MRID 42447802; Acceptable), was conducte d with the waterflea Daphnia magna . The study resulted in a NOAEC of 1.29 mg a.i./L. The LOAEC in the study is 2.62 mg a.i./L, based on reduced length and number of offspring produced compared to the control.

In addition to toxicity testing with the activ e ingredient, the registrant has submitted a study (MRID 42732501; Acceptable) with the degradate, DADK, to evaluate the potential chronic effects to aquatic invertebrates. Based on th e results with the daphnids, the NOAEC is 3.3 mg a.i./L, based on reduction in length and number of offspring produced compared to the control at the 5.9 mg a.i./L treatment level.

Estuarine/marine Invertebrates: Acute Exposure (Mortality) Studies
A 96h acute toxicity study (MRID 106197; Acceptable) with pink shrimp ( Penaeus duorarum ) is

available for metribuzin. The EC 50 

### from the mean-measured concentration is 48.3 mg a.i./L.

Several acute toxicity studies (MRI Ds 106197 and 42094501; Acceptable, MRID 0043851; Supplemental) examining the effect of metribuzin on larval Eastern oyster ( Crassostrea virginica ) is available for metribuzin. The EC 50 

### s ranged from 40.7 – 49.8 mg a.i./L.

A 96h shell deposition study (MRID 47023411; Supplemen tal) with Eastern oyster is available

for metribuzin. The EC 50 

### , based on mean-measured concen trations, is 52 mg a.i./L .

Results on pink shrimp and Eastern oyster larval and shell deposition studies indicate metribuzin is classified as slightly toxic to estuarine/marine invertebrates on an acute exposure basis. For a protective assessment on estuarine/marine i nvertebrates, the larval Eastern oyster EC 50 

### of 40.7 mg a.i./L will be used for RQ calculation.

Toxicity to Aquatic Plants
A 14-day aquatic vascular plant study with Lemna gibba (MRID 43893501; Supplemental)

resulted in an IC 50 

### and NOAEC, based on frond weight, of 130 and 18 μg a.i./L, respectively.

Three 5-day aquatic nonvascular plant studies (MRIDs 43133601 and 43921001; Acceptable, MRID 42438301; Invalid) with the green algae, Pseudokirchneriella subcapitata (formerly Selenastrum capricornutum ), obtained an IC 50 

### as low as 8.09 μg a.i./L. The corresponding NOAEC is 2.33 μg a.i./L.

A 5-day aquatic nonvascular plant study (MRI D 43826101; Acceptable) with the freshwater diatom, Navicula pelliculosa , resulted in an IC 50 

### and NOAEC of 11.9 and 8.9 μg a.i./L, respectively.

A 5-day aquatic nonvascular plant study (MRID 43867701; Acceptable) with the marine diatom,

Skeletonema costatum , resulted in an IC 50 

### and NOAEC of 8.84 and 5.78 μg a.i./L, respectively.

### -49 of 61- A 5-day aquatic nonvascular plant study (MRID 43893502; Supplemental) with the blue-green algae, Anabaena flos-aquae , resulted in an IC 50 

### and NOAEC of 17 and 9.7 μg a.i./L, respectively.

For a protective assessment on a quatic nonvascular plants, the IC 50 

### and NOAEC of 8.09 and 2.33 mg a.i./L, respectively, will be used for RQ calculation, while the duckweed IC 50 

### and NOAEC of 130 and 18 μg a.i./L, respectively will be used to calculate RQs for aquatic vascular plants.

Toxicity of Metribuzin to Terrestrial Animals

Toxicity to Birds

Birds: Acute Exposure (Mortality) Studies
An avian acute oral toxicity study with the Northern bobwhite quail (MRID 00255025; Acceptable) is available for metribuzin. The LD 50 

### for avian acute effects is 169.2 mg a.i./kg-bw. Metribuzin is categorized as moderately nontoxic to upland game birds on an acute oral exposure

basis. There are no acute oral da ta available for passerines, the t oxicity to passerines exposed to metribuzin is not known; a study should be s ubmitted to satisfy guide line requirements.

Two avian subacute dietary studies are availabl e for metribuzin, one w ith bobwhite quail (MRID 262228; Acceptable) and the other with ma llard duck (MRID 0065507; Acceptable). No mortalities were reported in either study at the highest concen tration tested (4,000 mg a.i./kg diet for quails and 5,000 mg a.i./kg diet for ducks). The LC 50 

### of >4,000 mg a.i./kg-diet will be used for RQ calculation to assess risk to avian species vi a the dietary route. Me tribuzin is categorized as practically nontoxic on a sub acute dietary exposure basis.

Birds: Chronic Exposure (Growth, Reproduction) Studies
Effects to avian species from chronic exposur e are assessed with one-g eneration reproduction studies. Two studies, one with mallard duck ( Anas platyrhynchos ) and one with bobwhite quail ( Colinus virginianus ) are used to evaluate the chronic toxicity of metribuzin to avian species. In the mallard study (MRID 43860501; Acceptable) the hi ghest dose tested was 368 mg a.i./kg-diet and no effects were reported. The NOAEC was the highest concentration tested. The quail study (MRID 43926601; Acceptable) determined an NOAEC of 385 mg a.i./kg-diet; however, there was a statistically signifi cant reduction in body weight at 14- day post-hatch at all levels (NOAEC<62 mg a.i./kg-diet) tested with no othe r effects observed. This effect appears not be treatment related since no reproductive paramete rs were affected in either study. The LOAEC for mallard duck is 386 mg a.i./kg-diet and for bobwhite quail is >385 mg a.i./kg-diet.

Toxicity to Mammals

Mammals: Acute Exposure (Mortality) Studies

Effects to mammals are assessed with the acute oral toxicity study with the laboratory rat ( Rattus norvegicus ) and laboratory mouse ( Mus musculus ). The lowest LD 50 

### from both studies (MRID 00106158) is the mouse LD 50 

### at 711/698 mg a.i./kg-bw (male/fema le); therefore, metribuzin is categorized as slightly toxic to mamma lian species on an acu te exposure basis.

### -50 of 61- Mammals: Chronic Exposure (Growth, Reproduction) Studies
The two-generation study with th e laboratory rat is used to as sess potential for effects to mammals from chronic exposure. The study for metribuzin (MRID 40838401) determined a NOAEC for both parental and offspri ng of 30 mg a.i./kg-diet (1.5 mg a.i./kg/day). Effects at the LOAEC (150 mg a.i./kg-diet) include decrea sed body weights and body weight gains and hypertrophy of the hepatocytes.

Toxicity to Terrestrial Invertebrates
A honeybee acute contact study (MRID 028772; Acceptabl e) indicates metribuzin is practically nontoxic to adult honeybees on an ac ute exposure basis, with an LD 50 

### of 60.4 μg a.i./bee when exposed to technical metribuzin.

Toxicity to Terrestrial Plants
The results of the Tier II seedling emergence (MRID 42447803 and 43208301(for cotton); together Acceptable) and vegetative vigor (MRID 42447803; Acceptable) tests on non-target plant biomass are summarized below in Tables 1 and 2. Sensitivity varied widely across species, indicating that some species of plants ar e more sensitive to metribuzin. As expected with a pre-emergent and post-emergent herbicid e, the results are similar in both the seedling emergence and vegetative vigor studies.

Table 1. Non-target Terrestrial Plant Seedlin g Emergence Toxicity (Tier II) Data

Crop Type of Study Species EC 25 

### (lb a.i./A) NOAEC (lb a.i./A) Most sensitive
parameter

Monocots Corn 0.059 0.056 Dry weight

Onion 0.02 0.014 Survival

Wheat 0.024 0.014 Emergence and dry weight

Pea >0.225 0.113 Dry weight

Dicots Turnip 0.008 0.007 Emergence

Soybean >0.225 0.225 None

Cotton 0.0423 0.0281 Dry weight

Cucumber 0.029 0.014 Shoot height

Tomato >0.225 0.113 Survival

Sorghum 0.043 0.028 Dry weight

### -51 of 61- Table 2. Non-target Terrestrial Plant Vegeta tive Vigor Toxicity (Tier II) Data

Crop Type of Study Species EC 25 

### (lb a.i./A) NOAEC (lb a.i./A) Most sensitive
parameter

Monocots Corn >0.09 0.09 None

Onion 0.017 0.0112 Dry weight

Wheat 0.041 0.0225 Dry weight

Pea >0.09 0.09 None

Dicots Turnip 0.005 0.003 Dry weight

Soybean >0.09 0.045 Dry weight

Cotton 0.016 0.0028 Dry weight

Cucumber 0.024 0.0112 Dry weight

Tomato >0.09 0.09 None

Sorghum >0.09 0.045 Dry weight-52 of 61-Appendix BIncident ReportsEIIS Pesticide Summary Report: General InformationMetribuzin (101101)Incident #DateCountyStateCertaintyLegal.Formul.Appl. MethodTotal MagnitudeAQUATICAgricultural AreaI000636-0125/11/1985SCOTLANDMO2UNTHOUSANDSPONDI008768-0076/3/19992UNN/RN/R200PLANTSAgricultural AreaI005880-037OutagamieWI2UNSprayN/RI005880-043WALWORTHWI3MAN/RUnknownI005880-011LAFAYETTEWI3MASpray1700 ACRESI005880-018OUTAGAMIEWI2UNSprayUNKNOWNI005880-044RACINEWI3MASoil incorporationUnknownI005880-049SAUKWI3MASprayUnknownI005880-022WAUSHARAWI3MAN/RSoil incorporatedUNKNOWNI005880-040WINNEBAGOWI3MAN/RUnknownI005880-020WAUSHARAWI2UNSprayUNKNOWNI005880-027WAUKESHAWI3MASprayUNKNOWNWednesday, June 13, 2012Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable.Page 1 of 6Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), U=Unknown.-53 of 61-Incident #DateCountyStateCertaintyLegal.Formul.Appl. MethodTotal MagnitudeI005880-034OUTAGAMIEWI3MASoil incorporationUnknownI005880-033FOND DU LACWI3MASoil incorporationUNKNOWNI005880-039OUTAGAMIEWI3MASoil incorporationUnknownI005880-017FOND DU LACWI2UNSprayUNKNOWNI005880-006DANEWI3MASprayUNKNOWNI005880-024OUTAGAMIEWI2UNN/RUNKNOWNI005880-0555/18/1997MN3UNSprayUnknownI005879-0086/4/1997TAMAIA2MASprayUNKNOWNI005879-0096/6/1997GRUNDYIA2MASprayUNKNOWNI005879-0157/9/1997BUCHANANIA2UNSprayUNKNOWNI016232-0034/22/2005ID2RUBroadcast60 acresI016978-01111/7/2005ID2RUNR200 acresALFALFAI010210-0073/6/2000OH3MAFN/R90%I012982-0074/10/2002ShelbyOH3MDFBroadcast90% of cropI014123-0195/14/2003Twin FallsID2MWDGBroadcast38 acresI014123-0255/14/2003Twin FallsID2RUWDGBroadcast38 acresAsparagusI015278-0016/20/2003MalheurOR2RU67 acresBeanWednesday, June 13, 2012Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable.Page 2 of 6Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), U=Unknown.-54 of 61-Incident #DateCountyStateCertaintyLegal.Formul.Appl. MethodTotal MagnitudeB000622-0015/15/1986StarkOH2UNSprayN/RBean, garbonzoI011814-0124/12/2001SAN JOAQUINCA3MAFN/RALLBeansI013563-0061/24/2001San JoaquinCA2UNN/R110 acresCORNI008079-0024/30/1998JASPERIA2RUN/RGROUND/BROADC300 ACRESASTI007755-0075/5/1998BOONEIA2RUN/RBroadcast200 ACRESI008002-00110/11/1998CALHOUNIA2UNBroadcast80 ACRESI008002-00210/12/1998CARROLLIA2RUBroadcastALL 330 ACRESI008002-00310/13/1998GRUNDYIA2RUBroadcastALL 2400 ACRESI010460-0046/2/2000CALHOUNMI4UNDFN/RUNKNOWNI010460-0056/10/2000KANKAKEEIL4MADFN/R50%I011814-0115/29/2001STEARNSMN3MAFN/R50% OF FIELDI011662-0045/30/2001BUCHANANIA3MAFN/R50% OF CROPI011814-0136/4/2001CERRO GORDOIA3MAFN/R75% OF FIELDI011814-0076/8/2001SAUKWI3MAFN/R75%I011814-0096/11/2001LINNIA3MAFN/R46% OF FIELDI011814-0106/11/2001LINNIA3MAFN/R48.6%I012177-0047/26/2001HALLNE2RUDFN/R55% OF CROPWednesday, June 13, 2012Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable.Page 3 of 6Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), U=Unknown.-55 of 61-Incident #DateCountyStateCertaintyLegal.Formul.Appl. MethodTotal MagnitudeCorn, fieldI012366-0344/14/2001CASSIN2UN65.0 acresI012982-0095/13/2002VernonMO2RUDFBroadcast60 acresI015291-0266/4/2004RipleyIN2RUDF96 acresFIELDI008664-0044/13/1999CARROLLMO2RUDFBROADCAST80 ACRESBOOMN/RI005880-030DODGEWI2UNSprayUNKNOWNB000609-0016/5/1986MorrowOH2UNSprayN/RB000603-0065/18/1997IN2UNN/RN/R3Potatoi017245-009MorrowOR3UNDF2 Poplar TreesI020459-0335/15/2000BentonWA2UNI016595-0287/8/2005BonnevilleID2RUF2000 acresRight-of-way, roadI019442-0017/19/2007BrownOH2MIRyegrassI016962-0279/8/2004YamhillOR2RUBroadcast38 acresSoybeanB000625-0015/15/1986DakotaMN2RUSprayN/RWednesday, June 13, 2012Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable.Page 4 of 6Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), U=Unknown.-56 of 61-Incident #DateCountyStateCertaintyLegal.Formul.Appl. MethodTotal MagnitudeI001131-0016/27/1994PULASKIAR2RUN/RBroadcastUNKNOWNI007371-0085/20/1997PA4MAN/RN/RI005879-0106/17/1997CLINTONIA2MASprayUNKNOWNI012366-0125/12/2000MACOMBMI2UNBroadcast320 acres of 367I014106-0015/15/2003ArkansasAR2RUEC227 acresI014102-0015/15/2003PrairieAR2RUEC250 acresI015291-0356/24/2004Cerro GordoIA2RUDF90 acresI016595-0307/5/2005Cerro GordoIA2RUWDGBroadcast50% of 7 acresI016903-00310/10/2005HuronOH2RUECBroadcast230 acres of soybeanSoybeansI016328-0375/31/2005ScottIN2RUWDGBroadcast385 acresWHEATI011508-0021/24/2001CLOUDKS3MAFN/RUNKNOWNWheat, winterI013942-0063/27/2003LancasterVA2RUBroadcast32 acresI014029-0053/27/2003LancasterVA2RUBroadcast32 acresI014123-0245/2/2003DouglasOR2RUBroadcast80% 0f 200 acresI014123-0185/3/2003MortonOR2RUBroadcast80% of 200 acresI014123-0125/16/2003EssexVA2RUBroadcast70 AcresI014676-00411/13/2003VA2MWDGBroadcast34 acresWednesday, June 13, 2012Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable.Page 5 of 6Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), U=Unknown.-57 of 61-Incident #DateCountyStateCertaintyLegal.Formul.Appl. MethodTotal MagnitudeI014978-0013/24/2004DelawareIn2RUWDGBroadcast65 acresTERRESTRIALN/RI007334-0016/18/1998WhiteIL2UNSpray4Wednesday, June 13, 2012Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable.Page 6 of 6Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), U=Unknown

### -58 of 61- Appendix D. Results from Screening Imbibition Program (SIP) and the Screening Tool for Inhalation Risk Assessment (STIR)

The S creening I mbibition P rogram (SIP v.1.0, Released June 15, 2010) was used to calculate an upper bound estimate of exposure us ing metribuzin solubility (1200 mg/L, @ 25oC), the most

sensitive acute and chronic av ian toxicity endpoints (Bobwh ite quail with acute oral LD 50 

### of 169.2 mg a.i./kg-bw, acute dietary LC 50 

### of >4000 mg a.i./kg diet and mallard duck with lowest reproduction NOAEC of 368 mg a. i./kg-diet) and the most sensitive acute and chronic mammalian toxicity endpoints (Mouse LD 50 

### =698/711 mg a.i./kg-bw (male/female) and rat NOAEL = 1.5 mg a.i./kg-bw. Based on the outpu t, exposure through drinking water alone is potential chronic risk to small birds and ma mmals. Results from SIP are shown below.

Inhalation is another po tential exposure route for terrestria l vertebrates. Based on the vapor pressure of metribuzin (9.1 x10 -7 

### torr), risk to birds, terrestr ial-phase amphibians, reptiles, and mammals from inhalation is not expected. The 4-hr LC 50 

### inhalation study using rats was greater than 0.709 mg/L (MRID 46105408). The STIR model (Screening Tool for Inhalation Risk) was

used to evaluate inhalation risk to birds. Th e definitive acute oral values for both birds and

mammals were used in the model. Based on ST IR, risk to birds and mammals from inhalation alone is not expected. Results from STIR are shown below.

### -59 of 61- SIP Version 1.0. August 19, 2010
Table 1. Inputs

Parameter Value

Chemical name Metribuzin Solubility (in water at 25 o C; mg/L) 1200

Mammalian LD 50 (mg/kg-bw) 698 Mammalian test species other Body weight (g) of "other" mammalian species 20g

Mammalian NOAEL (mg/kg-bw) 30 Mammalian test species laboratory rat Body weight (g) of "other" mammalian species

Avian LD 50 (mg/kg-bw) 169.2 Avian test species northern bobwhite quail Body weight (g) of "other" avian species Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 368 Bobwhite quail NOAEC (mg/kg-diet) 385 NOAEC (mg/kg-diet) for other bird species Body weight (g) of other avian species NOAEC (mg/kg-diet) for 2nd other bird species Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic Upper bound exposure (mg/kg-bw) 206.4000 206.4000 Adjusted toxicity value (mg/kg-bw) 262.4901 1.1537 Ratio of exposure to toxicity 0.7863 178.8963

Conclusion* Exposure through drinking water alone is a potential concern for

mammals Exposure through drinking water alone is a

potential concern for

mammals

Table 3. Avian Results

Parameter Acute Chronic Upper bound exposure (mg/kg-bw) 972.0000 972.0000 Adjusted toxicity value (mg/kg-bw) 121.8967 18.2574 Ratio of exposure to acute toxicity 7.9740 53.2386

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.

### -60 of 61- Results From STIR Version 1.0, November 23, 2010



# Screening Tool for Inhalation Risk

This tool is designed to provide the risk assesso r with a rapid method for determining the potential significance of the inhalation exposure route to birds and mammals in a risk assessment.



# Input

Application and Chem ical Information

Enter Chemical Name metribuzin

Enter Chemical Use Registered Uses Is the Application a Spray? (enter y or n) y If Spray What Type (enter ground or air) air

Enter Chemical Molecu lar Weight (g/mole) 214.28 Enter Chemical Vapor Pressure (mmHg) 9.10E-07 Enter Application Rate (lb a.i./acre) 6

Toxicity Properties

Bird

Enter Lowest Bird Oral LD 50 (mg/kg bw) 169.2 Enter Mineau Scaling Factor 1.15 Enter Tested Bird Weight (kg) 1.58

Mammal

Enter Lowest Rat Oral LD 50 (mg/kg bw) 698

Enter Lowest Rat Inhalation LC 50 (mg/L) 0.709 Duration of Rat Inhalation Study (hrs) 4 Enter Rat Weight (kg) 0.02



# Output

Results Avian (0.020 kg)
Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 1.05E-02 Maximum 1-hour Vapor Inhalation Dose (mg/kg) 1.32E-03 Adjusted Inhalation LD50 1.68E+01 Ratio of Vapor Dose to Adjusted Inhalation LD 50 7.87E-05 Exposure not Likely Significant Maximum Post-treatment Spray Inhalation Dose (mg/kg) 5.76E-01 Ratio of Droplet Inhalation Do se to Adjusted Inhalation LD 50 3.44E-02 Exposure not Likely Significant



### Results Mammalian (0.015 kg)
Maximum Vapor Concentration in Air at Saturation (mg/m 3 ) 1.05E-02 Maximum 1-hour Vapor Inhalation Dose (mg/kg) 1.66E-03 Adjusted Inhalation LD50 3.61E+02 Ratio of Vapor Dose to Adjusted Inhalation LD 50 4.59E-06 Exposure not Likely Significant Maximum Post-treatment Spray Inhalation Dose (mg/kg) 7.25E-01 Ratio of Droplet Inhalation Do se to Adjusted Inhalation LD 50 2.01E-03 Exposure not Likely Significant

### -61 of 61- Appendix E: ECOSAR modeled es timates of degr adate toxicity

Comparison of Observed toxicity values and QS AR-generated endpoints (mg/L) for Metribuzin and its degradates by chemical class chos en in ECOSAR – Hydrazines ECOSAR class

Taxon Paren

t data Parent QSA

R Ratio of

parent data/paren t QSAR DADK

* QSAR DK* QSA

R DA* QSA

R 4- methyl

DADK

* QSAR 2- methyl

DADK

* QSAR 3-

NH3

DA* QSA

R Daphni

d LC50 4.2 16 0.26 16.4 53 5.0 14.2 14.2 11.4

Daphni

d ChV 1.29 1.21 1.07 1.29 5.1 0.31 1.07 1.07 0.836

*=Residue to be included in TTR

Comparison of Observed toxicity values and QS AR-generated endpoints (mg/L) for Metribuzin and its degradates by chemical class chos en in ECOSAR – Amides ECOSAR class

Taxon Parent

data Parent QSAR Ratio of parent data/parent QSAR DA* QSAR 3-NH3 DA* QSAR

FW fish 42 149 0.28 26 99

SW fish 85 131 0.65 23 87 Mysid 48 7 6.9 1.7 4.8

*=Residue to be included in TTR

Comparison of Observed toxicity values and QSAR-generated endpoints (mg/L) for the Metribuzin degradate DADK and other me tribuzin degradates by chemical class

chosen in ECOSAR – Car bonyl ureas ECOSAR class

Taxon DADK

data DADK QSAR Ratio of

DADK

data/DADK QSAR DK* QSAR 4-methyl

DADK* QSAR 2-methyl

DADK* QSAR

Daphnid

ChV 3.3 1.22 2.7 6.1 0.961 0.961

*=Residue to be included in TTR