### U. S. ENVIRONMENTAL PROTECTION AGENCY Washington, D.C. 20460

OFFICEOF *\TED S74? % PREVENTION, PESTICIDES 

# ,.$a $ AND TOXIC SUBSTANCES 

# a=.: 3. 9

4' PRflc~'8 

### Date: April 5,2005 

### Chemical: Thidiazwon 

### PC Code: 120301 

### DP Barcodes: D289980 D29 1684 D294536 D298740 D294537 

### MEMORANDUM SUBJECT: Environmental Fate and Effects Division's Phase 

### 2 Risk Assessment for the Reregistration Eligibility Decision of Thidiazuron for Use on Cotton TO: John Pates, Jr.; Chemical Review Manager; Reregistration Branch I1 SpecialReview and Reregistration ~iviiion (7508~) 

### FROM: William Evans, Biologist 

# 3- lex Clem, Environmental Scientist 

# &cp" 

# )il'ho"5
es Hetrick, Ph D., SeniorPhysical Scientist 

# /F~~ 

# 6' 

# V77d ward Odenkirchen,Ph.D., Senior Biologist
I EnvironmentalRisk Branch 

### I Environmental Fate and Effects Division (7507C) I I 

### APPROVED 

### BY: Sid Abel, Branch Chief, Environmental Risk Branch 

### I Environmental Fate and Effects Division (7507C) 

### ,/

-\ This memorandum summarizes the attached EnvironmentalFate and Effects Division's (EFED) Phase 2 Thidiazwon Environmental Risk Assessment for a proposed Reregistration Eligibility Decision (RED) for use on cotton. Thememorandum and attached assessment differ slightly from their previous analogs in that we have made appropriate corrections and modifications that were prompted the registrant's (Bayer Cropscience) commentsin their Phase 1Error Correction document dated February 4,2005. We are pleased to report that the errors Bayer detected essentiallydid not affect the risk characterization and conclusions we reached previously.

### Use of Thidiazuron. Thidiazuron is currently registered for use as a defoliant (herbicide) to aid in the harvest of cotton. The maximum single application rate is 

### 0.2 Ib ai/A. A second application isrecommended under low temperature conditions when defoliation does not reach the expected level, but the total of the two applications must not exceed 0.3 Ib ai/A. The intervalsbetween applications range from 

### 5-7 days in some of the labels, while the other labels make no recommendations in this regard. 

### EnvironmentalFate Summary In soil, thidiazuron is persistent, as evidencedby laboratory and field half-lives and rotational crop intervals on the order of one year. It has intermediate soil sorptioncoefficients (sorption coefficientsranged from 4.4 to 19Freundlich units). Such persistence and intermediate mobility would allow someyear to year accumulation over time and, therefore, more opportunityfor favorable conditions for runoff from application sites to occur. For example, with a one year soil half-life and without redistributionor dispersal from the site of application, theoretical build-up in soil would asymptotically approach twice that of annually applied amounts. Of course, given time and variable climaticconditions, redistributionor partitioning ofthidiazuron into other environmentalcompartments does occur (viarunoff, leaching, plant uptake, etc.); therefore, maximumbuild-up in surface soil averages less than the theoretical factor oftwo. When thidiazwon reaches surface water, photolysis is expected to be the major route of transformation; other degradative processes are essentiallynegligible by comparison. Aqueous photolysis is rapid, and occurs by branching in quantitativeyield into two photoproducts. One of the photodegradates is a structural isomer ofparent, whereas the other has a substantially altered chemical structure. Based on its solubilityand vapor pressure (Henry's law), and other laboratory evidence, thidiazuronis non-volatile. Based on its relatively low n-octanol/waterpartitioning coefficient, thidiazuron should not bioconcentrate. No foliar dissipation data are currently available, and since thidiazuron is used to defoliate cotton prior to harvest, dislodgement from or transformation idonleaves may be an important fate pathway. The effects ofthis uncertainty and alternativeassumptions are considered in the risk assessment. 

### Ecological Risk Summary This assessment is based on mainly on toxicitytesting with typical end use products (formulations) containing thidiazuron as the only active ingredient. In addition to parent thidiazuron, we have also factored into our assessment limited data for three of its transformation products (degradateslmetabolites). On the basis of testing onlywith thidiazuron and its degradates, apparent risks may be underestimated because: 1) in five of twelve registered products thidiazwon is co-formulated with either oftwo other registered herbicides, and there areno test data for any of these co-formulated products; 

### 2) there are no data for mixtures with adjuvants (tank-mix data), whichproduct labels state improve performance; and 3) there are no test data with mixtures that include organophosphate pesticides, which labels state may increase phytotoxicity. A fourthreason that risk may be underestimated is that product label statements about citrus and cantaloupe, for which we have no test data, clearlyimplythat these or other plant species may be more sensitivethan species for which we have test data. Thus, the absence ofphytotoxicity data for the cited mixtures and the absence of data for plants that are apparently more sensitive than those tested are substantial sources ofunquantified uncertainties that would reasonably and most likely lead to risk greater than owestimations. Highlights of our ecological risk concerns, based on toxicitytesting with typical end-use products containing thidiazuron as the only active ingredient and the modicum of data on three transformationproducts, are the following:

b Non-target Plants: Non-target terrestrial and semi-aquatic dicots, but not monocots, are at potential direct and indirect ecologicalrisks. Aquatic plants do not appear to be at risk.

b Mammals: Mammals are at potential chronic risk, but not acute.

b Birds: Potential chronic risk to birds cannotbe determined because of the absence of chronic data. Potential acuterisks to birds are below all levels of concern. A principal ecological risk concern for the proposed thidiazuron use on cotton is the potential risks to non-target plants. Ifnon-targetplants come into contact with thidiazuron, these plants may be killed or damaged enough to prevent the plant from reproducing or successfully competing with other plants for resources. The use of thidiazuron could apply selective pressure to dicots along field edges, resulting in changes in species composition. Even though thidiazuron is only applied at cottonharvest, application timing is a consequential factor to consider. Reproduction abnormalities are some of the plant injuriesthat can occur due to thidiazuron exposureduring particular developmental stages. Although the plant may survive, sterile florets or non-viable seed production can occur. This will have effects on the non-target plant populations in future years. Also, plant material serves as a primary food source for many species of animals. Ifthe available plant material (including seeds) is reduced due to the effects ofthidiazuron, this may have negative effects throughout the food chain. The risk assessment for terrestrial plants was based on risk quotients (RQs) calculated from toxicity studiesusing a typically formulated end-use product (TEP). However, it appears that no. surfactants or other adjuvants were added to the product during the studies, and all labels clearly state the addition of adjuvants has been shown to improve the performance. Therefore,the risk to terrestrialnon-target plants may be greater than thidiazuron RQs indicate. Hence, the production of actual tank-mix data would reduce some of the uncertainties associated with risk to plants.Additionally, in fourproductsthidiazuron is co-formulated either with the herbicide diuron or the herbicide dimethipin (see table in Use sectionof this document). 

### In these products, diuron comprises33% and thidiazuron 67% of the total active ingredients. In the other formulation, dimethipin comprises 80% ofthe total active ingredients, while thidiazuron comprises only20%. Potential effects of the addition of these other two chemicals are not factored into the risk assessment. Combining (adding) known effects ofthese other two chemicals with those for thidiazuron,or, alternatively, producing specific test data for these mixed products would reduce the risk uncertainties and more accurately portray the risk associated with their co-application. It is also importantto note that all labels listprecautions when applyingthe products adjacent to lettuce, citrus, or cantaloupe. The labels further state that mixing with organophosphatesmay increasenon-target crop phytotoxicity. Special restrictions to reduce 

### drift to lettuce and citrus appear on all the labels. 

### In addition, an incident was reported to have caused an estimated $350,000 of crop loss to 50 acres of lettucewhen thidiazuron allegedly drifted onto 150acres. Thidiazuron products can not be applied by air within '/z mile of lettuce or 5 miles downwind of the point of applicationwhen citrus is in flush (burst ofnew growth, as in springtime) in the Rio Grande valley of Texas. Ground applications are restricted to 100 feet away from lettuce and % mile downwind from the point of application for citrus. Labels do not specify a distance for cantaloupe. EFED currentlyhas no toxicity data for citrus or cantaloupe, and the data on lettuce indicate that it is the most sensitiveof all the crops tested thus far. Therefore, toxicity data on cantaloupeand citrus (which has a much larger spraydrift buffer distance than lettuce),may indicate that risk is even higher than indicated by the lettuce RQs. Acuterisk quotients for mammals did not exceed levels of concern (LOCs). However, chronic risk quotientsfor mammals did exceed LOCs, with RQs ranging from 

### 6.3 (15-g mammal feeding on short grass) to 0.01 (1000-g mammal feeding on seeds). To further investigate the chronic risk to mammals, in additionto the standard default foliar dissipation half-life of 35-days,EFED evaluated the impact of a hypothetical half-life as low as one day on thidiazuron residue concentrations on reducing risk. We also evaluatedpotential effects at predicted maximum and mean residues for single applications. 

### In these scenarios, chronic RQs would be reduced to the range of 2.4 (15-g mammal feeding on short grass) to 0.002 (1000-g mammal feeding on seeds), but still would exceed chronic LOCs. The 3-generation reproduction study with rats indicates a possible concern for endocrine disruption, based on significant effects on mean litter size in the F3b generation. When appropriate screening and/or testingprotocols have been developed, thidiazuron and its degradates may be subject to additional screening andlor testing to better characterize effects related to endocrine disruption in mammals or other organisms. Acuterisk quotientsfor birds did not exceed LOCs. Chronicrisk to birds cannot be evaluated because chronic datawere not submitted.Data Gaps Environmental Fate: Status 

### ofEnvivonmental Fate Data. Although some of the submitted fate studieshad deficiencies, taken as a whole and within the constraints stipulated in the fate assessment, the data enable the Agency to adequately assess the environmental fate of thidiazuron. Although no foliar dissipation studies are currently available to the Agency (these are not generallyrequired),having such data would make any fate assessment more precise, especially in the case of a defoliant such as thidiazuron. However, as discussed in the fate assessment, if dislodgement from or transformation idontreated plants were to be an important fatepathway, then EFED's inferences from existing fate studies and assumptions for exposure modeling for parent and potential degradates should reasonably and conservatively coverthe possibility. Ifthe registrant wishes to demonstrate that definitive data on foliar dissipation would substantiallyaffect any of our inferences, assumptions, or environmentalrisk conclusions, then the registrant should submit appropriate data. Otherwise, except for spray-drift requirements, the Agency needs no additional environmental fate studies at this time. Ecological Effects: The ecological toxicity data base is fairly complete, however, there are some additional key studiesthat could assist in reducing the uncertainties in this risk assessment. The details are summarized below. Non-target Terrestrial Plant 

### - Definitive tier 11EC25s and NOAECs are lacking for the vegetativevigor of all the monocots tested and for the seedling emergenceoftwo monocot species tested; this isbecause test concentrations were not low enough to establish these endpoints. However, risk quotients from the tests for which definitive endpoints were established were below levels of concern. Furthermore, concentrationsin those tests for which endpoints were not determined were sufficiently low to establish that, when compared to estimated field exposure concentrations that correspond to the currently-labeled application rates, risk quotients would not exceed any ofthe terrestrial plant LOCs. Therefore, sinceprojected risk quotientsfor monocots are below levels of concern, additional tier I1 testing with a typical end-use product that contains thidiazwon as the only active ingredient is not required at this time for these specific crops at currently-labeled application rates. However, there are other considerations. Even though all labels clearly state that the addition of adjuvants has been shown to improve performance, it appears that none were added the during the tests. Therefore, apparent risk to terrestrial non-target plants may be greater than present RQs indicate. The production of actual tank-mix data would reduce this uncertainty. Additionally, as previously mentioned, five of twelve registered thidiazuron products are mixtures with other herbicides. Four of the twelve are mixtures ofthidiazuron and diuron,with thidiazuroncomprising 67% and diwon 33% of the total active ingredients The fifthproduct is a formulation of thidiazuron (20% of total activeingredients) and preponderantly dimethipin (80% of total activeingredients). Potential effects of themixtures with these other two chemicals are not factored into the risk assessment. Combining (adding) the known effects for these other two chemicals with those for thidiazuron, or, alternatively, producing specific test data for these mixed products would reduce the uncertainties associated with their co-application and thereby more accurately portray risk. Concerning the potential for additional, undetermined risk, the current labels contain warnings and specific instructionsabout the use of thidiazuron in the vicinityof lettuce, cantaloupe, and citrus. The language from one of the labels is the following: 

### "Particular care should be taken when applying DroppB UltraTM adjacent to lettuce, citrus, or cantaloupe. " 

### "In addition, for citrus crops, do not applyDroppB UltraTM by air when citrus in flush is within Jive (5) 

### miles downwind ofthe point ofapplication. Do not apply DroppB UltraTM by ground when citrus in flush is within one-half(l/2) mile." Labels also statethat "do not app1y"distances hom lettuce are one-half (112)mile by air and 

### 100feet by ground. Despitethese warnings, no seedling emergence or vegetative vigor data have been submitted for cantaloupe or citrus. Data on citrus and cantaloupe would reduce uncertainty about potential increasedrisk by providing a better species-sensitivity distributionfor non-target plants. Therefore, EFED recommends definitive tier 11 studies for thidiazuron on citrus and cantaloupe, preferably with adjuvants and any other coformulated activeingredient added as part of the test materials. Birds 

## - Chronic risks to birds can not be quantitatively evaluated at this timebecause chronic data were not submitted. 

### In order to assess this potentialrisk, we recommend chronic testing with an upland game-bird species (bobwhite quail) and a waterfowl (mallard duck). 

### Recommended Label Language Ifthidiazuronis reregistered, the following statements shouldbe included in the "ENVIRONMENTAL 

### HAZARDS" labeling: For Manufacturing-Use Products "Do not discharge effluent containing this active ingredient into lakes, streams, ponds, estuaries, oceans, or other public waters unless this product is specifically identified and addressedin an NPDES permit. Do not discharge effluent containing this product into sewer systems without previously notifying the sewage treatment plant authority. For guidance, contact your State Water Boardor Regional Office of

### EPA."! 

### For End-Use Products "Do not apply directlyto water or to areas where surface water is present or to intertidal areas below the mean high water mark. Do not contaminate water when disposing of equipment washwater or rinsate." 

### Surface Water Advisory "This product may contaminate water through drift of spray in wind. Thisproduct has a high potential for runoff for several months or more after application. Poorly draining soils and soils with shallow water tables are more prone to produce runoff that contains this product. A level, well-maintained vegetative buffer strip between areas to which this product is applied and surfacewater features such as ponds, streams, and springs will reduce the potential for contamination ofwater from runoff. Runoff of this product will be reduced by avoiding applicationswhen rainfall is forecasted to occur within 48 hours. Sound erosion control practices will reduce this product's contribution to surface water contamination." 

### Groundwater Advisory "This chemical has properties and characteristics associated with chemicals detected in ground water. Use of this chemical in areas where soils are permeable, particularly where the water table is shallow, may result in groundwater contamination." 

### Spray Drift Management Drift is transport ofpesticides through air away from the target site, and includes, for example,

. spray drift and volatilization. Spray drift, the movement ofpesticide droplets off-target during or shortly after application, has been well studied, and is not dependent on the properties ofthe active ingredient. Short-rangespray-drift and resulting exposures to non-target organisms is quantified in our risk assessments. Currently, when specific label instructions are not available, we account for spray drift inboth drinking water and ecological exposure assessmentsby the use of default assumptions for the percentage of deposition based on application method. We have established default spray driftpercentages for pesticides for aerial application, ground application, and orchard airblast. Default values for drinking water exposure scenarios are 16%, 6.4%, and 6.3% of the application rate for aerial, ground boom and airblast applications, respectively. The default values for the drinking water exposure were generated using AgDRlFT version 1.03 which uses a semimechan(stic model (AGDISP) for aerial applications and is based an empirical data set (Spray Drift Task Force data) for ground boom and airblast applications. The derivation of the spray drift loading values is described in Appendix 

### B of the Guidance for Use of the Index Reservoir in Drinking Water Exposure Assessments and is based on the following application and wind speed assumptions:For ground boom applications nozzle height no more than 

### 4 feet above the ground or crop canopy wind speed is 10mph or less at the application site and, medium or coarser spray according to ASAE 572 definition for standard nozzles. For aerial applications boom width less than 75% of the wingspan or 90% of the rotaryblade, use ofupwind swath displacement, wind speed 3 

### - 10mph, and use medium or coarser spray according to ASAE 572 definition for standard nozzles. For orchardhineyard airblast applications spray is not directed above treeslvines, outward pointing nozzles are shut off at row ends and outer rows, and wind speed is 3 -10 mph at the application site as measured by an anemometer outside of the orchard/vineyard on the upwind side. Default values for ecological exposure scenarios are 5% for aerial applications and 

### 1% for ground applications, with no set value for orchard airblast. For the ecological assessment, the default values of 5% for aerial applications and 1% for ground applications were established based on open literature and research prior to establishment of the Spray Drift Task Force, and were therefore not generated using AgDRIFT. Testing ofthe default spray drift values for ecological assessments using AgDRIFT provides context for the default assumptions. Analysis ofthe 1 % ground application drift percentage using AgDRlFT (with the same assumptions as for drinkingwater outlined above) indicates that the default value likely underestimates drift from single events under relatively high drift conditions. A similar underestimation likely occurs for the 5% aerial drift value. EECs predicted for drinkingwater and ecological assessments arebased on the assumptions of drift outlined above for ground and aerial applications. Variance from these assumptions will result in differences in predicted concentrations. For the ecological assessment, as with the drinkingwater assessment, variance from the assumptions behind these default values could result in increased risk. 

### In general, a decrease in droplet size or increase in wind speed at the time of application will result in higher predicted EECs and risk to non-target organisms. Alternatively, if droplet size is coarser or wind speeds are lower, exposures due to drift would be lower. Transport resulting from volatilization is highly dependent on the properties ofthe active ingredient (e.g.,Henry's Law constant) as well as a number of environmental parameters. Based on its physicochemical properties,thidiazuron is not expected to volatilize.

## Phase 2 Environmental Fate and Effects Division's Risk Assessment for the Reregistration Eligibility Document For the Use of Thidiazuron on Cotton

### Table 

### of Contents

.................................. I

# . Environmental Risk Conclusions Page 4 of 134



### .............................. Environmental Fate Abstract Page 4 of 134



### .......................... Terrestrial Plant Risks of Concern Page 4 of 134



### ..................... Terrestrial Vertebrate Risks of Concern Page 5 of 134 11


### . Introduction


### .................................................... Page6of 134



### ....................................... Pesticide Mode ofAction Page 6 of 134



### .................................. Uses and Use Characterization Page 7 of 134



### ..................................... Risk Assessment Approach Page 

### 9 of 1.34



### ................................... Assessment Endpoints Page 9 of 134



### ..................................... Measures of Effects Page 

### 9 of 134



### .................................. Measures ofExposure Pare 11 of 134



### ............................... Aquatic Organisms Page 

### 11 of 134 Active Ingredient and Degradate Aquatic Organism Exposure Approach



### ........................................ Page 11 of 134 Terrestrial Plants


### .............. -; 

### ................. Page 1 2 of 1 34



### .............................. Terrestrial Animals Page 13of 134



### ................................ Risk Characterization Approach Page 13 of 134 Problem Formulation Analysis Plan


### ............................. Page 13 of 1 34 111


### .Integrated Environmental Risk Characterization


### ....................... Page 17of 134



### .................................... Risks to Aquatic Organisms Page 17of 134



### ............................. 

### ......... Risk to Birds


### . ; ; Page 1.7of 134



### .............................. Acute Risks 

### - Birds Page 17of 134



### ............................. Chronic Risk

. Birds Page 18 of 134



### ........................................... Risks to Mammals Page 18 of 134 Acute Risks

. Mammals


### ................................. Page 

### I

.

### 8 of 134



### .......................... Chronic Risk

. Mammals Page 18 of 134 Risks to Non-Target Insects


### .................................... Page 20 of 1.34 Risks to Terrestrial Plants


### ..................................... Page 21 of 134 Endocrine Diskption Assessment


### ............................... Page 43 of 134 Endangered Species Assessment


### ................................ Pace 44 of 134 

### IV


### .Environmental Fate Assessment


### ................................... Page 45 of 134 Basis


### ................................................ Page45of 134 Fate Assessment


### ....................................... Page 46 of 134 Abstract


### ..............................................Page 46 of 134 Physical/ChemicalProperties


### ....................... Page 47 of 134



### ...... Transformation Products (degradateslmetabolites) Page 5 1 of 134 V

.Drinking Water Assessment Summary


### ............................... Page 54 of 134 VI


### .Aquatic Hazard. Exposure. and Risk Quotient Calculation


### ............... Page 

### 56 of 134 Toxicity to Fish



### .............................................Page 56 of 134 Page 2 of 134I



### ................................ Toxicity to Aquatic Invertebrates Page 56 of 134



### ..................................... Toxicity to Aquatic Plants Page 57 of 134



### ............................................ Aquatic Exposure Page 57 of 134 RiskQuotients


### ........................................ Page58of 134 

### VII


### .Terrestrial Hazard. Exposure. and Risk Quotient Calculation


### ............ Pawe 58 of 134 Toxicity to Birds


### ............................................ Page 58 of 134 Toxicity to Mammals


### ......................................... Page 58 of 134 Toxicity to Non-target Insects


### .................................. Page 59 of 134 Toxicity to Earthworms


### ....................................... Page 60 of 134 Toxicity to Non-Target Plants


### ............................ Page 60 of 134 Terrestrial Plant Exposure and Risk Quotient Calculations


### ..... Page 61 of 134 Terrestrial Exposure for Birds and Mammals


### ................ Page 63 of 134 Terrestrial Risk Quotients


### ............................... Page 65 of 134 APPENDIX C: Model Input Parameters Derived fiom Environmental Fate Studies for Thidiazuron


### ............................................. Page 81 of 134 

### APPENDIX LIST APPENDIX A: Detailed Drinking Water Assessment Memo


### ................ Pape 66 of 134 APPENDIX

### B: Chemical Structural Formulas. Names


### ....................Pawe 78 of 134 APPENDIX D: GENEEC Input & Output Files for Ecological Assessment


### .... Page 84 of 134 APPENDIX 

### E: Ecological Hazard Data


### ................................ Page 89 of 134 APPENDIX 

### F: The Risk Quotient Method


### ............................. Page 106 of 134 APPENDIX G: Detailed Risk Quotients


### .............................. Pave 109of 134 APPENDIX 

### H: Data Requirements for Thidiazuron


### ...................... Page 129 of 134

Page 3 of 134

### I. Environmental Risk Conclusions Environmental FateAbstract In soil, thidiazuron is persistent, as evidencedby laboratory and field half-lives and rotational crop intervals on the order of one year. It has intermediate soil sorption coefficients (sorption coefficientsranged from4.4 to 19Freundlich units). Suchpersistence and intermediate mobility would allow some year-to-year accumulation over time and, therefore, more opportunity for favorable conditions for runoff from application sites to occur. When thidiazuron reaches surfacewater, photolysis is expected to be the major route of transformation; other degradative processes are essentially negligible by comparison. Aqueous photolysis is rapid, and occurs by branching in quantitative yield into two photoproducts. One of the photodegradates is a structural isomer ofparent, whereas the other has a substantially altered chemical structure. The photolysis process requires special exposure and modeling considerations. Based on its solubilityand vapor pressure (Henry's law), and other laboratory evidence, thidiazuron is non-volatile. Based on its relatively low octanol/waterpartitioningcoefficient, thidiazuron should not bioconcentrate. No data on foliar dissipation are currently available to EFED. Sincethidiazuron isused to defoliate cotton prior to harvest, dislodgement from or transformation idonleaves may be an important fate pathway. The effects of this uncertainty and alternative assumptions on the risk assessment are considered. Terrestrial Plant Risks of Concern Thidiazuron poses potential risks to terrestrial plants based on the results of a screening-level assessment. Therisk quotients exceed the levels of concern for non-endangered and endangered plants adjacent to treated sites as well as plants inhabiting semi-aquatic sites. This is especially true for dicots for both single and multiple applications. The RQs resulting from single applications at the maximum label rates range from 0.39 to 9.09 for non-endangered plants and up to as high as 52.63 for endangeredplants. The RQs for multiple applications range from 0.59 to 9.09 for non-endangered species and up to 52.63 for endangered species. 

### In additionto the RQ calculations from the maximum label rates, EFED completed a characterization of potential risks by assessing the effect ofRQ calculations using EECs predicted from modelingwith average application rates (0.05 - 0.07 lb ai/A) as reported in the BEAD QUA report. When the average application rates are compared to the maximum allowable application rates, RQs are reduced by at least one-half, but levels of concern are still exceeded, except for the single ground application for non-endangered species scenario. It shouldbe noted that RQs for this risk assessmentwere based on toxicity studies using the typical end-use product "Thidiazuron SC42" (presumablyDROPP SC (Reg. #: 264-700)). All labels clearly state the addition of adjuvantshas been shown to improve the performance, and yet Page 4 of 134no surfactants or adjuvants were added to the product duringthe studies. Therefore, the risk to

I terrestrial non-target plants maybe greater than RQs indicate. The production of core data using actual tank-mixes may assist in reducing some of the uncertainties associated with risk.

I Additionally, as previously noted, four thidiazuron products are mixtures (co-formulations) of thidiazuron (67% of total activeingredients) and diuron (33% oftotal active ingredients), and still another is a combination ofthidiazuron (20% oftotal active ingredients) and preponderantly dimethipin (80% of total activeingredients) (see table in section on Use and Use Characterization). Adding the known effects of these other two chemicals to those for thidiazuron, or, alternatively, having test data specifically for these products would reduce the uncertainties associated with their co-application and more realistically portray risk. Since the soleuse of thidiazuron is as a cotton defoliant, the primary concern is for non-target plants which inhabit areas near cotton fields. If suchplants are sensitiveto leaf drop and other symptoms which may result from thidiazuron exposure, death, severe damage, or reproductive impairment could occur. This damage could apply selective pressure to dicot plants along field edges and changes in species composition could occur. There is another reason to believe that our assessmentmay underestimate risk to terrestrial plants. All labels listprecautions when applying the products adjacentto lettuce, citrus, or cantaloupe. The labels further statethat mixing with organophosphates may increasenon-target crop phytotoxicity. Special restrictions to reduce spraydrift potential to lettuce and citrus appear on all the labels. Generation of toxicitydata for these crops and other plant species could assist in better characterizing the risks to non-target plants. To explore the apparentrisk posed by spraydrift,we used EFED's current AgDRlFT computer model and thidiazuron phytotoxicity data to estimate plant exposure as a function of downwind distancesfrom application areas. Since the current labels lack specific information on droplet size or boom height, we also looked at the effects ofvarying these. We then compared the various exposure distributions with toxicity level percentiles from the EClO to EC90 (in increments of ten). I As can be seen from the sequence ofthe following bar graphs, there is considerable variation with droplet size orboom height for the EC30 (the closest toxicitylevel to the EC25). The nospray zones for aerial applications for the EC30 effect levels range from slightly over 60 feet to greater than 1000 feet for lettuce, the most sensitivecrop tested so far. Ground application nospray zones for the EC30 vary from about 3 to 200 feet. Similar trends are demonstrated for the other crops for which slope data couldbe determined. 

### In addition, according to the labels, cantaloupeand citrusmany be more sensitivethan lettuce, and no data have been submitted on these crops. All the factors influencing the downwind drift distance, including droplet size, wind speed, boom height, method of application, and targeted toxidty effect shouldbe considered when placing restrictions on labels. Terrestrial Vertebrate Risks of Concern

I Page 5 of 134Thidiazwon maypose chronic risk to mammals, based on a screening-level assessment. Conclusions are derived from a three-generation rat study, the only chronic study currently available to EFED. From the study,the reproductive NOAEC and LOAEC values are 200 and 600 mglkg-diet, respectively, based on reduction in litter size in the F3b generation. When standard conversion factors are employed,the respective NOAEL and LOAEL values are 10 and I 30 mglkg-bwlday. To estimate risk, we used two screening-level methodologies, and found that they give different results. Preferably, EFED uses the NOAEL of 10mglkg-bwlday as the evaluation endpoint for RQ calculationsbased on the Nagy smallmammal assumptions ofpercent body weight consumed for the 15,35,and 1000g mammals. We then comparethe NOAEL (expressed as mglkg-bwlday) to a dietaryEEC adjusted for food consumption. When this method is used, the LOCs are exceeded I for herbivores/insectivores foraging in short grass, broadleaf forage, and small insects. The highest RQ is 8.5 (15-g mammal, short grass). EFED believes this analysis is reasonable because the percent reproductive impairment that is significant to a given species would be based on the reproductive strategy ofthat species. For long-lived species (K-selected), episodic reductions in reproductionmight not be of the same significance as short-lived species (r-selected). A shortlived species reproductive impairment could be enough to igpact any number of species with low generational survival rates and a dependance on high reproductive output forpopulation

I continuance (r-selected species). Another, lesspreferable, method of calculating risk quotients is to directly compare the NOAEC (expressed as mglkg-diet) to the dietary EEC for all the forage groups. Using the NOAEC of 200 mg/kg-diet, chronic LOCs are not exceeded for any of the food categories. 11. 

### Introduction Thidiazuron is undergoing review for reregistration under Section4 ofFIFRA as amended. It is currentlyregistered for use as a defoliant to aid in the harvest of cotton. Defoliation, or leaf abscission, is a natural process in all plants, but canbe manipulated in cotton plants to cause them to drop their leaves in a relatively short period of time to aid in the efficiency of cotton harvesting. 

### Pesticide Mode ofAction Thidiazuron is a phenylurea herbicide that is said to inhibitregrowth through photosynthetic electron transport inhibition at the photosystem 11receptor. Thismode of action increases the ethylene concentration in the leaves; this inhibits the transport of the hormone auxin, and results in leafdrop. While the defoliation process is quite complex, it can be simplified as being governedby two major compounds in the plant, auxin and ethylene. Auxin is a growth-promoting hormone that stimulatesleaf growth and development. Ethylene can be classified as a ripening agent that causes leafdrop. Leaves fall from the plant once ethylene moves fi-omthe leaf blade to the base of the petiole and stimulates the formation of an abscission (separation) layer. The amount of auxin or ethylene present in the leaves of the cottonplant is related to leaf age. Younger leaves Page 6 of 134I I have a higher level of auxin, whereas older leaves have lower levels of auxin and higher levels of 

### I ethylene. This is why older leaves are more conditioned for defoliationthan younger leaves. Furthermore, because of the hormone balance of younger leaves, low rates ofharvest aids often have no effect, and higher rates may actuallykill the leaf, leading to desiccation and leaf sticking.

I Eventually, all the leaves on a cottonplant age so they will defoliate naturally. However, cotton producers can manipulate these hormone levels with the use of defoliants so all the leaves abscise (separateand fall) at the same time. When these defoliants are applied, ethylene levels artificially increase so the abscission process begins. 

### Uses and 

### Use Characterization Thidiazuron is used exclusivelyas a cotton defoliant to aid in the uniform removal of both mature andjuvenile leaves. This facilitates machine harvesting and helps eliminate sources of gin trash and stains. Because of its purpose, thidiazuron is applied during the cottonharvesting period, which is typically in late August and early September. All labels indicate that citrus trees are particularly sensitiveto thidiazuron. All current products containing thidiazuron and their correspondingEPA registration numbers are listed in the followingtable. Product label statements about use indicate that the areas potentially at direct and/or indirect risk from the application ofthidiazuron in the manner prescribed by the labels are the cotton agronomic environments.

Page 7 of 134

- - - - - - -- - - - - ----

### ' 12%thidiazuron and 6% diuron mixture 50% thidiazuron and 25% diuron mixture 30.3% thidiazuron and 15.1 % diuron mixture 32.7% dimethipin and 8.4% thidiazuron mixture For cotton defoliqnt formulationuse only 

### EPA 

### Registration Number 264-622 264-634 264-66 1 264-700 264-82 1 400-505
51036-401 5 1036-402 5 1036-429 51036-430 72167-28 72167-30

As indicated in the table above, thidiazuron is used exclusively as a cotton defoliant or growth regulant. ~h;ee of the twelve registered thidiazuron products are mixed with diuron at half the concentration of thidiazuron. 

### In another product (Harvade4198SC), dimethipin is present at approximatelyfour times the concentration ofthidiazuron. 

### Product Name Dropp 50WP Cotton Defoliant GINSTAR EC Cotton ~efoliant'

Dropp Ultra Cotton Defoliant2

Dropp SC Cotton Defoliant GINSTARB4.5 SC Cotton ~efoliant~ Harvade 4 198SCHarvest Growth Regulant for Cotton4 Thidiazuron 50W Cotton Defoliant Thidiazuron Technical5 Thidiazuron-DiuronEC Cotton Defoliant' Thidiazuron 4SC Cotton Defoliant Nation's AG 11Thidiazuron Technical5 Thidiazuron 5OWSB Cotton Defoliant



### In the case ofthe mixed products, care must be taken when calculatingthe use rates for thidiazuron. This isbecause the "active ingredient" applicationrates given on the labels are for the sums both active ingredients. Since each compound is different in physicochemical properties and biological activity, it is more meaningful, useful, and transparent to separatethe rates for each. This risk assessmentwas conducted for that fraction of the application rate contributedby thidiazuron only. The maximum single application rate for all labels on which thidiazuron is the sole active

, ingredient is 0.2 lb ai/A (EPA Registration Numbers 264-622, 264-700, 51036-401', 51036-430, and 72167-30). A second application is recommendedunder low temperature conditions when defoliation does not reach the expected level, but the total ofthe two applications must not exceed 0.3 lb ai/A. The intervalsbetween applications range from 5-7 days in some of the labels, while the other labels make no recommendations with regard to intervals. Page 8 of 134The maximum single application rate when thidiazuron is mixed with diuron is 0.125 lb of thidiazuronper acre and 0.0625 lb of diuronper acre (EPA RegistrationNumbers 264-634,264- 661, and 51036-429). The combinedrate forboth active ingredients is 0.1875 lb ai/A, and since diuron also has the same mode of action as thidiazuron, the combined total use rate is approximatelythe same as in the products which contain only thidiazwon as the sole active ingredient. The total number of applications is not specified on any ofthese labels, however, the maximum combined activeingredient dosage is not to exceed 0.1875 lb ai/Aper season. When thidiazuron is mixed with dimethipin the maximum single applicationrate is 0.00625 Ib thidiazuron and 0.1 Ib dimethipin/A (EPA Registration Number 400-505). A second application may be required at a maximum rate per acre of 0.003 lb thidiazuron and 0.05 lb dimethipin 5 - 7 days after the initial treatment. The maximum yearly application should not exceed 0.01 lb thidiazuron and 0.16 lb dimethipinlAlyr. Risk Assessment Approach For terrestrialrisk, we consider the activeingredient thidiazuron only. For aquatic risk, in additionto parent thidiazwon, we include the compounds AE F132147 and AE C421200 (photodegradates ofthidiazwon produced in water) and the thidiazuron metabolite 

### AE F132 145. We do not consider any additional risk posed by the co-formulations of thidiazwon with either of the activeingredients diuron or dimethipin, (see previous section for specific products and concentrations of each) or by the addition of adjuvants (surfactants). Assessment Endpoints The typical assessment endpoints for screening-level pesticide ecologicalrisks are reduced survival and reproductive impairment forboth aquatic and terrestrial animal species. These effects extend to a consideration of direct acute and direct chronic exposures. The assessment endpoints for aquaticplants are impairments due to a decrease in alga cell density or macrophyte growth. Terrestrial plant assessment endpoints are impairments due to shoot weight, shoot length, or dry weight. There are currently no chronic assessment endpoints for reproductive impairment forplants. While these endpoints are measured at the individual level, they do provide insight about risks at higher levels ofbiological organization (e.g., populations). Measures of Effects The screening level risk assessment process relies on a suite of toxicity studiesperformed on a limited number of organisms in the followingbroad groupings: Birds (mallard duck and bobwhite quail) (see Toxicity to Birds section) Acute data are complete for this risk assessment Chronic data are not available. Mammals (laboratory rat) (see Toxicityto Mammals section) Acute data are complete for this risk assessment Chronic data are available from a 3-generation rat study No rabbit developmental study is available at this time. Page 9 of 134Freshwater fish (bluegill sunfish,rainbow trout, and fathead minnow) (see Toxicityto Fish section) Acute data are available for thidiazuron. Acute data are available for the AE F132145 metabolite and the 

### AE F132147 and AE C421200photodegradates, and these data are incorporated into the risk assessment. Chronic freshwater fish data are available for thidiazuron I Freshwater invertebrates (Daphnia magna) (see Toxicityto Aquatic Invertebrates section) Acute data are available for thidiazuron

• Acute data are available for the AE F132145 metabolite and the AE F132147 and AE C421200photodegradates, and these data are incorporated into risk I assessment Chronic data are available for thidiazuron Estuarinelmarine fish (sheepshead minnow) (see Toxicityto Fish section)
I Acute data are available for thidiazuron. No chronic data are available Estuarinelmarine invertebrates (Crassostrea virginica and Mysidopsis bahia) (see Toxicityto Aquatic Invertebrates section)

, Acute data are available for thidiazuron Chronic data are not available Algae and aquatic plants (see Toxicityto Aquatic Plants section) Data are available for green algae, blue-green algae, marine diatoms, and aquatic vascularmacrophytes for thidiazuron. Data are not available for freshwater diatoms. I Data are available for green algae for the 

### AE F132145 metabolite and the AE F132 147and 

### AE C421200photodegradates, and these data are incorporated into risk assessment. Terrestrial plants (corn, soybean, turnip, oats, wheat, tomato, onion, cabbage, lettuce,

, cucumber) (see Toxicityto Terrestrial Plant section) Data are available for thidiazuron Data are available for thidiazuron SC42 formulated product Within each of these very broad taxonomic groups, an acute and chronic endpoint is selected from the available test data, as the data sets allow. The selection is made from the most sensitive species tested within that organism group. Additional effects data were available for other taxa and for aquatic community effects measures. These have been incorporated into the risk characterization as other lines of evidence. These data include: Acute laboratorytoxicity study of technical and formulated product with oligochaete worms Toxicity data on beneficial insects laboratorytests for honeybee contacttoxicity laboratorytests for predatory mites and parasoid wasps Page 10 of 134

### In addition,a search ofEPA's publically accessible Ecotoxicity Database 

### (htt~://www.er>a.~ov/ecotox) for relevant toxicological studiesrevealed no additional data for effects on mortality, growth, behavior, reproduction, population, or ecosystem function for thidiazuron. 

### A completediscussion of-alltoxicitydata available for this risk assessment and the resultingmeasurement endpoints selected for each taxonomic group are included in SectionsVI and VII ofthis document. 

### Measures of Exposure Exposures estimated in the screening level risk assessment for non-target organisms are not specific to a given species. Rather, general taxonomic exposure assumptions are made that provide separateexposure measures for aquatic and terrestrial plants and animals. The approaches for each are discussed separately below. Aquatic Organisms In additionto parent thidiazuron, effects data are available for the aqueous photodegradates AE F132147 and AE C421200 and the metabolite AE F132145 in fish, aquatic invertebrates, and aquatic plants. These data suggest that exposure modeling for these degradates is warranted. The following sections describe the general analysis approach used for active ingredient and the three transformation products. Active Ingredient and Degradate Aquatic Organism Exposure Approach This risk assessment considers thidiazuron exposure in aquatic organisms (animals and plants) via the fraction ofpesticide dissolved in the water column. Thidiazuron is assumed to be introduced to surface waters via runoff and spray drift. Currently,no monitoring data are available that would provide information on thidiazuron levels in surface water bodies receiving runoff or spray drift from agricultural fields treated with the pesticide. Consequently, aquatic organism exposure is estimated through the use ofrunoff and spray drift models. Aquatic organism exposures are based on a set of standardized receiving surface water body assumptions (water body size, watershed size,proximityto field, etc.) that result in reasonable upper-level estimates of exposure. For this risk assessment the GENEEC model was used for making these exposure estimates. GENEEC is the most conservative exposure model available in OPP. It estimates exposure concentrations in aquatic environments representative of geographic locations where cotton is grown in large quantities. If exposure concentrationsresultingfrom the use of GENEEC yield risk quotientsbelow all aquatic levels of concern, it is concluded that direct and indirect aquatic risks would not occur. In this regard, EFED used the most sensitive toxicologicalendpoint available from data on thidiazuron and the photoproducts for each of the aquatic organism categories (i.e., fish, aquatic invertebrates, plants). For acute aquatic risk, no averaging time $or exposurewas assumed for this assessment. The use of the instantaneous peak assumes that instantaneous exposure is of sufficient duration to elicit acute effects onpar with those observed over more protracted exposure periods tested in the laboratory, typically 48 to 96 hours. For assessment of chronic aquatic invertebrate risks with thidiazuron, the peak water concentration was again used. This is a departure from the normal Page 11of 134assessmentwhere the 2 1 -day average, 1 -in-10year return frequency values are compared to the measurement endpoint for aquatic invertebrate chronic risks. The decisionto use a peak concentration exposuremeasure was predicated on the beliefthat the LOCs would not be exceeded even ifthe higher peak concentrations were utilized. As discussed in the Environmental Fate section of this document and in Appendix D, thidiazuron undergoes relatively rapid branching photolysis in water into only two photoproducts. Formation ofthese products is in constant ratio and in complementary stoichiometric yield with parent. The key features of these two photoproducts are as follows: Photoproduct I (AE F132347, see chemical structure in Appendix 

### B) is an isomer ofparent differing onlyin the relativepositions of the sulfur atom and the two nitrogen atoms in the 

### 5- membered ring. Like parent,photoproduct 

### I is moderately ecotoxic (slightlymore toxic than parent,based on the limited data discussed in the main text ofthis document). It has a reviewercalculated asymptotic experimental limit ofproduction of 77% ofparent at pH 

### 5, 28% at pH 7, and 17% at pH 9. Thisproduct was stable to furtherphotolysis under the experimental study conditions and durations (originalMRID 41188201, related follow-up MRIDs 413649 10 and 43075202, and fate overview document with MRID 44436901). SoiVsedimentsorption data and non-photolytic transformation data are available only for parent. However, based on its isomeric chemical structure, photoproduct I, except for photolysis, would be expected to have fate properties similarto parent. Photoproduct 

### II (AE C421200, chemical structure in Appendix 

### B) is a substantially degraded, practicallynon-ecotoxic product (based on the limited data discussed in the main text of this document),and has a complementary asymptotic limit ofproduction to photoproduct 

### I of23% of parent at pH 5, 72% at pH 7, and 83% at pH 9. This product was also stableto further photolysis under studyconditions. SoiVsedimentsorption data and non-photolytic transformation data are available only for parent. However, because of its degraded nature and a modicum of direct evidence indicatingthat photoproduct I1 is practically non-toxic for ecologicalrisk assessment purposes, EFED assumed that photoproduct 

### I1 does not contribute to ecological risk, and ignored its potentialpresence. Aquatic exposureconcentrations are derived from a combination of GENEEC model runs for the summation ofthidiazuron and its photoisomer as explicitly derived in Appendix D Terrestrial Plants The focus ofthe terrestrial plant exposureassessment is on terrestrial plants inhabiting dry and semi-aquatic areas. Potentialroutes of exposure to pesticides considered are runoff, spray drift and volatilization. Sincethidiazuron is non-volatile, volatilization is not a concern. Semi-aquaticareas are those low-lying wet areas that may be dry at certaintimes of the year. EFEDfs runoff exposureestimate in these areas is: (1) based on a pesticide's water solubility and the amount ofpesticidepresent in the top one inch of soil, (2) characterized as "sheetrunoff' (one treated acre to an adjacent acre) for dry areas, (3) characterized as "channelizedrunofff(10 treated acres to a distant low-lying acre) for semi-aquatic areas, and (4)based on percent runoff Page 12 of 134values of 0.01,0.02, and 0.05 for water solubilitiesof <10 ppm, 10-1 00 ppm, and >I00ppm, respectively.

I I Spray drift exposure from ground and overhead chemigation applications is assumed to be 1% of the application rate. Spray drift from aerial, airblast, and forced-air applications is assumed to be 5% of the application rate with an application efficiency of 

### 60%. The effects of multiple applications are addressedby summing the application rates from individual applications. TerrestrialAnimals The focus of the terrestrial wildlife exposure assessment is on birds and mammals with the exposure route emphasis on uptake through the diet. For exposure to terrestrial organisms, such I as birds and smallmammals, OPP looks at the residues of pesticides on food items, and assumes that organisms are exposed to a single pesticide residue in a given exposure scenario. For thidiazuron spray applications, estimation ofpesticide concentrations in wildlife food items I focuses on quantifyingpossible dietary ingestion ofresidues on vegetative matter and insects. The residue estimates are based on a nomogram that relates food item residues to a pesticide's application rate. Residuesmaybe compared directly with dietary toxicity data or converted to an oral dose, as is the case for smallmammals. The screening-levelrisk assessment for thidiazuron uses an upper bound predicted residue as the measure of exposure. For mammals, the residue concentrationis converted to daily oral dose based on fractions ofbody weight consumed daily, as estimated through mammalian allometric relationships. 

### Risk CharacterizationApproach For this assessment ofthidiazuron risks, the risk quotient (RQ) method isused to compare exposure and measured toxicity. Estimated environmental concentrations (EECs) are dividedby acute and chronic toxicity values. The RQs are compared to the Agency's levels of concern (LOCs). These LOCs are the Agency's interpretative policy, and are used to analyze potential risk to non-target organisms and the need to consider regulatory action. These criteria are used to indicate when a pesticide used as directed on the label has the potential to cause adverse effects on non-target organisms. Appendix 

### G ofthis document summarizesthe LOCs employed in this risk assessment. 

### Problem Formulation Analysis Plan In accordancewith 

### US EPA7s "Guidelines for Ecological Risk Assessment," April 1998, and "Overview of the Ecological Risk Assessment Process in the Office ofPesticideProgram," January 2004, an analysisplan and rationale were developed to determine if current label uses of thidiazuron indicate a likelihoodthat unreasonable adverse effects to nontarget and listed animals and plants could potentiallyimpact the reregistration eligibility decision under the Federal Insecticide, Fungicide, and Rodenticide Act, the Food Quality Protection Act, and the Endangered Species Act. Over the course of its assessment, OPP has attempted to refine its problem formulation by integrating registrant-submitted guideline data and various levels of exposure refinements and informationon usage to characterizethe environmental fate and ecological effects of thidiazuron and its degradates. Page 13 of 134Thidiazuron is exclusivelyused as a cotton defoliant to aid in the machine harvesting of cotton by removing both mature andjuvenile leaves. EFED made several assumptions concerning some ambiguities on the labels. Three ofthe product labels list diuron as an additional active ingredient, and another label lists dimethipin,but none of these labels report the applicationrates of each activeingredient separately. EFED quantitatively considered the ribk resulting from thidiazurononly, rather than the combination of the two active ingredients. Thidiazuron rates were calculated from total product applicationrates and product chemical composition. 

### The possible additive orsynergistic effects resulting from the consideration of the other active ingredients were not evaluated. Additional informationprovided by BEAD and other sources identified more typical use rates and frequencies in addition to the maximum rates which are routinelyused in screening level assessments. These typical rates were considered in the terrestrial plant risk characterization. The risk assessment considers aquatic and terrestrial risks for parent thidiazuron. 

### In addition, it considers risksposed to aquatic organisms from AE F132347 and 

### AE C421200 (photodegradates formed in water) and the metaboliteAE F132345by using aquatic exposure concentrations derived from a combination of GENEEC model runs for the summation ofthidiazuron and its photoisomer as explicitlyderived in Appendix D. Risk to terrestrial plants from the formulated product, Thidiazuron SC42 (DROPP) is considered in the risk assessment. Exposure from foliar routes of exposure are primarily explored for terrestrial and aquaticplants and animals. However, this risk assessment does not take into account atmospheric transport, other than spray drift, in estimation of environmental concentrations. Further, it does not account for ingestion ofresidues by animals in drinking water or contaminated grit, ingestionthrough preening activities, or uptake through inhalation or dermal absorption by terrestrial animals. Exposure to terrestrial animals isbased primarily on dietary consumption of foliar residues, whereas aquatic exposures assume that all potential routes of direct exposure are accounted for and are based on standard surface water modeling used in EFED. As previously discussed, exposure to terrestrial plants Inhabiting dry and semi-aquatic areas involves runoff assumptions based on the water solubility and the amount ofpesticide present in the top one inch of soil. This runoffexposure is characterized as "sheet runoff' (onetreated acre to an adjacent acre) for dry areas, and "channelizedrunoff' (10 treated acres to a distant lowlying acre) for semi-aquatic areas. Terrestrial plant spray drift exposure assumptions are based on 1 % ofthe application rate for ground applications and 5% for aerial applications with an applicationefficiency of 60%. Maximum application rates on vulnerable soils for representative crops are selected for modeling environmental concentrations for this screening-level deterministic (risk quotient based) risk assessment. This assessment is not intended to represent a site or time-specific analysis; i.e., assessments are intended to represent a national level exposure based on vulnerable soils as opposed to being regionally specific. However, if exposures exceed LOCs, the assessment will be refined to includehigher-tiered models with spatially specific use scenarios. Likewise, the most sensitive toxicity endpoints are used from surrogate test species to estimate treatmentrelated direct effects on acute mortalityand chronic reproductive, growth, and survival Page 14of 134assessment endpoints. Toxicity tests are intended to determine pesticidal effects on birds, mammals, fish,terrestrial and aquatic invertebrates and plants. These tests include short-term acute, subacute and reproduction studies and are typically arranged in a hierarchical or tiered system that progresses from basic laboratory tests to applied field studies. These studies are used to evaluate the potential of a pesticide to cause adverse effects, determine whether further testing is required, and to determine the need forprecautionary label statements to minimize the potential adverse effects to nontarget animal and plants 

### (CFR 40 

## 5 158.202,2002). The conceptual model used to depict the ecological

### risk associatedwith thidiazuron was initially generic and assumed that thidiazuron was capable of affecting terrestrial and aquatic animals 

# Conceptual 

# ModelforThicliazuron Ask

# Assessment

Thidiaaurmapplied to

### agriculturalfield



## Attribute 

## CfTF mO= 

### ,Aquaticplants 

### Pquaticinvertetn-ates Mudtic

### vertwes

Individualfish 

### Rdm sulvival 

### Mutedrepoducticn Rparianhe Terrestrial plants 

### Terrestrial

### insects

- 

### l-lab~tat integrity Decreased

### &er quality 

### wucedccwer 

### Streamdestabilizatrcn 

# "4

Terrestrial 

### Birds 

### lvhmmls

provided environmental concentrations were sufficientlyelevated as a result of labeled uses. This initial conceptual model is presented below.

Page 15of 134

- - - - - - - -- -----However, through an iterativeprocess of examining fate and effects data, the conceptual model has been refined to reflect the exposure pathways and the organisms for which risk is most likely. Based on OPPs screening level assessment,the refined conceptual model for depicting the risks of thidiazuronprimarily focuses on risk to terrestrial plants. Additionally, there are concerns aboutpossible chronic effects to small mammals, depending on the methodology and toxic endpoints used to calculate the risk quotients. Further, since there are no chronic data currently available for birds, chronic risk to birds is undetermined. The refined conceptual model for depicting risks to nontarget terrestrial plants is presented below. 

## Refined ConceptualModel for a Screening level

Assessment of Thdiazuronum on Cotton

Page 16 of 134

- - - --- -- ---- 

### Source: Aerial and ground Application to Cotton


### Thidiazuron/Degradates/Products

Terrestrial Plant Exposure from SprayDrift, Runoff, and Sheet Runoff

Receptor: Plants Adjacent to treated sties



## v 

## v 7 

### Direct and Indirect Acute Effects to Acute Effects to Chronic Effects to Non-endangered Non-endangered Non-endangered and and Endangered Plants and Endangered Plants Receptor: Plants in Semi-Aquatic Areas Receptor: Mammals in and Adjacent to treated sites

### 111. Integrated Environmental 

### Risk Characterization 

### Risks to Aquatic Organisms The results of the risk assessment suggest that acute and chronic risk quotientsfor all freshwater and marine fish and invertebrates are below all levels of concern established'by the Agency's screening-level assessment. The acute risk quotientsranged from <0.0003 (marine fish) to 0.002 (freshwater fish and estuarine invertebrates). Chronicrisk quotients ranged from 0.002 (freshwater fish) to >0.1 (freshwaterinvertebrates). 

### In addition, the acute risk quotients for the non-endangered and endangered species are well below all established levels of concern for aquatic plants. The definitive acute risk quotientsranged from 0.0005 to 0.013 and the endangered speciesrisk quotientsranged fiom 0.006 to 0.2. Although there may be some uncertainty with respect to chronic risk to freshwater and marine invertebrates because a definitiveNOAEC value could not be obtained, it ispossibleto estimate chronic risk based on a 21-day EC,,value which was obtained in the chronic freshwater invertebratestudy. The 21-dayEC,, value, was 720 yg/L based on the length ofthe test organisms. Using this generated EC,, value, the definitive 21-day RQ value of 0.015 is well below the chronic level of concern. 

### In order for the chronic aquatic invertebrate LOC to be exceeded, the test would have to be repeated to test levels lower than 11 pg/L (nearly 10-fold the current test level of 100 yg1L). It is doubtful that definitiveNOAECILOAECs would exceedthe chronic levels of concern. Even if the persistence and intermediate mobility were taken into account where some year-to-year build-up in soil would occur (asymptotic limit twice that of annually applied amounts), the resultingRQs would stillnot exceed any aquatic LOCs. 

### Risk to Birds Acute Risks 

### - Birds Acute risks to birds for this use are below all levels of concern. To determinepotential acuterisk to birds, we use exposure data from Hoeger and Kenaga (1972), as modified by Fletcher et al. (1994). These data provide maximum and mean residue concentrations of a pesticide on various terrestrial food items on the basis of a one pound per acre application in the field. Predicted residue concentrations are available for short grass, tall grass, broad-leaved plantslsmall insects, and seedsllarge insects. Toxicant concentrations on food items following multiple applications are predicted using a firstorder residue decline method, EFED's "ELLFATE" model, which allows determination of residue dissipation over time incorporating degradation half-life. Predicted maximum and mean EECs resulting frommultiple applications estimates the highest one-day residue, based on the maximum or mean initial EEC hom the first application,the total number of applications, intervalbetween applications,and a first-orderdegradation rate, consistent with 

### EFED policy. The input parameters for the cotton scenario were based on a maximum single application of 0.2 Page 17 of 134lbs a.i.1A. For multiple applications, a follow-up application of 0.1 lb ai/A at an interval between 5 and 7 days is allowed on all labels, and for this scenarioEFED used the ELLFATEprogram to estimate the maximum residue concentrations occurring over a 99-day period based on a 35-day foliar dissipation half-life and a 7-dayintervalbetween applications. The first application was run at 0.2 lb ai1A. To factor in the second application of 0.1 lb ai/A (on day 6), the maximum residue concentrations from it were added to those remaining from the first application (on day 0). Acute data submitted for thidiazuron indicatethat the dietaryLC5Os were greater than 5000 mg/kg-diet for bobwhite quail and mallard duck. The LD5Os were greater than 3 160mglkg-bw for both species. Sincethe results from both the dietary LC50 and the oral gavage LD50 classify thidiazuron as practically non-toxicto birds and the formulations are non-granular, the dietary LC50 forbobwhite quail was selected for risk quotient calculations. The resulting acute risk quotients (Appendix 

### G) at all sites were below all levels of concern using the most sensitiveLC50 of >5000 mglkg-diet. The highest RQ observed for two applications of 0.2 Ib ai/A for birds foraging in short grass was c0.013. Chronic Risk - Birds Chronic risks to birds cannot be quantitativelyevaluated at this timebecause chronic data were not submitted. However, available data showing that chronic levels of concern for mammals are exceeded and that thidiazuron is persistent in the field suggest that there is also potential for chronic risk to birds should they be of equal of greater sensitivitythan mammals. 

### Risks to 

### Mammals Acute Risks 

### - Mammals Acute risks to mammals were evaluated using the rat LD50 of 

### >2000 mglkg-bw. There were no acute LOCs exceeded (Appendix 

### H). The highest risk quotient observed for the 15 g mammal foraging on short grass is <0.03, well below the endangered species LOC of 0.1. Chronic Risk 

### - Mammals The results from the 3-generation rat studywas used to assess chronicrisk to mammals. This studywas classified as core-supplemental in 1995 due to several deficiencies in the study design. Most notable ofthese was that there was no measure of food consumption and the amount of food consumed was estimatedby using default food consumption values developedby the FDA many years ago. Since this study is the only chronic study currentlyavailable, EFED will use this data for this assessment. Thereproductive NOAEC and LOAEC values based on reduction of litter size are 200 and 600 mglkg-diet, respectively. By standard conversion factors the NOAEL and LOAEL are 10 and 30 mglkg-bwlda, respectively. The mean litter size data from the study is summarizedin the
Page 18 of 134following table and indicatethat significant reductions are occurring in the F3b generation at the highest dose, and possibly the lowest as well.



### ** statisticallysignificant atp<0.01 

### * statistically significant atp<0.05



### Reduction in Mean Litter Size for the Three-GenerationRat Study

For calculating the chronic 

### RQ values, the NOAEL of 10mg/kg/dayand the LOAEL of 30 mg/kg/daybased on reduced litter size in a 3-generation reproduction study in the rat were selected. 

### In the second group of litters of the third generation, there was a statistically significant decrease in litter size at the lowest dose tested (3mgikgiday). This apparent reduction in litter size is not considered to be related to exposure to thidiazuron for the followingreasons: 1)The effect was only observed in the second group of litters (F3b) in the third. generation. There was no indication of an effect at this dose level in any of the other generations or in the first group of litters in the same generation (F3a). Ifthis were a genuine effect, it would likely have appeared in other generations at this dose level. High Dose (30rnglkg-bw/day) 11.2 10.3 7.9 9.9 9.3 9.6"

2) There was no dose-response. No decreasesin litter size were observed at the mid-dose level of 10mg/kg/day. Mid Dose (10 mg/kg-bwlday) 12.1 12.1 9.0 9.8 9.5 11.4

3) 

### In the F2a generation, the litter size of the controlgroup was less than the litter size for the low-dose group in the F3b generation. The variability of the litter sizesin the control group indicatethat the apparentreduction in litter size at the low dose is not likelyto be toxicologically significant. Low Dose (3 mg/Kg-bw/day) 11.6 13.2 9.0 11.0 9.0 9.1"" Generation
Fla Flb F2a F2b F3a F3b

Using the NOAEL of 10mg/kg-bwidayisreasonable because the percent ofreproductive impairment that is significant for a given species would be based on their reproductive strategy. I For long-lived (K-selected species), episodic reductions inreproduction might not be ofthe same significance as short-lived (r-selected) species. Reproductive impairment for a short-lived species could be enough to impact any number of species with low generation survivalrates and a dependance on high reproductive output for population continuance (r-selected species). Control

10.4 12.8 8.7 10.3 10.3 12.2

Page 19of 134

___ _- -. - _ - -_ __ ---___ _ _ . -To calculate mammalian risk quotients, we preferentially use the Nagy small mammal assumptions ofpercent body weight consumed for the 15,35,and 1000g mammals and divide the dietary EEC adjusted for food consumption by the NOAEL (expressed as mglkg-bwlday). The resultingrisk quotients are presented in Tables 7 and 8 of Appendix 

### H and indicate that LOCs are exceeded for mammals 

### (herbivores/insectivores)foraging in short grass and broadleaf forage and small insects. The risk quotientsrange fiom 6.33 (short grass) to 0.01 (large insects). The chronic LOCs are not exceeded for mammalian granivores. A less-preferred method of calculatingrisk quotients is to divide the dietaryEEC for each ofthe forage groupsby the NOAEC (expressed as mgkg-diet). Using the NOAEC of 200 mglkg-diet, the chronicLOCs are not exceeded for any of the food categories. Theserisk quotients are presented in Table 9 of Appendix 

### H. There are uncertaintiesassociated with the risk quotient exceedances. As mentioned above, there was no measure of food consumption in the study or the amount ofpesticide consumed. Further, there are no measured foliar dissipationhalf-life data to evaluate residue concentrations; therefore, the EFED standard default foliar half-life of 35 days was used. However, even if a

I foliar dissipation half-life of one day were used, LOCs are still exceeded, as indicated by risk quotientsthat range from 4.6 to 0.02 for herbivores/insectivores. Chronic risk can also be evaluated for single applications for maximum Fletcher values for predictedmaximum and mean residues. Using the default 35-day foliar half-life and a maximum single application rate of 0.2 lb ai/Aresulted in risk quotientsexceeding the chronic LOCs for the same food categories as multiple applications, except that the RQs ranged fiom 4.6 to 0.02 for herbivores/insectivores (coincidentallythe same as range as multiple applications using a one day foliar dissipation half-life. Additionally, EFED looked at the impact of a reduced application rate on mammalian risk. In I this regard, LOCs would be exceeded unless the use rate for each oftwo applications separated by 7 days is reduced by a factor of approximately twenty to 0.014lb ai/A. 

### Risks 

### to Non-Target Insects EFED currently does not estimate risk quotientsfor terrestrial non-target insects. Whenever an LD,, is < 11 pghee, an appropriate label statement isrequired to protect foraging honeybees. The acute contact toxicity studyto honeybees revealed a contact LD,, > 100pghee for the technical thidiazuron and a contact 

### LD,, >98.1 &bee for the SC42 formulated product. This classifiesthidiazuron technical and.theformulated product as practically non-toxic to honeybees. The two other non-target insect OECD studies,which investigated the lethal and sub-lethal effect of the SC42water miscible suspension concentrate 500 g/L on the parasitoid wasp (Aphidius rhopalosiphi) and the predatory mite (Typhlodromuspyri),were found not to show statistical differences from the controls for mortalities or reproduction effects. The wasp study showed the percent mortalitywas 12.5%in the highest exposed concentration of 0.2 lb ai/A compared to 10%in the controls. Thepercent reduction when compared to the controlwas 27.3 and 38.1% in the 100 and 200 g ailha treatment groups, respectively. In the predatory mite studythe Page 20 of 134mortalitieswere 8% in the treated group compared to 13%inthe untreated group, and the mean number of eggsper female was 9.32 in the control group compared to 8.99 in the 200 g ailha treatment. Since these studies showedno statisticallysignificant effects at the highest maximum single rate (0.2 lb ai/A), there is little concern for non-target insects. 

### Risks to Terrestrial Plants RQs for terrestrial plants in 

### dry and semi-aquatic areas are calculated for multiple and single spray applications for endangered and non-endangered species. As mentioned in the exposure section, the runoff scenarios are based on solubility, and since the solubilityof thidiazuron is 

### 31 mg/L (ppm), the percent runoff value used in the risk quotient calculations was 0.02. A 60% efficiency factor is also included for aerial applications. The detailed procedures for terrestrial exposure and plant risk quotient calculations are discussed in the terrestrialexposure section of this assessment. The detailed exposure and risk quotient calculations are tabulated in detail in Appendix 

### H, and a summary of the resulting RQs for single applications ispresented below.



## * Exceeds terrestrialplant Levels of Concern (LOC) 

### Multiple spray applications 

### - All thidiazuron labels allow two applications. The sum of these is a maximum of 0.3 lb ai/A/yr (0.2 lb ai/A for the first application and up to 0.1 1b ai1A for the second application). Only one label specifies that intervals between applications shouldbe between 5-7 days. Since there are no residue data over time for either one or two applications, we used the same procedure here to estimate exposure concentrations that we stated previously forbirds. That is, we used exposuredata from Hoeger and Kenaga (1972), as modified by Fletcher et al. (1 994), and the 

### ELLFATE program for calculation. From these we estimatedthe maximum residue concentrationsoccurring on short grass over a 99-day period based on the default 35-dayfoliar dissipation half-life and a 7-dayintervalbetween applications. Again, the Page 21 of 134first application was run at 0.2 lb aiiA, and to factor in the second application of 0.1 1b aiiA (on day 6), the maximum residue concentrations from it were added to those remaining from the first application (on day 0). The detailedexposure and risk quotient calculations are tabulated in detail in Appendix 

### H, and a summary ofthe resulting RQs is presented below.

Nonendangered

Endangered Seedling Monocot ~0.1783 >0.05 - B0.07 i >0.22 - >0.35

............................................................. ............................................ Emergence 

### ! a <. .................................... i Dicot 0.0152 0.59 - 0.86 i 2.63 - 4.14"

............................................. ........................ +............................................................. + : ...................................... Vegetative Monocot >0.1783 <0.02 - >0.06 

### i <0.02 - >0.06

.................................................. ........................................ Vigor 

## ;..

.... .'.

........................................... i Dicot 0.0011 

## ; 2.73 - 9.09" i 2.73 - 9.09" ........................+............................................................. A ............................................ <...................................... Seedling Monocot 0.1783 

### i 0.05 - 0.07 0.22 - 0.35 Emergence 

### ! .............................................................+............................................ <...................................... i Dicot 0.0111 

## ; 0.81 - 7.18' 3.6- 5.68"

................... i Vegetative 

### i Monocot 0.1783 0.02 - 0.06 0.02 - 0.06 ! ...................................... Vigor ~................. ......................................................................................... A i Dicot 0.00019 

### i 15.79- 52.63" ' 15.79- 52.63" 

## * Exceeds terrestrialplant Levels of Concern (LOC) Potential risks to terrestrial plants arepossiblebecause RQs exceed the LOCs. This is especially true for dicots for both single and multiple applications to plants inhabitingdry and semi-aquatic areas. The RQs resulting from single applications to dicotsrange from 0.39to 9.09 for nonendangeredplants and up to 53 for endangeredplants. The multiple applications RQs to dicots range from 0.59 to 9.09 for non-endangered species and up to 53 for endangered species. Risk to monocot species appear to be substantially lower. However, definitiveEC25s and NOAECs have not been determined because tier 

### IT tests were not conducted for some ofthe more sensitive species such as onion and oats. These EC25s range from >0.05 to >0.35 and are presented in more detail in the Appendix 

### C. Definitive tier 

### I1EC25s and NOAECs are lacking for the vegetative vigor of all the monocots tested and for the seedling emergence oftwo monocot species tested because test concentrations were not low enough to establish these endpoints. However, risk quotientsfrom the tests for which definitiveendpoints were established were below levels of concern. Furthermore, compared to the labeled applicationrates for field use and corresponding estimated field exposure concentrations, the lowest concentrations for the tests for which endpoints were not
Page 22 of 134determined were adequate to establishthat risk quotients would not exceed any ofthe terrestrial plant LOCs at current application rates for thidiazuron. Thidiazuron inhibitsregrowth by uptake through the roots and foliage. When thidiazuron is applied, ethylene levels artificially increase so the defoliation (leafdrop) process begins. Ifnontarget plants which are more sensitive than cotton come into contact with thidiazuron, the leaves of these plants maybe killed or severely damaged. As a result, the plant may die, or the damage maybe sufficient to prevent the plant from reproducing or successfully competing with other plants for resources. The use ofthidiazuron could apply selective pressure to dicots along field edges resulting in changes in species composition. Even though thidiazuronis only applied at cotton harvest, application timing is a consequential factor to consider.Reproduction abnormalities are some of the plant injuriesthat can occur due to thidiazuron exposwe during particular developmental stages. Late season annuals complete I their life-cycle in one year beginning with seed germination, plant growth, and reproduction. Late season spraying of thidiazuroncould cause defoliation during the plant growthphase which

I can directly affectpopulations and may reduce their capability to reproduce. Biennials are plants that complete their life cycles in two years, producing foliage the first year and flowersthe followingyear. Defoliation resulting fiom applications of thiadiazuron in the late season may inhibit these plants from reproducing the followingyear. Perennials areplants that grow throughout the year and produce flowers andlor seeds at some point in their growing season. Late blooming perennials may be impactedby sprayingofthidiazuron during their blooming phase and thidiazuronmay inhibit the plants' ability to adequatelyreproduce.Althoughthe plant I may survive, sterile florets or non-viable seed production can occur. This could have effects on I non-target plant populations' ability to sustain 

### a viable population in future years. Plant material serves as a primary food source for many species of animals. If the available plant material (includng seeds) isreduced due to the effects ofthidiazuron, this may have negative effects throughout the food chain. The exceedances discussed above were calculated using maximum applications rates derived fiom the thidiazuron labels. 

### EFED completed a characterization of potential risks by assessing the effect of calculating RQ using EECs predicted from modeling with average application rates (0.05 

### - 0.07 lb ai/A) as reported in the 

### BEAD QUA report. 

### In the tablebelow the average application rates are compared to the maximum allowable application rates. Although the RQs at the average rates are reduced by at least one-half, only the risk to non-endangered species caused by the single ground application would be eliminated in all categories expect dicot plants (vegetativevigor).

Page 23 of 134Seedling Monocot ....; ; + ; + ................................. ................................. .............................. ................................. .............................. emergence i 2.63 : Dicot

............ ................................................................. .................................+................... ................................. ; *

.................................
.. Vegetative 

### i

. Monocot 

### i

, ............................................ ; ................................. ; -!
..................... ................................. ................................. vigor i 1.82 1.82 i Dicot

.................................. ;... ...........................A..................................%.........................

................................. .........; , ................. ............... Single Aerial Application 

### - Non-Endangered Species (max. 0.2 lb aiIA; average 0.07 lb ailA)

............................. ................................7..............................T.................................T.... .._............................................................ ....... Seedling Monocot i .;
................................... ................................. .......... 6 % ,..................... .................................. Emergence 1.97 : Dicot

................. ................................. ................................. ; + -! ............ ; -!

.............................. .................... ................................. ................

Vegetative 

### ! Monocot i

.............................. .................................. ............................... A ;... $ .................................. .................................. Vigor i 3.18 9.09 9.09 i Dicot 3.18

.......................................... ;... ............................%..........................

.................................. ; %................................. ................................ Single Ground Application

### - Endangered Species (max. 0.2 lb aiIA, average 0.07 lb ailA)

........................................................................ ................................................................................................................... ............

Page 24 of 134 ,' Seedling ; Monocot i ; 6 + *

.............................. ................................. ................................. ................................. ................................. Emergence 3.6 : Dicot 

### ! 1.32

.................................. ................................. ; + ; ; .................................. ................................ .............................. .................................

Vegetative 

### ! Monocot

........ + 4 ................................. ; ..............................+.................................+ ................................. ......................... Vigor i 3.68 i Dicot 10.53 10.53 

### [ 3.68

......... ;.. ............................A......................... ;.....

................................. ................................ Single Aerial Application - Endangered Species (max. 0.2 lb ailAlyr; average 0.07 lb ailNyr)

.................................. -.- ...........................T................................. T ...................................................................................... .....

.......... Seedling

.................................................................. Monocot i ; ; -! ................................. ................................. ................................. Emergence 

### ! 1.08 2.7 : Dicot 1.07

......................................................... .................................. ;.................................A *

................................. .. .................................

Vegetative Monocot i

................................. ;..............................A ..................................; $................................. .!................................. Vigor i 18.42 i 52.63 : i Dicot 52.63 : 18.42Page 25 of 134 

## . Multiple Ground Applications 

### - Non-Endangered Species (Maximum Application: 0.2 lb ailA 1"App.; 0.1 lb ailA Zndapp; 7 day intervals; ) (Average Application: 0.07 lb ailA 1' App.; 0.035 lb
.... aiiA Zndapp; 7 day intervals; )

... ..................................................................................................................... ...........-.. .............................................................. Seedling Monocot 

### !

.. , ................................ ..............* * ; .................................................................... ................ ................................. Emergence i 4.14 

### ! Dicot 1.38

.. ..s..................................,................................. ; ..............................*.................................+..............................
. ................................

Vegetative 

### i Monocot 

## i

........................ 1 * 

# .................................... : !
.............................. ......... .................................. ................................. Vigor 2.73 2.73 i Dicot ; ...............................%.................................&...............

..... ..................A..................................%.................................
........................... Multiple Aerial -Applications 

### - Non-Endangered Species (Maximum Application: 0.2 lb ai1A 1"App.; 0.1 lb ailA tndapp; 7 day intervals; ) (Average Application: 0.07 lb ailA 1"App.; 0.035 lb aiiA fndapp; 7 day intervals; )

............................................................................ .......................................................................................................................... .. Seedling Monocot i

......... .................................................................+........................ ; ................................. ................................... 

# . Emergence i 2.63 ; Dicot 1.32 ; ..............................+.................................+................................. .................................... ................................. ................................

Vegetative 

### i Monocot A 

### i

.................................

# .. *
I............................... .................................................................... vigor i ................................. 4.55 9.09 9.09 i Dicot 4.55 ;........ ........A...........;............\...........A ................................ ................................. Multiple Ground Applications 

### - Endangered Species (Maximum Application: 0.2 lb aiiA 1' App.; 0.1 lb ailA tndapp;7 day intervals; ) (Average Application: 0.07 lb aiIA 1' App.; 0.035 lb ai1A 2ndapp; 7 day intervals; )

...................................................................................................................................................................... :
................................. Seedling j Monocot 

### ! ;.................................+......................... ........ ; ................................. .,................................. ............................... Emergence 

### i 5.68 : Dicot 1.89

........... ................................. .; ..............................&.................................+...................... ; .,................................. ...............................

Vegetative 

### ! Monocot 

## 1

........ ,..............................*......................... ;.................................A ................................. +................................. Vigor i 5.26 i Dicot 15.79 

## 1 15.79 

## 1 5.26

....... .................... : ............................................................................................................................................................... ............The risk assessment for terrestrial plants was based on RQs calculated from toxicity studies using a TEP (typical end-useproduct). Theproduct used in this case was "Thidiazuron SC42", presumably DROPP SC (EPA Registration Number 264-700).,However, it appears that no surfactants or adjuvants were added to the product during the study, and all labels clearly state the addition of adjuvants has been shown to improve the performance. Therefore, the risk to terrestrialnon-target plants maybe greater than RQs indicate. Theproduction of actual tank-mix datawould reduce some ofthe uncertainties associated with risk. - Additionally, as previously stated, five of twelve thidiazwon products are formulated as mixtures with other herbicides (see table in section on Use and Use Characterization). In four ofthe mixed products, thidiazwon comprises 67% oftotal active ingredients and diuron the remaining 33%. 

### In the 

### fifth co-formulated product, thidiazuron comprises only 20% ofthe total active ingredients, while dimethipincomprises the remaining 80%. Plant data on these products with typical adjuvantswould reduce the undetermined risk associated with these mixtures and more precisely portray risk. 

### An alternativeto the submission of such data, assumingno synergism or antagonism among compounds, would be to simplyadd the known effects for these other two chemicalsto those for thidiazuron. Finally, all labels listprecautions when applyingthe products adjacent to lettuce, citrus, or cantaloupe. The labels further statethat mixingwith organophosphatesmay increase non-target crop phytotoxicity. Special restrictions to reduce drift potential to lettuce and citrus appear on all the labels. Thidiazuron products cannot be appliedby air within % mile of lettuce or 5 miles downwind of the point of application when citrus is in flush in the Rio Grande valley of Texas. Grpund applications arerestricted to 100 ft downwind from the point of application for lettuce or ?4mile downwind from the point of application when citrus is in flush. No restrictions are prescribed for cantaloupe. EFED currently has no toxicity data for citrus or cantaloupe, and the Page 26 of 134data on lettuce indicatethat it is the most sensitiveof all the crops tested so far. Toxicitydata on these additional crops may indicatethat risk maybe even higher than indicated by the RQs. 

### Phytotoxicity and Downwind Distance -Spray drift from aerial and ground applications may also impact non-target plants or other crops grown adjacent to cotton, although the densityof the spray droplets is expected to be considerably lower in these areas. Thidiazuronlabels do not have many restrictions on how and under what conditions the product maybe applied. For example, there are no restrictions on droplet size orboom height. Using EFED's current AgDRIFT computer model and registrant phytotoxicity data, it is possible to estimatedistances downwind from application areas at which aparticular toxic effect level would be experiencedby a particular tested plant species. These estimatescan be presented for combinations of aerial and ground applications for varying spraydroplet size in the form ofthree-dimensionalbar charts. To calculate the EC,, 

# .,, values in increments of 10, the EC2,values from the seedling emergence and vegetativevigor studies are used in conjunction with the toxicity slopes from each ofthese studies1. Unfortunately slopesfor only two ofthe ten crops for seedling emergencetests and four of the ten crops tested for vegetative vigor are currently available. These EC,, - 

# ,,values and the maximum applicationrate for cottonwere entered into an Excel spreadsheet with Tier 1 Ag DRIFT (version 2.01). Calculated downwind deposition levels were then compared to the EC,, - 90 values to identify the downward distance at which the EC,, - 

# ,,values would be reached. The few crops for which downwind distances couldbe calculated include lettuce and turnip for the seedling emergencetests, and lettuce, cucumber, tomato, and soybean for the vegetative vigor tests. Although these crops were the most sensitive in the available two tests, the current labels containwarnings and specific instructionsconcerningthe use ofthidiazuron on lettuce, cantaloupe, and citrus. The language from one ofthe labels is the following: "Particular care should be taken when applyingDvoppB UltraTM adjacent to lettuce, citrus, or cantaloupe. " "Inaddition, for citrus crops, do not applyDroppB UltraTM by air when citrus in flush is within five (5) miles downwind of thepoint of application. Do not applyDroppB ultraTM by ground

I when citrus in flush is within one-half(l/2) mile." The longprotective distances on labels for citrus imply that it, or other plants, may be substantiallymore sensitivethan other tested crops, includinglettuce, for which "do not apply" distances are much shorter. Despite the warnings, no seedling emergence or vegetative vigor data have been submitted for cantaloupeor citrus. Submission of such datawould allow a better characterization of the distributionofplant toxicity, and a better comparative measure of the necessary downwind distances and droplet sizes necessary to protect plants.

The followingequation is used to calculatethe various EC, levels: [~~~~/10~~~~~'~'~~~] 

### x 10-"/~'~*" =EC, where a = 1.28, 0.84. 0.54, 0.25, 0, -0.25, -0.54, -0.84, -1.28 for EC,,, EC,,, EC,,, I EC,,, EC,,, EC,,, EC,,, EC,,, EC,,, respectively. A normal toxicity distributionis assumed. Page 27 of 134Thebar graphs for the data for which we have slopes arepresented on the following pages for aerial and ground application under varying droplet sizes. Following the graphs is a discussion of their interpretationand 

### EFED policy for terrestrial plants.

Page 28 of 134

,Aerial: Coarse Spray (Seedling emergence)

Page 29 of 134Aerial: Medium Spray (Seedling emergence)



# I Percent Effect- " 97

Page 30 of 134Aerial: Fine Spray (Seedling emergence)

.turnip
lettuce

IU Percent Effect 80 90

Page 31 of 134Aerial: Coarse Spray (Vegetativevigor)

Page 32 of 134Aerial: Medium Spray (Vegetative vigor)

Percent Effect

Page 33 of 134NO-Spray Zone (ft) 

## / I cucumber

## / Aerial: Fine Spray (Vegetative vigor)

Uu YU Percent Effect Bsoybean

tomato

Page 34 of 134No-SprayZone 

# 1 (ftI Ground: Low Boom, Medium-Coarse Spray (Seedling emergence)

Page 35 of 134Ground: Hlgh Boom, Medium-Coarse Spray (Seedling Emergence)

Page 36 of 134Ground: Low Boom, Medium Spray (Seedling emergence)

No-Spray Zone (ft)

Page 37 of 134Ground: Hlgh Boom, Medium Spray (Seedling emergence)

NO-Spray 50- Zone (ft) 40- 30- 20 I0

Page 38 of 134No-Spray (ft) Ground: Low Boom, Medium-Coarse Spray (Vegetative vigor)

Zone

Page 39 of 134No-Spray Zone (ft)Ground: Hlgh Boom, Medium-Coarse Spray (Vegetative vigor)

-T. Percent Effect ' " 80

Page 40 of 134Ground: Low Boom, Medium Spray (Vegetative vigor)

Page 41 of 134Ground: Hlgh Boom, Medium Spray (Vegetative vigor)



### I Zone /ft)

Page 42 of 134

m -EFEDpolicy with regard to non-endangered terrestrial plants is that the LOC is exceeded when the environmental exposureconcentration is greater than the EC2.5. 

### In the case ofthidiazuron, aerial application is the most common mode of application, and, as demonstrated in the charts above, no-spray zones for the EC,, effect levels range from > 60 ft for course spraysto over 1000 ft. for fine sprays for the most sensitivecrop tested so far (lettuce). Ground applications indicate



# . that no-spray zones for the EC,, effect level range from < 3 ft for low boom, medium-course spray to 

### <200 ft for high boom medium sprays. The charts also show similar trends for the other crops. The endangered species terrestrial plant LOC is exceeded when the environmental concentration is greater than the EC,,. Aerial applications of thidiazuron indicate that the no-spray zone the EC,, effect level ranges fi-om>95 ft. for course spraysto > 1000ftfor fine sprays for lettuce. Ground applications ranges from 

### >95 ft for low boom, medium course sprays to < 1000ft for high boom, medium sprays. The results of this analysis indicate that downwind distance for a specificEC, can be determined I for four ofthe cropswhich were tested. However, two crops, cantaloupe and citrus, lack the toxicity data with which to determine a downwind drift distance. This is important sincethese two crops are listed as being extremely sensitiveto thidiazuron. All the factors influencing the downwind drift distanceincluding droplet size,wind speed,boom height, method of application, and targeted toxicity effect should be considered when placing restrictionson labels. 

### Endocrine Disruption 

### Assessment The 3-generation reproduction studywith rats indicates the potential for endocrine disruption, based on significant effects on mean litter size in the F3b generation. The reproductive NOAEC and LOAEC values based on reduction of litter size are 200 and 600 mgikg-diet, respectively. By standard conversion factors, the NOAEL and LOAEL, are 10and 30mgkg-bwlda, respectively. This reproductive effect could be an indicatorofpotential endocrine disruption in mammals or other organisms. EPA is required under the Federal Food, Drug, and Cosmetic Act (FFDCA), as amendedby the Food Quality ProtectionAct (FQPA), to develop a screeningprogram to determine whether certain substances (including all pesticide active and other ingredients) 

### "may have an effect in humans that issimilar to an effect produced by 

### a naturally occurring estrogen, or other such endocrine effects as the Administrator may designate.

### " Following the recommendations of its Endocrine Disruptor Screening and TestingAdvisory Committee (EDSTAC), EPA determined that there was scientificbases for including, as part ofthe program, the androgen and thyroid hormone systems, in additionto the estrogen hormone system. EPA also adopted EDSTACYs recommendation that the Program include evaluations ofpotential effects in wildlife. For pesticide chemicals, EPA will use The Federal Insecticide, Fungicide, and Rodenticide Act 

### (FIFRA) and, to the extent that effects in wildlifemay help determine whether a substance may have an effect in humans, FFDCA authority to require the wildlife evaluations. As the science develops and resources allow, screening of additional hormone systemsmay be added to the Endocrine Disruptor ScreeningProgram (EDSP). When the appropriatescreening and/or testing protocolsbeing considered under the Agency's EDSP havebeen developed, thidiazuron and its
Page 43 of 134



### -- - - -- - - -- - - - - -- - -degradates may be subjected to additional screening and/or testing to better characterize effects related to endocrine disruption. 

### Endangered Species Assessment The Agency's level of concern for endangered and threatened non-target terrestrial plants and mammals is exceeded for the use ofthidiazuron on cotton. Action Area For listed species assessment purposes, the action area is considered to be the area affected directly or indirectly by the Federal action and not merely the immediate area involved in the action. At the initial screening-level,the risk assessment considers broadly described taxonomic groups and so conservatively assumes that listed species within those broad groups are collocated with the pesticide treatment area. This means that terrestrial plants and wildlife are assumed to be located on or adjacentto the treated site and aquatic organisms are assumed to be located in a surfacewater body adjacent to the treated site. The assessment also assumes that the listed species are located within an assumed areawhich has the relatively highest potential exposureto the pesticide, and that exposures are likely to decrease with distance

### from the treatment area. Section

### II of this risk assessment presents the pesticideuse sites that are used to establish initial collocation of species with treatment areas, Ifthe assumptions associated with the screening-level action area result in RQs that are below the listed species LOCs, a "no effect" determination conclusion is made with respect to listed species in that taxa, and no further refinement of the action area is necessary. Furthermore, RQs below the listed species LOCs for a given taxonomic group indicate no concern for indirect effects upon listed species that depend upon the taxonomic group coveredby the 

### RQ as a resource. However, in situations where the screening assumptions lead to RQs in excess of the listed species LOCs for a given taxonomic group, a potential for a "may affect" conclusion exists and maybe associated with direct effects on listed species belonging to that taxonomic group or may extend to indirect effects upon listed species that depend upon that taxonomic group as a resource. 

### In such cases, additional information on the biologyof listed species, the locations ofthese species, and the locations ofuse sites couldbe considered to determinethe extent to which screening assumptions regarding an action area applyto a particular listed organism. These subsequent refinement steps could consider how this informationwould impact the action area for a particular listed organism and maypotentially include areas of exposurethat are downwind 

### and downstream ofthe pesticide use site. 

### Species Affected Thepreliminary risk assessment for listed species indicates that thidiazuron exceeds the endangered species LOCs for the followingcombinations of analyzed uses and species:

• Use of thidiazuron on cottonindicate that chronic LOCs are exceeded for mammals foraging on short grass and broadleaf forage and small insects. These risks couldbe mitigated by reducing the use rates approximately 20-fold to 0.014 lb ai/acre. Page 44 of 134Use of thidiazuronon cotton results inpotential risks to listed species ofplants. County-level location data for listed species (terrestrialplants and mammals) were compared with county-level information on crop production to identify coarsely overlaps of listed species with the proposed labeled uses ofthidaizuron. This analysis was limited to those counties with 10or more acres of land inproduction for the labeled crops. The results are presented below:



# 11 Oklahoma 

# I - 

# I

Numbers ofListed Plant and Mammal Speciesin Stateswith at Least 10

### Acres of Cotton



# I[South Carolina 

### 10 

### - 

# II State

Arkansas California Florida Georgia Kansas Louisiana Mississippi Missouri New Mexico North Carolina

IV. 

### EnvironmentalFate Assessment Number of Listed Species

Tennessee Texas Virginia

Basis 

### Plants 2 49 5 14 1



### -
- 5 5 17

This assessment is based on an integration of 1) environmental fate studydata from previously reviewed studies, in some cases with subsequent amendments, addenda, or other written explanatory responses or updated information;2) environmental fate study data from the current review ofnew fate studies submitted to support the re-registration ofthidiazuron; 3) intrinsic 

### Mammals



### - 9 4 3



### - 2 1 1 5 3

4 19 2

Page 45 of 134 

### 2 

### 3 1physical/chemicalproperties; and 4) information from product labels. As with all EFED fate assessments, it does not take into consideration any alteration of the environmental fate properties of thidiazuronthat may be associated with the addition of co-formulated pesticides (currently diuron or dimethipin); so-called "inert" ingredients (formulants); tank mixtures with other pesticides, for example, organophosphates, for which label statements indicate increased phytotoxicity; or tank mixes with adjuvants, such as surfactants or oils, for which product label statements indicate "improved performance." Status ofEnvironmental Fate Data Although some of the submitted fate studies had deficiencies, taken as a whole and within the constraints stipulatedin the fate assessment, the data enable the Agency to adequately assess the environmental fate ofthidiazuron. Although no foliar dissipation studies are available to the Agency at this time (these are not generally required), having such data would make any fate assessment more precise, especially in the case of a defoliant such as thidiazuron. However, as discussed in the fate assessment, if dislodgement from or transformation inlon treated plants were to be an important fate pathway, then EFED's inferences from existing fate studies and assumptions for exposuremodeling for parent and potential degradates should reasonably and conservatively cover the possibility. Ifthe registrant wishes to demonstrate that definitive data on foliar dissipationwould substantiallyaffect any ofEFED's inferences, assumptions, or environmentalrisk conclusions, the registrant should submit appropriate data. Otherwise, except for spray-drift requirements, the Agency needs no additional environmental fate studies at this time. Required field spray-drift and spray droplet-sizespectral data have not been submitted. However, since the applicant is a member of the Spray Drift Task Force (SDTF), the registrant maybe able to satisfy the spray-related requirements with data the SDTF has submitted to the Agency. , Fate Assessment

----- Abstract. In soil, thidiazuron is persistent, as evidencedby laboratory and field half-lives and rotational crop intervals on the order of one year. It has intermediate soil sorption coefficients. Such persistence and intermediate mobility would allow some year-to-year accumulationover time and, therefore, more opportunity for favorable conditions for runofffrom application sites to occur. With a one-year half-life, build-up in soil could asymptotically approachtwice that of annually applied amounts. When thidiazuron reaches surface water photolysis is expected to be the major route of transformation; other degradativeprocesses are essentially negligible by comparison. Aqueous photolysis is rapid, and occursby branching in quantitative yield into two photoproducts. One ofthe photodegradates is a structural isomer of parent, whereas the other has a substantially altered chemical structure. The photolysis process requires specialmodeling considerations. Based on its solubility, vapor pressure, and other laboratory evidence, tbdiazuron is non-volatile. Based on its relativelylow octanol/waterpartitioning coefficient, thidiazuron shouldnot bioconcentrate. No data on foliar dissipation are available to EFED. Since tbdiazuron is used to defoliate cotton prior to harvest, dislodgementfromor transformation idonleaves may be an important fate pathway. The effect ofth~s uncertainty and alternative assumptions on the risk assessment are considered.
Page 46 of 134Physical/Chemical Properties Thidiazuron's chemical structural formula, various names and table ofphysical/chemical properties are as follows: Common Name: Other Designations: IUPAC name: CAS name: CAS No.: PC Code No.: Empirical formula: Molecular Weight: SMILES string: Thidiazuron AE B049537, SN 49537, NC 19211, Hoe 080279 I -Phenyl-3-(I,2,3-thiadiazol-5-yl)urea N-Phenyl-N'-I,2,3,-thiadiazol-5-yI urea 51707-55-2 (330-54-1 also found) 120301 C, H8 N4

### 0s 220.25 O=C(Nclcccccl)Nclcnnsl

Page 47 of 134

7 - - - -----Physical and GLN 830.6302 830.6303 830.6304 830.6313

830.6314

830.631 5 830.6316
830.6317 830.6319 830.6320
830.7000
830.7050 830.7100 830.7200 830.7220 830.7300 830.7370
830.7550

830.7840

As the table shows, thidiazuron is a weak organic acid with a pKa of approximately 8.9. Therefore, at pHs found in most aquatic and terrestrial environments, it existsmainly in neutral form (299% neutral at pH 7 or below, 88% atpH 8, and 42% at pH 9). Thidiazuron is nonvolatile, as indicated by its reviewer-calculated Henry's Law constant (H = 3 

### x atm m3/mol and dimensionless

### K, = 1x 10'" at 20 OC) and by collateral data showingthe absence of thidiazuron in collectiontraps for volatileproducts in various laboratorydegradation and

830.7950

Page 48 of 134 --- Chemical Properties of

Requirement C o l o r Physical state Odor Stability to normal and elevated temperatures, metals, and metal ions Oxidation/reduction: chemical incompatlb~litv Flammability Explodability Storage stability Miscibility Corrosion characteristics pH
UVNisible absorption Viscosity Melting point Boilinq D0int Relative Density Dissociation constants inwater Partitioncoefficient. (n-octanollwater), shake flask method Water solubility: column elution method; shake flask method

(ritprl) A = Acceptable; N = Unacceptable (see Deficiency); N/A = Not Applicable.; G = Data gap; I= In progress or need upgrade Vapor pressure Thidiazuron (from product MRlD 459340-01

I< ,, ,,

,, ,, ,,

'I I, I'

,, ,, ‘A

459340-01
459340-01

459340-01
459340-01
459340-01 N

A 459340-01

459340-01 413649-01

(cited) 41 3649-06

(cited)
413649-06 417862-02

(cited)

942460-01 chemistry Status

A A A A

A

N A A
I N A

I
A
A

A N

A A A
A

A review) Resultor Deficiency TGAI: yellow Brown; PAI: Brown TGAI: amorphous solid; PAI: crystalline solid TGAl & PAI. characteristics Sulfur l~ke odor TGAI: None PAI: None TGAI: No reactionwith-H20, KMnO,, Zn or CO, PAI: No reaction with-H,O, KMnO,. Zn or CO,

TGAI: exotherm onset observed at 116.3"C PAI: NA 1year under progress
1 year under progress
TGAI: 5.21 @ 20% PAI: 6.50 A max = 238 nm; e = 985 M-' cm-'

PAI: 223% (decomposition)

TGAI: 0.324 gmlcc at 20 "C PAI: pKa = 8.86 25 "C
PAI: K olw = 50.0 (25 OC, pH = 7.3)

PAI: water = 31.0 mglL (pH = 7.0; 25 'C) organic solvents (gll):acetone, 6.67; CH2C1,,0.003; ethyl acetate, 1.10; hexane, 0.002; MeOH, 4.20; Toluene, 0.40 (all measured at 20 "C)

A PAI: 3.5 x 10‘~ Pa @ 20 "Cmetabolism studies. Its relatively low n-octanol to water partitioning ratio of approximately 50 indicates little likelihood ofbioconcentration. 

### Persistence--Degradation/Metabolism Half-lives In standard laboratory studies,thidiazuron did not hydrolyze (MRID 42069203), and was stable against anaerobicmetabolism in water 

### (MRID 42666101) and soil 

### (MRD41945201). Thidiazuronwas relatively long-lived in aerobic soil. As a measure ofits persistence, laboratory aerobic soil metabolism half-lives2in four soils were approximately 206 (173-254), 253 (1 87- 393), 436 (310-737), and 140(119-170) days (95% confidence intervals in parentheses as a measure of precision). The first three listed half-lives are derived fiom MRID 461 196013, the fourth from 

### MRlD 419501014. The average ofthese four values is 259 days, and the one-tailed upper 90% confidencebound for the mean, which is used for 

### EFED standard environmental modeling purposes, is approximately 363 days (259-day averageplus a confidence level of 104days). Soil metabolites are identifiedin a Transformation Products (degradateslmetabolites) subsectionbelow. Crop rotational intervals also provide a measure of thidiazuron's persistence in soil. Product labels list rotational crop intervals as long as one year. Another index ofthidiazuron's persistence 

### in soil is dissipation in terrestrial field studies. It should be recognized, however, that field dissipation is punctuated by variable climatic events, and generally involves a combinationofphysical dispersal/transport (leaching, runoff, volatilization) and chemical and/orbiochemical transformation. Furthermore, transformation does not necessarily imply detoxification, since byproducts may also be toxic. Results from terrestrial field studies are as follows:

'~alf-lives are based on first-order linear regression oftime (x-axis) versus the logarithm of the relative concentration (percentof radioactivity) oftbdiazuron (y-axis). These experimental half-lives were then adjustedby the reviewer to the EFED standard temperature of 25 "C and to the standard soilmoisture content of 75% of 113-bar water potential (suction) by the methods described in the next footnote. 3~RID 461 19601,Allan, J.G., 2003; EFED review 24 May 2004. Experimentalhalf lives were adjustedby the reviewer to the EFED standard temperature of 25 "Cby use ofthe Arrhenius equation and to the standard soil moisture content of 75% of 113-barwater potential (suction) by use ofthe Walker equation, as described in the Data EvaluationRecord (DER). Actual study conditions were 20 "C and 40% maximum water holding capacity (MWHC); under these conditions half-lives were 163, 355, and 322 days, respectively, as extrapolated from study periods lasting 160-1 68 days.
4 MRTD 41950101, Feyerabend, M., 1991;EFED review 28 Apr 1993. Previous reviewer incorrectly ' reportedthe half-life as 11 1days at 21 "C and 78% of 1/3-bar. The 111-day value was the registrant-reported DT50, not the half-life. Based on this reviewer's calculation using standard semi-logarithmic transformed data,the experimental half-life is 182 days (95% confidencerange of 155-221 days). After adjustmentto 25 "C and 75% of 113-bar soilwater potential by the method described by the reviewer in the DER for MRID 461 19601 (seeprevious footnote), the standardhalf-life becomes 140 (1 19-170)days. (The registrant's calculatedhalf-life using untransformed, simple first-orderdata was 147 days (no confidence range reported.) Page 49 of 134

### In three supplemental, bare-ground field studies (MRID 44454001), each conducted for 18 months, linear first-order dissipationhalf-lives were 237 days (California), 173days (Florida), and 161days (North Carolina). Reviewer-calculated respective times required for 90% loss,based on simple first-orderkinetics were approximately 800, 600, and 500 days. Corresponding registrantcalculated DT90 values, based on a two-compartment model, were 1190,655,and 475 days. Although these measures offieldpersistence are conventionally reported, because ofthe inherent variability and randomness in dissipationprocesses, they shouldbe interpreted onlyin a crude, qualitative sense. Threetransformation products were sporadicallyidentified,but were most frequentlybelow the limit of quantitation; therefore, a kinetic pattern could not be established. 

### In another supplemental study in Florida (MRID 41 76 1105),there was no significant dissipation of thidiazuron during a nine-month studyperiod in which only small amounts oftwo transformation products were detected. Identified soil transformation products and observations concerning mobility are discussed separate subsections below. Thus, laboratory aerobic soilmetabolism studies, product label statements,and field dissipation studies show a general consistency and a similardegree ofpersistence for thidiazuron. The demonstrated persistence would allow some year to year accumulation. With the hypothetical assumption that there is no significant physical movement ofthidiazuron from a site of application for several years, then, with the upper 90% confidence bound half-life of approximately one year and with uniform annual applications, the asymptotic limit ofbuild-up in

. soil would result in soil concentrations that would approach twice that ofthe yearly application amount. Photolysis ofthidiazuronrequires specialconsideration. 

### In water (original MRID 41 188201, related follow-up MRIDs 41364910 ,43075202, and fate overview documentMRID 44436901), it undergoes relativelyrapid (seebelow), pH dependent, branching photolysis into two photoproducts. Formation oftheseproducts is in constant ratio, and in complementary stoichiometricyield with parent. A product originally identified as "photoproduct 

### I" and subsequently identified as 

### AE F132347 (see chemical structure in Appendix B) is an isomer of parent differing only in the relative positions of the sulfur atom and the two nitrogen atoms in the 5-memberedring. Like parent, photoproduct 

### I ismoderately ecotoxic (slightlymore ecotoxic than parent,based on limited data). It has a reviewer-calculated asymptotic experimental limit of production of approximately 77% ofparent at pH 5,28% at pH 7, and 17%at pH 9. This product was stableto furtherphotolysis under the experimental studyconditions and durations. Photoproduct I1 

### (AE C421200) is a significantly degraded, practically non-ecotoxic product, and has a compleme*tary reviewer-calculated asymptotic limit ofproduction to photoproduct 

### I of 23% ofparent at pH 5,72% atpH 7, and 83% at pH 9. This product was also stable to further photolysis under studyconditions. Under standard,ideal laboratory exposureconditions, the pH dependent photolysis half-lives were approximately one to two hours (adjusted to twelve hours of sun per day). [Note: When these half-lives areput directly into current EFED aquatic modeling scenarios, because ofwater depth, clarity, and other factors, the effective or practical photolysis half-lives become equivalentto approximatelyfive to ten days.] For the purpose of aquatic ecological exposure assessment,we protectively assumed the pH 5 results for which 77% ofparent reaching water is convertedto the Page 50 of 134stable isomerphotoproduct 

### I (AE F132347). Under these conditions, the thidiazuron photolytic half-life was 1.44hours (0.0602 days). Half-lives at higher pHs were somewhat shorter (approximately 6% shorterat pH 7 and approximately40% shorter at pH 9. To further simplify exposure estimates for aquatic ecological assessment, rather than separately apportioning parent and photoproduct 

### I exposures and toxicities, we chose to add exposure concentrations ofparent and photoproduct 

### I (ignoring the practically non-toxicecotoxic photoproduct 

### II), and use the toxicity of the slightlymore ecotoxic photoproduct 

### I for parent also. Whether we use this simplified procedure or add the separate contribhtions fromparent and photoproduct 

### I makes no meaninghl difference in the aquatic ecologicalrisk assessment in this particular case. Appendix 

### D describes in detail the special quantitative procedure used for estimating aquatic exposure concentrations. For surfacedrinking water sources for humans, we provide two other altematives, depending on potential human health concerns forparent and photoproducts; these alternatives are discussed in the Drinking Water Assessment Appendix A. Because ofthidiazuron's demonstrated persistence in soil, modeled concentrations in water could be underestimatedby as much as a factor oftwo. A unacceptable laboratory soil photolysis study conducted on thin-plated soil sampleshad numerous flawsand inconsistencies(MRID 00156241 and MRID 41 364902, the latterbeing essentiallya re-submission of a published version of the unpublished former; and fate overview document MIUD 44436901, which summarized study issues and responses). Thepreviously cited unacceptability of the study is confirmedby the current reviewer (who has noticed even additional study irregularities). Ostensibly, the study authors maintained that soilphotolysis was occurring at a relativelyrapid rate, with a half-life on the order of one hour or less, and that the only significant product was the isomer photoproduct 

### I (AE F132347). Thereviewer notes that photoproduct 

### I is the same photoisomer found in the aqueous photolysis studydiscussed above. 

### In view of the studyunacceptability and the inherent marked physical differences between the effectiveness ofphotolysis on soil that is plated thin (0.5 

### rnm) on glass 

### an that applied on soil in the field, the registrant and the Agency are in agreement that terrestrial field studies would serve to determine the relativeimportance of soilphotodegradation. 

### In all field studies (the four studies discussed above), thidiazuron was sprayed on bare soil without incorporation. 

### In these studies thidiazuron was long-lived, and there was onlyminimal evidence of photolysis. Hence, to whatever extent photolysis may occur inlon field soil, it is definitely a slow process. TransformationProducts (degradateslmetabolites) , Chemical structures, chemical names, and other forms ofpast and present identifiers are in Appendix 

### B. Naming conventions, different company codes for the same compounds, and incorrectlynamed compounds havebeen 

### and can easilybe tedious sources of confusion and potential error. Major photodegradates in water and soil have alreadybeen discussed. In the two submitted laboratory aerobic metabolism studies identified above, no major (defined as > 10% of applied radioactivity) organic transformation products were isolated or identified in any - of a total of four soils tested. 

### In the most recent study (MRID 461 19601),the three soilstested were treated with thidiazuron radiolabeled with 14C in the thiadiazol-ring position; in the other

I Page 5 1of 134study (MRID 41950101), the one soil was treated with thidiazuron uniformly radiolabeled with 

### 14Cin the phenyl ring. Such labelinginsures that major molecular changes can be monitored. 

### In the three soils treated with the thidiazol-ring label (MRID 461 19601),the only organic transformation product identified was AE F 132345 (thidiazolylurea or 

### 1,2,3-thiadiazol-5-ylurea). In the soil in which metabolism was fastest, AE F132345 appeared to reach an approximately flat maximum concentrationofroughly 6-9% of applied radioactivity during the period fi-om approximately 88 days to studyend at 168 days. Thebroad plateau is evidence that AE F132345 would not form in greater yield, and that it maybe a persistent metabolite. Maximum concentrations of

### AE F132345 in the other two soilswere roughly 1%to 3%. Extracted substances that were not identified in any soil at any sampling interval comprised no more than roughly 1-6% of applied radioactivity. Non-extracted 

### 14C material (so-called "bound" residues) in these soils increased variably from approximately 16-32%of applied at study end. 

### In one soil, 

### 14C0,reached a broad totalplateau of 5-12% of applied radioactivity during later study periods. 

### In the two other soils, 14C0,totaled around 1-2%and 6-8%, respectively, during later study periods. For all three soils, volatile organics totaled 50.1% of applied radioactivity. The data evaluation record (DER) for the three-soil studyhas additional details for individual soils, and a brief comment on a postulated transformation pathway. 

### In the one soil treated with the uniformly labeled phenyl ring (MRID 41950101), three very minor metabolites were identified,and at least one thesemay havebeen an initial impurity. All concentrationsof each were

## <0.8% of applied radioactivity. The three minor metabolites were: AE F132347 (0.8%), the compound that may have been an initial impurity and which is the same compound identified above as photoproduct 

### I; phenylurea (0.3%); and AE F147706 (0.8%). (Appendix 

### B shows chemical structures and has various past and present forms of identification.) Of extracted substances, approximately 3% of applied radioactivity was not identified. By the end of the 361-day study, unextracted ("bound") residuesincreased to approximately45% of applied, and 

### 14C0,accounted for approximately 2 1 %. 

### In the supplemental terrestrial field studies cited above (MRID 44454001 and MRID 41761 105), three transformation products were detected, but rarely above the limit ofquantitation of 0.01parts per million (ppm). The three compoundswere AE F132345, AE F132347 (photoproduct 

### I), and phenylurea. Since they were almost never detected above the limit of quantitationof 0.01ppm for any sampling interval, no kinetic analysis is possible for them. The maximum concentrationsfor the sporadic detections ofthese products ranged, without correlation, from roughly <4% to perhaps as high as 19% ofthe maximum concentration ever detected for parent. Thus, based on laboratory and field studies, thidiazuron undergoes very slow transformation in soil by aerobic metabolism, with an indefinite contribution from photolysis. Laboratory studies further suggest that the identified transformation products will slowlybe convertedin soil into the carbonpool ofbound residues, carbon dioxide, and other products ofmineralization.

Page 52 of 134Mobilityin Soil Based on batch equilibrium sorption coefficients in four soils (MRID 41364909, three German standard soils and one United Kingdom soil), thidiazuron has intermediate mobility, as indicated by Freundlich adsorption coefficients of approximately4.4,7.3, 16, and 19Freundlich units. Slopes (1111) of the isotherms ranged from approximately0.7-0.8. Sorptioncorrelated reasonably well with organic carbon, and respective Freundlich coefficientsnormalized for organic carbon (Kfoc) were approximately 900, 800, 800, and 500. Soil textural identification and detailed sorptionvalues are in Appendix 

### C. In the four supplemental terrestrial field studies in bare soil discussed above, no significant leaching was apparent for parent or transformation products. However, because of imposed experimental limitationsthat were common to each study (for example, limits of quantitation and the absence of a water balance or use of a tracer) potential for leaching was not clearly established. However, based on the intermediate range of its sorptioncoefficients and the supplemental field evidence, leaching should not be major route of dissipation. Model-estimated potential exposure to thidiazuron from surface and ground drinking water source are presented in the separateDrinking Water section of this document. The one major metabolite found in laboratory aerobic soil studies, 

### 1,2,3-thiadiazol-5ylurea (also identified as thidiazolylurea, 

### AE 132345, and ZK 85290 ), had somewhat lower sorption coefficients than parent. 

### In four United States soils, its Freundlich adsorption coefficients were approximately 1.5, 8.3,2.0, and 1.7Freundlich units. Values for llnranged from approximately 0.8-1. Sorption also correlated reasonably well with organic carbon, and respective Freundlich coefficientsnormalized for organic carbon (Kfoc) were approximately 200,280, 170, and 340. Soil textural identificationand detailed sorption values are in the Data Evaluation Record 

### (DER) for 

### MRID 44436902. As was the case for parent in the same supplemental field studies, no significant leachingpattern was evident for this metabolite, which was detected sporadically and without correlationat c0.05ppm. However, as previously stated, potential for leaching was not clearlyestablished in the field.

No data on foliar dissipation are available to EFED. Sincethidiazuron is used to defoliate cotton prior to harvest, dislodgement from or transformation idonleaves may be an important fate pathway. Although photolysis was the rapid, major route oftransformation in water, in field soil parent was long-lived with only minimal evidence ofphotolysis or leaching. However, in laboratory plates of thin soil, the photoisomer AE F132347 (photoproductI) was a quickly-fonned major degradate. Thus, whetherphotolysis in or on cotton plants is a major fate process is unclear, and can be decided onlyby experiment. However, based on available data, ifphotolysis were to be substantial on foliage, it is a reasonable inference that the samemajor structural isomer formed in water and soil also be produced on foliage. 

### In this case, EFED's modeling assumptions forparent and the photoisomer should cover the possibility, and, within standard model limitations,our estimated water exposureconcentrations remain essentiallythe same.

Page 53 of 134It bears repeatingthat thidiazuronispersistent in soil, as evidencedby laboratory and field halflives of the order of one year, and that it has intermediate soil sorption coefficients. Such persistence and intermediatemobility allows some year-to-year build-up in soil over time and: therefore, greater opportunityfor favorable conditions for runoff from application sitesto occur. With the hypothetical assumptionthat there is no significant physical movement of thidiazuron from a site of application for several years, then, with a one-year half-life and uniform annual applications, the asymptotic limit ofbuild-up would result in soil concentrations that would approachtwice that of the yearly application amount. Runoff concentrations would be affected similarly. V. 

### Drinking Water Assessment Summary There are no useful water monitoring data for thdiazuron in EFED's standard monitoring sources5. The exposureestimates in this assessment come from the two 

### EFED Tier 1 screeninglevel models: 1) FIRST (Ver. 1.0;Aug. 1,2001) for surface water concentrations resulting from runoff and spray drift into 

### an Index Reservoir and 2) SCI-GROW (Ver. 2.3; Nov. 4,2003) for ground water concentrations resulting from leaching. These models and their descriptions are available at the EPA internet site:

As described in the Fate Assessment, when thidiazuron reaches surface water photolysis is expected to be the major route of transformation; other degradative processes are essentially negligible by comparison. Aqueous photolysis is rapid, and occurs by branching in quantitative yield into the two photoproducts identified as AE F132347 and 

### AE C421200. The first is a structuralisomer ofparent, while the latterhas a substantially altered chemical structure. The photolysis process, chemical identification,and special modeling and computational considerationsare in Appendix 

### A. Ground water is not expected to be impacted by these degradates because all field studies show that parent is long-lived in soil (half-lives of the order of one year) with onlyminimal evidence ofphotolysis. Modeling Results. The followingtable shows the FIRST-derived potential surface water concentrations for the threerespective combinations of 1)parent plus both aqueous photodegradation products (most conservative), 2) parent plus photodegradate 1, and 

### 3) parent only (least conservative). Degradate modeling isbased on mass balance using simultaneous decline and formation over time. All reported concentration combinations are in terms ofparent - mass chemical equivalents. However, concentrations for each photodegradate can easilybe separated. The tabulated exposure concentrations are for a single aerial application at a maximum rate of 0.3 lb a.i.lacre. However, as specifically illustrated in Appendix 

### A, whether the total annual maximum is applied all at once or is split in two (as specified on product labels), differences are

5~~~~'s Pesticides in Ground Water Database has no thidiazuron data. The United States Geological Survey (USGS), as part of a large water monitoring program, does not analyzefor thidiazuron. The EPA STORET water quality databases have no useful information. Page 54 of 134negligible for the particular case ofthidiazuron because of its long life in soil. Again, complete model inputloutput tables with detailed explanations of the computational procedures used to handle the photodegradates are in Appendix A.


### SurfaceWater Concentrations (derived from FIRST model, Ver. 1.0)

Parent Only 3.4 

# I 0.068 PEAK DAY (ACUTE) DEGREES OFPROTECTION CONCENTRATION b or pg/L) Parent +Both Photoproducts 3.5 Parent +AE F132347 (photoproduct 1)

The next table shows the SCI-GROW-estimatedpotential groundwater exposure concentration. Groundwaterisnot expected to be impacted by photodegradates because all field studies show that parent is long-lived in soil (half-lives on the order of one year) with onlyminimal evidence of photolysis or leaching. However, as previously discussed, dislodgeability, photolysis (or other chemical changes) in or onplant surfaces are uncertain. Therefore, it is possible that photodegradates identified in water and soil or other compounds may form in or on cotton plants, reach the soil surface at unknown rates, and be subject to unknown degrees of leaching or runoff. EFED's assessment cannot specifically account for this absent information. However, based on all available fate evidence, it appears that photodegradation would be the most likely candidate for any rapid degradation ofthidiazwon that may occur on plants. If this is the case, then, to a first approximation, the physical and chemical fate properties ofthe photodegradates shouldbe similar to parent, and any resulting loss inparent would be offsetby production ofphotodegradates. Therefore, combined concentrations of all these compounds should approximatethose given in the table forparent only. ANNUAL AVERAGE (CHRONIC) CONCENTRATION (ppb or pg/L) 1 .O



### Groundwater Concentration (derivedfrom SCI-GROW regression model, Ver. 2.3 ) 3.5



# I Acute and Chronic Concentration*: 0.066 ppb 

### (pg/L) 0.82

*As also noted in Appendix A, the SCI-GROW-estimated groundwater concentration given here is an extrapolation beyond the regression model limits for Koc. SCI-GROW was developedusing Koc values ranging from approximately 32 to 180mL/g of organic carbon, whereas the median Koc value for thidiazuron is 783 mL/g. Extrapolation increases uncertainty, but without ability to estimate confidence.

Page 55 of 134VI. 

### Aquatic Hazard, Exposure, and Risk Quotient Calculation Appendix 

### F summarizes the results for toxicity studies material to this risk assessment. Discussions of the effects ofthidiazuron, formulated product, and degradates on aquatic taxonomic groups arepresented in the following sections. 

### Toxicity to Fish An acute freshwater fish toxicity classification (slightly toxic, moderatelytoxic, and practically non-toxic) for thidiazuroncannot be definitively established because available acute toxicity data 

### (MRID 420692-01 and 420692-02) do not establish an LC50 (the endpoint criticalto classification). However, the available data forparent thidiazuron indicate that no mortality nor signs of intoxicationwere observed at the highest concentration tested 19 and 32 mg/L. Additional acute freshwatertoxic testing was performed on three metabolites ofthidiazuron. The LC50 for the photodegradate 

### AE F132347 was established at 6,700 pg/L (MRID 462035-08), indicatingthat this degradate is more toxic than the parent thidiazuron. This compound is classified as moderately toxic to freshwater fish. The metabolite (AE F132345) indicated that the LC50 was >101,000 

### yg/L 

### (MRID 462035-15) and suggest that this compound as practically nontoxic to freshwater fish. 

### In addition the metabolite (AE C421200) LC50 could not be determined definitively, but it was tested up to 103,000 pg/L, and the results also suggest classification ofthis metabolite as practically non-toxic to freshwater fish. The acute thidiazuronLC50 for marine fish was not determinedby available toxicitydata (MRID 41 8461-01). Lack of an LC50, precluded a toxicity classification. However, the data do suggest that the NOAEC for thidiazuron is at least as high as the highest dose tested (36,000 yg/L), which isjust above the established solubilitylimit ofthe compound (31,000 pg/L). No sub-lethal effects were observed in this study. Because of the lack of a reported LOAEC, the NOAEC result from this study is uncertain. However, it is unlikely that a repeat of the studywill generate 

### an acute lethalityendpoint consistent with screeningrisk assessment methods that would be at environmentally relevant concentrations. There are no data for either the formulatedproduct or the degradates. 

### A chronic toxicity studywas submitted for freshwater fish early life-stage (fathead minnow) for parent thidiazuron. The NOAEC of the parent was 5,700 pg/L based on hatchability, fky survival, and total survival 

### (MRID 421320-02). A chronic full life cycle test was not submitted for freshwater fish or marinelestuarine fish. 

### Toxicity to Aquatic Invertebrates Acute freshwater invertebrate data were submitted for the parent thidiazuron and the LC50 of 5,700 pg/L (MRID 464053-03) classifies the parent as moderatelytoxic to freshwater invertebrates. A previous study conducted in 1979 determinedthe LC50 to be 10,000 pg/L (MRID 0998 19).

Page 56 of 134Acute freshwater invertebrate studies on the major transformation products were also submitted. The LC50 for the photodegradate AC F132347 was >12,000 pgL (MRID 462035-09). The LC5Os for the AC F132345 metabolite (MRJD 462035-16) and the 

### AE C421200photodegradate (MRID 462035-12) were >98,000 pg/L. Acute marine invertebrate studies show that the mysid shrimp (MRID 418416-02) and the eastern oyster embryollarvae (MRID 421320-01) LC5Os are 3,240 and 5,384 pg/L, respectively. This classifies thidizuron as moderately toxic to marine acute invertebrates. No studies were submitted for any of the metabolites. A chronicdaphnid toxicity study was also available for thidiazuron. The LOAEC was determined to be 400pg/L based on length (MRID 421320-021436650-01). Even though a definitive NOAEC could not be obtained, the 21-dayEClO was found to be 720 pg/L. No chronic data were submitted for marine invertebrates. 

### Toxicity to Aquatic Plants Aquatic plant testing was conducted on the parent thiadiazwon. The E50 was determinedto be >24,000 pg/L for the vascular plant (Lemna gibba)based on frond count as the most sensitive parameter. TheNOAEC and EC05 were determined to be 8,600 and 570 pg/L, respectively 

### (MFUD 462035-06). Non-vascular plant data were submitted for the green alga (Selenastrum copricornatum),blue-green algae (AnabaenaJlos-aquae), and the marine diatom (Skeletonema costatum)Skeletonema costatum). The most sensitive ofthese non-vascularplants was the marine diatom with a E50 of 850 

### pg/L, aNOAEC of 110pg/L, and EC05 of 56 pg/L. No data are currentlyavailable for the freshwater diatom (Naviculapelliculosa).

/ Additionalnon-vascular plant data (green alga) was submitted for the photodegradate AE F132347, the metaboliteAC F132345, and the photodegradate AE C421200. The most sensitiveofthese metabolites was determined to be the AE F132347 photodegradate, with EC50, NOAEC, and EC05 values of 980,220, and 3 10 pg/L, respectively. All these studies were considered as Tier 1 studies and classified as supplemental because they were conducted for 3 days instead of 5 days as required by the USEPA. 

### Aquatic Exposure Aquatic exposure and the special emphasis on photolysis in water is discussed in the Environmental Fate Assessment sectionofthis document and in greater detail in.Appendix 

### D. Aqueous photolysis israpid, and occursby branching in quantitativeyield into the two photoproducts identified asphotoproduct I (AE F132347) and photoproduct 11

### (AE C421200) (see chemical structures in Appendix 

### B). The first is a structural isomer ofparent, while the latter has a substantiallyaltered chemical structure. For reasons previously stated, includingthe toxicity data available for degradates, the exposure concentrations used for the aquaticrisk assessment are the time dependent summations of the concentrationsofparent thidiazuron and its photoisomer (photoproduct I). Exposure
Page 57 of 134concentrations were derived from a combination of GENEEC model runs, as given explicitly in Appendix D. Resulting concentrations forparent plus the photoisomer are in the following table:



### Risk Quotients Estimated EnvironmentalConcentrations (ppb or 

### pg/L)

The methodology for calculatingRQs is presented in Appendix 

### G. The resultingRQs for the parent toxicity values arepresented in detail in Appendix 

### H. Peak



### 11

VII. Terrestrial Hazard, Exposure, and Risk Quotient Calculation Appendix F providestabular summaries of the toxicity studies material to the risk assessment for thidiazuron. The toxicities ofthidiazuron, formulated products, and degradates are discussed below for each terrestrial taxonomic group studied. 

### Toxicity to Birds 4-Day Avg. 11

Acute testingthrough oral gavage oftechnical thidiazuron to bobwhite quail indicates that the 

### LD,, is >3 160mglkg-body weight 

### (MRID 099819). A similar study was not submitted for the mallard duck. However, a Japanese quail study with the formulated product CP 503 WP indicated a LD50 >9989 mglkg-bw (4995 mg ailkg-bw). These LD5O values classifythidiazuron as practically non-toxicto birds. 

### 21-Day Avg. 9.7 

### 60-Day Avg. 8.6

The dietary LC,, for both species

### is > 5000 mg/kg-diet for the technicalthidiazuron. No sublethal effects or other treatment related effects were observed in any ofthese studies. This classifies technicalthidiazuron as practically non-toxic to birds. Chronic testing of thidiazuron was not submitted. Details of the results are tabulated in Appendix F. 

### 90-Day Avg. 8.2



### Toxicity to Mammals Acute testingthrough oral gavage oftechnical Thidiazuron 

### (AE Bo49537 00 

### ID99 0003) to laboratoryrats indicates that the LD,, is >2000 mg/kg-bodyweight. This classifies the technical thidiazuron as a category 

### III compound. For chronic mammalian risks a two generation rat or mouse study, and/or the developmental rabbit study are more relevant than the longer term mammalian carcinogenicity1oncogenicity studies. No rabbit developmental study is available at this time. Thereview of the two generation rat studyis currently in progress within HED, so EFED is using the results fiom a previous three generation rat studyon the thidiazuron technical. This studywas classified as CoreISupplemental because several deficiencies were noted including the following:

Page 58 of 134Pup body weights were only submitted for lactation day 21. The guidelines require body weight data on days 0,4(pre- and post-cull), 7, 14, and 21. There was no measure of food consumption. The amount ofpesticide consumed was estimatedby using default food consumption values for the laboratory rat developedby FDA years ago. A dietaryanalysiswas conducted but was not provided in the report. Little detail was provided on the mating design. For example, EPA guidelines specify that siblingfrom the same litters should not be mated. It was unclear if this guideline was followed. The reproductive/offspring NOEL was 200 ppm (10mg ailkghwlda)based on a decrease in litter size. Toxicity to Non-target 

### Insects Acute contact toxicity studiesto honeybees revealed contact LD,,s of > 100 pg ai /bee for thidiazuron technical and >98.1 pg ai /bee for the SC42 water miscible suspension concentrate 500 g/L (MRID 462035-01,462035-18). These results classify thidiazuron as practically nontoxic to non-target insects. 

### In addition, a 72-hour acute oral toxicitytest was conducted for the SC42water miscible suspension concentrate500 g/L in accordance with OECD guidelines 

### (MRID 462035-19). This studyresulted in an oral contact LD,, of>197.8 pg ai/bee. Two other non-target insect studiesinvestigated the lethal and sub-lethal effect of the SC42 water miscible suspensionconcentrate 500 glL on the parasitoid wasp (Aphidiusrhopalosiphi) and the predatory mite, Typhlodromuspyri,when exposed on a glass surface. These studieswere performed to satisfy the 

### OECD guideline requirements, and although scientifically sound, do not fulfill the 

### OPP guideline requirement. The parasitoidwasp study (MRID 46203520) exposed 4 replicates (10 waspslreplicate) for 48 hours, at concentrations of 100 and 200 

### g ailha (0.1 and 0.2 lb ai/A). Thepercent mortality was 5 and 12.5%,respectively, as compared to 10%in the controls. Therefore, it was concluded that the LC,, was 

### > 200 g a.i.lha (0.2 lb ai1A). To determine reproductive successthrough parasitation, 15 wasps were placed on aphid-infested oat plants. One day later the wasps were removed and the plants kept for 12 additional days. The parasitation rate was determinedby counting the number ofmummies for each individualwasp. Thepercent reductions when compared to the control were 27.3 and 38.1% in the 100 and 200 g ailha treatment groups, respectively. 

### In the predatory mite study 

### (MRID 46203521) 5 replicates (20 miteslreplicate) were exposed to 200 g ai/ha (0.2 lb ai/A) via a floating glassplate. Dead mites and escapees (mites that left the glass plate and were found stuck in the water barrier) were counted as mortalities. Mites were observed over a 14-day period; the mortalities were 8% in the treated group and 13%in the untreated group. To measure reproductive performance the number of eggs per female was
Page 59 of 134determinedby counting the numbers of females and eggs from day 7 to day 14. The mean number of eggs per female was 9.32 in the control group and 

### 8.99 in the 200 g ai/ha treated group. 

### Toxicity to Earthworms Acute toxicity studies to earthworms (Eisenia foetida) were performed in accordancewith OECD guidelinesfor the thidiazuron 

### SC 500 

### G/L (42.6% ai), the AE F132347 photodegradate, and the 

### AE F132345 metabolite 

### (MRID #s 46203522,46203507, and 46203514). All studies exposed earthworms at nominal test concentrations of 62.5, 125,250,500, and 1000mglkg for 14 days. Endpoints observed included mortality and worm body weights. A definitive LC,, based on I mortality was not determined for any ofthe tested compounds, however, sub-lethalNOAECs and LOAECs were determined based on worm body weight loss. The results are presented in the table
I below.


### Test Substance

AE F132347 photodegradate

AE F132345

metabolite XC,, > 1000mg produc 

### Toxicity to Non-TargetPlants LC50 

### (mg am9 >426" 31000

Terrestrial plant testing (seedling emergence and vegetative vigor) isrequired for herbicides that have terrestrialnon-residential outdooruse patterns and that may move offthe application site through volatilization (vaporpressure >1.0 

### x 10'5mmHg at 25OC) or spraydrift (aerial or irrigation)andlor that may have endangeredor threatened plant species associated with the application site. Currently, terrestrialplant testing is not required forpesticides other than herbicides except on a case-by-casebasis 

### (e.g., labeling bears phytotoxicity warnings, or incident datafliterature indicaate phytotoxicity). Since thidiazuronisused as a defoliant on cotton to inhibit regrowth and removal ofboth mature andjuvenile leaves in cotton, non-target terrestrial plant data are required. 

### NOAEC 

### (mg ailkg) 125 250

For seedlingemergence and vegetative vigor testing the followingplant species and groups should be tested: (1) six species of at least four dicotyledonous families, one species ofwhich is soybean (Glycine max) and the second is a root crop, and (2) four species of at least two monocotyledonous families, one ofwhich is corn (Zea mays). 

### LOAEC (mg ai/kg) 250 500

Tier 

### I tests measure the response ofplants, relativeto a control, at a test level that is equal to the highest use rate (expressed as Ibs ai/A). If effects are observed in this test, the registrant is required to proceed to the Tier I1 level. Page 60 of 134Tier 

### I terrestrialplant testing for the seedling emergence test conducted in 1991 showed that the response of the tested plants was less than 25% when compared to the controls. However,the vegetativevigor test conducted in 1990 indicated negative growth response (>25%) in one ofthe four monocots (onion) and five of the six species of dicotstested. Tier 

### I1 tests measure the response ofplants, relative to a control, and five or more test concentrations. Terrestrial Tier 

### I1 studies are required for all low dose herbicides (thosewith the maximum use rate of 0.5 lbs ai/A or less) and anypesticide showing a negative response equal to or greater than 25% in Tier 

### I tests. Theregistrant may opt to proceed directly to Tier 

### I1 testing. Recent data submitted (2003) combined tier I and 

### I1 testing for seedling emergence and vegetative vigor 

### (MRID#s 459085-01 and 459215-01) for the SC42 formulated product. The seedling emergence tests indicated negative growth responses to plant emergence for onion and oat by more than 25% at the maximum single application label rate of 0.2 lb ai/A. This would indicate that a need exists for tier 11testing for these two monocot species. All other tested species showed definitive results or an EC2, above the maximum single application rate. Similarresults were indicated for the vegetative vigor tests. Negative growth responses below the EC2,level were indicated for all the monocots at the maximum single application rate. This indicatesthat tier 

### IItesting will need to be performed for these monocot species. All ofthe dicot plants were tested at the tier 

### I1 level with the exception ofturnip and cabbage and since these plants are not among the most sensitivedicots tested, further testing will not be required. The results from these tests are detailed in Appendix 

### F and summarizedin the tablebelow.

0.0152/ 0.0031 Tomato

Terrestrial Plant Exposure and Risk Quotient Calculations To calculate the RQs for non-endangered plants the EC,, value of the most sensitivespecies in the seedlingemergence studyis compared to runoff and drift exposure to determinethe RQ (EECitoxicityvalue). The EC2,value of the most sensitivespecies in the vegetative vigor studyis
Page 61 of 134compared to the drift exposureto determine the acute RQ. RQs are calculated for the most sensitivemonocot and dicot species. To calculate the RQs for endangered plants, the NOAEC or EC,, value of the most sensitive species in the seedling emergence study is compared to runoff and drift exposure (EECItoxicity value). The NOAEC or EC,, value ofthe most sensitive species in the vegetative vigor studyis compared to the drift exposureto determine the acute RQ. Exposureto terrestrial plants inhabiting dry and semi-aquatic areas may be exposed to pesticides from runoff, spraydrift or volatilization. Volatilization is not included in this assessment. Semiaquatic areas are those low-lying wet areas that maybe dry at certaintimes ofthe year. EFED's runoff exposure estimateis: (1) based on a pesticide's water solubilityand the amount ofpesticide present on the soil surface and its top one inch, (2) characterized as "sheetrunoff' (one treated acre to an adjacent acre) for dry areas, (3) characterized as "channelized runoff" (10 treated acres to a distant low-lying acre) for semi-aquatic areas, and (4) based onpercent runoff values of 0.01, 0.02, and 0.05 for water solubility of<loppm, 10-100ppm, and >I00ppm, respectively. Spray drift exposurefrom ground and overhead chemigation applications is assumed to be 1%of the application rate. Spray drift from aerial, airblast, and forced-air applications is assumed to be 5% of the application rate with an application efficiency of 60%. The effects of multiple applications are addressedby summing the application rates from individual applications. EECs are calculated for the followingapplication methods: (1) unincorporated ground applications, (2) incorporated ground application, and (3) aerial, airblast, forced-air, and chemigation applications. Formulas for calculating EECs for 

### dry areas adjacent to treatment sites and EECs for semi-aquatic areas follow. 

### EEC Formulas: Calculating EECs for terrestrial plants 

### inhabit in^ drv areas adiacentto treatment sites Unincorporated ground application: Runoff = maximum applicationrate (lbs aiIA) x runoffvalue 

### x number of applications Drift = maximum application rate x 0.01 Total Loading =runoff (Ibs ailacre) 

### + drift (lbs ai/A) 

### Incorporated ground application: Runoff = [maximum applicationrate (Ibs ai/A) +minimum incorporation depth (cm.)]x runoff value x number of applications Drift = maximum application rate x 0.01 (Note: drift is not calculated ifthe product is incorporated at the time of application.) Total Loading =runoff (lbs ai/A) 

### + drift (lbs ai/A)

Page 62 of 134

### Aerial, airblast,forced-air, and chemigation applications: Runoff =maximum application rate (lbs ai/A) x 0.6 (60% application efficiency assumed) 

### x runoff value x number of applications Drift = maximum applicationrate (lbs ai1A) x 0.05 Total Loading =runoff (lbs ai/A) 

### + drift (lbs ai1A) 

### CalculatinpEECs 

### for terrestrial plants inhabiting semi-aauatic low-lvin~ areas Unincorporated ground application: Runoff =maximum applicationrate (lbs ai/A) x runoff value 

### x 10 acres x number of applications Drift = maximum application rate 

### x 0.01 Total Loading =runoff (lbs ai1A) 

## + drift (lbs ai/A) 

### Incorporated ground application: Runoff = [maximumapplication rate (lbs ai1A)lminimum incorporation depth (cm)] 

### x runoffvalue x 10 acres 

### x number of applications Drift = maximum application rate 

### x 0.01 (Note: drift is not calculated ifthe product is incorporated at the time of application.) Total Loading =runoff (lbs ailA) 

### + drift (Ibs ai1A) 

### Aerial, airblast, and forced-air applications: Runoff =maximum application rate (lbs ailacre) x 0.6 (60% application efficiency assumed) x runoffvalue x 10 acres

### x number of applications \ Drift = maximum applicationrate (lbs ai1A) x 0.05 Total Loading =runoff (lbs ailA) 

## + drift (lbs ai/A) runoffvalues = 0.01, 0.02, and 0.05 for water solubilityof <10 ppm, 10-100 ppm, and >I00ppm, respectively Incorporation depth: Use the minimum incorporation depth prescribed in the label. 

### Terrestrial Exposure for Birds and Mammals Terrestrialexposure estimations differ for the groups ofterrestrial organisms. One major difference in the way in which exposure scenarios are evaluated for terrestrial species is the methodologyused for non-granular and granular applications. Since the sole use of thidiazuron is limited to spray applications to cotton, exposure scenarios were only considered for nongranular applications. Toxicant concentrations on terrestrial food items are based on data from by Hoerger and Kenaga (1 972) as modified by Fletcher et al. (1994) that determined residue levels on various terrestrial
Page 63 of 134items immediately following toxicant application in the field. These values are summarizedin the table below. 

### Estimated Environmental Concentrations on Avian and Mammalian Food Items (ppm) Following a SingleApplication at 1 

### lb ai/A) EEC (PP~) 

### EEC (PP~) Food Items Predicted Maximum Residue' Predicted Mean Residue' Short grass 240 85 Tall grass 110 

### 36 Broadleafjforage plants and 135 small insects Fruits, pods, seeds, and large 15 7 insects 

# : modified by Fletcheret al. (1994). Toxicant concentrations on food items followingmultiple applications are predicted using a firstorder residue decline method, EFED's "FATES" model, which allows determination ofresidue dissipationover time incorporating 

### a degradation half-life. Predicted maximum and mean EECs resulting fiom multiple applications estimates the highest one-day residue, based on the maximum

I or mean initial EEC from the first application, the total number of applications, interval between applications,and a first-order degradation rate, consistent with EFED policy. The cotton scenario was based on two applications spaced 7 days apart. The first applicationwas at the maximum single application rate of 0.2 lbs a.i./acre. The second at 0.1 lbs a.i./acre, since the maximum allowable total yearly applicationrate is 0.3 1bs ailA. All the above scenasiosused the default 35-dayfoliar dissipation half-life sinceno suitabledata were available. For comparativepurposes, residues were also calculated based on a 1 -day foliar dissipationhalf-life to observe the effects on the risk quotients. Results are discussed in the risk characterization section. Dietary exposure to mammals from liquid sprays is based upon EFED's draft 1995SOP for mammalian risk assessments and methods used by Hoerger and Kenaga (1972) as modifiedby Fletcher 

### et al. (1994). The concentration ofthidiazuron in the diet that is expected to be acutely lethalto 50% ofthe test population (LC,,) is determinedby dividing the LD,, value (usually a rat LD,,) by the amount of food, aspercent (decimal of) body weight consumed. A risk quotient is then determined by dividingthe EEC by the derived LC,, value. Acute RQs are calculated for three separateweight classes ofmammals (15,35, and 1000 g), each presumed to consume four different kinds of food (grass, forage, insects, and seeds). Chronic mammalian RQs are calculated using the most sensitiveNOAEC fiom the 2-generation rat study and the residue concentration expected on food items from Hoerger and Kenaga (1972) as modified by Fletcher et al. (1994).

Page 64 of 134

### Terrestrial Risk Quotients The methodology for calculating RQs ispresented in Appendix 

### G. Resulting RQs for the parent toxicity values are presented in detail in Appendix 

### H.

Page 65 of 134

-- - - -- ---.MEMORANDUM_ 24 August 2004 Subject: 

### Thidiazuron (PC 120301): Drinking Water Assessment (D244574) From: Alex Clem, Environmental Scientist, EFEDIERB 1 (7507C) Peer Review: James Hetrick, SeniorPhysical ScientistEFEDIERB 1 (7507C) Through: Sid Abel, Chief, EFEDIERB 1 (7507C) To: Felicia Fort, Team Leader, HEDIRRB 1 (7509C)
This memorandum provides you with the potential drinking water exposure concentrations for thidiazuronin surfacewater and ground water resulting from its existing use as a cotton defoliantharvest aid. Sincethe HED MARC has not yet convened, at this time EFED is also 

### informing you oftwo major transformation products formed in surface water (not ground water) that may be of potential toxicological interest to you. We also describe three reasonable exposure alternativesfor surfacewater involvingthidiazuron and the two by-products. There are no useful water monitoring data for thidiazuron in EFEDYs standard monitoring sources6. Our exposure estimates come from the two EFED Tier I screening-level models: 1)FIRST (Ver. 1.O; Aug. 1,2001) for surface water concentrations resulting from runoff and spray drift into an Index Reservoir and 2) SCI-GROW (Ver. 2.3; Nov. 4,2003) for ground water concentrations resulting from leaching. These models and their descriptions are available at the EPA internet site: htt~://www.epa. govloppefed1 /models/water. Before proceeding further, we now provide an environmental fate capsule for thidiazuron7. This providesbasic background forplacing the drinking water assessment in perspective. Included within are key assumptions, limitations or uncertainties. Environmental Fate 

### Capsule: 

### In soil, thidiazuron ispersistent, as evidencedby laboratory and field half-lives ofthe order of one year. It has intermediate soil sorption coefficients. Such persistence and intermediatemobility would allow some year to year accumulation as well as time and, therefore, opportunityfor favorable conditions for runoff from application sites to occur. With the hypothetical assumption that there is no significant physical movement ofthidiazuron

6~~~~'s Pesticides in Ground'Water Database has no thidiazuron data. The United States Geological Survey (USGS), as part of a large water monitoring program, does not analyze for thidiazuron. The EPA STORET water quality databases have no useful information.
7~ more complete environmental fate assessmentis included in the EFED science chapter of the RED, which also includes sources of all model input parameters. Page 67 of 134fi-oma site of application for several years, then, with a one year half-life and uniform annual applications, the asymptotic limit ofbuild-up would result in soil concentrations that would approach twice that ofthe yearly application amount. Runoff concentrations would be affected similarly. When thidiazuronreaches surface water, photolysis is expected to be the major route of transformation; other degradative processes are essentially negligibleby comparison. Aqueous photolysis israpid, and occursbybranching in quantitative yield into two photoproducts. One of the photodegradates is a structural 'isomer ofparent, while the other has a substantially altered chemical structure. These degradates are identified below and in Appendix 1by chemical names, structuralformulas, and other designations. The photolysis process and special modeling considerationsare discussed brieflybelow and in detail in Appendix 2. Ground water is not impacted by these degradates because all field studies show that parent is long-lived in soil (halflives of the order of one year) with onlyminimal evidence ofphotolysis. The structural isomer is 

### AE F132347 or photoproduct I (seeAppendix 1 for chemical identification). It has a maximum experimental limit ofproduction of 77% ofparent equivalents at pH 5,28% at pH 7, and 17% at pH 

### 9. Photoproduct I was stableto further photolysis under experimental study conditions. The second photodegradate is 

### AE C421200 or photoproduct 

### II (seeAppendix 1for chemical identification). Photoproduct 

### II is substantially different from parent thidiazuron, and has a complementary asymptotic limit ofproduction to photoproduct I of 23% ofparent at pH 5,72% at pH 7, and 83% atpH 9. Thisproduct was also stableto further photolysis under study conditions. Thus, at different environmental pHs, parent is always quantitativelyconverted in complementary proportions into the two photodegradates. Assumptions/Limitations/Uncertainties: SinceEFED does not know yet whether the two photodegradates in surfacewater will be of toxicological concern to HED, we assume that they maybe, and present three alternativeexposure combinations that coverthe range of potential surfacewater exposures that includeparent and the two aqueous photoproducts. One alternative is the most conservative; a second, least conservative; and a third is intermediate in nature. These are discussedbelow and in more detail in Appendix 2. Among the three exposure assessments, there is no meaningful difference in peak (acute) surface water exposureconcentrations. The only significantchange for any of the three is in the annual average (chronic) concentrations. We have no data on foliar dissipation. Sincethidiazuron is used to defoliate cotton prior to harvest, dislodgement from or transformation in or on leaves maybe an important fate pathway. Although photolysis was the rapid, majorroute of transformation in water, in field soilparent was long-lived with onlyminimal evidence ofphotolysis or leaching. However, in laboratory plates of thin soil, the photoisomer AE F132347 (photoproduct I) was a quickly formed major degradate. Thus, whether photolysis in or on cotton plants is a major fate process is unclear, and can be decided onlyby experiment. However, based on available data, ifphotolysis were to be substantialon foliage, it is a reasonableinference that the same structural isomer would form. 

### In this case, ow surface water assumptions and three options still coverpossibilities,and, within standard model limitations,our estimated surface water exposure concentrations remain essentiallythe same.
Page 68 of 134Modeling

### Results. Table 1shows the FIRST-derivedpotential surface water concentrations for the three respective combinationsof 1)parent plus both aqueous photodegradation products (most conservative), 2) parent plus photodegradate 1, and 3) parent only (least conservative). Degradate modeling is based on mass balance using simultaneous decline and formation over time. All reported concentration combinations are in terms ofparent mass chemical equivalents. However, if desired, concentrationsfor eachphotodegradate can easilybe separated. Inspection ofthidiazuronproduct labels shows that no more than two annual applications of thidiazuron by aerial or ground spray are allowed; their summation is not to exceed 0.3 lb of the activeingredient (a.i.)per acre. The maximum single applicationrate is no more than 0.2 lb a.i./acre, with split applicationsas close as five to seven days apart. The exposure concentrationswe give below are for a single aerial application at a maximum rate of 0.3 lb ailacre. However, as specificallydiscussed and illustrated in Appendix 2, whether the total annual maximum is applied all at once or is split in two (as specified onproduct labels), differencesare negligible for the particular case ofthidiazuron because of its long life in soil. Complete model input/output tables with detailed explanations ofthe computational procedures used to handle the photodegradates are in Appendix 

### 2.

Table 1. Surface Water Concentrations (derived from FIRST model,Ver. 1.0) PEAK DAY (ACUTE) DEGREES OF PROTECTION CONCENTRATION b or pgL) Parent

### +Both Photoproducts

Table 2 shows the SCI-GROW-estimated potential groundwater exposure concentration. Groundwateris not expected to be impactedby photodegradates because all field studies show that parent is long-lived in soil (half-lives ofthe order of one year) with onlyminimal evidence of photolysis or leaching. However, as previously discussed, dislodgeability, photolysis (or other chemical changes) in or on plant surfaces isuncertain. Therefore, it ispossible that photodegradates identified in water and soil or other compounds may form in or on cotton plants, reach the soil surface at inknown rates, and be subject to unknown degrees of leaching or runoff. Our assessment, of course, cannot specifically account for this absent information. However, based on all available fate evidence, it appears that photodegradation would be the most likely candidatefor any rapid degradation ofthidiazuron that may occur on plants. Ifthis is the case, then, to a first approximation, the physical and chemical fate properties ofthe photodegradates should be similarto parent, and any resulting loss in parent would be offset by production of ANNUAL AVERAGE (CHRONIC) CONCENTRATION (ppb or pg/L)

Parent 

### +AE F132347 (photoproduct 1) Parent Only

Page 69 of 134 3.5 1.0 3.5 3.4 0.82 0.068photodegradates. Therefore, combined concentrations of all these compounds should approximate those given for Table 

### 2 for parent only.



### Table 

### 2. Groundwater Concentration (derivedfrom SCI-GROW regression model, Ver. 2.3 )

Acute and Chronic Concentration*: 0.066ppb 

### (pg/L)
*As noted in Appendix 3, the SCI-GROW-estimated groundwater concentration given here is an extrapolation beyond the regression model limits for Koc. SCI-GROW was developed using Koc values ranging from approximately 32 to 180nL/g of organic carbon,whereasthe median Koc value for thidiazuron is 783 mug. Extrapolation increases uncertainty, but without ability to estimate confidence.

Page 70 of 134APPENDIX A-1 Chemical Structures, Names, and Other Designations for Thidiazuron and Two Photoproducts

Thidiazuron 

### (AE B049537; SN 49537; NC 19211; Hoe 080279; DROPP) IUPAC name: 

### 1-phenyl-3-(1,2,3-thiadiazol-5-y1)urea. CAS name: 

### N-phenyl-W- 1,2,3-thiadiazol-5-ylurea. CAS No: 

### 5 1707-55-2(330-54-1also found). SMILES string: 

### O=C(Nc 

### 1ccccc1)Nc 

### 1cnns

### 1

AE F132347; 

### ZK 79173; 

### ZK 80178; photoproduct 

### I; photothidiazuron (peak 3 in MRID 41188201) IUPAC name: 

### 1-phenyl-3-(l,2,5-thiadiazol-3yl)urea CAS name: 

### N-phenyl-N'- l,2,5-thiadiazol-3ylurea CAS No: 

### Not reported.

N-C-N

AE C421200; photoproduct 

### I1 (peak 1in MRID 41188201)



### Page 71 of 134

- - -- - --APPENDIX A-2 INPUT/OUTPUT TABLES FOR FIRST (EQPA EX RESERVOIR SCREENING TOOL)

(A Tier I Simulation Model for Drinking Water Exposure Assessment) (Version 1.0; August 1, 2001) WITH

i EXPLANATION OF THE BASIS FOR APPLICATION RATES AND FOR HANDLING THE SPECIAL CASE OF AQUEOUS PHOTOLYSIS Product labels specify no more than two annual applications of thidiazuron by aerial or ground spray, their summation not to exceed 0.3 lb of the active ingredient (a.i.) thidiazuron per acre. The maximum single application rate is no more than 0.2 lb a.i./acre, with split applications as close as five to seven days apart. However, as indicated in the FIRST input/output tables below for model runs numbered as 201 and 202, which are for a hypothetical single, aerial application at the maximum total annual rate of thidiazuron of 0.3 lb/acre, whether the total annual maximum is applied all at once or is split variously, [for example, (0.1 + 0.2) lb/acre or, as illustrated in runs 203 and 204 below, (0.15 + 0.15) lb/acrel, differences are negligible for our purposes for the particular case of thidiazuron. In water, photolysis is the major route of transformation for thidiazuron; other processes are essentially negligible by comparison. Aqueous photolysis is rapid (see below), pH dependent, and occurs by branching into two photoproducts. The process merits special modeling consideration, as will be discussed. , Formation of the two photoproducts is in constant ratio and in complementary stoichiometric yield with parent. Photoproduct I (AE F132347, see chemical structure in Appendix 1) is an isomer of parent differing only in the relative positions of the sulfur atom and the two nitrogen atoms in the 5-membered ring. The Health Effects Division (HED)should evaluate the relevance of this compound to human health. Photoproduct I has a reviewer-calculated asymptotic experimental limit of production of 77% of parent at pH 5, 28% at pH 7, and 17% at pH 9. This product was stable to further photolysis under experimental study conditions and durations (original MRID 41188201, related follow-up MRIDs 41364910 and 43075202, and fate overview document MRID 44436901). Photoproduct I1 (AE C421200, chemical structure in Appendix 1) is a substantially degraded product, and has a complementary asymptotic limit of production to photoproduct I of 23% of parent at pH 5, 72% at pH 7, and 83% at pH 9. This product was also stable to further photolysis under study conditions. HED should consider any relevance of this compound to human health. Of the three compounds, soil/sediment sorption data and non-photolytic transformation data are available only for parent. In the absence of these data for the photoproducts, we assume they share the same properties as parent. For photoproduct I, because of its particular isomeric chemical structure, we have a relatively high de,gree of confidence in this assumption. For photoproduct 11, because of its altered structure, we have a lower degree of confidence. However, photoproduct I1 is formed in lower yield at more typical pHs, and any error introduced in the modeling analysis described below by assuming that its fate properties are equivalent to those of parent and photoproduct I would have virtually no effect on peak exposure concentrations, and only a minor effect on chronic exposure concentrations.

Page 

### 72of 134For the purposes of this assessment, of the seven possible combinations of parent plus two photoproducts, two cover the high and low ends of potential exposure. A third combination, is intermediate between the extremes, and could be considered as a reasonable alternative. In any of the possible cases, the only significant differences in exposure occur in the annual average (chronic) concentrations. The two extreme combinations and the intermediate alternative are the following: 1) The high end of exposure (most conservative for risk assessment) corresponds to including parent plus both photoproducts

(parent 

### + photoproduct I + photoproduct II). This is equivalent to saying that, in effect, parent did not photolyze or that photolysis is "turned off". There is also the inherent assumption that all three compounds have equivalent toxicities. Results for this high-end exposure analysis, are given in the table below for model run number 201. 2) The low end of exposure (least conservative for risk assessment) corresponds to including only parent thidiazuron concentrations as a function of time. Photolysis is "turned on," but any potential exposure risk from photoproducts I and I1 is ignored. Results for this low-end exposure analysis, are given in the table below for model run number 202. 3) The third combination is parent + photoproduct I. This is an intermediate combination between the extremes, and, based on chemical structural similarity, could be considered as a reasonable exposure alternative. For the purposes of the third alternative, we assume the pH 5 results for which parent was slightly more stable and for which 77% of parent reaching water is converted to the isomer photoproduct I (AE F132347). Under these conditions, the thidiazuron photolytic half-life, after adjustment of continuous experimental radiation intensity to 12 hours of solar intensity at 40 deg. North latitude at end of March or beginning of September, was 1.44 hours or 0.0602 days. These are reviewer-calculated values from MRID 41188201, page 40, Table 5a; and page 36, Table 2, and are in close agreement with those of the study author. Alteration of latitude or date of application have but minor influence on results for our purposes. Half-lives at higher pHs were somewhat shorter (approximately 6% shorter at pH 7 and approximately 40% shorter at pH 9, based on same study Table 21, and would result in lower chronic exposures. With the restrictions on chemical kinetics imposed by current standard Agency simulation models, including FIRST, in order to determine the exposure contributions from parent and photoproduct I, it is necessary to do some external calculations using the output from two simulations or "runs." As described and derived below, one model run is with aqueous photolysis "turned off," (model run number 201), the other with photolysis "turned on" (model run number 202). This is an accurate, simple accounting procedure, and allows the full time-dependent capabilities of the FIRST model to be utilized. The following reviewer-derived formulas provide the combined exposure concentrations for parent thidiazuron and the isomer photoproduct I for the described photolysis process:

Page 73 of 134ci (t) = 0.77 [Cp (201) - Cp (202) 1 , where C!i(t) = concentration of photoisomer as a function of time 0.77 = the branching fraction of parent that is photolyzed to photoisomer Cp(201) = concentrations of parent given in Run 201 below, which are concentrations that would result if parent were stable to photolysis (photolysis "turned off") Cp(202) = concentrations of parent given in Run 202 below with observed photolysis "turned on." Therefore, the summation of parent and photoisomer concentrations is given by: Conc. of Parent + Conc. of Photoisomer = Cp(202) + 0.77 [Cp(201) 

## - Cp(202)I Rounding to two digits, Table 1 shows the resulting drinking water sums of parent and the photoproduct I isomer derived from the FIRST runs 201 and 202 below: Table 1 PEAK DAY (ACUTE) 

# I ANNUAL AVERAGE (CHRONIC)

Table 2. RUN No. 201 for Thidiazuron on Cotton (Most Conservative with Photolysis "Turned Off")

.................................................................... RATE (#/Ac) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE (MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

.................................................................... .300( .300) 1 1 494.0 31.0 AERIAL(~~.~) 20.0 .O CONCENTRATION (PP~ or pg/L)

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

.................................................................... METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RuNOFF (RESERVOIR) (RES

### . -EFF) (RESER. ) (RESER. )

....................................................................

363.00 2 N/A .OO- .OO 726.00 726.00 CONCENTRATION (PP~ or pg/L)

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB) Ver 1.0 AUG 1, 2001

.................................................................... PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

Page 74 of 134Table 3. RUN No. 202 for Thidiazuron on Cotton (Least Conservative with Photolysis "Turned On")

.................................................................... RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE (MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

.................................................................... .300( .300) 1 1 494.0 31.0 AERIAL (16.0) 20.0 .O

METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES
. -EFF) (RESER. ) (RESER. )

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

.................................................................... PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

.................................................................... 3.442 -068

As can be seen from the three tables above, the only significant change for any combination is in the annual average (chronic) concentrations. Tables 4 and 5 below for runs 203 and 204 are for split applications, but otherwise correspond, respectively, to the above runs 201 (photolysis "turned offn)and 202 (photolysis "turned on"). As can be seen, there is no meaningful difference between corresponding runs 201 and 203 or between 202 and 204. Therefore, the effect of splitting thidiazuron applications can be neglected.
Table 4. RUN No. 203 for Thidiazuron on Cotton with Split Applications

(Most Conservative with Photolysis "Turned Off")

....................................................................

RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE (MULT) INTERVAL KOC (PPM ) (%DRIFT) AREA (IN)

.................................................................... .I50( .298) 2 7 494.0 31.0 AERIAL(16.0) 20.0 .O

METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES

### . -EFF) (RESER. ) (RESER. )

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

.................................................................... PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

Page 75 of 134Table 5. RUN No. 204 for Thidiazuron on Cotton with Split ~pplications (Least Conservative with Photolysis "Turned On")

....................................................................

RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE (MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

.................................................................... .I50( .298) 2 7 494.0 31.0 AERIAL (16.0) 20.0 .O FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

.................................................................... METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES

### . -EFF) (RESER. ) (RESER. )

....................................................................

363.00 2 N/A 0.0602 7.46 726.00 7.39 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

.................................................................... PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONI

### c) CONCENTRATION CONCENTRATION

.................................................................... 3.355 .066

Page 76 of 134

---- -- - - --APPENDIX A-3 ., INPUT/OUTPUT TABLE FOR SCI-GROW A SCREENING MODEL FOR EXPOSURE TO PESTICIDES THROUGH GROUNDWATER (Version 2.3; Nov. 4, 2003)
Chemical: Thidiazuron

........................................................................ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

........................................................................ 0.300 1.0 0.300 7.83~+02' 230.0

........................................................................ Groundwater Screening Concentration (pg/L or ppb) = 6.60~-02'
'The groundwater value estimated from the SCI-GROW regression model is an extrapolation beyond tested model limits for Koc. SCIGROWwas developed using Koc values ranging from approximately 32 to 180mL/g of organic carbon, whereas the median Koc value for thidiazuronis 783. Using extrapolatedvalues increases uncertainty without ability to estimate confidence beyond subjective, qualitative statements.

Page 77of 134



### ---- -- - - - ---- --

### APPENDIX 

### B: Chemical StructuralFormulas, Names, and Other Designations for Thidiazuron and TransformationProducts

Page 78 of 134Thidiazuron 

### (AE B049537; SN 49537; 

### NC 19211;Hoe 080279;DROPP) IUPAC name:1

### -phenyl-3-(l,2,3-thiadiazol-5-y1)wea.

CAS name:

### N-phenyl-M-1,2,3-thiadiazol-5-ylwea. CAS No: 51707-55-2 (330-54-1 also found). SMILES string: O=C(Nc 1 ccccc1)Nc1 cnnsl

Thidiazolurea (AE F132345; ZK 85290) IUPAC name: 

### 1,2,3-thiadiazol-5-ylurea. CAS name: Not reported. CAS No: Not reported.

AE P132347; ZK 79173; ZK 80178; photoproduct I; photothidiazuron(peak 3 in 

### MRID 41188201) IUPAC name: 1 

### -phenyl-3-(1,2,5-thiadiazol-3yl)urea CAS name: &-phenyl-&'-I ,2,5-thiadiazol-3ylurea CAS No: Not reported.

Page 79 of 134AE C421200; 

### photoproduct I1 

### (peak 

### 1 in 

### MRID 41188201)



### ZK 44483; BTS 13225 IUPAC 

### name: phenylurea CAS 

### name: phenylurea CAS 

### No: not reported

IUPAC 

### name: 1 

### -(3-hydroxypheny1)-3-(1,2,3-thiadiazol-5-y1)urea CAS 

### name: N-(3-hydroxypheny1)-g- 

### l,2,3-thiadiazol-5-ylurea CAS 

### No: not reported 

### Other names: 1 

### -m-hydroxyphenyl-3-(1,2,3-thiadiazol-5-y1)-urea 

### N-m-hydroxyphenyl-N y -(1,2,3-thiadiazol-5-y1)urea

Page 80 of 134



## ----- -- - - - -

### APPENDIX C: 

### Model Input Parameters Derived from Environmental Fate Studies for Thidiazuron

Page 81 of 134

### Model In~ut Parameters Study Hydrolysis (161-1)
Photolysis in water (161-2)

Photolysis on soil (161-3) Not a model input. 

### Derived from Environmental Fate Model Input Value(s) Stable (atpH 5,799)

-- - - Assume 77% ofparent reaching water is converted to the stable photoisomer AE F132347 (photoproductI). Parent TI12 = 0.0602 days (1.44hours) at pH 5 afteradjustment of continuous experimentalradiationintensity to 12 hours solarintensity at 40 deg.North latitude at end of March or beginning of September. (Somewhat shorter TI12 values at pH 7 (approx.6% shorter) and pH 9 (approx. 40% shorter). Degradates: Branching transformation into only two photoproducts in stoichiometric yield. Photoproduct I (AE F132347) is a photoisomer of parent, that, like parent, is moderately ecotoxic (but slightlymore toxic than parent). It has an asymptotic experimental limit of production of 77% of parent at pH 5,28% at pH 7, and 17% at pH 9. Stable to further photolysis under study conditions. Photoproduct I1 (AE C421200) is asignificantly degraded, practically nonecotoxic product, and has an asymptotic limit of production of 23% of parent at pH 5,72% at pH 7, and 83% at pH 9. Stable to further photolysis under study conditions. In spite ofnumerous study flaws, inconsistencies, and irregular kinetics, TI12 in laboratory soil plates is apparently relatively short. However, the major identified transformation product, AE F132347 (photoproduct I) is the same photoisomer found in aqueous photolysis. In field studies on bare soil, parent was long-livedwith only minimal evidence of photolysis. 

### Studies for Thidiazuron Comments MRID 42069203 Tschampel, M., 1991 EFED review 28 Apr 1993 MRID 41188201; MRID 41364910 (a supplement to MRID 4 1188201 responding to deficiencies cited in DER; addresses characterization of previously unidentified photodegradates); MRID 43075202 (an addendumin response to DER for MRID 41188201that addresses light sources and their comparability); MRID 44436901 (EnvironmentalFate Overview summarizingDER issues and responses).

Supplemental. Essentially the same study authored by Klehr, Iwan, and Riernann was submittedwith MRID 00156241(1981) and MRID 41364902 (1983). The latter MRID is a essentially a published version of the former. EFED review 28 Apr 1993. MRID 44436901 (EnvironmentalFate Overview summarizingDER issues and responses).

Page 82 of 134

- 

### ---- - - ---Page 83 of 134 Aerobic Soil Met. (162-1). All half-lives adjusted by this reviewer to 25 "C and 75% of 113bar soil suction. MRID 41950101: 140 days--phenyl label, German standard sandy loam soil 2.3. MRID 46119601: 206,436, and 253 days-- thiadiazol label in sandy loam (UK), loamy sand (NC), and silt loam (Il), respectively. Anaerobic Soil (162-2)

AnaerobicAquatic Met. (162-3) Aerobic Aquatic Met. (162-4) Sorption (163-1) Upper 90% one-tail C.1: TI,=363 days N=4 (140,206,436, and 253 days) Mean TI12 = 259 days Std. Dev. =2 127 days 90% C.I. =2 104 days (Upper 90% T,, =Mean + 90% C.I.)

Essentially Stable [431-day extrapolated regression half-life from anaerobic period lasting 90 days (from day 30 to day 120) at 21C. Large 95% C.I. in halflife of 230-3400 days (0.6-9.0 years);rsq = 0.39.1 Stable
No data submitted. Default = 2 x aerobic soil TI12 T1/2 = 2 x 364 days =728 days Sand: German Std. Soil # 2.1 Loamy sand: German Std. Soil #2.2 Sandy loam: German Std. Soil #2.3 Sandy clay loam:UK, Schering #I71 Respectively (Freundlich units): Kflads Kfloclads l/n r2 4.36 908 0.721 0.997 16.2 786 0.771 0.999 7.33 780 0.719 0.999 18.8 494 0.817 1.000 Koc model is appropriate 

### (12 = 0.88) N =4 values Min Kf, Kfoc: 4.36,494 Max Kf, Kfoc: 18.8, 908 Median Kfd, Kfoc: 1 1.8, 783 Average Kfd, Kfoc: 11.726.9, 7422176 MRID 41950101, Feyerabend,M., 1991; EFED review 28 Apr 1993. Reviewer incorrectly reported half-life as 111 days at 21 "C and 78% of 113- bar. Value shouldbe 182 days (based on serni-log transformed data). Halflife becomes 140 days after adjustment to 25 "C and 75% of 113-bar soil water potential. MRID 461 19601,Allan, J.G., 2003; EFED review May 2004. Half-lives at 20 "C and 40% MWHC were 163, 355, and 322 days, respectively, extrapolated from study periods of 160-168days. MRID 4 1945201, Feyerabend,M., 1991. EFED review 28 Apr 1993.

MRID 4266601, Leake and Allan, 1993;EFED review May 2004. No data submitted.

MRID 41364909, Bruhl, R., 1988. EFED review 28 Apr 2004. Foreign soils, 3 German standard soils and 1 United Kingdom soil; not able to compare these 4 soils with USDA classification.\ 

### APPENDIX D: GENEEC Input & 

### Output Files for Ecological Assessment

Page 84 

### of 134INPUT/OUTPUT TABLES FOR GENEEC2 (A Tier I Simulation Model for Aquatic Ecological Exposure Assessment) (Version 2.0; August 1, 2001) WITH EXPLANATION OF THE BASIS FOR APPLICATION RATES AND FOR HANDLING THE SPECIAL CASE OF AQUEOUS PHOTOLYSIS
Product labels specify no more than two annual applications of thidiazuron by aerial or ground spray, their summation not to exceed 0.3 lb of the active ingredient (a.i.) thidiazuron per acre. The maximum single application rate is no more than 0.2 lb a.i./acre, with split applications as close as five to seven days apart. However, as indicated in the GENEEC input/output tables below for model runs numbered as 101 and 102, which are for a hypothetical single, aerial application at the maximum total annual rate of thidiazuron of 0.3 lb/acre, whether the total annual maximum is applied all at once or is split variously, [for example, (0.1 

### + 0.2) lb/acre or, as illustrated in runs 103 and 104 below, (0.15 

### + 0.15) lb/acre], differences are negligible for our purposes. Photolysis is a special modeling consideration for thidiazuron. Thidiazuron undergoes relatively rapid branching photolysis in water into only two photoproducts. Formation of these products is in constant ratio and in complementary stoichiometric yield with parent. Photoproduct I (AE F132347, see chemical structure in Appendix 11) is an isomer of parent differing only in the relative positions of the sulfur atom and the two nitrogen atoms in the 5-membered ring. Like parent, photoproduct I is moderately ecotoxic (slightlymore toxic than parent, based on the limited data discussed in the main text of this document). It has a reviewer-calculated asymptotic experimental limit of production of 77% of parent at pH 5, 28% at pH 7, and 17% at pH 9. This product was stable to further photolysis under the experimental study conditions and durations (original MRID 41188201, related follow-up MRIDs 41364910 and 43075202, and fate overview document with MRID 44436901). Soil/sediment sorption data and non-photolytic transformation data are available only for parent. However, based on its isomeric chemical structure, photoproduct I, except for photolysis, would be expected to have fate properties similar to parent. Photoproduct I1 (AE C421200, chemical structure in Appendix 11) is a substantially degraded, practically non-ecotoxic product (based on the limited data discussed in the main text of this document), and has a complementary asymptotic limit of production to photoproduct I of 23% of parent at pH 5, 72% at pH 7, and 83% at pH 9. This product was also stable to further photolysis under study conditions. Soiljsediment sorption data and non-photolytic transformation data are available only for parent. However, because of its degraded nature and a modicum of direct evidence indicating that photoproduct I1 is practically non-toxic for ecological risk assessment purposes, we assume that photoproduct I1 does not contribute to ecological risk, and ignore its potential presence. For the purposes of this assessment, we shall protectively assume the pH 5 results for which parent was slightly more stable and for which 77% of parent reaching water is converted to the stable isomer photoproduct I (AE F132347). Under these conditions, the thidiazuron photolytic half-life, after adjustment of continuous experimental radiation intensity to 12 hours of solar intensity at 40 deg. North latitude at end of March or beginning of September, was 0.0602 days or 1.44 hours. These are reviewer-calculated values from MRID 41188201, page 40, Table 5a; and page 36, Table 2, and are in close Page 85 of 134agreement with those of the study author. Alteration of latitude or date of application have but a minor influence on results for our purposes. Halflives at higher pHs were somewhat shorter (approximately 6% shorter at pH 7 and approximately 40% shorter at pH 9, based on same study Table 2). To further simplify exposure estimates, rather than separately apportioning parent and photoproduct I exposures and toxicities, we chose to add exposure concentrations of parent and photoproduct I (ignoring the practically nontoxic photoproduct 11), and use the toxicity of the slightly more toxic photoproduct I for parent also. Whether we use this simplified procedure or add the separate contributions from parent and photoproduct I makes no meaningful difference in the risk assessment in this particular case. With the restrictions on chemical kinetics imposed by current standard Agency simulation models, including GENEEC, in order to determine the exposure contributions from parent and photoproduct I, it is necessary to do some external calculations using the output from two simulations or "runs." One model run is with aqueous photolysis "turned off," the other with photolysis

'turned on." The following, reviewer-derived formulas account for the photolysis process and risk assessment approach described above: Ci (t) = 0.77 [Cp (101) - Cp (102) 

### 1 , where Ci(t) = concentration of photoisomer as a function of time 0.77 = the branching fraction of parent that is photolyzed to the photoisomer Cp(lO1) = concentrations of parent given in Run 101 below, which are concentrations that would result if parent were stable to photolysis (photolysis "turned off") Cp(102) = concentrations of parent given in Run 102 below with observed photolysis "turned on." Therefore, the summation of parent and photoisomer concentrations is: Conc. of Parent + Conc. of Photoisomer = Cp (102) + 0.77 [Cp(101) 

### - Cp (102) 1 Rounding to two digits, the resulting aquatic exposure concentration summations derived from the GENEEC runs and used for the aquatic risk assessment are:

Applying the same methodology to the results of runs 103 and 104 for split applications gives the analogous equation: Concentrations (ppb or pg/L)

Conc. of Parent + Conc. of Photoisomer = Cp(104) + 0.77[Cp(103) - Cp(104)l Peak

11

As is apparent from the tables, corresponding pairs of concentrations are virtually the same as for the single application at the maximum annual rate In all cases, peak concentrations are virtually the same. Minor decreases in the summation of parent and the photoisomer concentrations over time reflect primarily the 77% conversion to photoproduct I. 4-Day Avg. 11 21-Day Avg. 9.7 60-Day Avg. 8.6 90-Day Avg. 8.2RUN No. 101 FOR Thidiazuron ON Cotton 

### * INPUT VALUES *

....................................................................

RATE (#/Ac) NO-APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP

ONE (MULT) INTERVAL Koc (PPM ) (%DRIFT) (FT) (IN)

.................................................................... .300( -300) 1 1 494.0 31.0 AERL-B( 13.0) .O .O FIELD AND STANDARD POND HALFLIFE VALUES (DAYS)

.................................................................... METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND)

....................................................................

364.00 2 N/A -00- .OO 728.00 728.00 GENERIC EECs (IN MICROGRAMS/LITER (PPB)) Version 2.0 Aug 1, 2001

.................................................................... PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

.................................................................... 10.87 10.84 10.65 10.23 9.93

RUN No. 102 FOR Thidiazuron ON Cotton * INPUT VALUES *

.................................................................... RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP

ONE (MULT) INTERVAL KOC (PPM ) (%DRIFT) (FT) (IN)

.................................................................... .300( -300) 1 1 494.0 31.0 AERL-B( 13.0) .O .O FIELD AND STANDARD POND HALFLIFE VALUES (DAYS)

.................................................................... METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) IIAIN/RUNOFF (POND) (POND-EFF) (POND) (POND)

....................................................................

364.00 2 N/A -0602- 7.46 728.00 7.39 GENERIC EECS (IN MICROGRAMS/LITER (PPB)) Version 2.0 ~ug 1, 2001 PEAK MAX 4 DAY MAX 2 1 DAY MAX 60 DAY MAX 90 DAY GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

Page 87 of 134

- 

### ---------
- --- --RUN No. 103 FOR Thidiazuron ON Cotton * INPUT VALUES *

....................................................................

RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP

ONE (MULT) INTERVAL Koc (PPM ) (%DRIFT) (FT) (IN)

FIELD AND STANDARD POND HALFLIFE VALUES (DAYS)

.................................................................... METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (POND) (POND-EFF) ( POND) (POND 1

GENERIC EECs (IN MICROGRAMS/LITER (PPB)) Version 2.0 Aug 1, 2001 PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

RUN No. 104 FOR Thidiazuron run1 ON Cotton * INPUT VALUES *

.................................................................... RATE (#/Ac) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP

ONE (MULT) INTERVAL KOC (PPM) (%DRIFT) (FT) (IN)

.................................................................... .150( .298) 2 7 494.0 31.0 AERL-B( 13.0) .O .O FIELD AND STANDARD POND HALFLIFE VALUES (DAYS)

.................................................................... METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND)

....................................................................

364.00 2 N/A .0602- 7.46 728.00 7.39 GENERIC EECs (IN MICROGIIAMS/LITER (PPB)) Version 2.0 Aug 1, 2001

.................................................................... PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

.................................................................... 10.23 9.52 6.37 3.18 2.19

Page 88 of 134

### APPENDIX E: Ecological Hazard Data

Page 89 of 134EPA PC Code: 120301 - Thidiazuron Technical (AE B049537 00 ID99 0003) Rainbow 42069202, trout 99.3 >19,000 >19,000 M, S slightly toxic Schupner, Coreb et. al. 1991. Bluegill 42069201, sunfish 99.3 >32,000 >32,000 M, S slightly toxic Schupner, coreb et. al. 1991. EPA PC Code: 120301 - Thidiazuron Photodegradate (AE F132347)

Rainbow 6700 (5700 

### - 2300 97.4 w:w M, S moderately toxic Blankinship core trout 7900) , AS.., et. al., 2003. EPA PC Code: 120301 - Thidiazurqn metabolite (AE F132345)

Rainbow 97.4 w:w >101,000 2300 M, S moderately toxic Palmer, trout core S.J., et.al,

2003. EPA PC Code: 120301 

### - Thidiazuron Photodegradate (AE ~421200)

Rainbow 98.4~:~ >103000 103,000 M, S Practicallynon- Palmer, trout core toxic S.J., et.al., 2003. M=mean-measured chemical concentrations,N=nominal chemical concentrations;F-T=flowhrough; S=static. he compound was tested to the limits of solubility. No mortalities were observed.

Page 90 of 134

# ~PA PC Code: 120301

### - Thidiazuron Technical (AE B049537 00 ID99 0003) 

# II 462035-03, Daphnia 99.5 5,700 (4700 - 1200 M, S moderately Blankinship, 9500) core magna wlw toxic A.S..,et. al., 2003. EPA PC Code: 120301

### - Thidiazuron Technical (AE B049537 00 ID99 0003) (Accession# Daphnia (9000 5,6001 N, S mOderatel~ 099819), magna 98.4 -II,IOO) core toxic Brown. A., 1979. 

# I~PA PC Code: 120301 

### - Thidiazuron PhotometaBOlite (RE F132347) 462035-09, Daphnia 97.4 >12,000

### * 5100 M, S Blankinship, core

### * Slightly toxic magna wlw A.S.., et. al., 2003. EPA PC Code: 120301 

### - Thidiazuron Urea meta~~lite (AE ~132345) Daphnia 462035-16, magna 91 wlw >98,000 12000 M, S Slightly toxic Palmer, S.J., core 2003. ~~EPA PC Code: 120301

### - ThidiazuronPhotometaBOlite (AE C421200) 

# II Daphnia 462035-12, magna 98.4 >99,000 24000 M, S Slightly toxic Palmer, S.J., core 2003. "M=rnean-measuredchemical concentrations,N=nominal chemical concentrations:F-T=flow-through: S=static. " z A definitive LC50 could not be determined because the compound was tested to the limit of solubility. A definitive LC50 could not be determined due to the lack of a 50% mortality at the highest test level.

Page 

### 91 of 134

-- - - - - - --EPA PC Code: 120301 

### - Thidiazuron Technical (AE B049537 00 ID99 0003) Sheephead 99.3 418461-01, >36,000 <36,000 M,S slightly toxic Schupner,J.K. minnow Coreb et a1 1991 I' --. --.)
A// *. 11 a M=mean-measuredchemical concentrations,N=nominal chemical concentfations;F-T=flow-through; S=static.

A definitive LC50 could not be determined because the compoundwas tested to the limit of solubiky.

Page 92 of 134

-*--- - --A -- - -- 

## ---.

# IIEPA PC Code: 120301 

### - Thidiazueon Technical (AE B049537 00 ID99 0003) 418461-02, Mysid shrimp 99.3 3,240 (2,890 1400 M, S moderately toxic Schupner, core - 3,770) J.K., 1991. Eastern oyster- 421320-01, 5,384 (4,768 1.06 99'3 - 6,157) M, F-T moderately toxic Ward, S.G., core larvae/embryo 1991. "M=rnean-measured chemical concentrations,N-ominal chemical concentrations;F-T=flow-through;S=static.

Page 93 of 13499.5 6000

99.5 860 1101 Growth rate & Plantbiomass

97.4 980 220 I 3 10 Cell density

Page 95 of 134Marine diatom (Skeletonema costatum) EPA PC Code: 120301

### - Thidiazuron Urea metabolite (AE F132345) 

# 11 Vascular Plant

.._............ ..................................................................................................................................................................... -...................... 

# (1 Duck weed 

# )I (Lemnagibba)

............................................................................................................................................................................................................. 

# 11 Nonvascular Plants

................................................... ..__ ".............................................................................................................................. .......................

Greeen Algae 462035-17, (Scenedesmus w'w 3400 1300 Cell density mean Supplementa Desjardins, subspicatus) ai 1200 D. et.al., 2003. .._

..................... .............................................................................................................................................................. -...................... Freshwater diatom (Navicula pelliculosa)

............................................................................................................................. ...................................................... ...................... ..- - -

Blue-green algae(Anabaenaflosaquae)

............................................................................................................................................................... "...........................................

Marine diatom (Skeletonema ,: costaturn) 

# ~IEPA PC Code: 120301

## - Thidiazuron Photodegradate (AE C421200)

..............a ...........................................................................................................................................................................

Vascular Plants

.................... .............................................................................................................................................................. -..................... Duck weed (Lemna ~ibba)



# .............................................................................................................................................................................................................

Nonvascular plants Green Algae 462035-13, (Scenedesmus 98.4 70000 49'000 Cell density mean Desjardins, 53,000 Supplementa subspicatus) D. et.al., 2003. Freshwater diatom (Navicula pelliculosa) Blue-green algae (AnabaenaflosPage 96 of 134

# II Marine diatom (Skeletonema 

# 1) costaturn) 

# I " Since the study duration was for 3 days instead of 

### 5, the study can onlybe classified as a Tier 1 study.

EPA PC Code: 120301

### - Thidiazuron Technical (AE B049537 00 ID99 0003)
No sub-lethaleffects 00066168 60 or othertreatment practically non- (Accession Bobwhite quail 98.43 >3160 related effects were # 099819), core toxic observed. Fletcher,D. 1979. Table 

### 8: Acute Toxicity to Thidiazuron to Birds (oral administration)

EPA PC Code: 120301

### - Thidiazuron formulated product (CP 503 WP 50) 00038144, 9989a NOsub-lethaleffects practically non- (Accession Japanese Quail 50 >9989"

. observed toxic # 095969), Supplemental Ross, D., Species



### I 1976. " The LD50 is 4995 mg aikg-bw when adjusted to 100% ai. \

Page 97 of 134 Yo a.i. LD509 mglkg-bw

(conf. interval) NOABC,mglkgbw Effects Toxicity Classification (based on a.i.) MRID, Author,

Year StatusNo sub-lethal effects or other treatment 5000 related effects were Fletcher, Core observed. No sub-lethal effects or other treatment 52 related effects were Bowers, Core observed.
No sub-lethal effects or other treatment 5000 related effects were observed.
No sub-lethal effects or other treatment related effects were

Page 98 of 134

# IIEPA PC Code: 120301

### - Thidiazuron Technical (AE B049537 00 ID99 0003) 

# II laboratory rat 

# 11 (Rattus 98.7 46121501, >2000 CategoryI11 Coleman, Acceptable

# 11 nowegicus) D.G., 2001 

### " Status (acceptability) based on HEDs guidelines.

Page 99 of 134

# 'I~PA PC Code: 120301

### - Thidiazuron Technical SN 49537 

# II 200 ppm 600 (30 429589-01, 3-generation Core- 100 (10 mgkg mgkg - Decreased F, litter size at 200 ppm Rees, S.J., reproductive (rats) 1992. Supplementary bwida) b~ida)~ " Status (acceptability)based on HEDs guidelines.

. 

### - -, - Based on decreaseepidermal spermcounts.



# ~PPA PC Code: 120301

### - Thidiazuron Technical (AE B049537 00 ID99 0003) 

# II Honey bee (Apis mellifera) >loo 462035-01, Kling 

# 11 Practically non-toxic A., 2003. 

# II EPA PC Code: 120301 -ThidiazuronAE B049573 00 SC42 (formulated product) 

# II 462035-18, Honey bee (Apis 41.9 >98.1 Practically non-toxic Waltersdorfer, A., coreb mellifera) 2002. " Sup~lemental for Oral LD50 of >105.25 rrnibee. ~ui~lemental for Oral LD50 of >197.8 igTbee. 

# I@PA PC Code: 120301

### - Thidiazuron Technical (AE B049537 00 ID99 0003) 

# I1 Predatory mite (Typlodromus pyri) 41.9 462035-21, NIA Supplemen Waltersdorfer, A., 2002.. tal" ~~EPA PC Code: 120301 -ThidiazuronAE B049573 00 SC42 (formulated product) 

# II Parasoid wasp 462035-20, (Aphidius 4 1.9 >0.1782 NIA Waltersdorfer, A,, Coreb 3007

a Non-gu~dehne study

Page 100of 134~~EPA PC Code: 120301 -Thidiazuron, SC 500 GL 

# I1 

# II Earthworm (Eiseenia foetide) , 42.6 53.3" 462035-22Niestedt K.M., 2003. Supplementar ~~EPA PC Code: 120301

### - Thidiazuronphotometaboite (AE F132347) 

# II 462035-07, 250 Sindermann, et. al., ~upplemental~ 2003. 

# I~PAPC Code: 120301

### - Thidiazuronphotometaboite (AE F1323457) 

# II 462035-14, Earthworm (Eiseenia 9 1 1000 62.5 Sinderrnann, et. al., supplementalb foetide) 2003. " LC,, and NOEC > 1000 and 125mg productkg Performed under OECD guidelines. Not required by EPA. Terrestrial Plants Terrestrial plant testing (seedling emergence and vegetative vigor) is required for herbicides that have terrestrial non-residential outdoor use patterns and that may move off the application site through volatilization (vapor pressure >1.0 x 10"mm Hg at 25OC) or drift (aerial or irrigation) andlor that may have endangered or threatened plant species associated with the application site. Currently, terrestrial plant testing isnot required for pesticides other than herbicides except on a case-by-case basis (e.g.,labeling bears phytotoxicity warnings incident data or literature that demonstrate phytotoxicity). For seedling emergence and vegetative vigor testing the following plant species and groups should be tested: (1) six species of at least four dicotyledonous families, one species ofwhich is soybean (Glycinemax) and the second is a root crop, and (2) four species of at least two monocotyledonous families, one ofwhich is corn (Zea mays). Tier 1 tests measure the response ofplants, relative to a control, at a test level that is equal to the highest use rate (expressed as lbs ai/A). If effects are observed in this test, the registrant is required to proceed to the Tier 2 level. Terrestrial Tier 2 studies are required for all low dose herbicides (those with the maximum use rate of 0.5 lbs ai/A or less) and any pesticide showing a negative response equal to or greater than 25% in Tier 1tests. The registrant may opt to proceed directly to Tier 2 testing.

Page 101of 134Tier 2 tests measure the response of plants, relative to a control, and five or more test concentrations. Results of Tier 1and 2 toxicity testing on the technical1TEP material are tabulated below.

<25 none <25 none <25 none

<25 none

<25 none

Page 102of 134<25 none

increased suckering

>25 necrosis, weight inhibition necrosis, leaf darkening, deformity, height inhibition deformity, height >25 inhibition

Page 103 of 134

- - -- "- 

### ----- - - -onion'

wheat
Dicot

turnip (root 0.17831 emergence, shoot '0'1783 >0.1783 length, dry weight,
emergence Supplemental
Core Supplemental 0.17831 emergence, shoot 459085-01, >0.1783 length, dryweight, Teineira,D., 2003. Core

0.17831 emergence, shoot 0.1783 length, dry weight, <0.0223/ shoot length, dry 0'0410 0.0031 weight l1 emergence,dryweight 0.0039 0.17831 emergence, shoot '0'1783 ~0.1783 length, dry weight 0.17831 emergence, shoot 50'1783 s0.1783 length, dryweight Supplemental
Core
Core Supplemental Supplemental cabbage 0.17831 emergence, shoot >'.I7" <O. 1783 length, dry weight Supplemental 'Tier 2 tests will need to be performed because oat and onion sensitivity indicated a 25% reduction in growth. 'Conducted as Tier 2 tests.

Page 104of 134

# Ip PC Code: 120301 -ThidiazuronAE 8049573 00 SC42 (formulatedproduct)

onion 0.17831 shoot length, <O. 1783 dry weight Core 

# I1 corn 0.17831 shoot length, <0.1783 dryweight, Core 

# I1 oat 0.17831 shoot length, <0.1783 dry weight, Core wheat 0.17831 shoot length, 459215-01, 0.1783 Teixeira, Core dryweight, D., 2003. 

# II Dicot 2 soybean 0.01111 shoot length, 0.0024 dry weight, Core 

# II turnip (root crop) >0.1783 0.17831 shoot length, <0.1783 dry weight Core 0.00019/ 0.00005 dryweight Core cucumber 2 0.00561 0.0075 dry weight Core
0'02221 shoot length 0.0098 Core cabbage >0.1783 0.17831 shoot length, <0.1783 Core dryweight 'Tier 2 tests will need to be performed to determinethe most sensitivemonocot species. *Conductedas Tier 2 tests.

Page 105of 134

### APPENDIX F: The Risk 

### Quotient Method

Page 106 of 134The Risk Quotient Method is the means used by EFED to integrate the results of exposure and ecotoxicitydata. For this method, RQs (RQs) are calculatedby dividing exposure estimatesby ecotoxicity values (i.e.,RQ =EXPOSURE/TOXICITY),both acute and chronic. These RQs are then compared to OPP's levels of concern (LOCs). These LOCs are criteriaused by OPP to indicate potentialrisk to non-target organisms and the need to consider regulatory action. EFED has defined LOCs for acute risk, potentialrestricted use classification, and for endangered species. The criteriaindicate that a pesticideused as directed has the potentialto cause adverse effects on nontarget organisms. LOCs currently address the following risk presumption categories: (1) acute 

### - there is a potential for acute risk; regulatory action may be warranted in addition to restricted use classification; (2) acute restricted use - the potential for acuterisk is high, but this may be mitigated through restricted use classification L (3) acute endangered species - the potential for acute risk to endangered species is high, regulatory action maybe warranted, and (4) chronic risk - the potential for chronic risk is high, regulatory action maybe warranted. Currently, EFED does not perform assessments for chronic risk to plants, acute or chronic risks to non-target insects, or chronicrisk from granularhait formulations to mammalian or avian species.

4 The ecotoxicitytest values (i.e.,measurement endpoints) used in the acute and chronic RQs are derived from required studies.Examples of ecotoxicity values derived from short-term laboratory studiesthat assess acute effects are: (1) LC,, (fish and birds), (2) LD,, (birds and mammals), (3) EC,, (aquatic plants and aquaticinvertebrates), and (4) EC,, (terrestrial plants). Examples of toxicity test effect levels derived from the results of long-term laboratory studies that assess chronic effects are: (1) LOAEL (birds, fish, and aquatic invertebrates), and (2)NOAEL (birds, fish and aquatic invertebrates). The NOAEL is generally used as the ecotoxicity test value in assessing chronic effects. Risk presumptions, along with the correspondingRQs and LOCs are summarized in Table G-1.

Page 107 of 134

-- --- - - -Acute Risk EECILC,, or LD,Jsqft or LD,,/day 0.5 Acute RestrictedUse EECILC,, or LD,Jsqft or LD,,/day (or LD,, < 50 mgkg) 0.2 Acute Endangered Species EECLC,, or LD,,/sqft or LD,,/day 0.1 Chronic Risk EEChTOAEC 1 Wild Mammals1 Acute Risk EECILC,, or LD,Jsqft or LD,,/day 0.5 Acute Restricted Use EECLC, or LD,olsqfior LDdday (or LD,, < 50 mgkg) 0.2 Acute Endangered Species EECLC,, or LD,,Isqft or LD,,Iday 0.1 Chronic Risk EEC/NOAEC 1 Aquatic Animals2 I Acute Risk EECILC,, or EC,, 0.5 Acute RestrictedUse EECLC,, or EC,, 0.1 Acute Endangered Species EECILC,, or EC,, 0.05 ChronicRisk EECLNOAEC 1 Terrestrial and Semi-Aquatic Plants Acute Risk EECIEC,, 1 Acute Endangered Species EECIEC,, or NOAEC 1 Aquatic Plants2 Acute Risk EECIEC,, 1 Acute Endangered Species EECIEC,, or NOAEC 1 LD5,1sqft = (mglsqft) 1(LD, 

### * wt. of animal) LD,,Iday = (mg of toxicant consumedday) 1(LD,, 

### * wtof animal) Table 

### 1: Risk Presumptions and 

### LOCs

EEC = (ppm or ppb) in water Risk Presumption RO

Page 108 of 134 I

I

- F - - - - - LOC Birds'APPENDIX 

### G: Detailed 

### Risk Quotients

Page 109of 134Pome Fruit (0.32 Ib ailA1App.;3 applyr; 10 day intervals; ground and air blast equipment) Freshwater Fish 6700' 5700 11.00 9.70 8.60 0.002 0.002 Estuarine fish >36,000 No data 11.00 9.70 8.60 < 0.0003
Freshwater Invert. 5,700 <I00 11.00 9.70 8.60 0.002 > 0.10

Estuarine Invert. (shrimp) 3,240 Nodata 11.00 9.70 8.60 0.003
Estuarine Invert. (oyster) 5,384 No data 11.00 9.70 8.60 0.002

a 

### * indicates an exceedance of endangered SpeciesLevel of Concern (LOC). ** indicates an exceedanceofAcute RestrictedUse LOC. *** indicates an exceedance ofAcute Risk LOC. + indicates an exceedance of ChronicLOC. ThidiazuronphotodegradateAE F132347 *Estimated on the assumption that acute to chronic ratio for estuarine invertebrates applies to freshwater invertebrates.

Page 110 of 134

# II Cotton (0.2 lb ai/A; single applicationaerial equipment5% drift) lpular Plant Aquatic Vascular Plant (Lemna gibba) >24,000 Nonvascular Plants Green algae (Selenastrum capuicornutum)

...................................................... algae (Anabaena 0s-aquae) 6000 

# II Marine diatom (Skeletonema costaturn) 860 I' a * indicates an exceedenceofAcute Risk LOC b ** indicates an exceedenceof listed Endangered SpeciesLOC. e There are currentlyno endangered nonvascularplant species

Page Illof 134



### --- -- 

### ----Short grass >SO00 No data 62.62 < 0.013 Tall grass 15000 No data 30.54 < 0.006 Broadleafforage, small insects 15000 No data 37.48 < 0.008 Fruit, pods, seeds, laru~ inc~ote >So00 Nn data - .- 

### --.- 7.lU < U.UU1 ELLFATEprogram. (Assumed peak residue values (day 6) from first a~olicatinn at n 7 lh ~ila n~~-~ :-lr:-j 11. .I. r A - -, lo ail^ Ior second application.) a 

### * indicates an exceedence ofEndangered SpeciesLevel of Concern (LOC), ** indicates an exceedenceof Acute Restricted Use LOC. *** indicates an exceedence ofAcute Risk LOC. + indicates an exceedence of Chronic LOC.

Page 112of 134Page 113of 134

P - 

### --- - - - - a Predicted Acute Toxicity Maximum Chronic Chronic Chronic Toxicity ~ood'1tems Residue Acute RQ Threshold,NOEC RQb RQb LC,, (Max. (Mean (mg ailkg-diet) (mg ai/kg-diet) (EEC)(mg Residue) Residue ai/kg-diet) Cotton (0.2lb ai/A/App.) Short grass >5000 No Data 48.0 < 0.010 

## - Tall grass 15000 No Data 22 < 0.004 

### - Broadleafforage, , 15000 No Data 27 < 0.005 - small insects Fruit, pods, seeds, >5000 No Data 3.0 < 0.001 - - large insects * indicates an exceedenceofEndangered SpeciesLevel of Concern (LOC). ** indicatesan exceedenceof Acute Restricted Use LOC. 

### *** indicates an exceedenceof Acute Risk LOC. + indicates an exceedenceof Chronic LOC.Cotton (0.2 Ib ai/A lSt A Short grass Broadleaf 15 95 forage, small insects Large insects Short grass Broadleaf 35 66 forage, small insects Large insects Short grass 1000 15 Broadleaf forage, small insects
Page 1 14of 13415 21 Seeds 12000 4.16 < 0.0004 1.94 < 0.0002 35 15 Seeds 12000 4.16 < 0.0003 1.94 < 0.0001 1000 3 Seeds 12000 4.16 < 0.0001 1.94 < 0.00003 I ELLFATE program. (Assumed peak residue values (day 6) &om first application at 0.2 lb aifA and added initial residue value at 0.1 lb a1fA for second application.) b~~ = EEC
I LD,, 1 %Body wt consumed ! 1 

# I

i

i

* indicates an exceedence ofEndangered Species Level of Concern (LOC). ** indicates an exceedence ofAcute Restricted Use LOC. *** indicates an exceedence ofAcute Risk LOC.

Page 116of 134 

### Table 6: 

### Mammalian (Granivore) Acute Risk Quotient Calculations for Spray Applications Animal Body -

Weight (g) % Body Weight Consumed (melkg-bw) Scenario

Cotton (0.2 lb ail* I" App.; 0.1 lb ri/A zndapp; 7 day intervals; ground and air blast equipment) (mglkg-diet) Acute ~~~i~i~

Threshold, LD50 (mglkg-diet) Acute RQ Predicted Mean Residue Levels EEC Predicted Maximum Residue Levels EEC " Acute RQ21 Seeds 10 4.16 0.09 

### t I i 1

35 15 Seeds 4.16 0.06 1.94 0.03 10 1000 3 Seeds 4.16 0.01 1.94 0.01 10 'ELLFATEprogram. (Assumed peak residue values (day 6) &omfirst application at 0.2 lb ai/A and added initial residue value at 0.1 lb ai/A for second application.) RQ = EEC x % body weight consumed - NOEL * indicates.an exceedence of Chronic Level of Concern (LOC). 

### i Table 

### 8 :Mammalian (Granivore) Chronic Risk Quotient Calculations for SprayApplications (NOAEL = 10 me/kg-bwlda) Animal

Body Weight (g)

ll~hort grassTable 9 :Mammalian Chronic Risk Quotient C~lculations for Spray Applications (NOAEC =

### 200 mglkg-diet)

Page 119of 134 % Body Weight Consumed

Scenario (mg/kg-diet) Scenario

Chronic Toxicity Threshold, NOAEC (mglkgCotton (0.2 Ih aiiA I" App.; 0.1 Ib aiiA 2""app; 7 day intervals; ground and airblast equipment) (mg/kg-diet)

dict)Chronic Toxicity Threshold, NOAEL (mg/kgbw/da) Chronic RQ "

Predicted Maximum Residue Levels EEC

Cotton (0.2 Ib aiiA I" App.; 0.1 lb aiIA fn*app;7 day intervals; ground and air blast equipment) Predicted Mean Residue Levels (mglkg-diet) Predicted Mean Residue Levels EEC Predicted Maximurn Residue Levels

Chronic RQ 

### " (mgkg-diet) EEC EEC"

Chronic KQ 

### " Chronic RQ 

### "Cotton 

### -groundApulications (0.2 Ibs ailaclapp.) 0.2 0 0.02 0.004 0.040 0.002 0.006 0.04 Cotton -aerial avplications (0.2 Ibs ailaclapp.) 0.2 0 0.02 0.002 0.020 0.010 0.012 0.030 Assumed drift at I% for ground applicationsand 5% for aerial applications. 

### Non-endangered Plant Risk Quotients

## - Single Spray Applications of Thidiazuron The EC2,value ofthe most sensitive species in the seedling emergence study is compared to runoff and drift exposure to determine the 

### RQ (EECItoxicityvalue). The 

### EC,, value ofthe most sensitive species in the vegetative vigor studyis compared to the drift exposure to determine the acute 

### RQ. RQs are calculated for the most sensitive monocot and dicot species for ground and aerial applications.

Page 

### 121of 134Cotton - GroundApplications (0.2 Ibs ailaclapp.) Monocot <O. 1783 NIA 0.006 > 0.03 SeedEmerg. Dicot 0.0152 N/A 0.006 0.39 Monocot >O. 1783 0.002 NIA < 0.01 0.002 NIA < 0.01 Veg Vigor Dicot

. 0.001 1 0.002 N/A 1.82 * 0.002 N/A 1.82 * Cotton -AerialApplications (0.2 Ibs ai/ac/app) Monocot <O. 1783 NIA 0.012 > 0.07 N/A 0.03 0.17 Seed Emerg. Dicot 0.0152 N/A 0.012 0.79 NIA 0.03 1.97 * Monocot 20.1783 0.01 N/A < 0.06 Veg Vigor 

### - - Dicot 0.0011 0.01 N/A 9.09 * 0.01 NIA 9.09 * indicates an exceedence ofAcute Risk LOC.

Page 

### 122of 

### 134Endangered Plant Risk Quotients

## - Single SprayApplications of Thidiazuron The endangeredplant RQs are calculated by comparing the NOEC or EC, value of the most sensitive speciesin the seedling emergence studyto runoff and drift exposure (EECItoxicity value). The NOEC or EC, value ofthe most sensitive speciesin the vegetative vigor study is compared to the drift exposure to determine the acute RQ. RQs are calculated for the most sensitivemonocot and dicot species.

Monocot 0.1783 NIA Seed Emerg. Dicot 0.01 11 NIA Table 

### 12: Acute Endangered Terrestrial Plant Risk Quotient Calculations For Single SprayApplications of thidiazuron

Monocot 0.1783 0.002 Veg Vigor Dicot 0.00019 0.002 Scenario Toxicity Threshold, NOEC or EC,, (Ib ailac)


# I1 Cotton -Aerial A~ulications (0.2 Ibs aiiaclapp) Monocot 0.1783 NIA Seed Emerg. Dicot 0.01 11 NIA Cotton - CrormdApplications (0.2 Ibs ailaclapp)

Page 123of 134 Plants Adjacent to Treated Sites

Total Drift

(Ib ailac) Plants in Semi-aquatic Areas

Total Drift

(Ib ailac) Total Loading(Sheet runoff 

### + Drift) (I b aihac) RQ" Total Loading (Channel runoff 

### +Drift) (Ib ailac) 1U.yTable 

### 12: Acute Endangered Terrestrial Plant Risk Quotient Calculations For Single Spray Applications of thidiazuron

Page 124of 134 Scenario Toxicity Threshold, NOEC or EC,, (Ib ailac) 

# i Monocot 0.1783 0.01 N/A 0.06 0.01 N/A 0.06 Veg Vigor Dicot 0.000 19 0.0 1 N/A 52.63 

### * 0.01 N/A 52.63 

### * "Indicates acute risk to endangered plants I I Most of the thidiazuron labels recommend a second application not to exceed a seasonal total of 0.3 lb ai/A. The number of days between 

## 1 the intervals is not stated on any of the labels so 

### EFED has assumed a somewhat conservative scenario of 7 days between applications. For
1 multiple spray applications the environmental concentrations and the RQs would increase accordingto a linear relationship at the most , conservative level. The estimated environmental concentrations for dry and semi-aquatic areas with an assumed runoff of 2% are tabulated I 

## I below.

1 Plants Adjacent to Treated Sites

Total Drift

(Ib ailac) Plants in Semi-aquatic Areas

Total Drift

(Ib ailac) Total Loading(Sheet runoff 

### +Drift) (Ib ailac) RQ" Total Loading (Channel runoff 

### +Drift) (Ib ailac) 

# w"Cotton (0.2 Ib ai/A 1"App.; 0.1 Ib ai/A 2"*app; 7 day intervals; ground applications) 0.276 0 0.02 0.006 0.06 0.003 0.009 0.063 Cotton (0.2 lb ai/A lSt App.; 0.1 lb ai/A 2"*app; 7 day intervals; aerial applications) n 776 n n n:, n nnq n n? n ni n ni? n 04 

### ' Assumed short grass peak residue value (day 6) from first application at 0.2 Ib ai/A and added initial residue value at 0.1 lb ai/A for second application.

Assumed drift at 1%for ground applications and 5% for aerial applications. 

### Non-endangered Plant Risk Quotients

## - Multiple Spray Applications of Thidiazuron The RQs for multiple applications are determined in the samemanner as single applications. The 

### EC,, value of the most sensitive species in the seedling emergence and vegetative vigor studies are compared to runoff and drift exposure.) The RQs are calculated for the most sensitivemonocot and dicot species for aerial and ground applications..

Page 125of 134lotton (0.2 Ib ai/A 1" App.; 0.1 Ib ailA Indapp; 7 day intervals; ground applications) Monocot 

### <o. 1783 N/A 0.009 Seed Emerg. Dicot 0.0152 N/A 0.009 Monocot >O. 1783 0.003 N/A Veg Vigor Dicot 0.001 1 0.003 N/A Jotton (0.2 Ib ai/A 1" App.; 0.1 Ib ai/A 2ndapp; 7 day intervals; aerial applications) Monocot <O. 1783 NIA 0.013 Seed Emerg. Dicot 0.0152 N/A 0.013 Monocot >O. 1783 0.01 NIA < 0.06 0.01 N/A < 0.06 Veg Vigor Dicot 0.001 1 0.01 N/A 9.09 * 0.01 NIA 9.09 * indicates an exceedence of Acute Risk LOC.

Page 126 of 134

### Endangered Plant 

### Risk Quotients

## - Multiple Spray Applications of Thidiazuron The RQs for multiple applications ofthidizuron are determined in the samemanner as single applications. The NOEC or EC,, value of the most sensitive species in the seedling emergence and vegetative vigor studies are compared to runoff and drift exposure. RQs are calculated for the most sensitive monocot and dicot species for ground and aerial applications.

otton (0.2 Ib ai/A 1'' App.; 0.1 Ib ai/A 2"*app;7 day intervals; aerial applications)

Veg Vigor Monocot Page 127of 134

### APPENDIX 

### H: Data Requirements for Thidiazuron

Page 129of 134Photodegradation inWater
summarizing previous DER issues and

Photodegradation on Soil

Page 130 of 134reported half-life as 1 1 1 days at 2 1 OC and 78% of 113-bar. Value should be 182 days (based on semi-log transformed data). Half-life becomes 140days after adjustment to 25 "C and 75% of 113-bar Aerobic Soil Metabolism soil water potential. (German standard sandy loam soil 2.3)

respectively. (Half-lives at 20 OC and 40% MWHC were 163,355, and 322 days,

Terrestrial Field Dissipation

Page 131of 134Page 132of 134Avian Dietary LC,,

Freshwater Fish LC,, Metabolite (AE F132345)

Freshwater Invertebrate

Page 133of 13472-5 i 850.15 FreshwaterFish Full LifeCycle NA
122- i 850.41 l(a) 

## ; 122- ; 

## - 850.415 l(b) 

## ;
122-2 i 850.44
123- 

# : 850.4225 l(a> i 123- i 850.425 l(b) i

123-2 

### ; 850.44 Seed Germ./Seedling Emergence Vegetative Vigor Aquatic Plant Growth Seed Germ./Seedling Emergence (Tier2)

141-1 i 850.302

I I I I This test may be recommend if chronic mammalian issues can not be resolved Vegetative Vigor (Tier 2)' Aquatic Plant Growth (Tier 212 

# 1 141-2 

# / 850.303 Core

Core TGAI

TGAI

42.6 a.i.

Honey Bee Acute Contact
no Honey Bee Residue on Foliage 

# I Core 418213-01

418191-01

459085-01,

42.6 a.i.

TGAI

These tests are,highly recommended for cantaloup and citrus due to the high sensitivity of these crops as evidenced in label warnings. 459215-01

459085-01
TG A1 41.9

Page 134of 134 462035-01 462035-18