UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, DC 20460 

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

4/17/13 

MEMORANDUM 

SUBJECT: Terbutryn. Drinking Water Risk Assessment (Revised) 

PC Code: Terbutryn: 080813 I DP Barcode No.: 41 0486 

Decision No.: NA I File Symbol: 5383-RGI 

Regulatory Action: New Active Ingredient Registration 

Risk Assessment Type: Single Chemical I Case No.: 4023 

TXR No.: N/A 

FROM: 

TO: 

THRU: 

Background 

I CAS No: 886-50-0 

William J. Hazel, Ph.D., Chemist /J /(;)cit, ./7 / 

Risk Assessment and Science Supp~tt~h (RASs~ Antimicrobials Division (751 OP) 

Stacey Grigsby 

Regulatory Management Branch II (RMBII) 

Antimicrobials Division (751 OP) 

Timothy 

Steven 

Risk Assessment 

Weiss, 

Leighton, 

Chief 

and 

Team 

Science 

~ Leader 

Support 

I------

Branch 

~ ~ 

(RASSB) 

Antimicrobials Division (751 OP) 

In July 2009, Troy Chemical Corporation submitted an application to EPA requesting the 

registration of a product containing a new active ingredient terbutryn [2-(tertbutylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] (EPA File Symbol 5383-RGI). Troy 

has also applied for registration of three industrial end-use products containing 

terbutryn: Troysan® Terbutec (5383-RGO, 99.0% terbutryn), Polyphase® 71 OS (5383-

RUN, 8% terbutryn and 14% 3-iodo-2-propynyl butyl carbamate), and Troysan®V662 

(5383-TBD, 48% terbutryn). The proposed uses in these applications are for material 

preservation of joint cements, stuccos, sealants, paints, primers, sealers, and industrial 

coatings. 
Dietary Exposures and Risks 

There are no registered food uses so dietary exposure and risk are limited to direct and 

indirect exposure to water including drinking water. 

1) Estimated Level of Terbutryn in Water 

The agency utilized conservative assumptions to estimate terbutryn levels in water. EPA 

calculated estimated environmental concentrations (EEC) of terbutryn in water of 9 and 

18 ppb by assuming that 50% or 100%, respectively, of houses, decks, and fences in 

the watershed had been painted with terbutryn-preserved paint. These EECs are acute 

(peak) figures that are most appropriate for single-day drinking water assessments in 

terms of duration. However, as terbutryn does not induce adverse systemic effects from 

a single dose, an acute dietary risk assessment is not appropriate and has not been 

conducted. Dietary risk due to terbutryn is only chronic (:~6 months in duration) for which 

an arithmetic mean water concentration would be a more appropriate value. However, 

the available model for antimicrobials is not refined enough to provide average water 

concentrations. Therefore, EPA used the acute (peak) value in the dietary assessment 

even though it greatly overestimates chronic dietary risk due to drinking water exposure. 

In reality, the agency does not expect terbutryn to contaminate drinking water as a 

result of this use. 

Conservative modeling results were based on the following parameters and inputs: 

a) The leaching rate used was the highest reported rate; 

b) All (1 00%) or half (50%) of the houses in the watershed (as well as fences, 

decks, etc.) were painted with paint containing terbutryn. As this is a new use, no 

houses have yet been painted with these products. Typically, the market share 

increases for several years and then levels off. Both the 50% and 1 00% painted 

figures are considered conservative. 

c) There are 10 houses per hectare (representative of high density construction) 

and 10 hectares in the watershed, i.e., 100 houses supplying leachate to the 

water body. 

d) All leached terbutryn goes into the same water body, and it does not degrade or 

sorb. In reality there are always lawns and hard surfaces between the houses 

and water body and, as the water passes through these surfaces, part of the 

terbutryn will be adsorbed to the soil particles and lower concentrations will reach 

the water body. 

e) The model uses a small farm pond as the surrogate water body, which is 

considered to be unrealistic for drinking water. Much larger reservoirs are used 

for drinking water sources and, if modeled, would be expected to further reduce 

the water concentration. 

f) These calculations and the water concentration (EEC) derived from the model is 

an acute (peak) value, whereas the risk assessment is for chronic exposure. An 

average water concentration would be a more appropriate value to use in the 

assessment but this is not available from the model. 

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2) Dietary Risk of Terbutryn 

The agency utilized a cPAD of 0.001 mg/kg/day (0.1 mg/kg/day + 1 OOx) from the 2-year 

rat feeding study (MRID 00035923) with the most sensitive endpoint. The dose of 0.001 

mg/kg/day from the 2-yr rat study is conservative, perhaps overestimating toxicity by a 

factor of 10-100 because of the dose spacing: the NOAEL is 0.1 mg/kg/day but the next 

higher doses are 15 and 150 mg/kg/day. The agency notes that the NOAEL of 12 

mg/kg/day in male rats from the newer 2-yr rat study may be closer to where the true 

NOAEL lies because the dose spacing is much closer (1 .2, 4.0, 12, and 25 mg/kg/day). 

Terbutryn does not induce adverse systemic effects due to a single dose; therefore, an 

acute dietary risk assessment has not been conducted. 

Drinking water consumption and risk were based on a DEEM-FCID-NHANESIWWEIA 

(2003-2008) model run using the 18 ppb EEC level and the cPAD if 0.001. The results 

indicate that, even with an extremely conservative estimate of the terbutryn level in 

drinking water, all infants were at 97% of the cPAD, children 1-2 were at 54% of the 

cPAD, and the total U.S. population was at 38% of the cPAD. When the somewhat 

more refined EEC of 9 ppb is modeled, these apparent risks decline to 49%, 27%, and 

19%, respectively. 

3) FQPA Considerations 

Under the Food Quality Protection Act (FQPA), P.L. 104-170, which was promulgated in 

1996 as an amendment to the Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA) and the Federal Food, Drug and Cosmetic Act (FFDCA), the Agency was 

directed to "ensure that there is a reasonable certainty that no harm will result to infants 

and children" from aggregate exposure to a pesticide chemical residue. The law further 

states that in the case of threshold effects, for purposes of providing this reasonable 

certainty of no harm, "an additional tenfold margin of safety for the pesticide chemical 

residue and other sources of exposure shall be applied for infants and children to take 

into account potential pre- and post-natal toxicity and completeness of the data with 

respect to exposure and toxicity to infants and children. Notwithstanding such 

requirement for an additional margin of safety, the Administrator may use a different 

margin of safety for the pesticide residue only if, on the basis of reliable data, such 

margin will be safe for infants and children." 

There are no existing tolerances or exemptions from tolerance for terbutryn. Dietary 

exposure to terbutryn is limited to drinking water through potential leaching of terbutryn 

from paint into surface water. As there are potential exposures to terbutryn through 

drinking water that will also involve exposures of infants and children, the data on 

developmental, reproductive, and neurotoxic effects of terbutryn were examined. The 

data on developmental and reproductive toxicity of terbutryn (two developmental toxicity 

studies and one multi-generation reproduction toxicity study) showed no indication of 

developmental or reproductive toxicity to offspring from in utero or post-natal exposure 

to terbutryn. Also, there are no indications of neurotoxicity of terbutryn from the 

available subchronic, developmental, or reproductive toxicity data. The Agency has no 

residual uncertainties regarding age-related sensitivities for women of child bearing age 

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or infants and children based on the absence of sensitivity observed in the 

developmental and reproductive toxicity studies for terbutryn. In addition, there are no 

residual uncertainties regarding exposure as conservative model inputs have been used 

to estimate exposures to terbutryn in drinking water as discussed in section F above. 

For these reasons, the default 10x FQPA Safety Factor can be reduced to 1x. 

Aggregate Risk 

An aggregate risk assessment considers food, drinking water and residential 

sources of exposures. There are no registered food uses. For both children and 

adults, the adverse effects in the studies used to assess residential dermal and 

inhalation risks (decreased body weight and body weight gain) are different than 

the effects in the chronic toxicity study (decreased hemoglobin and erythrocytes) 

used in the chronic drinking water assessment, aggregation of chronic drinking 

water and residential risks is not appropriate. (U.S. EPA 2013b). 

The only risks that need to be aggregated are due to residential applicator 

exposures. These aggregate risks are addressed in the terbutryn exposure and 

risk assessment. (U.S. EPA 2013c). 

References 

U.S. EPA 2013a. Memorandum: Terbutryn: Estimated Environmental 

Concentrations (EEC) for Terbutryn Used in Outdoor Paints. Memorandum from 

Siroos Mostaghimi to Jacqueline Campbeii-McFarlane, Product Manager. DP Barcode: 

0407718. 

U.S. EPA 2013b. Memorandum: Terbutryn: Toxicological Review and Hazard 

Assessment for the Proposed Uses as a Material Preservative. Memorandum 

from Jonathan Chen, Ph.D., Toxicologist to Stacey Grigsby, Product Manager. 

DP Barcode: 0407711. 

U.S. EPA 2013c. Memorandum: Updated Occupational and Residential 

Exposure Assessement for Terbutryn. Memorandum from Nathan Mottl, 

Biologist to Jacqueline Campbeii-McFarlane PM 34, DP Barcode: 0407712. 

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