Proposed Registration of the New Material Preservative Active Ingredient, 

Terbutryn

I Proposed Decision: The Agency is proposing to register new registrations for products

containing the new active ingredient, terbutryn. The proposed label uses include material 

preservation in joint cements, stuccos, sealants, paints, primers, sealers, and industrial coatings. 

Terbutryn was initially registered by EPA in 1969 as an herbicide to control weeds in various 

grain crops. All terbutryn product registrations in the U.S. were voluntarily canceled in 1990-

1991. Subsequently, Troy Chemical Corporation submitted applications to EPA for material 

preservation uses. Terbutryn is an alternative to formaldehyde as a material preservative and 

these registrations are expected to lessen the chance of risks posed by products that release 

formaldehyde to the extent these new products are used. 

II. Human Health Risk Assessment Summary: The toxicological database for terbutryn is 

complete. Terbutryn is mildly irritating to eyes and mildly or slightly irritating to skin. 

Terbutryn is not a dermal sensitizer. Terbutryn is of moderate acute toxicity by oral, dermal, or 

inhalation routes of exposure. In subchronic and chronic toxicity studies, decreased body

weight, body weight gain, hematological effects and decreased food index were observed. 

Normochromic anemia evidenced by significant decreases in erythrocyte count, hemoglobin, and 

hematocrit was observed and noticed in some subacute and subchronic studies. In the chronic 

toxicity study, a statistically significant and dose-related decrease in hemoglobin and 

erythrocytes in females was considered as the primary adverse effect. Mucosal thickening of the 

small intestine and submucosal lymphoid hyperplasia in the pyloric region of the stomach were 

noticed in the 6-month dog study. 

Acute Tox: Low to moderate acute toxicity via the oral, dermal, and inhalation routes of exposure 

(Toxicity Categories III-IV). Terbutryn is not a dermal irritant or sensitizer.

Developmental Tox: Not teratogenic to either species (rabbit or rat), based upon decreased food 

consumption increased food index, decreased body weight gain and stool, changes in rabbits 

skeletal variations in developing fetuses were present at doses causing maternal toxicity (i.e. 

diarrhea, decreased body weight, decreased body-weight gain).

Repro. Tox: No reproductive effects were reported.

Neurotoxicity: There is no neurotoxicity study available on technical terbutryn. However, no 

signs of neurotoxicity were observed in the sub-chronic, chronic, developmental and 

reproductive toxicity studies with terbutryn. There is no evidence that the nervous system is a 

target.

Carcinogenicity: The Scientific Advisory Panel (SAP) concluded “tumors were induced at 

multiple sites on at the highest dose, which exceeded a maximum tolerated dose (MTD). Good 

dose-response data were not available due to the large spread between doses. Therefore the 

panel believes that an interim category C is appropriate, but that this could be reduced to a 

category D if negative data from ore appropriate doses were submitted. Furthermore, the panel 

does not believe a quantitative risk assessment (for the carcinogenic effects) is justified since 

positive tumor Data occurred only at doses that exceeded the MTD”. 
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The FQPA Safety Factor : 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

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.For these reasons, the default 10x FQPA Safety Factor was reduced 

to 1x.

Aggregate Risk: An aggregate risk assessment considers food, drinking water and residential 

sources of exposure. 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. A short- and 

intermediate-term aggregate risk assessment was conducted for terbutryn for both occupational 

handlers and residential handlers. Dermal and inhalation exposures for these populations were 

aggregated, as the studies and endpoints selected for the dermal and inhalation routes are the 

same. 

Drinking Water Assessment: Drinking water consumption and risk were based on a DEEMFCID-NHANESIWWEIA (2003-2008) model run using the 18 ppb EEC level and the cPAD of 

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.

Occupational and Residential Risk: Risk to commercial and residential painters applying in-can 

preservatives in paint are not of concern. Occupational exposures to workers during the 

manufacturing process of mixing and loading terbutryn into joint cements, coatings (e.g., paints), 

sealants, and stuccos are not expected to be of concern provided the worker wears dermal and 

inhalation personal protective equipment (PPE). Dermal PPE would include chemical resistant 

gloves, long-sleeve shirts and gloves for both liquid and wettable powder products. Inhalation 

PPE would include half face respirator with appropriate cartridges and/or filters. Inhalation PPE 

is only required for workers mixing/loading products that are formulated as wettable powders.

III. Environmental Fate/Ecological Risk Assessment Summary: 

Environmental Fate: Persistence: Terbutryn is considered moderately-persistent to persistent in 

aerobic and anaerobic conditions with half-lives of 35-169 days and moderately persistent to 

persistent in soil with a half-life of 67 days in aerobic soil. 

Mobility: Terbutryn is moderately mobile to immobile in aerobic and anaerobic conditions with 

reported organic carbon partitioning coefficients ranging from 1,490-12,442 L/KG-oc indicating 

a potential to absorb on to particles and bind to sediments.

Mode of Degradation: Terbutryn degrades primarily by photodegradation in shallow, clear, wellmixed water. Under other conditions, aerobic metabolism is expected to be the primary route of 

degradation. Terbutryn also degrades slowly under conditions of aerobic and anaerobic aquatic 

metabolism. There is no evidence of degradation via hydrolysis. The major degradates include 

compounds with intact triazine rings and loss of side chains.
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Ecological risk: Birds: Submitted acute oral and subacute dietary toxicity data for birds indicate 

that terbutryn is essentially nontoxic acutely to birds and ducks. 

Mammals: Practically non-toxic to small mammals. No LOCs were exceeded.

Terrestrial: There is no exposure to terrestrial organisms at the use site (i.e., manufacturing 

facilities). Additionally, in-service use of joint cements, coatings (e.g., paints), sealants, and 

stuccos preserved with terbutyrn is considered to have insignificant or minimal exposure because 

application sites are not habitat for terrestrial organisms and bioaccumulation in the food chain is 

not considered a route of concern.

Fish and Aquatic Invertebrate: All RQs for fish and aquatic invertebrates as well as aquatic plants 

were below LOC values, and therefore the proposed use in paints does not create any apparent 

ecological risks of concern. The other proposed material preservative uses are expected to have 

similar (e.g., stucco) or lower exposure and therefore similar or lower environmental risks than 

the modeled outdoor architectural paint scenario. 

IV. Risk Mitigation: Workers involved in the manufacturing process of mixing and loading 

terbutryn into joint cements, coatings (e.g., paints), sealants, and stuccos, must wear chemical 

resistant gloves, long-sleeve shirts and gloves for both liquid and wettable powder products. 

Inhalation PPE including half face respirator with appropriate cartridges and/or filters is also 

necessary for workers involved in the manufacturing process that use wettable powders.