Introduction

The Antimicrobial Division (AD) Regist ration Review Team has evaluated the

status of the human health assessments for terbuthylazine (PC Code 080814) and the terbuthylazine registration review case (C ase 2645). Terbuthylazine is currently registered as an algaecide and microbiocid e/microbiostat used to control algae and slime-forming algae, fungi, and bacteria in water systems such as recirculating cooling water towers, recirculating evaporative conde nser water systems, recirculating heat exchanger water systems, and decorative and ornamental fountains. Mixing, loading and applying these products must be done through closed mixing/loading systems with PPE (long-sleeve shirt, long pants, and chemical re sistant gloves). There are four registered products (one technical product (95% a.i.)., one manufacturing use product, and two end use product formulated as a flowable liquid at concentrations between 4 to 44.7% a.i..). All of the terbuthylazine registered uses are non-food uses. Currently, there are no tolerances or exemptions from the requireme nt of a tolerance, and there are also no

indirect food uses.

Terbuthylazine used to be registered as an s -triazine herbicides. The s -triazines act as inhibitors of photosynt hesis and disturb enzymatic processes in plants (J. Agric. Food

Chem. 1999

, 47, 2733-2737)

. Tolerances were originally es tablished for terbuthylazine in or on corn fodder and forage, corn grain (i ncluding popcorn grain), and sorghum forage and grain (40 CFR 180.333). Howe ver, terbuthylazine is no longer used as a herbicide

and these tolerances were revoked in 1992 (53 FR 4860, 56 FR 14471, and 57 FR 30132). Products formulated for end-use we re first registered as algaecide and microbicides/microbistats starting in 1986.

The primary source of information for this assessment are the risk assessments and supporting documents for the reregistra tion eligibility deci sion (RED) documents,

which were finalized in Marc h, 1995. The purpose of this scre en is to determine whether sufficient data are available to support registration re view, report on whether risk

assessments have been conducted and to re port whether new human health assessments are needed to support the regi stration review process.

The available data for terbuthylazine i ndicates that this compound is slightly soluble in water. Terbuthylazine has a low va por pressure (e.g. <1E-6 mm Hg), is stable to hydrolysis and photolysis, and degrades slowly under aerobic condi tions and anaerobic conditions in sediment. For these reasons, the te rbuthylazine are likely to persist in water and soils. Table 1 presents the chemical identity of terbuthylazine.

2Section 1. Chemical Identity

Table 1. Chemical Identity of Terbuthylazine

Common

Name Terbuthylazine

CAS name 1,3,5-Triazine-2,4- diamine, 6-chloro-N-(1,1- dimethylethyl)-N'-ethyl-; and, s-Triazine, 2-(tert-but ylamino)-4-chloro-6- (ethylamino)-

PC Code 080814 CAS registry

number 5915-41-3

Registration

Review Case

No. 2645

Structure

Section 2. Toxicology

The Agency reviewed the toxicity database for terbuthylazine. EPA confirmed that no additional toxicity data will be needed for registration review since the exposure patterns are non-food uses and the application is rest ricted to closed mixing/loading systems only. No toxicity studies have been submitted since the RED and no toxicity data was called in

for the RED.

Acute Toxicity

According to the existing RED, there are acceptable acute toxicity data available for the generic active ingredient of terbuthylazine. A battery of tests (acute oral, dermal, inhalation, primary eye, primary skin, and dermal sensitization) was conducted using terbuthylazine and all were considered acceptable. A toxicity category of III was assigned based on a oral LD 50 study in rats. The dose in rats was 1000 - 1590 mg/kg for males and 1503 mg/kg for females. A toxicity category of III was also assigned for acute dermal toxicity testing of terbuthylazin e with a LD50>2,000 mg/kg for rats. Acute inhalation toxicity testing of terbuthylazine indicated a toxicity category of III with a LC50 greater than 5.3 mg/L over a 4 hour exposur e period. Skin and ey e irritation testing

3of terbuthylazine in rabbits show ed the compound to be slightly irritating to skin and mild to moderate irritants to eyes with a toxici ty category of III for skin and eye irritation effects. Terbuthylazine is not a dermal sensitizer as evidenced by a guinea pig study.

Sub-chronic Toxicity

According to the RED, the toxicity data bases for terbuthylazine were considered complete for non-food uses. Acceptable data on reproductive toxicity is not available to the Agency at this time. However, a 2-ge neration reproduction study in the rat is not required to support reregistration of terbuthylazi ne since for its current non-food uses . In the future if food uses are proposed a 2-gene ration reproduction study wi ll be required to support registration. The Agency does expect not expect that additional inhalation toxicity study will be needed for registrati on review since open pouring of the liquid is prohibited based on the RED and the existing label restrictions.

Dermal Toxicity

In a repeated dose dermal toxicity study (MRIDs 40514802 and 42059804), terbuthylazine (technical, 97.1% a. i.) was applied daily to the in tact skin of 5 male and 5 female New Zealand White rabbits for 29 consecutive days. The doses of 0.05, 0.5 or 500 mg/kg/day were applied for 6 hrs/day under an occlusive wrap. At 500 mg/kg/day, reduced body weight gain compared to cont rols at day 28 was observed in males (-36%) and females (-39%). Food consumption was also decreased (-76% and -89% of controls during week 1 in males and females; between -1 1% to -54% of controls at other times). The LOAEL of 500 mg/kg/day is based on decreased body weight gain and food consumption in males and females and, in one female, hypothermia, cachexia and mortality. The NOAEL is 0.5 mg/kg/day.

Another dermal toxicity study was consid ered in determinat ion of appropriate toxicity endpoints for shor t- and intermediate-term occupational and residential risk assessment for the RED. In this study male and female New Zealand White rabbits were dermally exposed to terbuthylazin e (technical, 99.8% a.i.) at 0, 5, 50 or 500 mg/kg/day. Effects were seen at the 5.0 mg/kg/day dose. Seve ral clinical signs exhibited in treated animials included dyspnea, p iloerection, sedation and curved body posture.

Dermal rritation was seen for all animals. The LOAEL of 5.0 mg /kg/day is based on clinical signs in males and fe males. No NOAEL was reported.

Inhalation Toxicity

There was no inhalation study available. The existing RED did not called in an inhalation toxicity study (90-day) (870.3465) and mitigated risk by requiring closed mixing/loading systems For registration review , EPA reviewed the labels and notice that

all labels are restricted to closed mi xing systems that reduce inhalation exposure

concerns.

Developmental Toxicity

4According to the RED, a rabbit developmental toxicity study (MRID 00130744),

female New Zealand White rabbits were dos ed by gavage from days 7 through 19 of gestation with terbuthylazi ne (technical, 98.5% a.i.) at 0, 0.5, 1.5 or 4.5 mg/kg/day. No signs of maternal toxicity were observed at any dose tested (in a preliminary study, body weight loss was observed at 12.5 mg/kg/day bu t not at 5 mg/kg/day in the rabbit). The maternal toxicity LOAEL is greater than 4.5 mg/kg/day. The maternal toxicity NOAEL is equal to or greater than 4.5 mg/kg/day. No signs of developm ental toxicity were observed in the rabbit at any dose test ed. The NOAEL for developmenta l toxicity is equal to or greater than 4.5 mg/kg/day. The LOAEL for developmental toxicity is greater than 4.5 mg/kg/day. Although an LOAEL for developmen tal toxicity was not established, this study is considered adequate fo r regulatory purpose s since (1) the data indicate that the

rabbit is not more sensitive than the rat fo r developmental toxicity since the NOAEL is not significantly lower in the rat (4.5 mg/kg/day vs. 5.0 mg/kg/day, respectively), as described below, and (2) the rabbit preliminar y study indicated that maternal toxicity was observed at 12.5 mg/kg/day.

In a rat developmental toxicity study (MRID 41962701), female rats were administered 0, 1, 5 or 30, mg/kg/day terbut hylazine (technical, 96.4% a.i.) by gavage on days 6 through 15 of gestation, inclusive. Maternal toxicity was observed at 30 mg/kg/day as significantly reduced body weight gain (60% less than controls) during the treatment period compared to controls and food intake was also reduced (18%). The maternal toxicity LOAEL is 30 mg/kg/day based on decreased body weight gain and food intake. The maternal toxicity NOAEL is 5 mg/kg/day. Developmental toxicity was also observed at 30 mg/kg/day based on a dose-re lated increased incidence of absent ossification of the posterior pha lanx of anterior digit 2 (30% litter incidence vs. 10% of the controls). The developmental toxicity LOAEL is 30 mg/kg/day based on absent ossification in anterior digit 2. The deve lopmental toxicity NOAEL is 5 mg/kg/day.

Mutagenicity

The Agency identified several mutagenicity studies in the RED. These studies included two bacterial gene mutation assa ys submitted to satisfy guideline 870.5100, one in vitro cell gene mutation study (870.5300) , two chromosome aberration assays submitted to satisfy guideline 870.5385, and two unscheduled DNA synthesis (UDS) studies. The RED DCI did not specify the need for any other mutage nicity studies and no new mutagenicity studies were submitted since the RED. Th e Agency does not anticipate the need for the additional mutagenicity studi es for registration review and the results indicate that terbuthylazine doe s not appear to not exhibit negative mutagenic effects in

the studies submitted.

870.5100 Bacterial reverse mutation test

There were two gene mutation assays. In the first study, Terbuthylazine was negative for reverse gene muta tion in Salmonella typhimurium strains in assays when

tested with or without metabol ic activation up to li mits of solubility (5 mg/ml) in two independently conducted studies (MRIDs 00108817 and 00140816;MRID 41634001).

870.5300 In vitro cell gene mutation test

5In a mouse L5178T/TK+/- assay, terbuthyl azine did not cause increased mutation frequency with or without metabolic activ ation when tested up to 1 mg/ml (MRID 00151618).

870.5385 Mammalian bone marrow chromosomal aberration test

Terbuthylazine did not induce unsche duled DNA repair in cultured rat hepatocytes at test c oncentrations up to 125 F g/ml or 1000 F g/ml in two independently performed studies (MRIDs 41391801 and 42059806; MRID 00151619). Terbuthylazine was also negative when tested for unscheduled DNA repair at concentrations of up to 125

F g/ml in cultured human fibroblasts (MRID 00151620).

870.5550 Unscheduled DNA synthesis in mammalian cells in culture

Terbuthylazine did not induce unsche duled DNA repair in cultured rat hepatocytes at test c oncentrations up to 125 F g/ml or 1000 F g/ml in two independently performed studies (MRIDs 41391801 and 42059806; MRID 00151619). Terbuthylazine was also negative when tested for unscheduled DNA repair at concentrations of up to 125

F g/ml in cultured human fibroblasts (MRID 00151620).

Chronic Toxicity and Carcinogenicity

Mouse:

In a 2-year chronic feeding/ carcinogenicity study (MRID 00156487), terbuthylazine (technical, 98% a.i.) was administ ered in the diet to mice at dose levels of 0, 30, 150 or 750 ppm (males: 0, 3.28, 16.99 or 86.76 mg/kg/day; females - 0, 3.22, 16.66 or 88.54 mg/kg/day). Percent body weight ga in of males in the 750 ppm group was decreased by approximately 10%, while in females it decreased by approximately 23% throughout most of the study. Food consumpti on in males at 750 ppm was decreased by approximately 20% throughout most of the st udy. The LEL for systemic toxicity is 750 ppm based on decreased body weight in fe males and a possible decrease in food consumption in males. The NOAEL for systemic toxicity is 150 ppm. There was no evidence that administration of terbuthylazine wa s associated with an increase in tumors.

Rat: In a 2-year chronic feeding/ carcinogenicity study (MRID 00156486), terbuthylazine (technical, 96.8% a.i.) was admi nistered for 24 months to rats at dose levels of 0, 30, 150 or 750 ppm (males: 0, 1.24, 6.97 or 41.47 mg/kg/day; females: 0, 1.37, 7.81 or 52.80 mg/kg/day). At 30 ppm and above, decreased body weight gain was observed in males (10%, 28% and 49% less than controls at week 54, low to high dose) and females (12%, 32% and 47% at week 54, low to high dose). At 30 ppm and above, food consumption was decrease d in males (9%, 14% and 25 % at 54 weeks) while in females only at 150 ppm and above (10% at 54 weeks). The NOAEL is less than 30 ppm.

Terbuthylazine was associated with increas ed incidence of testicular interstitial cell tumors in males and mammary gland carci nomas in females, but only at a dose at

6which excessive systemic toxicity was also observed. The Office of Pesticide Program's Health Effects Division (HED) Carcinogenici ty Peer Review committee considered the systemic toxicity observed at 750 ppm to be excessive (exceeding the maximum tolerated dose or MTD) and the slight increases in tumo r incidence to be of uncertain relevance to human cancer risk assessment (see "Carcinogenicity", below).

In a second 2-year chronic feeding/carc inogenicity study designed to determine a NOEL for chronic systemic toxicity (MRID 00157342), terbuthylazin e (technical, 98% a.i.) was administered to rats at dose le vels of 0, 6 or 30 ppm (males - 0, 0.35 or 1.6 mg/kg/day; females - 0, 0.36 or 1.6 mg/kg/day). At 30 ppm there were decreases in percent body weight gain in males (7% less) and females (12% less) as well as decreases in food consumption in males (6% less than controls) and females (11% less) as compared to controls. The LOAEL for system ic toxicity is 30 ppm based on transient decreases in body weight and food consump tion consistent with another study. The NOAEL for systemic toxicity is 6 ppm. Ter buthylazine administration was not associated

with an increase in tumors at the doses tested.

On May 25, 1994 (Peer Review Document dated August 24, 1994), the Agency's Carcinogenicity Peer Review Committee classified terbuthylazine as a Group D Carcinogen (inadequate evidence to determine carcinogenicity in humans). The incidence of benign interstitial tumors in testes of male rats and of mammary gland carcinoma in female rats was increased, but the incr ease was only observed at a dose at which excessive toxicity was observed (750 ppm). The classification was assigned because although terbuthylazine is structur ally related to other s-triazi nes that induce similar types of tumors, tumors were only observed at a dose that exceeded the MTD and were only seen in one species.

Section 3. Dietary Assessment

Dietary

Dietary (food) exposures are not anticipated as a con cern. Terbuthylazine is not expected to be introduced into the food. Ter buthylazine is no longer used as a herbicide

and these tolerances were revoked in 1992 (53 FR 4860, 56 FR 14471, and 57 FR 30132).There are no existing food use tolerances for the active ingredient, no registered

food uses and no indirect food uses.

Drinking Water

The registered uses of tebuthylazin e (e.g., recirculating cooling water and decorative and ornamental fountains) are not expected to result in contamination of surface water and ground water. However, the need for a dietary drinking water exposure assessment for terbuthylazine will be determined upon review of environmental fate data the Agency anticipates requiring. The environm ental data will be useful to determine if terbuthylazine can pass through wastewater tr eatment facilities into drinking water or migrate into residential groundw ater wells as a result of its current use patterns. Therefore, the need for a drinking water a ssessment will be revised upon submission and review of the anticipated environmental fate data.

7Section 4. Aggregate Exposure

In examining aggregate exposure, EP A takes into account the available and reliable information concerning exposures to pesticide residues in food and drinking water, and non-occupationa l pesticide exposures.

Food exposures of concern are not anticipat ed as a concern based on the fact that terbuthylazine is not expected to be intr oduced into the food, there are no a food use tolerances, no registered food uses and no i ndirect food uses. Reside ntial exposure is not expected. The need for a drinking water a ssessment will be revised upon submission and review of the anticipated environmental fate data; therefore, the need for an aggregate will be evaluated once a decision is made on the drinking water assessment.

Section 408(b)(2)(D)(v) of FFDCA require s that, when considering whether to establish, modify, or revoke a tolerance, th e Agency consider "available information” concerning the cumulative effects of a part icular pesticide's residues and "other

substances that have a comm on mechanism of toxicity.”

Section 5. Cumulative Exposure

During the risk assessment stage for regist ration review, the Agency will address the possibility that terbuthylazi ne shares a common mechanis m of toxicity with other

members of the Triazine Common Mechanis m Group (CMG) and whether terbuthylazine should be included in a cumulate exposure group with the rest of the triazines.

The Agency examined the triazine class of pesticides with respect to a potential common mechanism of toxicity. Th is examination may be found at http://www.epa.gov/oppsrrd1/cumulativ e/triazines/triazinescommonmech.pdf . Several

members of this class have been identif ied as causing toxici ty through a similar mechanism of action. Specifically, atrazine, simazine, propazine, and certain degradates are considered to act through disruption of the hypothalamic- pituitary-gonadal axis to attenuate the luteinizing hormone surge. As a result of th is attenuation, exposure of the animal to estrogen is continuous, prov iding an environment conducive to the development of mammary gland tumors. Mamma ry gland tumors have been observed in female rats after administration of these chemicals, and the postulated mode of action of the triazine pesticide atrazine has been revi ewed by the FIFRA Scientific Advisory Panel and has been found to be pl ausible (U.S. EPA, 2000).

Although there are no tolerances for terbuthylazine, the Agen cy has not been able to determine if there is a need for a drinking wa ter assessment for regist ration review, thus the Agency cannot at this time say definitiv ely that terbuthylazine does not involve exposure to the general public. The Agency will reevaluate if a dri nking water assessment is needed once it receives the applicable environmental fate data during the risk assessment process. The Agency will then be able to make a determination of the need

8for aggregate and cumulative assessment based on the Agency’s determination of drinking water since this is th e only applicable potential e xposure to the general public.

Section 6. Endocrine Disruption

As required under FFDCA section 408(p) , EPA has developed the Endocrine Disruptor Screening Program (EDSP) to dete rmine whether certain substances (including pesticide active and other ingred ients) may have an effect in humans or wildlife similar to an effect produced by a “natur ally occurring estrogen, or othe r such endocrine effects as the Administrator may designate.” The ED SP employs a two-tiered approach to making the statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a chemical substa nce to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are found to have the potential to inte ract with E, A, or T hormonal systems will proceed to the next stage of the EDSP wher e EPA will determine which, if any, of the Tier 2 tests are necessary based on the avai lable data. Tier 2 testing is designed to identify any adverse endocrine related eff ects caused by the substance, and establish a dose-response relationship between th e dose and the E, A, or T effect.

Between October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, which c ontains 58 pesticide ac tive ingredients and 9 inert ingredients. This list of chemicals was selected based on the potential for human exposure through pathways such as food and wa ter, residential activity, and certain postapplication agricultural s cenarios. This list should not be construed as a list of known or likely endocrine disruptors.

For further information on the status of the EDSP, the policies and procedures, the list of 67 chemicals, the test guidelines and the Tier 1 screening battery, please visit our website: http://www.epa.gov/endo/.

Terbuthylazine is not among the group of 58 pesticide active ingredients on the

initial list to be screened under the EDSP. Under FFDCA sec. 408(p) the Agency must screen all pesticide chemicals. Accordingl y, EPA anticipates issuing future EDSP test orders/data call-ins for all pesticide active ingredients.

Section 7. Occupational/Residential Exposure

An occupational and/or residential exposur e assessment is required for an active ingredient if (1) certain toxico logical criteria are triggered and (2) there is potential exposure to handlers (mixers, loaders, applicat ors, etc.) during use or to persons entering treated sites after application is complete. For the terbuthylazine, the Agency does not expect occupational and or residential handl er exposure concerns since the application occurs in closed liquid pump systems for occupational settings only. In addition, the registered uses also recommend personal protective equipment (PPE) when handling terbuthylazine. As a result the Agency does not anticipate th e need to conduct occupational and residential handler dermal and inhalation risk assessments since exposure is minimized by engineer ing controls as well as PPE.

910 Postapplication Exposure

The Agency did not identify potential occupational postapplication exposures for terbuthylazine in the previous RED. Thus, the Agency does not expect any postapplication exposure concer ns for registration review.

Section 8. Incidents

In the OPP database, there were two incide nts recorded for terbuthylazine. However, these incidents were likely a re sult of misuse of these products.

Section 9. Anticipated Data Needs

The Agency does not anticipate the need for any hazard or exposure data for terbuthylazine for registration review based on its current registered uses which prevent exposure based on engineering contro ls (e.g. closed mixing/loading).

Section 10. Tolerances

There are no tolerances or exemptions fr om tolerances for th e terbuthylazine active ingredients and no registered food uses. Since the only regi stered uses are for non-food uses and no dietary assessment is needed, no tolerances or exempti ons from tolerances will be needed to support the existing active i ngredient registered us es of terbuthylazine.

Section 11. Overall Conclusions

The Agency reviewed the hazard and exposure databases for tebuthylazine and anticipates that additional human health data wi ll not be needed at this time. The Agency has not been able to determine if there is a need for a drinking water assessment for registration review, thus the Agency ca nnot at this time say definitively that terbuthylazine does not involve exposure to the general public. The Agency will reevaluate if a drinking wate r assessment is needed once it receives the applicable environmental fate data during the risk assessm ent process. The Agency will then be able

to make a determination of the need for aggregate and cumulative assessment based on the Agency’s determination of drinking water since this is the only applicable potential exposure to the general public. The Agency did not identify any specific need for additional label change s at this time.

Section 12. Reference

• Reregistration Eligibility Decision (RED) Terbuthylazine, March, 1995. http://www.epa.gov/pesticides/reregistration/status.htm