Docket Number: EPA-HQ-OPP-2010-0453 

www.regulations.gov 

United States Chemical Safety March 2011 

Environmental Protection and Pollution Prevention 

Agency (7510P) 

Terbuthylazine Final Work Plan 

Registration Review 

March 2011 

 

 

Docket Number: EPA-HQ-OPP-2010-0453 

www.regulations.gov 

TABLE OF CONTENTS

Terbuthylazine Registration Review Team .................................................................... 1

I. INTRODUCTION..................................................................................................... 2

II. SUMMARY OF COMMENTS RECEIVED ON PRELIMINARY WORK 

PLAN .................................................................................................................................. 2

III. RISK ASSESSMENT AND DATA NEEDS ........................................................... 2

IV. TIMELINE ................................................................................................................ 7

V. GLOSSARY of TERMS & ABBREVIATIONS .................................................... 8

 
Docket Number: EPA-HQ-OPP-2010-0453 

www.regulations.gov 

Terbuthylazine Registration Review Team

Human Health & Environmental Effects 

Nathan Mottl 

Najm Shamim 

Risk Management

Eliza Blair 

Lance Wormell 

Office of General Counsel

Philip Ross 

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I. INTRODUCTION

This is the Environmental Protection Agency’s (EPA or “the Agency”) Final 

Work Plan (FWP) for the registration review of terbuthylazine (Case 2645). The FWP 

includes the expected registration review timeline. The work plan also addresses public 

comments received concerning the Preliminary Work Plan in the Summary Document 

which was posted in the terbuthylazine registration review docket, and any other 

comments concerning the initial docket postings. The Summary Document provided 

information on what EPA knows about the pesticide and what additional risk analyses 

and data or information the Agency believes are needed to make a registration review 

decision. 

The Agency is implementing the Registration Review program pursuant to 

Section 3(g) of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and will 

review each registered pesticide every 15 years to determine whether it continues to meet 

the FIFRA standard for registration. Changes in science, public policy and pesticide use 

practices will occur over time. The registration review program is intended to make sure 

that, as the ability to assess risk evolves and as policies and practices change, all 

registered pesticides continue to meet that statutory standard. The public phase of 

registration review begins when the initial docket is opened for each case. Information on 

this program is provided at: http://www.epa.gov/oppsrrd1/registration_review/. 

The Terbuthylazine Preliminary Work Plan was entered into the docket for this 

registration review on September 29, 2010. The 60-day comment period ended on 

November 29, 2010. The Preliminary Work Plan document is available on 

www.regulations.gov, docket number EPA-HQ-OPP-2010-0453. 

II. SUMMARY OF COMMENTS RECEIVED ON PRELIMINARY WORK 

PLAN

The Agency received no comments from registrants or the public during the 

comment period. The anticipated data needs, work plan and timeline described in the 

Preliminary Work Plan remain as they were presented initially. 

In the Preliminary Work Plan, the Agency solicited comments on three specific 

topics: environmental justice, water body impairment, and trade irritants. No comments 

or information were received during the comment period concerning these issues. This 

document makes final the work plan for the terbuthylazine registration review process. 

III. RISK ASSESSMENT AND DATA NEEDS

 Terbuthylazine (PC Code 080814), first registered as an herbicide in 1975, is now 

registered for use solely as a slimicide in industrial recirculating cooling water 

applications and ornamental fountains. There are four registered products. A 

Reregistration Eligibility Decision (RED) for terbuthylazine was issued by EPA in 1995. 

The RED can be located at http://www.epa.gov/pesticides/reregistration/status.htm. 

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Human Health Risk 

 

The Agency has reviewed all the available information on toxicology and human 

exposure regarding terbuthylazine and does not anticipate that additional data will be 

needed for this registration review case. If the results from the environmental fate data 

(see below) indicate that terbuthylazine has the potential to pass through wastewater 

treatment plants and into drinking water, the need for a drinking water assessment will be 

revisited. 

Further information is available in “Summary of Human Health Effects Data for 

the Terbuthylazine Registration Review Decision Document”, dated July 19, 2010. 

Dietary and Drinking Water Assessment

The need for a drinking water exposure assessment will be revisited upon 

submission and review of the environmental fate data the Agency anticipates requiring 

through Registration Review. These environmental fate data will be used to determine if 

terbuthylazine has the potential to pass through wastewater treatment facilities into 

drinking water or migrate into residential groundwater wells as a result of its current use 

patterns. 

Occupational and Residential Assessment

 An occupational and/or residential exposure assessment is required for an active 

ingredient if (1) certain toxicological criteria are triggered and (2) there is potential 

exposure to handlers (mixers, loaders, applicators, etc.) during use. 

 Currently, application to recirculating cooling water systems and ornamental 

fountains is required by the label to be closed-system only. In the event that the product 

needs to be handled, personal protective equipment is required by the label in the form of 

a long-sleeved shirt, long pants, shoes, socks, chemical-resistant gloves, and the 

availability of a chemical-resistant apron for spills. As a result, the Agency does not 

anticipate the need to conduct occupational and residential handler dermal and inhalation 

risk assessments since exposure is minimized by the required engineering controls as well 

as the required personal protective equipment. At this time, the Agency anticipates that 

no additional exposure data will be needed for this registration review. 

Tolerances

 There are no current tolerances or exemptions from tolerances for the active 

ingredient terbuthylazine, and no registered food uses. 

Aggregate/Cumulative Exposure & Risk

 In examining aggregate exposure, EPA takes into account the available and 

reliable information concerning exposures to pesticide residues in food and drinking 

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water, as well as non-occupational pesticide exposures. Based on current use patterns, an 

aggregate risk assessment will not be needed for terbuthylazine. Residential exposure is 

not expected and the need for a drinking water exposure assessment will be determined 

upon submission and review of the environmental fate data the Agency anticipates 

requiring. 

 Section 40(b)(2)(D)(v) of FFDCA requires that, when considering whether to 

establish, modify, or revoke a tolerance, the Agency considers “available information” 

concerning the cumulative effects of a particular pesticide’s residues and “other 

substances that have a common mechanism of toxicity.” EPA has not yet determined 

whether terbuthylazine has a common mechanism with other compounds; however, 

during the risk assessment stage for registration review, the Agency will address the 

possibility that terbuthylazine shares a common mechanism of toxicity with other 

members of the Triazine Common Mechanism Group (CMG) and whether terbuthylazine 

should be included in a cumulative exposure group with the those triazines. 

 Unlike other pesticides for which EPA has followed a cumulative risk approach 

based on a common mechanism of toxicity, EPA has not yet examined terbuthylazine for 

a possible common mechanism of toxicity with other chemicals. Terbuthylazine is a 

member of a class of pesticides collectively referred to as “triazine” pesticides, and is 

structurally similar to some of them. The Agency has examined the some members of the 

triazine class of pesticides with respect to a potential common mechanism of toxicity; this 

examination may be found at 

http://www.epa.gov/oppsrrd1/REDs/triazine_cumulative_risk.pdf. Several members of 

this class have been identified as causing toxicity through a similar mechanism of action; 

specifically, they disrupt endocrine hormone production and have been shown to cause 

mammary gland tumors in rats. 

 For information regarding EPA’s efforts to determine which chemicals have a 

common mechanism of toxicity and to evaluate the cumulative effects of such chemicals, 

see the policy statements released by EPA’s Office of Pesticide Programs concerning 

common mechanism determinations and procedures for cumulating effects from 

substances found to have a common mechanism on EPA’s website at 

http://www.epa.gov/pesticides/cumulative/.

 Because a data call-in program already exists to specifically address endocrine 

concerns (“Endocrine Disruptor Screening Program”, described below) the Agency does 

not anticipate that it will ask for endocrine-related data at this time. However, if studies 

are received in response to an Endocrine Disruptor Screening Program data call-in, such 

data will be considered as part of a future risk assessment. 

Anticipated Human Health Data Needs:

 All human toxicology and exposure data requirements have been fulfilled for the 

active ingredient terbuthylazine. The Agency has reviewed the available data for 

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terbuthylazine and expects that no additional toxicity or exposure data will be needed for 

registration review. 

Further information is available in “Summary of Human Health Effects Data for 

the Terbuthylazine Registration Review Decision Document”, dated July 19, 2010. 

Anticipated Physical/ Chemical Property Data Needs 

 All product chemistry data requirements have been fulfilled for the active 

ingredient terbuthylazine. Therefore, the Agency does not anticipate needing additional 

product chemistry data at this time. 

Further information and detailed justifications for the studies that are anticipated 

as being needed are available in “Terbuthylazine: Product Chemistry / Environmental 

Fate and Eco-Effects Scoping Document”, dated July 28, 2010 . 

Environmental Fate and Ecotoxicity 

No environmental fate and ecological risk assessments have been performed for 

terbuthylazine. The Agency has reviewed the environmental fate and ecological hazard 

databases for terbuthylazine. Based on its review, EPA believes the following 

environmental fate and ecological hazard risk assessments are needed to ensure that the 

registration review case meets FIFRA standards: 

• Environmental fate 

• Ecological hazard 

• Endangered species assessment 

The Agency expects that it will need to conduct environmental fate and ecological 

risk assessments for slimicides that potentially pass through waste water treatment plants 

(WWTPs) and may be discharged into terrestrial and aquatic environments. 

Endangered Species 

 The Agency has not conducted a risk assessment that supports a complete 

endangered species determination for terbuthylazine. The ecological risk assessment 

planned during registration review will allow the Agency to determine whether 

terbuthylazine’s use has “no effect” or “may affect” federally listed threatened or 

endangered species (listed species) or their designated critical habitats. When an 

assessment concludes that a pesticide’s use “may affect” a listed species or its designated 

critical habitat, the Agency will consult with the U.S. Fish and Wildlife Service and/or 

National Marine Fisheries Services (the Services), as appropriate. 

 On January 19, 2011, the Center for Biological Diversity and the Pesticide Action 

Network North America filed a lawsuit in the United States District Court for the 

Northern District of California, against the Environmental Protection Agency (EPA) for 

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allegedly failing to undergo consultation with the United States Fish and Wildlife Service 

and the National Marine Fisheries Service regarding the effects of over 350 pesticides, 

including terbuthylazine, on over 200 endangered and threatened species throughout the 

United States (Center for Biological Diversity, et al. v. EPA, et al., No. C 11-00293 

(N.D.Cal.). 

Anticipated Environmental Fate and Ecological Data Needs 

The Agency anticipates needing the following data in order to conduct a complete 

environmental fate and ecotoxicity assessment, including an endangered species 

assessment for all uses: 

Environmental Fate Risk Assessment Data Needs: 

o (GLN 835.3110) Ready Biodegradability 

o (GLN 835.1110) Activated Sludge Isotherm 

Ecological Risk Assessment Data Needs: 

o (GLN 850.5400) Aquatic plant growth (algal), Tier II

Further information and detailed justifications for the studies that are anticipated 

as being needed are available in “Terbuthylazine: Product Chemistry / Environmental 

Fate and Eco-Effects Scoping Document”, dated July 28, 2010 . 

Endocrine Disruptor Screening Program

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess 

potential adverse outcomes from exposure to chemicals. Collectively, these studies 

include acute, subchronic and chronic toxicity, including assessments of carcinogenicity, 

neurotoxicity, developmental, reproductive, and general or systemic toxicity. These 

studies include endpoints which may be susceptible to endocrine influence, including 

effects on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual 

maturation, fertility, pregnancy rates, reproductive loss, and sex ratios in offspring. For 

ecological hazard assessments, EPA evaluates acute tests and chronic studies that assess 

growth, developmental and reproductive effects in different taxonomic groups. As part 

of its most recent registration decision, EPA reviewed these data and selected the most 

sensitive endpoints for relevant risk assessment scenarios from the existing hazard 

database. However, as required by FFDCA section 408(p), terbuthylazine is subject to 

the endocrine screening part of the Endocrine Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including 

pesticide active and other ingredients) may have an effect in humans or wildlife similar to 

an effect produced by a “naturally occurring estrogen, or other such endocrine effects as 

the Administrator may designate.” The EDSP employs a two-tiered approach to making 

the statutorily required determinations. Tier 1 consists of a battery of 11 screening assays 

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to identify the potential of a chemical substance 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 interact with E, A, or T hormonal systems will 

proceed to the next stage of the EDSP where EPA will determine which, if any, of the 

Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to 

identify any adverse endocrine-related effects caused by the substance, and establish a 

dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. 

Between October 2009 and February 2010, EPA issued test orders/data call-ins for the 

first group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert 

ingredients. terbuthylazine is not among the group of 58 pesticide active ingredients on 

the initial list to be screened under the EDSP. Accordingly, as part of registration review, 

EPA will issue future EDSP orders/data call-ins, requiring the submission of EDSP 

screening assays for terbuthylazine. For further information on the status of the EDSP, 

the policies and procedures, the list of 67 chemicals, future lists, the test guidelines and 

the Tier 1 screening battery, please visit our website: http://www.epa.gov/endo/. 

IV. TIMELINE

 The Agency has created the following estimated timeline for the completion of 

the terbuthylazine registration review: 

Activities Estimated Month/Year

Phase 1: Opening the docket 

Open Public Comment Period for Terbuthylazine Docket Completed September 2010

Close Public Comment Period Completed November 2010

Phase 2: Case Development 

Develop Final Work Plan (FWP) Completed January 2011 

Issue DCI March 2012 

Data Submission March 2013 

Open Public Comment Period for Preliminary Risk Assessments September 2015 

Close Public Comment Period December 2015 

Phase 3: Registration Review Decision 

Open Public Comment Period for Proposed Reg. Review Decision March 2016 

Close Public Comment Period June 2016 

Final Decision and Begin Post-Decision Follow-up 2016 

Total (years) 6 

Next Steps:

A Data Call-In (DCI) will be developed regarding the data gaps listed under the 

“Risk Assessment and Data Needs” section. Also, human health and ecological risk 

assessments will be conducted for all uses. 

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V. GLOSSARY of TERMS & ABBREVIATIONS

ai Active Ingredient 

AR Anticipated Residue 

ASTM American Society for Testing and Materials 

AWPA American Wood Preserver’s Association 

CFR Code of Federal Regulations 

cPAD Chronic Population Adjusted Dose 

CSF Confidential Statement of Formula 

CSFII USDA Continuing Surveys for Food Intake by Individuals 

DCI Data Call-In 

DEEM Dietary Exposure Evaluation Model 

DFR Dislodgeable Foliar Residue 

DNT Developmental Neurotoxicity 

DWLOC Drinking Water Level of Comparison 

EC Emulsifiable Concentrate Formulation 

EDWC Estimated Drinking Water Concentration 

EEC Estimated Environmental Concentration 

EPA Environmental Protection Agency 

EUP End-Use Product 

FDA Food and Drug Administration 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FFDCA Federal Food, Drug, and Cosmetic Act 

FQPA Food Quality Protection Act 

FOB Functional Observation Battery 

GENEEC Tier I Surface Water Computer Model 

IR Index Reservoir 

LC50 Median Lethal Concentration. A statistically derived concentration of a 

substance that can be expected to cause death in 50% of test animals. It is 

usually expressed as the weight of substance per weight or volume of water, air 

or feed, e.g., mg/l, mg/kg or ppm. 

LD50 Median Lethal Dose. A statistically derived single dose that can be expected to 

cause death in 50% of the test animals when administered by the route indicated 

(oral, dermal, inhalation). It is expressed as a weight of substance per unit 

weight of animal, e.g., mg/kg. 

LOC Level of Concern 

LOAEL Lowest Observed Adverse Effect Level 

μg/g Micrograms Per Gram 

μg/L Micrograms Per Liter 

mg/kg/day Milligram Per Kilogram Per Day 

mg/L Milligrams Per Liter 

MOE Margin of Exposure 

MRID Master Record Identification (number). EPA's system of recording and tracking 

submitted studies. 

MUP Manufacturing-Use Product 

NA Not Applicable 

NAWQA USGS National Ambient Water Quality Assessment 

NPDES National Pollutant Discharge Elimination System 

NR Not Required 

NOAEL No Observed Adverse Effect Level 

OPP EPA Office of Pesticide Programs 

OPPTS EPA Office of Prevention, Pesticides and Toxic Substances 

PAD Population Adjusted Dose 

PAIRA Pure Active Ingredient Radiolabelled 

PCA Percent Crop Area 

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PDP USDA Pesticide Data Program 

PHED Pesticide Handler's Exposure Data 

PHI Preharvest Interval 

ppb Parts Per Billion 

PPE Personal Protective Equipment 

ppm Parts Per Million 

PRZM/EXAMS Tier II Surface Water Computer Model 

Q1* The Carcinogenic Potential of a Compound, Quantified by the EPA's Cancer 

Risk Model 

RAC Raw Agriculture Commodity 

RASSB Risk Assessment and Science Support Branch 

RED Reregistration Eligibility Decision 

REI Restricted Entry Interval 

RfD Reference Dose 

RQ Risk Quotient 

SCI-GROW Tier I Ground Water Computer Model 

SAP Science Advisory Panel 

SF Safety Factor 

SLN Special Local Need (Registrations Under Section 24©) of FIFRA) 

TGAI Technical Grade Active Ingredient 

TEP Typical End-Use Product 

USDA United States Department of Agriculture 

UF Uncertainty Factor 

WPS Worker Protection Standard