Page 2 of 22

I. EXECUTIVE SUMMARY

The Antimicrobials Division (AD) has evaluated the proposed use of the new 

active ingredient 2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine (i.e. 

terbutryn) as an industrial microbiocide. Terbutryn was previously registered as a 

herbicide on February 1987, but these registrations were later canceled after a FIFRA 

1988 data call in was issued. No terbutryn reregistration eligibility decision (RED) 

document was issued. 

Troy Corporation has initiated the request for new active ingredient registrations 

of terbutryn as a material preservative. Terbutryn is a solid at room temperature and as a 

result the compound is not expected to volatilize. Terbutryn has an estimated vapor 

pressure of 0.000225 Pa at 25 °C (1.68 x 10-6 mm Hg) (MRID 47810507). Terbutryn 

Technical (5383-RGI) is used to formulate three industrial use products Troysan® 

Terbutec (5383-RGO), Polyphase® 710S (5383-RUN), and Troysan®V662 (5383-TBD). 

The new proposed labels indicate that terbutryn is to be used as an industrial 

microbiocide for the preservation of paints, coatings, caulks, adhesives and similar 

materials. EPA will examine exposure to occupational workers and residential handlers 

of products preserved with terbutryn. 

EPA will assess exposure to occupational workers while mixing/loading liquid 

and wettable powder pesticide products used to preserve joint cements, coatings, paints, 

sealants, and stuccos. EPA has historically used exposure to latex paint as a surrogate or 

a reasonable worst case screening estimate for exposures to other preserved products such 

as joint cements, coatings, sealants, and stuccos. EPA has determined that there is a 

potential for short-term (ST) [defined as 1-30 days] and intermediate-term (IT) [defined 

as 1 to 6 months] occupational and ST residential handler exposures to latex paints. EPA

has not developed a post-application inhalation exposure scenario for the use of paints 

because terbutryn is not expected to volatilize. In addition, a dermal post-application 

exposure assessment to paint was not conducted because paint will dry soon after 

application. This assessment uses toxicological endpoints developed from a recent EPA

toxicology memorandum for terbutryn (U.S. EPA, 2013a).

Conclusions

• Occupational applicator exposure was assessed using the highest labeled rate of 

0.11% active ingredient (a.i.). The dermal margin of exposure (MOEs) for the 

brush/roller and airless sprayer are not of concern (calculated dermal MOEs are more

than the target MOE of 100). The short-term residential applicator dermal risks are 

not of concern for all residential handler scenarios for painting using a brush/roller 

and the airless sprayer using the highest labeled application rate of 0.11% a.i. 
Page 3 of 22

• Since the inhalation toxicological endpoint is based on an oral no-observable-adverseeffect level (NOAEL), an extra 10X uncertainty factor (UF) is applied to account for 

extrapolation from the oral route to the inhalation route. The inhalation MOEs do not 

exceed the level of concern (e.g., calculated MOEs are greater than the target MOE of 

1,000) for occupational and residential exposures.

• Occupational workers during the manufacturing process of mixing and loading

terbutryn preservatives into joint cements, coatings, sealants, and stuccos were 

assessed. Risks are not expected to be exceeded 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.

• The NOAEL used for the dermal risk assessment is based on an oral study; the 

calculated dermal exposures were adjusted for dermal absorption of 35%. 

II. BACKGROUND

A. Action Requested

The Agency developed an assessment based on the new proposed uses and

calculated the short- and intermediate risks to occupational and residential exposures to 

terbutryn antimicrobial products.

B. Use Profile

Table 1 presents the chemical identity of terbutryn. According to the information 

available terbutryn is a powder, is not particularly soluble in water (22 mg/L), and has a 

melting point of 104oC. Terbutryn is a solid at room temperature and is not expected to 

volatilize. 

Table 1. Chemical Identity

Common Name Terbutryn

Chemical name 2-(tert-butylamino)-4-(ethylanino)-6-

(methylthio)-s-triazine

PC Code 080813

CAS registry 

number

886-50-0

Case No. None
Page 4 of 22

Table 1. Chemical Identity

Structure

Empirical 

Formula

C10H19N5S1

Table 2 presents the antimicrobial use sites of three industrial end-use products: 

Troysan® Terbutec (5383-RGO), Polyphase® 710S (5383-RUN), and Troysan ® V662 

(5383-TBD). The proposed antimicrobial labeled uses for these products are as a material 

preservative for joint cements, coatings, sealants, and stuccos. 

 

Table 2: Proposed Antimicrobial Use Sites for Terbutryn*

Use Site Product/Formulation

Application 

Rate

(% product)

Application 

Rate 

(% ai by 

weight)

Joint cements

Troysan® Terbutec

(powder)

99% a.i.

0.03-0.10 0.03-0.10

Polyphase® 710S

(liquid)

14% a.i.

0.5-1.5 0.05-0.12

Troysan ®V662

(liquid)

48% a.i.

0.05-0.2 0.04-0.11

Coatings

Troysan® Terbutec

(powder)

99% a.i.

0.02-0.10 0.02-0.10

Polyphase® 710S

(Liquid)

14% a.i.

0.5-1.4 0.04-0.11

Troysan ®V662

(liquid)

48% a.i.

0.05-0.2 0.04-0.11

Sealants

Troysan® Terbutec

(powder)

99% a.i.

0.02-0.10 0.02-0.10
Page 5 of 22

Table 2: Proposed Antimicrobial Use Sites for Terbutryn*

Use Site Product/Formulation

Application 

Rate

(% product)

Application 

Rate 

(% ai by 

weight)

Polyphase® 710S

(Liquid)

14% a.i.

0.5-1.5 0.04-0.11

Troysan® V662

(Liquid)

48% a.i.

0.05-0.2 0.096-0.24

Stuccos

Troysan® Terbutec

(powder)

99% a.i.

0.02-0.10 0.02-0.10

Polyphase® 710S

(Liquid)

14% a.i.

0.5-1.5 0.04-0.11

Troysan® V662

(Liquid)

48% a.i.

0.05-0.2 0.04-0.11

* Based on proposed labels dated 1/16/12

C. Criteria for Conducting Exposure Assessments 

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

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

exposure to handlers (mixers, loaders, applicators) during use or to persons entering 

treated sites or exposed to vapors after application is complete. Dermal and inhalation 

toxicological endpoints are needed to assess short-, and intermediate-term worker 

exposures. There is a potential for applicator exposures to in-can preservatives in paints 

in occupational and residential settings. In addition, an occupational worker may become 

exposed while mixing/loading active ingredients when formulating preservatives for joint 

cements, coatings, sealants, and stuccos products.

In this document, representative scenarios were assessed by using unit exposure

data to estimate occupational and residential handlers’ exposures. Unit exposures are 

estimates of the amount of exposure to an active ingredient a handler receives while 

performing various handler tasks and are expressed in terms of micrograms or milligrams 

(1 mg = 1,000 μg) of active ingredient per pounds of product handled. A series of unit 

exposures have been developed that are unique for each scenario typically considered in 

assessments (i.e., there are different unit exposures for different types of application 

equipment, job functions, and levels of protection). Appendix A provides the 

calculations for unit exposure, exposure, and MOEs.
Page 6 of 22

D. Review of Human Research 

This risk assessment relies in part on data from studies in which adult human 

subjects were intentionally exposed to a pesticide or other chemical. These studies, 

which comprise the Pesticide Handlers Exposure Database (PHED) and the Chemical 

Manufacturers Association (CMA) database have already had ethical reviews and can be 

used in risk assessments.

III. SUMMARY OF HAZARD CONCERNS FOR TERBUTRYN

The Agency has reviewed all toxicity studies submitted for terbutryn in the

Agency hazard assessment memorandum (U.S. EPA, 2013a). Table 3 summarizes the 

applicable toxicological doses and endpoints used for this occupational and residential 

assessment. More detail description is provided in the hazard assessment memorandum.

Since the dermal No Observed Adverse Effect Level (NOAEL) was selected 

based on results of oral studies, calculated dermal exposures were adjusted for a dermal 

absorption value of 35% (MRID 00157844). The oral NOAEL was also selected for the 

inhalation route. Therefore, a 10X uncertainty factor has been included for the inhalation 

route based on the lack of an inhalation specific toxicity study. The body weight used for 

both the dermal and inhalation assessment is 80 kg based on the Exposure Factors 

Handbook (U.S. EPA, 2011). 

On December 23, 1987, the Agency presented the study results of previously 

submitted terbutryn chronic toxicity/carcinogenicity studies to the FIFRA Scientific 

Advisory Panel (SAP). The SAP concluded that “tumors were induced at multiple sites

only at the highest dose, which exceeded a maximum tolerated dose (MTD). Good doseresponse data were not available due to the large spread between doses. Therefore the 

SAP assigned terbutryn as an interim category C (a possible human carcinogen), but also 

decided to reduce the assigned category to a category D if negative data from more 

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.”

In 2011, the agency reviewed a newly submitted 2-year rat carcinogenicity study 

and concluded that although, cancer was detected at the highest dose tested (600 ppm), 

the toxicological significance of pancreatic acinar adenoma results were questionable. 

The cancer effect (i) did not show a clear dose- dependency manner; (ii) the effect was 

seen in male rats only; and (iii) the control group has incidences of acinar adenoma

(21%) that are higher than the historical control incidences (2-14%) (U.S. EPA 2012a).

For all dermal and inhalation exposure scenarios, uncertainty factors (UF) of 10x 

for interspecies extrapolation and 10x for intraspecies variation (total UF of 100x) were 

used. The level of concern (LOC) for occupational and residential dermal and inhalation 

risks is for margins of exposure (MOEs) less than 100. In addition, an extra 10X 

database uncertainty factor for route to route extrapolation was applied to the existing 

inhalation LOC since it is based on the 90-day oral toxicity study. 
Page 7 of 22

Table 3. Summary of Toxicological Doses and Endpoints for Terbutryn

Exposure

Scenario

Dose Used in Risk 

Assessment, UF 

Special Level of 

Concern for Risk 

Assessment

Study and Toxicological Effects

Short (1-30 days) 

Incidental Oral 

NOAEL=10 

mg/kg/day

Residential/

Occupational MOE = 

100

(10x for inter species 

variation, and 10X for 

intra-species variation)

Rabbit Developmental Study

(MRID# 000152763)

LOAEL = 50 mg/kg/day 

based upon decreased food 

consumption, increased food index, 

decreased body weight gain and stool 

changes in rabbits at 50 mg/kg

Intermediate -Term 

(1-6 Months) 

Incidental Oral 

NOAEL=10 

mg/kg/day

Residential/

Occupational MOE = 

100

(10x for inter species 

variation, and 10X for 

intra-species variation)

6-month dog study (MRID 

00029152)

LOAEL = 25 mg/kg/day (based on 

mucosal thickening of various 

segments of the small intestine and 

submucosal lymphoid hyperplasia in 

the pyloric region of the stomach was 

observed) 

Relative dermal 

absorption rate 

35% (MRID 00157844)

Short (1-30 days) 

Incidental Dermal

BMDL = 18.5 

mg/kg/day

Residential/

Occupational MOE = 

100

(10x for inter species 

variation, and 10X for 

intra-species variation)

90-day Oral Toxicity Study in Rats

(MRID# 47810501)

LOAEL = 70 mg/kg/day 

based upon decreased body weight 

and body weight gain. 

Intermediate –Term 

(1-6 Months) 

Incidental Dermal

BMDL = 18.5 

mg/kg/day

Residential/

Occupational MOE = 

100

(10x for inter species 

variation, and 10X for 

intra-species variation)

90-Day Oral Toxicity Study in Rats

(MRID 47810501)

LOAEL = 70 mg/kg/day based on 

decreased body weight and body 

weight gain. 

Short , Intermediate, 

Long -Term 

Inhalation

BMDL = 18.5 

mg/kg/day

Residential/

Occupational MOE = 

1000

(10x for inter species 

variation, 10X for intraspecies variation and 

10X database 

uncertainty for route to 

route extrapolation)

same as for dermal exposure above. 

Cancer (oral, dermal, 

inhalation)

Group C carcinogen; quantitative risk assessment is not needed.
Page 8 of 22

IV. OCCUPATIONAL EXPOSURES AND RISKS

For terbutryn, potential occupational handler exposures can occur while 

mixing/loading preservatives and applying paints. Dermal and inhalation exposures are 

expected to occur for both settings.

A. Occupational Handler Exposures and Risks 

Due to the lack of product-specific/chemical-specific exposure monitoring data, 

surrogate data from the Estimates of Worker Exposure from The Pesticide Handler 

Exposure Database (PHED) Version 1.1 dated August 1998 (U.S. EPA, 1998) was used 

for unit exposures for wettable powders and the Chemical Manufacturers Association 

(CMA) antimicrobial exposure study (U.S. EPA, 1999: DP Barcode D247642) was used 

for estimating liquid pour unit exposures (UE). 

Based on use data and label instructions, the agency believes that terbutryn exposures 

may occur over a short-term (1-30 days) term or intermediate-term (1-6 month) exposure. 

The risk assessment (see Table 4) developed for occupational handlers are based on 

mixer/loader and applicator exposures.

a. Mixer/loaders 

Worker exposure may occur while mixing dust/powder or liquid formulation by 

scenarios: open pour of wettable powders or liquid pour to preserve joint cements, 

coatings (e.g., paints), sealants, and stuccos. The term “open pour” refers to the 

resulting worker exposure from physically transferring a dust/powder or liquid from a 

drum into the material preservative slurry by pouring from large containers (often drums) 

to smaller containers. Worker exposure from transferring the preservative by connecting/ 

disconnecting a chemical metering pump from a tote or by gravity flow is often known as 

the “liquid pump” scenario. The agency identified the following mixer/loader scenarios:

• Exposure while mixing/loading wettable powder products used to preserve joint 

cements, coatings (e.g., paints), sealants, and stuccos (wettable powder unit 

exposure data was used as surrogate data for the dust/powder formulation); and

• Exposure while mixing/loading liquid products used to preserve joint cements, 

coatings (e.g., paints), sealants, and stuccos.

Use of a liquid pump and water soluble packaging of wettable powders are examples of 

engineering controls which are intended to limit and minimize mixer/loader exposure.

b. Applicators 

An applicator is a worker applying the treated material. The Agency derived 

anticipated use patterns from current labels and based our decisions on the types of 

equipment and techniques used antimicrobial applications. The Agency identified the 

following mixer/loader scenarios:
Page 9 of 22

• Application of preserved coatings (which are represented through the use 

of latex paint) by professionals (brush/roller); and

• Application of preserved coatings (which are represented through the used 

of latex paint) by professionals (airless sprayer).

c. Data and Assumptions for Handler Exposure Scenarios 

A series of assumptions and exposure factors served as the basis for completing 

the occupational handler risk assessments. The assumptions and factors used in the risk 

calculations include: 

• MOEs were calculated for the short- and intermediate-term duration for dermal 

and inhalation exposures using the appropriate endpoints in Table 4.

• Since the short- and intermediate-term dermal endpoints are based on oral studies,

a dermal absorption factor of 35% was used to adjust the oral endpoint value to 

estimate dermal exposure for short- and intermediate-term durations (Health 

Effects Division policy document, 2010: Interim Guidance: Estimating Dermal 

Absorption Factors for Use in Human Health Risk Assessments). Since the shortand intermediate-term inhalation endpoints are based on oral studies and no 

inhalation absorption data are available, toxicity by the inhalation route is 

considered to be equivalent to that by the oral route. 

• In October 2011, Exposure Factors Handbook updated the recommended body 

weight to 80 kg (U.S. EPA, 2011). The agency used the updated body weight of 

80 kg for this assessment.

• For non-cancer assessments, the agency traditionally assumes the maximum 

application rates allowed by labels in its risk assessments (see Table 2).

• The average occupational workday is assumed to be 8 hours.

• For the occupational assessment, the dermal and inhalation unit exposure values 

were taken from the Pesticide Handler Exposure Database (U.S. EPA, 1998). The 

specific unit exposures used in this assessment are described in the bulleted list 

below.

i. Mixer/loaders 

 For open mixing/loading of wettable powders, the occupational PHED 

dermal and inhalation unit exposure values were used (PHED scenario 

4). The wettable powder unit exposure data were used as surrogate 

data for the dust/powder formulation. The dermal UEs for workers 

wearing long-sleeve shirt and long pants or full coveralls are 0.17 

mg/lb a.i. with gloves and 3.7 mg/lb a.i. without gloves. The inhalation 
Page 10 of 22

UE is 0.043 mg/lb a.i. for baseline (no respirator) and 0.0043 mg/lb a.i.

for a half- or full-face respirator (providing a 90% protection factor).

 For liquid pour (open mixing/loading), the CMA dermal and 

inhalation unit exposure values for were used. The dermal UE for 

workers wearing long-sleeve shirt and long pants or full coveralls and 

gloves is 0.135 mg/lb a.i and the inhalation UE for baseline (no 

respirator) is 0.00346 mg/lb a.i. There is no CMA ungloved dermal 

UE for the liquid pour preservatives scenario; a dermal UE of 50.3 

mg/lb a.i. was used for workers not wearing gloves, taken from the 

CMA liquid pour cooling tower scenario. 

ii. Applicators

For in-can preservative products such as paint, applied by a 

professional painter, the agency used the UEs from the PHED surrogate 

table (1998) assuming that the painter wears long pants, long sleeves, and

no gloves for brush/roller and airless sprayer application methods (note: 

aerosol cans are not commonly assessed unless they are specified on the 

label). Gloves or respirators are not a viable mitigation option for in-can 

preservative products such as paints because it is not feasible to label these 

types of end-use products with the biocide information.

 For roller/brush scenarios, the occupational PHED dermal and 

inhalation unit exposure values for paintbrush applications (PHED 

scenario 22) were used (single layer of clothing). The dermal UE

representing a single layer of clothing is 180 mg/lb a.i. for ungloved 

replicates. The inhalation UE is 0.28 mg/lb a.i. 

 For airless sprayer scenarios, the occupational PHED dermal and 

inhalation unit exposure values for airless sprayer application (PHED 

scenario 23) were used. The dermal UEs representing a single layer of 

clothing is 38 mg/lb a.i. for ungloved replicates. The inhalation UE is 

0.83 mg/lb a.i.

• There are three basic risk mitigation approaches considered appropriate for 

controlling occupational exposure. These include administrative controls, use of 

personal protective equipment (PPE), and the use of engineering controls. 

Occupational handler exposure assessments were completed by the agency using 

baseline, and PPE.

• The baseline clothing level for occupational exposure scenarios is generally an 

individual wearing long pants, a long-sleeved shirt, shoes, socks, no chemicalresistant gloves, and no respirator. The first level of mitigation generally applied 

is PPE, which may include addition of chemical resistant-gloves, an additional 
Page 11 of 22

layer of clothing, and/or a respirator. Mitigation was achieved using PPE; 

engineering controls was not necessary. 

The quantity handled/treated values were estimated based on information from 

various sources. The following assumptions were made:

 For the open pour/liquid pour mixing/loading scenarios to support 

the preservation of joint cements, coatings (e.g., paints), sealants, and 

stuccos: 20,000 lbs (approximately 2,000 gallons, where material 

density is 10 lb/gal) (AD assumption).

 For the roller/brush painting scenario, it was assumed that 50 lbs 

(approximately 5 gallons of paint with a density of 10 lb/gal) of treated 

paint are used (AD assumption).

 For the airless sprayer painting scenario, it was assumed that 500 lbs 

(approximately 50 gallons of paint with a density of 10 lb/gal) of 

treated paint are used (AD assumption).

d. Exposure Calculations and Results

For all dermal exposure scenarios, uncertainty factors of 10x for interspecies 

extrapolation and 10x for intraspecies variation (total UF of 100x) were used. Dermal 

occupational exposure and risk resulting in MOEs greater than or equal to 100 will not 

exceed the agency’s level of concern. Inhalation occupational exposure and risk resulting 

in MOEs greater than or equal to 1,000 will not exceed the agency’s level of concern. 

Summaries of the risks for occupational handlers are included in Table 4. 

Dermal

The short- and intermediate-term dermal risks exceed the agency’s level of 

concern only for baseline attire (i.e., long-sleeve shirt, long pants, shoes, socks, and no 

gloves) for the mixer/loader occupational handler scenarios with both wettable powder 

(dermal MOE 58) and liquid formulations (dermal MOE 4). With the addition of 

chemical resistant gloves for the mixing/loading scenarios, the short- and intermediateterm dermal risks are > 100 and are thus not of concern. The baseline dermal MOEs 

(ungloved) are 420 for the brush/roller scenario and 190 for airless sprayer applicator 

scenario and are thus not of concern.

Inhalation

The short- and intermediate-term inhalation risks do not exceed the agency’s level 

of concern at baseline (no respirator) for any of the occupational handler scenarios (target 

MOE of 1,000). 
Page 12 of 22

Aggregate Risk Index (ARI) Method: 

The ARI was devised as a way to aggregate MOEs that have dissimilar UF’s. 

MOEs for each route of concern are compared against UF’s which reflect the nature, 

source, and quality of the data, and the FQPA mandate to protect susceptible infants and 

children. The ARI method automatically considers each route’s potency when routespecific NOAELs are used. If the MOE/UF ratios for each route of exposure are treated 

as fractions, they can be adjusted to a common denominator of 1. The ARI is then 

calculated as follows: 

ARI= 1[1/(UF/MOEinhalation )+ 1/(UF/MOEdermal)]

The ARI is always compared against 1. This allows for direct comparisons 

between routes and between chemicals. As a general rule, an ARI greater than or equal to 

1 is of little concern, but an ARI less than 1 suggests a risk of concern. 

The short- and intermediate-term ARIs exceed the agency’s level of concern only 

for baseline attire (i.e., long-sleeve shirt, long pants, shoes, socks, and no gloves) for the 

mixer/loader occupational handler scenarios with both wettable powder (ARI 0.43) and 

liquid formulations (ARI 0.04). With the addition of chemical resistant gloves for the 

mixing/loading scenarios, the short- and intermediate-term dermal risks do not exceed the 

agency’s level of concern (e.g., ARI>1). 

B. Occupational Postapplication Exposures and Risks

Dermal and inhalation exposures are expected to occur to bystanders as a result of 

material preservative applications in industrial settings. Currently, no data are available 

to assess this scenario; however, exposures are expected to be less than handler exposure. 

Terbutryn is a solid at room temperature and as a result the compound is not expected to 

volatilize since its vapor pressure is 1.68E-6 mm Hg (U.S. EPA 2013b). 
Page 13 of 22

Table 4. Short and Intermediate Term Risks Associated with Occupational Handlers using Terbutryn

Exposure 

Scenario

Method of 

Application

Unit Exposure

(mg/lb a.i.)

App. 

Rate

Quantity 

Handled/ 

Treated per 

day

Absorbed Daily Dose 

(mg/kg/day)d MOEse Total ARI(LOC = ARI <1)

Dermal Inhalation Dermal Inhalation

Dermal 

(LOC = MOE 

<100)

Inhalation 

(LOC = MOE 

<1000) Baseline 

Dermal + 

Inhalation

PPEGloves 

Dermal + 

Inhalation

PPE-Gloves 

Dermal + 

PF10 Resp.

Inhalation Baseline a

PPEGloves bBaseline aPF10

Resp. c

Baseline a

PPEGloves b

Baseline aPF10 

resp. c

Baseline a

PPEGloves b

Baseline a

PF10 

Resp. c

Mixing/Loading 

Preservation of 

Joint Cements, 

Coatings (e.g. 

paints), Sealants, 

and Stuccos

Open Pour 

Wettable 

Powder 

(PHED)

3.7 0.17 0.043 0.0043

0.1% ai 

by 

weight

20,000 lbs 0.32 0.015 0.011 0.0011 58 1300 1700 N/A 0.43 1.5 N/A

Liquid Pour

(CMA) 50.3 0.135 0.00346 N/A

0.11% 

ai by 

weight

20,000 lbs 4.9 0.013 9.7E-4 N/A 4 1400 19,000 N/A 0.04 8.1 N/A

Applicators 

Application of 

Paint by 

Professionals

Brush/Roller 

(PHED) 180 N/A 0.28 N/A 0.11% 

ai by 

weight

50 lb 0.044 N/A 0.0002 N/A 420 N/A 94,000 N/A 4 N/A N/A

Airless Sprayer

(PHED) 38 N/A 0.83 N/A 500 lb 0.093 N/A 0.0058 N/A 190 N/A 3200 N/A 2 N/A N/A

N/A= Not applicable. Bold = MOE exceeds the Agency’s level of concern.

a Baseline Dermal: Long-sleeve shirt, long pants, no gloves. Baseline Inhalation: No respirator.

b PPE Dermal with gloves: baseline dermal plus chemical-resistant gloves.

c PF10 Elastomeric half face respirator with appropriate cartridges and/or filters. Confirmatory inhalation study required for inhalation MOEs <100.

d Absorbed Daily dose (mg/kg/day) = [unit exposure (mg/lb ai) * absorption (1.0 for ST/IT inhalation and 0.35 for ST/IT dermal) * application rate * quantity treated / Body weight (80 kg).

e MOE = NOAEL (mg/kg/day) / Absorbed Daily Dose [Where ST/IT NOAEL = 18.5 mg/kg/day for dermal and inhalation exposures]. 

f Total MOE =1 / [1/(Dermal UF) + (1/(Inhalation UF)]. The dermal UF=100 and the inhalation UF=1,000.
14 of 22

V. RESIDENTIAL EXPOSURES AND RISKS

Based on the use patterns on the labels, the EPA has determined potential 

residential handler exposures are a result of secondary handler dermal and inhalation 

exposure from applying joint cement, coating (e.g., paints), sealant, and stucco treated 

with terbutryn.

A. Residential Handler Exposures and Risks

The representative residential handler scenarios assessed were the application of

in-can preservative products such as paint, using a brush/rollers and airless sprayers

(described in Table 5). The application of paint was assessed using PHED data and 

equations outlined in Appendix A. 

1. Data and Assumptions for Handler Exposure Scenarios 

The assumptions and factors used for residential painter scenarios include:

Unit Exposure Values: Unit exposure values were taken from the PHED data presented 

in HED’s Residential SOPs (U.S. EPA, 2012b). 

• For the airless sprayer scenario,

Dermal Unit Exposure Data Summary: 

The recommended dermal unit exposures for applications of pesticide-containing 

paints or stains using an airless sprayer is based on a lognormal distribution fit 

with exposure monitoring data from PHED . PHED monitored 15 applications of 

approximately 5 gallons of pesticide-containing stain with an airless sprayer. 

While another study was available that was also reasonably representative of 

residential applications, PHED employed exposure monitoring methods that best 

represented the type of clothing a homeowner or amateur applicator would wear 

(i.e., shorts, short-sleeve shirt, no chemical-resistant gloves).

Inhalation Unit Exposure Data Summary: 

The recommended inhalation unit exposures for applications of pesticidecontaining paints or stains using an airless sprayer is based on a lognormal 

distribution fit with exposure monitoring data from Formella, T. (1995) [EPA 

MRID 43600102] and PHED. Formella, T. (1995) monitored 36 applications of 

approximately 5 gallons of pesticide-containing paint inside and outside houses 

for approximately 22-81 minutes using an airless sprayer. PHED monitored 15 

applications of approximately 5 gallons of pesticide-containing stain with an 

airless sprayer. Both studies were reasonably representative of residential 

applications with inhalation exposures of the same general magnitude, thus a 

composite data set was utilized. 
15 of 22

• For the brush scenario,

Dermal Unit Exposure Data Summary:

The recommended dermal unit exposures for applications of pesticide-containing 

paints or stains using a brush is based on a lognormal distribution fit with 

exposure monitoring data from PHED. PHED monitored 15 applications of 

approximately 1 gallon of pesticide-containing paint to an interior bathroom for

approximately 34-94 minutes with 2- or 4-inch brushes. This was the only 

available study for this exposure scenario.

Inhalation Unit Exposure Data Summary: 

The recommended inhalation unit exposures for applications of pesticidecontaining paints or stains using a brush is based on a lognormal distribution fit 

with exposure monitoring data from PHED. PHED monitored 15 applications of 

approximately 1 gallon of pesticide-containing paint to an interior bathroom for

approximately 34-94 minutes with 2- or 4-inch brushes. 

Quantity handled/treated: The quantities handled/treated were estimated based on 

information from various sources and assumptions.

• For the airless sprayer in paint applications, it is assumed that 150 lbs 

(approximately 15 gallons) of treated paint will be used. This is based on the 

coverage of 200 ft2

/gallon and a house size of 40 x 30 x 20 ft (surface area of 

2,800 ft2)(U.S. EPA, 2012b).

• For the brush/roller in paint applications, it is assumed that 20 lbs 

(approximately 2 gallons) of treated paint will be used. This is based on the 90th

percentile value of 8 gallons of latex paint used per year divided by the mean 

frequency of 4 painting events/year (U.S. EPA, 2011, 2012b). 

Duration of Exposure: The duration of exposure for most homeowner applications of 

paint products is believed to be best represented by the short-term duration (1 to 30 days). 

The reason that short term duration was chosen is because the different scenarios (i.e. 

methods of application) are assumed to be episodic, not daily. In addition, homeowners 

are assumed to use different paint products with varying actives, not exclusively 

terbutryn treated products (U.S. EPA, 2011).

2. Exposure Calculations and Results

The resulting short-term exposures and MOEs for the representative residential 

handler scenarios are presented in Table 5. 

Dermal
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The short-term dermal risks do not exceed AD’s level of concern for all 

residential handler scenarios. 

Inhalation

The short-term inhalation risks do not exceed AD’s level of concern for all of the 

residential handler scenarios.

Aggregate Risk Index (ARI) Method: 

The ARI was devised as a way to aggregate MOEs that have dissimilar UF’s. 

MOEs for each route of concern are compared against UF’s which reflect the nature, 

source, and quality of the data, and the FQPA mandate to protect susceptible infants and 

children. The ARI method automatically considers each route’s potency when routespecific NOAELs are used. If the MOE/UF ratios for each route of exposure are treated 

as fractions, they can be adjusted to a common denominator of 1. An ARI less than 1 

indicates a risk concern. The ARI is then calculated as follows: 

ARI= 1[1/(UF/MOEinhalation )+ 1/(UF/MOEdermal)]

The short-term ARIs do not exceed the agency’s level of concern for all of the 

residential handler scenarios. 

Table 5. Short-Term Terbutryn Residential Handlers Exposures, MOEs, and ARIs

Exposure 

Scenario

Method of 

Application

Unit Exposure

(mg/lb ai)

Application 

Rate

Quantity 

Handled/ 

Treated 

per day

Absorbed Daily Doseb

(mg/kg/day) MOEc Aggregate Risk Index (ARI)

(LOC<1)

Dermala Inhalati

on Dermal Inhalation

Dermal 

(LOC = 

MOE <100)

Inhalation 

(LOC = 

MOE 

<1000)

Painting

Brush/roller 450 0.2 0.11% ai by 

weight

20 lbs

(2 gal) 0.043 5.5E-5 430 4.4E+5 4.2

Airless 

sprayer

160 0.56 0.11% ai by 

weight

150 lbs 

(15 gal) 0.12 0.0012 160 1.6E+4 1.5

Bold = MOE exceeds the Agency’s level of concern. 

Revised based on latest HED residential SOPs (February 2012)

a All dermal unit exposures represent ungloved replicates. The brush/roller and airless sprayer unit exposures 

represent short sleeve and short pant replicates. 

b Absorbed Daily dose (mg/kg/day) = [unit exposure (mg/lb ai) * absorption (1.0 for ST inhalation and 0.35 for 

ST dermal) * application rate * quantity treated / Body weight (80 kg).

c MOE = NOAEL (mg/kg/day) / Absorbed Daily Dose [Where ST NOAEL = 10 mg/kg/day for dermal and 

inhalation exposures]. 

RI= UF/MOE, ARI=1/[(1/UF/MOE dermal+1/UF/MOE inhale)]
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B. Residential Post-application Exposures and Risks

Postapplication/bystander inhalation exposures for use of paints (vapor exposure 

to adults and children) were not assessed because terbutryn is a solid at room temperature 

and therefore is not expected to volatilize since its vapor pressure is 1.68E-6 mm Hg (US 

EPA 2013b). 

VI. NON-DIETARY AGGREGATE EXPOSURE

An aggregate risk assessment considers food uses, drinking water and residential 

exposures. There are no registered food uses. For both children and adults, because the 

adverse effects in the studies used for dermal and inhalation endpoints (decreased body 

weight and body weight gain) and utilized for the residential risk assessment are different 

than the effects in the chronic study (decreased hemoglobin and erythrocytes) used in the 

chronic drinking water assessment, aggregation of chronic drinking water and residential 

risks is not appropriate.

The only risks that need to be aggregated would be residential applicator 

exposures. The Agency combined short-term residential risks for dermal and inhalation 

applicator exposures because the toxicological effects were the same for both the dermal 

and inhalation routes. Residential applicator were aggregated for both dermal and 

inhalation exposures and are represented by ARIs and do not exceed the Agency’s level 

of concern. 

VII. RISK CONCLUSIONS

• Exposure to commercial painters was assessed using the highest labeled rate of 0.11% 

active ingredient (a.i.). The calculated dermal margins of exposure (MOEs) for the 

brush/roller and airless sprayer scenario (420 and 190 respectively) were higher than 

the level of concern (100) and are therefore not of concern. 

• Residential risks for the residential painter applying in-can preservatives in paint were 

not of concern. The short-term residential applicator dermal risks are not of concern

for all residential handler scenarios for painting using a brush/roller and the airless 

sprayer using the highest labeled application rate of 0.11% a.i. 

• Since the inhalation toxicological endpoint is based on an oral no-observable-adverseeffect level (NOAEL), an extra 10X database uncertainty factor (UF) is applied to 

account for extrapolation from the oral route to the inhalation route. Calculated 

inhalation MOEs for occupational handlers were in excess of the target MOE of 1000 

and thus are not of concern.
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• Occupational exposures to workers during the manufacturing process of mixing and 

loading terbutryn into joint cements, coatings (e.g., paints), sealants, and stuccos were 

assessed. Risks 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. 

VIII. REFERENCE

USEPA, 1997. Exposure Factors Handbook. Volume I-II. Office of Research and 

Development. Washington, D.C. EPA/600/P-95/002Fa.

USEPA. 1998. PHED Surrogate Exposure Guide. Estimates of Worker Exposure from 

the Pesticide Handler Exposure Database Version 1.1. Washington, DC: U.S. 

Environmental Protection Agency.

USEPA, 2000. Residential SOPs. EPA Office of Pesticide Programs Human Health 

Effects Division. Dated April 5, 2000.

U.S. EPA, 2011. Exposure Factors Handbook. EPA/600/R-10/030. October 2011. 

www.epa.gov/ncea.

U.S. EPA, 2012a. Memorandum from Jonathan Chen. Subject: Terbutryn: Evaluation of 

the Rat Combined Chronic Toxicity/Carcinogenicity Study – “Fankhauser, H. (2001) 24-

Month carcinogenicity and chronic toxicity study in rats. Syngenta Crop Protection AG, 

Stein, Switzerland. Laboratory Study No.: 951040, May 8, 2001. MRID 48348901. 

Unpublished.” DP Barcode: D386095.

USEPA, 2012b. Standard Operating Procedures for Residential Pesticide Exposure 

Assessment. Health Effects Division. Office of Pesticide Programs. 

http://www.epa.gov/pesticides/science/residential-exposure-sop.html#datacomp

January 2012.

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

Assessment for the Proposed Uses as a Material Preservative. Memorandum from 

Jonathan Chen, PhD., Toxicologist to Stacey Grigsby, Product Manager. DP Barcode: 

D407711.

U.S. EPA 2013b. Memorandum: Review for 5383-RGI. Memorandum from Chris Jiang, 

Chemist to Jacqueline Campbell-McFarlane PM 34/Stacey Grigsby, DP Barcode: 

D367948.
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APPENDIX A

UNIT EXPOSURES
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Using surrogate unit exposure data, maximum application rates from labels, and 

EPA estimates of daily amount handled, exposures and risks to handlers were assessed. 

The exposure/risks were calculated using the following equations:

AD uses unit exposure to assess handler exposures to pesticides. Unit exposures 

are estimates of the amount of exposure to an active ingredient a handler receives while 

performing various handler tasks and are expressed in terms of micrograms or milligrams 

of active ingredient per pounds of active ingredient handled. AD has developed a series 

of unit exposures that are unique for each scenario typically considered in our 

assessments (i.e., there are different unit exposures for different types of application 

equipment, job functions, and levels of protection). The unit exposure concept has been 

established in the scientific literature and also through various exposure monitoring 

guidelines published by the U.S. EPA and international organizations such as Health 

Canada and OECD (Organization for Economic Cooperation and Development).

Once the data for a given exposure scenario have been selected, the data are 

normalized (i.e., divided by) by the amount of pesticide handled resulting in standard unit 

exposures (milligrams of exposure per pound of active ingredient handled). Following 

normalization, the data are statistically summarized. The distribution of exposure for 

each body part (e.g., chest, upper arm) is categorized as normal, lognormal, or “other” 

(i.e., neither normal nor lognormal). A central tendency value is then selected from the 

distribution of the exposure for each body part. These values are the arithmetic mean for 

normal distributions, the geometric mean for lognormal distributions, and the median for 

all “other” distributions. Once selected, the central tendency values for each body part 

are composited into a “best fit” exposure value representing the entire body. 

1. Daily Exposure

Daily dermal or inhalation handler exposures are estimated for each applicable 

handler task with the application rate, quantity treated/handled in a day, and the 

applicable dermal or inhalation unit exposure using the following formula:

Daily Exposure: E = UE x AR x AT (Eq. 1)

Where: 

E = Amount (mg or μg ai/day) deposited on the surface of the skin that is available for dermal 

absorption or amount inhaled that is available for inhalation absorption;

UE = Unit exposure value (mg ai/lb ai) derived from August 1998 PHED data or from CMA 

1999 data;

AR = Maximum application rate based on a logical unit treatment, such as acres (A), square 

feet (sq. ft.), gallons (gal), or cubic feet (cu. ft). Maximum values are generally used (lb 

ai/A, lb ai/sq ft, lb ai/gal, lb ai/cu ft); and

AT = Normalized application area based on a logical unit treatment such as acres (A/day), 

square feet (sq ft/day), gallons (gal/day), or cubic feet (cu ft/day).

2. Daily Dose

The daily dermal or inhalation dose is calculated by normalizing the daily 

exposure by body weight and adjusting, if necessary, with an appropriate absorption 
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factor. Since the short- and intermediate-term dermal endpoints are based on oral studies 

a dermal absorption factor of 35% was used to estimate dermal exposure for short- and 

intermediate-term durations. Since the short- and intermediate-term inhalation endpoints 

are based on oral studies and no inhalation absorption data are available, toxicity by the 

inhalation route is considered to be assumed to be 100% of the oral dose. Daily dose was 

calculated using the following formula:

Daily Dose: ADD = E x ABS (Eq. 2)

 BW

Where:

ADD = Absorbed dose received from exposure to a chemical in a given scenario (mg 

active ingredient/kg body weight/day);

E = Amount (mg ai/day) deposited on the surface of the skin that is available for 

dermal absorption or amount inhaled that is available for inhalation absorption;

ABS = A measure of the amount of chemical that crosses a biological boundary such as 

lungs (% of the total available absorbed); and

BW = Body weight determined to represent the population of interest in a risk 

assessment (kg).

3. Margins of Exposure

Non-cancer inhalation and dermal risks for each applicable handler scenario are 

calculated using a Margin of Exposure (MOE), which is a ratio of the daily dose to the 

toxicological endpoint of concern.

Margins of Exposure: MOE = NOAEL or LOAEL (Eq. 3)

ADD

Where:

MOE = Margin of exposure, value used to represent risk or how close a 

chemical exposure is to being a concern (unitless);

NOAEL or LOAEL = Dose level in a toxicity study, where no observed adverse effects 

(NOAEL) or where the lowest observed adverse effects (LOAEL) 

occurred in the study; and

ADD = Average daily dose or the absorbed dose received from exposure to a 

chemical in a given scenario (mg ai/kg body weight/day).

In addition to the target MOEs that were used for the analysis, a series of 

assumptions and exposure factors served as the basis for completing the handler risk 

assessment. Each general assumption and factor for both residential and occupational 

assessments is detailed below. Assumptions specific to the use site category are listed in 

each separate section of this document. The general assumptions and factors include:

• AD has patterned this risk assessment on a series of likely representative scenarios for 

each use site that are believed by AD to represent the vast majority of terbutryn uses.

• Based on the adverse effects for female rats, the average body weight of 70 kg for 

handlers was used to complete the non-cancer risk assessment. Exposure factors used 

to calculate daily exposures to handlers were based on applicable data, if available. 
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When appropriate data were lacking, values from a scenario deemed similar were 

used.

• The maximum application rates allowed by labels were assumed.