REVISED DRAFT

Tributlytin-containing Compounds

Tributyltin oxide (TBTO)

Tributyltin benzoate (TBTB)

Tributyltin maleate (TBTM)

Occupational and Residential Exposure Assessment

Office of Pesticide Programs

Antimicrobials Division

U.S. Environmental Protection Agency

One Potomac Yard

2777 South Crystal Drive

Arlington, VA 22202-4501

Date: June 26, 2008
Page 1 of 43

TABLE OF CONTENTS

EXECUTIVE SUMMARY .................................................................................................................................... 2

1.0 INTRODUCTION................................................................................................................................... 5

1.1 Purpose ................................................................................................................................................ 5

1.2 Criteria for Conducting Exposure Assessments................................................................................... 5

1.3 Chemical Identification........................................................................................................................ 7

1.4 Physical/Chemical Properties.............................................................................................................. 7

2.0 USE INFORMATION ............................................................................................................................ 8

2.1 Formulation Types and Percent Active Ingredient ............................................................................. 8

2.2 Summary of Use Pattern and Formulations ........................................................................................ 8

3.0 SUMMARY OF TOXICITY DATA ....................................................................................................... 9

3.1 Acute Toxicity ..................................................................................................................................... 9

3.2 Summary of Toxicity Endpoints........................................................................................................ 10

4.0 RESIDENTIAL EXPOSURE ASSESSMENT ...................................................................................... 13

4.1 Summary of Registered Uses............................................................................................................. 13

4.2 Residential Exposure ......................................................................................................................... 13

4.2.1 Residential Handler Exposures ................................................................................................ 14

4.2.2 Residential Post-application Exposures ................................................................................... 16

4.2.2.1 Textiles ......................................................................................................16

4.2.2.2 Mattresses...................................................................................................19

4.2.3 Data Limitations/Uncertainties..........................................................................22

5.0 RESIDENTIAL AGGREGATE RISK ASSESSMENT AND CHARACTERIZATION ..................... 24

6.0 OCCUPATIONAL EXPOSURE ASSESSMENT ................................................................................. 24

6.1 Occupational Handler Exposures....................................................................................................... 26

6.2 Occupational Post-application Exposures.......................................................................................... 31

6.4 Data Limitations/Uncertainties.......................................................................................................... 35

7.0 REFERENCES....................................................................................................................................... 36

APPENDIX A: Summary of CMA and PHED Data ............................................................................................ 37

APPENDIX B: MCCEM Output (Fogging)..................................................................................37
Page 2 of 43

EXECUTIVE SUMMARY 

This document is the Occupational and Residential Exposure Chapter of the 

Reregistration Eligibility Decision (RED) document for the tributlytin (TBT)-containing 

compounds including tributyltin oxide (TBTO), tributyltin benzoate (TBTB), and tributyltin 

maleate (TBTM). It addresses the potential risks to humans that result from its direct use in 

occupational settings and resulting treated articles in residential settings. 

TBT is used as a bacteriostat, microbicide/microbistat, fungicide, slimicide, algaecide, 

antifoulant, virucide, disinfectant, sanitizer, miticide, and insecticide. TBT is formulated as a 

soluble concentrate. TBT concentrations in products range from 0.3 to 53 percent (i.e., 74489-1).

The product is used in the following use categories: agricultural premises, commercial/ 

institutional/industrial premises and equipment, material preservatives, industrial processes and 

water systems, antifouling coatings, and wood preservations (i.e., stains/water sealants). 

Examples of uses for TBT in these settings include its use by residential and commercial painters 

(as a wood preservative), as a material preservative incorporated into textiles, metalworking 

fluids, oilfield injection systems, laundry additive, sonar domes, and in industrial process water 

systems such as pulp and paper mills, cooling tower water (recirculating cooling towers), etc. 

The durations and routes of exposure evaluated in this assessment include short-term 

(ST), intermediate-term (IT), and/or long-term (LT) durations for the inhalation, dermal, and 

oral routes of exposure. The oral, dermal, and inhalation endpoints for all durations (ST/IT/LT 

durations) are based on the same study. The BMD10 (bench mark dose) of 0.03 mg/kg/day

(NOAEL of 0.025 mg/kg/day and LOAEL of 0.25 mg/kg/day) is used for all durations. The 

adverse effect for this endpoint is based on immunosupression. Because the toxicological 

endpoints selected for inhalation, dermal, and oral routes of exposure are not female-specific, a 

body weight of 70 kilograms is used in the assessment. EPA’s level of concern (LOC) for 

occupational and residential TBT inhalation, dermal, and oral routes of exposures is 100 (i.e., a 

margin of exposure (MOE) less than 100 exceeds the level of concern). The level of concern is 

based on 10x for interspecies extrapolation and 10x for intraspecies variation. An additional 

10x special sensitivity factor is applied to the non occupational population. 

This occupational and residential assessment was based on examination of the product 

labels that describe the uses. It has been determined that there are residential products of TBT 

that are applied directly (e.g., wood stain preservative) as well as an in-can preservative use (e.g., 

laundry additive 10466-24). Occupational handlers may be exposed in the manufacturing of 

other products (e.g., textiles), during treatment of water systems, agricultural poultry, farm 

premise applications, commercial painters, and metalworking fluids (MWF). Post-application 

exposures are likely to occur in residential settings by contacting treated articles such as clothing

or in occupational settings such as reentry into poultry/animal premises. The representative 

scenarios selected by EPA for assessment were evaluated using maximum application rates as 

stated on the product labels. The representative scenarios are believed to represent high-end uses 

resulting in dermal, inhalation, and incidental oral exposures.
Page 3 of 43

To assess the handler risks, EPA used surrogate unit exposure data from the Chemical 

Manufacturers Association (CMA) antimicrobial exposure study and the Pesticide Handlers 

Exposure Database (PHED). Post application/bystander exposures were assessed using EPA’s 

standard assumptions (e.g., Health Effects Division’s (HED) Standard Operating Procedures 

(SOPs) for Residential Exposure Assessment). 

Residential Handler Risk Summary

Dermal

The residential handler dermal exposure scenarios are best represented by the short-term 

duration (i.e., staining with a paint brush and/or airless sprayer are considered to be intermittent 

in nature). The short-term dermal MOEs for the paint brush and airless sprayer are both < 1, and 

therefore, the risks are of concern. The residential target MOE is 1000.

Inhalation

For the residential painting inhalation assessment, the inhalation MOEs were less than 1 

which is below the target MOE of 1000 for the brush and airless application techniques, and 

therefore, are of concern.

Residential Post Application/Bystander Risk Summary

Dermal & Oral

The residential post-application short- and intermediate-term dermal and incidental oral risks 

were assessed for children and/or adults coming in contact with or wearing treated textiles such 

as clothing. Dermal risks are of concern using the transfer residue study developed for a 

screening-level assessment (i.e., toddler dermal MOE = 35). A second residue transfer study was 

conducted to refine the transfer of residues. This study determined the residues to be <10 ppb. 

However, there is insufficient information available in the study to assume that a reasonable 

certainty of no harm would occur from a child exposed to TBTO-treated fabric using the revised 

methodology. In addition, the incidental oral exposures from children mouthing treated fabric is 

of concern (oral MOE = 2). Furthermore, the dermal MOEs are also of concern for dermal 

contact on TBT-treated mattresses (MOE is 8 for children when using the transfer residue data 

from the first residue transfer study).

Inhalation 

Based on the application methods, inhalation exposure is expected to be minimal.

Occupational Handler Risk Summary

In summary, for the non fogging agricultural uses the inhalation MOEs are greater than 

100, and therefore not of concern. Some of the dermal MOEs for the same scenarios are above 

and some below the target MOE of 100. However, the use of chemical resistant gloves was not 

assessed for all scenarios because the data were not available. Based on the low application rate 

(i.e., 0.00033 lb ai/gallon), the magnitude of the MOEs, and assuming that chemical resistant 
Page 4 of 43

gloves would afford substantial reduction in exposure, these dermal MOEs do not appear to be of 

concern if gloves are required on the labels (confirmatory data would be required). The MOEs 

for the material preservative use are below the target MOE of 100. Potential mitigation for 

material preservative additives would be to require closed loading systems. The industrial 

process and water system uses also need to be restricted to closed loading systems. At this time, 

it is unclear how the antifouling coatings are applied and additional information on the 

application techniques are requested. Finally, the commercial applications of stains indicate 

MOEs of concern (i.e., MOEs less than 1).

Occupational Post Application/Bystander Risk Summary

Based on the application methods, inhalation post-application exposures are expected to 

be minimal except for the machinist using TBT-treated cutting fluids. The dermal and inhalation 

MOEs for machinists are 3 and 36, respectively. The risks are of concern for the machinist.

Data Limitations and Uncertainties:

There are a number of uncertainties associated with this assessment and these have been 

reiterated from Sections 4.2.3 (residential) and 6.4 (occupational). The data limitations and 

uncertainties associated with the handler and post-application exposure assessments include the 

following:

· Surrogate dermal and inhalation unit exposure values were taken from the proprietary

Chemical Manufacturers Association (CMA) antimicrobial exposure study (USEPA, 1999: 

DP Barcode D247642) or from the Pesticide Handler Exposure Database (USEPA, 1998) 

(See Appendix B for summaries of these data sources). Most of the CMA data are of poor 

quality therefore, EPA requests that confirmatory monitoring data be generated to support the 

values used in these assessments. 

· The quantities handled/treated were estimated based on information from various sources, 

including HED’s Standard Operating Procedures (SOPs) for Residential Exposure 

Assessments (USEPA 2000, and 2001). In certain cases, no standard values were available 

for some scenarios. Assumptions for these scenarios were based on EPA estimates and could 

be further refined from input from registrants. 
Page 5 of 43

1.0 INTRODUCTION

1.1 Purpose

In this document, EPA’s Antimicrobials Division (AD) presents the results of its review 

of the potential human health effects of occupational and residential exposure to TBT-containing 

compounds (TBTO, TBTB, TBTM), case number 2620. The information presented in this 

Occupational and Residential Exposure chapter is for use in EPA's development of the TBT

Reregistration Eligibility Decision (RED) document. 

1.2 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 potential exposure to 

handlers (mixers, loaders, applicators, etc.) during use or to persons entering treated sites after 

application is complete. For TBT, both criteria are met. Toxicological endpoints were selected 

for short-, intermediate-, and long-term dermal, inhalation, and incidental oral exposures to TBT. 

There is the potential for exposure in a variety of occupational and residential settings. 

Therefore, risk assessments are required for occupational and residential handlers as well as for 

occupational and residential post application exposures that can occur as a result of TBT use.

In this document, handler 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 active ingredient 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). 

The unit exposure concept has been established in the scientific literature and also through 

various exposure monitoring guidelines published by the USEPA and international organizations 

such as Health Canada and OECD (Organization for Economic Cooperation and Development). 

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:

Daily Exposure: Daily inhalation and dermal handler exposures are estimated for each 

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

applicable inhalation unit exposure using the following formula:

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

Where: 

E = Amount (mg ai/day) inhaled or contacted dermally that is available for absorption;
Page 6 of 43

UE = Unit exposure value (mg ai/lb ai) derived from August 1998 PHED data or from 1992 CMA data;

AR = Maximum application rate based on a logical unit treatment, such as square feet (sq. ft.), gallons 

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

and

AT = Normalized application area based on a logical unit treatment such as square feet (sq ft/day), 

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

Daily Dose: The inhalation and dermal doses are calculated by normalizing the daily

exposure by body weight and adjusting, if necessary, with an appropriate absorption factor. An 

absorption factor of 100% was used for inhalation exposures. An absorption factor was not 

necessary for dermal exposures because a route-specific dermal endpoint is available. Daily dose 

was calculated using the following formula:

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

BW

Where:

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

scenario (mg active ingredient/kg body weight/day);

E = Amount (mg ai/day) inhaled or contacted dermally that is available for 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).

Margins of Exposure: Non-cancer inhalation and dermal risks for each applicable 

handler scenario are calculated using a Margin of Exposure (MOE). This is the ratio of the daily

inhalation or dermal 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 = Systemic toxicity level where no observed adverse effects (NOAEL) or where 

the lowest observed adverse effects (LOAEL) occurred in the study (mg ai/kg 

body weight/day); and

ADD = Average daily dose in a given scenario (mg ai/kg body weight/day).

In addition to the target MOEs presented in Table 3.2 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:
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· The TBT products have a large number of use patterns that are difficult to completely capture 

in this document. As such, EPA has patterned this risk assessment on a series of likely

representative scenarios for each use site that are believed by EPA to represent the vast 

majority of TBT uses.

· Based on the adverse effects for the endpoints, the body weight of 70 kg is used for the 

inhalation and dermal and oral routes of exposure. 

· Exposure factors used to calculate daily exposures to handlers were based on applicable data, 

if available. When appropriate data were lacking, values from a scenario deemed similar 

were used.

· The maximum application rates allowed by labels were assumed. 

1.3 Chemical Identification

Molecular structures for tributlytin-containing compounds are illustrated in Figure 1.

HO

O

O

O

Sn CH3

CH3

H3C

Figure 1. Molecular Structures of TBTO, TBTB, and TBTM, respectively.

1.4 Physical/Chemical Properties

Table 1.2 shows physical/chemical characteristics that have been reported for TBT (TBT 

Product Chemistry Chapter).

Table 1.2. Physical/Chemical Properties of TBT

Parameter TBTO TBTB TBTM 

Molecular Weight (g/mol) 596 411 405.13

Half life in air 0.125 days 0.241 days 2.5 hrs

Boiling Point ( ̊C) 417 390 415

Water Solubility (mg/L) 0.0896 0.257 4.086

Vapor Pressure (mm Hg at 25  ̊C) 7.8E-6 1.34E-6 1.74E-7
Page 8 of 43

2.0 USE INFORMATION

2.1 Formulation Types and Percent Active Ingredient

TBT is used as a bacteriostat, microbicide/microbistat, fungicide, slimicide, algaecide, 

antifoulant, virucide, disinfectant, sanitizer, miticide, and insecticide. TBT is formulated as a 

soluble concentrate. TBT concentrations in products range from 0.3 to 53 percent (i.e., 74489-1). 

2.2 Summary of Use Pattern and Formulations

The Agency determines potential exposures to handlers of pesticide products by

identifying exposure scenarios from the various application methods that are plausible, given the 

labeled uses. The following Use Site Categories (USC) was identified based on a review of the 

TBT product labels: 

n (I) Agricultural premises and equipment;

n (III) Commercial, institutional and industrial premises and equipment;

n (VII) Material preservatives;

n (VIII) Industrial processes and water systems;

n (IX) Antifouling coatings; and 

n (X) Wood preservatives.

Specific uses within these use categories are identified in Table 2.1. From Table 2.1, 

EPA has selected representative exposure scenarios to assess TBT in this document. These 

scenarios were selected to be representative of the vast majority of uses and are believed to 

provide high-end degrees of dermal, inhalation, or incidental ingestion exposure. The 

representative scenarios assessed in this document are shown in Table 4.1 (residential) and Table 

6.1 (occupational).

Table 2.1. Potential Use Scenarios Based on Product Labels for TBT.

Use Site Category Example Use Sites Scenarios

Use Site Category I

Agricultural premises and 

equipment

·

Use Site Category III

Commercial, institutional and 

industrial premises and 

equipment

· Polymers 

Use Site Category VII

Material Preservatives

Used in the production of 

various household, institutional 

and industrial items

Addition to products during manufacture, 

including:

· Polymers 

Use Site Category VIII

Industrial processes and water 

systems

Used on fresh water supplies for 

commercial and industrial 

systems

· Addition to water for recirculating 

cooling towers

·

Use Site Category 
Page 9 of 43

Antifoulant coatings

Use Site Category 

Wood preservatives

Used in preservation of wood 

products

3.0 SUMMARY OF TOXICITY DATA

3.1 Acute Toxicity

The acute toxicity data for TBT are summarized below in Table 3.1. The acute toxicity

database for the tributyltin compounds is considered incomplete; the battery of acute toxicity

studies required for labeling purposes has not been submitted by the registrants for each of the 

tributyltin compounds (tributyltin oxide, tributyltin maleate and tributyltin benzoate) grouped in 

this hazard assessment. The available data does show that exposure to tributyltin oxide and 

tributyltin maleate can result in severe oral and dermal toxicities (Toxicity Category II). 

However, tributyltin oxide and tributyltin maleate are not dermal sensitizers. Dermal and oral 

exposures to tributyltin benzoate can potentially cause moderate (Toxicity category III) to severe 

(Toxicity category II) toxicities, respectively. 

Table 3.1. Acute Toxicity Profile for Technical (95.0- 97.5 % a.i.) Tributyltin

Compounds

Guideline 

Number

Study Type MRID 

Number

Results Toxicity 

Category

Tributyltin Oxide

870.1100

(§ 81-1)

Acute Oral – Rat 00085004,

92172013

LD50 =180 mg/kg (males)

LD50 =150 mg/kg 

(females)

LD50 =170 mg/kg 

(combined)

II

870.1100

(§ 81-1)

Acute Oral – Rat 00085003,

92172004

LD50 =193 mg/kg (males)

LD50 =123 mg/kg 

(females)

LD50 =160 mg/kg 

(combined)

II

870.2600

(§ 81-6)

Skin Sensitization –

Guinea pigs

00104789, 

92172014

Non sensitizer Not 

applicable

Tributyltin Maleate

870.1100

(§ 81-1)

Acute Oral – Rat 43851201 LD50 = 224.7 mg/kg II

870.2600

(§ 81-6)

Skin Sensitization –

Guinea pigs

44142303 Non sensitizer. Not 

sensitizing; minimal 

irritation in response to 

induction, but no increase 

in response to challenge 

dose

Not 

applicable
Page 10 of 43

Tributyltin Benzoate

870.1100

(§ 81-1)

Acute Oral – rat

Purity

42415801 LD50 =115 mg/kg (males)

LD50 =115 mg/kg 

(females)

LD50 =115 mg/kg 

(combined)

II

870.1200

(§ 81-2)

Acute Dermal – rat

Purity

42415802 LD50 > 2000 mg/kg 

(combined)

III

870.2500

(§ 81-5)

Primary Dermal 

Irritation – rabbit

Purity

42415803 Severe Irritation I

3.2 Summary of Toxicity Endpoints

Table 3.2 summarizes the toxicological endpoints for TBT.

Exposure

Scenario

Dose Used in Risk 

Assessment

(mg/kg/day) 

Special Sensitivity*, 

UF, Target MOE, 

for Risk Assessment

Study and Toxicological Effects

Dietary Risk Assessments

Acute Dietary

(females 13-49 and 

general population)

No appropriate endpoints were identified in the oral toxicity studies that represent a single 

dose effect for the general population and females 13-49. In addition, the current use 

patterns for the tributyltin-containing chemicals do not indicate the potential for direct or 

indirect dietary exposures. Therefore, an acute dietary risk assessment is not required.
Page 11 of 43

Exposure

Scenario

Dose Used in Risk 

Assessment

(mg/kg/day) 

Special Sensitivity*, 

UF, Target MOE, 

for Risk Assessment

Study and Toxicological Effects

Chronic Dietary

(all populations)

BMD10 = 0.03 

mg/kg/day based on 

immunosupression 

(established by

EPA/IRIS and used to 

estimate their oral RfD 

of 0.0003 mg/kg/day). 

Special Sensitivity = 10

UF = 100 (10x interspecies extrapolation, 10x 

intra-species variation)

Chronic RfD (cRfD) = 

0.00003 mg/kg/day

Although the current use 

patterns for the tributyltincontaining chemicals do 

not indicate the potential 

for chronic dietary

exposures, this endpoint is 

selected for future 

reference. A chronic 

dietary risk assessment is 

not required at this time. 

Open Literature Study

Vos et al., (1990) Immunotoxicity of 

bis(tri-n-butyltin)oxide in the rat: 

Effects on thymus-dependent 

immunity and on nonspecific 

resistance following long-term 

exposure in young vs aged rats. 

Toxicol. Appl. Pharmacol. 105:144-

155.

NOAEL = 0.025 mg/kg/day

LOAEL = 0.25 mg/kg/day based on 

immunotoxicity (depression of IgE 

titers and increase in T. spiralis larvae 

in muscle) following 4 months and 

16.5 months of exposure to Tributyl 

Tin Oxide. (Review by EPA/IRIS, 

1997). 

Non-Dietary Risk Assessments

Incidental Oral

Short-Term 

(1-30 days) and 

Intermediate-Term 

(1- 6 months) 

BMD10 = 0.03 

mg/kg/day based on 

immunosupression 

(established by

EPA/IRIS and used to 

estimate their oral RfD 

of 0.0003 mg/kg/day). 

Special Sensitivity = 10

UF = 100 (10x interspecies extrapolation, 10x 

intra-species variation)

Target MOE = 1000

Open Literature Study

Vos et al., (1990) Immunotoxicity of 

bis(tri-n-butyltin)oxide in the rat: 

Effects on thymus-dependent 

immunity and on nonspecific 

resistance following long-term 

exposure in young vs aged rats. 

Toxicol. Appl. Pharmacol. 105:144-

155.

NOAEL = 0.025 mg/kg/day

LOAEL = 0.25 mg/kg/day based on 

immunotoxicity (depression of IgE 

titers and increase in T. spiralis larvae 

in muscle) following 4 months and 

16.5 months of exposure to Tributyl 

Tin Oxide. (Review by EPA/IRIS, 

1997). 
Page 12 of 43

Exposure

Scenario

Dose Used in Risk 

Assessment

(mg/kg/day) 

Special Sensitivity*, 

UF, Target MOE, 

for Risk Assessment

Study and Toxicological Effects

Dermal

(all durations)

BMD10 = 0.03 

mg/kg/day based on 

immunosupression 

(established by

EPA/IRIS and used to 

estimate their oral RfD 

of 0.0003 mg/kg/day). 

Special Sensitivity = 10

UF = 100 (10x interspecies extrapolation, 10x 

intra-species variation)

Target MOE occ. = 100

Target MOE res. = 1000

Open Literature Study

Vos et al., (1990) Immunotoxicity of 

bis(tri-n-butyltin)oxide in the rat: 

Effects on thymus-dependent 

immunity and on nonspecific 

resistance following long-term 

exposure in young vs aged rats. 

Toxicol. Appl. Pharmacol. 105:144-

155.

NOAEL = 0.025 mg/kg/day

LOAEL = 0.25 mg/kg/day based on 

immunotoxicity (depression of IgE 

titers and increase in T. spiralis larvae 

in muscle) following 4 months and 

16.5 months of exposure to Tributyl 

Tin Oxide. (Review by EPA/IRIS, 

1997). 

Inhalation

(all durations)

BMD10 = 0.03 

mg/kg/day based on 

immunosupression 

(established by

EPA/IRIS and used to 

estimate their oral RfD 

of 0.0003 mg/kg/day). 

Special Sensitivity = 10

UF = 100 (10x interspecies extrapolation, 10x 

intra-species variation)

Target MOE occ. = 100

Target MOE res. = 1000

Open Literature Study

Vos et al., (1990) Immunotoxicity of 

bis(tri-n-butyltin)oxide in the rat: 

Effects on thymus-dependent 

immunity and on nonspecific 

resistance following long-term 

exposure in young vs aged rats. 

Toxicol. Appl. Pharmacol. 105:144-

155.

NOAEL = 0.025 mg/kg/day

LOAEL = 0.25 mg/kg/day based on 

immunotoxicity (depression of IgE 

titers and increase in T. spiralis larvae 

in muscle) following 4 months and 

16.5 months of exposure to Tributyl 

Tin Oxide. (Review by EPA/IRIS, 

1997). 

Dermal Absorption Although there is no guideline dermal toxicity study (range-finding study only) and no 

acceptable dermal absorption study (75% recovery of 113Sn-tributyltin oxide), a 15% dermal 

absorption factor for tributyltin oxide has been used (EPA/HED) for route-to-route 

extrapolation. 

UF = uncertainty factor, NOAEL = no observed adverse effect level, LOAEL = lowest observed adverse effect level, 
Page 13 of 43

RfD = reference dose, MOE = margin of exposure, NA = Not Applicable

*The Special Sensitivity factor is applied to a selected dose if there is evidence of increased susceptibility

to children from non-dietary exposures to pesticides. Several published literature show that tributyltin 

oxide causes depression of immune functions dependent on the thymus, particularly in young animals. 

This is a critical effect that occurs at doses lower than those causing other toxicities. Therefore, application 

of this factor provides adequate protection to the most sensitive population, children.

4.0 RESIDENTIAL EXPOSURE ASSESSMENT 

4.1 Summary of Registered Uses

There are registered products containing TBT that can come in contact with adults and/or 

children. For example, there are TBT products that can be applied directly by the homeowner.

The consumer products include EPA Reg. Nos. 577-539, 577-544, 1022-511, 7313-6, 8177-71, 

9339-14 that are for preserving wood such as siding, shingles, fences, decks, millwork, etc. 

Articles treated with TBT in occupational settings may also have the potential for postapplication residential exposure. For example, there are TBT treated articles such as textiles 

including mattress pads, ticking, and covers. Additionally, there are labels such as 3090-123 

listing textile treatments with restrictions for no food contact or diapers. However, there are no 

other clothing restrictions, and therefore, it is assumed clothing worn by adults and/or children 

can be treated.

4.2 Residential Exposure

The exposure scenarios assessed in this document for the representative uses of TBT

selected by EPA are listed in Table 4.1. The table also shows the maximum application rate 

associated with the representative use and the EPA label registration number. Handler dermal 

and inhalation exposures are assessed for the wood preservative use. Post-application dermal, 

inhalation, and/or incidental ingestion exposures are assessed for treated articles including 

clothing and mattress. Post-application/bystander inhalation exposures are expected to be 

minimal for most uses, except for drift occurring during the airless spray painting. The 

inhalation bystander exposure to aerosols generated during painting are assumed to be less then 

that of the applicator and are therefore not assessed separately. 
Page 14 of 43

Table 4.1. Representative Uses Associated with Residential Exposure to TBT.

Representative Use Application 

Method Exposure Scenario

Example 

Registration 

Number

Application Rate

Wood Preservative · Brush and 

airless 

sprayer

(Note: dip not 

assessed 

separately)

ST Handler: adult 

dermal and inhalation.

1022-511

(577-539, 577-

544, 1022-511, 

7313-6, 8177-

71)

0.062 lb ai/gallon

[8.3 lbs per gal density x 

0.75% ai = 0.062 lb 

ai/gallon of stain]

Textiles (a)

(exposures to treated 

articles are 

represented by 

exposure to clothing

and mattress)

· NAa ST Post-app: wearing 

treated clothing, adult 

dermal; child 

incidental ingestion 

and dermal 

ST Post-appl: Sleeping 

on treated mattress;

adult dermal and child

incidental ingestion 

and dermal

3090-123

(textile)

10466-24

(mattress)

0.05% ai or 500 ppm TBT

[1% pesticide product by 

weight of material treated 

x 5% ai in formulated 

product = weight fraction 

of 0.0005 ai or 0.05% ai or 

500 ppm]

0.056% ai or 560 ppm

TBT

[3.5% formulated product 

by weight of goods x 1.6% 

ai in formulated product = 

weight fraction of 0.00056 

ai or 0.056% ai or 560 

ppm]

(a) The handlers scenarios for textiles were not assessed for residents because the products can only be applied 

occupationally.

4.2.1 Residential Handler Exposures

The residential handler scenarios described in Table 4.1 were assessed to determine 

dermal and inhalation exposures. The scenarios were assessed using PHED data and the 

equations in Section 1.2, “Criteria for Conducting Risk Assessment.” A summary of the PHED 

data are presented in Appendix A.

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

HED’s Residential SOPs (USEPA, 1997)

· For the airless sprayer scenario, measured PHED dermal and inhalation unit exposure 

values for a residential handler applying a pesticide using an airless sprayer to stain the 

siding of a residential home were used as a surrogate for this scenario. These unit 
Page 15 of 43

ungloved exposure values (79 mg/lb a.i. for dermal and 0.83 mg/lb a.i. for inhalation) 

represent a handler wearing short pants and a short sleeve shirt, with no gloves. 

· For the brush/roller scenario, measured PHED dermal and inhalation unit exposure 

values for a residential handler applying a pesticide using a paint brush to the interior of a 

bathroom were used as a surrogate for this scenario. These unit exposure values (230 

mg/lb a.i. for dermal and 0.28 mg/lb a.i. for inhalation) represent a handler wearing short 

pants and a short sleeve shirt, with no gloves.

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

from various sources, including EPA estimates. 

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

(approximately 2 gallons) of treated stain 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. 

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

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

coverage of approximately 200 ft2/gallon and a house size of 40 x 30 x 20 ft 

(surface area of 2,800 ft2).

Duration of Exposure: The duration of exposure for most handler homeowner uses is believed 

to be best represented by the short-term duration (1 to 30 days). The reason that short term 

duration was chosen to be assessed is because painting is episodic in nature, not daily. In 

addition, homeowners are assumed to use different products with varying activities, not 

exclusively TBT treated products (e.g., in-can paint preservative).

Results

The resulting short-term inhalation and dermal exposures and MOEs for the 

representative residential handler scenarios are presented in Tables 4.2. The calculated 

inhalation and dermal MOEs are below the target MOE of 1000 for all scenarios. Therefore, the 

risks exceed EPA’s level of concern. 

Table 4.2 TBT Short-Term Residential Handler Inhalation and Dermal MOEs.

Unit Exposure

(mg/lb a.i.)

Daily Dose 

(mg/kg/day) c

MOE d

(Target MOE = 

1000)

Exposure 

Scenario

Application 

Method

Application 

Method Application Ratea

Quantity 

Handled/ 

Treated per dayb

Inhalation Dermal Inhalation Dermal Inhalation Dermal

Paint brush 2 gallons 0.28 230 5E-4 0.061 60 <1 Staining/

Painting Airless 

sprayer

0.062 lb ai/gal

15 gallons 0.83 79 0.011 0.16 3 <1

a Application rates are the maximum application rates determined from EPA registered label for TBT (i.e., 0.75% ai in 

EPA Reg. No. 1022-99; next highest rate is 0.5% ai).

b Amount handled per day values are estimated.
Page 16 of 43

c Daily dose (mg/kg/day) = [unit exposure (mg/lb a.i.) x application rate (lb ai/gal) x quantity treated (gal/day) x 

absorption factor (100% for inhalation and 15% dermal)]/ Body weight (70 kg).

d MOE = NOAEL / Daily Dose. [Where short-term inhalation and dermal BMD10 = 0.03 mg/kg/day]. Target MOEs = 

1000.

4.2.2 Residential Post-application Exposures

For the purposes of this screening level assessment, post-application scenarios represent a 

high end exposure scenario for all products represented. As shown in Table 4.1, representative 

post-application scenarios assessed include wearing treated clothing and sleeping on mattresses 

(dermal exposure to adults and children and incidental oral exposure to children). 

4.2.2.1 Textiles

Dermal Exposure to Adults and Toddlers from Contacting Treated Clothing

There is the potential for dermal exposure to adults and children from wearing clothing 

treated during manufacturing with TBT as a preservative (i.e., bacteriostatic/fungistatic). A postapplication assessment assuming no laundering by the homeowner was conducted as a 

conservative measure (i.e., the effect on dislodgeable residues over time during washing is not 

quantifiable at this time). It should be noted that not all articles of clothing are treated with TBT

products or worn on a continuous basis. In general, it is believed that most treated textiles used 

in a residential setting will result in exposures occurring over a short-term time duration (1 to 30 

days) because residents are assumed to be exposed to treated textiles with varying active 

ingredients, not exclusively TBT treated textiles. Nonetheless, the short-term dermal 

toxicological endpoint is protective of the intermediate- and long-term durations because the 

same endpoint value is used to assess all durations.

Exposure Calculations

Potential doses are calculated as follows:

PDD = W x % applied x % a.i. x % transfer

BW

where: 

PDD = potential daily dose (mg/kg/day);

W = weight of clothing worn (g/day);

% applied = percent of product applied (%);

% a.i. = percent active ingredient in product (%); 

% transfer = percent transferred (%); and 

BW = body weight (kg).

And
Page 17 of 43

W = (SW/SSA) * BSA

where:

W = weight of clothing worn (g/day);

SW = weight of medium shirt (g);

SSA = surface area of medium shirt (cm2); and

BSA = surface area of body covered (cm2).

Assumptions

· The formulated product is applied at rates as high1% by weight of the textiles and the 

formulated product itself is 5% ai (1% formulated product by weight of textile x 5% ai = 

0.0005 weight fraction or 0.05% ai in textiles or 500 ppm TBT in textiles).

· The median surface area of clothing contacting skin for a 3-year-old toddler is 5,670 cm2

(total body surface area minus the head) (USEPA, 1997). For adults, the median surface 

area is 16,900 cm2 (total body surface area minus the head) (USEPA, 1997). 

· The textile density is 10 mg/cm2based on the density of mixed cotton and synthetics 

(HERA 2003). It is assumed that the mixed cotton/synthetic is used to cover the body for 

both adults and toddlers, minus the head surface area. Therefore, the total amount of 

fabric worn per day is equal to the density of the fabric (10 mg or 0.01 grams per cm2) 

times the surface area covered (5,670 cm2for toddlers, 16,900 cm2for adults), or 56.7 

g/day for toddlers, and 169 g/day for adults.

· Potential doses were initially calculated using a conservative residue transfer factor of 

100%, which assumes that all residues are transferable from clothing surfaces to the skin. 

In cases where the MOEs did not meet the Agency’s target MOE, potential doses were 

also calculated using a less conservative residue transfer factor of 5%, which is based on 

the amount of residue assumed to be transferable from carpeted surfaces (USEPA, 2000 

and 2001). In these cases, confirmatory data are needed to support the use of the lower 

transfer factor. In this revised assessment, two mattress ticking leaching studies were 

submitted for TBTO. Although these studies used mattress ticking, not clothing, it does 

provide measured residues transferred from a fabric. In the first study (Thomson

Research Associates Report No. RG-2002-03-01), Ultra-Fresh 300DN was applied at 

2.58% formulated product (1 % TBTO in product) to the mattress ticking. Exposure was 

simulated using an artificial sweat solution applied to a piece of poly/cotton fabric, 

weighted, and rolled over the treated mattress ticking 350, 700, and 1,400 times to 

simulate exposure for 1, 2, and 4 weeks, respectively. This simulated 50 movements per 

night for an individual. The results of this study indicated up to 0.41 ug/cm2was 

transferred from the mattress ticking when simulated for 4 weeks. Therefore, the amount 

available on a daily basis is 0.41 ug/cm2/ 28 days = 0.015 ug/cm2. A second study

(Thomson Research Associates Report No. RG-2004-03-01) applied 1.72% formulated 

product (1 % TBTO in product) and monitored the residue transfer using a less abrasive 

monitoring technique. The second study indicated no leaching of TBTO residues (LOD = 

10 ppb). Insufficient information was available in the second study to calculate the 

amount of TBTO in ug/cm2 transferred from the mattress ticking (i.e., weight of material 

not provided to convert the 10 ppb concentration to ug/cm2). Therefore, MOEs at 1⁄2 LOD 
Page 18 of 43

are not presented. The first study was designed to simulate the “worst-case” of residue 

transfer as a screening-level assessment. The methodology for the “worst-case” scenario 

was then refined to attempt to develop a “reasonable worst-case”. However, neither 

method provided information linking residue transfer to actual human exposure. The first 

study appears to be representative of the high end residue transfer to be used as a 

screening-level assessment. But there is insufficient information available in the second 

study to assume that a reasonable certainty of no harm would occur from a child exposed 

to TBTO-treated fabric using the methodology of the second study. This revised TBT

assessment would have provided a range of risks from these two studies if the LOD of 

100 ppb could be converted to ug/cm2. Nonetheless, the second study can not be 

confirmed as being designed to represent a reasonable certainty of no harm and the 

incidental oral component of the treated clothing would still be the risk driver for this use 

on textiles. Note: The application rates in these studies (i.e., 2.58% and 1.72% by weight 

product containing 1% TBTO) are less then the maximum labeled rate for TBTO (i.e., 5% 

product by weight containing 1% TBTO).

· Toddlers (3 years old) are assumed to weigh 15 kg. This is the mean of the median values 

for male and female toddlers (USEPA, 1997). For adults, a body weight of 70 kg has 

been assumed. (USEPA, 1997). 

Results

The calculations of the short-term dermal doses and MOEs for adults and toddlers 

wearing treated clothing are shown in Table 4.3. The dermal MOEs for adults and toddlers are 

less than the target MOE of 1000 assuming a 100% and 5% residue transfer factors and the 

results of one of the two TBTO leaching studies. Note: A second study indicated that the 

residue transfer was less then 10 ppb; however there is insufficient information in the study to 

convert the 10 ppb to ug/cm2and it is not possible to determine if the second study is 

representative of a high end exposure potential. Therefore, the risks are of concern.
Page 19 of 43

a. Weight of clothing worn (g/day) = (Density of fabric 0.01 g/cm2) * (surface area of body covered, cm2) * 1 outfit/day

b. Absorbed Daily Dose (mg/kg/day) = [(weight of clothing worn, g/day) * (percent a.i. in product, %) / 100 * (percent of 

product applied, %) / 100 * (percent residue transferred from clothing to skin, %) * (dermal absorption factor, 0.15) *

(conversion factor, 1000 mg/g)] / (body weight, 15 kg child and 70 kg adult). – or -- Absorbed daily dose (mg/kg/day) = 

Surface area exposed (cm2) x measured residue (ug/cm2) x 15% dermal abs x unit conversion ug to mg (1/1000) x (1/15 kg 

child BW).

c. Dermal MOE = BMD10 (mg/kg/day) / Daily Dose [Where dermal BMD10 = 0.03 mg/kg/day]. Target MOE = 1000.

Incidental Oral Exposure to Toddlers Mouthing Treated Textiles (Clothing/Blankets)

Exposure Calculations

There is the potential for incidental oral exposure to toddlers from mouthing textiles treated 

with TBT.

Potential doses are calculated as follows:

PDD = C x SE x SA 

BW

where: 

PDD = potential daily dose (mg/kg/day);

C = concentration on clothing (mg/cm2);

SE = saliva extraction efficiency (%);

SA = surface area mouthed (cm2/day); and

BW = body weight (kg).

Table 4.3: Dermal Post-application Exposures and MOEs for Toddlers and Adults 

Contacting Treated Clothing

Exposure 

Scenario

Weight of 

clothing 

worn 

(g/day)a

Surface Area 

Exposed

(cm2)

Measured 

Residue

(ug/cm2)

Percent residue 

transferred from 

clothing to skin (%)

Daily doseb

(mg a.i./ kg/day)

Dermal MOEc 

(Target 

MOE=1000)

Maximum Labeled Rate: 5% product by weight (product containing 1% TBTO)

100 0.284 <1

Toddler 56.7 5,670 NA

5 0.0142 2

100 0.181 <1

Adult 169 16,900 NA

5 0.0091 3

Study #1 Application Rate: 2.58% product by weight (product containing 1% TBTO)

Toddler NA 5,670 0.015 NA 0.00085 35

Study #2 Application Rate: 1.72% product by weight (product containing 1% TBTO)

Toddler NA 5,670 <10 ppb NA Need more information to convert 

LOD of 10 ppb to ug/cm2
Page 20 of 43

And

C = % a.i. x % applied x W

where:

C = concentration on clothing (mg/cm2);

% applied = percent of product applied (%);

% a.i. = percent active ingredient in product (%); and

W = weight of clothing (mg/cm

2

).

Assumptions

· The formulated product is applied at rates as high1% by weight of the textiles and the 

formulated product itself is 5% ai (1% formulated product by weight of textile x 5% ai = 

0.0005 weight fraction or 0.05% ai in textiles or 500 ppm TBT in textiles).

· The textile density is 10 mg/cm2based on the density of mixed cotton and synthetics 

(HERA 2003). 

· The saliva extraction efficiency was 50% (USEPA, 2000 and 2001).

· The surface area of textiles mouthed by toddlers is 100 cm2(professional judgment).

· Toddlers (3 years old) are used to represent the 1 to 6 year old age group. For three-year 

olds, the median body weight is 15 kg (USEPA, 1997).

Results

Table 4.4 shows the calculation of the short- and intermediate-term oral dose and oral MOE 

for toddlers mouthing treated textiles. The MOE value is less than target MOE of 1000 for the

maximum concentration allowed on the label (MOE is ). 

Table 4.4: Incidental Oral Exposures and MOEs for Toddlers Wearing Treated 

Textiles (Clothing/Blankets)

Weight of 

clothing (g/cm2)

% Product 

Applied

Concentration 

on clothinga

(mg/cm2)

Surface area 

mouthed 

(cm2/day)

Saliva 

extraction 

efficiency 

(%)

Potential daily 

dose 

(mg a.i./kg/day)

Incidental Oral 

MOEc(Target MOE 

=1000)

0.01 1% 0.005 100 50 0.017 2

a. Concentration on clothing (mg/cm2) = (5 percent a.i. in product, %) / 100 * (1 percent product applied, %) / 100 * (weight 

of clothing, g/cm2) * 1,000 mg/g 

b. Potential Daily Dose (mg/kg/day) = (concentration on clothing, mg/cm2) * (surface area mouthed, cm2/day) * (saliva 

extraction efficiency, %)/100 / (body weight, 15 kg).

c Oral MOE = BMD10 (mg/kg/day) / Potential Daily Dose [Where short- and intermediate-term incidental oral BMD10= 0.03

mg/kg/day]. Target MOE = 1000.

Note: The dermal and incidental oral exposure occurring from textiles should also be reported as a total 

exposure (i.e., dermal and oral combined) because of the same toxicological effect is used for both 

routes of exposure. However, the two routes of exposure were not combined at this time because the 

risks are of concern individually.
Page 21 of 43

4.2.2.2 Mattresses

Mattress pads, ticking, and mattress covers can be treated with TBT during the 

manufacturing process. Therefore post application dermal exposures to treated mattresses may

occur. It was assumed that exposure to a textile mattress cover will represent exposure to all 

other mattress components. Since the mattress cover is actually impregnated with TBT both 

short- and intermediate-term exposures durations were assessed.

Dermal Exposure to Treated Mattress Covers

Exposure Calculations

Short- and Intermediate-term exposures - There the potential for short- and 

intermediate-term exposures leading to systemic effects when adults and children come into 

contact with mattress covers treated with TBT, through the regular use of the mattress. Dermal 

exposures and MOEs were calculated for children and adults contacting treated mattresses in 

residential homes. To determine short and intermediate-term exposures to TBT in mattresses, 

the following equation was used:

PDD = D x WF1 x WF2 x PF x SA x DA

BW

where:

PDD = Potential daily dose (mg/kg/day)

D = Mattress textile weight density (mg/cm2)

WF1 = Weight fraction of TBT in the mattress cover (%)

WF2 = Weight fraction of TBT transferred from the mattress cover to skin (cover)

PF = Protection factor from single layer of clothing/sheet (%)

SA = Body surface area contacting mattress (cm2/day)

DA = Dermal absorption (%)

BW = Body weight (kg)

Assumptions

· Mattress covers are treated at the rate of 3.5% formulated product by weight of goods x 1.6% 

ai in formulated product = weight fraction of 0.00056 ai or 0.056% ai or 560 ppm (EPA Reg. 

No. 10466-24).

· The mattress cover density is assumed to be 10 mg/cm2based on the density of mixed cotton 

and synthetics (HERA 2003). 

· In the initial TBT assessment, default residue transfer factors of 100% and 5% were used. In

this revised assessment, two mattress ticking leaching studies were submitted for TBTO. In 

the first study (Thomson Research Associates Report No. RG-2002-03-01), Ultra-Fresh 

300DN was applied at 2.58% formulated product (1 % TBTO in product) to the mattress 
Page 22 of 43

ticking. Exposure was simulated using an artificial sweat solution applied to a piece of 

poly/cotton fabric, weighted, and rolled over the treated mattress ticking 350, 700, and 1,400 

times to simulate exposure for 1, 2, and 4 weeks, respectively. This simulated 50 movements 

per night for an individual. The results of this study indicated up to 0.41 ug/cm2was 

transferred from the mattress ticking when simulated for 4 weeks. Therefore, the amount 

available on a daily basis is 0.41 ug/cm2/ 28 days = 0.015 ug/cm2. A second study (Thomson 

Research Associates Report No. RG-2004-03-01) applied 1.72% formulated product (1 % 

TBTO in product) and monitored the residue transfer using a less abrasive monitoring 

technique. The second study indicated no leaching of TBTO residues (LOD = 10 ppb). 

Insufficient information was available in the second study to calculate the amount of TBTO in 

ug/cm2 transferred from the mattress ticking (i.e., weight of material not provided to convert 

the 10 ppb concentration to ug/cm2). Therefore, MOEs at 1⁄2 LOD are not presented. The first 

study was designed to simulate the “worst-case” of residue transfer as a screening-level 

assessment. The methodology for the “worst-case” scenario was then refined to attempt to 

develop a “reasonable worst-case”. However, neither method provided information linking 

residue transfer to actual human exposure. The first study appears to be representative of the 

high end residue transfer to be used as a screening-level assessment. But there is insufficient 

information available in the second study to assume that a reasonable certainty of no harm 

would occur from a child exposed to TBTO-treated fabric using the revised methodology. 

This revised TBT assessment would have provided a range of risks from these two studies if 

the LOD of 100 ppb could be converted to ug/cm2. Nonetheless, the second study can not be 

confirmed as being designed to represent a reasonable certainty of no harm. Note: The 

application rates in these studies (i.e., 2.58% and 1.72% by weight product containing 1% 

TBTO) are less then the maximum labeled rate for TBTO (i.e., 3.5% product by weight 

containing 1.6% TBTO).

· The protection factor reducing exposure to TBT residues in the mattress from the use of a 

sheet or clothing is 50% based on PHED protection factor for a single layer of clothing (US 

EPA 1998).

· The child skin area contacting the mattress was assumed to 3,283 cm

2

(50% of the total 

surface area of a toddler) (NAFTA guidance per US EPA 1997).

· The adult skin area contacting the mattress was assumed to 9,220 cm2(50% of the total 

surface area of an adult) (NAFTA guidance on surface areas per US EPA 1997).

· The chemical specific dermal absorption study is 15%.

· The body weight of a child was assumed to be 15 kg.

· The body weight of an adult was assumed to be 70 kg

Results

Table 4.5 shows the calculation of the short and intermediate-term dermal exposures and 

MOEs for children and adults contacting treated mattress covers. The dermal MOEs are below

the target MOE of 1000, and therefore are of concern for adults and children contacting the cover 

and assuming 100% and 5% transfer to skin and the results of one of the two TBTO leaching 

studies. Note: A second study indicated that the residue transfer was less then 10 ppb; however 
Page 23 of 43

there is insufficient information in the study to convert the 10 ppb to ug/cm2and it is not possible 

to determine if the second study is representative of a high end exposure potential. Therefore, the 

risks are of concern. 

Table 4.5. Short- and Intermediate-term Dermal Exposures and MOEs for Children and Adults Contacting 

Treated Mattress Covers

Duration % a.i.

Mattress 

density 

(mg/cm2)

Fraction 

transferred 

to skin

Skin surface 

area contacting 

mattress 

(cm2/day)

Protective 

factor

(%)

Dermal 

Absorption

(%)

ST and IT 

Exposure a

(mg/kg/day)

Dermal MOE 

(Target MOE 

= 1000) b

Children

100% 3,283 50% 15% 0.092 <1

ST/IT 0.056

%

10

5% 3,283 50% 15% 0.0046 7

Adults

100% 9,220 50% 15% 0.055 <1

ST/IT 0.056

%

10

5% 9,220 50% 15% 0.0028 11

Study #1 Application Rate: 2.58% product by weight (product containing 1% TBTO)

ST/IT

Children

0.026

%

NA 0.015 

ug/cm2 3,283 50% 15% 0.0037 8

Study #2 Application Rate: 1.72% product by weight (product containing 1% TBTO)

ST/IT 

Children

0.017

%

NA <10 ppb 3,283 50% 15%

Need more information to 

convert LOD of 10 ppb to 

ug/cm2

a Equations used to estimate exposure are presented above for estimates based on percent transferred. For study 

numbers 1 and 2 the absorbed daily dose (mg/kg/day) = Surface area exposed (cm2) x measured residue (ug/cm2) x 15% 

dermal abs x 50% protection factor from sheets x unit conversion ug to mg (1/1000) x (1/15 kg child BW). 

B Dermal MOE = BMD10/dermal dose [Where: ST and IT dermal BMD10 = 0.03 mg/kg/day; Target MOE = 1000]. 

4.2.3 Data Limitations/Uncertainties

There are several data limitations and uncertainties associated with the residential handler 

and post-application exposure assessments. These include the following:

· Surrogate dermal and inhalation unit exposure values were taken from the Pesticide 

Handler Exposure Database (USEPA, 1998) (See Appendix B for summaries of the data 

source). Some of the PHED data are of poor quality, therefore, EPA requires that 

confirmatory monitoring data be generated to support the values used in these assessments. 

· The quantities handled/treated were estimated based on information from various sources, 

including HED’s Standard Operating Procedures (SOPs) for Residential Exposure 

Assessments (USEPA, 2000 and 2001). In certain cases, no standard values were available 
Page 24 of 43

for some scenarios. Assumptions for these scenarios were based on EPA estimates and 

could be further refined from input from registrants. 

· Two residue transfer studies were submitted for TBTO. Both studies reported results for 

the mattress ticking. The data are also used in this review for estimating risks to the 

clothing. The first of two studies was designed to simulate the “worst-case” of residue 

transfer as a screening-level assessment. The methodology for the “worst-case” scenario 

was then refined to attempt to develop a “reasonable worst-case”. However, neither 

method provided information linking residue transfer to actual human exposure. The first 

study appears to be representative of the high end residue transfer to be used as a screeninglevel assessment. But there is insufficient information available in the second study to 

assume that a reasonable certainty of no harm would occur from a child exposed to TBTOtreated fabric using the revised methodology. This revised TBT assessment would have 

provided a range of risks from these two studies if the LOD of 100 ppb could be converted 

to ug/cm2. Nonetheless, the second study can not be confirmed as being designed to 

represent a reasonable certainty of no harm. Note: The application rates in these studies 

(i.e., 2.58% and 1.72% by weight product containing 1% TBTO) are less then the 

maximum labeled rates for TBTO.

5.0 RESIDENTIAL AGGREGATE RISK ASSESSMENT AND CHARACTERIZATION 

The inhalation, dermal, and oral endpoints are based on the same toxicological 

study/effects, and therefore, it would be appropriate to estimate aggregate MOEs. The residential 

uses that could potentially be aggregated are the paint applications, the textiles, and the 

mattresses. There is the likelihood of co-occurrence for two of the uses but it would be unlikely

that all three uses would co-occur because of the limited frequency a resident paints coupled with 

not all paints and/or textiles are treated with TBT. Therefore, residential uses could be 

aggregated for two of the uses. However, at this time the risks are of concern for each of the 

individual uses, and therefore, there is no need to aggregate the risks.

6.0 OCCUPATIONAL EXPOSURE ASSESSMENT

The exposure scenarios assessed in this document for the representative uses selected by

EPA are shown in Table 6.1. The table also shows the maximum application rate associated with 

the representative use and the appropriate EPA Registration number for the product label. It

should be noted that for the calculation of application rates in which 8.34 lb/gal is noted, the 

product is assumed to have the density of water because no product-specific density is available. 

Potential occupational handler exposure for TBT can occur in six Use Categories: 

agricultural premises and equipment; commercial/institutional/industrial premises and 

equipment; material preservatives; and industrial processes and water systems; antifouling

coatings; and wood preservatives.
Page 25 of 43

Table 6.1. Representative Exposure Scenarios Associated with Occupational Exposures to 

TBT

Representative Use Method of 

Application Exposure Scenario Example Registration # Application Rate

Agricultural Premises and Equipment (Use Category I)

Agricultural/farm/

poultry

structures/buildings 

and equipment

Brush, mop, wipe, 

spray, and fogger for 

poultry farm 

buildings and poultry 

hatcheries 

(incubators, hatchers, 

hatchery rooms)

ST/IT Handler:

Inhalation

Dermal

65020-12 Liquid: 0.00033 lb ai/gal

[(0.5 oz formulated product x 

1 % ai x 8.34 lb/128 oz) / (1 

gal water) = 0.00033 lb 

ai/gal]

Fogger: 1.3E-6 lb ai/ft3

[(1 gal formulated product x 

8.34 lb/gal density x 1 % ai)

/ (6000ft2x 10 ft ceiling) = 

1.3E-6 lb ai/ft3as the 

maximum rate representing 

poultry farm buildings]

Commercial/Industrial/Institutional Premises (Use Category III)

(See wood 

preservative 

category for 

commercial painters 

using treated stain)

NA NA NA NA

Material Preservatives (Use Category VII)

Caulks, sealants, 

adhesives, etc

Liquid pour

Metered pump

ST/IT Handler: 

Inhalation

dermal

5383-47

(67360-3, 

1529-30, and 

1529-35)

0.145% ai 

[0.5% formulated product x 

29% ai = 0.145% ai or 1450 

ppm ai]

MWF Liquid pour

Machinist

ST/IT/LT 

handler/machinist:

Dermal

Inhalation

5383-47 0.145% ai in cutting oil

[0.5% formulated product x 

29% ai = 0.145% ai or 1450 

ppm ai]

Industrial processes and Water Systems (Use Category VIII)

Pulp and Paper Metered pump ST/IT Handler: 

Inhalation

dermal

47371-29 Initial: 0.014 lb ai/ton

Continuous: 0.007 lb ai/ton

[Initial: 9.6 oz/ton paper

Continuous feed: 4.8 oz/ton 

paper. 

Where 9.6 oz product x 

2.25% ai x 8.34 lb/128 oz = 

0.014 lb ai/ton paper]
Page 26 of 43

Table 6.1. Representative Exposure Scenarios Associated with Occupational Exposures to 

TBT

Representative Use Method of 

Application Exposure Scenario Example Registration # Application Rate

Recirculating 

Cooling Water

Liquid pour

Metered pump

ST/IT Handler: 

Inhalation

dermal

5185-399 Initial: 0.089 lb ai/1000 gal

Continuous: 0.022 lb 

ai/1000 gallons of water

[Initial: 40 oz product x 

8.34 lb/128 oz x 3.4% ai 

/1000 gallons water

Continuous feed: 10 oz 

product x 8.34 lb/128 oz x 

3.4% ai /1000 gallons water]

Oil fields and 

petrochemical water 

injection systems

Liquid pour

Metered pump

ST/IT Handler: 

Inhalation

dermal

5185-399 Initial: 0.089 lb ai/1000 gal

Continuous: 0.022 lb 

ai/1000 gallons of water

[Initial: 40 oz product x 

8.34 lb/128 oz x 3.4% ai 

/1000 gallons water

Continuous feed: 10 oz 

product x 8.34 lb/128 oz x 

3.4% ai /1000 gallons water]

Antifouling Coatings (Use Category IX)

Sonar Domes & 

Hulls

Unknown ST/IT Handler:

Inhalation

Dermal

(assumed)

1225-11

74489-01

5.78 % ai in formulation

53% ai in formulation

Wood Preservatives (Use Category X)

Staining 

(commercial 

painters)

Paint brush,

Airless sprayer

ST/IT Handler:

Inhalation

Dermal

1022-511

(577-539, 577-

544, 1022-511, 

7313-6, 8177-

71)

0.062 lb ai/gallon

[8.3 lbs per gal density x 

0.75% ai = 0.062 lb 

ai/gallon of stain]

6.1 Occupational Handler Exposures

The occupational handler scenarios included in Table 6.1 were assessed to determine 

inhalation and dermal exposures. The general assumptions and equations that were used to 

calculate occupational handler inhalation and dermal risks are provided in Section 1.2, Criteria 

for Conducting the Risk Assessment. The majority of the scenarios were assessed using CMA 

data and Equations 1-3. However, for the occupational scenarios in which CMA data were 

insufficient, other data and methods were applied. 
Page 27 of 43

Unit Exposure Values (UE): Inhalation and dermal unit exposure values were taken from the 

proprietary Chemical Manufacturers Association (CMA) antimicrobial exposure study (USEPA, 

1999b: DP Barcode D247642) or from the Pesticide Handler Exposure Database (USEPA, 1998).

· For the mopping scenario, the CMA dermal and inhalation unit exposure values for 

ungloved mopping were used (71.6 mg/lb a.i. and 2.38 mg/lb a.i., respectively). These 

values are based on data collected from six replicates in which the applicator mopped the 

floor and received exposure via contact with the mop or with the bucket.

· For the wiping scenario, the CMA dermal and inhalation unit exposure values for 

ungloved wiping were used (2,870 mg/lb a.i. and 67.3 mg/lb a.i., respectively). These 

values are based on data collected from six replicates (dental technicians) who used a 

finger pump sprayer to apply the product and then wiped the surfaces with a paper towel

· For the low pressure handwand scenarios, the CMA dermal and inhalation unit exposure 

values for ungloved use of a low pressure spray were used (191 mg/lb a.i. and 0.681 

mg/lb a.i., respectively). These values are based on data collected from eight replicates in 

which the applicator hand sprayed carpet using 200 psi, then used a push broom rake to 

raise the carpet nap.

· For the high-pressure spray scenario, the PHED dermal and inhalation unit exposure 

values for liquid/open pour/high pressure spray (PHED scenario 35) were used (single 

layer of clothing and gloves). The dermal and inhalation unit exposure values are 2.5 

mg/lb a.i. and 0.12 mg/lb a.i., respectively.

· For the liquid pour scenarios for materials preservatives, the unit exposure depends on the 

material being treated. The following CMA unit exposures were available and used for the 

assessment of the risk associated with the treatment of the specified materials.

o Metalworking fluid: CMA metal fluid gloved data. The dermal UE is 0.184 mg/lb a.i. 

and the inhalation UE is 0.00854 mg/lb a.i.. The values are based on 8 replicates 

where the test subjects were wearing a single layer of clothing and chemical resistant 

gloves. 

o Sealants, caulks, grout, etc: CMA preservative gloved data. The dermal UE is 0.135 

mg/lb a.i. and the inhalation UE is 0.00346 mg/lb a.i.. The values are based on 2 

replicates where the test subjects were wearing a single layer of clothing and chemical 

resistant gloves. Although this unit exposure is based on minimal replicates, the 

exposure value is similar to the one found in PHED for a similar scenarios. 

o Fogging: It is assumed that most of the exposure to the handler will be due to 

preparing the fogger, and that the handler leaves the room immediately after fogging 

commences. Therefore, the available CMA disinfectant liquid pour dermal and 

inhalation unit exposure values were used. The dermal and inhalation unit exposure 

values are 36.5 mg/lb a.i. and 1.89 mg/lb a.i., respectively. This value is based on data 

collected from two gloved replicates involving pouring a disinfectant product from a 

jug into sterilization trays designed for dental instruments, adding water and 

instruments to the tray, removing the instruments, and discarding the old solution.
Page 28 of 43

· For the liquid pump scenarios, AD has recently developed definitions and exposure 

methodology guidance when working with closed loading and delivery systems in 

commercial and industrial settings. Closed loading systems are engineering controls that are 

“...designed to prevent human exposure and should not require human intervention to 

eliminate exposure” (CDPR 2003). Closed transfer systems that require the worker to open 

pour the concentrate into a transfer system are not considered under this definition of closed 

loading systems because the initial exposure for the open pour will require a quantitative 

assessment. Although closed loading and delivery systems are designed to prevent or 

eliminate exposure, zero exposure is difficult to obtain. Even though analytical techniques 

can measure residues at extremely low levels, for practical purposes at some point these 

residues can be considered negligible or minimal. To account for the fact that some residues 

are available for dermal contact (and to a lesser degree available for inhalation exposure), 

EPA is requiring that appropriate PPE be worn by the worker. 

Negligible exposure can be considered to result from the use of systems that are designed to 

drip less than 2 mL per coupling as in dry coupling or metering pumps that are closed on both 

ends. The second category, minimal exposure, has been established because some closed 

systems are not entirely enclosed or have not been engineered to reduce drips to 2 mL, but for 

practical purposes effectively reduce exposure such that risks are not of concern. Minimal 

exposure can be considered to result from closed systems that are designed to prevent or 

eliminate inhalation and dermal exposure but are not engineered to a specification (e.g., 

volume expected to be discharged). 

In the case of TBT, EPA expects that occupational exposures will be negligible or minimal 

assuming that label-specified PPE (i.e., coveralls, long pants, long-sleeved shirts, and 

chemical resistant gloves) and label-specified closed delivery and loading systems such as dry

coupling and closed system metering pumps are consistently utilized. Therefore, a 

quantitative exposure and risk assessment is not warranted and the risks can be considered 

not a concern.

· 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 inhalation exposure value is 0.28 mg/lb a.i. The dermal unit exposures are 180 mg/lb a.i. 

for ungloved replicates and 24 mg/lb a.i. for gloved replicates. 

· For airless sprayer scenarios, the occupational PHED dermal and inhalation unit exposure 

values for airless sprayer application (PHED scenario 23) were used (single layer of 

clothing). The inhalation exposure value is 0.83 mg/lb a.i. The dermal unit exposures are 38 

mg/lb a.i. for ungloved replicates and 14 mg/lb a.i. for gloved replicates. 

Quantity handled/treated: The quantity handled/treated values were estimated based on 

information from various sources. The following assumptions were made:
Page 29 of 43

· For the low-pressure handwand scenario, it was assumed that 10 gallons of solution are used 

in agricultural uses.

· For the high-pressure spray scenario, it was assumed that 40 gallons of solution are used. 

· For the mopping scenario, it was assumed that two gallons of solution are used.

· For the wiping scenario, it was assumed that 0.26 gallons were used based on standard 

assumptions of the amount used for hard surface disinfection.

· For the fogging scenario in the agricultural use site category, it was assumed that a poultry

house of 600 ft x 66 ft x 10 ft or 39,600 ft 2 area or 396,000 ft3 volume is treated. 

· For the liquid pour scenarios, the quantity of the chemical that is handled depends on the 

material that is being treated. The following values were used for the different materials to 

be treated:

o Metalworking fluid: 2,502 lbs (approximately 300 gallons, based on the density of 

water, 8.34 lb a.i./gal) 

o Adhesives and Textiles: 10,000 lbs (standard AD assumption).

o Oil fields: Up to 5 gallons of product are assumed to be open poured in some 

instances before a metering system is employed.

· 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 stain are used (standard AD assumption).

· For the airless sprayer in the painting scenario, it was assumed that 500 lbs (approximately

50 gallons of paint with a density of 10 lb/gal) of treated stain are used. (standard AD 

assumption).

Duration of Exposure: The MOEs were calculated for the short- and intermediate-term 

durations for occupational handlers using the appropriate endpoints in Table 3.2. 

Exposure Calculations and Results

The resulting inhalation and dermal exposures and MOEs for the representative 

occupational handler scenarios are presented in Table 6.2. In summary, for the non fogging 

agricultural uses the inhalation MOEs are greater than 100, and therefore not of concern. Some 

of the dermal MOEs for the same scenarios are above and some below the target MOE of 100. 

However, the use of chemical resistant gloves was not assessed for all scenarios because the data 

were not available. Based on the low application rate (i.e., 0.00033 lb ai/gallon), the magnitude 

of the MOEs, and assuming that chemical resistant gloves would afford substantial reduction in 

exposure, these dermal MOEs do not appear to be of concern if gloves are required on the labels 

(confirmatory data would be required). The MOEs for the material preservative use are below 

the target MOE of 100. Potential mitigation for material preservative additives would be to 

require closed loading systems. The industrial process and water system uses also need to be 

restricted to closed loading systems. At this time, it is unclear how the antifouling coatings are 

applied and additional information on the application techniques are requested. Finally, the 

commercial application of stains indicate MOEs of concern (i.e., MOEs less than 1).
Page 30 of 43

Table 6.2. Short- and Intermediate-Term Risks Associated with Occupational Handlers

Unit Exposure

(mg/lb a.i.) 

Daily Dose 

(mg/kg/day)a

MOEb 

(Target MOE = 

100) Exposure Scenario

Method of 

Application

Inhalation Dermal 

Applicatio

n Rate

Quantity 

Handled/ 

Treated per 

day Inhalation Dermal Inhalation Dermal 

Agricultural Premises and Equipment (Use Site Category I )

Brush-on 0.28

180 no 

gloves

(24 

gloves)

5 gal 6.6E-6

0.0006

4

4500

47 

(350 

gloves)

Wipe 67.3 2870 0.26 gal 8.2E-5

0.0005

3

360 57

Mop 2.38 71.6 2 gal 2.2E-5 0.001 1300 300

Spray 

(hand held)

0.681 191 10 gal 3.2E-5 0.0014 930 22

Spray

(mechanical)

0.12 2.5

0.00033

lb ai/gal

40 gal 2.3E-5 7.1E-5 1300 420

Agricultural/farm/

poultry

structures/buildings 

and equipment

Fogger 1.89 36.5

1.3E-6 

lb ai/ft3

396,000 ft30.014 0.040 2 <1

Commercial, Institutional and Industrial Premises and Equipment (Use Site Category III )

(See wood preservative category for commercial painters using treated stain)

Material Preservatives (Use Site Category VII)

Liquid pour 0.00346 0.135 

(gloves) 2000 lbs 0.00014 0.00084

210 36 Caulks, adhesives, 

grout, etc. 

(manufacturing 

process) Liquid pump 0.000403 0.454

0.145% ai

10,000 lbs 8.3E-5 0.014 360 2

MWF Liquid pour 0.00854 0.184 0.145% ai 300 gal 

(2,500 lbs) 0.00044 0.0014 68 21

Industrial Processes and Water Systems (Use Site Category VIII)

Pulp and Paper Metering pump 0.000265

0.00454

(gloves)

0.014 lb 

ai/ton 500 tons

Recirculating 

Cooling Water Metering pump 0.000265

0.00454

(gloves)

0.089 lb 

ai/1000 gal 5E7 gallons

Closed loading systems are expected to 

result in minimal exposure. Specify closed 

loading system on label along with long 

pants, long sleeved-shirts, and chemical 

resistant gloves.

Pour liquid 0.45

10.1

(gloves)

5 gal

product

(41.7 lbs)

Oil fields and 0.0091 0.031 3 3

petrochemical 

water injection 

systems Metering pump 0.000265

0.00454

(gloves)

0.089 lb 

ai/1000 

gallons 

treated 

(3.4% ai)

Up to 

420,000 

gallons

See closed loading language above.

Antifouling Paints (Use Site Category IX)

Sonar Domes & 

Hulls

Specialty use. Application rates and methods are unknown.

Wood Preservatives (Use Site Category X)

Painting/staining Paint brush 0.28 180 0.062 5 gallons 0.0012 0.12 24 <1
Page 31 of 43

Table 6.2. Short- and Intermediate-Term Risks Associated with Occupational Handlers

Unit Exposure

(mg/lb a.i.) 

Daily Dose 

(mg/kg/day)a

MOEb 

(Target MOE = 

100) Exposure Scenario

Method of 

Application

Inhalation Dermal 

Applicatio

n Rate

Quantity 

Handled/ 

Treated per 

day Inhalation Dermal Inhalation Dermal 

(commercial) Airless sprayer 0.83 38 lb ai/gal 50 gallons 0.037 0.25 <1 <1

a Absorbed Daily dose (mg/kg/day) = [unit exposure (mg/lb a.i.) x absorption factor (dermal 0.15) x application rate x quantity treated / Body weight 

(70 kg).

b MOE = NOAEL (mg/kg/day) / Daily Dose [Where ST and IT inhalation BMD10 = 0.03 mg/kg/day]. Target MOE = 100.

6.2 Occupational Post-application Exposures

Occupational post-application dermal and inhalation exposures are assumed to be 

negligible except for the machinist exposed to TBT-treated metalworking fluids. 

Metalworking Fluids: Machinist

There is a potential for dermal and inhalation exposure when a worker handles 

treated metalworking fluids. This route of exposure occurs after the chemical has been 

incorporated into the metalworking fluid and a machinist is using/handling this TBT treated endproduct.

Dermal Exposures

Exposure Calculations

Short-, intermediate- and long-term exposure estimates were derived using the 2-hand 

immersion model from ChemSTEER. The model is available at 

www.epa.gov/opptintr/exposure/docs/chemsteer.htm. The 2-hand immersion equation is as 

follows: 

PDR = SA x % a.i. x FT x FQ

BW

where: 

PDR = Potential dose rate (mg/kg/day);

SA = Surface area of both hands plus the forearms (cm2);

% a.i. = Fraction active ingredient in treated metalworking fluid (unitless)

FT = Film thickness of metal fluid on hands (mg/cm2)

FQ = Frequency of events (event/day); 

BW = Body weight (kg)
Page 32 of 43

Assumptions

· The surface of area of both hands and forearms is 2013 cm

2

(USEPA 1997)

· The body weight of an adult is 70 kg (USEPA 1997)

· The percent active ingredient in treated metalworking fluid is 1450 ppm (i.e., 0.145% ai) 

calculated from 0.5% formulated product x 29% ai (EPA Registration No. 5383-47).

· For short-, intermediate- and long-term durations, the film thickness on the hands is 1.75 

mg/cm2, which was extracted from the document entitled, “A Laboratory Method to 

Determine the Retention of Liquids on the Surface of Hands” (USEPA 1992). The film 

thickness methodology represents a machinist immersing both hands in metalworking fluid 

and then partially cleaning hands with a rag. The film thickness was chosen because the 

dermal endpoint for short-, intermediate- and long-term durations is based on systemic 

effects.

Inhalation Exposures

Exposure Calculations

A screening-level intermediate and long term inhalation exposure estimate for treated 

metalworking fluids has been developed using the OSHA PEL for oil mist. The equation used 

for calculating the inhalation dose is:

PDR = PEL x IR x % a.i. x ED

BW

where:

PDR = Potential dose rate (mg/kg/day);

PEL = OSHA PEL (mg/m3);

IR = Inhalation rate (m

3 /hr)

% a.i. = Fraction active ingredient in treated metalworking fluid (unitless) 

ED = Exposure duration (hrs/day); 

BW = Body weight (kg)

Assumptions

· The high-end oil mist concentration is based on OSHA’s Permissible Exposure Limit 

(PEL) of 5 mg/m3 (NIOSH, 1998).

· The percent active ingredient in treated metalworking fluid is 1450 ppm (i.e., 0.145% ai) 

calculated from 0.5% formulated product x 29% ai (EPA Registration No. 5383-47).

· The inhalation rate for a machinist is 1.0 m

3 /hr.

· A machinist is exposed to the metalworking fluid 8 hours a day, for 5 days a week.

· The body weight of an adult is 70 kg (USEPA 1997).
Page 33 of 43

Dermal and Inhalation Results

Table 6.3 shows the calculation of the absorbed daily dose and MOE for a machinist 

working with metalworking fluids. The dermal and inhalation MOE values are below the target 

MOE of 100 for all durations. 

Table 6.3. Short-, Intermediate-, and Long-Term Risks Associated with Postapplication 

Exposure to Metalworking Fluids treated with BNS (Machinist)

Dermal Inputs Inhalation Inputs Absorbed Daily Dose 

(mg/kg/day)

MOE

% 

a.i.

Hand & 

Forearm 

Surface 

Area 

(cm2)

Film 

thickness 

(mg/cm2)

Frequency 

(event/day)

OSHA 

PEL

(mg/m3)

Inhal. 

rate 

(m3/hr)

Exposure 

Duration 

(hrs/day)

Dermal a

(mg/kg/day)

Inhalation.

b 

(mg/kg/day)

Dermal MOE 

(Target MOE = 

100)c

Inhalation MOE 

(Target MOE = 

100)d

0.145 2013 1.75 1 5 1.0 8 0.011 0.00083 3 36

a Dermal Daily Dose (mg/kg/day) = [(% active ingredient * hand & forearm surface area* dermal absorption factor (1)* film thickness 

(mg/cm2)* Frequency (event/day)] / Body weight (70 kg).

b Inhalation Daily Dose (mg/kg/day) = % active ingredient * OSHA PEL (mg/m3) * Inhalation rate (m3/hr) * exposure duration (hr/day) * 

inhalation absorption factor (1)/ body weight (70 kg)

c Dermal MOE = BMD10 (mg/kg/day) / Daily Dose (mg/kg/day) [Where: ST/IT/LT dermal BMD10 = 0.03 mg/kg/day; target MOE = 

100]. 

d Inhalation MOE = BMD10 (mg/kg/day) / Daily Dose (mg/kg/day) [Where: inhalation BMD10 = 0.03 mg/kg/day for all durations; target 

MOE = 100 for all durations]

Fogging (Poultry farm building)

Post-application inhalation exposure (to aerosols) was assessed for entry into a poultry

farm building after a fogging application. The inhalation exposures and resulting REIs are based

on modeling of the aerosols from the maximum application rate. Fogging poultry farm buildings 

based on the label rate is assumed to be the high end of the air concentrations (mg/m3) when 

fogging the incubators, hatchers, and hatchery rooms. The air concentration applied and the air 

exchange rates of the structure are used to estimate the REIs. Therefore, nuances in the treatment 

of poultry farm buildings versus poultry hatcheries are based on the target air concentration 

application rate. Any dermal post application is presumed to be negligible. The inhalation 

exposure assessment was conducted using the Multi-Chamber Concentration and Exposure 

Model (MCCEM v1.2). MCCEM estimates average and peak indoor air concentrations of 

chemicals released from products or materials in houses, apartments, townhouses, or other 

residences. Although the data libraries contained in MCCEM are limited to residential settings, 

the model can be used to assess other indoor environments. 

The MCCEM model was executed utilizing the rate of 1.3E-6 lb ai/ft3(EPA Reg No. 

65020-12 states to fog 1 gallon of product per 6,000ft2 of floor space and EPA assumed 10 ft 
Page 34 of 43

ceilings to calculate an air concentration per volume) for poultry houses. Upon commencement 

of fogging activities, TBT labels state that the building should be well ventilated and not entered 

until 1 to 4 hours after fogging. If the building must be entered, the label states individuals 

entering the building must wear a self-contained respirator approved by NIOSH/MSHA, goggles, 

long sleeves and long pants. Therefore, exposure was calculated for a person entering the 

building 1, 2, and 4 hours after all the applied fogger has been deployed. The following 

assumptions were included along with the standard input parameters of the MCCEM model.

· The area being fogged is a one-chamber barn with dimensions of 600ft x 66ft x 10ft (AD 

standard assumption).

· For the poultry structures, the air exchange rate is 4 per hour based on the rate for a poultry

barn (Jacobson, 2005).

· Fogging occurs instantaneously, so that the entire mass of product is mixed homogeneously

with the indoor air as soon as fogging commences. 

· It is assumed that all of the aerosols are inhalable and/or respirable.

A detailed report is presented in Appendix B, including air concentrations reported for 

every 10 minutes for several days. Upon entry after 1 hour, the 8-hour time weighted average 

(TWA) air concentration for a worker exposed for 8 hours the MOEs is less then the target MOE 

of 100 (i.e., MOE = 17). However, the MOE is greater than the target MOE of 100 if the REI is 

set at 2 hours and there are 4 air exchange rates per hour (ACH). If specific REIs are warranted 

for hatcheries that differ from 2 hours, a comparison of the fogging concentration rates (e.g., 

mg/m3) should be discussed during mitigation.

Table 22. Short and Intermediate Term Inhalation Risks Associated with Postapplication Exposure to TBT

After Fogging a Poultry House

Parametera Value Rationale

Dimensions

600 ft x 66t x10 ft,

39,600 ft2floor area,

396,000 ft3(11214 m3)

volume

Standard AD assumption

Air Changes per Hour (ACH)*4/hr Jacobson, 2005

Activity Pattern*

Time Weighted Average (TWA) 

starting at expiration of 1 and 4 hr 

REI

Based on product’s re-entry interval

Concentration of Fogging Liquid Not needed lb ai/gal Product Label (65020-12)

Use rate 1.3E-6 lb ai/ft3

Product label states to fog 1 gal 

product/6000 ft2x 10 ft ceiling 

(ceiling height assumed)

Concentration in room after fogging 

(initial concentration rate at time 0)* 20.61 mg ai/m3

See Appendix B spreadsheet

Body Weight 70 kg (adult) NAFTA (USEPA, 1997)

Inhalation Rate 1.0 m3/hr NAFTA Light Activity for Adults 

(USEPA, 1997)

MCCEM OUTPUT 1 hour

REI

2 hour

REI

4 hour

REI
Page 35 of 43

Table 22. Short and Intermediate Term Inhalation Risks Associated with Postapplication Exposure to TBT

After Fogging a Poultry House

Parametera Value Rationale

Concentration after appropriate REI 

(mg/m3)

0.377 0.0069 2.3E-6 MCCEM calculated air concentration

8-hour Time Weighted Average

(TWA) air concentration (mg/m3)

0.016

(TWA 

from 1 to 

9 HAT)

2.9E-4

(TWA 

from 1 to 

9 HAT)

9.7E-8

(TWA 

from 4 to 

12 HAT)

MCCEM-calculated 8-hr TWA air 

concentration starting after REI for 8 

hour working shift 

Dose (mg/kg/day) 0.0018 3.3E-5 1.1E-8

(TWA Air Conc.) x (Exposure Time 

of 8 hr) x (Inhal. Rate) / BW (70kg)

Short-term MOE 17 910 2.7E+6 BMD10 (0.03 mg/kg/day) / Dose

*Used as MCCEM input. Default values from MCCEM were used for all inputs not listed in the table above.

HAT = hours after treatment.

6.4 Data Limitations/Uncertainties

There are several data limitations and uncertainties associated with the occupational 

handler and post application exposure assessments. These include:

· Surrogate dermal and inhalation unit exposure values were taken from the proprietary

Chemical Manufacturers Association (CMA) antimicrobial exposure study (USEPA, 1999: 

DP Barcode D247642) or from the Pesticide Handler Exposure Database (USEPA, 1998) 

(See Appendix B for summaries of these data sources). Since the CMA data are of poor 

quality, the Agency requires that confirmatory data be submitted to support the occupational 

scenarios assessed in this document.

· The quantities handled/treated were estimated based on information from various sources, 

including HED’s Standard Operating Procedures (SOPs) for Residential Exposure 

Assessments (USEPA, 2000 and 2001), and personal communication with experts. In 

particular, the use information for the pulp and paper processing, drilling mud uses, and 

cooling water tower uses are based on personal communication with biocide manufacturers 

for these types of uses. The individuals contacted have experience in these operations and 

their estimates are believed to be the best available without undertaking a statistical survey

of the uses. In certain cases, no standard values were available for some scenarios. 

Assumptions for these scenarios were based on EPA estimates and could be further refined 

from input from registrants. 
Page 36 of 43

7.0 REFERENCES

USEPA. 1992. A Laboratory Method to Determine the Retention of Liquids on the Surface of 

Hands, Exposure Evaluation Division, Office of Pollution Prevention and Toxic, USEPA, EPA 

747-R-92-003, September, 1992.

USEPA. 1996. Office of Research and Development, Descriptive Statistics Tables from a 

Detailed Analysis of the National Human Activity Pattern (NHAPS) Data; EPA/600/R-96/148, 

July 1996. Data Collection Period October 1992 - September 1994 . 

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

Development. Washington, D.C. EPA/600/P-95/002Fa. August 1997.

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. 1999. Evaluation of Chemical Manufacturers Association Antimicrobial Exposure 

Assessment Study (Amended on 8 December 1992). Memorandum from Siroos Mostaghimi, 

PH.D., USEPA to Julie Fairfax, USEPA. Dated November, 4 1999. DP Barcode D247642.

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

Division. Dated April 5, 2000.

USEPA. 2001. HED Science Advisory Council for Exposure. Policy Update, November 12. 

Recommended Revisions to the Standard Operating Procedures (SOPs) for Residential Exposure 

Assessment, February 22, 2001. 
Page 37 of 43

APPENDIX A: Summary of CMA and PHED Data
Page 38 of 43

Chemical Manufacturers Association (CMA) Data:

In response to an EPA Data Call-In Notice, a study was undertaken by the Institute of 

Agricultural Medicine and Occupational Health of The University of Iowa under contract to the 

Chemical Manufacturers Association. In order to meet the requirements of Subdivision U of the 

Pesticide Assessment Guidelines (superseded by Series 875.1000-875.1600 of the Pesticide 

Assessment Guidelines), handler exposure data are required from the chemical manufacturer 

specifically registering the antimicrobial pesticide. The applicator exposure study must comply

with the assessment guidelines for Applicator Exposure Monitoring in Subdivision U and the 

Occupational and Residential Exposure Test Guidelines in Series 875. For this purpose, CMA 

submitted a study on 28 February, 1990, entitled "Antimicrobial Exposure Assessment Study

(amended on December 8, 1992)" which was conducted by William Popendorf, et al. It was 

evaluated and accepted by Occupational and Residential Exposure Branch (OREB) of Health 

Effect Division (HED), Office of Pesticides Program (OPP) of EPA in 1990. The purpose of this 

CMA study was to characterize exposure to antimicrobial chemicals in order to support pesticide 

reregistrations (CMA, 1992). The unit exposure values presented in the most recent EPA 

evaluation of the CMA database (USEPA, 1999b) were used in this assessment.

The advantages of CMA data over other surrogate data sets is that the chemicals and the job 

functions of mixer/loader/applicator were defined based on common application methods used 

for antimicrobial pesticides. A few of the deficiencies in the CMA data are noted below:

· The inhalation concentrations were typically below the detection limits, so the unit exposure

values for the inhalation exposure route could not be accurately calculated. 

· QA/QC problems in the study included a lack of or low recovery of either/or field 

fortification, laboratory recoveries, and storage stability information.

· Data have an insufficient amount of replicates.

The Pesticide Handlers Exposure Database (PHED):

The Pesticide Handlers Exposure Database (PHED) has been developed by a Task Force 

consisting of representatives from Health Canada, the U.S. Environmental Protection Agency

(EPA), and the American Crop Protection Association (ACPA). PHED provides generic 

pesticide worker (i.e., mixer/loader and applicator) exposure estimates. The dermal and 

inhalation exposure estimates generated by PHED are based on actual field monitoring data, 

which are reported generically (i.e., chemical specific names not reported) in PHED. It has been 

the Agency’s policy to use surrogate or generic exposure data for pesticide applicators in certain 

circumstances because it is believed that the physical parameters (e.g., packaging type) or 

application technique (e.g., aerosol can), not the chemical properties of the pesticide, attribute to 

exposure levels. [Note: Vapor pressures for the chemicals in PHED are in the range of E-5 to E-7 

mm Hg.] Chemical specific properties are accounted for by correcting the exposure data for 

study specific field and laboratory recovery values as specified by the PHED grading criteria.

PHED handler exposure data are generally provided on a normalized basis for use in exposure 

assessments. The most common method for normalizing exposure is by pounds of active 
Page 39 of 43

ingredient (ai) handled per replicate (i.e., exposure in mg per replicate is divided by the amount 

of ai handled in that particular replicate). These unit exposures are expressed as mg/lb ai 

handled. This normalization method presumes that dermal and inhalation exposures are linear 

based on the amount of active ingredient handled.
Page 40 of 43

Appendix B

MCCEM Output

Air Concentration Estimates for Fogging Poultry Houses
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Time (days)

Time 

(hour)

Conc Outdoors 

(mg/m3) Conc Zone 1 (mg/m3) Conc@Person(mg/m3)

0 0 0 20.61 0

0.00694444 0.1666666 1.12E-55 10.5816 10.5816

0.0138889 0.3333336 1.70E-55 5.43277 5.43277

0.0208333 0.4999992 2.00E-55 2.78928 2.78928

0.0277778 0.6666672 2.15E-55 1.43207 1.43207

0.0347222 0.8333328 2.23E-55 0.735252 0.735252

0.0416666 0.9999984 2.27E-55 0.377492 0.377492

0.0486111 1.1666664 2.29E-55 0.193811 0.193811

0.0555555 1.333332 2.30E-55 0.0995064 0.0995064

0.0625 1.5 2.31E-55 0.0510884 0.0510884

0.0694444 1.6666656 2.31E-55 0.0262297 0.0262297

0.0763888 1.8333312 2.31E-55 0.0134668 0.0134668

0.0833333 1.9999992 2.31E-55 0.00691413 0.00691413

0.0902777 2.1666648 2.31E-55 0.00354984 0.00354984

0.0972222 2.3333328 2.31E-55 0.00182255 0.00182255

0.104167 2.500008 2.31E-55 0.000935733 0.000935733

0.111111 2.666664 2.31E-55 0.000480423 0.000480423

0.118055 2.83332 2.31E-55 0.000246658 0.000246658

0.125 3 2.31E-55 0.000126639 0.000126639

0.131944 3.166656 2.31E-55 6.50E-05 6.50E-05

0.138889 3.333336 2.31E-55 3.34E-05 3.34E-05

0.145833 3.499992 2.31E-55 1.71E-05 1.71E-05

0.152778 3.666672 2.31E-55 8.80E-06 8.80E-06

0.159722 3.833328 2.31E-55 4.52E-06 4.52E-06

0.166667 4.000008 2.31E-55 2.32E-06 2.32E-06

0.173611 4.166664 2.31E-55 1.19E-06 1.19E-06

0.180555 4.33332 2.31E-55 6.11E-07 6.11E-07

0.1875 4.5 2.31E-55 3.14E-07 3.14E-07

0.194444 4.666656 2.31E-55 1.61E-07 1.61E-07

0.201389 4.833336 2.31E-55 8.27E-08 8.27E-08

0.208333 4.999992 2.31E-55 4.25E-08 4.25E-08

0.215278 5.166672 2.31E-55 2.18E-08 2.18E-08

0.222222 5.333328 2.31E-55 1.12E-08 1.12E-08

0.229167 5.500008 2.31E-55 5.75E-09 5.75E-09

0.236111 5.666664 2.31E-55 2.95E-09 2.95E-09

0.243055 5.83332 2.31E-55 1.52E-09 1.52E-09

0.25 6 2.31E-55 7.78E-10 7.78E-10

0.256944 6.166656 2.31E-55 4.00E-10 4.00E-10

0.263889 6.333336 2.31E-55 2.05E-10 2.05E-10

0.270833 6.499992 2.31E-55 1.05E-10 1.05E-10

0.277778 6.666672 2.31E-55 5.41E-11 5.41E-11

0.284722 6.833328 2.31E-55 2.78E-11 2.78E-11

0.291666 6.999984 2.31E-55 1.43E-11 1.43E-11

0.298611 7.166664 2.31E-55 7.32E-12 7.32E-12

0.305555 7.33332 2.31E-55 3.76E-12 3.76E-12

0.3125 7.5 2.31E-55 1.93E-12 1.93E-12
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0.319444 7.666656 2.31E-55 9.90E-13 9.90E-13

0.326389 7.833336 2.31E-55 5.08E-13 5.08E-13

0.333333 7.999992 2.31E-55 2.61E-13 2.61E-13

0.340278 8.166672 2.31E-55 1.34E-13 1.34E-13

0.347222 8.333328 2.31E-55 6.88E-14 6.88E-14

0.354166 8.499984 2.31E-55 3.53E-14 3.53E-14

0.361111 8.666664 2.31E-55 1.81E-14 1.81E-14

0.368055 8.83332 2.31E-55 9.31E-15 9.31E-15

0.375 9 2.31E-55 4.78E-15 4.78E-15

0.381944 9.166656 2.31E-55 2.45E-15 2.45E-15

0.388889 9.333336 2.31E-55 1.26E-15 1.26E-15

0.395833 9.499992 2.31E-55 6.47E-16 6.47E-16

0.402778 9.666672 2.31E-55 3.32E-16 3.32E-16

0.409722 9.833328 2.31E-55 1.71E-16 1.71E-16

0.416666 9.999984 2.31E-55 8.76E-17 8.76E-17

0.423611 10.166664 2.31E-55 4.50E-17 4.50E-17

0.430555 10.33332 2.31E-55 2.31E-17 2.31E-17

0.4375 10.5 2.31E-55 1.19E-17 1.19E-17

0.444444 10.666656 2.31E-55 6.09E-18 6.09E-18

0.451389 10.833336 2.31E-55 3.12E-18 3.12E-18

0.458333 10.999992 2.31E-55 1.60E-18 1.60E-18

0.465277 11.166648 2.31E-55 8.24E-19 8.24E-19

0.472222 11.333328 2.31E-55 4.23E-19 4.23E-19

0.479166 11.499984 2.31E-55 2.17E-19 2.17E-19

0.486111 11.666664 2.31E-55 1.11E-19 1.11E-19

0.493055 11.83332 2.31E-55 5.72E-20 5.72E-20

0.5 12 2.31E-55 2.94E-20 2.94E-20