**UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

**WASHINGTON, D.C. 20460**

**12/18/2007**

![](media/image1.png){width="5.330555555555556in"
height="0.4777777777777778in"}

**[MEMORANDUM]{.underline}**

**SUBJECT:** **Estimated Environmental Concentrations for Tributyltin
Oxide (TBTO) Leached from Wood into Soil and Water**

**From: Siroos Mostaghimi, Ph.D., Senior Scientist**

**Risk Assessment and Science Support Branch (RASSB)**

**Antimicrobials Division (7510P)**

**To: Norm Cook, Chief**

**Risk Assessment and Science Support Branch (RASSB)**

**Antimicrobials Division (7510P)**

**Chemical NO: 083001**

**CAS Registry Number: 56-35-9**

**Attached please find the result of modeling for leaching of TBTO from
wood into soil and water.**

> **Introduction**

This report presents estimates of environmental concentrations of
bis(tri-n-butyltin) oxide (TBTO) in soil, surface water, and sediment
pore water resulting from the use of TBTO as a wood preservative. TBTO
is registered for use as a bacteriostat, micorbicide/microbistat,
fungicide, algaecide, antifoulant, slimacide, virucide, disinfectant,
sanitizer, miticide and insecticide. TBTO is also registered for use on
agricultural farm buildings and equipment, commercial and industrial
water cooling systems, medical buildings and equipment, textiles,
adhesives, caulks, and plastics.

The methodology for this analysis is consistent the methodology used
previously for the wood preservative AMICAL This methodology was based
on an environmental risk assessment previously prepared by the Rohm and
Haas Company (2006) for 4,5-dichloro-2-n-octyl-3(2H)-isothiazolone
(DCOIT), as well as a lumber leaching methodology developed by Krahn and
Strub (1990) . In this methodology, leaching of TBTO from treated wood
surfaces is modeled to estimate soil loadings and concentrations. The
estimated soil concentrations and other input data are used with EPA's
PE5 PRZM-EXAMS Model Shell (version 5.0) to estimate concentrations in
surface water and sediment pore water.

Section 1 of this memorandum presents the estimation of environmental
concentrations of TBTO in soil. Estimates of dissolved surface water and
sediment pore water concentrations of TBTO are presented in Section 2.
Section 3 identifies key assumptions, limitations, and uncertainties of
this analysis. Section 4 identifies referenced literature.

**1. Estimation of TBTO Concentrations in Soil**

This section describes the estimation of environmental concentrations of
TBTO in soil. Soil concentrations of TBTO were estimated for six wood
preservative use scenarios developed by Rohm and Haas (2006):
transmission pole, fence post, fence, deck post, deck, and house. Data,
assumptions, and calculations for these use scenarios are presented in
Section 1.2. Section 1.1 describes the approach used with all use
scenarios to estimate TBTO leaching from treated wood surfaces. Section
1.3 describes how soil concentrations estimated for each use scenario
were used to estimate soil compartment loading rates for use with the
PE5 model.

1.  **Cumulative Quantity of TBTO Leached Out of Wood**

Leaching of TBTO from treated wood surfaces was estimated based on
chemical properties and a treated lumber leaching methodology developed
by Krahn and Strub (1990).

Krahn and Strub (1990) conducted a field experiment to measure rainfall
leaching of an antisapstain chemical from treated wood. Stacks of
treated lumber (2 feet x 4 feet x 16 feet) were placed outdoors above
leachate collection trays, and leachate was collected following a
five-hour rainfall event. The volume of leachate collected, the
concentration of the leachate, and the surface area of lumber exposed to
rainfall were then be used to calculate the mass of antisapstain
chemical released per square meter of wood surface during the five-hour
rain cycle. Kahn and Strub (1990) then used this experiment to devise a
general protocol for estimating antisapstain leaching and surface runoff
from a lumber yard containing 16 lumber stacks of various ages.

Versar (2005) applied the Krahn and Strub (1990) protocol to estimate
runoff of the antisapstain chemical ADBAC from a hypothetical lumber
yard. First, Versar (2005) developed Equation 1 to estimate leaching
from a lumber stack and single five-hour leaching cycle.

**Equation 1**

> $$C_{i} = \frac{M_{o}}{V_{\text{leachate}}} \times \left\lbrack e^{- \left\lbrack \frac{\text{SA}_{\text{top}}I}{\text{SA}_{\text{total}}K_{\text{OC}}Z} \right\rbrack t_{i - 1}} - e^{- \left\lbrack \frac{\text{SA}_{\text{top}}I}{\text{SA}_{\text{total}}K_{\text{OC}}Z} \right\rbrack t_{i}} \right\rbrack$$

Where:

*C~i~* = Concentration of leachate produced during a five-hour leaching
cycle *i* (ppm or

mg/L)

*M~o\ ~* = Mass of chemical applied to leachable portion of wood at time
*t = 0* (131,467.61 mg from spreadsheet attached with this memorandum)

*t~i~* = Time at which leaching cycle *i* ends (each leaching cycle is 5
hours) (i + 5 hrs)

*V~leachate~* = Volume of leachate per stack of lumber (119 L calculated
from Krahn and

Strub, 1990)

*SA~top~* = Surface area of the top of a stack of lumber (5.95 m^2^
calculated from

Krahn and Strub, 1990)

*SA~total~* = Total surface area of the exposed to rain (i.e., all
surfaces except bottom; 13.4

m^2^ calculated from Krahn and Strub, 1990)

*I* = Rainfall Intensity (0.003 m/hr from Versar, 2005)

*K~OC~* = Organic carbon partition coefficient (5080 mL/g from EPA,
2007)

Z = Surface thickness of leachable wood (0.01 m from EPA, 2004)

Parameter values and sources for this Equation 1 are shown with the
parameter definitions. In this equation, the chemical-specific leaching
behavior is predicted using the organic carbon partition coefficient
(Koc). For more explanation of how this Equation 1 was derived, refer to
ICF (2007b) and Versar (2005).

Rohm and Hass (2006) estimated soil environmental concentrations using
cumulative leaching data obtained from an aqueous leaching study in
which a block of treated wood was immersed for 14 days. To make the TBTO
analysis consistent with the Rohm and Hass (2006) methodology, the
rainfall leaching equation (i.e., Equation 1) to calculate cumulative
leaching of TBTO after 67 five-hour rain cycles totaling 13.9 days
(i.e., approximately equivalent to the 14-day immersion study). The
cumulative quantity of TBTO leached per m^2^ of treated wood over the
13.9 day time period was calculated to be 85.8 mg/m^2^. All calculations
are provided in an Excel spreadsheet submitted with this memorandum.

2.  **TBTO Use Scenarios**

Six TBTO use scenarios defined by Rohm and Haas (2006) were used to
estimate post-application environmental concentrations in soil. The use
scenarios included application of TBTO to from transmission poles, fence
posts, fencing, deck posts, decking, and wood clad houses into soil.
Spreadsheets containing calculations for each scenario are provided with
this memorandum.

1.  **Transmission Poles**

The environmental concentration in soil following application of TBTO to
a transmission pole was estimated by first calculating the quantity of
TBTO leached into the volume of the soil surrounding a transmission
pole, as shown in Equation 2. This value (Q~pole~) is the product of the
sum of the treated wood surface areas above and below ground and the
cumulative quantity of TBTO leached per 1 m^2^ of treated wood over a 14
day period.

**Equation 2:**

*Q~pole~ = (Area~AG~+Area~BG~)\*Q~LT~*

Where:

*Q~pole~* = Estimated quantity of TBTO leached into the volume of soil
surrounding

> a transmission pole (6.09E-04 kg)

*Area~AG~* = Wood surface area above ground (5.5 m^2^ from Rohm and
Haas, 2006)

*Area~BG~* = Wood surface area below ground (1.6 m^2^ from Rohm and
Haas, 2006)

*Q~LT~* = Cumulative quantity of TBTO leached out of 1 m^2^ of treated
wood over a

> 14 day period (8.58E-05 kg/m^2^ from Section 1.1)

Next, the concentration of TBTO in the soil surrounding the transmission
pole was calculated by dividing the estimated quantity of TBTO leached
into the soil surrounding the transmission pole (Q~pole~) by the product
of the volume of wet soil and the bulk density of wet soil:

**Equation 3:**

*C~soilpole~ = (Q~pole~\*CONV~kgmg~)/(V~soil~\*RHO~soil~)*

Where:

*C~soilpole~* = Estimated concentration of TBTO in soil surrounding a
transmission pole (1.49 mg/kg)

*Q~pole~* = Estimated quantity of TBTO leached into the volume of soil
surrounding a

transmission pole (6.09E-04 kg from Equation 2)

*CONV~kgmg~* = Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

*V~soil~* = Wet soil volume (0.24 m^3^ from Rohm and Haas, 2006)

*RHO~soil~* = Bulk density of wet soil (1,700 kg~ww~/m^3^ from Rohm and
Haas, 2006)

2.  **Fence Posts**

Environmental concentrations of TBTO in soil from treated fence posts
were estimated by first calculating the quantity of the TBTO leached
into the volume of the soil surrounding a fence post, as shown in
Equation 4. Q~FencePost~ is the product of the sum of the wood surface
area above and below ground and the cumulative quantity of TBTO leached
per m^2^ of treated wood over a 14 day period.

**Equation 4:**

*Q~FencePost~ = (Area~AG~+Area~BG~)\*Q~LT~*

Where:

*Q~FencePost~* = Estimated quantity of TBTO leached into the volume of
soil

surrounding a fence post (6.86E-05 kg)

*Area~AG~* = Wood surface area above ground (0.6 m^2^ from Rohm and
Haas, 2006)

*Area~BG~* = Wood surface area below ground (0.2 m^2^ from Rohm and
Haas, 2006)

*Q~LT~* = Cumulative quantity of TBTO leached from 1 m^2^ of treated
wood

over a 14 day period (8.58E-05 kg/m^2^ from Section 1.1)

Using Equation 5, the concentration of TBTO in the soil surrounding the
fence post was then calculated by dividing the estimated quantity of
TBTO leached into the soil surrounding the fence post (Q~FencePost~) by
the product of the volume of wet soil and the bulk density of wet soil:

**Equation 5:**

*C~soilFencePost~ = (Q~FencePost~\*CONV~kgmg~)/(V~soil~\*RHO~soil~)*

Where:

*C~soilFencePost~* = Estimated concentration of TBTO in soil surrounding
a fence post (0.82 mg/kg)

*Q~FencePost~* = Estimated quantity of TBTO leached into the volume of
soil surrounding

a fence post (6.86E-05 kg from Equation 4)

*CONV~kgmg~* = Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

*V~soil~* = Wet soil volume (0.049 m^3^ from Rohm and Haas, 2006)

*RHO~soil~* = Bulk density of wet soil (1,700 kg~ww~/m^3^ from Rohm and
Haas, 2006)

3.  **Fence**

The environmental concentration of TBTO in soil following application to
a fence was estimated by first calculating the quantity of the TBTO
leached into the volume of the soil surrounding a one meter length of
fence. As shown in Equation 6, this value (*Q~Fence~*) is the product of
the surface area of wood per meter of fence and the cumulative quantity
of TBTO leached per m^2^ of treated wood over a 14 day period.

**Equation 6:**

*Q~Fence~ = Area~Fence~\*Q~LT~*

Where:

*Q~Fence\ ~*= Estimated quantity of TBTO leached into the volume of soil
surrounding

a one meter length of fence (1.72E-04 kg)

*Area~Fence~* = Wood surface area per meter of fence (2 m^2^ from Rohm
and Haas, 2006)

*Q~LT~* = Cumulative quantity of TBTO leached per m^2^ of treated wood
over a

14 day period (8.58E-05 kg/m^2^ from Section 1.1)

Using Equation 7, the concentration of TBTO in the soil surrounding the
fence was calculated by dividing the estimated quantity of TBTO leached
into the soil surrounding the fence (Q~Fence~) by the product of the
volume of wet soil and the bulk density of wet soil:

**Equation 7:**

*C~soilFence~= (Q~Fence~\*CONV~kgmg~)/(V~soil~\*RHO~soil~)*

Where:

*C~soilFence~* = Estimated concentration of TBTO in soil surrounding a 1
m length

of fence (10.09 mg/kg)

*Q~Fence~* = Estimated quantity of TBTO leached into the volume of soil
surrounding

the fence (1.72E-04 kg from Equation 6)

*CONV~kgmg~* = Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

*V~soil~* = Wet soil volume (0.01 m^3^ from Rohm and Haas, 2006)

*RHO~soil~* = Bulk density of wet soil (1,700 kg~ww~/m^3^ from Rohm and
Haas, 2006)

4.  **Deck Post**

The concentration of TBTO in soil surrounding a treated deck posts was
estimated by first calculating the quantity of the TBTO leached into the
volume of the soil surrounding a deck post. As shown in Equation 8, this
value (*Q~DeckPost~*) is the product of the sum of the surface area of
treated wood above and below ground and the cumulative quantity of TBTO
leached per m^2^ of treated wood over a 14 day period.

**Equation 8:**

*Q~DeckPost~ = (Area~AG~+Area~BG~)\*Q~LT~*

Where:

*Q~DeckPost~* = Estimated quantity of TBTO leached into the volume of
soil surrounding

> a deck post (1.03E-04 kg)

*Area~AG~* = Wood surface area above ground (0.9 m^2^ from Rohm and
Haas, 2006)

*Area~BG~* = Wood surface area below ground (0.3 m^2^ from Rohm and
Haas, 2006)

*Q~LT~* = Cumulative quantity of TBTO leached out of 1 m^2^ of treated
wood

> over a 14 day period (8.58E-05 kg/m^2^ from Section 1.1)

Then, Equation 9 was used to calculate the concentration of TBTO in the
soil surrounding the deck post. In Equation 9 the estimated quantity of
TBTO leached into the soil surrounding the deck posts (Q~DeckPost~) is
divided by the product of the volume of wet soil and the bulk density of
wet soil:

**Equation 9:**

*C~SoilDeckPost~ = (Q~DeckPost~\*CONV~kgmg~)/(V~soil~\*RHO~soil~)*

Where:

*C~soilDeckPost~* = Estimated concentration of TBTO in soil surrounding
a deck post (0.98 mg/kg)

*Q~DeckPost~* = Estimated quantity of TBTO leached into the volume of
soil surrounding a

deck post (1.03E-04 kg from Equation 8)

*CONV~kgmg~* = Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

*V~soil~* = Wet soil volume (0.062 m^3^ from Rohm and Haas, 2006)

*RHO~soil~* = Bulk density of wet soil (1,700 kg~ww~/m^3^ from Rohm and
Haas, 2006)

5.  **Deck**

The environmental concentration of TBTO in soil associated with a
treated deck was estimated by first calculating the quantity of the TBTO
leached into the volume of the soil surrounding a deck. As shown in
Equation 10, Q~Deck~ is the product of the wood surface area above the
soil and the cumulative quantity of TBTO leached from 1 m^2^ of treated
wood over a 14 day period.

**Equation 10:**

*Q~Deck~ = Area~Deck~\*Q~LT~*

Where:

*Q~Deck~* = Estimated quantity of TBTO leached into the volume of soil
surrounding

the deck (2.06E-03 kg)

*Area~Deck~* = Wood surface area above soil (24 m^2^ from Rohm and Haas,
2006)

*Q~LT~* = Cumulative quantity of TBTO leached per m^2^ of treated wood
over

a 14 day period (8.58E-05 kg/m^2^ from Section 1.1)

The concentration of TBTO in the soil surrounding the deck was then
calculated with Equation 11, in which the estimated quantity of TBTO
leached into the soil surrounding the deck (Q~Deck~) is divided by the
product of the volume of wet soil and the bulk density of wet soil:

**Equation 11:**

*C~soilDeck~= (Q~Deck~\*CONV~kgmg~)/(V~soil~\*RHO~soil~)*

Where:

*C~soilDeck~* = Estimated concentration of TBTO in soil surrounding the
deck (0.50 mg/kg)

*Q~Deck~* = Estimated quantity of TBTO leached into the volume of soil
surrounding the deck (2.06E-03 kg from Equation 10)

*CONV~kgmg\ ~*= Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

*V~soil~* = Wet soil volume (2.4 m^3^ from Rohm and Haas, 2006)

*RHO~soil~* = Bulk density of wet soil (1,700 kg~ww~/m^3^ from Rohm and
Haas, 2006)

6.  **House**

The environmental concentrations of TBTO in soil surrounding a treated,
wood-clad house was estimated by first calculating the quantity of the
TBTO leached into the volume of the soil surrounding a house. This
quantity, which is estimated with Equation 12, is the product of the
treated wood surface area above the soil and the cumulative quantity of
TBTO leached per m^2^ of treated wood over a 14 day period.

**Equation 12:**

*Q~House~ = Area~House~\*Q~LT~*

Where:

*Q~House~* = Estimated quantity of TBTO leached into the volume of soil
surrounding

a house (1.07E-02 kg)

*Area~House~* = Wood surface area above soil (125 m^2^ from Rohm and
Haas, 2006)

*Q~LT~* = Cumulative quantity of TBTO leached per m^2^ of treated wood
over

a 14 day period (8.58E-05 kg/m^2^ from Section 1.1)

Then, the concentration of TBTO in the soil surrounding the house was
calculated (see Equation 13) by dividing the estimated quantity of TBTO
leached into the soil surrounding the house (Q~House~) by the product of
the volume of wet soil and the bulk density of wet soil:

**Equation 13:**

*C~soilHouse~ = (Q~House~\*CONV~kgmg~)/(V~soil~\*RHO~soil~)*

Where:

C~soilHouse~ = Estimated concentration of TBTO in soil surrounding the
house (12.6 mg/kg)

Q~House~ = Estimated quantity of TBTO leached into the volume of soil
surrounding

the house (1.07E-02 kg from Equation 12)

CONV~kgmg~ = Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

V~soil~ = Wet soil volume (0.5 m^3^ from Rohm and Haas, 2006)

RHO~soil~ = Bulk density of wet soil (1700 kg~ww~/m^3^ from Rohm and
Haas, 2006)

Soil concentrations calculated for the six use scenarios are summarized
in Table 1.

**Table 1. Summary of Estimated Environmental Concentrations of TBTO in
Soil for Six Use Scenarios**

+------------------------+--------------------+-----------------------+
| **TBTO Use scenario**  | **TBTO Mass (ai)   | **TBTO Concentration  |
|                        | Leached into Soil  | (ai) in Soil (mg/kg   |
|                        | Associated with    | wet weight)^1,3^**    |
|                        | Treated Wood       |                       |
|                        | Surface            |                       |
|                        | (kg)^1,2^**        |                       |
+------------------------+--------------------+-----------------------+
| Transmission Pole      | 6.1E-04            | 1.5                   |
+------------------------+--------------------+-----------------------+
| Fence Post             | 6.9E-05            | 0.82                  |
+------------------------+--------------------+-----------------------+
| Fence                  | 1.7E-04            | 10\.                  |
+------------------------+--------------------+-----------------------+
| Deck Post              | 1.0E-04            | 0.98                  |
+------------------------+--------------------+-----------------------+
| Deck                   | 2.1E-03            | 0.50                  |
+------------------------+--------------------+-----------------------+
| House                  | 1.1E-02            | 13                    |
+------------------------+--------------------+-----------------------+
| **^1^** All values are |                    |                       |
| rounded to two         |                    |                       |
| significant digits.    |                    |                       |
|                        |                    |                       |
| **^2^** TBTO mass      |                    |                       |
| leached into soil      |                    |                       |
| associated with        |                    |                       |
| treated wood surfaces  |                    |                       |
| is calculated with     |                    |                       |
|                        |                    |                       |
| Equations 2, 4, 6, 8,  |                    |                       |
| 10, and 12.            |                    |                       |
|                        |                    |                       |
| **^3^** TBTO mass      |                    |                       |
| leached into soil      |                    |                       |
| associated with        |                    |                       |
| treated wood surfaces  |                    |                       |
| is calculated with     |                    |                       |
|                        |                    |                       |
| Equations 3, 5, 7, 9,  |                    |                       |
| 11, and 13.            |                    |                       |
+------------------------+--------------------+-----------------------+

**2.** **Dissolved Surface Water and Sediment Pore Water Concentration
Modeling**

EPA's PE5 PRZM-EXAMS Model Shell (PE5) was used to simulate transport of
TBTO from soil to a surface water body. In this modeled scenario, the
water body is assumed to be a farm pond adjacent to a fruit orchard
where the contaminated soil is located. Soil compartment loading rates
based on the soil concentration estimates in Table 1 were entered into
PE5 to estimate concentrations of TBTO in dissolved surface water and
sediment pore water. PE5 was run for each of the six TBTO use scenarios
identified in Section 1.2 (e.g., deck, fence post).

The PE5 model requires hectare-scale estimates of TBTO released in soil
(kg TBTO per ha) as an input value. The hectare-scale loading rates are
estimates of the amount of TBTO released in the soil compartment in a
one-hectare area. For all use scenarios, it was assumed that five
treated wood units (e.g., transmission poles, houses) are present per
hectare. Therefore, the hectare-scale loadings were calculating by
multiplying the TBTO mass leached into soil per treated wood unit (i.e.,
the middle column in Table 1) by five units per hectare. This approach
is consistent with the methodology developed by Rohm and Haas (2006).
Table 2 shows the resulting TBTO loadings per hectare.

Additional inputs for the PE5 runs include various chemical-specific
properties and assumptions. Table 3 lists the inputs to the PE5 runs,
including input values, units, and information sources. Assumed values
were chosen according to suggestions from Dr. Ronald Parker at EPA's
Office of Pesticide Programs (Parker, 2007).

The PE5 model calculates multiple-year chemical concentrations in the
water and benthic sediments, which are then reported, for each year, the
single-day peak concentration, the maximum 24-hour, 96-hour, 21-day,
60-day, and 90-day mean concentrations, and the mean annual
concentration (EPA, 2006a). Model outputs display the upper 10
percentiles of the single-year results (e.g., the upper tenth percentile
of the mean annual concentrations).

The results of the Express model runs for TBTO are presented in Tables 4
and 5. Table 4 reports dissolved surface water concentrations in µg/L
and Table 5 reports sediment pore water concentrations in µg/L.

**Table 2. Calculation of TBTO Loading Rates in Soil per Hectare**

+-------------+---------+--------+-------+--------+--------+--------+
| **Soil      | **TBTO  |        |       |        |        |        |
| Loading**   | Use     |        |       |        |        |        |
|             | Sce     |        |       |        |        |        |
|             | nario** |        |       |        |        |        |
+-------------+---------+--------+-------+--------+--------+--------+
|             | **Trans | *      | **Fe  | **Deck | **     | **H    |
|             | mission | *Fence | nce** | Post** | Deck** | ouse** |
|             | Pole**  | Post** |       |        |        |        |
+-------------+---------+--------+-------+--------+--------+--------+
| TBTO Mass   | 6.1E-04 | 6      | 1.    | 1      | 2      | 1      |
| Leached     |         | .9E-05 | 7E-04 | .0E-04 | .1E-03 | .1E-02 |
| into Soil   |         |        |       |        |        |        |
| Associated  |         |        |       |        |        |        |
| One Unit of |         |        |       |        |        |        |
| Treated     |         |        |       |        |        |        |
| Wood        |         |        |       |        |        |        |
| Surface     |         |        |       |        |        |        |
| (kg)^1^     |         |        |       |        |        |        |
+-------------+---------+--------+-------+--------+--------+--------+
| TBTO Mass   | 3.1E-03 | 3      | 8.    | 5      | 1      | 5      |
| Loading per |         | .4E-04 | 6E-04 | .2E-04 | .0E-02 | .4E-02 |
| Hectare     |         |        |       |        |        |        |
| (           |         |        |       |        |        |        |
| kg/ha)^1,2^ |         |        |       |        |        |        |
+-------------+---------+--------+-------+--------+--------+--------+
| **^1^** All |         |        |       |        |        |        |
| values are  |         |        |       |        |        |        |
| rounded to  |         |        |       |        |        |        |
| two         |         |        |       |        |        |        |
| significant |         |        |       |        |        |        |
| digits.     |         |        |       |        |        |        |
|             |         |        |       |        |        |        |
| **^2^**     |         |        |       |        |        |        |
| Mass        |         |        |       |        |        |        |
| loadings    |         |        |       |        |        |        |
| per hectare |         |        |       |        |        |        |
| equal the   |         |        |       |        |        |        |
| TBTO mass   |         |        |       |        |        |        |
| leached     |         |        |       |        |        |        |
| into soil   |         |        |       |        |        |        |
| per unit    |         |        |       |        |        |        |
| (e.g.,      |         |        |       |        |        |        |
| t           |         |        |       |        |        |        |
| ransmission |         |        |       |        |        |        |
| pole) times |         |        |       |        |        |        |
| five units  |         |        |       |        |        |        |
| per         |         |        |       |        |        |        |
| hectare.    |         |        |       |        |        |        |
+-------------+---------+--------+-------+--------+--------+--------+

**Table 3. PE5 Inputs**

+------------------------------------+----------+------+--------------+
| **Parameter**                      | *        | *    | **Source**   |
|                                    | *Value** | *Uni |              |
|                                    |          | ts** |              |
+------------------------------------+----------+------+--------------+
| OPP/EFED Scenario: CA Fruit        | CA Fruit |      | EPA          |
| Orchard                            |          |      | A            |
|                                    |          |      | ssumption^1^ |
+------------------------------------+----------+------+--------------+
| Meteorological File: PE5 default   | w9       |      | EPA, 2006a   |
|                                    | 3193.dvf |      |              |
+------------------------------------+----------+------+--------------+
| EXAMS Environment: Standard Pond   | pon      |      | EPA, 2006a   |
|                                    | d298.exv |      |              |
+------------------------------------+----------+------+--------------+
| Field Size                         | EPA Pond |      | EPA, 2006a   |
+------------------------------------+----------+------+--------------+
| Runoff Flow                        | None     |      | Parker, 2007 |
+------------------------------------+----------+------+--------------+
| Molecular weight                   | 596      | g/   | EPA, 2007    |
|                                    |          | mole |              |
+------------------------------------+----------+------+--------------+
| Henry\'s Law Constant              | 6.80E-05 | atm  | EPA, 2007    |
|                                    |          | m^3^ |              |
|                                    |          | /mol |              |
+------------------------------------+----------+------+--------------+
| Vapor pressure                     | 7.50E-06 | mm   | EPA, 2007    |
|                                    |          | Hg   |              |
+------------------------------------+----------+------+--------------+
| Solubility                         | 8.96E-02 | mg/L | EPA, 2007    |
+------------------------------------+----------+------+--------------+
| Soil Partition Coefficient (Koc)   | 5080     | mL/g | EPA, 2007    |
+------------------------------------+----------+------+--------------+
| Chemical Application Method (CAM): | 4        |      | EPA          |
| Incorporated Uniform with Depth    |          |      | A            |
|                                    |          |      | ssumption^2^ |
+------------------------------------+----------+------+--------------+
| Incorporation Depth                | 2.54     | cm   | EPA          |
|                                    |          |      | A            |
|                                    |          |      | ssumption^3^ |
+------------------------------------+----------+------+--------------+
| Soil Compartment Loading Rate/     | See      | k    | Calculated   |
| Application Rate                   | Table 2  | g/ha |              |
+------------------------------------+----------+------+--------------+
| Application Efficiency             | 1        |      | Parker, 2007 |
+------------------------------------+----------+------+--------------+
| Spray Drift                        | 0        |      | Parker, 2007 |
+------------------------------------+----------+------+--------------+
| Number of applications             | 1        |      | Parker, 2007 |
+------------------------------------+----------+------+--------------+
| IPSCND: Method of post-harvest     | 1        |      | Parker, 2007 |
| foliar pesticide disposition       |          |      |              |
+------------------------------------+----------+------+--------------+
| Hydrolysis half life (pH 7)        | 245      | days | Maguire,     |
|                                    |          |      | Tkacz 1988;  |
|                                    |          |      | EPA 2007     |
+------------------------------------+----------+------+--------------+
| Aquatic photolysis half life       | 90       | days | Maguire et   |
|                                    |          |      | al, 1983;    |
|                                    |          |      | EPA 2007     |
+------------------------------------+----------+------+--------------+
| Water half life                    | 505      | days | EPA, 2007    |
+------------------------------------+----------+------+--------------+
| Benthic half life                  | 1095     | days | Fent, Hunn   |
|                                    |          |      | 1995         |
+------------------------------------+----------+------+--------------+
| Soil half life                     | 127      | days | EPA, 2007    |
+------------------------------------+----------+------+--------------+
| ^1^ California fruit orchard       |          |      |              |
| scenario from the orchard          |          |      |              |
| scenarios available in PE5.        |          |      |              |
|                                    |          |      |              |
| ^2^ Chemical application method 4, |          |      |              |
| the default incorporation CAM,     |          |      |              |
| which assumes uniform              |          |      |              |
| incorporation with a depth         |          |      |              |
| specified by the user.             |          |      |              |
|                                    |          |      |              |
| ^3^ A depth of 1 inch (\~2.54 cm). |          |      |              |
+------------------------------------+----------+------+--------------+

**Table 4. 10^th^ Percentile Estimated Environmental Concentrations of
TBTO in Dissolved Surface Water from Runoff as a Consequence of Leaching
from Treated Wood**

+---------------+------------+-------+-------+-------+-------+-------+
| **Use         | **Instanta | **96  | **2   | **6   | **9   | **A   |
| scenario**    | neous^1^** | -Hour | 1-Day | 0-Day | 0-Day | nnual |
|               |            | ^1^** | ^1^** | ^1^** | ^1^** | ^1^** |
|               | **(µg/L)** |       |       |       |       |       |
|               |            | **(µg | **(µg | **(µg | **(µg | **(µg |
|               |            | /L)** | /L)** | /L)** | /L)** | /L)** |
+---------------+------------+-------+-------+-------+-------+-------+
| Transmission  | 3.3E-03    | 2.    | 1.    | 6.    | 5.    | 2.    |
| Pole          |            | 6E-03 | 4E-03 | 6E-04 | 4E-04 | 6E-04 |
+---------------+------------+-------+-------+-------+-------+-------+
| Fence Post    | 1.5E-02    | 1.    | 6.    | 2.    | 1.    | 1.    |
|               |            | 2E-02 | 3E-03 | 7E-03 | 9E-03 | 1E-03 |
+---------------+------------+-------+-------+-------+-------+-------+
| Fence         | 4.0E-02    | 3.    | 1.    | 7.    | 5.    | 3.    |
|               |            | 2E-02 | 7E-02 | 4E-03 | 2E-03 | 0E-03 |
+---------------+------------+-------+-------+-------+-------+-------+
| Deck Post     | 2.5E-02    | 2.    | 1.    | 4.    | 3.    | 1.    |
|               |            | 0E-02 | 0E-02 | 5E-03 | 2E-03 | 8E-03 |
+---------------+------------+-------+-------+-------+-------+-------+
| Deck          | 1.1E-02    | 8.    | 4.    | 2.    | 1.    | 8.    |
|               |            | 5E-03 | 4E-03 | 1E-03 | 7E-03 | 5E-04 |
+---------------+------------+-------+-------+-------+-------+-------+
| House         | 5.7E-02    | 4.    | .     | 1.    | 9.    | 4.    |
|               |            | 6E-02 | 4E-02 | 1E-02 | 4E-03 | 6E-03 |
+---------------+------------+-------+-------+-------+-------+-------+

**^1^** All values are rounded to two significant digits.

**Table 5. 10^th^ Percentile Estimated Environmental Concentrations of
TBTO in Sediment Pore Water from Runoff as a Consequence of Leaching
from Treated Wood**

+--------------+------------+-------+-------+-------+-------+-------+
| **Use        | **Instanta | **96  | **2   | **6   | **9   | **A   |
| scenario**   | neous^1^** | -Hour | 1-Day | 0-Day | 0-Day | nnual |
|              |            | ^1^** | ^1^** | ^1^** | ^1^** | ^1^** |
|              | **(µg/L)** |       |       |       |       |       |
|              |            | **(µg | **(µg | **(µg | **(µg | **(µg |
|              |            | /L)** | /L)** | /L)** | /L)** | /L)** |
+--------------+------------+-------+-------+-------+-------+-------+
| Transmission | 4.4E-04    | 4.    | 4.    | 4.    | 4.    | 2.    |
| Pole         |            | 4E-04 | 4E-04 | 2E-04 | 0E-04 | 5E-04 |
+--------------+------------+-------+-------+-------+-------+-------+
| Fence Post   | 1.8E-03    | 1.    | 1.    | 1.    | 1.    | 1.    |
|              |            | 8E-03 | 7E-03 | 6E-03 | 6E-03 | 0E-03 |
+--------------+------------+-------+-------+-------+-------+-------+
| Fence        | 4.9E-03    | 4.    | 4.    | 4.    | 4.    | 2.    |
|              |            | 9E-03 | 7E-03 | 5E-03 | 3E-03 | 8E-03 |
+--------------+------------+-------+-------+-------+-------+-------+
| Deck Post    | 2.9E-03    | 2.    | 2.    | 2.    | 2.    | 1.    |
|              |            | 9E-03 | 8E-03 | 7E-03 | 6E-03 | 6E-03 |
+--------------+------------+-------+-------+-------+-------+-------+
| Deck         | 1.4E-03    | 1.    | 1.    | 1.    | 1.    | 8.    |
|              |            | 4E-03 | 4E-03 | 4E-03 | 3E-03 | 0E-04 |
+--------------+------------+-------+-------+-------+-------+-------+
| House        | 7.7E-03    | 7.    | 7.    | 7.    | 7.    | 4.    |
|              |            | 7E-03 | 6E-03 | 3E-03 | 0E-03 | 3E-03 |
+--------------+------------+-------+-------+-------+-------+-------+

**^1^** All values are rounded to two significant digits.

**3. Assumptions/Limitations**

-   Because wood leaching studies are not available for TBTO, the
    cumulative release of TBTO from treated wood was derived using a
    method developed by Krahn and Strub (1990) which estimates leaching
    from wood treated with antisapstain chemicals. This methodology
    simulates leaching of TBTO from treated wood exposed to rainfall.

-   An input to the Krahn and Strub (1990) methodology ICF used to
    calculate cumulative release of TBTO from treated wood is the mass
    of the active ingredient applied to the leachable portion of the
    wood. This value was calculated using information from the label for
    a specific TBTO product, Flexguard Waterbase Preservative
    (Registration No. 9339-14). The mass calculation requires the
    percent active ingredient of the product as it is applied (2.76%),
    the maximum number of applications of the product (2), and the
    minimum application rate of the product. The label specifies an
    application rate of "275 ft^2^/gal or less." 275 ft^2^/gal was used
    as the application rate. However, higher application rates (i.e.,
    fewer square feet covered per gallon) would be expected to result in
    higher environmental concentrations in soil, surface water, and
    sediment pore water

-   Estimation of the mass of TBTO applied per square foot of treated
    lumber required an assumption about the density the antisapstain
    product. EPA assumption about the density of antifoulant paint, 10
    lb/gal (EPA, 2006b) was used.

-   The estimate of cumulative release of TBTO assumed that all of the
    active ingredient was absorbed into the wood when the product was
    applied.

-   This methodology does not address a number of physical and
    environmental variables (e.g., chemical formulation, wood surface
    texture, ambient temperature, soil type, soil moisture, and soil pH)
    that may affect the release of TBTO from treated wood and subsequent
    movement in environmental media. In addition, the methodology does
    not address chemical or biological degradation.

-   This analysis uses assumptions about the surface areas of wood
    treated for six TBTO use scenarios, as well as assumptions about the
    number of treated surfaces per hectare. These assumptions, which
    were obtained from Rohm and Haas (2006) may over- or under-estimate
    the potential for TBTO releases to soil associated with the six
    scenarios.

-   The methodology includes an assumption that soil, surface water, and
    sediment pore water concentrations are affected by only one of the
    six TBTO use scenarios at a time.

-   The PE5 model estimates concentrations in sediment pore water.
    Concentrations of TBTO adsorbed to sediment are not calculated.

-   EPA (2007) reported that TBTO is essentially stable to hydrolysis at
    pH 5, 7 and 9 but specific half-lives were not reported. Maguire and
    Tkacz (1985) reported that tributyltin is susceptible to
    biodegradation in water with half-lives between 6 days and 35 weeks
    (245 days). 245 days was chosen as it represents the most
    conservative estimate (i.e., the longest period of time that TBTO
    will persist in water).

-   EPA (2007) reported that it TBTO is essentially stable to photolysis
    at pH 5, 7, and 9 but specific half-lives were not reported. Maguire
    et al. (1983) reported that photodegradation in water will be at
    least a few months; therefore a value of 90 days was used.

-   The anaerobic half-life for TBTO was used for a water half-life as
    it was the only specific aquatic metabolism reported by EPA (2007).

-   EPA (2007) did not report a benthic half-life for TBTO. Fent and
    Hunn (1995) reported that half-lives in anaerobic sediment are in
    the range of 2-3 years (730-1095 days). 1095 days was chosen as it
    represents the most conservative estimate (i.e., the longest period
    of time that TBTO will persist in benthic soil).

**4. References**

Carbone, J. and Jacobson, A. 2006. Environmental risk assessment of
DCOIT for wood preservative applications. Report \# 06R-1006. Rohm and
Haas Company. 9 February 2006.

EPA, 2007. "TBT Oxide Fate Profile," Power Point Presentation by Jim
Breithaupt, US Environmental Protection Agency. Document provided by
Siroos Mostaghimi, U.S. Environmental Protection Agency, 16 November
2007.

EPA, 2006a. "PE5 User's Manual for PRZM EXAMS Modeling Shell, Version
5.0." Environmental Fate and Effects Division. Office of Pesticide
Programs, U.S. Environmental Protection Agency. November 15 2006.

EPA, 2006b. "Draft, Antimicrobials Division's (AD) Standard Operating
Procedures (SOPs) for Residential and Occupational Exposure
Assessments." Prepared by: Cassi Walls,Talia Milano, and Timothy
Leighton, Antimicrobials Division, U.S. Environmental Protection Agency,
November 2006.

Fent, K and Hunn, J, 1995. Organotins in freshwater harbors and rivers:
Temporal distribution, annual trends and fate. [Environmental Toxicology
and Chemistry]{.underline}. Vol. 14. No. 7: 1123-1132.

EPA, 2007. Revised Estimated Environmental Concentrations for AMICAL
Leached from Wood into Soil and Water using PE5 PRZM-EXAMS Model Shell.
Memorandum from Siroos Mostaghimi to Norm Cook, U.S. Environmental
Protection Agency,, November 28, 2007

Krahn, P. and Strub R. 1990. Standard leaching test for antisapstain
chemicals: Regional Program Report 90-10. Environment Canada.
Conservation and Protection, Pacific and Yukon Region North Vancouver,
BC. 1990.

Maguire, RJ, Carey JH, Hale, EJ, 1983. Degradation of the tri-n-butylin
species in water. [Journal of Agricultural and Food
Chemistry.]{.underline} 31: 1060-5.

Maguire, RJ, Tkacz, RJ, 1985. Degradation of the tri-n-butylin species
in water and sediment from Toronto Harbor. [Journal of Agricultural and
Food Chemistry.]{.underline} Vol. 33: 947-53.

Parker, Ronald. 2007. Office of Pesticide Programs. U.S. Environmental
Protection Agency. Personal communication with ICF. November.

Rohm and Haas, 2006. Environmental Risk Assessment of DCOIT for Wood
Preservative Applications. Prepared by John P Carbone and Andrew H.
Jacobson, Rohm and Haas Company, Spring House, PA. Company Report
06R-1006. February 9, 2006.

Williams, M. and Bradley, A., 1996. Aqueous Availability of TBTO 48:
Final Report: Lab Project Number: 42782: ABC 42782. Unpublished study
prepared by ABC Laboratories Europe, Ltd. 78 p. MRID 43997001.

Versar, 2005. \"ADBAC Antisapstain Modeling (TAF 1-4-10, CM-43),\"
memorandum to Najim Shamim, U.S. EPA, from Ron Lee and Jignasha Patel,
Versar, Inc., December 5, 2005.

File: MyFiles\\2007 reports\\TBTO\\ Estimated Environmental
Concentrations for Tributyltin Oxide (TBTO) Leached from Wood into Soil
and Water.

CC: RASSB Chemical File

Siroos Mostaghimi, RASSB