United States Office of Water EPA-822-F-02-003 

Environmental Protection 4304T December 2002 

Agency 

Fact Sheet 

Notice of Ambient Water Quality Criteria 

Document for Tributyltin (TBT) - Draft 

Summary 

The U.S. Environmental Protection Agency has published a draft ambient water quality criteria 

document for tributyltin (TBT) for scientific and technical input. Draft acute and chronic criteria 

recommendations have been developed to protect aquatic life in both freshwater and saltwater. 

When finalized, these draft criteria can form the basis for state and tribal water quality standards. 

Background 

The U.S. Environmental Protection Agency (EPA) 

has published a draft ambient water quality criteria 

document for tributyltin (TBT) for scientific and 

technical input. This document contains draft 

ambient water quality criteria to protect aquatic 

organisms and their uses. These draft criteria are 

technical information for states and tribes and, in 

themselves, have no binding legal effect. When 

finalized, these criteria can form the basis for state 

and tribal water quality standards. These draft 

TBT criteria are published pursuant to Section 

304(a) of the Clean Water Act. 

What is tributyltin? 

Tributyltin is one of several organotin compounds 

with several industrial uses. Organotins are 

organometallic compounds; they contain one or 

more direct links between a carbon atom and a 

metal atom. 

How is TBT used? 

Tributyltin is primarily used as a biocide in 

antifouling paints applied to ship hulls to keep 

barnacles and other organisms from attaching to 

the hull. TBT remains effective over long periods 

on the ship hull because it is released very slowly 

from the hull into the water column over time. 

This keeps organisms from attaching to the hull. 

What are the environmental effects of TBT? 

Tributyltin is extremely toxic to aquatic life. It is 

especially toxic to bivalves, such as oysters and 

other mollusks. It is an endocrine-disrupting 

chemical that causes severe reproductive effects 

in aquatic organisms. In addition, recent studies 

show that exposure to TBT makes oysters very 

susceptible to infection and death from exposure 

to pathogens. 

What are the new draft criteria 

concentrations? 

In August 1997, EPA published a draft ambient 

water quality criteria document for TBT which 

contained freshwater and saltwater criteria. 

With this notice, EPA is issuing new draft 

criteria for TBT. The primary difference 

between the initial draft and the new draft 

criteria is that the saltwater chronic criterion has 

been lowered from a four-day average of 0.01 

ug/l, not to be exceeded more than once in three 

years, to a four-day average of 0.001 ug/l, not to 

be exceeded more than once in three years. EPA 

set the criterion at this level to protect saltwater 

organisms from the adverse reproductive effects 

of tributyltin that have been observed in 

laboratory and field studies and because 

exposure to TBT can make saltwater organisms 

more vulnerable to infection from pathogens. 

Freshwater Aquatic Life: 
EPA has determined that, except possibly where a 

locally important species is very sensitive, 

freshwater aquatic life and their uses should not be 

affected unacceptably if the four-day average 

concentration of tributyltin does not exceed 0.063 

ug/L more than once every three years on the 

average and if the one-hour average concentration 

does not exceed 0.46 ug/L more than once every 

three years on the average. 

Saltwater Aquatic Life: 

EPA has determined that, except possibly where a 

locally important species is very sensitive, 

saltwater aquatic life and their uses should not be 

affected unacceptably if the four-day average 

concentration of tributyltin does not exceed 0.001 

ug/L more than once every three years on the 

average and if the one-hour average concentration 

does not exceed 0.38 ug/L more than once every 

three years on the average. 

What are the environmental benefits from these 

new draft criteria? 

The new TBT draft criteria provide more 

protection for commercially and ecologically 

important species, including oysters. The revised 

saltwater chronic criterion protects saltwater 

organisms from the adverse growth and 

reproductive effects of TBT. 

How do I obtain a copy of the document? 

Copies of the complete document, titled 

"Ambient Aquatic Life Water Quality Criteria 

for Tributyltin (TBT) - Draft" (EPA-822-B-02-

001) may be obtained from EPA’s Water 

Resource Center by phone at 202-566-1729, or 

by e-mail to waterpubs@epamail.epa.gov, or by 

conventional mail to EPA Water Resource 

Center, RC-4100T, 1200 Pennsylvania Ave., 

Washington, DC 20460. The document is also 

available electronically at: 

www.epa.gov/waterscience/criteria/tributyltin.