USEPA: Ambient Aquatic Life Water Quality Criteria for Tributyltin (TBT) - Final
AMBIENT AQUATIC LIFE WATER QUALITY CRITERIA FOR
TRIBUTYLTIN
December 2003
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF WATER
OFFICE OF SCIENCE AND TECHNOLOGY
HEALTH AND ECOLOGICAL CRITERIA DIVISION
WASHINGTON D.C.
This final document is guidance only. It does not establish or affect legal rights or obligations. It does not establish a binding norm and cannot be finally determinative of the issues addressed. Agency decisions in any particular situation will be made by applying the Clean Water Act and EPA regulations on the basis of specific facts presented and scientific information then available.
EXECUTIVE SUMMARY
BACKGROUND: Tributyltin (TBT) is a highly toxic biocide that has been used extensively to protect the hulls of large ships. It is a problem in the aquatic environment because it is extremely toxic to non-target organisms, is linked to imposex and immuno-supression in snails and bivalves, and can be persistent. EPA is developing ambient water quality criteria for TBT through its authority under Section 304(a) of the Clean Water Act (CWA). These water quality criteria may be used by States and authorized Tribes to establish water quality standards for TBT.
CRITERIA:
Freshwater: For TBT, the criterion to protect freshwater aquatic life from chronic toxic effects is 0.072 µg/L. This criterion is implemented as a four-day average, not to be exceeded more than once every three years on the average. The criterion to protect freshwater aquatic life from acute toxic effects is 0.46 µg/L. This criterion is implemented as a one-hour average, not to be exceeded more than once every three years on the average.
Saltwater: For TBT, the criterion to protect saltwater aquatic life from chronic toxic effects is 0.0074 µg/L. This criterion is implemented as a four-day average, not to be exceeded more than once every three years on the average. The criterion to protect saltwater aquatic life from acute toxic effects is 0.42 µg/L. This criterion is implemented as a one-hour average, not to be exceeded more than once every three years on the average.
The saltwater chronic criterion for TBT differs from the criterion that was originally proposed for public review (0.010 µg/L). The development of the saltwater chronic criterion for TBT considers four lines of evidence: v (1) the traditional endpoints of adverse effects on survival, growth, and reproduction as demonstrated in numerous laboratory studies; (2) the endocrine disrupting capability of TBT as observed in the production of imposex in field studies; (3) that TBT bioaccumulates in commercially and recreationally important freshwater and saltwater species; and (4) that an important commercial organism already known to be vulnerable to a prevalent pathogen was made even more vulnerable by prior exposure to TBT.
For these reasons, the criterion to protect saltwater aquatic life from chronic toxic effects is set at 0.0074 µg/L.
This document provides guidance to States and Tribes authorized to establish water quality standards under the Clean Water Act (CWA) to protect aquatic life from acute and chronic effects of TBT. Under the CWA, States and Tribes are to establish water quality criteria to protect designated uses. While this document constitutes U.S. EPA’s scientific recommendations regarding ambient concentrations of TBT, this document does not substitute for the CWA or U.S. EPA’s regulations; nor is it a regulation itself. Thus, it cannot impose legally binding requirements on U.S. EPA, States, Tribes, or the regulated community, and it might not apply to a particular situation based upon the circumstances. State and Tribal decision-makers retain the discretion to adopt approaches on a caseby- case basis that differ from this guidance when appropriate. U.S. EPA may change this guidance in the future.