API PUBL 4751-2005

$22.75

Evaluation of Water Quality Translators for Mercury

Published By	Publication Date	Number of Pages
API	2005	52

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Description

This report discusses the technical issues and constraints associated with translation of a mercury fish tissue concentration into a water quality criterion, in the use and implementation of the Environmental Protection Agency’s fish-tissue-based criterion for methylmercury (0.3 mg methylmercury/Kg wet weight fish tissue). The report focuses on available analytical methods for evaluating mercury in fish and water; proposed methods for translating a fish tissue concentration for mercury into a concentration in water; and implementation of the mercury criterion in the development of Total Maximum Daily Loads (TMDLs) and water quality-based effluent limits (WQBELs). The approaches to criteria translation are, in order of preference: (1) derive site-specific bioaccumulation factors (BAFs), (2) use a bioaccumulation model, or (3) use EPA’s national default translators. The collection of site-specific data allows for the most accurate assessment of bioaccumulation; however, validation of methylmercury analytical techniques is necessary to increase the certainty of results. Models have the potential to account for environmental factors contributing to data variability, but at present the available models are limited to reservoirs and lakes in a few geographic regions. Improvements in national default translators do not decrease the importance of site-specific translators. National default values are likely to be inaccurate on a site-specific basis, given the very high degree of variability observed in mercury bioaccumulation rates. Research is needed to improve the national default translators currently proposed by EPA, and additional data would increase the effectiveness of the translator calculation methods by reducing variability and minimizing the uncertainty of the resulting default values. Given the many uncertainties associated with mercury translators, their use should be limited to cases where site-specific fish tissue data reveal the tissue-based water quality criterion has been exceeded, and point sources make up a significant contribution of the total mercury loading to the water body.

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