API PUBL 4751-2005 pdf download.Evaluation of Water Quality Translators for Mercury.
For many facilities, the major issue in developing mercury translators is incorporating the fish tissue mercury criterion into a discharge permit limit. Permits may be reopened and reassessed as part of a TMDL implementation. At least 45 states have fish consumption advisories due to mercury and over 1,000 water bodies are listed as being impaired due to mercury, thus triggering TMDLs. Several methods are generally used in developing mercury TMDLs: (1) the concentration in fish tissue; (2) the concentration in the water column; or (3) the concentration in sediment. Of the three methods, using a fish tissue concentration as the TMDL target is the most direct measure of the desired endpoint, protection of human health. Determining how to allocate loadings among point and nonpoint sources is the next major part of a TMDL. EPA (2002a, 2004a) offers three approaches to allocation of loadings, depending upon the relative contributions of point source and nonpoint source loadings. First, where point source loadings dominate, the TMDL should specify reductions in these loadings, alone or together with nonpoint source loadings, to attain water quality standards (WQS). Second, where point source loadings are small, reductions in nonpoint sources are expected to achieve the TMDL. The third scenario also involves relatively small contributions from point sources, but reductions in nonpoint sources are not expected to be sufficient to attain WQS. The approaches used to implement a mercury TMDL will vary depending upon the allocations, as described above. Where there are waste load allocations (WLAs) to point sources, the traditional method to implement a TMDL is likely to be used (i.e., through the NPDES permit). The implementation of effluent limitations for mercury and other pollutant parameters can be approached through several mechanisms including reasonable potential and development of WQBELs.
This report summarizes the issues associated with translation of a mercury fish tissue concentration into a water quality criterion. Section 2 presents an overview of the analytical methods available for analyzing total mercury and methylmercury in fish tissue, water, and sediment. Section 3 provides an analysis of the methods and models available to translate the fish tissue concentration into a water quality criterion. Section 4 describes the impacts of the mercury water quality criteria on TMDL development and NPDES permits. Finally, Section 5 discusses the applicability of these issues for other metals. Although the report addresses many topics, it also identified several areas where additional research or study is necessary to fully understand mercury translation in the environment. The following bullets summarize the key findings and recommendations for additional study: • Validation of methylmercury analytical techniques is necessary to increase the certainty of results. • Research is needed to improve the national default translators currently proposed by EPA. EPA’s data set of BAF, f d , and K D values should be updated with more recent studies. Additional data would increase the effectiveness of the translator calculation methods by reducing variability and minimizing the uncertainty of the resulting default values. • 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. Models have the potential to account for environmental factors contributing to this variability, but at present the available models are limited to reservoirs and lakes in a few geographic regions.
This report presents an overview and discussion of the use of the ambient water quality criterion for methylmercury developed by the U.S. Environmental Protection Agency (EPA) in 2001 (66 FR 1344). Unlike all other previous water quality criteria for the protection of human health, the criterion for methylmercury was issued as a fish tissue concentration (i.e., 0.3 mg methylmercury/Kg wet weight fish tissue), as the fish consumption pathway is the main route of exposure to mercury in the environment. As a result, enforcement of water quality standards based upon this criterion requires either fish tissue sampling or the conversion of the criterion to a concentration in water, especially for the development of National Pollutant Discharge Elimination System (NPDES) permits. Because many permitted dischargers will be faced with meeting the methylmercury criterion, this report focuses on (1) available analytical methods for evaluating mercury in fish and water;; (2) the proposed methods for translating a fish tissue concentration for mercury into a concentration in water; and (3) implementation of the mercury criterion in the development of Total Maximum Daily Loads (TMDLs) and water quality-based effluent limits (WQBELs). EPA (2002a, 2004a) draft Guidance for Implementing the January 2001 Methylmercury Water Quality Criterion addresses these issues and is discussed below in each relevant section. Issues regarding mercury are significant because of mercury’s complex cycling in the environment, high bioaccumulative potential, and high toxicity. Generally, inorganic mercury is deposited to water bodies through atmospheric deposition (the major pathway), runoff, stormwater discharge, or other industrial or municipal discharges. Once in the water body, mercury deposited in sediments or dissolved in water may be methylated by bacteria to form methylmercury. Methylmercury is highly bioaccumulative and is the form of mercury that is accumulated up the food web.