Criteria for Mercury Under the Great Lakes Water Quality Initiative, 1994 Environmental Conference Proceedings

B.W. Schwab, M.W. Gerath, J.P. Unwin

On April 16, 1993, U.S. EPA proposed guidance for establishing water quality standards intended to support protection of the Great Lakes system under the Clean Water Act. In this paper, the approach and values U.S. EPA applied to factors used in calculating criteria for mercury in this proposed rule are considered. The review suggests some problems concerning the values used to calculate mercury criteria for the Great Lakes Guidance. More importantly, the validity of using certain portions of the method, specifically the calculation of Bioaccumulation Factors (BAFs) is questionable. It is both simpler and more consistent with the U.S. EPA-stated preference to obtain field data for determining BAFs. Based on findings concerning mercury biogeochemistry, it is distinctly possible that when such data is collected it will be found that single values for BAFs cannot be applied to the entire Great Lakes Basin. The variability in criteria values driving from the various parameter values applied here indicate that it is quite uncertain what the appropriate values for criteria should be. In view of the extreme potential cost of compliance with the criteria for mercury as developed in the Great Lakes Guidance, it seems cost-effective to obtain information to reduce the uncertainties.