Scientific Review of Cyanide Ecotoxicology and Evaluation of Ambient Water Quality Criteria - David Dzombak, Robert W. Gensemer, Robert Santore, David

The USEPA?s ambient water quality criteria (AWQC) for cyanide were developed in 1984. Recently, however, concerns have arisen that the AWQC for cyanide have been problematic to implement and may not accurately reflect either the toxic forms or bioavailable concentrations of cyanide in water, sediments, and tissues of aquatic organisms. Also, the cyanide criteria typically have been implemented based on total cyanide concentrations rather than the free cyanide concentrations that formed the basis of the criteria calculations. New knowledge on cyanide toxicity, cyanide speciation and its measurement, and the relative toxicity of bioavailable cyanide species suggested that a re-evaluation of the aquatic toxicity data and chemistry that serve as the basis of the current national criteria is warranted. In response to these concerns, studies sponsored by the Water Environment Research Foundation (WERF) evaluated the formation and fate of cyanide in municipal wastewater effluents. Kavanaugh et al. (2003) evaluated the reliability of several analytical methods for measurement of cyanide species at low (ppb) concentrations, along with studies to evaluate the sources, transport, and fate of cyanide species in wastewater treatment plants (WWTPs) and receiving waters. Results indicated that potentially toxic forms of cyanide can be generated in WWTPs from several chemical processes, including dissociation of thiocyanate by chlorination or UV disinfection, chlorination in the presence of
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