Use of an integrated mercury food web model for ecological risk assessment.

We developed an integrated food web model for mercury, using the CATS (Contaminants in Aquatic and Terrestrial ecoSytems) model developed by Traas and co-workers (Traas, T.P.; Stäb, J.A.; Kramer, P.R.G.; Cofino, W.P.; Aldenberg, T. Modeling and risk assessment of tributyltin accumulation in the food web of a shallow freshwater lake. Environ. Sci. Technol. 1996, 30 (4), 1227-1237). It was translated into the MatLab mathematical programming language and been adapted for the modeling of mercury. Mercury CATS now models four species of mercury (unreactive mercury, zero valent mercury, divalent mercury, and methylmercury) and their environmental and interactions using the mercury speciation kinetics model article by Bale (Bale, A.E. Modeling aquatic mercury fate in Clear Lake, Calif. J. Env. Eng. 2000, 126 (2), 153-163.) as a guideline. The mercury cycling kinetics include methylation of divalent mercury, photo-oxidation of zero valent mercury, reduction of divalent mercury, adsorption and desorption of divalent and methylmercury, volatilization of zero valent mercury, and uptake into the food web. A lake food web consisting of phytoplankton, rooted vegetation, zooplankton, crayfish, freshwater clams, amphipods, chironomids, eels, killifish, bass, and ospreys traces growth of the various compartments, uptake of both divalent and methylmercury, and the movement of both divalent and methylmercury through the food web via feeding relationships. This model design is sufficiently flexible that the incorporation of new scientific information can be easily done as our understanding of both the organisms and mercury's environmental chemistry increases.