Intraspecific comparisons of metal bioaccumulation in the juvenile Atlantic silverside Menidia menidia

We experimentally assessed the uptake, loss and resulting tissue distribution of Am, Cd, inorganic Hg(II), methylmercury (MeHg), Se and Zn in 2 North American populations (Nova Scotia and South Carolina) of juvenile Atlantic silverside Menidia menidia from aqueous and dietary sources using a radiotracer technique. Northern silversides (Nova Scotia) have a higher rate of ingestion and growth compared to their southern (South Carolina) counterparts to overcome a shorter growing season. Uptake rate constants from the dissolved phase were highest for MeHg and lowest for Cd. Assimilation efficiencies of ingested metals were highest for MeHg (82 to 89%) and lowest for Am (0.3 to 1.9%). No pronounced difference in metal uptake was noted between the 2 populations, except for MeHg after aqueous exposure, and Cd after dietary exposure, where South Carolina fish retained more metal. Elimination rate constants did not vary significantly between populations and exposure routes (except for Hg(II) after a dietary exposure) indicating that both populations process metals at the same rate. The tissue distribution of each metal in the fish varied among metals and exposure routes. Using a metal bioaccumulation model, the calculated steady-state body burden of metal was highest for Zn, and lowest for Am. Calculated body burdens were higher in South Carolina silversides for Am, Cd, and Zn. For all metals except Am, the diet is the dominant exposure route. Of the metals investigated, MeHg and Zn in both populations and Cd in the South Carolina population are expected to biomagnify at this trophic step.