Mercury dynamics in sediments and the foodweb of the Detroit River (Ontario, Michigan)

Mercury contamination is still an important issue, although the major input from riverine industries was stopped in the early 1970s. Bottom sediment and biological samples were collected in 2000 and sediment cores in 2001 in order to assess and continue monitoring mercury in the Detroit River aquatic system.; Analyses of mercury in fish samples revealed mercury's preference to accumulate in dorsal muscle tissue, which provides the best measure of the mercury burden in the whole body and is also the easiest tissue to collect. Mercury levels in fat tissue were below detection limit, which prove that mercury does not behave like organic contaminants, therefore PCBs biomagnification models can not be applied for mercury biomagnification. Methylmercury and total mercury had similar trends with depth for all the sediment cores analyzed and the MeHg/TotHg ratio had low values (<0.1%) as was found in previous studies. The total mercury data available for sediment, Carp and Esocide (Northern Pike and Muskellunge) for the last 3 decades demonstrates an evolution of mercury contamination from high concentrations in the early 1970s followed by a minimum in late 1980s and an increase in late 1990s to the present. By analyzing the system at a smaller scale, dividing the Detroit River into “Upstream” and “Downstream” parts for 1999–2001, a positive correlation between mercury concentrations in water and Carp and between sediment and Esocide species was observed, which may suggest that biomagnification is a slow and complicated process.