Partitioning and transport of total and methyl mercury in the Lower Fox River, Wisconsin

To investigate transport and partitioning processes of Hg-T in the Fox River, we coupled detailed time series data of total mercury (Hg-T) at the river mouth with transect sampling in the Lower Fox River. Unfiltered Hg-T concentrations in the Fox River during the study period (April 1994-October 1995) ranged from 1.8 to 182 ng L-1 with a median of 24.8 ng L-1, predominantly (93.6%) in the particulate phase. These levels were significantly elevated compared with other large tributaries to Lake Michigan (Hurley, J. P.; Shafer, M. M.; Cowell, S. E.; Overdier, J. T.; Hughes, P. E.; Armstrong, D. E. Environ. Sci Technol. 1996, 30, 2093-2098). Transect sampling revealed progressively increasing water column Hg-T concentrations and Hg-T particulate enrichment downstream, which were consistent with trends in sediment Hg-T levels in the river. Resuspended sediments are likely the predominant source of Hg from the Fox River into Green Bay. Despite elevated Hg-T concentrations, methyl mercury (MeHg) concentrations were relatively low, suggesting limited bioavailability of Hg-T associated with sediments.