Distribution and flux of toxaphene in the water and sediment of the upper Great Lakes

The current research examined toxaphene in Lakes Superior and Michigan to determine spatial and temporal trends in concentration, homolog distribution, water/particle partitioning (K_p), the fluxes between media, and the potential for the existence of significant non-atmospheric sources. Data were also presented on the organochlorine pesticides nonachlor and chlordane. There were no clear spatial trends in either lake (except Green Bay) and toxaphene net air/water flux showed consistent volatilization during all times tested. In general, volatilization decreased epilimnetic concentrations during stratified conditions, and then lake-wide mixing during overturn increased surface concentrations. In Lake Michigan, the mean dissolved toxaphene concentration in Green Bay was significantly lower than in the open lake during isothermal conditions due to minimal hypolimnetic recharge. Average surficial dissolved toxaphene concentrations in Lake Superior averaged 0.91 ng/L in 1997 and 0.73 ng/L in 1998. Dissolved toxaphene concentrations for Lake Michigan averaged 0.40 ng/L in 1997 and 0.35 ng/L in 1998. Toxaphene homolog distributions showed significant differences between dissolved and particulate phases in water and sediments and the homolog distribution in Lake Michigan water was enhanced in lower chlorinated homologs compared to Lake Superior. Toxaphene K _p varied with season, and showed varying dependence on POC (no correlation in Lake Superior; seasonal correlation in Lake Michigan). The overall average log K_p value for Lake Superior was 4.93 and for Lake Michigan was 4.49. Sediment analysis in Lake Michigan demonstrated that Green Bay is not likely a significant source of toxaphene to the northern basin of the lake. However, there were elevated concentrations and inventories of all compounds studied at the southern end of Green Bay, reflecting likely point-source inputs. Concentration trends from a dynamic mass balance model were consistent with measured values. The assertion of no significant non-atmospheric toxaphene sources to Lake Superior was supported by model results, a lack of spatial differences in dissolved and sediment concentration, seasonal concentration fluctuations, and a homolog fingerprint similar to air. Model results were also used to estimate toxaphene half-lives of 19.5 years for Lake Superior and 9.5 years for Lake Michigan and were the basis for evaluating fish consumption advisory trends.