Partitioning of dissolved thallium by seston in Lakes Erie and Ontario

The fate of thallium (Tl) was traced in the epipelagic and coastal waters of Lake Erie (in 2000) and Lake Ontario (in 2001) sampled during the summer period of thermal stratification. Fractionation of ²⁰⁴Tl bound to particulate matter was conducted to trace the scavenging potential of various seston size ranges (0.2-2 μm, 2-20 μm, and 20-210 μm). Added [ ²⁰⁴Tl]-Tl(I) scavenged by seston over 1-3 days was 0.34-4.05% in Lake Erie and 0.09-0.21% in Lake Ontario, where scavenging was correlated with suspended particulate matter content and chlorophyll a concentration. There was no consistent trend with respect to Tl scavenging by a particular size fraction, except at coastal sites in Lake Erie where most Tl was scavenged by the 2-20 μm seston. Partition coefficients (K_d) of Tl scavenging by seston in Lake Ontario were 938-1483 L·kg^-1. At the same pelagic site in Lake Ontario, [²⁰⁴Tl]-dimethylthallium partitioned into seston (K_d = 807 ± 258) to a lesser degree than added Tl(I) (K_d = 998 ± 297), a finding consistent with laboratory assays of these two Tl species. These results suggest that the plankton food web plays a role in the geochemical cycle of this toxic metal in the water column of the lower Great Lakes.