Bioconcentration of inorganic and organic thallium by freshwater phytoplankton

Uptake of inorganic Tl(I) and dimethylthallium, (CH₃) ₂Tl⁺, by Chlorella spp. (Chlorophyta) and the diatom Stephanodiscus hantzschii (Heterokontophyta) were measured using radio-tracer techniques in water from Lakes Erie and Superior (North America). Uptake of both Tl(I) and dimethylthallium was bioactive. Uptake of [ ²⁰⁴Tl]-Tl(I) was greater in Lake Superior water than in Lake Erie water due to the greater K content in Lake Erie that inhibits Tl(I) uptake by phytoplankton but not that of [²⁰⁴Tl]-dimethylthallium. Volume-based bioconcentration factors for Tl(I) after 72 h of exposure were 5 × 10 ⁴ and 1.1 × 10⁴ for Chlorella sp. and S. hantzschii; for dimethylthallium they were 7.8 × 10² and 8.3 × 10³. Both Tl(I) and Tl(III) were concentrated similarly by Chlorella spp. These results suggest that chlorophytes, but not diatoms, accumulate Tl(I) to a greater extent than dimethylthallium. Greater bioaccumulation factors of inorganic Tl are possible in waters containing low amounts of K⁺; water quality guidelines seeking to protect biota from deleterious effects of Tl should consider the role of K.