Bioconcentration of inorganic and organic thallium by freshwater phytoplankton

Uptake of inorganic Tl(I) and dimethylthallium, (CH 3 ) 2 Tl + , by Chlorella spp. (Chlorophyta) and the diatom Stephan‐odiscus 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 [ 204 Tl]‐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 [ 204 Tl]‐dimethylthallium. Volume‐based bioconcentration factors for Tl(I) after 72 h of exposure were 5 × 10 4 and 1.1 × 10 4 for Chlorella sp. and S. hantzschii ; for dimethylthallium they were 7.8 × 10 2 and 8.3 × 10 3 . 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.