Effects of exposure to high concentrations of waterborne Tl on K and Tl concentrations in Chironomus riparius larvae

Thallium (Tl) is a non-essential metal which is released into the environment primarily as the result of anthropogenic activities such as fossil fuel burning and smelting of ores. The ionic radius of monovalent Tl+ is similar to that of K+ and Tl+ may thus interfere with K+-dependent processes. We determined that the acute (48 h) lethal concentration where 50% of the organisms do not survive (LC50) of Tl for 4th instar Chironomus riparius larvae was 723 μmol L− 1. Accumulation of Tl by the whole animal was saturable, with a maximum accumulation (Jmax) of 4637 μmol kg− 1 wet mass, and KD of 670 μmol Tl l− 1. Tl accumulation by the gut appeared saturable at the lowest four Tl concentrations, with a Jmax of 2560 μmol kg− 1 wet mass and a KD of 54.5 μmol Tl l− 1. The saturable accumulation at the gut may be indicative of a limited capacity for intracellular detoxification, such as storage in lysosomes or complexation with metal-binding proteins. Tl accumulation by the hemolymph was found to be linear and Tl concentrations in the hemolymph were ~ 75% of the exposure concentration at Tl exposures > 26.9 μmol L− 1. There was not a significant decrease in whole animal, gut or hemolymph K during exposure to waterborne Tl at any of the concentrations tested (up to 1500 μmol L− 1). The avoidance of hypokalemia by C. riparius larvae may contribute to survival during acute waterborne exposures to Tl.