TOXICITY AND BIOACCUMULATION OF THALLIUM IN HYALELLA-AZTECA, WITH COMPARISON TO OTHER METALS AND PREDICTION OF ENVIRONMENTAL-IMPACT

Thallium (Tl) is an extremely toxic but little studied metal. For Hyal ella azteca exposed in Lake Ontario water, a 25% reduction in survival (the LC25) occurred at about 48 nmol litre(-1) after 4 weeks. Body co ncentrations of Tl, which were proportional to water concentrations, a veraged 290 nmol g(-1) dry mass at the LC25 Growth was reduced at slig htly lower concentrations. Concentrations affecting reproduction were variable at < 50% of the LC25. On a water-concentration basis Tl was m ore toxic than Ni, Cu or Zn, but less toxic than Cd or Hg to Hyalella; toxicity to Pb was similar. On a body-concentration basis, the toxici ties of Tl, Cd, Hg and Pb were all similar. Unlike Cd, Tl toxicity and uptake was affected by K concentrations in the water, and not by Ca, Mg, Na or other ions. Toxicity was proportional to uptake, and body co ncentrations were better predictors of toxicity than water concentrati ons in media with varying K concentrations. Preliminary measurements o f Tl and Cd uptake by Hyalella from Hamilton Harbour and Lake Ontario sediments suggested that total bioavailable metal concentrations were greater in deep-water sediments from Lake Ontario than in sediments fr om the harbour. The ratio of bioavailable metal to the toxic threshold was slightly higher for Cd than for Tl, but well below 1 for both met als. (C) 1998 Elsevier Science Ltd. All rights reserved.