The aquatic insect Chaoborus as a biomonitor of trace metals in lakes

We tested larvae of three species of the widespread lacustrine insect Chaob orus as potential biomonitors of the trace metals Cd, Cu, Pb, and Zn. Chemi cal and biological measurements were made in a large number of lakes coveri ng a wide range of pHs and trace metal concentrations and distributed over a large geographical area. Concentrations of Cu and Zn in sediment and wate r varied widely among lakes but not in animals, suggesting that the insects regulate these essential metals over a wide range of environmental concent rations and consequently would be of little use for monitoring Cu or Zn. Al though lead concentrations in the Chaoborus species varied more widely than did those of Cu or Zn, we were not able to relate larval Pb concentrations consistently to those in sediment or water, suggesting that further resear ch on this metal is needed. Cadmium concentrations in Chaoborus were not we ll explained by total Cd concentrations in either sediment or water. We fou nd that Cd concentrations in animals were better predicted by free Cd ion c oncentrations provided that we took into account competition between hydrog en ions and free cadmium ions at biological uptake sites. This result is co nsistent with the mainly laboratory based free-ion activity model and sugge sts that this model would provide an effective theoretical framework for th e use of Chaoborus larvae as Cd biomonitors in nature.