0 1998, by the American Society of Limnology and Oceanography, Inc. The aquatic insect Chaoborus as a biomonitor of trace metals in lakes

We tested larvae of three species of the widespread lacustrine insect Chaohorus as potential biomonitors of the trace metals Cd, Cu, Pb, and Zn. Chemical and biological measurements were made in a large number of lakes covering a wide range of pHs and trace metal concentrations and distributed over a large geographical area. Con-centrations of Cu and Zn in sediment and water varied widely among lakes but not in animals, suggesting that the insects regulate these essential metals over a wide range of environmental concentrations and consequently would be of little use for monitoring Cu or Zn. Although 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 research on this metal is needed. Cadmium concentrations in Chaoborus were not well explained by total Cd concentrations in either sediment or water. We found that Cd concentrations in animals were better predicted by free Cd ion concentrations provided that we took into account competition between hy-drogen ions and free cadmium ions at biological uptake sites. This result is consistent with the mainly laboratory-based free-ion activity model and suggests that this model would provide an effective theoretical framework for the use of Chaoborus larvae as Cd biomonitors in nature. Human activities have greatly increased the fluxes o