The importance of surface adsorption and pH in metal accumulation by chironomids

Abstract Metal body burdens of larval and adult chironomids varied nonlinearly with H+. Metal loss during emergence was an indicator of metal adsorption to the exoskeleton. This adsorbed portion was lower for chironomids collected from lakes of pH 4.4 or 6.1 than for those from lakes of pH 5.1 to 5.5. Pb accumulation was inversely proportional to pH, but Cd, Al, Cu and Ni body burdens were lower at pH 4.4 than at pH greater than 5.1. Short-term larval transplant experiments supported the field observations that surface adsorption can be an important component of the total metal burden of larval chironomids and that adsorption processes may be suppressed at low pH. Changes in metal content in live and dead chironomids exposed to different sediment types were not significantly different. Larvae from a lake of pH 4.4 showed an initial rapid phase of accumulation of Cd, Al, Mn, Ni, Zn and Cu when transplanted to sediments from a lake of pH 5.1. Laboratory and field data supported the hypothesis that surface adsorption contributes to total metal content in chironomids and is responsive to lake pH.