Aluminum accumulation in a lotic mayfly at low pH--a laboratory study

The authors experimentally studied the occurrence of aluminum (Al) accumulation in nymphs of the mayfly Heptagenia sulphurea at low pH (4.5). Nymphs were exposed to two Al concentrations (0.2 and 2 mg inorganic Al liter-1), and two exposure times (2 and 4 weeks), the longer time period also including a molting phase. The major part of the Al was deposited on/in the exuviae of the nymphs, as Al determination in nymphs showed a 70% decrease in Al content after molting. When nymphs were exposed for two instar periods, with a molt in between. Al content almost doubled (2.34 mg Al g-1 dry wt) compared with that of a one-instar treatment (1.24 mg Al g-1 dry wt). This indicated that Al also accumulated within the mayfly nymphs. Determination of Al in emerged adults confirmed that most of the metal was deposited externally on the nymphs. No clear indications of Al accumulation were found in this short-term experiment. The implications for food-web accumulation of Al are that internally accumulated Al may be transferred to terrestrial predators by mayflies and other aquatic insects that leave their final exuvium in the water. However, aquatic insects that make their final molt in the terrestrial environment, and thereby bring adsorbed Al out of the water are more likely vectors.