SHORT-TERM TOXICITY OF IRON (FE) AND LEAD (PB) TO THE MAYFLY LEPTOPHLEBIA-MARGINATA (L) (INSECTA) IN RELATION TO FRESH-WATER ACIDIFICATION

The mayfly Leptophlebia marginata was exposed to different concentrati ons of Fe2+ or Pb2+ at pH 4.5 and pH 7.0. The effects of the metals on escape behavior and survival of the mayflies were investigated during an exposure of 120 hours. (1) Whole-body metal loads (Fe; Pb) of the mayflies increased in a dose-dependent way at both pH levels. A signif icant effect of pH on metal concentration in the mayflies was only fou nd for Pb (p < 0.00 1). (2) In terms of mortality, both metals were mo re toxic at pH 4.5 than at pH 7. The 96 h-LC50 values for Fe were 106. 3 mg Fe l-1 at pH 7 and 89.5 mg Fe l-1 at pH 4.5. Those for Pb were > 5 mg Pb l-1 at pH 7 and 1.09 mg Pb l-1 at pH 4.5. (3) The mayflies los t their escape behavior, when exposed to the metals, the effects being more pronounced at low than at circumneutral pH for both metals (p < 0.05). The 96 h-EC50) values for Fe were 70.0 mg Fe l-1 at pH 7 and 63 .9 mg Fe l-1 at pH 4.5.