Transfer of microcontaminants from sediment to chironomids, and the risk for the Pond bat Myotis dasycneme (Chiroptera) preying on them

Transfer ratios of metals, PCBs, pesticides and PAHs from the sediment to chironomid larvae and adults collected in a highly contaminated area, the Biesbosch, were studied. Metal concentrations in larvae were 0.28 (Cd), 0.02 (Cr), 0.52 (Cu), 0.06 (Hg), 0.03 (Pb), 0.32 (Zn) times those found in standard sediment, on a dry weight basis. Hg and Zn were well transported to the adult stage. Dry weight ratios of contaminant residues in adults and in larvae were 0.38 (Cd), 0.23 (Cr), 0.62 (Cu), 1.03 (Hg), 0.08 (Pb), 0.94 (Zn). For PCBs and pesticides, the concentration ratios of chironomid larvae fat to sediment (dry organic matter) varied around 3.3, which is consistent with laboratory studies. Organochlorine residues in adult fat were comparable to those in larvae lipids. However, the concentrations of non-ortho PCBs were 1.7 times higher in adults. For polycyclic aromatic hydrocarbons (PAH), larval fat:sediment (organic matter) concentration ratios ranged from 0.004 to 0.1. Adult: larvae ratios for PAHs varied between 0.2 and 0.6. For naphthalene a much higher transport ratio of 2 was found. Chironomid adults are the most important potential food source of the Pond bat, which lives in low densities in the Biesbosch. The contaminant concentrations measured in the chironomids do not exceed diet levels that are thought to be safe for mammals. However, Pond bats collected in less contaminated areas contained PCB-concentrations of 9, 33 and 76 mg kg^–1 lipid weight, which are above concentrations that cause reproduction effects on Mink.