A comparison of the toxicity to laboratory mice and pipistrelle bats Pipistrellus pipistrellus of exposure to remedially-treated timber.

Many species of bats roost in roof spaces and can come into contact with pesticides used to treat roof timbers against rot. As part of a study to develop a test with laboratory mice which could be used to predict the likely toxicity of pesticides to bats, the toxic effects on pipistrelle bats Pipistrellus pipistrellus and laboratory mice (CFLP outbred-strain) of exposure to dieldrin-treated timber were compared. Dose (amount of dieldrin applied to the wood surface) - response (mortality) studies demonstrated that pipistrelle bats were 30 times more sensitive to dieldrin-treated wood than laboratory mice. However, dieldrin residues in the brain and liver of animals which had been poisoned were significantly higher in bats than mice. These residue data suggest that bats may be inherently less sensitive to dieldrin poisoning than mice and so it is likely that the 30-fold greater sensitivity of bats than mice to dieldrin-treated timber was a result of greater rate of uptake, per gram body weight, of the active ingredient from the wood surface and/or slower clearance from the body. The importance of differences in exposure and the reliability of residue data as an indicator of differences in inherent sensitivity to a chemical are discussed in terms of their importance when considering inter-species variation in toxic response.