Organochlorine residues in roof timbers and possible implications for bats

In Britain, many species of bat regularly use buildings as roosts. DDT, DDE, dieldrin (HEOD) and gamma-HCH (lindane) have been detected in carcasses of bats that had died a short while before they were found. Roof timbers may be a source of this contamination. This study reports concentrations of organochlorines in (i) roof timbers known to have been treated in the past (spot samples; n - 17) and (ii) timbers before and after treatment with commercial permethrin formulations (pre-treatment and post-treatment samples, n = 11). Gamma-HCH was detected in 13 spot samples and HEOD in 6. Where present, mean (±1 SE) concentrations in wood were 15·6±6·5μgg^-1 WW (n = 13) and 25·0±11·8 μg g^-1 WW (n = 6), respectively. DDT was not detected in any spot samples, but permethrin was detected in four () samples, but not in the corresponding pre-treatment samples; in one other pair of samples, concentrations of gamma-HCH increased from 74 to 2468 μg g^-1 WW after treatment. Both DDT and HEOD occurred in low (<2 μg g^-1 WW) concentrations in five post-treatment samples and in one and zero pre-treatment samples, respectively; the highest dieldrin concentration measured was 30·9 μg g^-1 WW. Permethrin was not detectable in any pre-treatment samples but was present in ten post-treatment samples in concentrations ranging from 93 to 2995 μg g^-1 WW. The spot results suggest that low concentrations of organochlorines can persist in treated roof timbers for at least 13 years post-treatment. Occasionally, these pesticide residues in timber may be of sufficient magnitude to result in bats absorbing a substantial proportion of a lethal dose. Results also suggest that there is organochlorine contamination of permethrin formulations and that the solvents used in new applications of pesticide may re-mobilise organochlorines already present in wood.