Organochlorine pesticide accumulation and genotoxicity in Mexican free-tailed bats from Oklahoma and New Mexico.

The summer population of Mexican free-tailed bats (Tadarida brasiliensis) at Carlsbad Caverns, New Mexico, declined from an estimated 8.7 million in 1936 to 200,000 in 1974; thereafter, it increased to approximately 700,000 in 1991. This decline has been attributed primarily to organochlorine (OC) pesticide contamination and habitat disturbance. Similar declines have been observed in other populations of this species. This study examined the potential genotoxic effects of OC pesticide contamination on two populations of T. brasiliensis. Pesticide accumulation, frequencies of chromosomal aberrancy, and nuclear DNA content variation in spleen and testicular tissues were examined in specimens collected from Carlsbad Caverns and Vickery Cave, a maternity colony in northwestern Oklahoma, during the summers of 1990 and 1991. Pesticide residues in brain and carcass tissues were identified and quantified by electron capture gas chromatography. Genotoxicity was examined with the standard bone marrow chromosomal aberration assay and flow cytometry. Statistical relationships among pesticide content, observed chromosomal aberrancy, and nuclear DNA content variation were examined. Both populations demonstrated significant levels of DDE contamination; however, the Carlsbad Caverns population showed consistently higher pesticide loads. Males also demonstrated higher levels than females. No statistical differences in chromosomal aberrancy or nuclear DNA content variation were observed among sexes, sites, or collected periods. Positive correlations were detected between brain and carcass DDE concentrations for all bats examined. A significant negative relationship was found between brain DDE concentration and coefficients of variation in spleen DNA content only for males.