Defluorination of sodium monofluoroacetate by soil microorganisms from central Australia

Abstract

Sodium monofluoroacetate (1080) is a commonly used vertebrate pesticide throughout Australia and New Zealand. However, little is known about the persistence of 1080 in arid environments, or whether soil microorganisms capable of defluorinating 1080 are present in soils from arid Australia. Soil samples (3 replicates) from central Australia were collected on seven occasions over an 8-month period, and the microorganisms capable of defluorinating 1080 were isolated. When grown in an inorganic medium containing 20 mM 1080 as the sole C source, 24 species were able to defluorinate 1080: 13 bacteria and 11 fungi. The abundance of these microorganisms appeared to be influenced by climatic conditions with the relative abundance of many species increasing after rain. The fungus Fusarium oxysporum had by far the greatest defluorinating ability, and defluorinated approximately 45% of added 1080 within 12 d. Defluorination of 1080 added to soil was significantly greater at pH 5.6 compared to pH 6.8, suggesting that the fungal species were important defluorinators in these soils. In a 28-d time course trial, defluorination of added 1080 by soil microorganisms appeared to asymptote after 21–28 d. The presence of these microorganisms in soil from central Australia indicates that 1080 can be used safely even in arid environments. 1080 is unlikely to persist in these soils, or to contaminate ground water. The implications of these findings with respect to the environmental safety of 1080 in other regions where 1080 baits are used are also discussed.