Bioavailability of genotoxic compounds in soils

Measurements were made of the bioavailability of mutagens with a bacterial genotoxicity assay specifically designed for use with the solid phase of soil. Short-term sorption of benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene, 9-phenylanthracene, captan, and aldicarb by six markedly different soils resulted in a 28.2 to >99% decline in availability for genotoxicity. This reduced bioavailability varied markedly with the soil and the compound. The reduced genotoxicity was not a result of the destruction of the compounds since, with few exceptions, >90% of each compound was recovered by Soxhlet extraction. The bioavailability of captan was correlated with surface area and organic C content, but the availability of the other mutagens was not correlated with other properties of the six soils. However, if soils with <0.7% organic matter were not considered, correlations were evident between organic C content and the bioavailability of the three polycyclic aromatic hydrocarbons (r values of 0.90 or higher) and aldicarb (r = 0.760). The amounts of dimethylbenz(a)anthracene, phenylanthracene, and benzo(a)pyrene removed from the soil by a mild extraction with n-butanol were correlated with bioavailability (r values of 0.870, 0.787, and 0.691, respectively), We suggest that genotoxicity, when measured by an organism growing in the soil itself, will vary greatly with soil type and may, in some instances, be predicted from soil properties or by a mild solvent extraction.