A study was conducted to determine the feasibility of devising a chemical assay to predict the bioavailability of organic compounds that become sequestered in soil. The recovery of atrazine and phenanthrene freshly added to soil varied appreciably among individual solvents, but the quantity extracted by each solvent declined as the test compounds persisted in soil. The percentage recovered by some extractants approximated either the percentage uptake by earthworms or bacterial degradation. Recovery by one extractant predicted bioavailability to both organisms. The data suggest that it is feasible to predict bioavailability of persistent organic compounds in soil by chemical procedures.

Abstract-A study was conducted to determine factors affecting the sequestration and changes in bioavailability as phenanthrene persists in soils. Phenanthrene became sequestered in seven soils differing appreciably in organic matter and clay content as measured by earthworm uptake, bacterial mineralization, or extractability. Phenanthrene also became sequestered as it aged in soil aggregates of various sizes as measured by decline in availability to a bacterium, a mild extractant, or both. Wetting and drying a soil during aging reduced the amount of phenanthrene recovered by a mild extractant and the rate and extent of bacterial mineralization of the hydrocarbon. After biodegradation of phenanthrene added to the soil, more of the compound remained if it had been aged than if it had not been aged. Wetting and drying the soil during aging further increased the amount of phenanthrene remaining after biodegradation. The rate and extent of bacterial mineralization of phenanthrene were less in leached than in unleached soil. Aging/ sequestration is thus markedly affected by soil properties and environmental factors.

Abstract-Earthworms (Eisenia foetida) assimilated decreasing amounts of atrazine, phenanthrene, and naphthalene that had been incubated for increasing periods of time in sterile soil. The amount of atrazine and phenanthrene removed from soil by mild extractants also decreased with time. The declines in bioavailability of the three compounds to earthworms and of naphthalene to bacteria were not reflected by analysis involving vigorous methods of solvent extraction; similar results for bioavailability of phenanthrene and 4-nitrophenol to bacteria were obtained in a previous study conducted at this laboratory. We suggest that regulations based on vigorous extractions for the analyses of persistent organic pollutants in soil do not appropriately estimate exposure or risk to susceptible populations.

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