Passive sampling devices as surrogates for evaluating bioavailability of aged chemicals in soil

The fraction of a chemical available to soil-dwelling organisms such as earthworms is not simply related to the concentration of that chemical in the soil determined through rigorous extraction methods. Aging is one of the processes that are known to affect exposure of chemicals to organisms by decreasing the available fraction in soil with time. Passive sampling devices (PSDs) are potentially direct chemical indicators for assessing bioavailability of hydrophobic pesticides (and other chemicals) in soil. In this study, a pesticide mixture (six organochlorine pesticides including aldrin, dieldrin, endrin, lindane, heptachlor, and p,p'-DDT) was aged in two types of soil (sandy loam and silt loam). Uptake rates and maximum concentrations of the chemicals in earthworms and PSDs placed into the soils were determined over 36 days. There was a general trend towards decreased chemical uptake in the aged soil and in the soil with higher organic carbon content (both initial uptake rates and maximum concentrations) for the PSD and the earthworms. However, those differences were not statistically significant (p ≤ 0.05) for the earthworms in sandy loam soil. Uptake rates into PSDs and maximum concentrations were observed to positively correlate with uptake rates and maximum concentrations in earthworms for both of the soil types studied. These results indicate that PSDs may be used as a surrogate for earthworms and provide a chemical test for assessing the biological availability of aged chemical residues in soil.