Evaluation of a passive sampling device as an indicator of available aged organochlorine pesticide residue in soil

The fraction of a chemical available to soil-dwelling organisms such as earthworms is not simply related to the concentrations of the chemical in soil determined through vigorous extraction methods. Aging is one of the processes known to affect bioavailability of chemicals to organisms by decreasing the available chemical with increasing residence time in soil. Passive sampling devices (PSDs) are potentially direct chemical indicators which can assess 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) for up to eight months. After chemicals were aged, earthworms and PSDs were placed into the soils, and initial uptake rates and maximum concentrations of the chemicals in earthworms and PSDs were determined over 36 days. There was a general trend towards decreased uptake of aged chemicals and of chemicals from soil with higher organic carbon content (both initial uptake rates and maximum concentrations) for both PSDs and earthworms. Maximum concentrations in PSDs were observed to positively correlate with maximum concentrations in earthworms for both soil types studied. To some extent, this was also true for uptake rates. Significant correlation coefficients (r=0.87 and 0.72; p < 0.05) were obtained between maximum concentrations in PSDs and earthworms for sandy loam soil and silt loam soil, respectively. Correlation coefficients were even better (r=0.91; p < 0.001) when maximum concentration data from the two soil types were combined. 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.