New Investigator Award Finalist: Utilizing thin-film solid-phase extraction to assess the effect of organic carbon amendments on the bioavailability of DDT and dieldrin to earthworms

Improved approaches are needed to rapidly and accurately assess the bioavailability of persistent, hydrophobic organic compounds in soils at contaminated sites. The performance of a thin-film solid-phase extraction (TF-SPE) assay using vials coated with ethylene vinyl acetate polymer was compared to an earthworm bioassay (Lumbricus terrestris). Experiments utilized, as a control, contaminated soil from a former orchard that received routine DDT and dieldrin applications >40 years ago. The soil was amended with four different organic carbon materials at 5% by weight to assess the change in pesticide bioavailability. In both assays, bioavailability of 4,4'-DDE, 4,4'-DDD, and dieldrin was higher than 4,4'-DDT in the control soil. Addition of organic carbon amendments significantly lowered bioavailability for all compounds except for 4,4'-DDT where bioavailability was significantly higher for three out of four amendments. Equilibrium concentrations of dieldrin and 4,4'-DDT + 4,4'-DDE in the polymer coating were strongly correlated with uptake by earthworms after 48 d exposure (R2 = 0.97; p < 0.001) indicating TF-SPE provided an accurate simulation of uptake by L. terrestris. In a further test of the TF-SPE method, estimated bioavailability of dieldrin and DDX residues in the orchard soil was compared with a soil that was spiked with the same compounds and aged for 90 days in the laboratory. Differences in residue bioavailability in the two soils were observed using TF-SPE. Dieldrin and DDX were only 18% and 11% less bioavailable, respectively, in the orchard soil relative to the spiked soil despite >40 years of aging. Results show that TF-SPE will be a useful tool in examining the potential risks associated with contaminated soils and to test the effectiveness of remediation efforts.