John Wiley & Sons, Ltd.

Comparison of earthworm and chemical assays of the bioavailability of aged 1,1‐dichloro‐2,2‐bis(p‐chlorophenyl)ethylene, 1,1,1‐trichloro‐2,2‐bis(p‐chlorophenyl)ethane, and heavy metals in orchard soils

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Orchard soils can contain elevated concentrations of 1,1‐dichloro‐2,2‐bis(p‐chlorophenyl)ethylene (p,p′‐DDE), 1,1,1‐trichloro‐2,2‐bis(p‐chlorophenyl)ethane (p,p′‐DDT), and heavy metals as a result of historical agrichemical applications. The bioavailability of p,p′‐DDE, p,p′‐DDT, As, Cd, Cu, and Pb from five field‐aged New Zealand orchards and three grazing soils was assessed by using a 28‐d bioassay with Aporrectodea caliginosa and chemical assays. Significant relationships were found between total soil and earthworm tissue concentrations for p,p′‐DDE (p < 0.001), p,p′‐DDT (p < 0.001), Cu (p < 0.001), and Pb (p < 0.01). Two neutral salt solutions, 0.01 M CaCl2 and 1 M NH4NO3, were used as surrogate measures of the bioavailability of heavy metals. Copper was the only heavy metal for which significant correlations were found between neutral‐salt‐extractable and earthworm tissue concentrations (p < 0.001). Up to 28% of the aged DDT residues were released from the soils by Tenax over a 24‐h extraction period. Significant relationships (p < 0.01) between the Tenax‐extractable and earthworm tissue concentrations for p,p′‐DDE and p,p′‐DDT showed that Tenax provides a good surrogate measure of the bioavailability of these compounds to A. caliginosa. Surprisingly, there was a similarly significant relationship (p < 0.001) between the total soil and earthworm tissue concentrations for p,p′‐DDE and p,p′‐DDT, suggesting that total soil concentrations alone were sufficient to predict uptake by A. caliginosa. These results demonstrate that the aged agrichemical residues in orchard soils, and particularly p,p′‐DDE and p,p′‐DDT, remain highly bioavailable to A. caliginosa despite decades of weathering and continue to present an environmental risk. Environ. Toxicol. Chem. © 2012 SETAC

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