John Wiley & Sons, Ltd.

Dry–wet cycles increase pesticide residue release from soil

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Soil drying and rewetting may alter the release and availability of aged pesticide residues in soils. A laboratory experiment was conducted to evaluate the influence of soil drying and wetting on the release of pesticide residues. Soil containing environmentally long‐termaged (9–17 years) 14C‐labeled residues of the herbicides ethidimuron (ETD) and methabenzthiazuron (MBT) and the fungicide anilazine (ANI) showed a significantly higher release of 14C activity (ETD:p< 0.1, MBT and ANI:p< 0.01) in water extracts of previously dried soil compared to constantly moistened soil throughout all samples. The extracted 14C activity accounted for 44% (ETD), 15% (MBT), and 20% (ANI)of total residual 14C activity in the samples after 20 successive dry–wet cycles in contrast to 15% (ETD), 5% (MBT), and 6% (ANI) in extracts of constantly moistened soils. In the dry–wet soils, the dissolved organic carbon (DOC) content correlated with the measured 14C activity in the aqueous liquids and indicated a potential association of DOC with the pesticide molecules. Liquid chromatography MS/MS analyses of the water extracts of dry–wet soils revealed ETD and MBT in detectable amounts, accounting for 1.83 and 0.01%, respectively, of total applied water‐extractable parent compound per soil layer. These findings demonstrate a potential remobilization of environmentally aged pesticide residue fractions from soils due to abiotic stresses such as wet–dry cycles. Environ. Toxicol. Chem. © 2012 SETAC

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