Dichlorodiphenyltrichloroethane (DDT), an organochlorine insecticide with known detrimental environmental effects, was banned in the United States in 1972. However, the repeated applications of DDT and its persistence and hydrophobicity have given rise to highly-contaminated soils resulting in bioaccumulation in the local food chain and a concern for converted historical orchards. A primary exposure route of DDX (DDX = DDT and its degradation products) for indigenous fauna is ingestion of earthworms. Assessing the risk of DDX exposure requires calculation of the bioaccumulation factor (BAF) of the earthworms consuming the soil. Although BAF have been extensively investigated in the laboratory, field studies are lacking. Thus, the goals of this study are to investigate the spatial variability of DDX in soil and earthworms, to quantify the changes in BAF of DDX, to evaluate the factors influencing BAF, to establish a model that can predict DDX concentration in earthworm using soil concentrations, and to optimize a soil sampling strategy to assess ecological risk. A field study was conducted on a 1.2-ha field historical orchard where DDT was heavily applied. The soil was amended with compost to decrease DDX bioavailability. Control pots of soil (no compost) were placed in a nearby field. Soil and earthworms were collected at 53 sampling points on a by 15-m x 15-m grid before compost was applied (time = 0 days) and in the spring and the fall for several years following treatment. Soil properties and the DDX concentrations in soil and earthworms were determined. Geostatistical analyses were performed to characterize DDX variability and its spatial distribution. Preliminary results showed that the concentration of DDX ranged from 0.1 to 11 µg/g dry weight soil. A spherical model was used to fit the experimental variogram. Leave-one-out-cross-validation showed a mean error of -0.005 and mean square deviation ratio of 1.008. Results of this work will be useful to land managers developing remediation strategies for contaminated soils.

Spatial variability of DDT in aged contaminated soil and its bioavailability to indigenous earthworms

256th National Meeting (2018)

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