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. Thus, remediation of the contaminated soil is needed. Composting is a potential remediation technique for DDT contaminated soil, due to its low cost and potential ability to reduce bioavailability. The effectiveness of composting to mitigate bioaccumulation factor (BAF) has been confirmed by laboratory studies. A plot study was then conducted to examine the feasibility of composting to decrease the BAF under field conditions. But, unlike controlled pot studies, great spatial variability in the field concentrations are typical which can lead to large uncertainties in the BAF using the traditional approach, i.e., assuming normal distribution of data and error propagation. Therefore, a Bayesian hierarchical modelling (BHM) approach was used for characterizing DDx concentrations and BAF, where concentrations were assumed to be log-normally distributed and hierarchically related. The aim of the current study was 1) to characterize and compare the concentrations, the BAF, and their uncertainties using the traditional approach and the Bayesian hierarchical modelling (BHM) approach, 2) to evaluate effect of composting, and 3) to draw implications for risk assessment. An 18-month small-scale plot study was conducted and consisted of seven replicated plots. Each plot was divided into four sub-plots two treatments (2-year compost and 4-month compost) and two controls (control without tillage and control with tillage). Soil and earthworms were sampled from each subplot, and DDT and its metabolites (together referred to as DDx) were measured. Results showed that the BHM is better in handling uncertainty in the concentration data than the traditional approach, suggesting that the BHM provides more reasonable results. The previously assumed linear relationship between soil and earthworm concentrations may result in overestimated risk at high soil concentration. In addition, tillage may mitigate BAF in a long-term scenario while composting may only mitigate bioaccumulation in short term. Results of this work will be useful for data analysis of full-scale field studies and ecological risk assessment.

Evaluation of DDT bioaccumulation in earthworms from a historically-contaminated orchard using Bayesian hierarchical modelling

2019 Fall National Meeting

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