Tenax TA extraction to assess the bioavailability of DDTs in cotton field soils

The rapid-desorbing fraction plays an important role in the bioavailability of organic pollutants in soil. In the present study, DDT's desorption from the cotton field soils was investigated by Tenax extraction. The results of the Tenax consecutive extraction (400 h) indicated that the rate constants were in the order of 10(-1), 10(-2), and 10(-4) h(-1) for the rapid, slow and very-slow desorption, respectively. The rapid-desorbing fraction was about 0.3 times the total soil DDTs, and about 2 times the Tenax 6 h-extracted fraction (single-point extraction). The rapid-desorbing fraction correlated well with the 6 h-extracted fraction (p<0.05), implying the feasibility of measuring the rapid-desorbing fraction with Tenax 6 h-extration. The strong correlation with the carrot accumulation suggested that Tenax 6 h-extrated fraction could serve as a good predictor of DDT's bioavailability to carrot roots. Risk assessment demonstrated that when based on the rapid-desorbing concentration and 6 h-extracted concentration, about 60.7% and 17.9% of the soil samples were moderately polluted, however, up to 78.5% were moderately polluted when based on the total soil DDTs concentration. The risk assessment might be more representative when based on Tenax extraction because of the strong correlation with the carrot accumulation. Our results provided implications for site risk assessment and cleanup strategies.