Bioavailable DDT residues in sediments: Laboratory assessment of ageing effects using semi-permeable membrane devices

We describe the reduction in bioavailability of DDT in contaminated soil after it was incubated as sediment for 365 d. Bioavailability was assessed using semi-permeable membranes. Contaminated soils from three cattle dip sites, one spiked paired uncontaminated site, and one spiked OECD standard soil were studied. Sandy soil with residues of 1880 mg/kg ∑DDT incurred since 1962, initially had 4.6% of ∑DDT available, reducing to 0.6% following 365 d. Clay soil (1108 mg ∑DDT/kg) had 4.1% initially available, reducing to 0.3% after 365 d. Freshly spiked soils had a greater amount of DDT initially available (10.9%), but this reduced to 1.5% by the end of the incubation. Of the DDT congeners, both o,p′-DDD and p,p′-DDD were most bioavailable in the soils, but also had the most significant decrease following incubation.