A cheap, effective technique to remove toxic polychlorinated biphenyls (PCBs) from contaminated soil has been developed in the US by scientists at Oak Ridge National Laboratory, Tennessee. The technique is considered an important advance since, unlike the biological remediation (disintegration) process developed by research workers in the early 1990s, it does not require mixing PCB-contaminated soil with river sediment. Sediment is the only element in the environment in which anaerobic bacteria thrive. These bacteria can degrade the persistent chlorine compounds, PCBs. The new technique uses two types of bacteria -- anaerobic, which do not require oxygen, and aerobic, which do. The two-stage treatment degrades 70 per cent of the PCBs in soil samples to harmless substances. Preliminary studies show that chemical reactions between the remaining PCBs and a solution of special suspended solids to which the toxic compounds are attached eliminate the rest of the PCBs ( Oak Ridge National Laboratory Review , Vol 29, No 3&4).
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