Abstract

There is a worldwide initiative to remove polychlorinated biphenyls (PCBs) from the environment because of their potential hazard. Animal experiments have shown they can produce liver damage, developmental defects and even cancer. Thirty per cent of the 310,000 tons of PCBs that have been produced globally are now considered as persistent toxicants in the environment. To date, only 4% have been successfully treated. Although a number of technologies are in existence for the treatment of persistent organic pollutants (POPs), they do have several drawbacks including the production of toxic volatiles in incinerators and high cost associated with these procedures. On the other hand, successful bioremediation is relatively inexpensive, as shown for polyaromatic hydrocarbons (PAH) degradation, with the added advantages of being able to be carried out in situ . In this study, preliminary experiments demonstrated that certain surfactants enhance PCB degradation in aqueous solution in the presence of enzymes, in a concentration-dependent manner. These surfactants have not been previously reported as enhancers in PCB degradation. Conditions were optimized before experiments with soil samples were performed. A soil sample (free of PCBs) was spiked with varying amounts of PCBs and internal standards. Samples were mixed at various speeds, temperatures, incubation periods and concentrations of surfactants, before the metabolites were extracted and mass analyzed. An aged PCB-contaminated soil sample was also studied. PCBs extraction recoveries for the spiked samples two hours after exposure to the toxicants were 93% whereas average recovery from the samples extracted after 60 days of toxicant exposure was 67%. Within 2 hours of incubation, 47, 28 and 14% of PCBs were biodegraded from the contaminated sample by the addition of surfactin, rhamnolipids and octyl glucoside respectively, at concentrations above their critical micelle concentrations. If the soil composition and mechanism for removal at a contaminated site are fully understood, in situ biodegradation can be exploited.