The Effects Of Aging Time On The Bioavailability Of PCBs And Their Anaerobic Remediation In The Sediments

Polychlorinated biphenyls(PCBs) belong to the class of persistent organic halogenates in the environment. They demonstrate refractory character, easily adopted by living tissues through the food chain. They accumulate in human and animal fat, are carcinogenic, teratogenic and mutagenic. Polychlorinated biphenyls exhibit reduced bioavailability in soils and sedimentswith the aging time, becoming even more difficult for degradation by microorganisms. Aging of PCBs in soils shows the influence to the bioavailability and extractability from soils. This paper reports the results of experimental study on:(1) the impact of aging of PCBs on the soil bioavailability, and(2) the influence of addition of electron donors, surfactants and structural analogs on anaerobic degradation of PCBs.The aging time affects the extractability and bioavailability of polychlorinated biphenyls(PCBs) in the soil. A 90 day’s aging study was conducted to estimate the extraction efficiencies of four extraction agents for PCB138, as well as the effects of aging time on Eisenia fetida which is used as the biological indicator. The results showed that the extraction efficiencies are in the following descending order: Ultra Sonic = Soxhlet > n-butanol > pure water. The extraction rates of mentioned agents above for PCB138 are decreased from 87-93%, 85-90%, and 50-60% to 70-76%, 65-73%, and 25-45%, respectively, and the total extraction amount of PCB138 is stable after 30-45 days. However, the extraction amount by pure water method showed non-repeatability which means fewer PCB138 can be extracted by pure water. The accumulation of fat in E. fetida was increasing during the first 30 days of aging and decreased a little after 30-60 days. This study demonstrated that the extractability of PCB138 decreased by n-butanol, US, and Soxhlet extraction methods as time aging, and the bioavailability for earthworms also decreased as the same process.Polychlorinated biphenyls(PCBs) present a problem of environmental pollution due their refractory character in respect of biological oxidation and, thus, accumulation in the environment at ratenher high conctrations in bottom sediments and soils. Three PCBs-PCB52, PCB138 and PCB153,- were chosen for this study as target pollutants in experimental research undertaken to biodegradability under anaerobic conditions, using original microflora. The results showed that after 25 months incubation, the degradation rate of PCB153 was 27.7 and 35.7%, when sodium lactate and volatile fatty acids(VFA) were used as electron donors, respectively. Under anaerobic incubation conditions with methane formers for 12 months, the degradation rate of PCB52 was 32.8 and 30.4% with addition of Tween 80 and TX-100 surfactants, respectively, whereas the degradation without surfactants did not exceed 16.3%. The degradation rate for PCB138 after 25 months was at the 38.8 and 40.5% and 45.3% level, when PCB61 and pentachloronitrobenzene(PCNB) and 4,4’-BB were used as co-metabolic substrates, respectively. Therefore, addition of surfactants, the electron donors, as well as co-metabolic substrates significantly enhance anaerobic degradation of PCBs.