Polychlorinated dibenzo-p-dioxins and dibenzofurans in sewage sludge: Sources and fate following sludge application to land

Municipal sewage sludge is ubiquitously contaminated with polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F). Whereas in Germany there are some industrial sources, associated in particular with the use of pentachlorophenol (PCP) in the textile industry, surface runoff and household wastewater play a more important role in most treatment plants. Most of the higher chlorinated PCDD/F congeners in sludge originate in textiles which become contaminated during production through the use of PCP. The PCDD/F, which are contaminants in technical PCP, are washed out of textiles in the washing machine and enter household wastewater. The lower chlorinated PCDD/F, on the other hand, reach sludge largely as the result of transport of atmospheric deposition to the treatment plant in surface runoff. Following application of sewage sludge to land, the PCDD/F are very persistent, with half lives in excess of 10 years. They accumulate in soils End can under some conditions enter the agricultural food chain. The potential risk of land application of sewage sludge increasing human exposure to PCDD/F depends on the level of sludge contamination, the intensity of sludge use and the agricultural practices.