Of the sewage sludge--or postprocessing sewage biosolids--produced annually in the United States, over half is applied to land. Sludges are treated to reduce odors and pathogens and their metal contents are regulated, but content of persistent organic pollutants such as polybrominated diphenyl ethers (PBDEs), chemicals found in brominated fire retardants and other products, has been largely ignored. PBDEs are considered emerging contaminants of concern because of their widespread use in consumer products, their persistence, and evidence that they may bioaccumulate and exert toxic effects at low levels.
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New research by Robert C. Hale and colleagues from the Virginia Institute of Marine Science in Gloucester Point, Virginia, shows that brominated flame retardant levels in sewage sludge samples from four different U.S. regions are 10-100 times higher than levels common in Europe. The researchers also found the flame retardants in 87% of fish sampled from Virginia waters, with some of the highest levels ever reported found in a sampling of five fish. The study was published in the 12 July 2001 issue of Nature.
Used extensively in electronic devices, furniture, automobiles, textiles, plastics, and polymers to reduce the risk of fire, PBDEs have been compared to polychlorinated biphenyls because of their structure and properties. Three different commercial formulations are sold as penta-, octa-, and deca-bromodiphenyl ether, with each mixture dominated by congeners (variations) with 5, 8, or 10 bromine atoms, respectively. The most bioaccumulative and apparently most toxic PBDEs contain 4-6 bromine atoms.
Penta-BDE is to be banned in Europe in 2003 because of concerns about its reported exponential increase in human breast milk and perceived health risks. Based on laboratory experiments, prolonged exposure is suspected of damaging the immune system, thyroid, and liver. A study by Swedish researchers in neonatal mice also links exposure to behavioral problems such as hyperactivity [see "Firesafe but Not Failsafe," p. A434 this issue).
Hale and colleagues analyzed treated sludge destined for land application from 11 different sources located in Texas, California, New York, Virginia, and Maryland. The total concentrations of penta-like BDEs in the sludges ranged from 1,100 to 2,290 µg/kg of dry weight, "suggesting that input was high and consistent, regardless of the region of origin and irrespective of pre-application treatment," the authors write. Total PBDEs were even higher, with a deca- form of PBDE present at concentrations of 84.8-4,890.0 µg/kg in the biosolids.
The researchers also found PBDEs in 87% of 334 fish from Virginia waters that they tested. A composite sample of fillets from five carp found in one stream contained 47,900 µg/kg total PBDEs, "rivaling the highest fillet burdens reported in the world so far," the report states.
"Our study indicates that pollutants with [persistent, bioaccumulative, and toxic] properties that are not tracked in the United States are present at relatively high concentrations in material that is widely applied to the land and that it has reached fish in many areas," says Hale. He says he views pollutants in sludge as an early indicator of dissemination, and that their presence in fish means they are moving up through the food chain--perhaps to humans.
Hale and colleagues report that the contributions of PBDE congeners in the sewage sludge samples matched those in the penta- commercial formulation, which is used as a flame retardant in polyurethane foam. These same congeners dominated the residues in fish. (However, the tetrabrominated congener BDE-47, a main ingredient in penta-BDE mixtures and the component found at highest concentrations in the environment, constituted the bulk.) The source of the sludge PBDEs is uncertain, but the authors believe that the breakdown of discarded polyurethane foam, which may contain up to 30% penta-BDE by weight, may be a factor.
The presence in U.S. sludge of high levels of congeners common in penta-BDE mixtures follows an emerging pattern, according to Åke Bergman, a professor of environmental chemistry at Stockholm University in Sweden. North America accounts for about 98% of the global demand of penta-BDE, estimated at about 8,290 metric tons in 1999. Environmental levels in Europe appear to be stabilizing in response to regulatory initiatives, but levels in North America appear to be rising still. In response to the high levels in fish found by the researchers, Virginia and North Carolina last year passed the first U.S. health limits for PBDEs in fish, at 5 ppm for tetrabromodiphenyl in fish fillets.
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