New data on a widely used flame retardant
New research suggests that the flame retardant Dechlorane Plus is ubiquitous in the environment and may break down into more bioaccumulative compounds.
Two new research papers published in ES&T document that the commonly used flame retardant Dechlorane Plus (DP) is found (DOI: 10.1021/es072039a) in the atmosphere of Europe and Asia, as well as North America, and present the first evidence (DOI: 10.1021/es0710104, to be published next week) that it is breaking down in the environment.
DP is manufactured by OxyChem, and the U.S. EPA lists it as a high-production-volume (HPV) chemical. Although DP has been used for more than 40 years, little toxicity data is available on it. Its structure is similar to that of banned organochlorine pesticides such as heptachlor, chlordane, and mirex, but its large molecular size is thought to hinder its bioavailability.
Xinghua Qiu and Ron Hites of Indiana University's School of Public and Environmental Affairs used tree bark samples to provide the first data on DP's prevalence in the atmosphere outside the Great Lakes region.
Tree bark is an effective passive sampler for airborne pollutants, Hites says. In addition to being highly porous, bark contains relatively high concentrations of lipids, "so it soaks up [the lipophilic compounds] we want to measure," he explains. Hites helped pioneer the technique of using bark from trees such as oaks, maples, and pines for this purpose 20 years ago (Environ. Sci. Technol. 1987, 21, 709–712) (PDF: 447KB).
The new research shows that atmospheric concentrations of DP near its only known manufacturing site, in Niagara Falls, N.Y., are 1–3 orders of magnitude higher than elsewhere in the U.S. The researchers found relatively high DP concentrations in bark samples from Korea and China, suggesting that the compound may also be manufactured in Asia, Hites says. Hites and Qiu document that the compound is found at low levels in European trees, but they did not find it in northern Canada.
The paper presents further evidence of tree bark's utility as a passive sampler and its ability to identify point sources of pollution, says Staci Simonich, an associate professor of chemistry at Oregon State University. Although the OxyChem plant is clearly a major source, DP's presence in household products such as electrical wire coatings and computer connectors suggests that indoor air also may be a significant source to the outdoor environment, adds Tom Harner, a research scientist at Environment Canada.
In the second paper, a team of Canadian researchers led by Ed Sverko, the head of organic analysis at Environment Canada's National Laboratory for Environmental Testing, looked at concentrations of DP in Great Lakes sediments. They documented that the concentrations of DP in sediments from Lake Ontario, where the water discharged from OxyChem's Niagara Falls plant ends up, were up to 60 times higher than those in nearby Lake Erie sediments.
The Canadian researchers analyzed the relative abundance of DP's two isomers in the sediment samples. They were surprised to find that the syn isomer varied significantly from the commercial formulation in the sediment samples taken from sites closest to OxyChem's Niagara Falls manufacturing facility. Samples from farther away, such as Lake Erie, tended to have isomeric profiles more similar to those of the commercial mixture. The researchers speculate that isomer-specific microbial degradation may be taking place.
Previous research has shown that Great Lakes fish, especially those at the top of the food chain, are more likely to take up the anti-isomer (Environ. Sci. Technol. 2007, 41, 2249–2254), points out Gregg Tomy, a research scientist in the Arctic Aquatic Research Division of Fisheries and Oceans Canada. In contrast, the Indiana University scientists' work shows that DP's isomer ratios in the atmosphere are very close to those of the commercial formulation.
Sverko, who is conducting his research at McMaster University (Canada), acknowledges that he and his colleagues stumbled upon DP degradation products in the environment "by mistake." When he was analyzing the compound, he did not notice that the glass liner on his gas chromatography/mass spectrometry system was dirty. Eventually, he and his colleagues realized that something in the impurities attacked the DP molecules to produce degradation products with fewer chlorine atoms. When they looked for these degradates in the environment, they found them in sediments from the Niagara River near the OxyChem plant.
The smaller compounds that form as the DP molecule loses chlorine atoms are likely to be more bioaccumulative, Sverko says. Sverko and Tomy are currently conducting studies to determine whether the degradates can be found in fish.
"Based on all the information we have seen and cooperative efforts with the EPA, we continue to believe that [DP] is a safe and effective product," says Richard S. Kline, vice president of communications and public affairs for Occidental Petroleum Corporation, OxyChem's parent company.
