Land application of biosolids was always thought to be a safe and effective method for disposing of the seven million tons of sludge produced each year. Now scientists at the Gloucester Points, Va.-based Virginia Institute of Marine Science are saying that that might not be the case.

According to a study, conducted by the institute and published in Nature, sludge in four different parts of the country shows high concentrations of brominated diphenyl ethers (BDEs). The compounds are used primarily as flame retardants in polyurethane foams.

According to the magazine, BDEs are stable and persist for a long time in the environment. The European Commission has recommended banning the BDEs that are used in foams.