Flame retardant chemicals have been added to various consumer goods from fabrics to electronics to protect people from fire. Among these chemicals, polybrominated diphenyl ethers (PBDEs) are a group of 209 compounds with 1 to 10 bromine atoms in their molecules. Commercial mixtures of PBDEs, commonly known as “penta”, “octa”, and “deca”, have been used extensively since the 1970s.  Their widespread use has caused rapid accumulation in the environment and in human body. This is a great concern because some PBDEs may cause similar toxicological effects as the well-known polychlorinated biphenyls (PCBs).

Rivers and lakes receive PBDEs primarily from rain, waste- and stormwater discharges, and PBDE-laden dusts falling from air. In the water, PBDEs tend to settle with solid particles to the bottom sediments, where they accumulate over time and may slowly transformed to other chemicals. This project was conducted to find out whether such transformations have been occurring, and if so, how extensive and how fast.

The researchers went to Arkansas where two of the main PBDE manufacturing facilities are located based on the expectation that contamination levels would be high. They collected sediment cores from six water bodies (Figure 1). Indeed, the concentrations of PBDEs in the sediments near the manufacturing facilities were found to be the highest ever reported for sediments in the world. The concentrations drop quickly with increasing distance from the facilities (Figure 2). In addition, the time trend of contamination, which was reconstructed from the layers of the collected sediment cores, matched the known record of historic PBDE production. These results suggest that the PBDE manufacturing facilities are largely responsible to the contamination of the local waters. 

Not surprisingly, a new chemical decabromodiphenyl ethane (DBDPE), which is one of the newer flame retardants used to replace PBDEs, was also found in the Arkansas sediments with the highest concentrations ever reported in the world. DBDPE accumulation increased sharply since the late 1990s as its production has increased (Figure 3). As was the case with PBDEs, the closer the sampling location to the manufacturing facilities, the higher the DBDPE levels in the sediments (Figure 2).

The Chicago metropolitan area is another region of this investigation, where it was found that sediment from water bodies receiving wastewater treatment plant discharges have significantly higher proportions of the more toxic form of PBDEs (the “penta”) compared to sites receiving PBDEs from air deposition only. Apparently, post-consumer PBDEs have contaminated the urban waterways, even with no manufacturing facilities nearby.

In this project, it was also found that PBDEs molecules having more bromines may “debrominate” into those with less bromines. This process, called debromination, was known to occur to PBDEs when they were placed under sunlight or by bacteria in wastewater treatment plants. This project showed that it could also occur in rivers and lakes, caused by both sunlight which penetrates into water and by certain bacteria in the sediment. To learn about the bacteria responsible to PBDE debromination, DNA was extracted from selected sediment samples to look for the types of bacteria that are known to do this reaction. This “pyrosequencing” resulted in the creation of 100,000 sequences that allow the researchers to uniquely identify nearly all the important bacteria in the sediments. The results suggest that the bacteria capable of transforming PBDEs in sediment face great competition for food and resources with other bacteria that naturally exist in the sediments.

The researchers of this project went on to study how the molecular structures of different PBDEs affect their persistence in the e...

Please report errors in award information by writing to: awardsearch@nsf.gov.