Hexabromocyclododecanes (HBCDs) are brominated aliphatic cyclic hydrocarbons used as flame retardants in thermal insulation building materials, upholstery textiles, and electronics. As a result of their widespread use and their physical and chemical properties, HBCDs are now ubiquitous contaminants in the environment and humans. This review summarizes HBCD concentrations in several environmental compartments and analyzes these data in terms of point sources versus diffuse sources, biomagnification potential, stereoisomer profiles, time trends, and global distribution. Generally, higher concentra tions were measured in samples (air, sediment, and fish) collected near point sources (plants producing or processing HBCDs), while lower concentrations were recorded in samples from locations with no obvious sources of HBCDs. High concentrations were measured in top predators, such as marine mammals and birds of prey (up to 9600 and 19 200 ng/g lipid weight, respectively), suggesting a biomagnification potential for HBCDs. Relatively low HBCD concentrations were reported in the few human studies conducted to date (median values varied between 0.35 and 1.1 ng/g lipid weight). HBCD levels in biota are increasing slowly and seem to reflect the local market demand. One important observation is the shift from the high percentage of the γ-HBCD stereoisomer in the technical products to a dominance of the α-HBCD stereoisomer in biological samples. A combination of factors such as variations in solubility, partitioning behavior, uptake, and, possibly, selective metabolism of individual isomers may explain the observed changes in stereoisomer patterns. Recommendations for further work include research on how HBCDs are transferred from products into the environment upon production, use, and disposal. Time trends need to be analyzed more in detail, including HBCD stereoisomers, and more data on terrestrial organisms are needed, especially for humans. Whenever possible, HBCDs should be analyzed as individual stereoisomers in order to address their fate and effects.

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The environmental safety of decabromodiphenyl ether (BDE-209), a widely used flame retardant, has been the topic of controversial discussions during the past several years. Degradation of BDE-209 into lower brominated diphenyl ether congeners, exhibiting a higher bioaccumulation potential, has been a critical issue. Here, we report on the degradation of BDE-209 and the formation of octa- and nonabromodiphenyl ether congeners under anaerobic conditions. Sewage sludge collected from a mesophilic digester was used as the inoculum and incubated up to 238 days with and without a set of five primers. Following Soxhlet extraction and a liquid chromatography cleanup procedure, parent compounds and debromination products were analyzed by GC/HRMS. In experiments with primers, concentrations of BDE-209 decreased by 30% within 238 days. This corresponds to a pseudo-first-order degradation rate constant of 1 x 10(-3) d(-1). Without primers, the degradation rate constant was 50% lower. Formation of two nonabromodiphenyl ether and six octabromodiphenyl ether congeners proved that BDE-209 underwent reductive debromination in these experiments. Debromination occurred at the para and the meta positions, whereas debromination at the ortho position was not statistically significant. All three nonabromodiphenyl ether congeners (BDE-206, BDE-207, and BDE-208) were found to undergo reductive debromination as well. No significant change of the BDE-209 concentration and no formation of lower brominated congeners was observed in sterile control experiments. To our knowledge, this is the first report demonstrating microbially mediated reductive debromination of BDE-209 under anaerobic conditions.

For many important classes of pesticides including phenylurea herbicides (PUHs) and triazines, photosensitized transformation may be the only relevant elimination process in surface waters. In this study, the dissolved organic matter (DOM) mediated phototransformation of PUHs has been investigated in laboratory and field experiments. The results indicate that, in surface waters, the photosensitized transformation of PUHs may be significant and occurs primarily by an initial one-electron oxidation most likely involving excited triplet states of DOM (3DOM*) constituents. Using isoproturon and diuron as model compounds, it is shown that for a given DOM, quantum yield factors determined in the laboratory at a few selected wavelengths can be used to quantify the overall DOM- mediated phototransformation of a given PUH under sunlight irradiation. Furthermore, it is demonstrated that this process can be modeled for a given surface water, by applying the program GCSOLAR and a simple algorithm for cloud cover for quantification of average daily light intensities. Finally, the model has been successfully applied to predict vertical concentration profiles of isoproturon and diuron in a small lake in Switzerland. To our knowledge, this is the first study in which DOM-mediated phototransformation of organic pollutants has been quantitatively validated in the field.

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Monochloramine disinfection of drinking water can result in the formation of the potent carcinogen N-nitrosodimethylamine (NDMA). To assess NDMA precursor concentrations in natural waters, samples from lakes, reservoirs, groundwaters, and isolated natural organic matter were exposed to relatively high concentrations of monochloramine. After 1 week, the concentration of NDMA ranged from approximately 0.1 to 0.8 nM. Application of a sensitive new GC/MS/MS technique and amendment of a sample with the known NDMA precursor dimethylamine (DMA) prior to chloramination indicated that only a small fraction of the NDMA produced during chloramination could be attributable to DMA. Chloramination of isolated natural organic matter and application of solid-phase extraction prior to chloramination suggested that natural organic matter accounts for a significant fraction of the precursors. However, the concentrations of NDMA precursors were higher in the epilimnion than the hypolimnion of two stratified reservoirs despite similar concentrations of dissolved organic carbon throughout the water column. Experiments performed to simulate the formation of NDMA during conditions comparable to those encountered in water treatment and distribution systems that use chloramine indicated that the concentration of NDMA produced from naturally occurring precursors usually will be less than 0.1 nM. The results indicate that chloramination of natural organic matter alone is unlikely to produce NDMA levels exceeding the current regulations.