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Environmental fate & pathways

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Releases of DecaBDE to the environment are expected to partion to air (0.5%), water (0.6%), soil (50%) and sediment (49.3%). In each of these environmental media, DecaBDE is expected to be highly bound to particulate matter.

In the environment, ca. 99% of DecaBDE releases are expected to partition to soil and sediment. DecaBDE is not readily biodegradable under aerobic conditions, and degradation in anaerobic environments has not been demonstrated in guideline- and GLP-compliant studies. A guideline- and GLP-compliant study 32 -week anaerobic sediment study showed no degradation of DecaBDE. Reports in the literature suggest that in laboratory studies a) perhaps 5% of the BDE 209 may undergo loss of 1 or at most 2 bromine atoms over a 238 d period in sewage sludge under anaerobic conditions in the presence of bacterial primers. This low percent loss of bromine is unlikely to produce degradants that can be distinguished from impurities in the commercial product which typically contains upt to 3% impurities (Gerecke et al. 2005), b) 2 out of 3 strains of highly adapted bacteria produced no evidence of debromination after 1 year incubation in one solvent, while the same 3 strains showed no evidence after 1 year incubation in a second solvent (He et al. 2006); and c) no evidence of debromination in a 10 month laboratory anerobic sediment study while after 3.5 years 1 of 3 sediment replicates had some evidence and BDE 209's half life was estimated to be well over a decade (Tokartz et al. 2008). No evidence of the degration of DecaBDE was found in a field study of agricultural soil to which sludge containing DecaBDE had been applied up to 20 years previously or which were periodically flooded with river sediment known to contain DecaBDE (Sellestrom et al. 2005). The literature is in general agreement that environmental sediment and soil congener patterns are consistent with that of the three former PBDE commerical products, (e.g. the penta-, octa- and decaBDE commercial products). Thus, there is little evidence that DecaBDE is biodegraded to any significant extent in soil or sediment either in the laboratory or the environment. DecaBDE is considered persistent with respect to biological degradation.

DecaBDE has been shown to be photolaible in the laboratory, especially when such studies are conducted in organic solvents. In the environment, DecaBDE will be highly particle-bound (ca. 100%), which will adversely impact its ability to undergo photolysis. Only those molecules on the particle surfaces are accessible to light. Partioning to air is expected to be minimal (0.05% of DecaBDE emissions). Thus, in-air photolysis is not expected to be a significant route of environmental degradation or source of degradants.

As demonstrated in studies of house dust exposed to sunlight, naturally-occuring substances diminish DecaBDE's photolytic degradation, while the total PBDE dust content decreases concurrently (Stapleton et al. 2006). The major fraction of DecaBDE's mass balance in such experiments remains unextracted and unaccounted for and is thought to be insoluble conglomerates. A field study where agricultural soil was spread with sewage sludge containing DecaBDE or flooded by sediment containing DecBDE concluded there was no evidence of photolysis after decades of exposure to sunlight (Sellstrom et al.). Thus, while able to undergo phtolysis in laboratory experiments, there is little evidence that photolysis is a route of DecaBDE degradation in the enviornment, and is considered persistent.

DecaBDE has been studied for bioconcentration, bioaccumulation, and biomagnification potential. A bioconcentration factor of < 50 was measured in a 6 wk fish bioconcentration study (CITI 1992). Uptake of DecaBDE from food rainbow trout over 120 d was ~0.02-0.13% of the dose (Kierkegaard et al.). Uptake by carp from food was ~0.39% of the dose over a 90 day period (Stapleton et al.). The food assimilation efficiency of DecBDE by lake trout was reported to be 0.3 (Tomy et al. 2004). Biomagnification was not observed in a food web of Lake Michicgan or the Baltic Sea (Kuo et al. 2010; Burreau et al. 2004). Accumulation by earthworms was not observed over a 56 d study or after decades of exposure in a field study (Sellstrom et al. 2005). These results indicate DecaBDE has minimal potential for bioconcentration, bioaccumulation, or biomagnification. This is consistent with its physcial/chemical properties and results of mammalian absorption, distribution, and elimination studies. For example, the rat absorbed approximately 0.33% of a dietary dose (NTP 1986).