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HexachlorobutadieneReportTo read the report please click here. SummaryCurrent levels of hexachlorobutadiene (HCBD) in the surface waters and sediments of the North Sea are unlikely to pose a risk to marine aquatic and sediment organisms living in the region. The assessment also indicates that toxicity to fish due to bioconcentration of HCBD is unlikely. Similarly there is little risk of toxic effects occurring in fish-eating mammals or birds. As environmental concentrations of HCBD decline then so will any residual risk. Applications and emissions of hexachlorobutadieneUse of HCBD in Europe has virtually ceased due to concerns about the substance's persistence, potential to bioaccumulate and toxicological properties. Historically HCBD was used as a solvent in the production of rubber and other polymers. It has also been used in hydraulic and heat transfer fluids, in agriculture as a seed dressing and fungicide and in a number of manufacturing processes such as production of aluminium and graphite rods. HCBD may still be used in some parts of the world. HCBD is still generated as a by-product of tetrachloroethylene and tetrachloromethane production, but improved manufacturing processes mean it is no longer detectable in either of these products. HCBD may enter the environment through the atmosphere and hydrosphere. Emissions in Europe in 1997 represented 2 kg/y in air and 100 kg/y in water, based on a survey of 76 sites from the European chlorine industry. This represents a reduction of 98% of emissions to air and 97% to water since 1985. Evaluation of Environmental RiskRisks associated with the use of any substance are determined by the hazard properties of the substance and exposure to it. Because of the low water solubility and bioaccumulative properties of HCBD, four scenarios were considered in the marine risk assessment. They are assessment of toxicity to: aquatic organisms; organisms living in sediments; and predators higher up the food chain. In addition, bioconcentration and body burden monitoring data were analysed to provide an alternative assessment of the risk to fish species. Hazard assessmentAquatic Organisms For HCBD, the evaluation of aquatic toxicity was based on 34 test results, including 25 for fish, seven for invertebrates, and two for algae. Of these five fish and no invertebrate or algae data were identified as being valid for risk assessment purposes. A further seven fish and three invertebrate data were considered with care. From the toxicological studies a PNEC value of 130 ng/l was derived. To address the potential for HCBD to bioconcentrate in fish, the most critical long-term NOEC for fish of 6.5 µg/l and the worst-case fish BCF of 17,000 l/kg was used to calculate a Critical Body Burden (CBB) for fish of 111 mg/kg wet weight. Organisms living in the sediment Toxicity studies on HCBD for sediment organisms are not available, so PNECsediment was derived from the PNECaquatic by applying the equilibrium partitioning method according to the EU TGD (Technical Guidance Document on risk assessment) resulting in a PNECsediment of 24.4 µg/kg d.w. Exposure assessment Exposure assessment was based on monitoring data available from samples taken from rivers of six European countries between 1994-1997. These contained some 10,000 HCBD concentrations, giving typical and worst case PECwater values of 5 and 12 ng/l respectively. Recent measurements from the EU COMMPS database (1998) indicate HCBD concentrations in estuarine or coastal sediment varying between < 0.2 and 3 µg/kg, typical values being close to 1 µg/kg. From this data, typical and worst case PECsediment values of 1 and 4 µg/kg d.w. are used in the risk calculations. Risk assessment calculationsBased on the available toxicological and monitoring data the PEC/PNEC ratios are 0.038 and 0.092 for typical and worst case scenarios in the aquatic compartment. These ratios indicate that the levels of HCBD in surface waters are unlikely to pose a risk to marine organisms living in the North Sea. To assess the risk of toxicity due to bioconcentration, the calculated worst-case CBB was compared with the concentrations of HCBD measured in marine fish collected at various locations around the UK, which ranged from non-detectable to 0.4 µg/kg flesh. The comparison showed that the actual concentrations of HCBD in marine fish are well below the CBB associated with toxic effects indicating that risks to fish through bioconcentration are unlikely. PEC/PNEC ratios for typical and worst-case exposure to organisms living in sediments are 0.045 and 0.16, respectively, indicating that HCBD is unlikely to pose a risk to sediment organisms. Assessment of risk to fish-eating predators (biomagnification) To assess the risk posed to predators eating fish contaminated with HCBD the Estimated Daily Intake of HCBD through eating fish (EDIfish) was compared with the Predicted No Effect Level of HCBD for predatory species (PNECoral/food). Three values were used to determine the NOAEL for HCBD: a PNECoral/food from chronic toxicity tests on rats of 0.2 mg/kg body wt/day; a PNECoral/food from sub-chronic toxicity tests on Japanese quail of 3 mg/kg body wt/day; and a PNECoral/food for reproductive toxicity tests on rats of 20 mg/kg body wt/day. The EDIfish was calculated at 0.06 µg HCBD/kg body weight/day for mink and 0.04 µg HCBD/kg body weight/day for eagle. As the EDIs of HCBD are several orders of magnitude below the NOAEL there is little risk of toxicological consequences associated with predators eating fish contaminated with HCBD. HCBD is metabolized and excreted rapidly the risk of bioaccumulation and secondary poisoning is low. t in the North Sea region. Both surface waters and sediments are showing a decreasing trend in pentachlorophenol concentrations with time. Due to further restrictions on PCP use in Europe, it is expected that monitoring levels in water and sediments will continue to decrease. Summary table for PEC/PNEC ratios for hexachlorobutadiene
North Sea Monitoring Data on Hexachlorobutadiene
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