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HexachlorobenzeneReportTo read the report please click here. SummaryCurrent levels of hexachlorobenzene in the surface waters and sediments are unlikely to pose a risk to marine aquatic and sediment organisms living the North Sea region. Bioconcentration in fish is far below the critical body burden. There is little risk of general toxicity in fish-eating mammals or birds. Adverse reproductive effects may occur in sensitive species. Production of hexachlorobenzene has been virtually eliminated in Europe, and environmental concentrations of the substance are expected to decline. Applications and emissions of hexachlorobenzeneProduction and use of hexachlorobenzene has been virtually eliminated in Europe and the US, following concerns about the substance’s persistence, potential to bioaccumulate and toxicological properties. Primarily the substance was used as a seed dressing and fungicide in agriculture. It also found applications in a number of industrial processes, such as in the manufacture of aluminium. In 1997, a World Health Organisation study indicated that the main sources of hexachlorobenzene emissions were agriculture, the chemical and metal industries, combustion processes, and landfills. An OSPARCOM study estimated that hexachlorobenzene emissions in the 15 OSPARCOM countries totalled 2,851kilograms in 1990. The figure for Europe was 8,040kilograms. Since 1985 Euro Chlor members have decreased emissions of hexachlorobenzene to water by 87% and to air by 97%--resulting in emissions of 100 kg/y to water and 4 kg/y to air in 1997. Identified hexachlorobenzene emissions are insufficient to explain observed atmospheric concentrations. Evaporation of hexachlorobenzene in soil from past contamination is thought to make a contribution, along with unidentified sources. Emission rates from identified sources suggest the concentration of hexachlorobenzene in the atmosphere will decline slowly as historic HCB is degraded in the atmosphere and sediments. 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, three scenarios were considered in the marine risk assessment of hexachlorobenzene. They include assessment of toxicity to: aquatic organisms; organisms living in sediments; and fish-eating predators. In addition, bioconcentration and monitoring data on body burden were analysed to provide an alternative assessment of the risk to fish species. Hazard AssessmentAquatic Organisms For hexachlorobenzene, the evaluation of aquatic toxicity was based on some 60 test results, including 6 for fish, 12 for invertebrates and 2 for algae which were identified as being valid for risk assessment purposes. Due to the low solubility of hexachlorobenzene in water, few studies were able to obtain any acute or chronic effects at or below the level of solubility. Nevertheless, a number of the studies were considered valid, even though the results represent a minimum value. Based on the available data, it was assumed that sensitivity of marine and freshwater organisms to hexachlorobenzene was quite similar. It was also assumed that chronic studies more closely represent the situation in the North Sea, where there are no local sources of the substance. Based on the test data, a PNEC for aquatic organisms in the marine environment of 0.37 µg/l was calculated. Using the most critical long-term NOEC for fish of 3.7 µg/l and a worst-case fish BCF of 2040 l/kg, a critical body burden (CBB) for fish of 7.5 µg/g ww could be determined. Organisms living in the Sediment As hexachlorobenzene is relatively insoluble in water, it migrates strongly towards sediment. Three valid studies provide data on the effects of treated sediments for four species of sediment-dwelling invertebrates. Based on these studies a PNEC for sediment organisms of 0.84 mg/kg of dry weight sediment was calculated. Fish Eating Predators—Secondary Poisoning As hexachlorobenzene has a high fat solubility, food can be a significant source of exposure to the substance. The level of hexachlorobenzene present in food that can be consumed by predatory species without producing chronic toxicity was based on a NOEC of 0.08 mg/kg bw/day obtained for liver toxicity in a 130-week rat study..A PNECoral/food for chronic toxicity was calculated at 8 µg/kg of bw/day applying a safety factor of 10 according to the EU-TGD. Two studies on the reproductive toxicity of hexachlorobenzene were used to estimate a PNECoral/food of 0.4 µg/kg bw/day. As fish-eating birds are considered to be at particular risk, two studies were used to derive a PNECoral/food of 10 µg/kg of bw/day for avian species. Exposure AssessmentThe concentrations of hexachlorobenzene in river waters, estuaries, coastal waters and sediments have mainly been obtained from the COMMPS database and a summary of the available monitoring data for marine waters is provided (see figure: North Sea monitoring data on hexachlorobenzene). Worst-case Predicted Environmental Concentrations for the aquatic and sediment marine environment were calculated at 8 ng/l, and 50 µg/kg dw, respectively. In addition, concentrations of hexachlorobenzene in marine fish and other organisms has been assessed. A worst-case PEC for fish was estimated at 3 µg/kg. Risk Assessment ConclusionsThe risk assessment was based largely on the methodologies prescribed by the EU-TGD, where the ratio of either the predicted environmental concentration (PEC) or for predators, the estimated daily intake (EDI), to the predicted no effect concentration (PNEC) are used as an indication of risk. A ratio of less than 1 indicates no risk—the smaller the number, the greater the assurance of low risk related to the assessment. Aquatic Organisms The PEC/PNEC ratio for surface water was 0.02 for the worst-case scenario, indicating that levels of hexachlorobenzene in the surface waters of the North Sea were unlikely to represent a risk to the marine environment. The actual concentration of hexachlorobenzene in the edible tissue of marine fish was 2,500-7,500 times lower than the critical body burden associated with toxic effects, supporting the above conclusion. Organisms living in sediments The PEC/PNEC ratio for sediments was 0.06 for the worst-case scenario, indicating that hexachlorobenzene did not pose a risk to sediment-dwelling organisms. Fish-eating Predators and Biomagnification The risk posed by hexachlorobenzene via uptake in the food chain was based on the following parameters: the Estimated Daily Intake (EDI)—the feed rate multiplied by the predicted environmental concentration in fish; the level of hexachlorobenzene present in fish which can be consumed without producing adverse effects (PNEC); and the potential for the predator to bioconcentrate hexachlorobenzene. Ratios of EDI to PNEC indicated no risk to predators, with the exception of sensitive species like mink, where adverse reproductive effects cannot be excluded. It was noted that environmental concentrations of hexachlorobenzene are decreasing and there will be a corresponding reduction in the risk of adverse effects in marine wild life. Summary table for PEC/PNEC ratios for hexachlorobenzene in various environmental compartments based on worst-case scenarios
North Sea Monitoring Data on hexachlorobenzene
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