Threshold concepts of toxicological concern are based on the possibility of establishing an exposure threshold value for chemicals below which no significant risk is to be expected. The objective of the present study is to address environmental thresholds of no toxicological concern for freshwater systems (ETNCaq) for organic chemicals. We analyzed environmental toxicological databases (acute and chronic endpoints) and substance hazard assessments. Lowest numbers and 95th‐percentile values were derived using data stratification based on mode of action (MOA; 1 = inert chemicals; 2 = less inert chemicals; 3 = reactive chemicals; 4 = specifically acting chemicals). The ETNCaq values were derived by multiplying the lowest 95th percentile values with appropriate application factors; ETNCaq,MOA1–3 is approximately 0.1 μg/L. A preliminary analysis with complete MOA stratification of the databases shows that in the case of MOA1 or MOA2, the ETNCaq value could be even higher than 0.1 μg/L. A significantly lower ETNCaqMOA4 value was observed based on the long‐term toxicity information in the European Centre for the Ecotoxicology and Toxicology of Chemicals database. Application of the ETNCaq value in a tiered risk‐assessment scheme may help chemical producers to set data‐generation priorities and to refine or reduce animal use. It also may help to inform downstream users concerning the relative risk associated with their specific uses and be of value in putting environmental monitoring data into a risk‐assessment perspective.
This risk assessment on 1,2-dichlorobenzene was carried out for the marine environment, following methodology given in the EU risk assessment Regulation (1488/94) and Guidance Document of the EU New and Existing Substances Regulation (TGD, 1996). Data from analytical monitoring programmes in large rivers and estuaries in the North Sea area were collected and evaluated on effects and environmental concentrations. Risk is indicated by the ratio of predicted environmental concentration (PEC) to predicted no-effect concentration (PNEC) for the marine aquatic environment. In total, 26 data for fish, 24 data for invertebrates and 17 data for algae were evaluated. Acute and chronic toxicity studies were taken into account and appropriate assessment factors used to define a final PNEC value of 37 microg/l. All available monitoring data indicate that 1,2-dichlorobenzene levels in estuaries are below 0.1 microg/l. Worst case concentrations in rivers are below 0.45 microg/l. With this value, calculated PEC/PNEC ratios give safety margins of 100 to 300, taking no account of dilution in the sea. 1,2-dichlorobenzene is not a 'toxic, persistent and liable to bioaccumulate' substance sensu the Oslo and Paris Convention for the Prevention of Marine Pollution (OSPAR-DYNAMEC) criteria. Environmental fate and effects data indicate that current use of 1,2-dichlorobenzene poses no risk to the aquatic environment.
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