Exposure Based Waiving in Environmental Risk Assessment: A Tiered Approach

The REACH legislation describes the “Exposure Based Waiving” (EBW) methodology, that allows reduction of animal tests and that facilitates the Chemical Safety Assessments. We introduced a tiered EBW decision strategy for the aquatic environment. Tier 0 in this strategy justifies waiving if it can be demonstrated that exposure of organisms to a chemical will be practically zero (i.e., if no environmental emissions during the full life-cycle of a chemical are to be expected. Tier 1 uses tabular data, derived from physical–chemical properties of a chemical and emission data, to identify whether the environmental exposure levels are less than the conservative toxicological reference value “Threshold of Toxicological Concern” (TTC). To this end, systematic exposure calculations have been carried out with a hypothetical chemical dataset, covering the full chemical spectrum for neutral organic substances. In tier 2, PEC and PNEC are to be assessed probabilistically in order to address the probability of effects. Following this strategy, risk can be shown to be sufficiently low, using minimal exposure and hazard data. Our tiered EBW concept is illustrated by a case study for the substance dibutylphthalate with the endpoint of fresh water aquatic risks.