Hazard grouping of nanomaterials for daphnia and algae toxicity: lessons learned from scientific projects for regulatory applicability

Given the numerous manufactured nanomaterials already on the market and expected in future, the effort for the individual investigation of hazard and risk would be enormous. To overcome this challenge, grouping of nanomaterials has been identified as one critical issue by the European Commission as well as the Organisation for Economic Co-operation and Development (OECD). In that context, several research projects have been carried out to deliver scientific input and develop approaches. This publication discusses experiences from several cases of two scientific projects with the aims to develop and review analogy hypotheses for grouping of different nanoforms of same substances for endpoints related to aquatic ecotoxicity from a regulatory point of view. Furthermore, by presenting examples of grouping attempts, it outlines the need for considerations of further aspects beside key physical–chemical parameters for grouping nanomaterials regarding environmental endpoints. The results substantiate previous educated guesses with strategically collected experimental data on issues that needs to be considered for grouping nanomaterials in regulatory context. Still, grouping of nanomaterials for the aim of joint assessment of ecotoxicity of nanoforms in a regulatory context is in its infants compared to grouping approaches of nanoforms for human health assessment. This publication features important aspects on possibilities and challenges of grouping nanomaterials for environmental hazard assessment.