H. Wigger, B. Nowack
Empa - Swiss Federal Laboratories for Materials Science and Technology,
Switzerland
Keywords: environmental risk assessment, nanomaterials, grouping, nanoform
Summary:
Engineered nanomaterials (ENMs) are intentionally designed in order to meet requirements for applications and are therefore used in many different nano-forms of the same parent material. Different grouping and read-across concepts are proposed to enable streamlined risk assessments by pooling several ENM or nano-forms into one category. In an environmental context, the concepts proposed so far are in their infancy and mainly focus on grouping by hazard categories. For a complete environmental risk assessment, the key requirement is to identify and to distinguish not only the production volumes of the ENMs but also the product applications of each nano-form. The aim of this work was to evaluate whether such a grouping is possible with the currently available data and which influence this form-specific assessment has on the environmental risks of ENMs. A functionality-driven approach was applied to match the material-specific property (i.e. crystal form/morphology) with the functions employed in the specific product applications. We demonstrate that for nano-TiO2, carbon nanotubes (CNTs), and nano-Al2O3, the total production volume can be allocated to specific nanoforms based on the functionalities used in the products. The differentiated assessments resulted in predicted environmental concentrations (PEC) for anatase vs. rutile nano-TiO2, single-wall vs. multi-wall CNTs and α- vs. γ-nano-Al2O3 that varied by a factor of 2 to 13 compared for the two forms. Additionally, the material-specific predicted no-effect concentrations (PNEC) for nano-TiO2, nano-Al2O3 and CNTs were derived from the ecotoxicological literature. The combination of this specific exposure and hazard assessment allowed for the first time a nano-form specific risk assessment. The risk characterization ratios for all nano-forms indicated no immediate risk for the considered ENM in freshwater systems. Finally, the results suggested that grouping and read-across concepts should include a nano-form release potential (based on production volume and product categories) for estimating the environmental exposure and separately consider specific nano-forms of ENMs such as nano-TiO2 in environmental risk assessments.