A.M. Belknap, J.O. Brien, G. Arvanitakis, J. Gauthier, M. Lapointe, K. Nguyen, M-C. Sauvé, D. Vladisavljevic, M. Zein Aghaji, Y. Zhang
Keywords: risk assessment, manufactured nanomaterials, human health, environment
Summary:Under the Canadian Environmental Protection Act (CEPA), 1999, chemical substances are considered either “new” or “existing” based on whether they are listed on Canada’s domestic substances list (DSL), an inventory of approximately 23,000 substances manufactured in or imported into Canada since 1984. Nanoscale forms of existing substances have not yet been explicitly assessed with regards to whether they are toxic or capable of becoming toxic under CEPA. A risk assessment framework (RAF) has been developed to communicate the approach to be used by the Government of Canada to perform risk assessments of existing NMs under CEPA. The RAF was established based on the traditional risk assessment paradigm for chemicals under Canada’s Chemicals Management Plan (CMP), incorporating unique aspects relevant to NMs. It outlines important issues regarding different elements in a nano-specific risk assessment, including key differences between chemicals and NMs including how variation in physical-chemical characteristics (e.g. size, shape, surface characteristics) may influence fate, exposure, adverse effects and risk. Consideration is given to managing uncertainties from data gaps in this emerging field, and options to fill these gaps using modelling, grouping, read-across and other tools and strategies as part of a weight-of-evidence. Environmental fate assessments will consider the potential for the NMs to ionize, agglomerate/aggregate and degrade under environmental conditions. It is recognized that methods to differentiate manufactured NMs from naturally occurring NMs and bulk substances are lacking. Appropriate fate models applicable to NMs (i.e. based on non-equilibrium, kinetically controlled partitioning) are also needed. Assessments of environmental and human health exposure will consider different lifecycle stages and potential for release from product and environmental matricies. Exposure will be quantified for relevant routes of exposure and scenarios taking into account data that may be received from targeted industry information gathering on NMs in Canada as well as other information sources such as the open literature, NM databases, international reports, funded research, etc. Environmental effects assessments consider bioavailable NM fractions in the form of a particle, dissolved ion, or agglomerated collection of particles, based on its solubility and respective proportions in environmental media. For human health effects assessments, in the selection of toxicological tests and endpoints for critical effects to assess risk the physical-chemical characteristics of the NM, dosimetry metrics, appropriateness of animal species/assays for NMs and relevance of exposure routes are taken into account. Interpretation of toxicological test results will also consider the sample preparation procedure and dispersion state of the NM in the study. Where appropriate special consideration will be given in human health assessment to fibre-shaped or high aspect ratio NMs with potential for inhalation exposure. Alternative testing, read-across and in silico methods will be used to fill human health effects data gaps. As a next step, following RAF development, assessment of high priority NMs will be conducted and will inform where potential refinements may be needed to the framework going forward.