Risk scoring and ranking of nanomaterials – a way forward?
Conference contribution, 2016
Assessing environmental and health risks of chemical substances is a formidable challenge. Where they will be transported in the environment, which organisms will be exposed to them, and what the effects will be, are difficult questions to answer. To enable such assessments, multi-media environmental fate models and (eco)toxicological data are often employed in so-called chemical risk assessments. Nanomaterials (NMs), having at least one dimension in the nanometre size range, are a new class of substances, and their risks have proven to be even more difficult to assess. This is because models developed for conventional chemical substances are generally not applicable to NMs. In order to still be able to say something about NMs’ risks, less complicated risk scoring and ranking methods have been developed. We have conducted a review of these methods, identifying 20 in total. In these methods, risk is not assessed in terms of comparing exposure and effects as in conventional chemical risk assessment, but instead scored and ranked on ordinal scales, for example from 1 to 5 or from green to red. They often follow decision tree-like frameworks, where different hazard-related properties, such as whether the NM is bound to a surface and is in the form of bio-persistent fibres, are employed to score and rank NMs. Some methods assess NMs specifically, some assess products containing NMs, and some assess labs using NMs. Human health risks - in particular occupational health - is more often covered than are environmental risks. These methods provide easy-to-understand scoring and ranking of NMs. However, some methods are complicated to the extent that they rival the complicatedness of conventional chemical risk assessments. The use of ordinal scoring scales in risk assessment has also been questioned due to their subjectivity and mathematical limitations, which include that common mathematical operations such as addition and multiplication are strictly not allowed for ordinal scales. Ultimately, the question is to which extent such scoring and ranking methods can escape uncertainties related to the release, environmental fate and potential effects on humans and other organisms? However, it is clear that risk scoring and ranking can be used for screening assessments and thereby aid prioritization for more detailed assessments. Methods employed should be transparent, relatively simple and assure that factors included are cautiously selected to include important aspects of NM release, fate, exposure and effects.