When asking if we have the right approaches for properly assessing if nanomaterials are hazardous, it is useful to consider how we test if substances more generally are hazardous. This is generally done within regulatory frameworks using standard test guidelines that are developed to address not just a single chemical, but also a whole range of different chemicals. This is achieved because test methods generally focus on adverse outcomes, which are more generic rather than mechanisms of toxicity, which may be more specific to a substance. Despite the wide array in which different toxic substance can cause us harm there are limited ways in which harm manifests itself such as inflammation, fibrosis, cancer or more specific effects on certain organs such as the liver, similarly manifesting in non-specific ways (e.g. elevation in alkaline phosphatase) that can be detected.
Within a recent review of the REACH toxicology Information Requirements (Hankin et al., 2011) it was considered that the basic properties and endpoints described in the OECD Test Guidelines were considered adequate and relevant for nanomaterials. Taking OECD TG 412 “Subacute Inhalation Toxicity: 28-Day Study” as an example of a test guideline that would be used to assess nanoparticles within a regulatory context, the overall approach such as use of range finding studies, test article concentrations (dose), animal numbers etc. is sufficiently generic to be applicable to a wide range of substances including nanomaterials. When considering the detection of harmful effects of exposure, the guidelines call for the analysis and reporting of a wide range of clinical parameters ranging from haematology, clinical chemistry as well as gross necropsy and detailed histolopathology in all tissues from respiratory to the reproductive system. Despite the mechanism of toxicity, it would be considered that given the detailed and body wide analysis that is required, should sufficient adverse response occur it would likely be detected. Whilst these guidelines are robust, they are not ideal and the OECD acknowledges that the Test Guidelines were not specifically designed for the testing of nanomaterials. It is considered that guidance on key experimental parameters such as the preparation, delivery of test substances to test system, exposure quantification, dose metrics, measurement, and metrology in all of these test guidelines needs to be improved. It is important that these and other important issues that may affect the relevance of standard test methods are raised and enacted upon to improve their applicability to nanomaterials to ensure the best tools are available for hazard assessment and this is an on-going process within the OECD Working Party on nanomaterials.
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