Health hazard classification of mixtures
In general the classification of hazards should be made on the basis of test data, where it exists. However, tests on animals are to be avoided where at all possible, which creates a problem for health hazards, as these are mainly identified through animal testing.
To overcome this difficulty, CLP includes a series of options to allow people to classify the health hazards of mixtures and avoid testing on animals (although other forms of testing such as in vitro tests are allowed):
- bridging principles, a specific form of read-across for closely-related mixtures which have already been tested
- comparison to published thresholds (this can apply to mixtures containing a single component with a particular health hazard; or to some types of hazard where the effects of several components with the same health hazard are not considered to be “additive”). A threshold can be substance-specific, and published as part of a Harmonised Classification; or it can be generic and based on the hazard classification limits.
- calculation methods (or algorithms), where there are several components with the same hazard but with varying levels of severity
- human experience, including epidemiological evidence, and experience from people handling the material. Some health hazards are only classifiable on the basis of how humans react to a substance or mixture.
- read-across to other mixtures which are not closely related enough to use the bridging principles, but which are close enough to allow evidence to be interpolated or extrapolated
- QSAR models, quantitative structure–activity relationship models used by toxicologists to read between substances (and mixtures) to model their hazardous properties. This is a new and growing field of work, and generally occurs during REACH registrations.
- weight-of-evidence, where all of the available evidence is reviewed to arrive at a hazard classification
To help with classifying the health hazards of mixtures, we have produced a series of forms to guide you through the process of classifying using the first three methods (bridging principles, followed by thresholds, and algorithms, all where applicable).
Health hazards mixture classification forms