EFSA Publishes Guidance on Grouping Chemicals for Exposure Assessments

The European Food Safety Authority (EFSA) published a Guidance Document on Scientific criteria for grouping chemicals into assessment groups for human risk assessment of combined exposure to multiple chemicals in December 2021.

EFSA explained in the Guidance that there are a number of challenges in conducting human health assessments of combined exposure to multiple chemicals (chemical mixtures), namely: the complexity of the problem formulation, the large number of chemicals that are potentially involved, and the toxicological profiles and human exposure patterns to the chemicals.

In the Guidance Document, EFSA proposes a framework to apply hazard-driven criteria for grouping of chemicals into assessment groups using mechanistic information on toxicity as the gold standard where available (i.e., common mode of action or adverse outcome pathway) through a structured weight of evidence approach. EFSA recommends that when such mechanistic data are not available, grouping may be performed using a common adverse outcome. In addition, EFSA explains that toxicokinetic data also can be useful for grouping, particularly when metabolism information is available for a class of compounds and common toxicologically relevant metabolites are shared. 

An advantage of prioritization methods is that they can be used to identify low-priority chemicals, according to EFSA. Once the low-priority chemicals are identified, the number of chemicals in an assessment group can be reduced. Combined risk-based approaches, risk-based approaches for single chemicals, and exposure-driven approaches are examples of prioritization methods listed in the guidance document.