Lessons Learned from the Grouping of Chemicals to Assess Risks to Human Health

In analogy to the periodic system that groups elements by their similarity in structure and chemical properties, the hazard of chemicals can be assessed in groups having similar structures and similar toxicological properties. Here we review case studies of chemical grouping strategies that supported the assessment of hazard, exposure, and risk to human health. By the EU-REACH and the US-TSCA New Chemicals Program, structural similarity is commonly used as the basis for grouping, but that criterion is not always adequate and sufficient. Based on the lessons learned, we derive ten principles for grouping, including: transparency of the purpose, criteria, and boundaries of the group; adequacy of methods used to justify the group; and inclusion or exclusion of substances in the group by toxicological properties. These principles apply to initial grouping to prioritize further actions as well as to definitive grouping to generate data for risk assessment. Both can expedite effective risk management.

Automated summary

Chemicals can be assessed for hazard in groups based on their similar structures and toxicological properties, similar to how elements are grouped in the periodic system. Strategies for chemical grouping have been used to support the evaluation of human health hazards, exposures, and risks, as shown in case studies. Structural similarity is commonly used as the basis for grouping, but it may not always be sufficient. Ten principles for grouping have been derived, including transparency, adequacy of methods, and consideration of toxicological properties, which can facilitate effective risk management.