Regulate to reduce chemical mixture risk

Abstract

Humans and wildlife are continuously exposed to multiple chemicals from different sources and via different routes, both simultaneously and in sequence. Scientific evidence for heightened toxicity from such mixtures is mounting, yet regulation is lagging behind. Ensuring appropriate regulation of chemical mixture risks will require stronger legal stimuli as well as close integration of different parts of the regulatory systems in order to meet the data and testing requirements for mixture risk assessment. Until about a decade ago, toxicologists, risk assessors, and regulators regarded risks from chemical mixtures as negligible, as long as exposures to all single chemicals in the cocktail were below the levels judged to be safe for each chemical alone (1, 2). However, an increasing body of scientific evidence has challenged this notion, showing that a neglect of mixture effects can cause chemical risks to be underestimated (see the figure). International bodies such as the World Health Organization now acknowledge the need for considering mixtures in chemical risk assessment and regulation (3). This would align toxicological risk assessment with the clinical sciences and their long tradition of investigating drug-drug interactions. Yet, with few exceptions, regulatory systems around the world still focus overwhelmingly on single-chemical assessments, and the translation of scientific evidence about mixture effects into better regulation is extremely slow.