Toxic Chemical Cocktails and Why You Should Know Your Limit

European regulatory and science advisory bodies are intensifying their focus on hazardous mixtures. Companies should pay heed. Over the last decade, though US regulators have worked on chemical mixtures, most initiatives to restrict chemicals in products and supply chains have come from Europe and have then impacted American manufacturers and retailers.

Increased knowledge of mixture effects means that levels of chemicals once judged by risk assessors and regulators to be safe when considered in isolation will no longer be deemed so innocent. Some scientists have applied the label of "something from 'nothing' " to such individually safe chemical doses that together form a toxic mixture. Scientists have also identified synergistic effects of chemical mixtures -- where toxic effects of individual chemicals are multiplied rather than just added.

The centuries-old idea that "the dose makes the poison" has been expanding to "the dose and timing make the poison" to account for the sensitivity of fetuses and other vulnerable populations. It should be further enlarged to "the dose, timing and mixture make the poison." This change in framing the toxicity issue is essential to move thinking beyond predominant quantitative risk assessment methods that emphasize risks of isolated individual chemicals. The existing chemical-by-chemical approach creates a false illusion of chemical safety and surely understates the cumulative risk posed by chemical mixtures.

Researchers at the University of California, San Francisco, have recently published fresh evidence of human exposures to chemical mixtures. Their report documents pregnant women's exposure to multiple chemicals that may harm development of their fetuses; many of the measured pollutants have been found in cord and fetal blood and amniotic fluid. Ninety-nine to 100 percent of the women had measurable levels of controversial chemicals found in products and supply chains, such as phthalates, brominated flame retardants and the perfluorinated compounds traditionally associated with non-stick cookware and stain- and grease-repellency treatments.

A December 2009 State of the Art Report on Mixture Toxicity (pdf) commissioned by the European Commission's Environment Directorate (the European Counterpart of USEPA) underscored the challenge of aligning quantitative risk assessment with the reality of multiple chemical exposures.

Products can contain more than one chemical, production sites can release chemical mixtures, and chemical mixtures are commonly found in air, water and food. The many biological mechanisms through which toxic impacts can occur add an additional level of complexity. This daunting challenge notwithstanding, the report recommended that European guidelines be developed for the assessment of chemical mixtures and that the legal mandate for assessing risks from mixtures be strengthened.