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.

The Environment Directorate convened a public workshop on the report and is consulting with various member states and EU scientific committees. Its goal is releasing an official position on this issue by early 2012.

The European report credits the US with employing the most advanced approaches to assessing mixtures. Mixture assessment in the US has been driven heavily by the Superfund program, which by its nature focuses on concentrated chemical brews. The Food Quality Protection Act of 1996 has also driven mixture assessment, requiring EPA to assess risks from mixtures of pesticides that act by the same biological mechanisms -- "common modes of action." The Safe Drinking Water Act Amendments of 1996 similarly required assessment of chemical mixtures, with an emphasis on the byproducts of disinfecting drinking water.

The U.S. National Academy of Sciences has also weighed in periodically. For example, in 2008, NAS responded to an EPA request to look at cumulative risk assessment for phthalates -- chemicals that have spurred concern in consumer markets for cosmetics, personal care, cleaning and polyvinyl chloride products. NAS recommended that phthalates and other chemicals that affect male reproductive development in test animals be considered in the cumulative risk assessment. As summarized by the EU report, NAS concluded that "A focus solely on phthalates to the exclusion of other chemicals would be artificial and could seriously underestimate the risk posed by phthalates."

The chemical industry is on alert. At the "ChemCon Americas" industry conference in Philadelphia in November 2010, AkzoNobel's director of product stewardship and regulatory affairs warned that chemical manufacturers need to acknowledge interactions among chemicals and be forward-looking in quantifying and predicting effects.

On February 15-16, 2011, the World Health Organization (WHO), the Organization for Economic Cooperation and Development (OECD) and the International Life Sciences Institute Health and Environmental Sciences Institute (ILSI/HESI) convened a workshop to consider risk assessment of combined exposures to multiple chemicals. The Natural Resources Defense Council expressed concern (pdf) to WHO about this non-public workshop. NRDC observed that ILSI is a corporate trade organization and no stakeholders from health or environmental advocacy organizations were meaningfully involved in scoping or planning the workshop.

Mixture analysis will surely lead to tightened regulation, but exponentially increased investment in green chemistry is a vastly preferable future path for addressing chemical risks, to speed elimination from the market place of those chemicals whose individual risks already are well known.

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