Here is a short but comprehensive overview of the currently regulatory system for chemicals in the US. Lead author is Emily Monosson, who is also taking up the issue of chemical mixtures in the article:
The FQPA [Food Quality Protection Acti] is changing the way pesticide residues are regulated by setting ‘health-based’ standards for ALL pesticides in foods. ‘All’ in this case means combined residues from several different pesticides, or, chemical mixtures. The importance of this amendment, with respect to chemical mixtures should not be underestimated. This is one of the first attempts to regulate the permitting of individual chemicals based on their potential for combined toxicity. It will require development of innovative and reliable techniques to address combined toxicity. Although we will discuss the methodology used to determine new pesticide limits later, we should point out that this combined approach for now is limited to similarly acting pesticides. Currently, the FQPA does not address pesticide mixtures that act through different mechanisms. For example, several different organophosphate pesticides may occur in combination along with arsenic. The mixtures assessment will consider the combination of organophosphates, but nonetheless will assess arsenic separately. The rational for only extending combined toxicity to similarly acting pesticides should become clear as we discuss the toxicological tools available for such work.
Together, the FFDCA and FIFRA regulate a large share of chemicals to which humans are likely to be exposed, by setting tolerances and allowable concentrations for chemicals, one chemical at a time, up until 1997. This is almost a one hundred year history of single chemical regulation. Not only does toxicology and regulatory policy have a long history based upon the single-chemical approach, but they must now address the reality of chemical mixtures. Although clearly the single-chemical approach has provided a strong foundation for chemical control, the utility or relevance of these techniques for addressing multiple chemical exposures is currently unclear.
Unfortuantely, I couldn’t find the promised discussion on why the legislation is restricted to similarly acting chemicals. Mental note to myself: Need to check the mentioned amendments. Guess it’s the old “mixtures of dissimilarly acting chemicals do not show a combination effect if all individual substances are at or below their toxicological thresholds”. Please see the rebuttal here.
