I’ve got some bad news. Toxicology seems to have a blind spot when it comes to the stew of chemicals we breathe, drink or otherwise absorb over the course of life. Currently federal standards for determining toxicity are based on whether single exposures to a specific chemical cause a given medical problem.
But growing bodies of medical evidence suggest that the cumulative tiny doses of chemicals we encounter over our lifetime can add up to disease. For instance, Deborah Cory-Slechta, a toxicologist at the Robert Wood Johnson Medical School, found that exposing lab animals to two common pesticides, paraquat and maneb, caused degeneration in the dopamine circuits that underlie Parkinson’s disease in humans. The damage only occurred if the exposure to one of the compounds was repeated (in this case, in the womb and again in adulthood), or to both pesticides in combination. Paraquat and maneb are quite distinct molecules, but the mixture or number or exposures produced the signature damage for Parkinson’s.
Such findings – and there are dozens of others like these – create a challenge for toxicology: an exposure just once to one of these chemicals resulted in no discernible damage. And up to this point that method – assessing the damage from exposure to a single chemical or class of chemicals for a limited time – has been the gold standard in tests of a chemical’s toxicity, our early warning system for protection.
But that method tells us nothing about how a given chemical might cause damage if we are exposed to it in combination with others, or over a lifespan. The reality is that we all are exposed to a mix of countless chemicals continually, a predicament for which toxicologists have as yet no assessment method.
Here is the toxicologist’s dilemma: The standard methods for assessing safe levels of exposure to a chemical fail to address the environmental realities. Interactions among synthetic chemicals lodged in our bodies defy basic assumptions underlying toxicology risk analysis.
Standard tests assess whether a compound kills cells. But very low doses may fail to kill cells while nevertheless damaging the cells’ ability to function properly. Worse, a single-chemical, one-time exposure in healthy adults tells us nothing about how a substance might affect children, the chronically ill or the aged — groups with greater susceptibility to harmful chemical impacts. And what happens when we breathe polluted air, a mixture of countless varieties of ultra-fine particles whose chemical composition varies from place to place and day to day?
Cory-Slechta says neurotoxicology should adopt a “multi-hit” model, in which insults to different target sites — either over time from one molecule or all at once from many — harm a biological system. That would be in keeping with toxicology’s main mission, safeguarding human health.
So what are we to do in the meantime?
Try the precautionary principle: Find out what’s actually in all the stuff we eat, put on our bodies or otherwise are exposed to, and avoid the bad ones. Use Environmental Working Group’s Skin Deep database, for example, to learn the truth about the chemicals in personal care products.
If each of us did three things, it could actually get companies to get rid of all those toxic chemicals:
- Know the true ecological impacts of what we buy.
- Favor improvements.
- Tell everyone we know.
Those three steps, if taken by enough shoppers, would shift the market share of products enough to get the attention of companies. The more we make it pay to drop toxic chemicals from products, the more efforts corporations will put into developing safer alternatives and giving their business to suppliers who innovate to find safer ingredients.
Economists call this a “virtuous cycle,” where sound information in the marketplace lets shoppers be smarter about their choices. That, in turn, creates a bottom-line incentive for companies to do the right thing. Let’s make virtue pay.
Adapted from Ecological Intelligence: The Hidden Impacts of What We Buy. Originally posted at ewg.org