Chemical Cocktail, Anyone?

I went to the annual meeting of the Society of Environmental Toxicology and Chemistry (Pacific Northwest Chapter) last weekend expecting to hear some of the latest research about how chemicals in the environment are affecting fish and wildlife. The very first presentation of the conference was indeed about fish, but the results have implications that people would do well to consider for their own health.

Jennifer Trowell, masters student at Simon Fraser University in Burnaby, BC, has been digging deep into the hows and whys of chemicals like PCBs that build up in fish and people. She’s doing that using the liver cells of rainbow trout, which is the site of the fish’s best defense against toxic chemicals that accumulate in their bodies.

Her research shows that sometimes mixtures of chemicals can be more potent than individual chemicals. She looked at the ability of the trout to detoxify chemicals alone and in mixtures. She conducted her research using chemicals known to build up, including PCBs and benzo(a)pyrene, a chemical found in exhaust fumes and other sources. What she found was dramatic differences in ability to break the chemicals down when they were presented in mixtures.

Most strikingly, Trowell found a 30-fold decline in the breakdown of benzo(a)pyrene in the presence of other chemicals.

As tests on chemicals in our bodies prove, fish aren’t the only animals exposed to many chemicals at a time. While the standard for toxicity testing has always been to look for the effects of a single chemical, more and more research has found they can have additive or even synergistic effects—where one plus one makes more than two.

Trowell thinks the drop-off in the trout’s ability to metabolize the chemicals is due to a traffic jam at a key enzyme responsible for that job. Future research could test whether that’s the case, and whether the fish has any way to compensate for this problem.

But this is just one of many studies sounding the alarm that a one-by-one assessment of chemicals just isn’t real life. Because of that, the Safe Chemicals Act, introduced in Congress last week, makes an attempt to include assessment of chemical mixtures. But as Trowell’s new research shows, we have a lot to learn about how biological systems respond to multiple chemicals. A more sensible approach would set a short phaseout timeline for the worst of the worst chemicals—the ones like those in her study that are toxic and build up in our bodies. The new law should also force reductions in other chemicals with known hazards.

Why should we wait for decades of assessment to figure out how chemicals interact in our bodies, when we know that they’re toxic on their own?

Cocktail photo courtesy of flickr user 96dpi