Map of life expectancy at birth from Global Education Project.

Monday, May 10, 2010

It's actually more complicated . . .

I expect most readers have seen news stories about the President's Cancer Panel report. The headline is that the panel claims that environmental exposures -- by implication at least, meaning mostly to human-produced chemicals -- make a far more important contribution to the burden of cancer than has been recognized. This has long been what I must, sadly, call an article of faith among environmentalists, but the report actually does not come to that conclusion, nor does it present any direct evidence for it. This spin must come from a press release, is the only conclusion I can make. In fact, in the executive summary, they say this:

At this time, we do not know how much environmental exposures influence cancer risk and related immune and endocrine dysfunction. Environmental contamination varies greatly by type and magnitude across the nation, and the lifetime effects of exposure to combinations of chemicals and other agents are largely unstudied. Similarly, the cancer impact of exposures during key “windows of vulnerability” such as the prenatal period, early life, and puberty are not well understood.

In other words, we don't know, but maybe it's worse than we think, so we ought to try to find out. That's a less exciting headline, but it has the virtue of being accurate.

Here's some context. Environmental epidemiology is a notoriously difficult endeavor. First, it's quite difficult to measure how much of any given agent people are exposed to. You can find people who live in a place where something or other is known to be in the air, for example, but they will all vary widely in how much time they spend at home, how much time they spend outdoors, how much they open the windows, etc. And living in that place also means that they likely have all sorts of other things in common that might be relevant to their cancer risk. We can try to measure and account for as many of those factors as we can think of, but we can't be sure we haven't missed the one that matters.

What is worse, it might be that exposure to X only matters if also Y. For example, radon exposure was found to increase the lung cancer risk of uranium miners, but it turned out to mostly be a synergistic effect with tobacco smoking. The effect was difficult to detect in non-smokers. Since smoking and environmental tobacco smoke were -- and still are -- by far the most powerful environmental cause of cancer, overwhelming everything else, people in public health (public healthists?) found it hard to get as excited about other kinds of exposures. Also, a lot of much hyped suspected links, for example between environmental endocrine disrupters such as many pesticides and breast cancer, haven't panned out.

Another inconvenient truth is that we do know about other environmental cancer risks, but they don't indict giant soulless corporations but rather your grandmother and your own sorry self. Smoked and grilled meat products and starchy fried foods contain carcinogens. Also, excessive alcohol consumption promotes cancer. And of course, so does getting a sunburn.

Now, we do know that some products of incomplete combustion -- ergo compounds found in motor vehicle exhaust and smokestack emissions -- called polycyclic aromatic hydrocarbons, are carcinogenic. More complicated versions called dioxins are found as contaminants in pesticides as well as smokestack emissions (including, by the way, your fireplace chimney) and paper mill effluent. A lot of reactive hydrocarbon compounds probably can cause genetic damage, mess with hormones, and just cause inflammation and irritation which makes cells divide more than usual, which also may increase cancer risk. The problem is that all of these exposures mix and match and interact, and that it probably matters how old you are and how long it lasts and whether you are overweight or underweight or male or female and what your particular genetic endowment is and who the hell knows what else.

Most chemicals approved for various uses, including as ingredients in food or food packaging, believe it or not, have not been adequately tested for safety. But that is also very hard to do. You can't do experiments by feeding them to people. You can feed stuff to mice, despite PETA's objections, but a) mice aren't people and b) you can't feasibly mimic human exposures. It's just too expensive to give millions of mice a tiny bit of something for a long time. Instead you have to give a small number of mice a whole lot of it. That just ain't the same thing; and mice don't live nearly as long as people anyway so you can't do twenty or thirty year follow up. And sorting out what people are exposed to from their natural history, and trying to relate that to their lifelong risk of cancer, is just really, really hard and can very easily lead you to wrong conclusions.

So yeah, we need to keep studying these questions, and we probably need to do it bigger and better. But so far there are only a few specific things we can tell you. Don't smoke. Don't do shots every night. Don't live near the highway. Maintain an appropriate body weight. Don't work as a hot tar roofer or a paver -- although somebody has to do it.


Linda Kelly said...

There is much to be said about exposure to chemicals and risk and pharmaceutical use and water. It’s all related, and we here at the Water Environment Federation commend you for this thoughtful blog. My not for profit water professionals organization lumps all potentially harmful elements into a category of Microconstituents as an umbrella term for pharmaceuticals and personal care products in water.

It is true modern science has produced innumerable products and medicines that have improved the quality and longevity of our lives and afforded many conveniences that we have come to take for granted. There are approximately 82,000 chemical compounds in commerce today and some of these are employed to produce these benefits. Not surprisingly, virtually all compounds used by humankind find their way into the earth’s air, water or soil. This is not a new phenomenon. What is new is that our analytical testing methods are more and more sensitive -- so sensitive that we can now detect the presence of compounds at very minute levels.

Continually refined analytical methods are providing improved insight into the sources, transport and disposition of these substances. The positive and potentially negative affect these compounds have on human beings and other organisms varies depending upon the nature of the compounds and type of exposure as well as factors such as concentration, dose or quantity and duration of exposure. To illustrate this point one can observe that pure water can be fatal if consumed in too great a quantity over too short of time period while other materials can pose unacceptable risks at very low concentrations.

Considerable study therefore precedes the introduction of new products or compounds. The Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA) have primary regulatory authority over the development, use and ultimate fate of these man-made compounds. There are also ongoing local, state, federal, academic and research association study efforts regarding their effects on aquatic life and human health. Such information and analysis is of value in shaping continuously evolving regulation of these materials’ manufacture, use and disposal.

Existing water and wastewater treatment processes significantly reduce the levels of such substances and to date state and federal regulatory authorities have not found cause to require further reductions. It is prudent and responsible, however, that local, state and federal agencies continue cooperative efforts to carefully monitor the presence and effects of such compounds.

The Water Environment Federation (WEF) is not a research organization, but a not-for-profit professional association, and we are committed to facilitating information about the water environment and wastewater treatment. . We hope to aid public and membership discourse on this highly technical subject. We also hope to acknowledge and support continuing efforts to safeguard the public and our environment against unacceptable impacts from these and other materials that find their way into the nations waters through conscientious monitoring and assessment.

Much research has been done; much more is in the works. For now, we can all do our part to protect our precious water resources on a daily basis and make smart choices about the products we use and the risks we take.

Linda Kelly
Water Environment Federation

Cervantes said...

I definitely agree that a lot of attention has been drawn to very low concentrations of compounds in water because of our greater ability to detect them. People shouldn't jump to any conclusions about the consequences of such contaminants as pharmaceutical metabolites so on. But it's prudent to do the best we can to understand them.

Jena said...

Further studies should be made and everybody should cooperate to come up with the best solution. Thanks for the info. By the way, this group of medical research assistants might interest and help you in some ways. More power!