Time to Heed the Evidence

By Sean Palfrey, MD

This essay is in response to: What are we learning about the relationship between environmental toxicants and cancer? How should our regulatory system respond to this information?

Two generations ago, Rachel Carson woke us up, and her book and others sounded a clarion call that should have changed the country’s laissez faire attitude about inventing, using, and discarding chemicals into our air, water, and soil before we studied them to reassure ourselves that they were harmless. But little actually ended up happening, at least in this country. We did ban DDT and several other chemicals, and the acute damage they were causing did decrease. We did pass the first Toxic Substances Control Act (TSCA), the National Cancer Act, and others, but even then, more than 30 years ago, TSCA was acknowledged as too little, too late. And now, decades later, we have discovered that many of these synthetic chemicals we were using, like the heavy metals, lead, and mercury, were indestructible (and unmetabolizable) so they ended up being bio-concentrated in humans, stored in our bodies, mobilized during pregnancy, and passed on from one generation to the next by maternal-fetal transmission.

Studies have shown that all newborn infants’ cord bloods appear to contain measurable levels of many industrial chemicals previously taken in by their mothers. We also thought that Darwin had it right that there was no such thing as “inheritance of acquired characteristics”, but now we know that, through epigenetics, we can pass on functional, if not structural, genetic changes acquired by a parent during their pre-pregnancy years, many of which are caused by agents floating around in our environment.

Some countries, and groups like the EU, have espoused the “precautionary principle,” requiring manufacturers and industries to show that new chemicals they want to use are generally harmless before they incorporate them into products or spill them out into the environment. But, just as it took the US 50-100 years to ban lead in house paint, it is taking many decades for our commerce-driven society to respond to warning signs that we might be poisoning ourselves in the relentless pursuit of profit.

We are concerned that environmental toxins may be causing the increased incidence of asthma, autism, ADHD, and other diseases that seem to be rising more rapidly than we can be explain on the basis of infectious diseases, behavioral changes, or parenting patterns. One of the disease groupings we are most concerned about as being at least partially caused by environmental pollution is cancers. Not all cancers are increasing in incidence (a decrease in smoking has had a very positive effect on lung cancer incidence), but in the pediatric age group, the incidence of some brain, hematologic, and endocrine tumors is increasing.

Last spring, the President’s Cancer Panel, a group of expert physicians, public health and policy experts, released a report stridently warning that many in the scientific and regulatory communities in this country were underestimating the number of environmentally-induced cancers caused by industrial and commercial chemicals. The panel warned that the lack of requirements for pre-use testing was extremely dangerous. For people with most human cancers, their local environment contains chemicals known to be associated with their types of cancer (“attributable risks”), and when people move from a low risk environment to a high risk environment, their risk and rates of cancer shift to match those of the new environment. When epidemiologically- associated specific occupational chemicals are removed from a particular work or living environment, the rates of associated cancers drop, just as lung cancers did after the decrease in cigarette smoking.

Of the 80,000 chemicals now in industrial use in the US only about 200 have been studied for carcinogenicity. Most studies are performed on laboratory animals, though some cellular genetic studies are now are being performed. Few studies relate in any way to humans, and none to fetuses, infants, and children, the highest risk populations. Because few have been peer reviewed and many have been performed under conditions where potential conflicts of interest exist, there is much controversy over the accuracy and relevance of the data. Most information comes from relational epidemiological studies in which rates of specific cancers are associated with geographic levels of exposure (farm and home pesticide use, factories emitting chemicals into the air, water or soil, down-wind or down water-flow exposures, occupational risks to workers or their families (employment in settings using specific chemicals)). Recent preconception, pregnancy, and early infancy exposures are associated with highest odds ratios for the development of cancers, but paternal as well as maternal exposures are also associated with increased risk to their children, and certain maternal and child genotypes are much more susceptible than others.

From these studies, the following, very incomplete, list of associations between pediatric cancer types and commonly-occurring substances has been compiled:

• Leukemias - exposures to pesticides, solvents, alcohols, benzene, vehicle exhaust, dioxin, and hydrocarbons (gasoline and fumes, paints, paint thinners, solvents, tars, roofing materials, benzene), some compounds in plastics.
• Nervous system tumors - exposures to insecticides (residential sprays, fumigant bombs, and herbicides (weed killers))
• Neuroblastomas – exposures to pesticides, benzene, alcohols, turpentine, and hydrocarbons including diesel fuels
• Non-Hodgkin’s lymphomas – exposures to horticultural and home pesticides
• Soft tissue sarcomas – exposures to yard pesticides
• Hepatoblastomas – exposures to hydrocarbons and petroleum products
• Wilms tumors – exposures to pesticides and hydrocarbons
• Urinary tract tumors – exposures to hydrocarbons
• Lung cancers – exposures to cigarette smoke

Other known common carcinogens include asbestos, formaldehyde, coke oven emissions, vinyl chloride, dichloromethyl ether, and aromatic amines from dyes.

Only associations with the very most common chemicals have been studied. There are another 79,000+ new, synthetic chemicals which have not been studied at all. We do not know the additive or synergistic effects of the multiple exposures that are obviously occurring every moment in our bodies. We know few of the genotypes that make individuals particularly susceptible. Since cancers often manifest themselves only decades after known exposures, it is impossible to estimate the risks of even documented exposures. Only a life-long study like the National Children’s Study, which would gather blood and other tissue samples from fetal life onward over decades, would have a chance to discover such long-term associations. We are only just beginning to learn how epigenetic changes occur, what the risks of preconceptional exposures are, and how great is the multigenerational build-up of our bodies’ burden of toxins.

Several years ago, because we had concerns about the universality of potentially harmful chemicals in the bodies of Americans, and because we wanted to see if health care workers had elevations of specific toxins, a group of doctors and nurses, including myself, submitted blood and urine samples for analysis. All of us had detectable levels of potentially significant carcinogens, as well as endocrine and CNS disrupters, regardless of our workplace, residence setting, or state.

We are all being exposed to thousands of new chemical agents that our bodies have never been exposed to before over the millions of years of evolution of our bodies’ metabolic and excretory defense systems. These chemicals enter our bodies through our skin, our lungs, and our gastrointestinal tract. We then pass them on to our children and they, too, build up levels because the chemicals cannot be metabolized or excreted. We are already far behind, and cannot hope to catch up with studying many of these substances in retrospect, but we can heed evidence that suggests that certain groups of chemicals are associated with cancers and other serious medical conditions. We can adopt the precautionary principle the way the EU and Canada are doing and require at least rudimentary safety studies on new agents before they are allowed to enter our environment. We can work on and pass meaningful TSCA reform and build in proactive as well as retroactive responses to new evidence of medical danger whenever it appears. We can reconfigure and fund the National Children’s Study which may offer us the only scientific hope of identifying those needles in a haystack, or drops of poison in our water supply that will jeopardize the health of our children’s grandchildren.

This time we must heed all of these warning signs, before it gets too late.

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