Who is Looking After Our Children?
CHAPTER 13
Combined Exposures to Multiple Chemicals May Greatly Enhance Their Toxicity
Much of the current complacency about human chemical exposures is due to the method of toxicity testing, based on animal studies, in which a single chemical is tested to find an estimated "safe" level for human exposure. (1) Such testing is mandated by the Delaney Amendment of 1958 which requires the testing of potentially toxic chemicals for carcinogenic properties. There are several flaws and inadequacies in this system, (2-3) but perhaps the greatest flaw is that it does not take into account the effects of simultaneous human exposures to multiple environmental chemicals and their additive effects. We have previously mentioned the study in which 10 volatile chemicals were collected from the breath, indoor air, outdoor air and drinking water of 400 residents of New Jersey, North Carolina and North Dakota. (4)
Considering the technical difficulties and expense of testing even one chemical, it is partly understandable why the testing of a vast variety of chemical combinations has not been required by our present laws. However, three recent publications point to the feasibility, as well as the urgent need for more such studies and reevaluation of our safety standards in this area. (5-7)
In our first example, an outbreak of three sick building syndromes (SBS) in two high schools and the Federal Department of Justice building in Washington DC led researchers from Georgetown University Medical Center and the National Institutes of Health to conclude that chronic fatigue syndrome is often associated with SBS. The symptoms of affected people included headaches, fatigue, muscle pains, rhinitis, sinusitis, memory problems, low grade fevers, eye irritation, and sensitivity to light. No single chemical was found above established safety levels. No viral or biologic agent was found. The authors suggested that the cause may have been low levels of contaminants acting "in concert" or synergistically to produce overlapping syndromes. (5)
The second example involved a study of environmental chemicals which are estrogenic; that is, they simulate the effects of the female hormone, estrogen, in the human body. The three chemicals studied (dieldrin, endosulfan and toxaphene) were too weak to affect biological systems when tested singly, but in combination, two of these chemicals were a thousand times more potent than either alone in their estrogenic effects. (6) The authors suggested such combinations may pose a risk for breast cancer and decrease human semen quality.
The final example concerns the Persian Gulf War Syndrome, a subject of historical as well as human and scientific interest. Of the three-quarters of a million service personnel involved in the Persian Gulf War, approximately 30,000 have complained of neurologic (nervous system) symptoms of unknown etiology. The study, which was performed on hens, involved three chemicals: the anti-nerve agent pyridostigmine bromide, which was given to some personnel, the insecticide permethrin, and an insect repellent applied to the skin. The toxic effects of each agent alone was minimal, but a combination of all three often led to severe neurologic damage. The authors postulated that the pyridostigmine bromide, which inhibits detoxification enzymes in the body, may have led to greater concentrations of the other two chemicals, both of which are potentially neurotoxic, to reach the nervous system. (7)
In the scientific realm these studies properly will be considered preliminary, and more studies will be called for. But studies take time, and time is running out for our children. In the final analysis, it is the parents who must protect the children.
References
1. Pesticides in Diets of Infants and Children. Washington DC: National Research Council; 1993:123-157.
2. Pesticides in Diets of Infants and Children. Washington DC: National Research Council; 1993:3
3. Mott L, Snyder K. Pesticide Alert. San Francisco: National Resources Defense Council, Sierra Club Books; 1987.
4. Wallace LA et al. The TEAM study: personal exposures to toxic substances in air, drinking water, and breath of 400 residents of New Jersey, North Carolina and North Dakota. Environ Research 43:290-307.
5. Chester AC, Levine PH. Concurrent sick building syndrome and chronic fatigue syndrome: epidemic neuromyasthenia revised. Clinical Infectious Diseases 18 (Suppl 1):1996:S43-S48.
6. Arnold SF, et al. Synergistic activation of estrogen receptor with combinations of environmental chemicals. Science. 1996;272;1489- 1492.
7. Abou-Donia MB, et al. Neurotoxicity resulting from coexposure to pyridostigmine bromide, DEET, and permitrin: implications of Gulf war chemical exposures. J Tox & Environ Health.1996;48:35-56.