Chemicals and chemical reactions are an integral part of everyday life. Photosynthesis occurs in plants, acids aid digestion, buffers balance the pH of blood, and, of course, industry uses many chemical reactions to produce modern products. However, more and more potentially toxic chemicals are becoming concentrated in our environment due to the continued and rapid industrialization of the world.
Products of industry, whether byproducts of manufacturing, such as heavy metals and polychlorinated biphenyls (PCBs), or finished products, such as antibiotics, pesticides, herbicides, batteries, fuels, and electronic equipment, are all potential toxins. Ground and surface waters used for drinking and fishing, soil used for agriculture purposes, and farmed animals raised with growth/production stimulators are all potential reservoirs of chemicals that can harm human health.
Heterocyclic Amines 20,21and Nitrates
Heterocyclic amines (HCAs) are carcinogenic compounds that form during cooking of all meats, including fish. In general, grilling causes the greatest amount of HCA formation, followed by pan-frying. Chicken products contribute the greatest quantity of HCAs in North American diets, compared with other meats, in part due to the quantity of chicken products consumed. Several cancers are associated with HCAs, including those arising in the colon and rectum, stomach, breast, lung, and prostate. Modification of cooking methods (such as microwaving) and reducing meat consumption are effective preventive steps.
The intake of cruciferous vegetables, such as broccoli and Brussels sprouts, has been found to increase HCA metabolism in humans by induction of hepatic detoxification enzymes.22-24
Nitrates
Nitrates and nitrites are used as preservatives in hot dogs, pickled meats, some cheeses, and other foods. They are metabolized in the body to form N-nitroso compounds, which are associated with gastric cancer. Nitrates are also a natural component of many vegetables, and produce commonly contains nitrate residues from fertilizers. However, despite the presence of nitrates in and on many fruits and vegetables, protection from gastric cancer is afforded by the consumption of these foods, presumably because of the inhibitory effect of vitamin C on the formation of N-nitroso compounds.
Other foods and nutrients also inhibit N-nitroso compound formation. These include polyphenolic compounds in fruits and vegetables;25 garlic and other allium species26; and vitamin E and selenium.27
Heavy Metals
Public health agencies and clinicians should educate the public regarding ways to minimize heavy metal exposures. Known exposures should be discussed immediately with a local poison control authority.
Elemental mercury is a well-known toxin. It is used in medical instruments, although less commonly than in the past, and in dental amalgam fillings. Family physicians may encounter patients who have inhaled elemental mercury resulting from spills at home or in schools, although these exposures may not lead to toxicity. Mercury also forms several compounds and is a common environmental pollutant, as a result of industrial processes.
Aside from occupational exposures, the main exposure route is through ingestion of fish, especially those high on the food chain, such as shark, tuna, and swordfish, and certain fish taken from some freshwaters. Dental fillings are not believed to present a public health hazard, although alternatives to amalgam fillings are available. Vaccines may contain thimerosal, a compound that includes mercury. However, the effective amount of mercury from vaccines is not currently considered unsafe, although debate about this will likely continue.
Mercury poisoning may cause digestive, respiratory, and neurologic disorders, and can be lethal. (The phrase "mad as a hatter" refers to neurologic sequelae of mercury exposures in the felt hat industry of the 19th century.) Mercury easily crosses the placenta in pregnant women and may cause birth defects, even in the absence of maternal symptoms.
Mercury toxicity is usually diagnosed by a blood test. Chelation is available for acute mercury toxicity.
Cadmium, a heavy metal common in the environment, can contribute to kidney and bone disease and is considered a probable carcinogen by the federal Environmental Protection Agency (EPA). Cigarettes are a common source of cadmium exposure. Incineration of household waste, particularly batteries, may release cadmium into the atmosphere, and industrial processes such as mining and land applications of sewage sludge can pollute water and air. Phosphate fertilizers commonly contain cadmium, and grain and vegetable crops easily absorb the metal through polluted irrigation waters.
Fish concentrate cadmium in their livers and kidneys, leading to toxicity in populations that commonly consume whole fish, especially fish taken from urban waters. Shellfish also concentrate cadmium.
Cadmium toxicity can be diagnosed through urine and blood tests, although blood generally shows evidence of acute exposures only. For this reason, prevention of excess exposure is of paramount importance. No well-studied and accepted chelating agent is available for cadmium in humans.
Lead is very common in landfills harboring old electronic devices (solder) and cathode ray tubes, in mine runoff areas, and in manufacturing facilities where lead is used in batteries, radiators, lead glazes, and other products. Groundwater and waterways may become contaminated from these sources, and many old houses still use lead pipes to connect to city water mains. In addition, older houses often have lead-based paint, which may flake and be consumed by small children.
Lead may also be present in toy jewelry, household crystal and glazed pottery used for serving foods and beverages, imported Mexican candy, and traditional medicines. For example, some Ayurvedic and Chinese medicines may contain lead, mercury, and arsenic.1,2 Air emissions, especially in areas where leaded gasoline is still available, may cause surface contamination of crops.
Lead poisoning can lead to nervous system and kidney damage, and can cause several nonspecific symptoms. It may also adversely affect fetal and childhood development, and fertility in men. During pregnancy and lactation, women can mobilize lead stored in bone from past exposures.
Lead poisoning is diagnosed through blood lead concentrations, among other laboratory findings, and chelation agents are available for treatment of patients with high levels or acute symptoms.
High-calcium diets may protect against lead accumulation by reducing gastrointestinal absorption of this mineral.3 High blood levels of vitamin C are also independently associated with lower prevalence of elevated blood lead concentrations.4 However, neither calcium nor vitamin C has yet been found to reduce body lead burden in randomized controlled clinical trials.
Arsenic is present in some pesticides, treated wood, and mining runoff. Exposures may also come from the smelting process. Arsenic is also a component of chicken feed supplements used to treat parasites,5 and often reaches drinking water, especially untreated well water. Exposure through water is of particular concern, because the arsenic compounds formed are readily bioavailable.
Long-term exposure is related to hyperkeratosis,6 as well as increased risk of skin and other cancers, including lung cancer. Exposure may result from occupational inhalation.
Arsenic poisoning is commonly diagnosed through urine tests, although hair and nail samples can also reveal exposure. Chelation therapy is available.
Pesticides12 and Antibiotics
Pesticides
Pesticides (including herbicides) are agents that can both beneficially and adversely affect public health. They are beneficial in that they can allow for increased food production and restrict animal-carried diseases. On the other hand, over 4 billion pounds are applied annually in the United States, so the prevention of unnecessary and accidental exposure through direct contact, or through water and food sources, is essential.
Several common classes of pesticides have the potential for adverse effects on the central nervous system: carbamates (carbaryl), organochlorines (lindane, DDT), organophosphates (malathion), and pyrethroids (permethrin). DEET is also commonly used to prevent mosquito and tick bites, and can be toxic if not used as directed or if ingested; hand-washing after application is essential.
Lindane and permethrin are available by prescription for the treatment of scabies. Permethrin is safer for infants, children, and during pregnancy, and is also available as an antilice shampoo.
It is estimated that 50% of lifetime pesticide exposure occurs in the first 5 years of life.13 Developing fetuses and children are at high risk of pesticide toxicity due to their rapid growth and developmental vulnerability. Some pesticides have the potential to disrupt endocrine pathways involving estrogen, androgen, and thyroid receptors. In addition, young children are particularly vulnerable, because they spend more time outdoors, often put their hands in their mouths, and ingest a much greater amount of food per unit body weight. For some pesticide residues, breast milk may contain several times the concentrations found in maternal blood samples.14
Acute pesticide ingestion can be treated with gastric lavage, charcoal, pralidoxime (for organophosphates), and atropine. Diazepam may also help prevent seizures.
Antibiotics
Untreated pharmaceuticals---such as the antihelminthic morantel, which is used widely in animal agriculture--may pass easily into soil and water supplies once released into the environment.15 Public health authorities are concerned that antibiotic use on farms may spawn antibiotic resistance. In Oklahoma, turkey, cattle, and chicken farms, and retail meats showed multi-antibiotic-resistant Klebsiella pneumonia bacteria, which could transfer the gene for resistance to E. coli.16 In developed countries, studies have suggested an association between antimicrobial use in farmed animals and the development of antibiotic resistance in humans.17 Some experts believe antibiotic resistance is more commonly due to antibiotic use in human patients or to contact with hospital environments.18 Others have suggested that the development of resistance in humans may be due, in some cases, to antibiotic-resistant microflora of farm animals contaminating products entering the human food supply and passing resistance genes on to human microflora.19
Foodborne Chemicals: Polychlorinated Biphenyls and Dioxins7,8
PCBs are synthetic organic chemicals that were used in many products before 1977. Over 1.5 billion pounds were produced in the United States. They now represent an environmental contaminant concentrated in fatty fish and other animal products (dairy products, eggs, and meats), and are also detectable in human tissues.
Evidence strongly suggests that PCBs are human carcinogens and adversely affect the immune, reproductive, nervous, and endocrine systems of animals and humans. PCBs can cross the placenta and may contribute to cognitive problems in children.9 PCBs also enter breast milk, although the contribution of this route of exposure to health effects in infants is not well established.10
Dioxins are usually byproducts of industrial processes, including incineration, although they also result from volcanic eruptions. Like PCBs, they are found mostly in animal products near the top of the food chain, and ultimately can affect animal and human immune, reproductive, nervous, and endocrine systems. Although less than 10% of dioxins are considered significantly toxic, their long half-life-about 7 years in the human body-makes them an important public health concern. Destroying dioxins requires incineration at temperatures above 850o to 1000o centigrade.11
Orders and What to Tell the Family
Orders
See Basic Diet Orders chapter.
What to Tell the Family
Many toxic chemicals are concentrated in fatty animal tissues (including fish liver and kidneys) or produced during cooking. To reduce exposure to these toxic chemicals, it is best to reduce consumption (and trim visible fat), as described in the basic diet orders.
Certain fish species are common sources of toxic exposures. While some evidence shows fish to be more healthful than other meats for various health outcomes (such as cardiovascular events), the toxic load of some fish species raises important concerns. This is of particular relevance for women prior to and during their childbearing years and for pregnant and lactating women. Despite the presence of some toxic chemicals in breast milk, the benefits of breast-feeding outweigh the presumed risks to the baby.
Organic produce is increasingly available. Nonorganically produced fruits and vegetables can be washed thoroughly with warm water and a soft brush to reduce pesticide residues. Certain fruits and vegetables, such as apples, berries, tomatoes, and grapes, tend to carry larger pesticide residues.
Household pesticides, if used at all, should be carefully stored. When they are used, family members and domestic animals should be protected from exposure for the period of time specified in the product instructions.
References
1. Saper RB, Kales SN, Paquin J, et al. Heavy metal content of ayurvedic herbal medicine products. JAMA. 2004;292:2868-2873.
2. US Department of Human Services, Centers for Disease Control and Prevention, National Center for Environmental Health, Frequently Asked Questions. Lead in Folk Medicine: Questions and Answers. Available at: http://www.cdc.gov/nceh/lead/faq/folk%20meds.htm. Accessed January 25, 2006.
3. Chuang HY, Tsai SY, Chao KY, et al. The influence of milk intake on the lead toxicity to the sensory nervous system in lead workers. Neurotoxicology. 2004;25:941-949.
4. Simon JA, Hudes ES. Relationship of ascorbic acid to blood lead levels. JAMA. 1999;281:2289-2293.
5. Lasky T, Sun W, Kadry A, Hoffman MK. Mean total arsenic concentrations in chicken 1989-2000 and estimated exposures for consumers of chicken. Environ Health Perspect. 2004;112:18-21.
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http://www.atsdr.cdc.gov/tfacts2.html. Accessed January 25, 2006.
7. US Environmental Protection Agency. Polychlorinated Biphenyls (PCBs). Available at: http://www.epa.gov/opptintr/pcb/index.html.
Accessed November 15, 2005.
8. World Health Organization. Dioxins and Their Effects on Human Health (fact sheet No. 225, June 1999). Available at:
http://www.who.int/mediacentre/factsheets/fs225/en/index.html.
Accessed November 15, 2005.
9. Jacobson JL, Jacobson SW. Intellectual impairment in children exposed to polychlorinated biphenyls in utero. N Engl J Med. 1996;335:783-789.
10. US Department of Health and Human Services, Centers for Disease Control and Prevention, Agency for Toxic Substances and Disease Registry. Toxicological Profile for Polychlorinated Biphenyls (PCBs). Available at: http://www.atsdr.cdc.gov/toxprofiles/tp17.html. Accessed January 26, 2006.
11. US Department of Health and Human Services, Centers for Disease Control and Prevention, Agency for Toxic Substances and Disease Registry. Toxicological Profile for Chlorinated Dibenzo-p-dioxins (CDDs). Available at: http://www.atsdr.cdc.gov/toxprofiles/tp104.html. Accessed January 26, 2006.
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13. Landrigan PJ, Mattison DR, Babich HJ, et al, for the Committee on Pesticides in the Diets of Infants and Children. Report on Pesticides in the Diets of Infants and Children. National Research Council. Washington, DC: National Academy Press; 1993.
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17. Padungton P, Kaneene JB. Campylobacter spp in humans, chickens, pigs and their antimicrobial resistance. J Vet Med Sci. 2003;65:161-170.
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19. Teuber M. Spread of antibiotic resistance with food-borne pathogens. Cell Mol Life Sci. 1999;56:755-763.
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