Chemicals and chemical reactions are a central part of everyday life: Acids are essential for digestion, chemicals maintain a balanced pH in the blood, photosynthesis occurs in plants, and, of course, industry uses many chemical reactions to produce modern foods and products. However, more and more potentially toxic chemicals are becoming concentrated in our environment due to the continued and rapid industrialization of many parts of the world.
Byproducts of manufacturing, such as heavy metals and polychlorinated biphenyls (PCBs), and finished products, such as antibiotics, pesticides, herbicides, batteries, fuels, and electronic equipment, can be potential toxins. Ground and surface waters used for drinking and fishing, soil used for agriculture purposes, and farmed animals raised with various chemical products all have potential effects on human health.
Many toxic chemicals are concentrated in fatty animal tissues (including fish liver and kidneys) or produced during cooking. Certain fish species are common sources of toxic exposures. This is of particular importance for women before and during their childbearing years and for pregnant and lactating women. It should be said that, despite the presence of some toxic chemicals in breast milk, the benefits of breast-feeding outweigh the possible 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.
Foodborne Chemicals: Antibiotics, Heterocyclic Amines, and Nitrates
Untreated pharmaceutical drugs may pass easily into soil and water supplies once released into the environment. Public health authorities are concerned that antibiotic use on farms may result in antibiotic resistance. In a study done in Oklahoma, bacterial samples from turkey, cattle, and chicken farms and from retail meat samples were shown to be resistant to several antibiotics and to be capable of transferring resistance to other bacterial species. Some experts have suggested that the development of resistance in humans may be due, in some cases, to antibiotic-resistant bacteria of farm animals that contaminate products entering the human food supply.
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, because of the long cooking times and high cooking temperatures. Chicken products contribute the greatest quantity of HCAs in North American diets, compared with other meats, in part due to the large quantity of chicken products consumed.
Several cancers are associated with HCAs, including cancers of the colon, rectum, stomach, breast, lung, and prostate. Modification of cooking methods (such as microwaving) and reducing or avoiding meat consumption are effective steps to prevent formation of HCAs.
The intake of cruciferous vegetables, such as broccoli and Brussels sprouts, may decrease HCAs in the body by causing the liver to more quickly eliminate them.
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 compounds that 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 vitamins and minerals in these foods. Other foods and nutrients that affect nitrate metabolism include fruits and vegetables, garlic and other allium species, vitamin E, and selenium.
Foodborne Chemicals: Heavy Metals
Public health agencies should educate the public regarding ways to minimize heavy metal exposures. Anyone who knows that he or she has been exposed should contact a local poison control authority.
- Mercury is a well-known toxin. Mercury poisoning may cause digestive, respiratory, and neurologic disorders, and can be lethal. It easily crosses the placenta in pregnant women and may cause birth defects, even in the absence of symptoms in the mother.
Mercury is used in medical instruments, although less commonly than in the past, and in some dental fillings. Mercury is also 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.
Mercury toxicity is usually diagnosed by a blood test.
- Cadmium can contribute to kidney and bone disease and is considered a probable carcinogen by the federal Environmental Protection Agency.
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 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 can have high levels of cadmium in their livers and kidneys, especially fish taken from urban waters and shellfish.
Cadmium toxicity can be diagnosed through urine and blood tests.
- Lead poisoning can lead to brain and kidney damage. It may also adversely affect fetal and childhood development, and may cause infertility.
Lead is very common in the environment and in households. It can be found in landfills that hold old electronic devices, in mine runoff areas, and in manufacturing facilities where lead is used in batteries, radiators, and other products. Groundwater and waterways may become contaminated from these sources, and many old houses still use lead pipes. In addition, older houses often have lead-based paint, which may flake off 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. Air emissions, especially in areas where leaded gasoline is still available, may cause surface contamination of crops.
Lead poisoning is diagnosed through blood testing.
High-calcium diets may protect against lead accumulation by reducing absorption of lead in the intestines. High blood levels of vitamin C are also associated with lower risk for lead poisoning. However, neither calcium nor vitamin C has been shown in controlled clinical trials to reduce lead in the body.
- Arsenic exposure may increase the risk for skin and other cancers, including lung cancer.
Arsenic is present in some pesticides, treated wood, and mining runoff. Arsenic is also a component of chicken feed supplements, and often reaches drinking water, especially untreated well water. Exposure through water is of particular concern, because the arsenic compounds formed are readily available for absorption into the body.
Arsenic poisoning is commonly diagnosed through urine tests, although hair and nail samples can also reveal exposure.
Foodborne Chemicals: PCBs, Dioxins, and Pesticides
Polychlorinated Biphenyls (PCBs) and Dioxins
- PCBs are synthetic 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 toxin that can be found 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 carcinogens and can damage the immune system, reproductive organs, the brain, and hormones. PCBs can cross the placenta and may contribute to mental problems in children. PCBs also enter breast milk, although it is not yet established if this contributes to poor health in infants.
- 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 the immune system, reproductive organs, the brain, and hormones. Although less than 10 percent of dioxins are considered significantly toxic, they can remain in the human body for decades-making them an important public health concern.
More than 4 billion pounds of pesticides (including herbicides) are used annually in the United States. 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 dangerous effects on the brain: carbamates (carbaryl), organochlorines (lindane and DDT), organophosphates (malathion), and pyrethroids (permethrin). Lindane and permethrin are available by prescription for the treatment of scabies. 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.
It is estimated that 50 percent of lifetime pesticide exposure occurs in the first five years of life. Developing fetuses and children are at high risk of pesticide toxicity due to their rapid growth and sensitive organs. Some pesticides have the potential to disrupt hormones. In addition, young children are particularly vulnerable because they spend more time outdoors and often put their hands in their mouths. For some pesticides, breast milk may contain several times the concentrations found in maternal blood samples.