What are pesticides? How do they affect the food chain?
Related cancers: Lymphomas, brain tumors, leukemias, and cancers of the breast, skin, stomach, prostate, and ovaries
Definition: Pesticides refer to any substance or mixture of substances intended for preventing, destroying, repelling, or lessening the damage of any pest. A pest is any living organism that could harm crops and people or other animals, or is in an undesirable location. Pesticides may be chemical, biological, or antimicrobial. They are released into the environment primarily through the spraying of insecticides on fruits and vegetables and other crops, such as corn, wheat, rice, and cotton, and by the use of herbicides on grass. Pesticides are believed to be responsible for a number of cancers.
Exposure routes: Ingestion, inhalation, absorption
Where found: Pesticides are found in the environment, in streams, rivers, lakes, groundwater, and the soil, including fields (where chlorophenols, particularly in the form of weed killers, build up over the years) and chemically treated lawns. DDT, banned in the United States in 1972, still exists in the soil and is stored in the fatty tissues of individuals; it may also be on products imported into the United States from countries where it is allowed.
Pesticides have entered the food chain: chemicals from pesticides get into groundwater or streams, then into the grass and other vegetation, then into herbivorous animals and then carnivorous and omnivorous animals such as humans. Those animals at the top of the food chain, such as humans or scavengers, fare worse than those below them, as the buildup of toxins is much greater at the top. In the aquatic food chain, chemicals from pesticides enter agricultural runoff or wastewater, then are taken up by algae and plankton, then small organisms, then larger fish, and finally humans. Fish containing mercury or other chemicals can be lethal to people.
At risk: People who produce or distribute pesticides, agricultural workers and people living in close proximity to fields, people who use pesticides in and around their homes, and people who eat fish or pesticide-treated fruits and vegetables
Etiology and symptoms of associated cancers: Studies have shown that human bodies contain hundreds more chemicals, including those contained in pesticides, than they did in the mid-twentieth century. Pesticides are linked to lymphoma, a cancer of the white blood cells. Of the two kinds of lymphoma, Hodgkin and non-Hodgkin lymphoma (NHL), the latter is most associated with pesticide carcinogens. Non-Hodgkin lymphoma begins when a blood cell (lymphocyte) becomes malignant and subsequently produces descendants of the single cell in which mutations (errors) have occurred. Although lymphoma can occur in any part of the body, tumors typically form in the lymphatic system, meaning bone marrow, lymph nodes, the spleen, and blood. The initial symptoms are usually perceived as swelling around the lymph nodes at the base of the neck, fever, fatigue, and unexplained weight loss.
Breast cancer is linked to organochlorine pesticides, which affect the endocrine system. Absorbed through ingested foods, the pesticides mimic, alter, or modulate hormonal activity and are therefore known as endocrine disruptors. Raising the activity and quality of estrogens the human body produces causes tumors to form. Pesticides are also linked to ovarian cancer, in that malignant ovarian tumors are endocrine related and hormone dependent.
Atrazine—used on some 75 percent of the United States corn crop, as of 2012, according to the EPA—exists in most drinking water supplies in the Midwest and has been linked to birth defects in farmers’ children. Long-term exposure to atrazine has been linked to weight loss, cardiovascular damage, retina and muscle degeneration, and cancer.
Organophosphate pesticides, which have largely replaced organochlorine pesticides, are connected with skin and eye problems, headaches, dizziness, nausea, vomiting, and abdominal pain. The thirty-seven compounds that make up this group destabilize a key enzyme in the brain known as cholinesterase, causing trauma to the brain and nervous system. Studies have related pesticide risk with respiratory problems, memory disorders, dermatologic conditions, cancer, depression, neurologic deficiencies, miscarriages, and birth defects. Primarily, these pesticides affect the nervous system by disrupting the enzyme that regulates acetylcholine, a neurotransmitter.
Definitive proof that DDT is a human carcinogen is still lacking, but it has been associated with liver and lung tumors, as well as lymphoma, in experimental animals, as reported in the Thirteenth Report on Carcinogens (2014). Epidemiological studies have further shown association with breast cancer, leukemia, multiple myeloma, and liver cancer in humans.
History: More than four thousand years ago, Sumerians dusted sulfur on their crops to kill insects, and more than two thousand years ago, ancient Greeks used pesticides to protect their crops. By the fifteenth century, arsenic, mercury, and lead—highly toxic chemicals—were used on crops to eliminate insects. During the seventeenth century, farmers used nicotine sulfate, derived from tobacco leaves, as an insecticide, and in the nineteenth century, pyrethrum, extracted from chrysanthemums, and rotenone, removed from roots of tropical vegetables, were used as pesticides.
In 1939 Swiss scientist Paul Müller discovered the potency of a compound made of carbon and hydrogen called dichlorodiphenyltrichloroethane (DDT), first used in World War II against typhus, plague, malaria, and dengue and yellow fevers. After the war, DDT use in the United States soared. Farmers killed pests such as boll weevils that were devastating cotton crops, and the government used low-flying crop-dusting planes to rid the forests of gypsy moths. Other parts of the world began using DDT to combat malaria; after homes and huts were sprayed in North Africa, Asia, India, and Zanzibar, the number of malaria cases declined drastically.
In 1962 Rachel Carson published Silent Spring, the product of more than four years of research, in which she maintained that pesticides were harming wildlife and the environment. Using meticulous documentation, Carson claimed that the government knew little about the dangers of pesticides. Although the book was criticized as well as praised, it spurred concerns about pesticides and other pollutants, leading to the beginning of the environmental movement and President Richard M. Nixon’s creation of the Environmental Protection Agency (EPA) in 1970. Soon the EPA targeted DDT, eventually banning it in 1972. Although time has proven Carson’s position on the harm from pesticides to wildlife correct, the idea that DDT is a human carcinogen is still being investigated.
In the years since its ban, DDT has been replaced by a huge array of insecticides, herbicides, and pesticides that have been tentatively linked with tumors and cancers of the lymphatic, endocrine, neurological, respiratory, and reproductive systems but have not been proven to be carcinogens. Although studies have shown an increase in the rates of tumors or cancers in agricultural areas where large amounts of pesticides are used, scientific proof of the connection is inconclusive. Because of the gap in time between exposure and the first symptoms of illness (frequently decades) and the inability to pinpoint a particular pesticide as the carcinogen, definite scientific proof is hard to provide.
Nevertheless, strict regulations are in effect: The EPA must approve any pesticide for sale or use in the United States, and the Food Quality Protection Act (1996) requires the oversight of the manufacture, distribution, and use of pesticides. Although the causal relationship between pesticides and cancer is hard to establish, pesticides have other proven health risks, and many people in the United States are trying to minimize or avoid their use. The EPA provides many suggestions on how to use pesticides more safely, and some people have turned to organically grown products as a way to avoid most pesticides.
Because of the carcinogenic potential of pesticides, the organic foods industry has grown. The Organic Foods Production Act (1990) authorized national standards for the production, handling, and processing of organically grown agricultural products. Essentially, organic farming is an ecological system that avoids chemical pesticides, promotes soil conservation, and integrates the parts of the farming system into an ecological whole. Although organic farming cannot guarantee that the soil does not contain pesticide residue, the practice follows methods designed to minimize contamination from air, soil, and water. Organic meat, poultry, eggs, and dairy products come from animals that are not given any antibiotics or growth hormones and that are raised on organically grown feed. Organic food is produced without using conventional pesticides or fertilizer made from synthetic ingredients or sewage sludge. Organic farms use cover crops, green manures, animal manures, and crop rotation to manage weeds, insects, and diseases and promote biological activity and long-term soil health.
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