The term agricultural chemicals refers to any substance involved in the growth or use of any plant or animal of economic importance to humans. An agricultural chemical might be a natural product, such as urea, or a synthetic chemical, such as dichlorodiphenyltrichloroethane (DDT). The agricultural chemicals used in more recent decades include fertilizers, pesticides, growth regulators, animal feed supplements, and raw materials for use in chemical processes.
In the broadest sense, agricultural chemicals can be divided into two large categories: those that promote the growth of a plant or animal and those that protect plants or animals. Plant fertilizers and animal food supplements constitute the first group, while pesticides, herbicides, animal vaccines, and antibiotics protect plants or animals.
Crops require a number of nutrients to remain healthy and grow normally. They require some in relatively large quantities, which are called “macronutrients,” and others in relatively small quantities, called “micronutrients.” Nitrogen (N), phosphorus (P), and potassium (K) are considered macronutrients, and boron (B), calcium (Ca), chlorine (Cl), copper (Cu), iron (Fe), magnesium (Mg), and manganese (Mn), among others, are micronutrients.
Synthetic fertilizers are designed to provide either a single nutrient or some combination of nutrients. Examples of single-component or straight fertilizers are urea (NH2CONH2), which supplies nitrogen, or potassium chloride (KCl), which supplies potassium. The composition of mixed fertilizers, those containing more than one nutrient, is indicated by the analysis printed on their container. An 8–10–12 fertilizer, for example, contains 8 percent nitrogen by weight, 10 percent phosphorus, and 12 percent potassium.
Synthetic fertilizers can be designed to release nutrients almost immediately (quick-acting) or over longer periods of time (time-released). They may also contain specific amounts of one or more trace nutrients needed for particular types of crops or soil. Controlling micronutrients is one of the most important problems in fertilizer compounding and use; the presence of low concentrations of some elements can be critical to a plant's health, whereas higher levels can be toxic to the same plants or to animals that might ingest the micronutrient.
Plant growth patterns can also be influenced by directly applying certain chemicals. Delaying ripening is important for marketing agricultural products because it extends the time a crop can be transported and stored on grocery shelves. Other kinds of chemicals used in the processing, transporting, and storage of fruits and vegetables include those that slow down or speed up ripening, reduce weight loss retain color, and control firmness.
The term agricultural chemical is most likely to bring to mind the range of chemicals used to protect plants against competing organisms: pesticides and herbicides. These chemicals disable or kill bacteria, fungi, rodents, worms, snails and slugs, insects, mites, algae, termites, or any other species of plant or animal that feeds upon, competes with, or otherwise interferes with the growth of crops. Such chemicals are named according to the organism against which they are designed to act. Some examples are fungicides (designed to kill fungi), insecticides (used against insects), nematicides (to kill round worms), avicides (to control birds), and herbicides (to combat plants).
Chemicals are also used to maintain and protect livestock. At one time, farm animals were fed almost exclusively on readily available natural foods. They grazed on rangelands or were fed hay or other grasses. In recent decades, carefully blended chemical supplements are commonly added to the diet of most farm animals. These supplements have been determined on the basis of extensive studies of the nutrients that contribute to the growth or milk production of cows, sheep, goats, and other types of livestock. A typical animal supplement diet consists of various vitamins, minerals, amino acids, and nonprotein (simple) nitrogen compounds. The precise formulation depends primarily on the species.
Genetic engineering has also become used more to alter crops and livestock. Cows injected with a genetically modified chemical, bovine somatotropin, produce a significantly larger quantity of milk. Researchers have modified crops in attempts to make them hardier, improve their size or color, or make them more resistant to disease and insects. Studies have shown that genetic modification of crops actually has increased use of pesticides, however.
Farmers have long understood the importance of replenishing the soil, and they have traditionally done so by natural means, using such materials as manure, dead fish, or compost. Synthetic fertilizers were first available in the early twentieth century, but they became widely used only after World War II (i.e., 1945). By 1990, farmers in the United States were using about 20 million tons (18.1 million metric tons) of these fertilizers a year. The introduction of synthetic pesticides in the years following World War II, which ended in 1945, produced spectacular benefits for farmers. More than 50 major new products appeared between 1947 and 1967, resulting in yield increases in the United States ranging from 400 percent for corn to 150 percent for sorghum and 100 percent for wheat and soybeans. Similar increases in less developed countries, resulting from the use of both synthetic fertilizers and pesticides, eventually became known as the Green Revolution.
By the 1970s, the environmental consequences of using synthetic pesticides became apparent. Chemicals were becoming less effective as pests developed resistances to them, and their toxic effects on other organisms had grown more apparent. Farmers were also discovering drawbacks to chemical fertilizers as they found that they had to use larger and larger quantities each year to maintain crop yields, resulting in increased material and labor costs.
Fertilizers can help crops grow, but overuse of the products can harm the environment. Along with pesticides, chemical fertizers can infiltrate community water sources. When they do, the chemicals affect drinking water and marine animal life, causing secondary public health problems. A U.S. Geological Survey study found that 70 percent of public and well water used for drinking had toxic compounds, pesticides, or nitrates from human sources.
The use of chemicals with livestock can have deleterious effects, just as crop chemicals have. In the 1960s, for example, the hormone diethylstilbestrol (DES) was widely used to stimulate the growth of cattle, but scientists found that detectable residues of the hormone remained in meat sold from the slaughtered animals. DES is now considered a carcinogen, and the U.S. Food and Drug Administration banned its use in cattle feed as of 1979. The use of antibiotics in food animals has likely contributed to antibiotic resistance in humans.
The food system is an important part of the U.S. economy, at about $1 trillion in annual sales and billions of dollars in exports each year. The average fertilizer use is 23.4 million tons (21 million metric tons) per year. Still, about 1 billion pounds of pesticide were applied in the United States annually, and 80 percent of it was used in agriculture. World consumption of fertilizer in 2018 is projected to surpass 200 million tons (181 million metric tons).
One solution to the environmental hazards posed by synthetic pesticides is the use of natural chemicals such as juvenile hormones, sex attractants, and antifeedant compounds. The development of such natural pest-control materials has, however, been relatively modest; the vast majority of agricultural companies and individual farmers continue to use synthetic chemicals that have served them so well for over a half century. Though the organic grower and food movement might have occurred in pockets around the country and world, it occurred mostly in response to public health concerns regarding chemicals used in agriculture. A 2010 U.S. Department of Agriculture survey found that there were organic farms in every state.
More public health funding is needed for improved tracking and research of harms related to food systems and agricultural chemicals. Many local communities have developed food policy councils to address chemicals and other issues related to food safety and sustainability. The American Public Health Association believes that public health workers and leaders could become more engaged in food system issues and promote adoption of comprehensive food safety policies.
See also American Public Health Association ; Chemical poisoning ; Food and Drug Administration ; Food safety .
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David E. Newton, EdD
Revised by Teresa G. Odle