4.2 Pesticides
4.3 Pesticides in Water
4.4 Effects of Pesticides on Soil Quality
4.5 Pesticides in the Atmosphere
4.6 Pesticide Drift
4.7 Pesticide Health and Environmental RIsks
4.8 Pesticide Economic Effects
4.9 Pesticide Toxicity
4_Pesticides-in-the-Environment
Pesticides in the Environment
Overview
Title Image: An agricultural worker sprays their crops with a chemical treatment by Tony Hawkes, Office of Protected Resources is in the Public Domain.
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Introduction
Lesson Objectives
- Discuss the effect of pesticides on the environment and human health.
- Discuss how agriculture would be different with or without pesticide use.
Key Terms
acute toxicity: how poisonous a pesticide is to an organism after a single short-term exposure
adsorption: a measure of how well a pesticide sticks to soil particles
chronic toxicity: the ability of a pesticide to cause adverse health effects over an extended period, usually after repeated or continuous exposure, which may last for the entire life of the exposed organism
drift: the movement of a pesticide from the application site by wind or air
leaching: pesticides that dissolve in water and absorb into the soil
persistence: a pesticide quality of substance stability and resistance to breaking down
pesticide: substances created to control pests
residues: pesticide that remains in the environment after an application or spill
runoff: pesticides that dissolve in water and flow away from the application site
solubility: a measure of the ability of a pesticide to dissolve in a solvent, usually water
Introduction
There are many variables that promote or discourage plant growth. Living things can infect plants, compete for resources, eat plants, or damage them in other ways. Humans have developed substances to control these pests and allow desired plants to maintain their health. These substances must be regulated and properly used so that they do not become harmful to humans and wildlife.
Pesticides
Plants are up against many different types of pests in the natural world. Other vegetation, rodents, insects, fungus, and bacteria are all considered pests when they are harmful to plants. Pesticides are synthetic organic chemicals used to control weeds in fields and lawns, and unwanted or harmful pests, such as insects and mites that feed on crops. Pesticides are divided into categories according to the target organisms they are designed to control (e.g., insecticides control insects).
Herbicides are by far the most commonly used pesticides in the United States. They range from nonselective to highly selective for control of specific weeds in specific crops, with different products having postemergence, preplant, and preemergence uses. Insecticides are second in usage, and fungicides are third.
Pesticides are a vital input in today's agriculture, protecting food and fiber from damage by insects, weeds, diseases, nematodes, and rodents. U.S. agriculture spends about 8 billion dollars annually on pesticides, which is about 70 percent of all pesticides sold in the country (Aspelin, 1997). It is estimated that each dollar invested in pesticide control returns approximately 4 dollars in crops saved (Pimentel, 1992). Nevertheless, pests still destroy nearly 13 percent of all potential food and fiber crops in the U.S. Farmers' expenditures on pesticides are about 4 – 5 percent of total farm production costs. More than 600 million pounds of pesticides are used each year in the United States to control many different types of weeds, insects, and other pests in a wide variety of agricultural and urban settings. National use of herbicides and insecticides on cropland and pasture has grown from 190 million pounds of active ingredient in 1964, to an estimated 630 million pounds in 1988. Though increased use has resulted in increased crop production and other benefits, concerns about the potential adverse effects of pesticides on the environment and human health have grown steadily.
The dependence of agriculture on chemical pesticides developed over the last 60 years as the agricultural sector shifted from labor-intensive production methods to more capital and chemical intensive production methods. Sixty years ago, most crops were produced largely without the use of chemicals. Insect pests and weeds were controlled by crop rotations, destruction of crop refuse, timing of planting dates to avoid high pest population periods, mechanical weed control, and other farming practices. While these practices are still in use, changes in technology, changes in prices, and government policies resulted in development of today's chemically intensive agriculture.
Usage of conventional pesticides on farms increased from about 400 million pounds (active ingredient) in the 1960s to over 800 million pounds in the late 1970s and early 1980s, primarily due to the widespread adoption of herbicides in corn production (Aspelin, 1997). Since that time, usage has been somewhat lower, ranging from about 700 to 780 million pounds per year. Pesticide usage in agriculture can vary considerably from year to year depending on weather, pest outbreaks, crop acreage, and economic factors such as pesticide prices and crop prices. Whereas the quantity of pesticides used by agriculture has fallen off slightly in recent years, total expenditures on pesticides by farmers are still increasing.
During the 1960s, agricultural pesticide use was dominated by insecticides, accounting for about half of all pesticides used. The quantity of insecticides applied fell as the organochlorines (DDT, aldrin, and toxaphene) were replaced by pyrethroids and other chemicals that required lower application rates. Today, 70 percent of the quantity of pesticides used in agriculture are herbicides. Corn leads all other crops-by a substantial margin-in total pesticide use. However, rice, potatoes, vegetables, and fruits actually use pesticides more intensively than corn and other crops. Minimum tillage practices are being adopted by many farmers; this not only reduces the need for machinery, labor, and energy inputs but also increases agriculture's dependency on pesticides even more. Pesticide use trends can vary markedly from one part of the country to another as farmers respond to local pest problems and as crop production patterns vary.
Pesticides in Water
Even as today's chemically intensive agriculture is partly responsible for providing abundant low-cost supplies of food and fiber, it has also created water quality problems. When the chemical revolution first started there was little concern about environmental consequences. Scientific testing indicated that DDT and other agricultural chemicals were generally not harmful to humans if used as directed. By the mid-1960s, however, there was a growing awareness that some agricultural chemicals were damaging the environment, as well possibly affecting humans. Awareness that agricultural chemicals were not staying on the fields, but were being washed into streams (runoff) and rivers and seeping into ground water (leaching), came about with the development of sensitive chemical testing procedures. Where the pesticides travel depend on different factors including precipication and pesticide solubility. Until the late 1960s these procedures did not become available for organochlorine pesticides—DDT, DDE, aldrin, dieldrin, heptachlor, and chlordane. The DDT problem was known before that time because Rachel Carson's book Silent Spring was released in 1962 and covered the issue, as well as because of identifiable bioaccumulation, resulting in detectable levels in animals high in the food chain.
In many respects, the greatest potential for adverse effects of pesticides is through contamination of the hydrologic system, which supports not only human life but also aquatic life and related food chains. Water is one of the primary means by which pesticides are transported from their application areas to other parts of the environment. Thus, there is potential for movement of pesticides into and through all components of the hydrologic cycle (see Figure 8.4.1.).
Today, pesticide levels in water are monitored routinely. Pesticide residues have been found in ground water, surface water, and rainfall. EPA began to emphasize ground water monitoring for pesticides in 1979 following discovery of 1,2-Dibromo-3-chloropropane (DBCP) and aldicarb in ground water in several states. In 1985, 38 States reported that agricultural activity was a known or suspected source of ground water contamination within their borders (ASIWPCA, 1985). Since then, several Federal and State agencies have developed programs to sample water resources and test for the presence of agricultural chemicals. Results published to date have shown that chemicals used in agricultural production have been found in ground water, sometimes at levels exceeding EPA's drinking water criteria (US EPA, 1990; Hamilton and Shedlock, 1992; Monsanto Agricultural Company, 1990; Kolpin, Burkart, and Thurman, 1994; Barbash et. al., 1999).
Effects of Pesticides on Soil Quality
The capacity of the soil to filter, buffer, degrade, immobilize, and detoxify pesticides is a function or quality of the soil. Soil quality also encompasses the impacts that soil use and management can have on water and air quality, as well as on human and animal health. The presence and bio-availability of pesticides in soil can adversely impact human and animal health, and beneficial plants and soil organisms. Depending on their adsorption, pesticides can move off-site, contaminating surface and groundwater and possibly causing adverse impacts on aquatic ecosystems.
Pesticides in the Atmosphere
Ideally, a pesticide stays in the treated area long enough to produce the desired effect and then degrades into harmless materials. Three primary modes of degradation occur
in soils:
• biological, which is breakdown by micro-organisms
• chemical, which is breakdown by chemical reactions, such as hydrolysis and redox reactions
• photochemical, which is breakdown by ultraviolet or visible light
The rate at which a chemical degrades is expressed as the half-life. The half-life is the amount of time it takes for half of the pesticide to be converted into something else, or its concentration is half of its initial level. The half-life of a pesticide depends on soil type, its formulation, and environmental conditions such as temperature or moisture. Some pesticides are more persistent, meaning they are resistant to breaking down and remain fairly stable in the environment. Other processes that influence the fate of the chemical include plant uptake, soil sorption, leaching, and volatilization (Figure 8.4.2.). If pesticides move off-site via wind—due to wind drift, runoff, or leaching, they are considered to be pollutants. Drift is the movement of a pesticide from the application site by wind or air. When pesticides dissolve in water, they can flow away from application sites in runoff or absorb into the soil through leaching.
The potential for pesticides to move off-site depends on the chemical properties and formulation of the pesticide, soil properties, application rate/method, pesticide persistence, frequency/timing of rainfall or irrigation, and depth to ground water.
The atmosphere is an important component of the hydrologic cycle to consider when assessing the impact of pesticides on the environment. As part of the hydrologic cycle (see Figure 8.5.1), precipitation (rain and snow) replenishes both surface and ground waters. Precipitation cleans the atmosphere of airborne pesticide vapors and particles and deposits them to the earth's surface, including lakes, rivers, and streams. In addition, dry deposition in the form of gaseous vapor and particulate matter also deposits airborne pesticides to the earth's surface. Pesticides in both precipitation and dry deposition can reach surface waters by direct deposition or surface runoff and can reach ground water by infiltration through the soil.
Long-range transport of pesticides can occur over hundreds to thousands of miles. Until the 1960s, atmospheric pollution from pesticide spray drift was generally thought of as a local problem. Long-range movement of long-lived pesticides through the atmosphere was believed to be minimal. The detection of DDT and other organochlorine compounds in Arctic and Antarctic fish and mammals have changed this notion. The atmosphere is now recognized as a major pathway by which pesticides can be transported and deposited in areas sometimes far removed from their sources. Toxaphene, for example, which was used on cotton in the Southern United States and banned in 1982, is still being transported into the Great Lakes region by southerly winds from the Gulf of Mexico. Once deposited on the earth's surface, the pesticide can revolatilize, re-enter the atmosphere, and be transported and deposited downwind repeatedly until it is finally degraded, sometimes over decades. This same process can also occur for the degradation products resulting from chemical or biochemical transformations of pesticides. Some pesticide degradation products are more toxic than the original compound.
Monitoring for pesticides in surface water was frequent in the 1960s and 1970s as studies were conducted that led to the banning of chlorinated hydrocarbon insecticides. Sampling in the 1980s and 1990s found that the four leading herbicides in use during that time—atrazine, metolachlor, alachlor, and cyanazine—were frequently detected in surface waters in agricultural regions (Atrazine in Surface Waters, 1992; Goolsby and Battaglin, 1993; Goolsby, Battaglin, and Thurman, 1993; Larson, Gilliom, and Capel, 1999; Baker and Richards, 1995). Highest levels occurred after planting and during the early part of the growing season. Most of the pesticides commonly used presently and, in the past, have also been found in the atmosphere, including DDT, toxaphene, dieldrin, heptachlor, organophosphorous insecticides, triazine herbicides, alachlor and metolachlor (USGS, 1995). These airborne pesticides return to the earth with rainfall to further contribute to water contamination. A recent report by USGS of a survey of pesticides in the Nation's waters concluded that pesticides were common in surface and shallow ground water in both urban and agricultural areas, but investigators were not able to determine if contamination is lessening or worsening (USGS 1999).
Chemical testing can detect the presence of a pesticide, as well as often measure how much of the pesticide is in the water; however, it cannot identify the source of the pesticide. It is not known what portion of observed residues originate from quasi-point sources within agriculture, such as applicator loading and mixing sites, or from nonagricultural sources. Since agriculture is the largest user of pesticides, it is likely that much of the pesticide residue found in the environment originated from agriculture (Figure 8.4.3). However, a significant, but unknown, portion of the pesticide residue originates from non-agricultural sources. Non-agricultural uses include home, lawn, and garden use; industrial use; pest control in forestry; weed control along roadsides, ditches, railways, and rights-of-way; and pest control by municipalities and local governments, golf courses, and the military.
Concerns about potential risks to human health and the environment resulted in the 1972 amendments to the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), which increased the stringency of health and safety data required to support a pesticide registration. EPA first banned use of some organochlorine pesticides for agricultural purposes in the 1970s and has since imposed use limitations on many other pesticides. The amendments also required that all existing pesticides be reregistered using current health and environmental standards. Chemical companies have responded to these regulatory pressures by marketing new chemicals that are thought to be less harmful to humans and the environment, or less likely to migrate from farm fields to contaminate ground water and surface water.
Pesticide Drift
Pesticide spray drift is the movement of pesticide dust or droplets through the air to any site other than the area intended, at the time of application or soon after. Pesticide droplets are produced by spray nozzles used in application equipment for spraying pesticides on crops, forests, turf, and home gardens. Some other pesticides are formulated as very fine dry particles; these are commonly referred to as dust formulations. Pesticide drift of sprays and dusts can affect people’s health and the environment, as well as damage nearby crops.
Pesticide Health and Environmental Risks
Pesticide drift can pose health risks when sprays and dusts are carried by the wind and deposited on other areas, such as:
- nearby homes, schools, and playgrounds,
- farm workers in adjacent fields,
- wildlife, plants, and streams, as well as other water bodies.
Pesticide Economic Effects
Pesticide drift can cause economic loss, including the following:
- Drift of herbicides can injure some crops. Crops on nearby farms can become unsellable if the drifting pesticide is not registered for use on the crop.
- State and local agencies receive thousands of complaints about drifting pesticides each year and spend substantial resources investigating drift complaints.
Pesticide Toxicity
In human exposure situations, toxicity by pesticides may be divided into three main types, based on the exposure time to the pesticide and how rapidly the toxic symptoms develop. Thus, workplace or environmental exposure may be described as acute, sub-chronic, and chronic.
Acute toxicity occurs from a single incident of exposure (single short-term exposure). The acute toxicity of a pesticide is used for the warning statements on the product label. When a farmer is exposed to a single dose of a pesticide, the incidence is referred to as acute exposure and the effect is called acute toxicity. Acute toxicity refers to how poisonous a pesticide is to an organism after a single short-term exposure. If the exposure is through contact with skin, it would be regarded as an acute dermal exposure event and the toxicity is called acute dermal toxicity. Similarly, acute oral exposure refers to a single dose of a pesticide taken by mouth, and acute inhalation exposure refers to a single dose inhaled. The acute toxicity is used to describe toxic effects that typically appear immediately or within a day—24 hours—of exposure. An active ingredient with a high acute toxicity can be lethal, even when a very small amount is absorbed.
Subchronic toxicity occurs from repeated incidents of exposure over several weeks or months; this is considered intermediate exposure, which is normally less than the lifetime of the exposed organism. The signal words displayed on the product label are selected on the basis of the acute toxicity of the pesticide product. Subchronic toxicity is the ability of a chemical compound to cause toxic health effects for over a year, but less than the lifetime of the exposed organism.
In cases of continuous exposure to a pesticide occurring repeatedly by an individual, the incidence is referred to as chronic exposure. Chronic toxicity occurs from repeated incidents of exposure for many months or years, and it is repeated long-term exposure, sometimes lasting for the entire life of the exposed organism. This effect can be reported as chronic dermal, chronic oral or chronic inhalation toxicity. Chronic toxicity is the ability of a pesticide to cause adverse health effects over an extended period, usually after repeated or continuous exposure, which may last for the entire life of the exposed organism. This type of pesticide toxicity is of concern not only to the general public, but also to those working directly with pesticides, given the potential exposure to pesticides found on/in commodities, water, and the air. It is measured in experimental conditions usually after a period of three months of either continuous or occasional exposure.
A pesticide that has high acute toxicity does not always have high chronic toxicity. Nor will a pesticide with low acute toxicity necessarily have low chronic toxicity. For many active ingredients, the toxic effects from single acute exposure are quite different from those produced by chronic exposure. The small amount of a pesticide that is absorbed from a single exposure is rather insufficient to cause illness, but absorption of the same small amount every day continuously can cause serious chronic illness or even death.
Dose, duration, and exposure issues for delayed toxicity are not comparable to those for chronic exposure. The effects of acute toxicity and chronic toxicity are dose-dependent; the greater the dose, the greater the effect. In characterizing the toxicity of a pesticide, it is evident that information is needed for the single-dose (acute) and the long-term (chronic) effects, including information for exposure of intermediate duration. For example, delayed toxicity may occur many years after exposure to a chemical. A major differentiation is that a delayed toxic reaction is not identical to the chronic adverse effects. In contrast to chronic exposure, which typically refers to continuous exposure to low levels of a toxicant, delayed toxicity can be a result of a single dose or a brief exposure event, producing a permanent effect. Consequently, epidemiological studies are important to the detection of further occurrences of delayed toxicity.
Pesticides and Health
Pesticides are common chemicals used to eliminate a great variety of unwelcome living organisms, particularly in agriculture. They are widely used in agriculture for the purposes of crop protection and in public health to control vector-borne infectious diseases. Because of high biological activity, and, in some cases, long persistence in the environment, pesticides may cause harmful effects to human health and to the environment.
The occurrence of harmful chemicals in the environment has become an issue of great debate in recent decades. Pesticides and other foreign substances in food products and drinking water, along with toxic pollutants in the air, pose an immediate threat to human health; in contrast to other long-acting contaminants gradually build up in the environment and in the human body, causing disease long after first exposure. It is also well known that many pesticides can accumulate in living species causing long-term and chronic effects. However, there are difficulties in defining chronic exposure and disease outcomes, given the existence of a large series of variables of interest, such as lifestyle, occupation, diet preferences, and smoking, all of which must be considered to establish a disease-exposure relationship in the epidemiological investigation.
Chemicals play an important role in the efforts of countries to achieve economic growth and fulfill their development objectives, but, as much as they are vital for ensuring food security and economic growth, incorrect and indiscriminate use can be disastrous both for human health and the environment. In this context, chemicals can have a dual nature; they can be either beneficial or harmful, depending on numerous factors, such as the amounts to which exposure occurs. Improper handling may result in severe acute poisonings; in some cases, adverse health effects may also result from long-term, low-level exposures.
As a result of widespread diffusion of pesticides, a great part of the population may be exposed to pesticides due to occupation. Several groups of people, characterized by quite different patterns and degree of exposure, face the risk of adverse effects. Occupational exposure typically occurs in workers involved in the manufacture of pesticides and among specific users in public health such as exterminators of house pests. In the agricultural sector, exposure to pesticides typically occurs among farmers and professional applicators of pesticides. Regarding the general population, individuals may be exposed to pesticide residues in food and drinking water on a daily basis or to pesticide drift in residential areas close to spraying areas. Although there has been emphasis on nonchemical pest management strategies, EPA regulation of pesticides has been the strongest measure to keep humans, animals, plants, and the environment protected from harmful pesticide chemicals.
Dig Deeper
Attributions
"Environmental Indicators of Pesticide Leaching and Runoff from Farm Fields" by R Kellogg, et al., United States Department of Agriculture, Natural Resources Conservation Service, is in the Public Domain.
"Farmers’ Exposure to Pesticides: Toxicity Types and Ways of Prevention" by C. Damalas and S. Koutroubas is licensed under CC BY 4.0.
Inanimate Life by George M. Briggs is licensed under a CC BY-SA 4.0, except where otherwise noted.
Introduction to Pesticide Drift by the Environmental Protection Agency is in the Public Domain.
"Pesticides in the Atmosphere" by the United States Geological Survey is in the Public Domain.
Pesticides in the Hydrologic System by the United States Geological Survey is in the Public Domain.
"Soil Quality Concerns: Pesticides" by the United States Department of Agriculture Natural Resources Conservation Service is in the Public Domain.
References
Aspelin, Arnold L. 1997. Pesticides Industry Sales and Usage: 1994 and 1995 Market Estimates. Office of Pesticide Programs, Environmental Protection Agency, Washington, DC, 35 pages.
Pimentel, David, et. al.. November 1992. Environmental and Economic Costs of Pesticide Use. BioScience 42(10):750-760.
Aspelin, Arnold L. 1997. Pesticides Industry Sales and Usage: 1994 and 1995 Market Estimates. Office of Pesticide Programs, Environmental Protection Agency, Washington, DC, 35 pages.
Association of State and Interstate Water Pollution control Administrators. America's Clean Water: The States' Nonpoint Source Assessment 1985. Washington, DC 1985. 24p.
US Environmental Protection Agency, National Pesticide Survey Project Summary, Fall 1990,10 pp.
Hamilton, Pixie A. and Robert J. Shedlock. 1992. Are Fertilizers and Pesticides in the Ground Water?: A Case Study of the Delmarva Peninsula. U S Geological survey Circular 1080. US Government Printing Office.
Monsanto Agricultural Company, The National Alachlor Well Water Survey (NAWWS): Data Summary, Monsanto Technical Bulletin, July 1990.
Kolpin, Dana W., Michael R. Burkart, and E. Michael Thurman. 1994. Herbicides and Nitrate in Near-Surface Aquifers in the Midcontinental United States, 1991. USGS Water Supply Paper 2413, US Government Printing Office. 34 pages.
Barbash, Jack E., Gail P. Thelin, Dana W. Kolpin, and Robert J. Gilliom. 1999. Distribution of Major Herbicides in Ground Water of the United States. USGS Water Resources Investigations Report 98-4245. US Government Printing Office, 57 pages.
Atrazine in Surface Waters: A report of the Atrazine Task Group to the Working Group on Water Quality. April 1992. USDA. 13 pages.
Goolsby, D.A., and Battaglin, W.A. 1993. Occurrence, distribution, and transport of agricultural chemicals in surface waters of the Midwestern United States, in Goolsby, D.A., and others, Eds, Selected papers on agricultural chemicals in water resources of the Mid-continental United States. U.S. Geological Survey Pen-file Report 93-418, p. 1-24.
Goolsby, Donald A., William A. Battaglin, and E. Michael Thurman. 1993. Occurrence and Transport of Agricultural Chemicals in the Mississippi River Basin, July through August 1993. U.S. Geological Survey Circular 1120-C. U. S. Government Printing Office. 22 pages.
Larson, Steven J., Robert J. Gilliom, and Paul D. Capel. 1999. Pesticides in Streams of the United States--Initial Results from the National Water-Quality Assessment Program. US Geological Survey, Water Resources Investigations Report 98-4222, US Government Printing Office, 92 pages.
Baker, David B. and R. Peter Richards. forthcoming, 1995. Herbicides in Ohio's Drinking Water: Risk Analysis, Reduction, and Communication. Proceedings of the Fourth National Conference on Pesticides: New Directions in Pesticide Research, Development, and Policy, Viriginia Water Resources Center, VPISU, Blacksburg, VA. 23 pages.
US Geological Survey, National Water Quality Assessment Program. 1995. Pesticides in the Atmosphere. US Department of Interior. 4 pages.
U.S. Geological Survey, 1999, The Quality of Our Nation's Waters--Nutrients and Pesticides: U.S. Geological Survey Circular 1225, 82 pages.