Agricultural health

BACKGROUND

Agricultural health is the study of environmental, occupational, dietary, and genetic factors that may affect the health of those who work or live in agricultural environments, including farmers (i.e., farm owners), farm families, and farm workers.

Agricultural workers may be subjected to health risks from exposure to a number of health hazards, including pesticides, fumes, toxic chemicals, fertilizers, dust, excessive sunlight, heat, and dangerous machinery.

As a group, agricultural workers have a higher risk of asthma and other respiratory diseases, certain cancers, spontaneous abortions (miscarriages), and neurological diseases.

The ongoing Agricultural Health Study (AHS) is being conducted by the National Cancer Institute (NCI), the National Institute of Environmental Health Sciences (NIEHS), and the U.S. Environmental Protection Agency (EPA). Many organizations are collaborating in the compilation of data that will provide needed insight into agricultural health.

Exposure to pesticides is a major focus of researchers in agricultural health. Pesticide exposure may occur through skin contact, inhalation, or contamination of groundwater. Pesticide exposure carries an increased risk of many types of cancer and neurological diseases.

Water used for drinking may become polluted by contaminated groundwater; possible contaminants include infectious diseases, pesticides, or other toxins.

Operation of farm equipment, such as tractors, is a common source of injury to farm workers. The risk of injury rises when the equipment does not have adequate safety features, such as tractor rollover bars; the risk also rises if the operator is young and/or inexperienced. Tractor injuries are more frequent on farms that are located on steep terrain because the risk of overturning is greater.

Aquaculture (also known as fish farming) has the same occupational risks as land farming, with the additional risk of injury from aeration equipment; aeration equipment supplies oxygen to ponds.

Livestock, such as cattle and swine, may also transmit diseases to farmers and their families. One animal-to-human transmissible disease is swine flu, a type of influenza that swine (pigs) may contract.

TECHNIQUE

Agricultural health organizations: In the United States, the National Institutes of Health (NIH) is conducting a major research project on agricultural health. This study, known as the Agricultural Health Study (AHS), began in 1993. It is being conducted with the collaboration of a number of groups, including the National Cancer Institute (NCI), the National Institute of Environmental Health Sciences (NIEHS), the U.S. Environmental Protection Agency (EPA), and the University of Iowa and Battelle Centers for Public Health Research and Evaluation. According to the NIH, more than 89,000 individuals are participating in this study.

European Foundation Centre: The European Foundation Centre, located in Brussels, Belgium, has published a document, European Perspectives on Global Health: A Policy Glossary, which addresses agricultural health from a global perspective (Europe, the Americas, and Africa). The document was prepared with the collaboration of the German Overseas Institute (Hamburg, Germany), now known as the German Institute of Global and Area Studies (GIGA); the World Health Organization (WHO; Geneva, Switzerland); Markerere Medical School (Uganda, East Africa); the Irish Forum for Global Health (Dublin, Ireland); Escola Nacional de Sa©de P©blica (Rio de Janeiro, Brazil); the People's Health Movement (Cape Town, South Africa); and the Swedish National Institute of Public Health (©stersund, Sweden). The following foundations are also collaborating in the study: Calouste Gulbenkian Foundation (Funda©©o Calouste Gulbenkian; Lisbon, Portugal), the Nuffield Trust for Research and Policy Studies in Health Services (London, England), Riksbankens Jubileumsfond (Stockholm, Sweden), and the Universal Education Foundation (Woodland Park, Colo.).

National Institutes of Health (NIH): The NIH is the United States' medical research agency. It provides direction and financial support to researchers throughout the United States and around the world through 37 institutes and centers. The NIH focuses on the health of children and teenagers, women', men', minorities, and seniors', as well as on wellness/lifestyle issues.

National Cancer Institute (NCI): The NCI is the U.S. federal government's principal agency for cancer research and training. The National Cancer Act of 1971 broadened the scope and responsibilities of the NCI through the creation of the National Cancer Program. The NCI coordinates this program, which conducts and supports research, health information dissemination, training, and other programs with respect to the cause, diagnosis, prevention, and treatment of cancer.

The NCI also supports rehabilitation from cancer as well as the continuing care of cancer patients and their families. In addition, the NCI supports and plans research projects around the world,; conducts research in its own laboratories and clinics; supports cancer education programs supports a national network of cancer centers; collaborates with organizations engaged in cancer research education; collects and disseminates information on cancer; and supports the construction of facilities necessary for cancer research.

National Institute of Environmental Health Sciences (NIEHS): The NIEHS is one of 27 research institutes and centers that comprise the NIH. The mission of the NIEHS is "to reduce the burden of human illness and disability by understanding how the environment influences the development and progression of human disease."

Environmental Protection Agency (EPA): The EPA is involved in the United States' environmental science, research, education, and assessment efforts. Its mission is "to protect human health and the environment. Since 1970, the EPA has been working for a cleaner, healthier environment for the American people."

European Foundation Centre (EFC; Brussels, Belgium): The EFC is an international association of foundations and corporate funders that states that its mission is "dedicated to creating an enabling legal and fiscal environment for foundations, documenting the foundation landscape, strengthening the infrastructure of the sector, and promoting collaboration, both among foundations and between foundations and other actors, to advance the public good in Europe and beyond." About 90% of the EFC's members are spread across Europe; the remaining members are based in Asia, North America, and South America.

German Institute of Global and Area Studies (GIGA; Hamburg, Germany): The GIGA reports that it is both the largest German research institute and one of the largest European research institutes for area studies and comparative area studies. The GIGA's research focuses on political, economic, and social developments in Africa, Asia, Latin America, North Africa, and the Near and Middle East.

World Health Organization (WHO; Geneva, Switzerland): The WHO is a specialized agency of the United Nations that acts as a coordinating authority for international public health. The WHO states that its objective is "the attainment by all peoples of the highest possible level of health."

Agricultural Health Study (AHS): The AHS is being conducted by the National Cancer Institute (NCI), the National Institute of Environmental Health Sciences (NIEHS), and the Environmental Protection Agency (EPA). The AHS includes about 50,000 farmers, 32,000 farmer wives, 2,000 nursery workers, and 5,000 commercial pesticide workers. Children of farm families are also included in some of the studies.

Information is collected from farm families via questionnaires and follow-up telephone interviews. Participants are asked to provide a buccal cell DNA sample for future analyses of genetic and environmental interactions, as well as information on demographic factors, medical characteristics, smoking history, alcohol use, and lifetime pesticide use (including 50 specific compounds). A total of 33,450 farmers (about 68%) and 23,775 spouses (about 75% of spouses) completed the first AHS follow-up interview. About 40% of participants provided buccal cell DNA samples.

The researchers also use state cancer registries and vital records to monitor cancer incidence and mortality.

The AHS reports that farmers in many countries, including the United States, have lower overall death rates for heart disease and cancers of the lung, esophagus, bladder, and colon. According to the AHS, these results may be due to dietary factors, lower smoking rates, and physically active lifestyles.

In contrast to lower death rates from heart disease and certain cancers, the rates for some health conditions (such as asthma, miscarriage, and neurological diseases) seem to be higher among agricultural workers than they are for the general population. The AHS suggests that this may be related to agricultural exposure to pesticides and other toxic substances. In addition, farming communities often have higher rates of cancers of the skin, lip, stomach, brain, and prostate; they also have higher rates of leukemia, non-Hodgkin's lymphoma (a cancer of the lymphatic system), multiple myeloma (a form of bone cancer), and soft tissue sarcomas (cancers of bone, cartilage, or fat). The rates for several of these tumors (i.e., non-Hodgkin's lymphoma, multiple myeloma, skin cancer, brain cancer, and prostate cancer) also appear to be increasing in the general population.

Although no one set of risk factors explains the higher cancer rates, the AHS states that the range of environmental exposures in the agricultural community is concerning. Farm workers and family members may be exposed to substances such as pesticides, engine exhausts, solvents, dusts, animal viruses, fertilizers, fuels, and specific microbes that may account for these elevated rates. However, available human studies have not determined which of these factors are linked to which cancers.

Complementing the AHS is a study of cancer risk among migrant and seasonal farm workers; this study was conducted by the Cancer Registry of Central California (University of California, San Francisco). It concluded that both migrant and nonmigrant workers in California, as well as in the rest of the United States, may have an increased risk of developing many forms of cancer compared to the general population. They found an elevated risk for lymphoma, leukemia, prostate cancer, brain cancer, and stomach cancer among these populations. They added that specific pesticides may be associated with this increased risk.

Groundwater contamination: Groundwater contamination impacts agricultural health, particularly in developing nations. A study of groundwater contamination in Manila, Bangkok, and Jakarta found that sewer leakage of human waste was a major source of contamination. The contaminants studied included nitrate (NO3-), nitrite (NO2-), and ammonium (NH4+). The characteristics of the nutrient contamination differed depending on the agricultural land use pattern. For example, high nitrate contamination was observed in the dry fields of Jakarta, while relatively lower levels of nutrients, consisting mainly of ammonium, were detected in Bangkok's paddy fields.

Groundwater contamination from pesticides is another agricultural health concern. Resistance to prevention of groundwater contamination, particularly in developing nations, occurs for a number of reasons: (1) the use of human waste ("night soil") for fertilization is common, and farmers are reluctant to change this traditional practice, which improves their crops at no cost; (2) sewage systems are limited or nonexistent, and upgrading these facilities is costly; and (3) educating farmers in these regions requires funding and dedicated personnel.

Occupational hazards: Tractors are responsible for a large number of fatal and nonfatal agricultural injuries. A lack of safety features, such as roll bars, increases the risk. Other farm equipment (such as mowers, trimmers, and combines) may expose farm workers to injuries. Farm animals, such as horses and oxen, may cause physical injuries to farm workers and may expose workers to diseases such as swine flu. (Swine flu is a type of influenza that infects pigs and may be transmitted to humans.)

Farmers may be unaware of the increased risk of injury due to inadequate safety equipment. Even in cases where the increased risk is known, farmers may be resistant to improving their equipment because of economic factors.

Aquaculture (also known as fish farming) has many of the same hazards as other types of farming; however, additional hazards are associated with maintaining the water environment and with nighttime work. A research project conducted by four U.S. universities and headed by the University of Kentucky identified risk factors and proposed simple solutions to those risks. A partial list of their proposed includes: Equipping tractors with rollover protective structures to reduce the risk of serious injury in the event that the equipment overturns. In addition, climbing a feed bin to open and close a feeding hatch exposes a worker to the risk of falling; this risk may be eliminated by using a pull-cable at ground level. Simple solutions were also presented to reduce injuries from large pond aerators, which mechanically dissolve oxygen into the water. Replacing metal paddles on hatchery troughs with plastic paddles reduces the risk of lacerations (cuts) and entanglement injuries if a worker's hair or clothing becomes caught in the paddles. Another simple solution to prevent entanglements in aerators that are operated by farm tractor power take-off shafts is to use electrically powered bubble aerators instead. These bubble aerators are safer than electrically powered paddle aerators because workers are shielded from moving parts.

Pesticides: Pesticide exposure is common among farm workers. Organophosphates are the basis of many insecticides; they poison insects, birds, amphibians, and mammals by causing the loss of the acetylcholinesterase enzyme (AChE) at nerve endings (through the action of phosphorus and halide ions). The result is an excess of acetylcholine (ACh), which is the impulse-transmitting substance in nerve endings. When the normal transmission of nerve impulses gets out of control, it disrupts communication between muscle cells, glandular cells, and autonomic ganglia, and within the central nervous system itself. The loss of a functioning nervous system often causes death.

Some evidence suggests that pesticides may contribute to cellular damage caused by oxidative stress. Researchers found that the white blood cells in orchard workers who were exposed to pesticides were significantly more damaged from oxidative stress than in individuals who were not exposed to pesticides.

Since the banning of organochlorine insecticides in the United States and Europe in the 1970s and 1980s, organophosphate insecticides have become the most widely used insecticides available today. (Organochlorines are chlorine-containing hydrocarbons. A well-known organochlorine is DDT.) Organophosphates kill pests in the same way as organochlorines; they may also cause human disease. The risk of toxicity increases with repeated exposure. Organophosphates were once considered to be biodegradable and safer than organochlorines; however, they have been found to be toxic and persistent in the environment. When they degrade, toxic metabolites may form.

Pesticides can spread through the environment by various means. For example, they may migrate into water supplies from runoff in agricultural fields, they may evaporate and drift in the atmosphere, or they may be consumed by animals and fish and then spread in various food chains.

In California, courts have addressed the problem of evaporated and wind-blown pesticides. A jury recently found that the unintended contamination of organic crops caused by pesticides (chlorpyrifos, diazinon, and dimethoate) from nearby fields violated the rights of organic-crop growers. Neither the state Department of Pesticide Regulation (DPR) nor the EPA has regulated this pesticide drift.

In a number of cases, less-toxic or nontoxic alternatives to a specific pesticide are available; however, farmers may shun their use because these chemicals may be (or are perceived to be) less effective. Alternatives to pesticides include rotating crops; growing a large variety of plants (polyculture); introducing sterile male insects to interfere with breeding; using trap crops, which lure insects away from the primary crop; and sterilizing the soil with steam.

THEORY/EVIDENCE

Cancer: A study of cancer risk among migrant and seasonal farm workers was conducted by the Cancer Registry of Central California (University of California, San Francisco). The authors noted that this study was hampered by the transitory nature of the work, high poverty levels, and lack of legal documentation for the workers. However, researchers concluded that both migrant and nonmigrant workers in California, as well as in the rest of the United States, appear to have an increased risk for many forms of cancer, including lymphoma, leukemia, prostate cancer, brain cancer, and stomach cancer, compared to the general population, Specific pesticides may also be associated with this altered risk.

The ongoing Agricultural Health Study (AHS) noted that farming communities often have higher rates of cancers of the skin, lip, stomach, brain, and prostate than the general population; they also have higher rates of leukemia, non-Hodgkin's lymphoma, multiple myeloma, and soft tissue sarcomas.

Groundwater contamination: Research on water system contamination in Southeast Asia suggests that the leakage of human waste from sewers was the major source of nutrient contaminants (nitrate [NO3-], nitrite [NO2-] and ammonium [NH4+]) in water. The authors stated that the level of contaminants was not excessive and that drinking groundwater presented a low risk to human health. However, they also cautioned that the increased nitrogen load and increased per-capita gross domestic product (GDP) in these developing areas may lead to increases in contamination levels in the future. They recommended continuous monitoring and management of the groundwater systems to minimize groundwater pollution in Southeast Asia. In addition, the researchers recommended that areas with similar cultural and geographic settings around the world be monitored.

Occupational injuries: Colorado State University conducted a review of 23,484 tractor-related injury claims from 1992 through 2004. The goals of this study were to (1) identify and describe tractor-related injuries, (2) assess medical and indemnity (insurance) costs associated with these injuries, and (3) determine factors that contributed to those injuries. They found that 642 claims were tractor-related. More than 60% of these tractor-related claims involved sprains/strains and contusions. A total of 21% of tractor-related claims were associated with the worker mounting or dismounting a tractor, and 10% were associated with the worker falling, jumping, or slipping off a tractor. Of all the claims linked to tractor mounting or dismounting, 35% involved the ankle and 15% involved the knee.

About 75% of the claims were medically related, with no insurance claims filed for equipment damage. The average medical claim cost was $319, and the average medical-plus-indemnity claim cost was $335. Claim costs associated with tractor-overturn injuries were higher than tractor-related injury claims in general. Inasmuch as a large percentage of tractor-related injury claims were linked to tractor mounting and dismounting, the authors suggested that tractor-design criteria related to these actions should be improved to reduce this risk.

A major source of both fatal and nonfatal injuries to farm children is the use of tractors and machinery. To address this problem and to adopt a "greener" approach to farming, dairy farmers in the upper Midwest and Northeast have adopted the technique called management-intensive grazing (MIG). MIG involves environmental modification; it decreases the reliance on and use of tractors and machinery (both of which are major sources of fatal and nonfatal injuries to children). An online survey specifically focused on the most hazardous farm worksite exposures for children based on injury surveillance data of tractors, machinery, large animals, heights, and water sources. Data were collected from 68 Wisconsin agricultural extension agents; these agents were knowledgeable about dairy operations in their counties in regard to benefits to children involved in MIG operations. Responses were received from 31 agents (a 46% response rate). The results of the survey suggested that children involved in MIG operations may have less exposure to farm machinery. However, the respondents often noted that they thought these children did have an increased overall worksite exposure, as well as specific increased exposure to all-terrain vehicles and animals. The authors concluded that further study was necessary to determine if a MIG system actually reduced the risk of injury to farm children.

The U.S. Department of Agriculture (USDA) reviewed their 2002 census of fatal occupational injuries data and found that six states within or near the Appalachian Mountains had the highest rates of agricultural tractor-overturn deaths in the nation. Regional geological and geographic data were examined to identify topographic features within the six states. (Topography is a detailed graph of the elevation within a given area.) Statistical analysis indicated that the majority of farms in these states were located on steep slopes and were small-acreage livestock facilities, their annual sales revenue was less than $10,000 a year, their total equipment was valued at less than $20,000, most tractors did not have rollover protective structures (ROPS), and the equipment operators worked at off-farm jobs more than 200 days each year (thus, they may have been less skilled at operating the equipment).

Infectious diseases: Human contact with domestic animals increases the risk of contracting an infectious disease. Currently, media attention has focused on swine flu, which is transmitted by infected pigs, and bovine spongiform encephalopathy (BSE), or mad cow disease, which is transmitted by infected cows. Bovine spongiform encephalopathy is a fatal neurodegenerative disorder of humans and animals. Swine flu is much more widespread and causes symptoms ranging from minor discomfort to death.

The University of Iowa College of Public Health (Iowa City, Iowa) conducted a two-year prospective study of influenza virus. Researchers found that swine workers and their non-swine-exposed spouses have a higher risk of influenza virus infections than the general public.

A literature review by the University of Western Ontario noted that transmission of BSE between individuals is very uncommon and that the illness behaves more like cancer than an infectious disease. Researchers believe that BSE is contracted through ingestion of infected brain or spinal cord tissue.

Pesticides: Demonstrating the health effects of pesticides may be difficult and is subject to debate. Some experts argue that no chemical is completely safe and that the benefits of some pesticides outweigh their negative impacts. Research and government policies have focused on short-term and heavy exposure; however, long-term exposure to pesticides in smaller doses has not been well studied. Some opponents of these chemicals have argued that small-dose exposures may be accumulative, that pesticides interact with other chemicals to produce increased toxicity, and that pesticides may disrupt complex processes in the body.

There are established guidelines for most chemicals (including pesticides) for how much exposure should be considered dangerous. Even within prescribed limits, the chemicals in pesticides have been found to be toxic; this finding suggests that the standards need re-examination.

Each region of the gastrointestinal tract has its own characteristics, which may affect the absorption of a pesticide. If a pesticide enters the bloodstream, its absorption will differ depending on how it is processed by various tissues and organs.

Pesticides may accumulate in body tissues, proteins, fat, and bones, making it difficult to determine the total amount of exposure. This volume of absorbed pesticides is a critical factor in making treatment decisions. In most cases handled by physicians, the information provided about exposure is incomplete and vague.

Respiratory disease: Many agricultural workers have an increased risk of respiratory disease. One of these at-risk groups is poultry workers. The dust in poultry barns contains endotoxins, which are toxic, disease-causing substances produced by bacteria. Currently, studies of endotoxins are under way using a device called the Marple cascade impactor; it filters the dust in poultry barns so that it can be analyzed. After the analysis is complete, researchers will be able to work on methods to reduce this toxic risk to poultry workers.

Researchers conducted a study of 533 children ages 6-13 who were living in an agricultural community in rural Saskatchewan, Canada. The following information was collected about each child: history of asthma or respiratory symptoms (cough, phlegm, or wheeze); the location of the child's home; and exposure to farming activities, including haying, harvesting, moving, or playing with hay bales; feeding livestock; cleaning or playing in barns; cleaning pens; and emptying or filling grain bins. The prevalence of asthma in the children was 18.8%, while that of respiratory symptoms was 39.8%; these percentages were the same for children who lived on farms and for those who did not live on farms. Children who were exposed to emptying and filling of grain bins had a higher risk of asthma, while those who played on or near hay bales or who cleaned animal pens had an increased risk of respiratory infections. The authors concluded that certain farming activities that were associated with dust and animals should be avoided; they appeared to be risk factors for asthma and respiratory symptoms in children.

HEALTH IMPACT/SAFETY

Compared to the general population, people living in agricultural areas are at increased risk of developing respiratory disease, certain types of cancer, and physical injury (i.e., from a tractor overturn). Exposure to pesticides, fumes, fertilizers, dust, solvents, animal viruses, specific microbes, excessive sunlight, and heat are often experienced by farm workers.

FUTURE RESEARCH OR APPLICATIONS

Data from the Agricultural Health Study (AHS), an ongoing, nationwide study of agricultural health that began in 1993, are expected to help many organizations in the United States and around the world improve their agricultural health standards. They will also help to promote research on specific topics, such as why agricultural workers are susceptible to certain types of cancer.

The health risks of current pesticides in use for agricultural purposes and the development of less-toxic pesticides (as well as pesticide alternatives) will continue to be a major focus of agricultural health research.

Fish farming (also known as aquaculture) is expanding rapidly around the world; therefore, it is expected that the amount of research in this field will increase as well.

As developing nations progress economically, they are expected to pay more attention to environmental factors, both in urban and rural areas. International organizations, such as the World Health Organization (WHO), are also expected to exert pressure on developing nations to improve their agricultural health standards.

AUTHOR INFORMATION

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

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