To many people, the words "rural life" conjure images of pastoral landscapes and farmers reaping the earth's bounty. The reality is, however, that agrarian systems present their own distinct hazards and rural communities face specific environmental health risks. The Environmental Health Sciences Research Center (EHSRC) at the University of Iowa in Iowa City is the only NIEHS center to focus primarily on rural environmental exposures and the effects that such exposures have on human health.
Most of Iowa is rural; of the 99 counties in Iowa, 88 are rural, and agriculture remains the primary industry. Thus, says James Merchant, a professor of preventive and internal medicine and the center director, it makes sense that this particular center emphasizes rural environmental health. Rural and agricultural exposures are viewed from several aspects, as reflected in the center's diverse research cores: cancer, pulmonary biology, occupational health, environmental assessment and control, and genetics and reproductive biology. The center also supports an administrative core and a community outreach and education core.
Agricultural Health Study
In the 1992 agricultural census, there were about 96,000 farms in Iowa, says Charles Lynch, a professor of preventive medicine and director of the cancer research core. About 40% of Iowa's population live in rural communities. Among the rural population, environmental cancer risks may include exposures to pesticides, chemical solvents, and excessive sunlight, among other hazards. Cancers of particular concern include non-Hodgkin's lymphoma, leukemia, and cancers of the prostate, stomach, and brain.
To assess the environmental cancer risks among rural populations, the center is taking part in a prospective cohort study called the Agricultural Health Study. This study is funded by the National Cancer Institute with assistance from the NIEHS and the EPA. The study began in 1992, with participants being drawn from Iowa and North Carolina. To date, 90,000 people have been enrolled in the study; of these, 58,500 reside in Iowa. Although the study's primary focus is cancer, Lynch indicates that the data could be applied to other disease research. "In time, this study will give us a nice opportunity to look at these exposures as they relate to causes of death and to cancer incidence," he says. "Additionally, there's an opportunity, we believe, to link our cohort to [other disease] database systems." Lynch also indicates that the center is in the early stages of exploring whether the Agricultural Health Study data could be linked to the Iowa birth defects registry. If so, the data may reveal relationships between environmental exposures and adverse reproductive outcomes. "The study will continue for many years, and it should give us good information that relates agricultural exposures to chronic disease," says Lynch. "That type of study is sorely needed, not only nationally . . . but internationally as well."
Phytoremediation
Few terms evoke the concept of urban decay as effectively as "brownfield," defined by the EPA as abandoned, idle, or underused industrial and commercial facilities where expansion or redevelopment is confounded by real or perceived environmental contamination. However, Jerald Schnoor, a professor of civil and environmental engineering and director of the environmental assessment and control research core, notes that the term can apply to rural areas, albeit with a twist on underlying causes; in rural areas, pesticide overuse and overfarming without allowing fields to recover can render land unproductive or unusable. For agricultural brownfields, phytoremediation, a biological process that uses plants to repair environmental damage, can be useful in two ways: first, it enhances bacterial activity in the rhizosphere, or soil zone surrounding the roots of a plant, and second, it actually draws contaminants from the soil into the plants.
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It's a dusty job, but someone has to do it. EHSRC researchers are investigating diseases such as toxic organic dust syndrome, caused by breathing dusts from moldy plant material, including grain, silage, and hay.
Photo credit: Kelley Donham |
Schnoor has conducted seminal research on phytoremediation. Early research by him and his colleagues illustrates the second utility by showing that hybrid poplar trees can remove agricultural chemicals from soil and water. Schnoor and colleagues planted hybrid poplar trees to remove nutrients from agricultural runoff. To their surprise, certain agricultural chemicals were removed as well. "We noticed that atrazine, alachlor, and some of the commonly used herbicides were decreasing in the groundwater as it ran through poplar tree plantations along the edges of the streams," Schoor recalls. "We didn't know why that was or what could be the reason, because normally people don't think of plants as treating organic chemicals." This finding prompted a long line of investigations, eventually proving that poplars could pick up atrazine and other agricultural chemicals [see EHP 103(12):1106 (1995)].
Schnoor notes that the proof of this ability was mostly grounded in lab work, but field work demonstrates that these findings are sound. For example, at one agricultural cooperative, years of mixing fertilizers and herbicides had left the site barren of plant life. Despite soil levels of atrazine of 140 parts per million and ammonia levels of 1,500 parts per million, the researchers were able to establish poplar trees and show that the trees degraded the contaminants. "It was a good thing . . . because if the state had decided to do a removal action--that is, to dig up these toxic soils--the agricultural cooperative would have gone bankrupt," states Schnoor. "Instead, for a much lower cost, we were able to create something that's aesthetically pleasing, and change what amounted to an agricultural brownfield into an active treatment by using hybrid poplars."
Rural Lung Disease
Despite the lack of smog, rural areas are not without environmental exposures that have implications for pulmonary health. "In terms of rural and agricultural lung disease, we have some very unique exposures," says David Schwartz, a professor of internal and preventive medicine and director of the pulmonary biology research core. These unique exposures include what is collectively referred to as organic dust, composed of bacteria, fungi, animal proteins, livestock fecal organisms, and mites, insects, and other arthropods. Owing to these exposures, agricultural workers and other rural residents appear to be at higher risk of developing asthma, bronchitis, and other forms of airway disease, he says.
"There's a variety of components of organic dust and these can cause allergic or nonallergic lung diseases," explains Peter Thorne, an associate professor of preventive medicine and an investigator in the pulmonary biology research core. Farm workers and families encounter these components through a variety of tasks associated with agriculture. Correspondingly, each of these tasks is associated with a different lung disease.
For example, one of the more prevalent lung diseases is organic toxic dust syndrome. Organic dust often contains endotoxin, a lipopolysaccharide from the cell wall of Gram-negative bacteria. Organic dust exposure is virtually unavoidable for many agricultural workers because their daily tasks bring them into contact with livestock amd stored grain in confined spaces. This dust is also brought into homes on the clothes of farm workers. When endotoxin is inhaled, it sets off a onetwo punch in the lung, says Schwartz. The first hit involves the recruitment of polymorphonuclear leukocytes to the lung. These cells surround the alveoli and deep airways, inducing inflammation and airflow obstruction. The second hit is delivered when inflammatory cells release cytokines and chemokines, prolonging the inflammatory response. Although the physiological airway response to endotoxin is reversible, Schwartz and his colleagues suspect that this response may play a role in permanent lung damage. However, the relationship between endotoxin and chronic airway disease has not been definitively explained, cautions Schwartz. "We don't know what causes the scarring and damage to the lung, but we think that the persistence of the inflammatory response results in the initiation and production of growth factors that might end up being very important in terms of the fibrotic response in the lungs," he says.
Outreach in the Community and Beyond
As at other NIEHS centers, work at the Iowa EHSRC touches on both local and international concerns. "Our community outreach and education program is really [focused on] two components," says Merchant. "One is Iowa and the Midwest--and we do consider our center to be a regional center--and the other is the international part of it."
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Farm wisdom. As part of the 1998 Environmental Health Sciences Institute for Rural Youth, investigator Craig Just and students sampled water from a stream adjacent to cornfields near Amana, Iowa, for agricultural contaminants.
Photo credit: Wayne Johnson |
Locally, the center has a special focus on children. In the education arena, the center sponsors the Environmental Health Sciences Institute for Rural Youth, through which high school students participate in an intensive week-long summer course in environmental health sciences at the university. The center plans to add a teacher education component to the institute to provide similar training for science teachers. In the environmental exposures arena, the center is involved in a clinical intervention study of childhood asthma. This study is funded through a recently received Specialized Center of Research grant. Schwartz, who oversees this grant, explains that through this study investigators hope to determine whether reducing exposure to endotoxin and other airborne agents has an effect on childhood asthma morbidity.
Internationally, the center has taken part in several projects in eastern Europe. For example, in response to some areas of eastern Europe where heavy metals have been accumulating in the soil for more than 50 years, Schnoor and his colleagues developed integrated assessment models to examine whether regional agriculture might pose a threat to human health. They found that gardening in these areas was generally safe, but discovered several "hot spots" where it would be inadvisable to grow garden produce for human consumption. Schnoor notes that the situation illustrates the link between a region's economy and its ability to affect environmental health policy changes; discouraging people from eating their garden produce is difficult when other food supplies are unavailable.
Expansion
Investigators are careful to point out that environmental exposures do not necessarily translate to disease. "We have been very perplexed by the fact that, of the people who get exposed [to endotoxin], only a percentage of them actually develop disease," says Schwartz. A promising explanation for this discrepancy may lie in an individual's genes, he says. The need for research on these links reflects the growing importance of molecular biology and genetics in the center's structure. Recently, the center established the genetics and reproductive biology core. "This new core represents an area of growth for the center, but one we're convinced is extremely important, particularly with regard to the Environmental Genome Project," says Merchant. "We feel that with our cohorts and our health registries, as well as our environmental registries, the University of Iowa is well positioned to do more work in this area."
The center's pilot grant program provides further room for growth. "The purpose of our pilot grant program is to provide initial support primarily for junior investigators to establish new lines of research," says Thorne, who administers this program. "We hope to stimulate them to come from other disciplines and apply their expertise to environmental health research." The program also serves to facilitate exploration of innovative directions for more established investigators, he adds. The center has commited approximately 12% of its budget to the program, and has funded 48 pilot grants in seven years. One of the goals of the program is to promote research that is seminal so that investigators can apply for further grants to establish full projects. As proof of success, Thorne points to the fact that from the first 40 pilot grants, a further $20 million in grant support has arisen. He says, "It's a good investment in future research."
Julia Barrett
Last Updated: March 1, 1999