April 6, 2007

The Agricultural Health Study (AHS) is the largest, most comprehensive study of agricultural health conducted in the United States. Almost 90,000 people are participating in the Agricultural Health Study — about 31,000 from North Carolina and 59,000 from Iowa. Participants include certified private pesticide applicators (farmers) and their spouses in North Carolina and Iowa and certified commercial pesticide applicators (5,000) in Iowa only.

Another important feature of the Agricultural Health Study is that it is one of the largest health studies of rural women ever conducted. About 3% of pesticide applicators in the study are women (1,359). Over half of the farmers' spouses are active in farm work, including mixing and applying pesticides.

The credibility of this study and the resulting research findings are high. AHS results were first released in late 2005 and new information was released in late 2006 and March 2007. The study will continue for at least another 10 years. Some individuals have been participating in the study for more than 14 years.

General Health Status of Agricultural Applicators

Previous studies of agricultural health indicated that farmers are healthier than the general population in some respects. For example, they live longer and are less likely to die from heart disease. Farmers are less likely to die of some cancers such as lung, esophagus, bladder and colon, probably because farmers are more physically active and less likely to smoke. For example, in the general population 28% of males and 23% of females smoke, while among the pesticide applicators studied, 17% of males and 10% of females smoke.

Data Collection on Study Participants

When the applicators and spouses were enrolled, the study collected detailed information about their health, their lifestyles (smoking, drinking, etc.), and medical history through a series of surveys. Participants were asked details about their pesticide practices, application methods, use of personal protective equipment, crops and livestock raised and other safety practices. The surveys also asked participants about potential environmental exposures. Between Iowa and North Carolina, a large percentage of applicators and their families are participating: 83% of eligible private applicators enrolled, 74% of spouses enrolled and 47% of commercial applicators enrolled.

The study made three general comparisons. First, investigators are comparing applicators and spouses to people in the general population of Iowa and North Carolina to see if there are differences in the cancer rates. Second, scientists compared applicators or spouses who have cancer or other diseases to those who don't to see if there are pesticide exposure or other factors that may have contributed to the disease. Third, the scientists also are comparing applicators or spouses using a particular pesticide to those not using it to see if there are any differences in the risk of cancer or other health problems. These comparisons can be made for types of farm exposures other than pesticides.

AHS Health Findings

Cancer

For cancer, investigators compared the rate of various types of cancer in applicators and spouses to the rates of those cancers in the general population of those states, adjusting for age and gender. Applicators are healthier than the general population and the overall rate for all types of cancer is lower than in the general population. The rates for 18 of 20 specific cancers are lower in applicators and spouses than in the general population.

Prostate Cancer

There is cause for concern with prostate cancer. The rate of prostate cancer is 14% higher in male applicators than in the general population, while the rate of skin melanomas is 50% higher among farm wives than in the general population. Scientists evaluated 45 pesticide active ingredients for their possible contribution to the risk of prostate cancer among applicators. They took into account the known risk factors for prostate cancer: family history (a brother or father with prostrate cancer), race or ethnicity (prostate cancer is more common among African-American men), and age (prostate cancer is more common in older men). The strongest result was seen with exposure to the fumigant methyl bromide. It's important to note that methyl bromide use continues to decline due to changes in agricultural practices.

There also was an association between exposure to historically used chlorinated pesticides and prostate cancer risk in men over 50. This group was old enough to have used aldrin, chlordane, DDT, dieldrin, endrin, hexachlor and toxophene. The five pesticides that are associated with an increased risk of prostate cancer in men with a family history of prostate cancer are the carbamate butylate (herbicide), and the organophosphate insecticides of chlorpyrifos, coumaphos, fonofos and the pyrethroid permethrin (animal uses).

Lung and Breast Cancer

Because lung and breast cancer are common cancers in the United States, scientists looked to see if there was any association between these cancers and pesticide exposure among participants. They found evidence that suggests an association between lung cancer and exposure to metolachlor and pendimethalin (herbicides) and chlorpyrifos and diazinon (insecticides). The scientists found no evidence of an association between breast cancer in farmer's wives and exposure to any of 50 pesticides evaluated.

However, researchers did find some evidence of higher breast cancer risk with the husband's use of certain pesticides such as 2,4,5-TP (a phenoxy herbicide no longer used, but known to be contaminated with the carcinogen, dioxin). An increased risk also was observed with the husband's use of the persistent organochlorine insecticide dieldrin, and for the first time for a fungicide called captan. Diazinon, an organophosphate insecticide used against soil pests, also was associated with a higher breast cancer risk with use by husbands, but ONLY in women with a family history of the disease, suggesting a possible gene-environmental interaction.

The herbicide 2,4-D is a long-used active ingredient, a phenoxy herbicide used on crops, lawns and gardens. Breast cancer risk was not increased with husbands use of 2,4-D.

Multiple Myeloma and Leukemia

The scientists also have evaluated pesticide users to see if the rates of any cancers are greater among those who are exposed versus those who are not exposed. Scientists found an association between alachlor and multiple myeloma and leukemia, cancers of the immune system and blood.

Respiratory Problems

Wheeze is a symptom of respiratory conditions, especially asthma. A wheezing sound is produced when you breathe if the airways deep in your lungs are narrowed. The scientists took into account known risk factors for wheeze, including asthma or allergies and smoking history, and were able to separate any impact of these influences from that of pesticides. With that in mind, the scientists learned that wheeze was associated with several types of farm exposures, including eight pesticides — paraquat, EPTC, parathion, malathion, chlorpyrifos, atrazine and alachlor, as well as with applications involving fogging and misting animals. Wheeze also was associated with other exposures on the farm, including using diesel tractors and frequent solvent use. Certain animal production practices also were associated with wheeze, including egg and dairy production and the daily performance of livestock/veterinary procedures.

Vision

Retinal degeneration is the leading cause of vision loss in older adults, but little is known about its causes. The most common form of retinal degeneration is macular degeneration, characterized by less visual acuity and loss of central field of vision. Agricultural health study scientists found a consistent association between applicators who reported retinal degeneration and use of fungicides. The association got stronger with increasing lifetime-days of fungicide use.

New information in the last few months has associated these fungicide active ingredients with retinal degeneration: benomyl, captan, chlorothanonil, copper ammonia carbonate, ferbam, maneb, metalaxyl, PCNB and sulfur. A second study looked at the relationship between retinal degeneration and pesticide use in farm wives and found the same results. The wives were nearly twice as likely to have retinal degeneration if they or their husbands used fungicides. The fungicides that drove this association were maneb, manocozeb and ziram.

Women's Reproductive Health

The Agricultural Health Study has given the scientists a unique opportunity to learn more about female reproductive health. In their studies, the scientists focused on women aged 21-40 years old. They learned that women who used pesticides of any type were more likely to experience longer menstrual cycles and missed periods. When they looked at those women who used pesticides thought to act like hormones (based on toxicology studies in animals), they saw even stronger associations with long cycles and missed periods. In addition, they saw an association between use of hormonally-active pesticides and bleeding between periods. The probable hormonally-active pesticides included in the study were lindane, atrazine and mancozeb or maneb. 

Diabetes

Additional results from the Ag Health Study became available in March 2007 concerning gestational diabetes. Of 11,273 women who became pregnant within 25 years after entering the study, 506 (4.5%) reported having gestational diabetes. Overall, 57% of women reported having mixed or applied pesticides at some time in their life, and the proportion was similar for those with and without gestational diabetes mellitus, the authors report in the journal Diabetes Care.

However, women who mixed or applied pesticides or repaired pesticide-related equipment during the first trimester of pregnancy had a more than twofold increased risk of developing gestational diabetes, the report indicates. In contrast, there was no increased gestational diabetes risk among women with residential exposures to pesticides or indirect exposures during the first trimester. 

Acknowledgement

Acknowledgment is provided to Julia Storm, North Carolina State University Agromedicine Institute and Dr. Suzanne M. Snedeker, Cornell University Sprecher Institute for Comparative Cancer Research for the adaption of their data and resources for this article.

Larry Schulze
Pesticide Education Specialist