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Pesticide problem: Exposure ups prostate cancer risk.

Pesticide problem: Exposure ups prostate cancer risk.

Synopsis by Heather Volk and Wendy Hessler 

Researchers identified an increased risk of prostate cancer among older men exposed to agricultural pesticides that drift into residential settings in the Central Valley of California.

This study of non-work-related exposures is the first of its kind to examine the relationship between prostate cancer in older populations and ongoing pesticide exposure from the surrounding environment.

Exposure to methyl bromide or a collection of organochlorine pesticides increased the risk of cancer by almost one and a half times. These same pesticides are associated with prostate cancer in farm workers.



Prostate cancer is the third most common cause of death from cancer in men and is calculated to affect as many as 1 in 6 men during their lifetime. The cancer affects the prostate gland, a small gland in the reproductive system that releases fluid to help carry sperm.

Common risk factors for prostate cancer are diet and genetics, though there is little research on environmental exposures . Those at highest risk include men older than 60, those with a family history of the disease and African American men. Also at increased risk are men with occupational exposures to a wide variety of chemicals – such as farmers, tire plant workers and painters – and those who eat a high fat diet or abuse alcohol.

Because many pesticides can mimic hormones, experts hypothesize that exposure may increase prostate cancer risk. In particular, methyl bromide and organochlorine pesticides are thought to be related to prostate cancer cause and risk.

Methyl bromide use has decreased in recent years because it contributes to ozone depletion. Additionally, the heavily regulated organochlorine pesticides are still used in agriculture though mandatory reporting of their application is required.

What did they do?

The researchers compared pesticide exposure from non-work sources during a 25-year period in older California men with and without prostate cancer. They looked at methyl bromide, the fungicide captan and the total of eight organochlorine pesticides because of their likely association with prostate cancer. Three other chemicals – maned, paraquat and simazine – were evaluated as control exposures.

The authors recruited 173 men aged 60 to 74 years old from 670 identified by the California Cancer Registry as being diagnosed with prostate cancer between August 2005 and July 2006 in Tulare, Fresno and Kern counties in Central California. In addition, Medicare lists and tax records were used to find 1,212 men aged 65 years and older without prostate cancer. Of those, 162 participated as study controls. 

To assess pesticide exposure, subjects recounted through calendars and questionnaires where they lived and their job history between the years of 1974 and 1999. The locations were matched with and compared to historical data of each area’s agricultural pesticide use. This information was gathered from California pesticide use reports and land use records.

Home and occupational pesticide exposures were self-reported. These and other potential personal exposure values were used to statistically adjust and account for non-agricultural pesticide exposures.

Since studies like this are often plagued by low response rates, the authors also estimated the risk of prostate cancer due to pesticide exposure for all cases (670 men), compared to controls (1,212 men) in the three central valley counties. They used only the address where each subject lived when they were diagnosed. This address was also matched to pesticide-use data from the California pesticide use reports.

What did they find?

Men exposed to methyl bromide had a 1.62-fold increased risk of prostate cancer compared to the men who were never exposed. Similarly, for organochlorine pesticides, a 1.64 increase risk was found for men exposed versus those non-exposed. Interestingly, men exposed to higher levels of the organochlorines had a two-fold increased risk when compared to unexposed men.

The authors also examined exposure to other commonly applied pesticides, including maned, paraquat and simazine. They found no association between these chemicals and prostate cancer. 

When all 670 cases and 1,212 controls were examined using only the address related to the cancer diagnosis or from the Medicaid record, a risk of 1.47 for prostate cancer was found for exposure to methyl bromide, 1.50 for organochlorines and 2.12 for captan.

What does it mean?

Lifetime, non-work-related exposure to certain pesticides used in a heavily agricultural region may increase the risk of prostate cancer in men by one and a half times. Specifically, casual exposure to methyl bromide and a collection of organochlorines used on crops appear to be related to the common – but sometimes deadly – cancer.

This is the first examination of prostate cancer risk among men exposed to pesticides in the surrounding environment rather than at work.

Extensive agriculture and its associated pesticide use makes long-term exposure to pesticides likely in this area of the United States. California itself ranks first of the 50 states in agricultural production, and within California, the highest production occurs in the three counties studied. Exposure can occur when pesticides sprayed on fields drift through the air into neighborhoods or contaminate drinking water.

Research from studies on men exposed at work also report increased prostate cancer risks among groups of agricultural workers. Examining populations of workers is different from studying those unintentionally exposed in the general population through the environment. But, this study suggests exposure outside of work carries as much risk of prostate cancer as exposure at work (1.3 for workers vs. 1.6 increased risk for non-work exposures).

The study method gets at two important issues many work-based studies cannot. First, the study looked at effects in a general population over a large area. Individuals who are working may be healthier than those who are not, creating bias in study results, and generally come from specific geographic locations and groups. Second, maps and reported state data on historical pesticide use provided more reliable exposure estimates than personal memory.

Taken together, there appears to be some similarities in risk between work and non-work exposures. Further research is required to fully understand if pesticide exposure may be a causal factor for prostate cancer.