(Beyond Pesticides, June 16, 2009) A study involving 678 individuals who apply pesticides, culled from a U.S. Agricultural Health Study of over 50,000 farmers, recently found that exposure to certain pesticides doubles oneâ€™s risk of developing an abnormal blood condition called MGUS (monoclonal gammopathy of undetermined significance) compared with individuals in the general population. The disorder, characterized by an abnormal level of a plasma protein, requires lifelong monitoring as it is a pre-cancerous condition that can lead to multiple myeloma, a painful cancer of the plasma cells in the bone marrow. The study will appear in the June 18 issue of Blood, the official journal of the American Society of Hematology.
â€śOur study is the first to show an association between pesticide exposure and an excess prevalence of MGUS,â€ť said lead author Ola Landgren, M.D., Ph.D., of the National Cancer Institute (NCI), which is part of the National Institutes of Health, U.S. Department of Health and Human Services. â€śThis finding is particularly important given that we recently found in a large prospective cancer screening study that virtually all multiple myeloma patients experienced a MGUS state prior to developing myeloma.â€ť
â€śAs several million Americans use pesticides, itâ€™s important that the risks of developing MGUS from the use of pesticides is known,â€ť added senior study author and NCI investigator Michael Alavanja, DrPH.
The blood of study participants, who were individuals licensed to apply restricted-use pesticides, was assessed for MGUS prevalence. The median age of participants was 60 years (range 30-94 years), and all lived in either Iowa or North Carolina. Participants also completed questionnaires providing comprehensive occupational exposure information for a wide range of pesticides, including information such as the average number of days of pesticide use per year, years of use, use of protective gear while applying pesticides, and pesticide application methods. Information on smoking and alcohol use, cancer histories of the participantsâ€™ first-degree relatives, and other basic demographic and health data were also obtained. Individuals with prior histories of lymphoproliferative malignancies (such as multiple myeloma or lymphoma) were excluded. Cancer incidence and mortality were monitored annually, and, after five years, follow-up interviews were conducted to update the information about participantsâ€™ occupational exposures, medical histories, and lifestyle factors.
For comparison, data were obtained from a large MGUS-screening study conducted by the Mayo Clinic, and the results from the pesticide-exposed group were compared with the assessments of 9,469 men from the general population of Olmsted County, Minnesota. The two groups were similar in terms of age, race, and educational attainment. Because of the low prevalence of women among workers who apply pesticides, women were excluded from the study.
In the pesticide-exposed group, no MGUS cases were observed among those who were less than 50 years of age, but the prevalence of MGUS in those older than 50 was 6.8 percent, which is 1.9 times higher than the general population study group of men in Minnesota.
The researchers also evaluated the potential association between MGUS prevalence and 50 specific pesticides for which usage data were known. Of the chemicals studied, a significantly increased risk of MGUS was observed among users of dieldrin (an insecticide), carbon-tetrachloride/carbon disulfide (a fumigant mixture), and chlorothalonil (a fungicide). The MGUS risk for these agents increased 5.6-fold, 3.9-fold, and 2.4-fold, respectively. Several other insecticides, herbicides, and fungicides were associated with MGUS, but not significantly.
â€śThere is great concern regarding the increase in frequency in mature B-cell malignancies in the Western world and what may be the cause of this. A number of reports in the past have linked exposure to pesticides with increased risk of these types of cancers, but the present study is the first to link agricultural work to a pre-malignant condition,â€ť said John G. Gribben, MD, DSc, Professor of Experimental Cancer Medicine at Barts and the London School of Medicine, who is not affiliated with the study. â€śIt is vital to assess the risk of workplace exposure and disease, and the results lend further support to providing safe workplace practices to limit exposure to potential carcinogens.â€ť
â€śOur findings are intriguing,â€ť stated Dr. Landgren. If replicated in a larger sample from our study and other large studies, further work should focus on gaining a better understanding of the molecular basis of MGUS and multiple myeloma. Ultimately, this will result in the identification of novel molecular targets involved in the progression from MGUS to multiple myeloma and in the development of targeted therapies.â€ť
According to Beyond Pesticides’ research on multiple myelomaâ€™s link to pesticide exposure, several previous studies show an increased risk. For example:
* A 2008 historical cohort study of occupation exposure in Sweden found an excess risk among male agricultural, horticultural and forestry workers use of pesticides multiple myeloma.
* A 2007 meta-analysis of 13 case-control studies on hematopoietic cancers (leukemia, NHL, and multiple myeloma) published between 1990 and 2005 found a significant positive association for occupational pesticide exposure of more than 10 years and all hematopoietic cancers (OR 2.18).
* A 1998 study of cancer mortality among Iowa farmers showed an excess of deaths for multiple myeloma.
* A 1996 Norwegian study found that agricultural exposure to pesticides for those cultivating potatoes is linked to multiple myeloma in males and females.
* A 1992 study looking at farmersâ€™ cancer risks found significant excesses for multiple myeloma.
* A 1985 study found that farmers, although tend to be health in many regards due to their physical activity and other attributes of living rurally and generally have fewer health problems, certain types of cancers are frequently found in excess in this group including multiple myeloma.
* A 1985 case-control study of New Zealand agriculture and forestry workers found a significant excess of patients with multiple myeloma (OR 2.22).
* A 1983 mortality study of Iowan farmers who died between 1964 and 1978 found an elevated mortality from multiple myeloma in association with herbicide and insecticide use.
Looking for information on specific pesticides? Find data on more than 80 pesticides commonly used in the U.S. in the Pesticide Gateway. Beyond Pesticides created this database tool to provide decision and policy makers, practitioners and activists with easier access to current and historical information on pesticide hazards and safe pest management, drawing on and linking to numerous sources and organizations that include information related to pesticide science, policy and activism.