Non-Hodgkin Lymphoma Linked to Herbicides in Two New Studies
Non-Hodgkin lymphoma (NHL) is a group of different types of malignant lymphatic diseases that share some features but not others. In two recent health surveys, herbicide exposure was highlighted as a significant NHL risk factor. A Swedish study focused on risks of exposure to various types of pesticides while a German study concentrated on occupational risk factors for a mostly rural population.
Both studies compared two groups of people who were similar with respect to age, sex, and regional residence. Using information from responses to survey questions as well as subjects' medical records, researchers compared people who had been diagnosed with non-Hodgkin lymphoma over a set period of years and others who did not have non-Hodgkin lymphoma.
Swedish scientists, following up on earlier studies, investigated the role that pesticides might play in the development of non-Hodgkin lymphoma. In their new study, they found that a significant risk factor was exposure to both herbicides and wood preservatives. Researchers did not find any overall increased risk from exposure to insecticides, fungicides or rodenticides.
Confirming earlier studies, phenoxy herbicides were found to be a link to increased risk for NHL. Researchers grouped data relating to 2,4-D and 2,4,5-T together to mirror pesticide use in earlier studies.
Examined separately, MCPA was found to have the highest risk factor for NHL. In the United States, MCPA is used on lawns and in agriculture.
Exposure to all other herbicides (i.e. non-phenoxy herbicides) also increased cancer risk. Of this group, glyphosate — the chemical in Roundup products — posed the greatest risk.
Researchers noted that the use of herbicides in Sweden has changed over the years. Sweden banned 2,4,5-T in the 1970s and later also banned of 2,4-D because of concerns about contamination by various dioxins. The use of MCPA and newer herbicides such as glyphosate became more prominent.
In Sweden, the incidence of non-Hodgkin lymphoma has le veled off in recent years and the researchers suggest this trend may result from the move away from 2,4,5-T and 2,4-D and other pesticides like DDT. New protective measures may also have reduced risks.
To assess occupational factors associated with NHL, German researchers surveyed residents of mostly rural counties in northern Germany, asking about work history and exposure to 50 "agents," such as herbicides, textile dust, electromagnetic fields, and paints.
The study looked at long-term employment trends. The results showed that those who worked in agricultural occupations (including forestry and fishermen) had an elevated risk for both high malignancy and low malignancy NHL when compared to their counterparts in the study.
Researchers also found elevated risk of high malignancy NHL for people with estimated exposure to herbicides. Farmers and gardeners who worked in horticulture or tree nurseries were the main occupations categorized as likely to be exposed to herbicides.
Other occupations were also linked. Technical salesmen, manufacturers' agents and construction workers had elevated risk for both the high and low malignancy groups. Low malignancy NHL was more common among blacksmiths, toolmakers, and machine tool operators.
Other occupational agents associated with both high and low malignancy NHL included diesel fuel, nitrates, organic dusts, chlorophenols and arsenic compounds. Potential exposure to arsenic compounds was largely linked to horticultural and tree nursery workers. The published study did not explain how these workers would have been exposed to arsenic, but arsenic has been used as a wood preservative and pesticide in Sweden.*
Eriksson, M. et al. 2008.
Pesticide exposure as risk factor for non-Hodgkin lymphoma including histopathological subgroup analysis.
International Journal of Cancer 123:1657-1663
Richardson, D.B., Terschuren, C., and W. Hoffmann. 2008.
Occupational risk factors for non=Hodgkin's lymphoma: a population-based case-control study in Northern Germany.
American Journal of Industrial Medicine 51:258-268.
*Navas-Acién, A et al. 2002. Occupation, exposure to chemicals and risk of gliomas and meningiomas in Sweden. American Journal of Industrial Medicine 42(3):214-227.