NEW YORK (Reuters Health) - Women exposed to organic solvents on the job face an increased risk of developing non-Hodgkin lymphoma (NHL), according to new research in the American Journal of Epidemiology.

NHL is a collective term for several different types of immune-system malignancies. According to the National Cancer Institute, there were 66,120 new cases of NHL in the US in 2008, and 19,160 deaths from the disease.

NHL incidence has risen by about 3% to 4% annually since the early 1970s, Dr. Tongzhang Zheng of the Yale School of Public Health in New Haven, Connecticut and colleagues note in their report. Past research has found an increased risk of NHL in occupations where people may be exposed to organic solvents -- for example, pesticide application, dry cleaning, and embalming -- Zheng and his team add.

An organic solvent is any solvent containing carbon, and many, for example benzene and carbon tetrachloride, are known carcinogens. Chlorinated solvents are organic solvents containing chlorine which are also known to be hazardous to human health and the environment.

Organic solvent exposure could be behind the increase in NHL cases, the researchers say, but research to date has had mixed results.

To get a clearer picture of the relationship between on-the-job exposure to the chemicals and NHL risk, the researchers analyzed data on probability and intensity of exposure to several different types of organic solvents -- based on both the industry a person worked in and their occupation -- for 601 women diagnosed with NHL in Connecticut between 1996 and 2000. The results were compared to data for 717 healthy "controls" without NHL.

Occupational exposure to chlorinated solvents in general increased NHL risk by 40%, the researchers found, while carbon tetrachloride exposure more than doubled risk. Formaldehyde exposure increased risk by 30%.

The likelihood of being diagnosed with NHL rose in tandem with both average and cumulative probability of organic solvent exposure and average and cumulative intensity of exposure. The data also suggested that benzene exposure boosted NHL risk.

"These results support a potential association between occupational exposure to organic solvents and the risk of NHL among women," Zheng and colleagues conclude. "Further evaluation of the relation between solvent exposure and risk of NHL and its subtypes is warranted."

SOURCE: American Journal of Epidemiology, January 15, 2009.

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