(Beyond Pesticides, December 17, 2007) People exposed to banned organochlorine pesticides and other toxic chemicals that persist in the environment are more likely to develop non-Hodgkin lymphoma (NHL), according to new research funded by the British Columbia Cancer Agency. The study, â€śOrganochlorines and risk of non-Hodgkin lymphomaâ€ť, was published in the International Journal of Cancer on December 15, 2007 and is so far the largest to examine organochlorines in plasma and their link to illness. The researchers measured the levels of pesticides or pesticide metabolites and congeners of polychlorinated biphenyls (PCBs) in the blood of 880 British Columbians, half with NHL and the other half control subjects. Several pesticide analytes and a number of congeners showed a significant association with NHL.
Non-Hodgkin lymphoma is the fifth most common cancer in Canada and the most common type of lymphoma. “We know that the incidence of non-Hodgkin lymphoma has been steadily rising for the past 30 years worldwide, but there hasn’t been clear evidence to explain the increase,” says Dr. John Spinelli, Ph.D., lead author and a senior scientist at the BC Cancer Agency. “Our study helps to provide answers to this puzzle by showing a strong link between these specific environmental contaminants and this particular type of cancer.” Participants with NHL showed much higher levels of environmental contaminants than the control group. Individuals who had the highest total exposure to PCBs showed almost twice the risk of NHL compared to those with the lowest exposure. The PCB congener with the strongest association had an odds ratio (OR) for the highest versus the lowest quartile of 1.83 [95% confidence interval (95% CI) = 1.18-2.84]. The strongest association among pesticides was observed for oxychlordane, a by-product of the pesticide chlordane. Individuals with the highest levels of oxychlordane had almost three times the risk of NHL [OR 2.68, 95% CI = 1.69-4.24) compared to those with the lowest exposure. Chlordane is classified by the U.S. Environmental Protection Agency (EPA) as a Group B2, probable human carcinogen. Other pesticide analytes that showed a significant association with NHL were Î˛-hexachlorocyclohexane, hexachlorobenzene, mirex, trans-nonachlor and p,p'-DDE (a contaminant of DDT).
These pesticides are old-generation synthetic pesticides, which previously were used extensively for insect control but banned in Canada in the 1970s and '80s. "We are also seeing incidence rates for NHL leveling off in recent years, and this provides further evidence that these contaminants are important because many of these chemicals are no longer in use or are being used at reduced and highly controlled levels," adds Dr. Spinelli. Today in Canada, PCBs are restricted for use only as insulating fluid in existing electrical equipment. In the past they have been used as flame retardants, hydraulic fluid, lubricating and cutting oil, and additives in pesticides, paints, and carbonless paper. Environmental data collected by the Ministry of Environment State of the Environment reports shows that more stringent regulation reduced the quantity of PCBs in use in Canada by 54% between 1992 and 2003, but traces of PCBs and other organochlorine chemicals still linger today though. Exposure to residuals can occur through the diet, particularly by eating meat since the chemicals are stored in the cells of animals. "We can't really avoid these contaminants," Dr. Spinelli said. "In fact they are still going to be in organic foods because although farmers aren't spraying these chemicals on crops any more, [residue] is still in the air and in the soil. There’s not much we can do to keep from being exposed to them,” he said, adding that environmental toxins are believed to be the cause of about 10 per cent of cancers.
“This study is very important because it adds to our understanding of how exposure to chemicals that have become very common in our environment increases our risk of developing lymphoma,” says Dr. Joseph Connors, M.D., Chair of the Lymphoma Tumour Group at the BC Cancer Agency and co-investigator on the study. Dr. Spinelli cautioned that more work needs to be done before the etiology of lymphoma can be pinpointed. “Looking strictly at environmental factors won’t provide the full picture,” he said Dr. Spinelli. “Our next step is to identify genetic factors that make individuals more susceptible to these environmental contaminants. In this way, we may be able to determine the mechanism by which contaminants increase the risk for lymphoma, and this knowledge may help to identify environmental risk factors earlier.” Philip Branton, scientific director of CIHR’s Institute of Cancer Research, added that the findings represent only a correlation. “This kind of study is suggesting there might be a link,” he said. “What we really need is a much larger, more comprehensive population study on cancer and the environment, and we’re trying to organize that.”