Quoted from Living Downstream:
While the incidence of Hodgkin lymphoma has declined, non-Hodgkin lymphoma has shot up—doubling in incidence since 1973. This increase is evident in both sexes and most age groups. Jackie Kennedy Onassis was killed by one of its most malignant incarnations. Between 1995 and 2005, its incidence increased faster among women than among men, although it still afflicts more men than women.
What do we know about the people who get this disease? We know that people who work in certain occupations are overrepresented among NHL patients. Farm workers and workers in dry-cleaning shops are certainly two. Firefighters, airplane mechanics, and foresters may be others. We also know that lymphoma is consistently associated with exposure to synthetic chemicals, including solvents, PCBs, and pesticides of many kinds, especially a class of weedkillers known as phenoxy herbicides.
In a 2007 publication, biostatistician John Spinelli and his colleagues in British Columbia reported on a study that measured PCBs in the blood of lymphoma patients and compared them to those of matched controls. He and his team found a relationship: high blood levels of certain types of PCBs raised non-Hodgkin lymphoma risk by moderate but significant amounts. This study, which corroborates others also reporting elevated lymphoma risk with PCB exposure, makes biological sense: PCBs are known immune suppressors; immune alterations are known to increase the risk for non-Hodgkin lymphoma. In 2009, the hypothesis that PCBs contribute to non-Hodgkin lymphoma via mechanisms that undermine immunity was strengthened by two other findings. The first was the discovery that infection with the Epstein-Barr virus makes PCB exposure an even more potent risk factor for lymphoma. The second was the discovery of an interaction between PCB exposure and certain genes. Specifically, researchers found that associations between PCB exposure and lymphoma risk were limited to individuals who happened to carry particular genetic variations. And the genes that conferred this vulnerability were involved in immunity or PCB metabolism.
Like PCBs, phenoxy herbicides are chlorinated compounds. Unlike PCBs, they were invented with warfare in mind. First synthesized in 1942, phenoxys were part of a never-implemented plan by the U.S. military to destroy rice fields in Japan. The most famous phenoxy is a mixture of two chemicals, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4-dichlorophenoxyacetic acid (2,4-D). This combination is called Agent Orange, and it was finally deployed between 1962 and 1970 by U.S. troops to clear brush, destroy crops, and defoliate rainforests in Vietnam. The military career of phenoxy herbicides was thus revived.
Linked to miscarriages and contaminated with dioxin, 2,4,5-T was eventually outlawed. By contrast, 2,4-D went on to become one of the most popular weed killers in lawns, gardens, and golf courses, as well as in farm fields and timber stands. It has been marketed under a schizophrenic collection of trade names: Ded-Weed, Lawn-Keep, Weedone, Plantgard, Miracle, Demise.
Evidence for a connection between phenoxy herbicides and non-Hodgkin lymphoma comes from several corners. Vietnam veterans suffer excess rates. So do golf course superintendents. So do farmers who use 2,4-D. Risk to farmers rises with the number of days per years of use, the number of acres sprayed, and the length of time they wear their application garments. In Sweden, exposure to phenoxy herbicides was found to raise the risk of lymphoma by sixfold.
Dogs also acquire lymphoma. One recent study showed that pet dogs living in households whose lawns were treated with 2,4-D were significantly more likely to be diagnosed with canine lymphoma than dogs whose owners did not use weed killers. Risk rose with number of applications: the incidence of lymphoma doubled among pet dogs whose owners applied lawn chemicals at least four times per year. A study of people, however, found no excess lymphoma among those exposed to residential pesticides.
Steingraber, Sandra. Living Downstream: An Ecologist’s Personal Investigation of Cancer and the Environment (pp. 54-56). Da Capo Press. Kindle Edition.