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2,4D Eptdemtology <br /> <br />2,4-D Epidemiology <br />There are more than 100 epidemiological studies pertinent to 2,4-D. <br />rage t or ~ <br />Taken together, the results aze equivocal or ambiguous, with some studies suggesting a relationship <br />between 2,4-D and non-Hodgkins lymphoma (NI-II.), a form of cancer. Ambivalency is not uncommon <br />in epidemiology when dealing with a noncazcinogen or a very weak cazcinogen. The studies most often <br />quoted are the Nations! Cancer Institute's (NCI) Kansas (1986) and Nebraska (1990) farmworker <br />studies, both of which received considerable media attention. NCI's larger and more recent <br />Iowa/Minnesota study, which showed no association between 2,4-D and cancer, has been generally <br />ignored by the media. The Kansas study, which did not develop information specific to 2,4-D, but dealt <br />with herbicide use in general, suggested a higher risk of NHL among farmers who applied herbicides <br />21 days a yeaz or more. The Nebraska study showed a statistically non-significant risk of NHL among <br />farmers applying 2,4-D for 21 days a year or more. Both studies relied heavily on information provided <br />by proxy respondents. That is, in many cases, the person chosen to participate in the study was not <br />available, so next-of--kin or neighbors were asked about the unavailable person's pesticide use over a <br />previous period of more than forty yeazs. Subsequent studies have shown that information on pesticide <br />use provided by proxies is often invalid. One study shows that proxy respondents tend to overstate the <br />use of the most widely known pesticides (such as 2,4-D) and understate the use of the lesser known <br />products. In the NCI Nebraska study, for example, when the information provided by the self- <br />respondents (i.e. the farmers themselves) is analyzed sepazately from the information provided by the <br />neighbors or next-of--kin, there is no association between 2,4-D and cancer (see Olsen, G.W. et al, <br />Journal ofAgromedicine Vol. 3(1) 1996). <br />The extensive toxicology of 2,4-D (i.e., animal feeding studies done under controlled laboratory <br />conditions in accordance with EPA GLPs) does not support the hypothesis that 2,4-D is a carcinogen, <br />and the cohort studies in the epidemiology generally agree with the toxicology. The ambivalence noted <br />above exists in the case-control studies, with several National Cancer Institute (NCI) studies most <br />often cited. These studies were based on questionnaires completed by members of a certain population <br />(usually consisting of a population of about 1,000 people) beheved to have been exposed to 2,4-D. No <br />actual exposure measurements were made, and exposure was assumed based on the memory of the <br />participants (Farmers or, in many cases, that farmers next of kin or neighbors, were asked about that <br />farmer's pesticide practices over the previous forty yeazs or more). Cohort studies aze long-term <br />studies (i.e., 20 yeazs or more) of a given population which include actual examination of medical <br />records and, in some cases, actual exposure measurements or exposure assessments. The most recent <br />cohort study pertinent to 2,4-D was conducted by the University of Miami School of Medicine, which <br />http://www.24d.org/epi.html 11 /15/98 <br />