an association, or sufficient evidence of a causal relationship between exposure to organophosphates and given health outcomes. It is important to remember, however, that not all health effects might be common and that dose and duration of exposure might play an important role in the occurrence of effects.
A number of well-conducted case–control studies show an increased risk of non-Hodgkin’s lymphoma (NHL) associated with exposure to specific OP and carbamate insecticides (see IOM, 2003 for discussion). By design, such studies assign specific exposures to individual subjects albeit without direct workplace or environmental measurements; in these studies, increased risks were observed with exposure to OP agents and carbamates in general and malathion, diazinon, lindane, and carbaryl in particular. However, there are too few studies with exposure measurements at the individual insecticide level to draw conclusions on any specific insecticide. The increase in risk estimates, especially those related to OP insecticides and carbamates, lends support to a possible association. The associations are consistently increased across various categories of type of use or source of exposure information (self-report or proxy respondent). In addition, the studies that have examined insecticide and pesticide use in general have shown increased NHL risks. The potential for downward bias resulting from a healthy-worker effect inherent in studies with occupationally exposed cases and population controls underscores the positive results.
The GW2 committee concluded, from its assessment of the epidemiologic literature, that there is limited/suggestive evidence of an association between chronic exposure to OP insecticides and non-Hodgkin’s lymphoma.
Although specific and accurate exposure information on insecticide use is difficult to ascertain in epidemiologic studies, most populations studied involve workers who use insecticides on a regular basis over the course of many years. Most of the studies discussed above reported an increased risk of leukemia, especially among those exposed to OP insecticides. The studies on specific OP agents—such as diazinon, dichlorvos, and malathion—and on the broader category of insecticides provided additional support for a conclusion on exposure to OP compounds. Most of the findings were of sufficient statistical power to detect a precise estimate of risk. Given that most studies included all types of leukemia