groups. Among the 29 currently exposed workers, 17.2% were oligospermic, compared with 11.1% of the 18 previously exposed workers. The study provides some evidence of an increased risk of oligospermia with carbaryl exposure. The proportion of oligospermic men among the carbaryl workers was nearly three times the proportion among the controls, and there was some evidence of an association with increased exposure. Because 29 of the carbaryl workers were currently exposed to carbaryl, it was not possible to determine whether oligospermia was a long-term outcome that would persist after cessation of exposure. Furthermore, the use of chemical workers as comparison subjects might mask an effect if they were exposed to spermatotoxic chemicals.
A second study of the same carbaryl workers (Wyrobek et al., 1981) examined the relationship between sperm shape abnormalities and exposure to carbaryl. When it was possible, the same semen samples were used in both studies. However, instead of using chemical workers as the control population, this study used newly hired workers at the carbaryl plant; those men provided semen samples at their pre-employment medical examination. Workers were assigned to one of three exposure groups on the basis of the type of job held during the preceding year: nonexposed (new hires), low dose, and high dose. For morphologic analyses, 500 sperm for each person were scored, with blinding as to exposure status. As in the study by Whorton and colleagues, the control group of new hires had a lower proportion (two of 34, or 5.9%) of oligospermic men than did the carbaryl production workers (seven of 48, or 14.6%). Morphological analyses showed increases in the proportion of abnormal sperm among the carbaryl workers (52% of 30 currently exposed and 50% of 18 previously exposed) versus the new hires (42% of 34); the results were similar after stratification on potential confounders, such as smoking, medical history, or previous exposure to hazardous agents. The proportion of men classified as teratospermic (defined in this study as having more than 60% abnormal sperm) was higher in the carbaryl workers than in the comparison group (14 of 49, or 28.6%, and four of 34, or 11.8%, respectively). A dose-response relationship was not found, although the measure of exposure was rather crude for such a determination. An inverse association between number of years worked with carbaryl and percentage of abnormal sperm was found; this was opposite the direction that was expected and could not be explained by the authors. Furthermore, it was expected that there would be differences due to age; however, among the carbaryl workers, the relationship between age and percentage of abnormal structure was opposite what was expected, in that younger men had a higher percentage of sperm abnormalities.
Several studies have examined the relationship between semen characteristics and exposure to broader categories of pesticides. Larsen and colleagues (1998a, 1999) studied traditional and organic farmers in Denmark and did not find an association between pesticide spraying and adverse effects on sperm concentration, motility, or morphology. The studies were prospective and controlled for several potential confounders including the period of abstinence and the delay from sample collection to analysis.
In a cross-sectional study on testicular function in 122 workers in ornamental-flower greenhouses, expert judgment was used to categorize workers into high-, medium-, and low-exposure groups (Abell et al., 2000a). The median sperm concentration and the median proportion of normal sperm were 60% and 14% lower, respectively, in the group with high estimated dermal exposure (n=13) than in the group with low estimated dermal exposure (n=44). Those differences remained after adjustment for potential confounders. However, the relevance of this study for the purposes of this report is limited by the exposure of the workers to more than 60 pesticides, including a number of fungicides.