Thirty-seven percent (16,489/44,624) of the licensed applicators reported ever using terbufos. Applicators, who reported using terbufos also reported applying a greater average number of other pesticides, were more likely to grow corn, reside in Iowa, drink alcohol in the last 12 months, and have a family history of cancer compared with applicators who reported never using terbufos (). Notably, the mean number of pesticides used increased across tertiles of terbufos intensity-weighted lifetime exposure-days. Distributions for smoking (pack-years), age, and education were not meaningfully different between those who used and those who did not use terbufos.
Baseline Characteristics by intensity-weighted lifetime exposure-days to terbufos, Agricultural Health Study (1993-1997)
Intensity-weighted lifetime exposure-days of terbufos were positively associated with the risk of all cancers combined, regardless of the referent group (). However, the exposure-response gradients were not monotonic and the test for linear trend was statistically significant (p trend = 0.004) only when the non-exposed were used as the referent group.
Hazard ratios for selected cancers, by intensity-weighted lifetime exposure-days to terbufos among Agricultural Health Study pesticide applicators (1993-1997)
Monotonic exposure response gradients among specific cancer sites and terbufos use were not readily apparent (). However, the risk estimates for terbufos use and several cancer sites were suggestive of potential associations. These sites include lymphatic-hematopoietic cancers and cancers of the prostate and lung. Cancers of the colon, bladder, oral cavity, kidney and melanoma were not associated with intensity-weighted lifetime exposure-day of terbufos.
The hazard ratios, regardless of the exposure category, for prostate cancer were slightly increased compared with non-users, although the exposure-response gradient was not monotonic (p trend = 0.12). No such increase in the HRs were observed when the low-exposed were used as the referent, although this would be expected given the initial jump in the incidence of prostate cancer observed among the low-exposed when the non-exposed were used as the referent group. For lung cancer, the HRs were slightly increased in the two highest exposure categories regardless of the referent group, although neither the exposure-response gradients were monotonic nor the p for trends statistically significant.
For the lymphatic-hematopoietic cancers combined, the HRs were increased in the two highest exposure categories, regardless of the referent group. The greatest HR was observed in the middle exposure category (>107-352 intensity-weighted lifetime exposure days). Similar patterns in risk were observed for leukemia and NHL, although the associations were substantially larger for leukemia than either NHL or all lymphatic-hematopoietic cancers combined. The tests for linear trend were not significant for any of these sites, regardless of the referent group.
We conducted additional sub-group analyses stratified by state of residence (i.e., Iowa and North Carolina) and found that the risk estimates were similar for all cancers combined and prostate cancer between pesticide applicators residing in Iowa and North Carolina (data not shown). For the other cancer sites, there were too few cases in North Carolina for meaningful analysis. Likewise, the number of commercial applicators was also insufficient for analyses stratified by applicator type (i.e., private and commercial). Notwithstanding, the results for the private applicators alone were largely unchanged (data not shown).