Cancer mortality in 3M chemical workers
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Cancer mortality in 3M chemical workers
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2013
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At the 3M facility in Cottage Grove, Minnesota, Ammonium Perfluorooctanoate (APFO) was formulated as a polymerization aid used in the production of commercial and consumer products from 1947-2002. APFO is in a class of perfluorocarbons (PFCs)--inert chemicals--that for many years were thought to be nontoxic. More recently, however, a growing interest has surfaced and attention has turned to the health effects from exposure to APFO, and its dissociated anion perfluorooctanoic acid (PFOA). Researchers and public health officials have noted the persistence of APFO and PFOA in the environment along with data that show it remains for a long period in the human body (Houde at al., 2006; and Olsen et al., 2007). Adverse health outcomes reported from several animal studies in conjunction with the noted positive association between APFO exposure and an increased risk of dying from prostate cancer found in workers at the 3M Cottage Grove, Minnesota location, have been the impetus for this research (Lundin et al., 2009; Butenhoff et al., 2002; and Kennedy et al., 2004). The current study evaluated the risk of death in workers based on a newly developed APFO/PFOA quantitative exposure data matrix. We evaluated workers' health outcomes using annual exposure estimates. These estimates were based on two exposure models; a cumulative model (potential cumulative dose, PCD) and a cumulative clearance weighted model (CCWD). Compared to previous epidemiological studies with this cohort, this study estimated a quantitative level of exposure that potentially contributes to negative health effects in humans. This was a retrospective occupational mortality study of 9,027 3M employees who worked a minimum of one year at one of two 3M locations (Cottage Grove and St. Paul plants) in Minnesota. The workers were followed from their first date of employment (beginning in 1947) until their date of death or until the study ended in 2008. Standardized mortality ratios (SMRs) were calculated using the Minnesota population as the referent population. The risk of a cancer death was evaluated using a time-dependent Cox proportional hazards (PH) model, which compared the workers' exposure over time to the non-occupationally exposed workers at the St. Paul location. There were a total of 2,979 identifiable deaths in the cohort, and of these there were 72 prostate cancer deaths, 48 pancreatic cancer deaths, 16 bladder cancer deaths, 24 kidney cancer deaths, 25 female breast cancer deaths, and 15 liver cancer deaths. The SMR for prostate cancer deaths in the Chemical Division workers was 1.18 based on 16 observed versus 13 expected deaths. All cancer-specific hazard rations (HRs) using annual continuous exposure estimates were at or below no effect level with increasing exposure to APFO/PFOA. The population was additionally divided into six exposure groups. The HRs for workers showed an increase in the risk of a prostate cancer death with increasing exposure groupings compared to the St. Paul group [HR=1.22, (95% CI: 0.57-2.61), and HR=1.27 (95% CI: 0.30-5.28)], for the top two exposure groups. These results were imprecise, but showed a dose-response relationship. This study explored the risk of cancer mortality associated with age and intensity of exposure. The findings show a non-significant elevated risk of cancer deaths in the highest exposure groups for cumulative exposure during age 40-49 [HR=1.96, (95% CI: 0.67-5.68), and HR=1.51 (95% CI: 0.47-4.90)], for bladder and liver cancers respectively. These results were imprecise and based on six bladder and seven liver cancer deaths. Previous studies of the Cottage Grove population have shown an increased risk of death from prostate cancer with increasing exposure to APFO/PFOA using qualitative exposure groupings (Gilliland and Mandel, 1993; and Lundin et al., 2009). Risk of death was determined based on workers' job title and did not explore quantitative dose estimates from air measurement data, as was done in the current study. In this study we evaluated risk based on worker-specific quantitative annual exposure estimates from a reconstruction of the inhalation exposure at Cottage Grove. Prostate cancer results for the Chemical Division and top two exposure groups from the current study support the previous results. The overall results for all cancers are inconsistent when evaluating the continuous exposure compared to exposure group rankings, with the exception of kidney cancer. Kidney cancer was consistently below unity across all analyses, while the remaining cancers only show modest increases in risk based on few cases.
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University of Minnesota Ph.D. dissertation. December 2013. Major: Environmental Health. Advisors: Bruce H. Alexander, Gurumurthy Ramachandran. 1 computer file (PDF); xii, 148 pages.
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