BMC Public Health 2008, 8:21 http://www.biomedcentral.com/1471-2458/8/21 Background The production of vinyl chloride (VC) and polyvinyl chlo- ride (PVC) entails the use of various chemicals (Table 1)[1], some of which are known to be toxic and poten- tially or definitely carcinogenic [2]. Indeed, a number of these compounds have been reported to induce cancer in the liver (prevalently hepatic angiosarcoma) [3-5], the hemolymphopoietic system (leukemias and lympho- mas), lung and brain [3,4]. Numerous investigators have analyzed a cohort of Italian VC-PVC workers, who had been the subject of a large class-action lawsuit [1]. One study on this cohort, updated in 1995, found an elevated death risk for all causes among the whole group of exposed (i.e., blue col- lar) workers, and specific death risks among specific sub- groups, such as liver cancer and liver cirrhosis among autoclave workers and lung cancer among PVC bag- gers[6]. On the contrary, other analyses on the same work- ers revealed a statistically significant reduced mortality from all deaths combined and a not statistically signifi- cant reduction of mortality from all tumors among the whole cohort [1,7,8]. Since these latter studies investi- gated the entire cohort – including both exposed and non- exposed workers – and used the general population of the Region where the plant is located (Veneto) as a reference, related analyses may well have hidden some health risk excesses. For this reason, the updated mortality of the same cohort was reanalyzed using an internal comparison group of non-exposed workers in order to describe the pattern of diseases specific for each subgroup of exposed workers. Methods Population under study The present update of the follow-up included 1658 employees (42253 person-years) who had worked in a large petrochemical plant located in Porto Marghera (Ven- ezia, Italy) for any period of time between July 1950 and July 1985. The follow-up period extended from January 1972 to December 1999; 248 deaths were registered. The classification and coding of previous studies were main- tained, both for job category (28 plant sectors, used as sur- rogates of homogenous exposures) [1,7] and for cause of death (ICD-9th revision [9]). Workers were classified according to their job categories in four large, but reasonably homogeneous, groups: auto- clave workers (n = 210, 5446 person-years), PVC baggers (n = 198, 4978 person-years), PVC compound workers (i.e., workers employed in the production of PVC granules from resins, n = 404, 10310 person-years) and technicians and clerks (n = 202, 5303 person-years). The above work- ers comprised 61% of the total workforce. An additional, more heterogeneous group, categorized as other blue collar workers (n = 644; 16216 person-years), included the plant employees in the remaining 24 sectors. As technicians and clerks, thanks to environmental work- place sampling, were found in a previous study to be a group with low (or null) exposure to toxic and carcino- genic agents, they were used as an internal reference in the present analysis [10]. This reanalysis considered all causes of death previously reported as being associated to an increased risk [3,4]. An analysis of changes in job category revealed that only 15 workers transferred from an exposed to an unexposed category, and that only nine moved from an unexposed to an exposed category. Overall, 81% of workers never changed their initial occupation. For this reason, the job category at hiring was used to split the workforce into dif- ferent categories. Statistical Analysis Considering overall mortality among all exposed subjects (i.e., the total blue collar workforce), the study had an estimated power of 0.80 to detect a univariate relative risk (RR) of 1.50 as significantly increased at a 0.05 level (two- sided). Table 1: Provisional list of chemicals [CAS number] used in the production of VC and PVC and related products Acetates Alcohol Sodium hydroxide [1310-73-2] Acetylene [74-86-2] Chlorofluoromethane [593-70-4] Sulphates [EDF-078] Acetone cyanhydrin [75-86-5] Ammonia [7664-41-7] Ethylene [74-85-1] Acids: Asbestos [1332-21-4] Hexane [110-54-3] acetic [64-19-7] Caprolactam [105-60-2] Dichloroethane [1300-21-6] hydrocyanic [74-90-8] Chlorine [7782-50-5] Diphenylmethane diisocyanate hydrochloric [7647-01-0] Dioxide [101-68-8] fluorhydric [7664-39-3] Fluorides [16984-48-8] Tetrachloroethane [79-34-5] nitric [7697-37-2] Hydramine Tetrachloroethylene [127-18-4] sulphuric [7664-93-9] Hydrogen [1333-74-0] Trichloroethylene [79-01-6] hypochlorous [7790-92-3] Sodium cyanide [143-33-9] Toluene diisocyanate [26471-62-5] Acrylonitrile [107-13-1] Potassium cyanide [151-50-8] Petrol Phosgene [75-44-5] Plasticizers Stabilizers Tedimon 31 [9016-87-9] Terephthalates Vinyl chloride [75-01-4] Polyvinyl chloride [9002-86-2]: Granules, compound, suspension, copolymers, emulsion. Page 2 of 8 (page number not for citation purposes)