Low mortality rates in industrial cohort studies due to selection for work and survival in the industry.
Occupational groups are often described as being relatively healthy because their mortality rates are lower than those of the national average. Although correct this confuses the issue for those who are interested in assessing the effects of exposure to a particular chemical. In a further analysis of data collected in a study of all men ever exposed to vinyl chloride monomer in the manufacture of polyvinyl chloride in Great Britain, three factors have been shown to contribute to the low mortality rates that were observed. The three factors: the selection of a healthy population for employment, the survival in the industry of the healthier men, and the length of time that this population has been pursued, have been quantified. The mortality experience within five years of entering this industry was shown to be as low as 37% of that expected; for circulatory disease and respiratory disease it was as low as 21%. There was a progressive increase in standardized mortality ratio with the length of time since entry so that the effect had almost disappeared 15 years after entry. To avoid confounding the selection effect with the survival effect the latter was measured by separating men who survived 15 years after entering the industry according to whether or not they were still in the industry after this period. Those who had left experienced an overall standardized mortality ratio some 50% higher than those still in the industry. This effect, although consistent in the age groups between 25 and 74 years and for all cause groups studied, was greatest in those aged between 25 and 44 years and for lung cancer and respiratory disease. (+info)
Measurement of some potentially hazardous materials in the atmosphere of rubber factories.
Two separate topics of work are outlined: methods for the measurement of chlorinated monomers in PVC and polychloroprene, and also methods for the measurement of these materials in factory air. Typical results which have been obtained in supplies of raw materials, in finished products, and in the working atmosphere at manufacturing operations are given. The second topic concerns the measurement of benzo[a]pyrene in the atmosphere of a tire manufacturing plant. This material is present in trace quantities in the mineral oils and carbon blacks used by the industry. The atmospheric concentrations present at various processes in this plant were measured on a daily basis over a period of two years, and the results obtained compared with results taken concurrently from an outside air station. It is shown that no significant quantities of benzo[a]pyrene are produced by tire manufacturing operations. (+info)
Dose-dependent fate of vinyl chloride and its possible relationship to oncogenicity in rats.
Studies on the fate of 14C-labeled vinyl chloride (VC) following oral administration and inhalation exposure in rats demonstrated that the disposition of VC in the body is a function of the dose. More importantly, from the data available, it appears that a correlation exists between doses of VC which cause tumors and those that saturate metabolic or detoxifying pathways. Additional studies characterized the depression of liver non-protein sulfhydryl content (primarily GSH) with the duration and concentration of exposure to VC. The results of these investigations indicate that statistical projections utilizing data collected from rats exposed to high doses of VC are invalid for predicting the hazard of low level exposure, because such projections violate a priori assumption that the dynamics governing the fate of VC in the body are unaltered. (+info)
Mortality and cancer morbidity in a group of Swedish VCM and PCV production workers.
The cohort of workers employed in a Swedish vinyl chloride/poly(vinyl chloride) plant since its start in the early 1940's has been followed for mortality and cancer morbidity patterns. Only 21 of the 771 persons could not be traced. Difficulties in establishing exposure levels at different work areas in the past makes an evaluation of dose-effect relationships impossible. A four- to fivefold excess of pancreas/liver tumors was found, including two cases later classified as angiosarcomas of the liver. The number of brain tumors and suicide do not deviate significantly from expected. Cardiovascular and cerebrovascular diseases, on the other hand, differ significantly from the expected. The discrepancies between previous reports on VCM/PVC workers and this report are discussed. The possible etiology of the cardiovascular deaths is also discussed. (+info)
Studies on the metabolism of vinyl chloride.
Vinyl chloride (VCM) is not carcinogenic by itself, it is bioactivated to the highly reactive alkylating oxirane chloroethylene oxide. Further metabolism, apparently, leads via an interaction of the primary alkylating metabolites with glutathion to S-(2-carboxy-methyl)-cysteine and thiodiacetic acid which are eliminated with the urine. Up to now, it has not been ascertained whether the oxirane alone is the essential carcinogenic factor or whether other metabolites are also involved in carcinogenicity. Likewise, it is still unknown whether the metabolites excreted in the urine might be used as biological criteria for exposure to VCM, because these metabolites probably can originate from a series of substances other than VCM. This problem could stimulate investigations on the possible carcinogenic activity of these substances. (+info)
Diffusion of residual monomer in polymer resins.
A simplified mathematical model which made use of Fick's laws of diffusion written in spherical coordinates was developed to describe the rate of diffusion of residual monomers from polymer resins. The properties of the monomer-polymer system which influenced the amount of monomer remaining in the polymer as a function of time were the diffusivity and solubility of the monomer in the polymer, and the particle size of the polymer resin. This model was used to analyze literature data on the diffusion of residual vinyl chloride monomer in polyvinyl chloride resins made by the suspension process. It was concluded that particle size of the resin was a significant parameter which should be taken advantage of in process equipment designed to remove residual monomer from PVC resins. The diffusivity of the monomer in the polymer was a function of the solubility of the monomer in the polymer. Monomer solubility can be determined from Henry's law. It was suggested that this model could be adapted to describe diffusion of monomers from any monomer-polymer system, and would be a useful approach to modeling the transport of nonreactive chemical additives from plastics. (+info)
Recent achievements and research initiated in the Swedish plastics and rubber industry.
The improvement in exposure conditions in the Swedish vinyl chloride producing industry is reported. The article comments on the technology and control methods by which the vinyl chloride concentration has been lowered to less than 1 ppm vinyl chloride. Two epidemiological retrospective cohort studies are presently under way on workers in PVC-utilizing industries and in the rubber industry. (+info)
Biological effects of vinyl chloride: an experimental study.
Plasma activities of alkaline phosphatase, (AP), transaminases and total lactate dehydrogenase (LDH) with isoenzymes were determined in mice inhaling 50 and 550 ppm vinyl chloride (VC). The animals were also autopsied and the tissue pathology was studies. The total LDH activity was elevanted in both dose groups along with a shift to cathodic enzymes. AP was increased in animals exposed to 500 ppm and transaminases were not at all changed. Enzyme changes occurred after the appearance of tumors. Alveologenic adenomas occurred in all animals at the higher dosage and in about half of the animals inhaling the lower dose. Subperitoneal and subcutaneous hemangiosarcomas were frequent in both dose groups; but especially among 50 ppm animals. Only one animal had a hemangiosarcoma of the liver. No liver fibrosis was seen. All primary subperitoneal and subcutaneous tumors were located in fat tissue. Telangiectasis was observed in two animals in the 500 ppm series. The importance of blood vessel changes in the toxicology of vinyl chloride is discussed. (+info)