Objective-To investigate whether the risks of mortality from brain cancer are related to occupational exposure to magnetic fields. Methods-A total of 112 cases of primary brain cancer were identified from a cohort of 84 018 male and female employees of the (then) Central Electricity Generating Board and its privatised successor companies. Individual cumulative occupational exposures to magnetic fields were estimated by linking available computerised job history data with magnetic field measurements collected over 675 person-workshifts. Estimated exposure histories of the case workers were compared with those of 654 control workers drawn from the cohort (nested case-control study), by means of conditional logistic regression. Results-For exposure assessments based on arithmetic means, the risk of mortality from brain cancer for subjects with an estimated cumulative exposure to magnetic fields of 5'4-13-4 uT.y v subjects with lower exposures (0.0-5.3 pT.y) was 1 04 (95% confidence interval (95% CI) 0-60 to 1-80). The corresponding relative risk in subjects with higher exposures (> 13 5 pT.y) was 095 (95% CI 0 54 to

Objectives-To study mortality among 4324 workers at two United Kingdom factories, Darwen, Lancashire and Wilton, Cleveland, producing polymethyl methacrylate (PMMA) sheet. The Darwen factory is still active, but the Wilton one was closed in 1970. Also, to investigate patterns of mortality after exposure to methyl methacrylate; in particular, mortality from colon and rectal cancer. Results-In the Darwen cohort, 622 deaths were identified and a further 700 deaths in the Wilton cohort. Mortalities for the cohort were compared with national and local rates and expressed as standardised mortality ratios (SMRs). In the subcohort of Darwen workers with more than minimal exposure to MMA, reduced mortalities compared with national and local rates, were found for all causes (SMR 94), and colorectal cancer (SMR 92), but mortality from all cancers was slightly increased (SMR 104). No relations were found with cumulative exposure to MMA. In the subcohort of Wilton workers, mortality from all causes of death was significantly reduced (SMR 89), but mortality from all cancers (SMR 103) and colorectal cancer (SMR 124) were increased. The excess of colorectal cancer was confined to employees with less than 1 year of employment. Conclusion-The study provided no clear evidence that employment at the factories or exposure to MMA had adversely affected the mortalities of workers. (Occup Environ Med 2000;57:810-817)

Several reported studies on the effects of polyvinyl chloride (PVC) dust in animals and man have been conflicting. The present study of the ventilatory function of 509 male workers exposed to PVC dust was made in 1977. Altogether 104 men exposed to PVC dust only, 112 men exposed to non-chlorinated solvents only, and 293 men exposed to a mixture of both completed the MRC questionnaire on respiratory function and performed simple spirometric tests (forced expiratory volume in one second and forced vital capacity). No differences were found between the three groups after allowance was made for age, height, and smoking. When exposure and smoking effects were considered separately, the latter was shown to be the dominant cause of reduced lung function. In this study work with PVC dust has not produced deleterious effects on ventilatory function.Polyvinyl chloride (PVC), a large tonnage raw material of fundamental importance to the plastics industry, is a white powder that was until recently considered to be inert. The basic material is formed from its monomer, the gas vinyl chloride (VCM). Although VCM and PVC have been synthesised for over 30 years, it is only in the past 10 years that the sinister nature of VCM has become apparent. VCM has been found to produce a wide spectrum of clinical conditions, the most important being angiosarcoma of the liver in workers exposed to high concentrations of the gas in PVC production plants. This was discovered in 1974 and because a small quantity of the gas is carried forward with the PVC powder to its containers, and thus to the formulating industries the effects, if any, of the PVC powder came into question. The chance of finding effects similar to those associated with VCM is considered remote, since the concentrations are greatly reduced. The possibility of pulmonary changes being caused by inhalation of the dust however, has led to experimental and clinical research.The cytotoxicity of various polymer dusts, including PVC, to suspensions of rat alveolar and peritoneal macrophages in culture' indicated that PVC caused deaths of cells similar in amount to kaolin, magnesium trisilicate, and polyethylene. These materials produced less than 2 % fibrogenicity compared with over 10 % for asbestos.On such evidence PVC had been considered inert and therefore incapable of producing lung changes.

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PADDLE OM, OSBORN AJ, PARKER ODJ. Mortality of employees in plants manufacturing 4,4'-bipyridyl. Scand J Work Environ Health 1991;17:175-8. A historical-prospective cohort study was conducted of 729 male employees of plants manufacturing 4,4'-bipyridyl. The cohort was studied because employment in some of the plants had beenlinked to malignantand nonmalignant skin lesionsattributed to exposureto tarry by-products. The overallmortalityexperience of the cohort did not show any statistically significant findings. More-detailedanalysis by subdivision of the cohort gave results that justified further inquiry into lung cancer incidence. A nested case-referent study did not indicatethat any occupational factor other than employment in a bipyridylplant was related to the incidence of lung cancer. The epidemiologic, toxicologic, and industrial hygiene information was assessed, and it was concluded that there was no evidence of a plausible occupational hazard of lung cancer to the bipyridyl workers, but that a follow-up of the cohort after an interval of five years should be undertaken.

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