A statistically significant direct strong correlation was found between the annual average daily concentrations of air benz[a]pyrene and the lung and the gastric cancer morbidity rates in males and females, skin, thyroid, and ovarian cancer in females. The certain interval of the measured concentration of benz[a]pyrene and the recorded morbidity rate was shown to be characteristic of each of the above-mentioned tumors.
The incidence of bladder cancer is unusually high in aluminium smelter workers. An epidemiological study showed that workers in Soderberg potrooms are at highest risk for bladder cancer, the adjusted overall relative risk being 2.39 (1.34-4.28). Exposure to polycyclic aromatic hydrocarbons, of which benz(a)pyrene (BaP) served as an indicator, seems to be the causative factor. The relative risk was evaluated at 12.38 for workers with 20 or more equivalent years of BaP exposure. Cigarette smoking contributed significantly to the appearance of bladder cancer in the population studied. There is a synergistic effect when cigarette smoking and BaP exposure are combined; the numbers in our population are too small to determine whether this interaction effect is multiplicative or additive. It is concluded that bladder cancer is associated with aluminium smelting (primarily with the Soderberg process).
As a result of retrospective studies on cancer mortality among workers engaged in the carbon black industry, it was found that the mortality rate from cancer of the lung, stomach and gastrointestinal tract within this cohort of workers is higher compared with the population of the surrounding district and distant to it.
We evaluated the benzo[a]pyrene (BaP) content in the smoke from 35 brands of Canadian cigarettes and 5 brands of Canadian tobaccos for roll-your-own cigarettes. For the cigarettes, mean values of BaP ranged from 3.36 ng to 28.39 ng per cigarette, roughly in proportion with declared tar values. The relationship between declared tar and yields of BaP, however, does not allow accurate prediction of one from the other. For the tobaccos, mean BaP values ranged from 22.92 ng to 26.27 ng (average, 24.7 ng) per cigarette. The implications of these findings are discussed with respect to overall exposure.
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To investigate the process of deciding on compensation claims by lung cancer patients exposed occupationally to coal tar pitch volatiles.
For each case of lung cancer the probability that it was caused (probability of causation (PC)) by coal tar pitch volatiles was expressed as an increasing function of cumulative exposure to benzo-a-pyrene-years. This was assessed from several exposure-response models fitted to data from a large epidemiological study of aluminum production workers. For some models, PC depended also on the smoking habit of the cancer patient.
Estimation of relative risk by exposure group indicated that over 50% of lung cancers were attributable to coal tar pitch volatiles (PC > 50%) at exposures above 100 micrograms/m3-years benzo(a)pyrene. A linear relative risk model indicated that 50% PC was first achieved at 342.2 micrograms/m3-years benzo(a)pyrene, or 190.1 micrograms/m3-years benzo(a)pyrene according to the upper 95% confidence limit for risk increment. Corresponding figures for a power curve model were 210.3 and 45.9. With these five figures as compensation criteria compensation would have resulted in 31.4%, 2.7%, 19.2%, 15.7%, and 39.2% of cancers studied, compared with an estimated total proportion of cancers studied attributable to coal tar pitch volatiles of 15%-26%. If risks due to coal tar pitch volatiles and smoking multiply, PC does not depend on the amount smoked. If the two risks are additive, however, PC depends on the amount smoked according to a formula, with the figures mentioned applying to an average smoking history (24.4 pack-years).
Because of its simplicity and because it falls within the range of criteria based on several more sophisticated approaches, we prefer the criterion of 100 micrograms/m3-years, based on the relative risks by exposure group. However, the compensation board of the Canadian province of Quebec, on consideration of these alternatives, has proposed as a criterion that the upper 95% confidence limit of PC for the patient be at least 50%, assuming an additive relative risk model and allowing for their smoking habit.
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The existence of polycyclic aromatic hydrocarbons (PAH) in the particulate phase of diesel engine exhaust has raised concern about a carcinogenic effect in workers exposed to exhaust from diesel engines. Some of the PAH are carcinogenic following inhalation by experimental animals and are associated with excess cancer mortality in some occupational exposures. Studies of occupational exposure to diesel exhaust show concentrations of PAH are above ambient levels but below the very high levels in occupations with demonstrated excess cancer mortality. A critical review of the epidemiologic evidence on the carcinogenicity of workplace exposure to diesel engine exhaust is suggestive of a carcinogenic effect but the existing data are sparse and contradictory. Further epidemiologic studies of this question are needed.