From 1990 to 1991, in Canada, there was no commercial activity involving more than one kilogram of BCME or CMME and it is highly unlikely that these compounds would be formed from other substances that may be present in the environment. Both substances are readily degraded by hydrolysis in aqueous media or by photo-oxidation in the atmosphere and, therefore, are not likely to accumulate within living organisms. No data were found concerning concentrations of these substances in the ambient environment in Canada. Because of their extremely short residence time, it is believed that levels in the environment are extremely low (if they exist at all), and there is no exposure that could potentially arise from the past use of these substances in Canada. Therefore, even though there is a complete absence of data concerning the environmental toxicity of these substances, as previously noted, there is no reason to suspect that adverse effects due to BCME or CMME could occur in organisms living in the Canadian environment.
Therefore, on the basis of available data, BCME and CMME are not considered to be "toxic" as defined under Paragraph 11(a) of the Canadian Environmental Protection Act.
The short persistence of BCME and CMME in the atmosphere and the extremely low levels of release preclude these substances from contributing to ozone layer depletion, global warming, or photochemical smog formation.
Therefore, on the basis of available data, BCME and CMME are not considered to be "toxic" as defined under Paragraph 11(b) of the Canadian Environmental Protection Act.
In all of the five cohorts of exposed workers conducted to date, an association has been observed between lung cancer and exposure to either BCME (Lemen et al., 1976; Nishimura et al., 1990) or CMME (Weiss, 1976; Maher and DeFonso, 1987; Collingwood et al., 1987). The type of lung cancer [predominantly small (oat) cell carcinomas], the standardized mortality ratios, the latency periods (10 to 24 years), and the average age of appearance of cancer (35 to 55 years) in populations exposed either to BCME or CMME have been remarkably consistent. The type and incidence of lung cancer in individuals exposed to BCME or CMME [predominantly small (oat) cell carcinomas, occurring in relatively young individuals after short latency periods] is distinct from that caused by tobacco. Tobacco is one of the potential confounders in such studies, where lung tumors are predominantly squamous cell carcinomas, occurring after long latency periods in individuals more than 60 years of age (Weiss, 1976; Pasternack et al., 1977). Moreover, in the study in which tobacco smoking was most extensively addressed, involving a population of workers exposed to CMME, the incidence of lung cancer was inversely related to the use of tobacco (Weiss, 1980). The association between exposure to either BCME or CMME and lung cancer is strong, with standardized mortality ratios ranging up to 21 (Nishimura et al., 1990) and 20 (Weiss, 1982), respectively. For CMME, there is also evidence of a positive relationship between a qualitative measure of exposure and mortality due to lung cancer. In two studies on occupationally exposed individuals, the standardized mortality ratios for deaths due to lung cancer peaked 10 to 20 years from the onset of exposure (Weiss, 1982; Maher and DeFonso, 1987). Furthermore, observation of an association between occupational exposure to BCME and CMME and the development of lung cancer is plausible, based on the results of early, rather limited carcinogenesis bioassays and on available data on the genotoxicity of BCME and CMME. Increases in the incidence of tumors predominantly of the respiratory tract were observed in studies of exposed animal species.
The observed association of lung cancer [predominantly small (oat) cell carcinomas] and occupational exposure to either BCME or CMME, therefore, fulfils the traditional criteria (i.e., consistency, strength, specificity, temporal relationship, exposure-response relationship, and plausibility and supporting experimental data) for assessment of causality in epidemiological studies. Consequently, on the basis of the available data, BCME and CMME have been classified in Group I ("Carcinogenic to Humans") of the classification scheme developed for use in the derivation of the "Guidelines for Canadian Drinking Water Quality" (Health and Welfare Canada, 1989).
Owing to the lack of available information on concentrations in several environmental media to which humans are exposed, it is not possible to quantitatively estimate the total daily intake of BCME or CMME by the general population of Canada. It is also not appropriate to estimate intake on the basis of fugacity modelling, owing to the lack of commercial activity reported for these compounds. Consequently, estimates of total daily intake cannot be compared to quantitative estimates of cancer potency to characterize risk and provide guidance in establishing priorities for further action under CEPA. Such values would be expected to be extremely low owing to the lack of reported use of these compounds in Canada and their rapid degradation in the general environment.
On the basis of available data, BCME and technical grade CMME have been classified as being "Carcinogenic to Humans" and are therefore considered to be "toxic" as defined under Paragraph 11(c) of the Canadian Environmental Protection Act.
This approach is consistent with the objective that exposure to non-threshold toxicants should be reduced wherever possible and obviates the need to establish an arbitrary "de minimis" level of risk for determination of "toxic" under CEPA.
On the basis of available data, neither BCME or CMME are considered to be "toxic" as defined under Paragraphs 11(a) and 11(b) of the Canadian Environmental Protection Act but both are considered to be "toxic" as defined under Paragraph 11(c) of the Canadian Environmental Protection Act.