Health risk assessment of a modern municipal waste incinerator

During the modernization of the municipal waste incinerator (MWI, maximum capacity of 180,000 tons per year) of Metropolitan Grenoble (405,000 inhabitants), in France, a risk assessment was conducted, based on four tracer pollutants: two volatile organic compounds (benzene and 1, 1, 1 trichloroethane) and two heavy metals (nickel and cadmium, measured in particles). A Gaussian plume dispersion model, applied to maximum emissions measured at the MWI stacks, was used to estimate the distribution of these pollutants in the atmosphere throughout the metropolitan area. A random sample telephone survey (570 subjects) gathered data on time-activity patterns, according to demographic characteristics of the population. Life-long exposure was assessed as a time-weighted average of ambient air concentrations. Inhalation alone was considered because, in the Grenoble urban setting, other routes of exposure are not likely. A Monte Carlo simulation was used to describe probability distributions of exposures and risks. The median of the life-long personal exposures distribution to MWI benzene was 3.2.10(-5) mu g/m(3) (20th and 80th percentiles = 1.5.10(-5) and 6.5.10(-5) mu g/m(3)) yielding a 2.6.10(-10) carcinogenic risk (1.2.10(-10)-5.4.10(-10)). For nickel, the corresponding life-time exposure and cancer risk were 1.8.10(-4) mu g/m(3) (0.9.10(-4)-3.6.10(-4) mu g/m(3)) and 8.6.10(-8) (4.3.10(-8)-17.3.10(-8)); for cadmium they were respectively 8.3.10(-6) mu g/m(3) (4.0.10(-6)-17.6.10(-6)) and 1.5.10(-8) (7.2.10(-9)-3.1.10(-8)). Inhalation exposure to cadmium emitted by the MWI represented less than 1% of the WHO Air Quality Guideline (5 ng/m(3)), while there was a margin of exposure of more than 10(9) between the NOAEL (150 ppm) and exposure estimates to trichloroethane. Neither dioxins nor mercury, a volatile metal, were measured. This could lessen the attributable life-long risks estimated. The minute (VOCs and cadmium) to moderate (nickel) exposure and risk estimates are in accord with other studies on modern MWIs meeting recent emission regulations, however.