sive contamination of the sampled area around the incinerator; the levels were within the typical range of cadmium levels in rural, unpolluted, British soils.
There are two dominant mechanisms through which plants can accumulate metals from the atmosphere. Materials in the vapor phase may be directly taken up into plants. Both vapor and particles may be washed out of the atmosphere by precipitation (wet deposition), and dry deposited directly on leaves. The increased concentration of mercury in the Carpi et al. (1994) study and the increased lead in the Bache et al. (1991) study were probably a consequence of wet deposition rather than vapor uptake. The significance of this conclusion is that wet deposition typically occurs in the immediate vicinity of a source, whereas vapor-phase uptake can occur on a regional basis. Yasuhara et al. (1987) showed that incinerators were not important contributors of dioxins and furans to local soil or sediment samples.
Thus, single-medium studies indicate that important dioxin and furan concentrations could not be detected in bovine milk, soil, or vegetation, but increases in lead could be found in soil and vegetation and increases in mercury could be found in moss and human hair samples collected near incinerators.
In addition to the single-medium studies, there have been several multimedia studies around incinerators. Laidlaw Environmental Services, Ltd. (LESL) has operated a hazardous-waste treatment, storage, and disposal facility in Sarnia, Ontario, for over 25 years. A component of this facility is a liquid-injection hazardous-waste incinerator that treats 120 × 106 L of waste per year. Emissions are controlled with a secondary combustion chamber, spray dryer, and fabric filter. Both LESL (Ecologistics 1993a,b) and the Ontario Ministry of Environment and Energy have conducted multimedia monitoring in soil and vegetation around the facility, including locations determined by air modeling to have the greatest potential concentration. Most organic chemicals were not detected in either study area or control locations. For example, in 1992, OCDD, typically the most-common congener, was not detected in soils at detection limits ranging from 0.0052-0.050 nanograms/gram (ng/g). The results obtained in those studies were evaluated by comparison of samples obtained from the study area to those obtained from a control area, and by comparison of concentrations in soil to those considered to be typical by the MOEE (1989). A comparison of the metals of the greatest potential toxicological significance to the “upper limits of normal” developed by MOEE is given in Table 4-12. On the basis of these studies, it was concluded that the facility was not a major source of metals or PCDDs and PCDFs in the environment.
Stubbs and Knizek (1993) analyzed vegetation in the vicinity of the greater Vancouver refuse incinerator and concluded that trends in soil and vegetation trace elements in the study area in the study period indicated little or no change due to the startup and operation of the facility. The results are given in Table 4-13. They also concluded that the facility had no measurable effect on trace-element or PAH concentrations in soil, vegetation, or vegetative growth in the