metals, polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), and total particulate matter. EPA (1991b) found no correlation between the amount of waste burned and ambient-air particle concentrations. It also found that the proportions of the different compounds in ambient air did not resemble those in the stack gas. It was concluded that the incinerator was not the primary source of PCDDs and PCDFs in the ambient air surrounding the facility.

Other studies have reported similar findings. Hunt et al. (1991) performed ambient-air monitoring for particulate- and vapor-phase PCDDs and PCDFs in the vicinity of the Bridgeport, CT, waste-to-energy facility. Measurements were taken before and after the plant became operational. The results showed little difference in ambient concentrations of chlorinated dibenzodioxins and furans between the preoperational phase (0.097 pg/m3) and the postoperational phase (0.088 pg/m3). Stubbs (1993) examined trace metals and air-quality measures in the vicinity of the greater Vancouver, British Columbia, municipal incinerator and concluded that startup and operation of the plant had no measurable effect on air quality. A detailed study of ambient air in the vicinity of a greater Detroit plant that burned refuse-derived fuel was undertaken. The study evaluated many potential chemicals of concern (PCDDs and PCDFs, respirable particles, metals, polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], chlorobenzenes, chlorophenols, and inorganic acids) at four monitoring sites over a period of 2.5 years. One of the monitors was installed at the expected point of maximal effect, as predicted by air-dispersion modeling. The results were analyzed with two-sample tests on means, multiple regressions, and principal-components analysis. All statistical procedures showed that there was no observable effect of the facility on the measured concentrations of any of the chemicals studied.

Single environmental media other than air have also been evaluated. Eitzer (1995) analyzed bovine-milk samples for chlorinated dibenzodioxins and furans from farms near a municipal solid-waste resource-recovery incinerator in Connecticut, and found no statistically significant differences between preoperational and postoperational concentrations. The facility was designed to incinerate up to 620 tons per day of municipal solid waste and was equipped with a spray dryer and fabric filter for emission controls. The preoperational phase consisted of 17 samples from 5 farms. The postoperational phase included 12 samples from the same farms. Student's T-tests showed no statistically significant differences at a 95% level of confidence between preoperational and postoperational results for any individual congener (the mean and standard deviation presented in Table 4-11 show that estimates have high uncertainty). Similar results were obtained for furans.

Ramos et al. (1997) analyzed bovine milk samples from 12 dairy farms in Spain and 23 samples of pasteurized bovine milk for PCDDs and PCDFs. They found that the levels of dioxins in the milk samples from farms located in rural



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