Managing the Health Impacts of Waste Incineration
Incineration destroys contaminated hospital wastes, reduces municipal waste volumes, and substantially cuts down on the amounts of hazardous chemical and biological wastes. But does this widespread practice threaten public health? This question was tackled in the September 2000 issue of the journal Environmental Science & Technology in an article penned by EETD's Thomas McKone and Katharine Hammond of UC Berkeley's School of Public Health. They write that in spite of continuing efforts to evaluate the health impacts of incinerated waste emissions, key data limitations still exist.
Hundreds of incinerators—industrial kilns, boilers, and furnaces—annually burn an estimated 3 million tons of municipal solid and other hazardous wastes. Emissions from incinerators are regulated through the 1990 Clean Air Act. As part of the Act, the Environmental Protection Agency has defined Maximum Achievable Control Technology (MACT) standards, which require incinerators to attain emission controls that reflect the average of the best-performing operations. However, a National Research Council (NRC) report released in November 1999 notes that MACT standards may not be sufficient to protect incinerator workers and regional populations. According to the NRC report, the low reliability of measured data and models, as well as imprecise data on intermedia transfer factors used to determine indirect exposure, are obstacles to regional-scale health assessments. Intermedia transfer refers to the exchange of pollutants between the air and soil, air and vegetation, air and water, soil and vegetation, and outdoor and indoor environments.
In the past, health concerns for waste incineration were focused on the communities living near the incinerator. The NRC report comprehensively identifies three potentially exposed populations: the local one, which inhales airborne emissions; workers, especially those who clean and maintain the pollution-control devices; and the larger regional population, who may be remote from any particular incinerator, but who consume food contaminated by one or more incinerators. Unfortunately, some of the MACT standards will not help people in all these categories. For example, workers who clean out air-pollution control equipment at municipal incineration plants have tested for elevated levels of dioxins and metals (arsenic, lead, cadmium, and aluminum) in both blood and urine. But the new standards will only require fewer emissions from a plant and not change the work conditions for people in the facility.
Uncertainties Characterizing Impacts
To characterize health impacts from incinerators, large amounts of data and models are required. But a lot of uncertainty is associated with these evaluations because the data and models must be used to characterize individual behaviors, engineered system performance, contaminant transport, human contact and uptake, and dose among large populations. The NRC report identified the issues of uncertainty and variability as having scientific and policy implications for attributing health impacts to incinerators. The committee noted that when the uncertainty and variability become large, interpreting or assigning relevance to the estimated magnitude of exposure and health risk become increasingly difficult.
One case in which uncertainty derives from exclusion is a health characterization based only on normal operating conditions. No data are available to evaluate actual emissions during start-up, which are normally higher than during routine operation. Consequently, evaluating exposure and potential health risks remains potentially erroneous because of this lack.
Emissions, Transport, and Exposure
The most difficult task for those who evaluate patterns of human exposures is tracking the concentration and movement of contaminants. Most pollutants are released as stack emissions to the atmosphere. As the pollutants spread, people who live close by can be exposed directly through inhalation, as well as by pollutant deposition to soil, vegetation, and surface water. People living at a distance from incinerators are also exposed through the same media. Unfortunately, multimedia, multipathway exposures remain poorly characterized and scientific studies, models, and direct measurements are lacking.
Exposures and health assessments are key steps in the analysis of a link between incinerator sources and human health risks. If properly conducted, these assessments can be useful in the development of an effective risk-management strategy. If efforts to characterize incinerator health impacts are to be useful, two essential research tools-models and measurements-must be better integrated. Models provide the means to integrate and interpret measurements, design hypothesis-driven experiments, and predict the effectiveness of risk-management strategies. Measurements, in turn, provide the tools needed for evaluating and improving models.
For more information, contact:
- Thomas McKone
- (510) 486-6163; fax (510) 486-6658
"Managing the Health Impacts of Waste Incineration," Environmental Science & Technology, September 1, 2000/Volume 34, Issue 17/pp.380 A-387 A
This work was sponsored by the U.S. EPA National Exposure Research Laboratory.