Excerpts from "Incineration: Decisions for the 1990s - A Guidebook for Citizens and Communities"

A joint project of Tellus Institute and JSI Center for Environmental Health Studies-Supported by the Jessie B. Cox Charitable Trust
Chapter 3: Estimating Community Health Risks, pp.37-43

New emissions control technologies and careful management to remove toxics from the waste stream and assure proper operating conditions at the plant can greatly reduce the emissions from modern incinerators. Nevertheless, some hazardous substances are released in air emissions and in water used for processing and toxics are concentrated in incinerator ash. The following are techniques for estimating risk to workers and residents in a particular community and a review of studies that have examined the health of workers and neighbors at operating incinerators.

Risk Assessment

A comprehensive risk assessment attempts to examine the full range of important factors to evaluate the overall risk to public health. They should follow the protocols recommended by the U.S.Environmental Protection Agency. Keep in mind that most risk assessments are done by those proposing an incineration project, so it is important to evaluate them critically.

Risk assessments, even when undertaken carefully following the EPA's protocol, are based on a large number of assumptions. They involve combining many different types of data. A risk assessment will include information about the size and characteristics of the incinerator, the type of waste to be processed, the weather and geography of the site, the location of neighbors and schools, results of toxicology and epidemiology studies, estimates of how much air a typical person breathes, and so on. This information is fed into a mathematical model to calculate health risks. Risks of alternative options should also be examined.

Multiple Toxins: Synergism

The effects of synergism are rarely predicted by risk assessments. Incinerators release several chemicals, often attached to each other on small particulate matter that can be inhaled. Risk assessments examine the risks of individual chemicals and then add them together. Studies have found that combinations of chemicals can act to produce combined health effects that don't simply equal the additive effects of each chemical taken alone: Multiple toxins, such as those formed during incineration, may result in more serious health risks than would be predicted for each contaminant individually. This is called a synergistic effect. Health hazards from combined exposures are difficult to precisely evaluate, but studies of exposure to cigarette smoke and to asbestos, however, illustrate the important effect they may have. The lung cancer risk for those who smoke two or more packs a day is ten times that of nonsmokers. The risk of those exposed to asbestos is five times that of those not exposed. Adding these risks would yield a risk of 15 times those not exposed. Due to synergistic effects the actual combined risk for heavy smokers exposed to asbestos has been found to be much higher: 55 times those who don't smoke and aren't exposed to asbestos. These effects of synergism therefore can be significant, yet are often unknown.

Site-Specific Data

A common failing of risk assessment reports is their inadequate use of site-based information. For example, to estimate how fast metals will leach through groundwater, many risk assessments rely on approximate values for soil properties published in scientific literature. The problem is that soil conditions at a particular site may be very different from "average".

Appropriate Health Outcomes

While risk assessments weigh the risk of cancer and of acute poisoning, other important health concerns may not be considered. Nervous system and respiratory disorders, effects on pregnancy outcomes, and developmental effects on children are among the additional types of health outcomes that should be included in discussions of incineration.

Susceptible Populations

Children, elders, and those with pre-existing health problems are at greater risk of adverse health effects from exposure to toxic chemicals.

Risks to workers and their families also deserve evaluation. Workers are usually much more highly exposed than residents. Their families may be at increased risk if dusts are carried home on clothing. In addition, the offspring of workers may be at risk of developing health problems as a result of worker exposure to chemicals which can adversely affect pregnancies and births.

Exposure Pathways

A risk assessment should consider not only air emissions, but process water and ash management risks as well. Fly ash remaining after incineration contains hazardous residues which may include heavy metals and dioxin. The more effective the emissions controls are, the more toxic the remaining ash. The handling and disposal of the ash requires extreme caution.

Another vital consideration is what happens to materials over time after they are released. Particles, for example, may accumulate indoors to much higher levels than the original levels present in ambient air. Or releases may form a film on surface waters or build up in soils, later to be taken up by plants and animals. Through the process, known as bioaccumulation, toxins released into the air may eventually be concentrated through the food chain, exposing people to additional risks in their food. A comprehensive risk assessment must consider pollutants emitted to air, water, and land and human exposures through inhalation, ingestion and skin contact.

Operating Conditions

It is difficult to measure actual emissions. Fluctuations in the composition of the waste stream, which can occur daily, have been shown to widely alter incineration by-products. Leaks, spills and accidental releases of hazardous gases such as ammonia are an important type of "upset". These acute hazards should be considered along with long-term risks.

Background Risks

The background status of health in the community is important to consider when weighing the impact of a new facility on residents. Each new exposure to a carcinogen adds to overall cancer risk. Adverse health effects from toxins such as lead depend upon the background levels of exposure and on preexisting health conditions. States usually collect information by community on cancer incidence rates. They also collect data on pregnancy outcomes, such as the proportion of low birthweight children, which can serve as an indicator of health status. Information on blood lead levels may also have been collected for children in the area.

State departments of environmental protection can assist in obtaining information on other health risks in the area including water and air quality, contaminated waste sites, and the industrial toxic releases. This background information is rarely included in risk assessments.

Health Studies:
Looking at workers and nearby residents.

While risk assessments predict future exposures and health impacts, what can we learn from experiences at operating incinerators. Several health studies about workers and nearby residents have been completed, but research in this area has many gaps.

Unfortunately, these studies are very difficult and expensive. One problem, for example, is that cancer effects won't show up for 10 to 20 years after exposure. In addition, it is nearly impossible to precisely measure what doses of toxins individuals receive once a chemical is released. These problems diminish the ability of a study to document an association between living near an incinerator and health, even if the incinerator has a real effect.

Nevertheless, some studies have identified adverse health problems arising from municipal solid waste incineration. One study found higher rates of respiratory disease associated with living closer to an incinerator in France. A study of children identified higher levels of cadmium in the hair of those living near refuse-derived fuel incinerators. Neurobehavioral toxic effects were found among those children with increased lead absorption.

The effects of ash processing, handling and disposal poses other risks to workers. Incinerator workers (particularly those who clean equipment) were found to have higher levels of mutagens in their urine when compared to water plant workers.

Interpretation of these studies is difficult because each incinerator uses slightly different technology, a different waste stream and operating procedures, and a different site. So far there are few studies to rely on. However results of studies of operating incinerators, along with the numerous studies showing health effects of individual substances emitted from incinerators, mean citizens should take a close look at proposals for new incinerators and compare it with the alternatives, Citizens should expect a systematic health study conducted, or at least reviewed, by an independent party whenever an incinerator is proposed.

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