Incinerator air emissions: inhalation exposure perspectives.

Inhalation Exposure Perspectives

Background

An entertainment telecast of the behind-the-scenes efforts for a new movie showed a series of quickly sequenced explosions on a ship in Boston Harbor. The explosions were spectacular. Huge fire balls were accompanied by billowing clouds of black smoke. When asked how they felt about the explosions, most local residents responded that they were pleased that such an event took place in their neighborhood. A few people were mildly disturbed that pictures and small items were shaken from walls and shelves; however, when the film's director offered to pay for damages, they were easily mollified.

Curiously, none of the people surveyed appeared concerned about the pollutants emitted into the local environment, although they may have had plenty to be concerned about. Depending upon the materials involved in the ship's construction and the materials burned during the fire, emissions may have contained heavy metals (paints and pigments), chlorinated dioxins and furans (halogenated plastics), and carcinogenic polynuclear aromatic hydrocarbons (e.g., benzo[a]pyrene).

If, instead of a thrilling Hollywood scene coming to the neighborhood, a temporary incinerator was going to be installed to clean up a local hazardous waste site, area residents would likely not embrace the incinerator with the same zeal as displayed for the exploding ship! The public usually has no practical method to evaluate the two types of events equitably. There is no universal regulatory requirement to analyze the exploding ship pollutants in the same manner that is mandated for incinerators. Both the public and regulatory officials need to step back periodically and attempt to analyze all kinds of events from a broader perspective and in a consistent manner.

Evaluation Approach

Members of the general public often have little training or experience in analyzing the impacts of technologic events on the environment or their health. For instance, most people acknowledge that something needs to be done about hazardous waste. However, newspapers are full of articles about communities fighting to keep new hazardous waste disposal facilities, particularly incinerators, out of their neighborhoods.

Where incinerators are proposed, the public can benefit by having an independent third party help sort out conflicting claims regarding such facilities. This third party should have nothing to gain or lose by the incinerator's implementation. However, the third party should be capable of understanding not only incineration and related pollution control technology, but also health risks associated with that technology. Such third-party evaluation can be obtained from a number of sources, including state and local health departments, colleges and universities, and consulting firms.

The Centers for Disease Control and Prevention (CDC) provides a third-party perspective for the U.S. Army's Chemical Demilitarization Program, which currently proposes to use incineration to destroy lethal chemical warfare stockpiles. These stockpiles contain obsolete nerve gases and mustard agents in various munitions and containers. CDC is required by law (Public Laws 91-121, 91-441, and 99-145) to review the potential effects that the Army's disposal plans and activities could have on public health, regardless of the technology used, and to make recommendations to ensure that public health is protected. CDC takes no part in the selection of disposal methods except to point out potential adverse health effects of the options presented.

In its review capacity, CDC has access to stack emission data from trial burns of various combinations of agents and munitions. To date, CDC has examined the data from five separate trial burns, for each of which at least three individual stack sampling runs took place (1-3). Each stack sampling run provided data on volatile and semivolatile organic compounds and on inorganic compounds such as metals and hydrogen chloride.

Regulatory agencies review trial burn data to see whether an incinerator meets certain standards. Standards, such as those for air emissions of particulates, hydrogen chloride, and other products of combustion, may or may not be based upon demonstrated health effects of the substances in question. An example of non-health based standards are the generic "destruction and removal efficiency" (DRE) requirements for particularly toxic or hard-to-destroy [TABULAR DATA FOR TABLE 1 OMITTED] hazardous chemicals in the waste. Such chemicals must be destroyed or removed from the stack emissions so that no more than 0.01% (0.0001% for chlorinated dioxins and furans and polychlorinated biphenyls) of the original chemical fed into the incinerator is ultimately emitted into the ambient air (4). These DRE standards are based upon the demonstrated capabilities of a properly designed and operated incinerator and air pollution control system (5).

Regulatory agencies also review organic "products of incomplete combustion" (PICs) and inorganic metals emissions measured during the trial burns (6, 7). Through the use of air dispersion models, they can predict the maximum likely air concentrations of these substances in surrounding communities. Based upon the predicted level and duration of exposure at these concentrations, they can estimate the degree of risk that the emission of these substances poses to the public's health.

CDC examined the trial burn data from Army lethal agent incinerators on Johnston Island (J.I.) in the Pacific Ocean in order to better understand the health implications of the air emissions from that facility. In terms of the regulatory review described above, the J.I. facility met all requirements, including the screening values used by the U.S. Environmental Protection Agency (EPA) to conduct health risk assessments. However, CDC decided to also examine the data with respect to other criteria of safe exposure levels.

These criteria include the series of "media evaluation guides" that the Agency for Toxic Substances and Disease Registry (ATSDR) developed to screen hazardous substances in the various media of the environment (8). ATSDR's screening values for carcinogens in the air are often more stringent than EPA's screening values for the same substances.

Where available, CDC used even more restrictive criteria for some carcinogens, such as the "Ambient Air Level Guides (AALGs)" developed by Dr. Edward Calabrese et al. (9). The AALGs, which are used to review the toxicologic implications of air pollutants, can be as low as one-tenth of the EPA screening values.

Using these more restrictive screening values, CDC found that the J.I. incinerator trial burn data still met all criteria for acceptability. At the location where people would have the highest levels of exposure, the levels of organic compounds usually were hundreds to thousands times lower than the most restrictive health screening values. Likewise, emissions of metals were generally well below levels of health concern. One metal, chromium, was present at about one tenth the Calabrese AALG. This translates into a cancer exposure risk of 1 excess death per 10 million exposed individuals. If EPA methods are used, the worst-case exposure risk for this metal would be i excess cancer death per 100 million exposed individuals. Health professionals generally consider any risk less than one excess death per 100 thousand to 1 million exposed individuals to be acceptable. For purposes of general comparison, a pedestrian's risk of being killed by a motor vehicle over a 70-year period is 2 in 1,000 (10).

Other Perspectives

The above evaluation techniques provide health officials with some understanding of the risks associated with incineration facilities. Another means of looking at such risks is to compare levels of toxicants emitted with the ambient levels of those toxicants in areas surrounding incinerators. For example, existing or background levels of various pollutants in ambient air can be compared with the maximum ground level concentrations (MGLCs) of released pollutants. These MGLCs are found by modeling the dispersion of measured stack emission pollutants. When there is no data base describing the ambient air quality in the area of concern, ambient air data from other locations can be used as a rough benchmark to make the sort of comparison described above. If the MGLC of any pollutant approaches or is above the typical ambient air concentration of that same pollutant, reviewers should closely examine the pollutant's potential to damage human health. Conversely, if the MGLC of a stack-released pollutant is less than one-tenth of its typical background ambient air concentration, the stack emissions of that pollutant are probably not significantly adding to human exposure levels.

At J.I., the prevailing winds result in MGLCs being located in uninhabited areas; consequently, we would not anticipate human health to be affected by stack emissions. Nevertheless, it is useful to examine the MGLCs for two reasons: first, the results of the J.I. trial burns should be predictive of what will be experienced in demilitarization incinerators within the continental United States (CONUS), where people may be downwind of the operations; second, for short periods fishermen or other boaters may be at the MGLC point for the J.I. incinerator.

Table i lists several MGLCs that were developed by using EPA's SCREEN air dispersion model (11) for pollutants emitted by various incinerators at the J.I. facility. These MGLCs, calculated as a 1-hour duration maximum exposure level, are compared with ambient air levels for the same pollutants in urban air. The incinerators reviewed are: the liquid waste incinerator (LIC) used to burn liquid lethal agent; the metal parts furnace (MPF) used to decontaminate empty casings or other metal containers that once held liquid agent; and, the deactivation furnace (DFS) used to destroy energetic or explosive materials removed from various munitions.

As can be seen in Table 1, the "1-hour" MGLCs for all but one substance (manganese) were generally well below urban air average values. Because the urban air values represent the averages of concentrations over extended time periods (usually a year), the J.I. data should be adjusted to allow for direct comparison with urban air data. Annual average exposure concentrations are usually about 10% of "1-hour" maximum concentrations: annual average exposure concentrations of the pollutants from the J.I. incinerators in Table 1 would thus be even further below the ambient air averages, and even manganese would not exceed ambient air values (14).

Both regulators and the public ask questions about the levels of chlorinated dioxins and furans emitted by incinerators. Chlorinated dioxins and furans, which can also be found in cigarette smoke, smoke from woodburning stoves, and automobile and diesel exhaust, have received tremendous scientific and media attention as potential human toxicants (15, 16).

Because there are many species of chlorinated dioxins and furans with varying degrees of suspected toxicity, a system of weighting factors has been developed to provide a rough estimate of the toxicity equivalent (TEQ) of mixtures of dioxins and furans. The TEQ represents the toxicity of any combination of species in terms of an equally toxic concentration of 2,3,7,8-tetrachlorodibenzo-p-dioxin, which is believed to be the most toxic congener. Using J.I. incinerator trial burn data, the TEQ levels of chlorinated dioxins and furans for the various incinerators can be compared with TEQ levels from other familiar combustion sources. For example, in 1991, researchers in Norway evaluated the TEQ levels(1) of light duty vehicles (e.g., automobiles) and heavy duty vehicles (trucks) driven under stress (going uphill) and non stress (going downhill or coasting) conditions (17). To determine the relative danger posed by J.I. emissions, the TEQ of the J.I. deactivation furnace system (DFS) incinerator (1) is compared with the TEQ of diesel trucks as measured in the Norway study. The DFS TEQ is typical of the TEQ found for other J.I. incinerators. It should be noted that diesel truck emissions of chlorinated dioxins has not been indicated as a significant source of human exposure to these substances.

The dioxin TEQ mass emission rate of the J.I. DFS incinerator averaged 22.29 picograms ([10.sup.-12] gram) per second (pg/s). Based upon the Norway vehicle study, a diesel truck traveling at an average speed of 40 miles per hour with an equal amount of uphill and downhill driving would emit approximately 89 pg/s, or about 4 times as much dioxin TEQ as the incinerator.

A similar comparison can be made of the dioxin concentration of cigarette smoke versus the dioxin concentration of incinerator emissions. Mainstream smoke (the inhaled smoke) from one cigarette yields from about 0.1 to 1 pg mass TEQ (18, 19). (Note that side stream smoke from a cigarette does not pass through the filter and thus may be higher in mass TEQ.) For the DFS incinerator, the maximum annual average ground level concentration is 2.04 x [10.sup.-4] picogram per cubic meter (pg/[m.sup.3]) of air. An adult who stays at this maximum concentration location continuously for a year and breathes 23 cubic meters of air each day would be exposed to the same dioxin TEQ as he or she would from smoking from 1.7 to 17 cigarettes per year. For further perspective, it should be noted here that actual human intake of dioxins is predominantly from dietary sources, even for heavy cigarette smokers (20).

Summary

The purpose of this review is not to provide a blanket justification for incineration as a means of treating hazardous materials. Rather, it is to show that both society and the regulatory community must evaluate all controllable sources of pollution in a consistent manner in order to determine which activities actually pose the greatest threat to the environment and human health. Only with the results of such evaluations can we make informed, intelligent choices about public health policy. When an incinerator or any major new facility is proposed, public debate of many issues, including public health, is likely to take place. We, as public health practitioners, must strive to obtain and give the community the best available information for their consideration in such debates.

To provide such information, CDC will continue to examine Army chemical disposal technology. We will analyze the chemical and physical characteristics of emissions and effluents, estimate potential human exposure to particular pollutants, and compare the levels of pollutants in emissions with levels from other sources of pollution already present in a community and with health screening values if they exist. We hope that all sources of air emissions may someday be similarly scrutinized, even exploding ships in harbors.

Footnote

1. The Nordic TEQ model used in the Norway study differed slightly from the International TEQ model used to evaluate J.I. emissions; however, the difference in results attributable to the model used was negligible.

REFERENCES

1. U.S. Army Environmental Hygiene Agency (1991), Inhalation Risk From Incinerator Combustion Products-Johnston Atoll Chemical Agent Disposal System, Health Risk Assessment Number 42-21-MQ49-92, Aberdeen Proving Ground, Md.

2. U.S. Army Environmental Hygiene Agency (1993), Inhalation Risk From Incinerator Combustion Products-Johnston Atoll Chemical Agent Disposal System, Health Risk Assessment Number 42-21-MIBE-93, Aberdeen Proving Ground, Md.

3. U.S. Army Environmental Hygiene Agency (1993), Inhalation Risk From Incinerator Combustion Products-Johnston Atoll Chemical Agent Disposal System, Health Risk Assessment Number 42-21-M1X6-93, Aberdeen Proving Ground, Md.

4. U.S. Environmental Protection Agency (1986), Permitting Hazardous Waste Incinerators-Seminar Publication, EPA/625/4-87/017, Cincinnati, Oh.

5. Oppelt, E.T. (1987), "Incineration of Hazardous Waste: A critical review," Journal of the Air Pollution Control Association, 37(5):558-586.

6. U.S. Environmental Protection Agency (1989), Guidance on PIC Controls for Hazardous Waste Incinerators, Volume V of the Hazardous Waste Guidance Series, Washington, D.C.

7. U.S. Environmental Protection Agency (1989), Guidance on Metals and Hydrogen Chloride Controls for Hazardous Waste Incinerators, Volume IV of the Hazardous Waste Guidance Series, Washington, D.C.

8. Agency for Toxic Substances and Disease Registry (1992), Public Health Assessment Guidance Manual, Atlanta, Ga.

9. Calabrese, E.J. and E.M. Kenyon (1991), Air Toxics and Risk Assessment, Lewis Publishers, Chelsea, Mi.

10. Harvard Center for Risk Analysis (1992), Annual Report 1992, Harvard School of Public Health, Boston, Ma, 1-13.

11. U.S. Environmental Protection Agency (1988), Screening Procedures for Estimating the Air Quality Impact of Stationary Sources, Research Triangle Park, NC.

12. Lioy, P.J. and J.M. Daisey (1987), Toxic Air Pollution-A comprehensive study of non-criteria air pollutants, Lewis Publishers, Chelsea, Mi.

13. U.S. Environmental Protection Agency (1984), Health Assessment Document for Chromium, Research Triangle Park, NC.

14. California Air Pollution Control Officers Association (1989), Air Toxics Assessment Manual, Cameron Park, Ca.

15. Agency for Toxic Substances and Disease Registry (1989), Toxicological Profile for 2,3, 7,8- Tetrachlorodibenzo-p-dioxin, Atlanta, Ga.

16. Agency for Toxic Substances and Disease Registry (1994), Toxicological Profile for Chlorodibenzofurans, Atlanta, Ga.

17. Oehme, M., S. Larssen and E.M. Brevik (1991), "Emission Factors of PCDD and PCDF for Road Vehicles Obtained by Tunnel Experiment," Chemosphere, 23(11-12): 1699-1708.

18. Lofroth, G. and Y. Zebuhr (1992), "Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in Mainstream and Sidestream Cigarette Smoke," Bulletin of Environmental Contamination and Toxicology, 48:789-794.

19. Muto, H. and Y. Takizawa (1989), "Dioxins in Cigarette Smoke," Archives of Environmental Health, 44 (3): 171-174.

20. Muto, H. and Y. Takizawa, (1992), "Potential Health Risk Via Inhalation/Ingestion Exposure to Polychlorinated dibenzo-p-dioxins and dibenzofurans," Bulletin of Environmental Contamination and Toxicology, 49:701-707.

21. U.S. Environmental Protection Agency, (1990), Methodology for Assessing Health Risks Associated with Indirect Exposure to Combustor Emissions-Interim Final, Washington, D.C.

Harvey W. Rogers, M.S., Environmental Engineer, Centers for Disease Control and Prevention, U.S. Public Health Service, 1600 Clifton Road NE, MS F-29, Atlanta, GA 30333.