Section 8: Airborne Toxic Substances
(Annex 15)

Observation

The sources of a majority of airborne toxic substances remain unmeasured and, in some cases, unidentified. This hinders the ability of the two governments to reduce atmospheric deposition of toxic substances. Resolving this problem will require an extension of monitoring activities beyond the current International Atmospheric Deposition Network.

Discussion

Two past biennial reports have noted that emission inventories needed to support the objectives of Annex 15 are inadequate. Currently, only mercury, dioxin and cadmium inventories are adequate for source-receptor modeling on a broad binational geographic scale. Inventories of most of the 11 Critical Pollutants are marginal.¹ Those for the balance of the Critical Pollutants and Level II Binational Toxic Strategy contaminants range from inadequate to largely non-existent. Existing data on point sources, such as factory and power plant smokestacks, need enhancement and assurance of quality. Other sources, such as burn barrels (barrels used for the open burning of rubbish), which can produce dioxin, require initial analysis. The governments are making some gains with pollution prevention initiatives to reduce emissions of toxic substances. Nevertheless, the focus and achievement of such programs could be sharpened and measured by improved knowledge of the dominant sources and their pathways.

Loadings of PCBs to Lake Michigan from unmeasured and often unknown sources are far greater than those that can be attributed to regulated point sources. While we know that hundreds of kilograms of PCBs enter the lake each year via the atmosphere, only about 30 kg per year can be attributed to regulated sources. Urban air plumes originating in Chicago and Gary, particularly in the summer, contain significant amounts of persistent toxic substances, such as PCBs, from various nonpoint sources, which can include transformer storage yards, landfills and brownfield industrial sites. These observations could well apply to other urban areas throughout the Great Lakes basin.

A number of techniques have been shown capable of estimating emissions from some of these sources. Applying such techniques to Critical Pollutants throughout the Great Lakes basin would provide important information to support more effective management actions.

To determine concentrations of several persistent toxic substances in the air, the governments use the binational Great Lakes Integrated Atmospheric Deposition Network of five master stations, one per lake basin, and 14 satellite stations. Studies focusing on Lake Michigan show that regional concentrations and loadings estimated from these data alone do not accurately represent actual deposition to that lake basin. For example, PCB concentrations at the Sleeping Bear Dunes master station were shown to be substantially lower than samples taken at another point on the eastern shore or adjacent to Chicago. Variations in concentrations across the basin were very pronounced. Similar determinations for the other lakes for this and other contaminants also would likely be inaccurate. Sampling at a number of other locales in the lake basins, including over water, and the development of better estimation tools are necessary to improve these regional deposition estimates and to develop and implement effective management programs and policies.