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Great Lakes Integrated Atmospheric Deposition Network

Scientific research in the 1980s showed the atmosphere to be an important source of many persistent toxic chemicals to the Great Lakes. The Integrated Atmospheric Deposition Network has been in operation since 1990, when Annex 15 of the Great Lakes Water Quality Agreement specified IADN by name.

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Master and satellite monitoring stations

IADN is a network of stations that monitor concentrations of persistent toxic chemicals in Great Lakes air and precipitation. Each Great Lake has one master station that offers the complete range of measurements. Ten satellite stations provide provide further details about levels of toxics in the air around the lakes. All but one of the Canadian satellite stations are precipitation-only. The U.S. satellite stations, IIT-Chicago on Lake Michigan and Cleveland on Lake Erie, provide the same monitoring as the master stations. They also provide useful information about levels of toxic substances in urban air and precipitation.

Over a million measurements have been made of the concentrations of PCBs, pesticides, PAHs, flame-retardants, and trace metals since the 1990s. The measurements determine the spatial and temporal trends of toxic chemicals in Great Lakes air, estimate the atmospheric loadings of the toxic chemicals to the Great Lakes, identify sources and/or source regions, and discover new emerging chemical threats to the Great Lakes.

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Atmospheric deposition of toxic chemicals to the Great Lakes

Although levels of persistent toxic chemicals in the air can generally be low, the large surface area of the Great Lakes results in major atmospheric inputs. Atmospheric deposition occurs when air pollutants move to the earth's surface from the air into water through rain and snow, falling particles, and absorption of gas. The atmosphere responds quickly to toxic reduction actions making atmospheric measurements an excellent way to track changes in persistent toxic chemicals concentrations across time and space.

Levels of certain persistent toxic chemicals have diminished considerably in the Great Lakes ecosystem over the past 30 years. Unfortunately, they continue to be at levels above those considered safe for humans. Fish consumption advisories in all five Great Lakes and their connecting channels are necessary. Emerging persistent toxic chemicals (e.g., flame retardants) in the Great Lakes ecosystem may pose new threats to human health and the environment. These emerging chemicals are screened in fish tissue by the Emerging Chemical Surveillance Program.

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IADN Management Actions

IADN tracks the success of regional, national, and international chemical reduction plans. Some successes include:
  • Atmospheric concentrations of many chlorinated pesticides as measured by IADN declined dramatically after national and international bans went into effect.
  • PCB sources like transformers, caulk and paint pigments have been identified because of the elevated levels of PCBs in urban areas.
  • PAH trends in both urban and rural air support increased pollution prevention efforts.
  • IADN identified several previously unrecognized persistent toxic chemicals including polybrominated diphenyl ethers and other flame retardants.

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