An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Great Lakes Integrated Atmospheric Deposition Network - Trends and Changes

PCB Concentrations

Atmospheric PCB concentrations continue to decrease. Concentrations are halving at a rate of about once every 15 years at all the U.S. sites. This suggests a somewhat consistent decrease across the Great Lakes region. PCBs remain higher in urban areas than in rural areas, with air concentrations are about 10 times greater. 

Organochlorine Pesticide Concentrations

Banned OCPs concentrations are generally declining in air. Chlordane, dieldrin, and DDT-related substances show halving times in the range of 7-13 years (Salamova et al. 2015). The fasted halving times observed are concentrations of a-HCH and g-HCH, falling quickly in air, with halving times of about 4 years at U.S. sites (Salamova et al 2015).

The insecticides, a-endosulfan and b-endosulfan, are still on the market, but they are slated to be eliminated in 2016. Even though endosulfan is currently in use, it is interesting that its vapor phase atmospheric concentrations around the Great Lakes are decreasing with halving times ranging from seven to thirteen years (Salamova et al 2015, Shunthirasingham et al., Article in Press). Discharges into the air may still happen due to emissions from its use and production in other areas of the world, and its presence in previously treated soils and in bottom sediments of rivers and lakes.

Polycyclic Aromatic Hydrocarbon

Total PAH Exitconcentrations in air show some important drops over time, with halving times ranging from seven to twenty-four years. PAH levels at Chicago and Cleveland are 10 times higher than the concentrations at the other IADN sites. However, the concentrations are also dropping most rapidly at these stations. Some attribute these drops to emission reductions from the implementation of the Clean Air Act. PAH concentrations are also decreasing at Eagle Harbor, the most remote IADN site in the US. 

Top of Page

Flame Retardant Concentrations

IADN has measured the concentrations of flame retardants since January 2005. Specifically measured in each sample were the atmospheric concentrations of polybrominated diphenyl ethers (PBDEs) and eight alternative halogenated flame retardants.   

The levels of almost all of these flame retardants were significantly higher in Chicago, Cleveland, and Sturgeon Point. For unknown reasons, the concentrations of pentabromoethylbenzene (PBEB) and hexabromobenzene (HBB) were relatively high at Eagle Harbor and Sturgeon Point. The concentrations of d-p-(α-Hydroxybenzyl)-phenylacetic Acid (DP) were also relatively high at Cleveland and Sturgeon Point, the two sites closest to this compound’s production site in Niagara Falls, New York. 

Concentrations of PBDEs are decreasing in Chicago and Cleveland. They are generally unchanged at the remote sites, Sleeping Bear Dunes and Eagle Harbor.

Concentrations of PBEB are decreasing at almost all sites except for Eagle Harbor, where PBEB levels were highest. HBB concentrations are decreasing at all sites except for Sturgeon Point, where HBB levels were highest. The reason for the relatively high levels of PBEB and HBB are not clear. DP concentrations are increasing with doubling times of 3-9 years at all sites except Cleveland and Sturgeon Point, where the concentrations are largely unchanged.

Atmospheric concentrations of the two main components of a flame retardant that is the primary replacement for penta-BDE based flame retardants, are rapidly increasing at all the five sites.