Integrated Atmospheric Deposition Network (IADN) 

Over the past few decades, the Great Lakes have been the recipient of many different persistent organic pollutants (POPs) from a variety of sources. In an attempt to better understand atmospheric deposition as one of these sources of contamination, the Integrated Atmospheric Deposition Network (IADN) was formed in 1990 through mandates of the Clean Air Act and Great Lakes Water Quality Agreement. The project is a joint venture between Environment Canada, the Ontario Ministry of the Environment, and the United States Environmental Protection Agency’s Great Lakes National Program Office which has provided funding to the Hites’ Laboratory to manage IADN. We operate five sites: the two urban sites  are in Chicago, IL and Cleveland, OH. A rural site is located at Sturgeon Point, NY. The two remote sites are at Sleeping Bear Dunes, MI and Eagle Harbor, MI.  At all the sites, vapor and particle phase air samples are collected every 12 days for 24 hours using a modified Anderson high-volume air sampler.  In addition, precipitation samples are collected using MIC sampler for each calendar month.  We measures 84 polychlorinated biphenyl (PCB) congeners or congener groups, 22 organochlorine pesticides (both banned and in use), 19 polycyclic aromatic hydrocarbons (PAHs), 43 flame retardants (both discontinued PBDEs and alternatives) in each of the phases. Click to view the IADN Field Sampling Procedure, the IADN Sample Preparation Procedure or the IADN GC Analysis Procedure. Long-term monitoring networks like IADN are essential in understanding the behavior of pollutants in the atmosphere and making the link between policy and science. For more information, visit the official IADN website.

Map of the United States IADN Sites.

LEGACY POPS  Back to top

With almost twenty years of collected data, one of the more interesting aspects of IADN is the analysis of long-term spatial and temporal trends of POP concentrations in the Great Lakes basin.  Our latest approach to the analyses of the temporal trends in POP concentrations includes harmonic multiple regression allowing combining concentrations for a specific compound or group of compounds in all three phases (vapor, particle, and precipitation) at all IADN sites together via calculating partial residuals of actual concentrations.  This allows us to integrate the data from all phases and sites, giving us a better overall depiction of the behavior of these chemicals in the Great Lakes region. This relatively simple approach indicated that the concentrations of PCBs in air around the Great Lakes are decreasing with an overall halving time of 17 ± 2 years, which is slow for a substance that was banned about 35 years ago. Phenanthrene, chrysene, and endosulfan showed halving times on the order of 10 years. The concentrations of several organochlorine pesticides were decreasing more rapidly; for example α- and γ-HCH (lindane) have halving times of about 3.5 years. It is somewhat surprising that, 40 years after it was banned, α-HCH is still present in the environment despite a relatively rapid elimination rate. Clearly, technical-HCH was heavily used in its heyday. The rapid halving times observed for α-HCH and γ-HCH(lindane) are consistent with the relatively high volatilities of these chemicals (for more details go here).

Partial residuals versus sampling date for the three phases combined for (A) PCBs, (B) phenanthrene, (C) chrysene, (D) endosulfans, (E) DDTs, (F) chlordanes, (G) γ-HCH or lindane, and (H) α-HCH.

BROMINATED FLAME RETARDANTS  Back to top

Over the last several decades, there has been a rapid growth in flame retardant industry , and there are now more than 175 chemicals classified as flame retardants. These chemicals are used in a variety of consumer products, including electronics, textiles, furniture, and toys.  Of these, at least 75 are brominated flame retardants (BRFs).  Among them, the polybrominated diphenyl ethers (PBDEs) have been widely used and are persistent and accumulate in the environment.  As a result, the use of the penta-, octa-, and deca-BDE commercial mixtures was restricted in the European Union, the production and use of the penta- and octa-mixtures in the United States was voluntarily phased out in 2004, and the production, import, and sale of the deca-BDE mixture in the United States will be discontinued by the end of 2013. These restrictions have led to an increased market demand for non-regulated flame retardants — or at least, flame retardants that are not in the news. These include decabromodiphenylethane (DBDPE) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), both of which have been marketed as alternatives to various PBDE formulations. In addition, “older” chemicals are sometimes being reintroduced to the market. These include hexabromobenzene (HBB) and pentabromoethylbenzene (PBEB), compounds that have apparently been manufactured for several decades.

In IADN samples, PBDEs were found in the gas, particle, and precipitation phases.  In general, the highest ΣPBDE concentrations were detected at the two urban sites (Chicago and Cleveland) and the lowest ΣPBDE concentrations  were measured at the remote Eagle Harbor (EH) site in all three phases. This spatial distribution pattern in  ΣPBDE concentrations can be explained by the fact that PBDEs are used in consumer products,  the abundance of which is proportional to population.

Concentrations of ΣPBDE, BDE-47, BDE-99, and BDE-209 in the atmospheric vapor phase, particle phase, and precipitation; the thin black lines represent the median, and the thick red lines represent the arithmetic mean; the boxes represent the 25th and 75th percentiles; the whiskers represent the 5th and 95th percentiles. Site abbreviations: EH Eagle Harbor, CH Chicago, SB Sleeping Bear Dunes, CL Cleveland, SP Sturgeon Point.

Overall, ΣPBDE concentrations are declining in the atmosphere of the Great Lakes with halving times of ∼6 years. The overall halving time of ΣPBDE concentrations is shorter than that of ΣPCBs (∼17 years), ΣPAHs (∼10 years), and ΣDDTs (∼9 years) reported recently for the same sites around the Great Lakes and using the same harmonic regression approach used here.  This may indicate that the 2004 production restrictions of penta- and octa-PBDEs are having an effect and that the concentrations of PBDEs in the atmosphere are declining faster than those of other persistent organic pollutants.

Similarly to PBDEs, highest levels of DBDPE and BTBPE were detected at urban sites Chicago and Cleveland. However, unlike PBDEs, the highest average HBB concentrations were observed at the rural Sturgeon Point site in the vapor phase. The concentration of HBB at the Sturgeon Point site is ∼6-10 times higher than the HBB concentrations in Cleveland and Chicago. This finding is remarkable given that there are no known HBB sources near Sturgeon Point. Surprisingly, PBEB concentrations in particles and precipitation were highest at Eagle Harbor. Considering that Eagle Harbor is a very remote site and few people live or work there, this observation is hard to explain. For more details go here.

Concentrations of DBDPE, HBB, PBEB, and BTBPE in the atmospheric vapor phase, particle phase, and precipitation; the thin black lines represent the median, and the thick red lines represent the arithmetic mean; the boxes represent the 25th and 75th percentiles; the whiskers represent the 5th and 95th percentiles. Site abbreviations: EH Eagle Harbor, CH Chicago, SB Sleeping Bear Dunes, CL Cleveland, SP Sturgeon Point.

DECHLORANE PLUS Back to top

Dechlorane Plus (DP) is a highly chlorinated flame retardant (see Figure 1). It is a substitute for Dechlorane, which was also marketed under the name Mirex as a pesticide and was banned in 1970s. Although DP is a high production volume chemical and has been in use for decades, it was found in the environment for the first time in IADN samples (for more details go here http://pubs.acs.org/doi/abs/10.1021/es051911h). In fact, DP was detected in samples from all IADN sampling sites, with relatively high levels in samples from Sturgeon Point. This observation suggests that the manufacturing facility of DP, OxyChem in Niagara Falls, New York, might be the main source of DP to the Great Lakes.

Concentrations of syn-DP, anti-DP, and ΣDP in the atmospheric vapor phase, particle phase, and precipitation. The thin black lines represent the median, and the thick red lines represent the mean; the boxes represent the 25th and 75th percentiles; the whiskers represent the 5th and 95th percentiles. Site abbreviations: EH EagleHarbor, CH Chicago, SB Sleeping Bear Dunes, CL Cleveland, SP Sturgeon Point.

The analysis of the temporal trends of the anti-DP concentrations shows that the concentrations of this compound are increasing in the atmosphere with the doubling time of ~10 years (for more details go here).

EMERGING POLLUTANTS Back to top

As it was mentioned above, PBDE commercial mixtures have been or will be voluntarily withdrawn from the market because of their tendency to leak from the materials where they has been used and to be-come ubiquitous in the environment.  In 2004, to replace these commercial PBDE mixtures, the flame retardant industry began to use alternative formulations called Firemaster 550, Firemaster BZ-54, and DP-45.  Firemaster 550 consists of about 35% of 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), about 15% of bis(2-ethylhexyl)-tetrabromophthalate (TBPH), and about 50% of aromatic phosphate es-ters. 5  Firemaster BZ-54 consists of about 70% of TBB and about 30% of TBPH.5  DP-45 contains TBPH only.

In a recent study, TBB and TBPH were identified and quantitated in gas and particle-phase air samples collected from six sites near the shores of the Great Lakes.  TBB and TBPH were detected in more than half of the samples collected from 2008 to 2010.  Urban areas, such as Chicago and Cleveland, showed the highest concentrations (0.36-290 pg/m3), while remote areas, such as Eagle Harbor and Sleeping Bear Dunes, exhibited the lowest levels (0.050-32 pg/m3).  The atmospheric concentrations of TBB and TBPH increased rapidly and significantly over this time period (see figure below), perhaps indicating that these compounds are replacing the polybrominated diphenyl ethers (PBDEs), which have been removed or soon will be removed from the marketplace (for more details go here).

Temporal trends of TBB and TBPH concentrations at urban and rural sites.