Tracking POPs across the planet
The most extensive analysis ever of POPs in air throughout the world contains some surprises.
A team of scientists from North America and Europe is publishing the most comprehensive analysis yet of global concentrations of persistent organic pollutants (POPs) in air today on ES&T’s Research ASAP website (10.1021/es060447t). Although some of the data have been presented at scientific conferences, this is the first time the information is being published in a peer-reviewed journal.
The researchers present information about levels of POPs in the air at 42 sites on 7 continents (view map). In addition to the “dirty dozen” POPs targeted by the Stockholm Convention, they provide data about some emerging contaminants under consideration for inclusion in the treaty, including the polybrominated diphenyl ether (PBDE) flame retardants and the pesticide endosulfan.
“It is very valuable and important that there is a way to expand the network of sampling sites because, at a global level, there is still a lack of field data,” says Martin Scheringer of the Swiss Federal Institute of Technology’s Institute for Chemical and Bioengineering. The data fill in important gaps identified by the parties to the Stockholm treaty, such as Africa and Asia, adds Cheryl Heathwood, the chief of Environment Canada’s hazardous air pollutant research division. No monitoring stations or regional agreements for gathering monitoring data exist in those areas, she points out.
“Due to the rapid response of air concentrations to changes in primary emissions, the atmosphere is expected to be a particularly useful sentinel of the ‘effectiveness’ of the [Stockholm] Convention,” the researchers write. The data fulfill the needs of the convention in terms of comparability because the same sampler type and method were used to obtain them, says the paper’s corresponding author, Tom Harner of Environment Canada’s science and technology branch. The sites were chosen to collect data on concentrations in urban and rural agricultural areas, at remote “background” locations far from human and agricultural activities, and at the north and south poles, adds the paper’s first author, Karla Pozo of Environment Canada.
Simple, passive sampling devices called PUF (polyurethane foam) disks, which require no electricity to operate, were used to collect the data. They look a bit like flying saucers and cost between $25 (when the scientists construct them themselves) and $100 (the going rate for professionally manufactured devices from Tisch Environmental). Such passive air samplers are “becoming an official method for looking at spatial patterns and temporal trends of POPs,” Harner says.
“In general, the results agree with what we know about use patterns of the target chemicals,” Harner says. As expected, the POPs found at some of the greatest concentrations were PCBs. The highest levels were detected at urban sites. The samples collected in Manila had a total of 2800 pg/m3 of all the 48 PCBs analyzed in the study.
The researchers also detected very high concentrations of endosulfans, in the nanograms-per-cubic-meter range, in the air of Bahia Blanca, Argentina, and Las Palmas, Canary Islands. These levels are consistent with endosulfan’s status as a current-use pesticide, and the data could be used to support the nomination of endosulfan for inclusion in a future iteration of the POPs treaty, Harner says. Newer, unpublished data from the study suggest that levels of endosulfan show an “interesting seasonal pattern,” peaking during the summer season for both hemispheres, Pozo adds.
“However, there have been instances where we see strange results—either very high concentrations [such as] in the case of pesticides... and in some cases elevated concentrations where we don’t expect them,” Harner says. He stresses that the data have gone through full quality assurance and quality control.
Most of the unexpectedly high concentrations reported in the study are for pesticides banned by the POPs treaty. The researchers detected high levels of hexachlorocyclohexanes (HCHs) at Chengdu, China (145 pg/m3 α-HCH; 68 pg/m3 γ-HCH); De Aar, South Africa (117 pg/m3 α-HCH; 67 pg/m3 γ-HCH); Harbin, China (132 pg/m3 α-HCH); and Georgia, U.S. (102 pg/m3 α-HCH). The researchers found notably high concentrations of chlordane (338 pg/m3) in the Philippines, and high levels of dieldrin (189 pg/m3) at Las Palmas, Canary Islands. They also report elevated concentrations of heptachlor at Bahia Blanca, Argentina, and the Philippines.
The data on the levels of airborne PBDEs in the new paper have not been presented previously, according to the researchers. Although the levels of airborne PBDEs are generally greatest near urban sites, as expected, the researchers found the highest concentrations at an agricultural site in Georgia, U.S. (24 pg/m3). The next highest concentrations were reported for California (19 pg/m3), Kuwait City (17 pg/m3), and Toronto (10 pg/m3). PBDEs are considered candidate POPs by the Stockholm treaty.
In some cases, the evidence presented in the new paper suggests that the emissions were due to new uses of the banned POPs, but the new data also highlight the importance of old sources. For example, the highest levels of p,p′-DDE, the compound that DDT is converted to in the environment, were at a site in California (232 pg/m3), where DDT has been banned since 1972. “The issue of emission of DDT and other legacy pesticides... from previously contaminated fields is an important one. It helps to explain why we continue to see these chemicals in the global atmosphere,” Harner says.
