How PCBs Are Like Grasshoppers
ANIRBAN MAHAPATRA
perature and organic content in More than a million tons of polyness indexswhich scientists can soil, they are still accumulating. chlorinated biphenyls (PCBs) were use to estimate a chemical’s longThey also confirmed that “secproduced from 1929 through the range transport. “We’re providing ondary fractionation,” or the leapmid-1970s, and of that amount, an expression that allows you to ing patterns by which PCBs roughly 10%, are still in the envidistinguish chemical loss provolatilize and settle away from ronment. This ubiquitous cesses in the atmosphere from primary sources, drives that trend. residuesdetected in the farthest the effect of distance itself,” he Finally, Miriam Diamond, and reaches of the planetsis highly colleagues from the Univermobile. PCBs move in grasssity of Toronto, Canada, rehopper patterns; volatilizing veal how cities, and from soil to air in warm especially downtown finanweather and falling to earth cial districts, store enormous miles away as temperatures volumes of PCBs that can cool. In the current issue of escape to air and contamiES&T, three research papers nate other areas (Environ. build on prior knowledge of Sci. Technol. DOI 10.1021/ PCB transport with findings es9012036). Diamond fothat help scientists relate cused exclusively on primary contamination Toronto, where she found sources to levels found elsethat 437 t (metric tonnes) of where. “They basically finePCBs lie sequestered in tune our understanding of Cities like Toronto are constructed from materials and contain electrical connections that can off-gas PCBs “closed sources,” such as how PCBs move from for decades, despite production bans (which do not electrical transformers, and sources to receptors,” exalso in polysulfide sealants plains Keri Hornbuckle, who preclude usage). used for building construcchairs the Department of explains. “These two factors are tion. Using a multimedia urban Civil and Environmental Engiwhat determine the chemical’s model, she and colleagues calcuneering at the University of Iowa. concentration at a point of obserlate that these combined stocks “There’s been a lot of work in this vation.” release up to 1.4 mg/m2 of PCBs area and these papers advance Yi-Fan Li, from Environment our understanding of those global to the atmosphere every year. Canada, and colleagues, address a processes.” What’s more, those annual emiscrucial aspect of the grasshopper Harald von Waldow and colsions amount to less than oneeffect: namely, that in colder leagues from the Institute for half of one percent of Toronto’s regionsswhich tend to sequester Chemical and Bioengineering, in total PCB inventory, which means PCBsssoil-to-air exchanges have Zurich, Switzerland, tackle the the city could off-gas the pollutyet to reach equilibrium (Environ. ants (almost) indefinitely. “You amorphous concept of “remoteSci. Technol. DOI 10.1021/ could argue this is a very small ness” (Environ. Sci. Technol. DOI es901871e). According to Hornemission,” Diamond concedes. 10.1021/es9030694). A common buckle, that is in part because “But we’re saying that PCBs are term in the PCB literature, rePCB reservoirs in warmer climates so persistent and have the potenmoteness refers to the distance supply new inputs of the chemitial to accumulate to the extent between a chemical’s source and cal to more extreme latitudes. Yithat even low emissions are probits point of observation in the enFan Li’s research team calculated lematic.” Adds Hornbuckle, vironment. Remoteness is also air-soil equilibrium rates, dubbed “Emissions from cities can wind chemical-specific, and its quantiKSA, for several regions of the up in arctic seals. What we need tative nature hasn’t been clearly globe: China, the West-Midlands to do is prioritize which sources defined. Heavier PCBs are lost of the U.K., Central and Southern around the world we’re going to quickly from the atmosphere, he Europe, and a longitudinal focus on next. And these papers explains, and thus stay closer to transect from the U.K. to Norway. help to move us in that direcsources, while lighter compounds They confirmed that lighter PCBs tion.” are apt to travel greater distances. havesin most placessreached In his paper, von Waldow introduces a new variablesthe remote-
equilibrium, while in remote areas, both due to the effect of tem-
2752 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / April 15, 2010
10.1021/es100696y
—CHARLES SCHMIDT
2010 American Chemical Society
Published on Web 03/22/2010
