Environmental ▼ News Sinking carbon plays important role in POPs’ distribution
ENVIRON. SCI. TECHNOL. 2002, 36, 4229–4237
A lot of attention has focused on the fluxes between air and water On a global scale, phytoplankton the accumulation of persistent orwere equal to the fluxes between uptake and particle sinking appear ganic pollutants (POPs) in cold rewater and phytoplankton and the to be as important as temperature gions like the Arctic, but the oceans sinking particle fluxes. in determining air–water fluxes. “It may actually be a bigger and more The modeling results suggest seems that not too many chemicals permanent sink because of the vast that phytoplankton uptake and parare prone to [cold condensation] areas they cover and the completeticle sinking are important in some and the masses of chemicals which ness of their removal end up being con(a) processes, suggest new densed, in terms of the 90°N modeling results reportglobal mass balance, ed in the October 15 can be relatively small,” 60°N issue of ES&T (pp. says Kevin Jones of 30°N 4229–4237). Lancaster University in POPs are thought to the United Kingdom, 0° accumulate in polar who supplied field data 30°S areas because of the soto test the new models. 60°S called cold condensation “Removal to deep ocean effect, first described by sediments could be a 90°S Don Mackay at Canada’s quantitatively more im180°W 90°W 0° 90°E 180°E Trent University (Enviportant sink than the (b) ron. Sci. Technol. 1996, Arctic,” he says. 90°N 30, 390A–396A), in which When pollutants at60°N pollutants tend to partitach to particles and tion out of air and into sink into deep waters, 30°N water at colder tempera“it is in essence remov0° tures. Air–water exchange ing those contaminants 30°S due to cold condensation from the global cycle,” is one process that conadds Joel Baker, an 60°S trols the global distribuaquatic chemist and ention of POPs, but “there is vironmental engineer 90°S 180°W 90°W 0° 90°E 180°E also a second effect due with the University of to phytoplankton uptake Maryland’s Chesapeake and vertical sinking,” Biological Laboratory. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 says Jordi Dachs of “There isn’t very rapid ng m–2 d–1 Spain’s Institute of exchange between the Global profiles of predicted air–water and particle sinking fluxes for Chemical and Environbottom waters and the (a) PCB 52, a POP with low hydrophobicity, and (b) PCB 180, a POP with mental Research (IIQABsurface waters in those moderate to high hydrophobicity. CSIC) in Barcelona, who parts of the ocean. So led the new study. areas, but not in others. “At low lationce it gets down there, it is going To determine how important tudes, the phytoplankton biomass is to be down there for a long time,” phytoplankton uptake and vertical low; therefore, the effect of this uphe explains. scavenging of POPs are on a global take and settling is not very imporThe work does not contradict scale, Dachs and colleagues modtant. But at mid- to high-latitude the cold condensation effect but eled how the two processes influareas, where phytoplankton biorather suggests there is another ence air–water exchange. They used mass is very high, this effect domimechanism that is causing enrichremote sensing data to estimate nates as a sink of POPs,” Dachs says. ment of contaminants in polar food wind speed and ocean temperature, The hydrophobicity of the polluwebs. “It’s not just the temperature which affect air–water exchange, tant also determines to some deeffect on deposition and the high and chlorophyll concentrations, gree whether particle sinking is lipid nature of the food webs, but which provide information about important. In general, the less hythe oceans in that region seem to the distribution of phytoplankton drophobic chemicals, such as the be very efficient at capturing these biomass. In addition, they included low chlorinated PCBs, do not intercompounds,” Baker says. In addifield measurements of atmospheric act much with organic matter, and tion to being cold at the high latipolychlorinated biphenyls (PCBs), the effect is less important, Dachs tudes, there is a lot of carbon in the polychlorinated dibenzodioxins, says. With the more hydrophobic surface waters that settles. “It’s a and furans in the models. The recompounds, however, the influence combination of those two things searchers assumed that all three of sinking organic matter is very that appear to be important.” processes were at steady state, so important, he says. —BRITT E. ERICKSON 402 A
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / NOVEMBER 1, 2002
