vironment at the University of Wisconsin Madison. “We have always acknowledged that people affect ecosystems and landscapes, but we still called them the same old thing and mapped them as if they were still entirely natural. But now, thanks to this work, we can better describe the real biosphere—the one dominated by human actions—in our maps, models, and ecological field studies.” The results emphasize the “artificial dichotomy” between people
NDMA forms from diuron A common agricultural pesticide that persists in surface waters and groundwater may be contributing to the formation of a highly carcinogenic byproduct during water treatment. In a new study published in ES&T (pp 1072–1077), Wei-Hsiang Chen and Thomas Young of the University of California Davis confirm that the presence of diuron leads to an increased level of NDMA, or Nnitrosodimethylamine, in water undergoing chlorination or chlor amination. The researchers have yet to elucidate a direct mechanism of formation. Previous work from various groups in the U.S. and Germany identified the basics of NDMA formation, but determining what compounds lead to nitrosamine and in what quantities has been difficult. Although NDMA is not a regulated byproduct of water treatment, it may be hundreds of times more hazardous to humans than the suite of compounds—trihalomethanes and haloacetic acids—tracked under U.S. EPA regulations. Herbicides and pharmaceuticals with DMA chains have long been suspected of being precursors to NDMA. Past research by Susan Andrews of the University of Waterloo (Canada) showed that one herbicide, thiram, can lead to NDMA formation in drinking-water systems. In that case,
the herbicide was applied inside water pipes to prevent plant roots from destroying the delivery infra structure. Diuron, which also has a DMA group at one end, is used widely Cl
H
N
C
N
CH3
N ’-(3,4-dichlorophenyl)-N,N-dimethylurea (diuron) CH3 CH3
+
N
Cl
CH3
HN
peak formation of the nitrosamine within a day of treatment. But higher levels of free chlorine seemed to suppress NDMA formation. That finding suggests that the transformation pathway could be very complex and that diuron could lead to other intermediary byproducts, the authors conclude. Cl
O Cl
who want a “Wal-Mart world” (a world of supermarkets and consumption) and those who want to preserve a more “pristine” nature, says Ramankutty. And that has a significant bearing on ecological restoration. Instead of attempting to restore ecosystems to their pristine state, scientists and managers should try to restore or conserve nature so as to allow the ecosystems to function in the presence of humans, he says. —RHITU CHATTERJEE
H Cl–N H
H Dichloroaniline (DCA)
O=N–N
H
+
CH3 HN CH3 Dimethylamine (DMA)
CH3 CH3
Wei-Hsiang Chen and Thomas Young
know this for a fact,” he adds. David Lobell, a researcher at Stanford University’s Program on Food Security and the Environment, agrees. “I think the main contribution is to introduce this concept of formally talking about humans as a central part of the way we think about ecosystems.” The paper will “revolutionize how we think about the earth’s biosphere,” says ecologist Jonathan Foley, director of the Center for Sustainability and the Global En-
N -nitrosodimethylamine (NDMA)
Diuron breaks down into DMA, a possible precursor to the toxic byproduct NDMA.
in agriculture and in clearing land for power lines and roads. In California, where diuron use peaks during the rainiest months of the year, such treatments amounted to 600,000 kilograms (about 1.4 million pounds) in 2004, report Chen and Young. Because of its persistence, diuron applications to the landscape could end up as a widespread nonpoint source of the chemical. In laboratory experiments, the researchers tracked the formation of NDMA under various conditions. When more chlorine was present than diuron, they found
If large amounts of diuron or any other precursor are present in water, that could lead to an “actionable” level of NDMA byproducts, notes David Sedlak of the University of California Berkeley. California’s NDMA notification level is 10 nanograms per liter. If diuron turns out to have a high conversion rate, 100 micrograms per liter of the herbicide could be enough to hit that bar. However, current environmental levels are about an order of magnitude lower, Sedlak says; this makes diuron less problematic, “but it is an indicator of how commonly used herbicides,
February 15, 2008 / Environmental Science & Technology ■ 981
pesticides, and pharmaceuticals might end up being NDMA precursors.” “During chloramination, almost every natural or manmade compound holding a dimethylamine group might serve as [a] precursor for NDMA,” comments Carsten Schmidt of Technologiezentrum Wasser (Germany). However, he clarifies, “the potency of NDMA formation might differ from one precursor to the other considerably.” Schmidt and colleagues soon will publish a report for the Awwa Research Foundation dis-
cussing, among other issues, the role of DMA in NDMA formation. Although DMA was “long thought to be one of the most reactive precursors,” Schmidt notes, it actually forms NDMA at concentrations about 80-fold lower than ranitidine, a drug for gastritis. Other researchers comment that high NDMA concentrations from diuron remain unlikely except in very specific circumstances, but experts who spoke to ES&T agree that the new study is important because of the widespread use of diuron in U.S. agriculture
and elsewhere. “The nonpointsource nature of diuron is intriguing because NDMA precursors have previously been attributed to wastewater,” notes William Mitch of Yale University, who has conducted research on NDMA formation. “It would be useful to follow up this study with field results quantifying the percent contribution of diuron to total precursors” of NDMA in a watershed, he adds. Such data will be key in determining what chemicals to restrict in runoff or other nonpoint sources. —NAOMI LUBICK
Promises of plug-in hybrids
California Cars Initiative
low PHEVs to replace up to 34% of today’s light-duty vehicle fleet. Michael Kintner-Meyer says As the automotive industry readies U.S. currently has sufficient spare that the results reported in the itself to churn out new test models nighttime electricity capacity to ES&T study are “pretty similar” to of plug-in hybrid electric vehicles charge a large fleet of PHEVs. those of his group at Pacific North(PHEVs), scientists are trying to “Given any sensible realistic west National Laboratory. Kintfigure out just how environmenpenetration of [PHEVs] into the ner-Meyer found that 43% of the tally friendly these automobiles marketplace, assuming they are current fleet could be replaced by are. Now, a new study in ES&T (pp accepted by consumers, the elecPHEVs with existing power-genera1185–1190) corroborates pretion capacity in the U.S. vious findings that PHEVs “Having plug-in hybrids can significantly reduce charge at night will make CO2 emissions compared our product less expensive,” with conventional vehicles. says Hawk Asgeirsson of However, the results also Detroit, Mich.-based DTE show that if PHEVs were to Energy. This is because it fully penetrate today’s fleet, would enable some of the the ultimate energy savings most efficient power plants and reductions in emisto operate at full capacity sions would depend on the (instead of being used only fuel economy of the vehicles at peak hours), thus driving they replace. down maintenance costs. Much like the hybrid vePHEVs are not comhicles on the road today, Plug-in electric cars like this prototype PHEV Toyota mercially available today, Prius, built by the nonprofit group California Cars PHEVs are battery-powered primarily because of high Initiative, could achieve 100 miles per gallon and reduce automobiles with a backup battery costs. However, the emissions and dependence on foreign oil. gasoline engine. Once the big automakers, includbattery’s charge is exhausting Ford Motor Co., are ed, the vehicles switch to gasoline tricity infrastructure can handle it busy making test PHEV models. for power, allowing the battery with ease,” says study author John Yet, even if the issue of cost is reto be recharged. However, unlike Sullivan, now a scientist at the Uni- solved, questions remain about the hybrids of today, PHEVs rely versity of Michigan Transportation the impacts of these vehicles comprimarily on electricity to charge Research Institute. PHEVs need pared with conventional gasoline their batteries to full capacity. about 10 hours of charging every and hybrid vehicles. Some of these Because electricity demand is night. If all the spare nighttime questions center around energy much lower at night, many power electricity were used to charge consumption and emissions of CO2 plants (about 40%) in the U.S. operPHEVs, 13% of all the fuel used naand other pollutants (plug-ins shift ate at reduced nighttime loads. Actionally for electricity generation the source of emissions from the cording to the new ES&T study, the would be consumed. This could alvehicles themselves to whatever 982 ■ Environmental Science & Technology / February 15, 2008
