of the Swiss Federal Institute of Technology Zurich. A delegation of Moldovan food producers who recently visited Switzerland found that addition of iodine to Swiss bread, baked goods, and cheese causes no change in the taste of these foods. About 60% of Swiss processed foods are made with iodized salt. Many countries with long-
standing iodization programs, including the U.S., The Netherlands, New Zealand, France, and Switzerland, have reported declining iodine levels (Eur. J. Cli. Nutr. 2001, 55, 162–166). To combat this decline, Swiss officials monitor iodine levels once every 5 years and adjust salt iodine levels accordingly. When the iodine level in salt was increased in Switzerland in
1998, urinary iodine rose and newborn infants had a more normal level of thyroid function, according to Zimmermann. “The best way to address this issue is to at least assure that iodized salt contains the amount of iodine it should, ideally to raise the iodine content of salt, and get the food processors to use iodized salt,” says Utiger. —REBECCA RENNER
Putting people on the map according to their geographic and climatic signatures as well as their distinctive plant and animal communities. For example, a rain forest biome differs in climate, Erle Ellis
Nature is no longer pristine. It is merely embedded within human systems, say a pair of eco-geographers in a study published in December 2007 in Frontiers in
Humans and nature live an intertwined existence across most of the planet, as evidenced in this village biome in Nepal.
Ecology and the Environment (DOI 10.1890/070062). By combining global data on human population distribution with those on landcover and land-use change, the researchers have remapped the biomes of the planet. Their findings reveal that humans dominate more than 75% of the earth’s ice-free land and that, of 21 newly identified biomes, only 3 are free of human influence. Ecologists have long used biomes to distinguish areas
geography, and organisms from a chaparral grassland biome. Biomes have been helpful to scientists in understanding changes in land cover and land use, the impacts of climate change on ecosystems and ecosystem function, and in crafting conservation plans. But until now, the dominant organism, Homo sapiens, has been consistently missing from the picture. “We consider the world mostly as either natural systems or, when we do include humans, it’s either
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urban or agriculture,” says study coauthor Erle Ellis of the University of Maryland Baltimore County. This is an oversimplification of the reality, he says. Earth systems expert Ruth DeFries of the University of Maryland College Park agrees. “It’s not just that humans dominate the landscape but both respond to the landscape and affect it at the same time,” she says. “Humans are part of the integrated system.” So with an aim to illustrate the more complex and widespread reality of human interactions with the landscape, Ellis and coauthor Navin Ramankutty of McGill University (Canada) set out to remap the biosphere. The so-called anthropogenic biomes or anthromes include urban and dense settlements, various village biomes, cropland biomes, rangeland, and forested biomes. The researchers further classified these new biomes according to human population density. A chief distinguishing feature of the anthromes is that they are “mosaics”, in which different types of ecosystems are mixed together to create complex, heterogeneous landscapes. For instance, onethird of global urban biomes are nested within densely populated village biomes or forested areas interspersed with croplands and housing. Traditional biomes, in contrast, are portrayed as homogeneous entities, spatially distinct from one another. “It’s a new map, it’s not a new idea,” says Ramankutty. “A lot of people who study land use in local communities or around the world
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,
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