News Briefs
ethanol is not really sustainable or renewable, says Heather MacLean, an environmental engineer at the University of Toronto. In addition, using fertilizers to grow more corn could worsen water quality problems, she points out. Moreover, a positive NEV will not tell you whether the fuel is renewable or will reduce reliance on foreign oil PHOTODISC
Concerns about reducing dependence on foreign oil and avoiding the groundwater pollution caused by MTBE have refocused attention on corn ethanol, which, after MTBE is the second leading fuel oxygenate used in the United States. The congressional debates over proposals to subsidize corn ethanol production have hinged on the fuel’s net energy value (NEV), but this number masks a host of environmental and economic impacts, some researchers assert. They say policy makers need to see a full life-cycle analysis of the automotive fuel, which might reveal that ethanol consumes significant amounts of fossil fuel, could degrade water quality, and become too costly if production is expanded. U.S. senators and representatives should not rely on NEV alone as an indicator of the fuel’s renewability, says Michael Wang, environmental analyst at Argonne National Laboratory. The NEV compares the amount of energy produced by a gallon of ethanol to the energy it takes to fertilize, grow, harvest, transport, and distill the corn. Nearly a dozen studies of NEV have come up with estimates ranging from an unfavorable value of –33,562 to a high of 30,589 British thermal units per gallon (Btu/gal), depending on the biases and assumptions of the researchers, says Susan Powers, an environmental engineer at Clarkson University. Perhaps the most accurate estimate was released in July by the U.S. Department of Agriculture (USDA) and concludes that corn ethanol has an NEV of 21,105 Btu/ gal, yielding 34% more energy than it takes to produce it. This study clearly lays out the boundaries of the analysis and states its assumptions: the corn yields are based on Midwest averages, and the most up-to-date facilities are used to make the fertilizers and to mill and distill the corn, Powers says. The USDA study also shows that significant amounts of fossil fuel, mainly coal and natural gas, are burned to produce ethanol fuel, making it a net emitter of greenhouse gases. For that reason, corn
because it leaves out key information, says Wang, coauthor of the USDA report. Current production of ethanol fuel is 1.6 billion gallons per year, which displaces only about 1% of the Btus in the 120 billion gallons of gas consumed each year in the United States. Thus, the fuel’s impacts are very modest, he says. Midwest senators who support corn subsidies would boost production from 1.6 billion gallons per year to 13 billion gallons per year, says Lester Lave, an economist at Carnegie Mellon University. When production climbs to 3–5 billion gallons per year, the markets for the process’s byproducts, primarily animal feed, will be saturated, driving up the cost of ethanol and making it unaffordable, he says. “At this point, it makes sense to switch to cellulosic ethanol from grass and trees, which does not require the fertilizers, pesticides, and soil disturbance associated with growing corn,” he says. When compared to MTBE and gasoline, ethanol is more renewable and has fewer environmental impacts, counters David Morris, an economist at the Institute for Local Self-Reliance, a nonprofit research organization. Organic growing practices and advances in technology can help ethanols become a beneficial fuel with lower greenhouse gas emissions and polluted runoff, he says. —JANET PELLEY
A draft guidance for assessing the toxicity of chemical mixtures has been published by the U.S. Agency for Toxic Substances and Disease Registry (ATSDR). The guidance recommends assuming that toxicities are additive—an approach that is consistent with the recommendations of the U.S. EPA and other agencies. ATSDR also published draft recommendations for determining the additive toxicity of six contaminant mixtures that are often found together: metals— arsenic, cadmium, chromium, and lead; BTEX compounds—benzene, toluene, ethylbenzene, and xylene; metals—lead, manganese, zinc, and copper; persistent chemicals found in breast milk; persistent chemicals found in fish; and chlorinated solvents. Draft Guidance Manual for the Assessment of Joint Toxic Action of Chemical Mixtures is found at www.atsdr.cdc. gov/interactionprofiles/ipga.html. Ship traffic in European waters pumped more than 163 million metric tons of air pollutants into the atmosphere in 2001, according to a new comprehensive survey by the European Commission (EC). These include nitrogen oxides, 3.6 million tons; sulfur dioxide, 2.6 million tons; carbon dioxide, 157 million tons; hydrocarbons, 134,000 tons; and particulates, 21,000 tons. The findings are expected to play a large role in EC efforts to curb shipping emissions, which are increasing even as land-based levels of air pollutants decline and contributing to problems of regional acidification, eutrophication, and groundlevel ozone formation, according to the EC. Quantification of Emissions from Ships Associated with Ship Movements between Ports in the European Community can be accessed at europa.eu.int/comm/environment/ air/background.htm.
NOVEMBER 1, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
PHOTODISC
Ethanol fuel benefits questioned
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