Overlooked impacts of bioproducts
Technology News –January 17, 2007

Bio-based fuel and plastics could reduce global warming, but they have other environmental impacts that should be factored into assessments of the products' "greenness".

The debate over whether plant-derived products are better for the environment than their petroleum-based counterparts has centered on the amount of energy that goes into growing the crops and making the products as well as the greenhouse gases that result from burning fuels. New research published today on ES&T’s Research ASAP website (DOI: 10.1021/es0606125) is the first to quantify the environmental impacts of the fertilizers, pesticides, and equipment that are used in soybean and corn agriculture. The work suggests that policy makers should rethink the benefits of bio-based fuels and plastics.

Rising oil prices and the pursuit of energy security have led to government subsidies in the U.S. for ethanol and biodiesel and a growing market for bio-based plastics, glues, and inks. Compared with petroleum-based products, these commodities are considered “green” because they come from plant sources—even though studies have shown that their production may require more fossil fuels—and because they emit less greenhouse gases.

But the environmental impacts of these products are not limited to global warming, says Amy Landis, a civil engineering graduate student at the University of Illinois at Chicago and a coauthor of the paper. Chemicals and heavy machinery used in soybean and corn farming could adversely affect soil, groundwater, and air quality.

Nitrogen and phosphorus in fertilizers and pesticides cause hypoxia and eutrophication, whereas air pollutants, emitted during the operation of farm equipment, have human health risks. “People keep having this argument about whether or not [bio-based products] are better for global warming, but you have to make your lens just a little bit bigger and look at the whole problem,” Landis says.

Landis and her colleagues compiled an expanded data inventory for use in bioproduct life-cycle assessments (LCAs) by including the flows of nitrogen, phosphorus, pesticides, and U.S. EPA criteria air pollutants such as nitrogen oxides, sulfur dioxides, and volatile organic compounds. Most inventories have overlooked these compounds.

The researchers modified a software model developed by the U.S. Department of Energy to estimate energy use and air emissions associated with crop production and developed an independent model to estimate pesticide runoff. They used data from nine states in the U.S. corn belt that together produced 80% or more of the country’s corn and soybeans in 2003. They considered corn and soybean agriculture as one system, because farmers typically rotate the crops on a yearly basis.

A key advance over past LCAs is that the researchers estimate a range of values for the factors they consider in their inventory, whereas past studies have estimated single values. For instance, they calculate phosphorus emissions at 0–0.65 grams per kilogram (g/kg) of corn; the most likely value is 0.1 g/kg. The total energy use is estimated at 2.3–3.3 megajoules/kg of corn.

Including this variability in LCAs is crucial for agriculture because “there’s no one way that people farm,” says Susan Powers, a civil and environmental engineer at Clarkson University. “Rather than just taking an average and saying all fields in the Midwest behave like this, they’re saying there’s a range.”

Thomas Seager, a civil engineer at Purdue University, says that having a range of values for emissions and energy use shows that the answer to whether bio-based products make environmental sense is not a simple yes or no. “Under some conditions, bio-based production might make a great deal of sense,” he says. “Under other conditions, it might be a bad trade, and that’s a distinction that up until now we just haven’t thought about.”

Academic and industry researchers should be able to plug the inventory data into their LCAs to weigh the environmental impacts of bio-based products. Officials with chemical producer DuPont are interested in using this data for the LCA of a polymer product that is partly plant-based, Landis says.

According to Seager, the paper should have immediate policy implications and cause decision makers to rethink their goals, especially in the corn-belt states, which are heavily subsidizing ethanol and biodiesel production plants. Biofuels have environmental benefits at the global scale and in urban areas, where they reduce smog precursors, he says, but “environmental costs may be felt in the [crop] production states. If we have increased hypoxia, eutrophication, or groundwater contamination, it’s going to be in the corn belt.” —PRACHI PATEL-PREDD

http://pubs.acs.org/subscribe/journals/esthag-w/2007/jan/tech/pp_bioproduct.html