Biodiesel fuels show variation in strength

In the transportation world, it is one of the trendiest ways to fight global warming: Stir a little vegetable oil into your fuel.

Biodiesel is a chemically created fuel from animal fats and vegetable oils that is blended with traditional diesel. The result emits fewer pollutants, such as sulfur, and is thought to be less of a contributor to climate change because it is from a renewable source. Governor Deval Patrick has filed a bill to require diesel fuels and some home heating oil to contain a minimum percentage of biodiesel by 2010. Communities from Keene, N.H., to Cambridge use it when possible in municipal vehicles, such as power snow plows and dump trucks.

But a study by a chemist at Woods Hole Oceanographic Institution shows that people might not be getting what they think from the pump. Fuels advertised as having 20 percent biodiesel actually had anywhere from 10 to 74 percent, the study of about 10 small-scale retailers found.

The percentage is important because too much biodiesel in fuel can clog fuel lines and too little would not get the environmental payoff people expect. Most diesel vehicles can use up to a 20 percent biofuel mix without any trouble.

"There is a lot of good feeling about biodiesel, but if we are going to sell it, we have to make sure what is being sold is accurately prepared," Christopher Reddy, the lead author on the study published in Environmental Science & Technology, said in a phone interview yesterday. He said his study confirmed the findings of a federal study two years earlier. Amber Pearson, a spokeswoman from the National Biodiesel Board, said yesterday that the study was from such a small sample of the nation's 1,300 biodiesel retailers it was hard to draw a conclusion.

Reddy was not even looking at blending percentages when he launched his study. He and colleagues stumbled on the discrepancy while studying the potential effects of a biodiesel spill in Buzzards Bay. While they determined that such an impact would probably be minimal in coastal regions, they discovered there were widely varying blends of the diesel they were studying.

Reddy thinks the problem is not deliberate. Most of the places he got samples from were small-scale operations that mix the fuels themselves. For Steve Russell, fleet superintendent in Keene, the study is a reminder. His municipal fleet runs on fuel with 20 percent biodiesel. Russell said he just got back from Los Angeles, where he heard complaints about the performance of biodiesel, some potentially because of the grade or quality.

"My retort was make sure your distributor is legitimate, ask for product testing sheets so you know what you are getting," he said.

Beth Daley can be reached at bdaley@globe.com.