Pollution Is Called a Byproduct of a ‘Clean’ Fuel - New York Times
Not necessarily that they are a bad idea, just that they need to be produced and processed properly.
Nominally clean byproducts can be hazardous...
According to the National Biodiesel Board, a trade group, biodiesel is nontoxic, biodegradable and suitable for sensitive environments, but scientists say that position understates its potential environmental impact.
“They’re really considered nontoxic, as you would expect,” said Bruce P. Hollebone, a researcher with Environment Canada in Ottawa and one of the world’s leading experts on the environmental impact of vegetable oil and glycerin spills.
“You can eat the stuff, after all,” Mr. Hollebone said. “But as with most organic materials, oil and glycerin deplete the oxygen content of water very quickly, and that will suffocate fish and other organisms. And for birds, a vegetable oil spill is just as deadly as a crude oil spill.”