The US Environmental Protection Agency's rejection of a formal request for a scaling back of national renewable fuel standards has bought mixed reactions from politicians and environmentalists.

Last week, the EPA finally rejected a request from the state of Texas, made in April, for a 50 per cent waiver of the renewable fuel standard (RFS), citing concerns over the effect of the targets on food prices

The RFS mandates that an increasing amount of fuel be ethanol-based in the coming years. It had required 5.14 billion barrels of ethanol to be produced in 2008, but the Energy Independence and Security Act passed in December raised it to nine billion.

Read more about the EPA's rejection here.