Ethanol can corrode plastic, rubber and metal parts in pre-2001 vehicles, according to Forbes. The burning of corn ethanol can also release harmful greenhouse gasses and carcinogens into the air.
As of 2014, most commercial fuel for cars is 15 percent ethanol. Vehicles which are not specifically branded as "flex fuel vehicles" are in danger of having their engines damaged by the use of gasoline with that amount of ethanol. Forbes reports that many car manufacturer warranties include clauses that state the warranty is void if the car runs on gasoline with 10 percent ethanol or more. Cars made after 2001, or the aforementioned "flex fuel vehicles," do not suffer the same negative consequences from the use of ethanol.
Ethanol also serves a danger to the environment. Ethanol releases greenhouse gasses and carcinogens into the air, including the chemical benzene. Another issue related indirectly to ethanol is the farming techniques which generate the corn for ethanol's manufacture. Wetlands and grasslands are plowed in order to farm more corn, and in the process carbon is released into the atmosphere. Additionally, the use of more fertilizer endangers the environment and harms wildlife habitats as the fertilizer is washed from the fields. Environmental Working Group contends that ethanol is a greater threat to the environment than Canadian tar sands.