Recently, ethanol was introduced to fuel supplies as our liberator from our dependence on fossil fuels and a reducer of our input of harmful greenhouse gases into the atmosphere. It was a domestic solution to our dependence on foreign oil. Policy shifts began mandating the incorporation of ethanol into fuel sources worldwide, and they continue to mandate higher ethanol concentration in fuel sources to this day. The United States Environmental Protection Agency, for example, has mandated an increase to 36 billion gallons of biofuel production by 2022. This new standard led to the production of over 12.5 billion gallons of ethanol in 2012. Similar mandates exist in other governments, including Brazil, the European Union, India, and China. Brazil mandates current gasoline to contain 25 percent ethanol. By 2020, European Union and Chinese gasoline is mandated to contain ten and fifteen percent ethanol, respectively. Similarly, gasoline in India is mandated to contain 20 percent ethanol by 2017. Such mandates could benefit society by reducing dependence on nonrenewable energy sources. But it turns out that there are several environmental costs to biofuels, some of which are not well understood.
Adding ethanol to fuel sources has raised public concern that we might be crippling the world’s food supply. As ethanol is being mandated at higher concentrations in fuel worldwide, more and more corn crop is being diverted from the food sector for energy production (http://www.cnbc.com/id/48477352). Yet corn can account (either directly or indirectly) for up to 70 percent of an American diet. It is fed to cattle, pigs, poultry, and us. High fructose corn syrup is a staple in foods commonly found in an American diet. We are dependent on it, and as such, some argue that you cannot use corn for fuel when it is needed to feed people. Still, others link corn’s use for ethanol to higher corn prices, raising everyone’s weekly grocery bill (http://www.cnn.com/2012/08/20/opinion/mcdonald-corn-ethanol). Although the safety and affordability of the food supply is a major concern when considering ethanol production, an arguably greater issue gets less attention: the effect ethanol has on our water resources.
Discussion regarding ethanol’s impact on water resources typically centers on the issue of water quantity rather than water quality. For example, it is frequently mentioned that current methods for ethanol production are unsustainable and require four gallons of water to produce one gallon of ethanol, twice the amount required to produce one gallon of gasoline. However, today we transport, store, and dispense gasoline and ethanol in greater quantities and in closer proximity than ever in our history. However, little is known about what happens when these chemicals are released to the environment together.
Oil and gas spills are inevitable. They will occur and release unwanted chemicals to the water supply. In 2011, The U.S. alone consumed 370 million gallons of gasoline per day. That gasoline must be extracted from the ground, transported to refineries, sent to the pumps, and ultimately dispensed into our vehicles. While advances can be made to reduce oil and gasoline spills, they cannot be altogether avoided when so much transport is involved. Pipelines will rupture, gas trucks will spill, and storage tanks will leak. We cannot use our resources trying to prevent every possible spill. We must focus on preventing the big ones, and planning for the small ones. Resources can be better allocated to better understand how oil chemicals will act once they are release to the environment, especially in the presence of ethanol.
Gasoline contains chemicals that are known to harm human health. One suite of chemicals, benzene, toluene, ethylbenzene, and xylenes (BTEX), is known to cause cancer. If they get into a drinking water supply, that water becomes contaminated to the point of uselessness. However, with less frequent access to clean water sources, it is essential to understand and clean up contaminated water. This is where ethanol plays a huge role. Until recently, gasoline spills released just that to the environment—gasoline. Although it is true that gasoline is a blend of hundreds of chemicals, they share similar characteristics allowing their interactions in the environment to be somewhat predictable. They are insoluble in water. They tend to stick onto sediment in the ground. They are broken down, albeit slowly, by bacteria. These few generalizations allow us to predict how these chemicals will move and break down throughout the environment. However, if ethanol is spilled with these chemicals, our predictions might be wrong.
Superficially, adding ethanol to fuel sources seems like a nonissue. We are replacing some toxic chemicals with a nontoxic substitute. One might think that any such replacement would only benefit water resources. Yet it is not that simple. Ethanol may completely change the way fuel chemicals, particularly BTEX, are transported throughout the environment. Without ethanol, BTEX does not readily dissolve in water. In fact, it tends to stick onto sediments in the ground. However, BTEX dissolves in ethanol, and ethanol, in turn, dissolves in water. Prior to adding ethanol, spreading of gasoline contamination is limited by its insolubility in water; it is essentially immobile. However, by dissolving these chemicals, ethanol may increase their mobility in water, effectively multiplying the area of water contamination.
However, there is an opposing force that counteracts the spreading of contamination: the break down of chemicals by bacteria (see our video about this issue here). Bacteria can best break down gasoline chemicals like BTEX when they are dissolved in water. When stuck to sediments, they are relatively unavailable to bacteria. Because adding ethanol dissolves BTEX, it may become more susceptible to break down and consequently is more quickly removed from the environment. Additionally, bacteria prefer to break down ethanol before BTEX. This has two possible implications: 1) bacteria will consume ethanol and not degrade BTEX, or 2) the degradation of ethanol will stimulate bacterial populations that, after ethanol is consumed, will begin degrading BTEX at a faster rate due to larger bacterial populations. The interplay between these processes has not been well-characterized. It is possible that one process can dominate depending on the environment in which they occur. For example, the process dominating gasoline break down may vary from an aquifer to a wetland or lake.
Ethanol amplifies the complexities of BTEX degradation. It is possible that ethanol may spread contamination from a centralized location to one which is widespread. Alternatively, it may enhance bacterial degradation of BTEX. Both scenarios are plausible, yet the consequences are opposite. With anticipated increases in global ethanol output, we need to strive to understand these complexities so we can appropriately respond to fuel spills in order to best protect the quality of our water resources. Could ethanol increase the spreading of oil contamination to the point that we need to rethink our decision to add it to fuel sources? Or is it the ideal clean-up supplement for oil spills? Its incorporation into fuel was meant to reduce pollution to the atmosphere, but could it instead be causing greater pollution to water resources? With more research, these questions are answerable, and the answers may cause us to reconsider adding ethanol to our fuel.
Brady Ziegler (’13)
Environmental Science (Chemistry Concentration) and Geology