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Introduction

This annotated bibliography reviews literature from Canada, Mexico and the United States related to the environmental effects of liquid biofuels, defined in most cases as ethanol and biodiesel. It focuses on academic, government or government-sponsored documents and studies developed in Canada, Mexico and the United States. It is not meant to be a comprehensive review of every study in North America on the environmental effects of biofuels, but instead to capture many of the important recent works on the topic.

Many of the studies focus on life cycle analyses, meaning the cumulative net impacts from the: production of biofuels crops; transportation of those crops to processing facilities; production of biofuels and various co-products that come from the biofuel production process, transportation to final customers, and the emissions from the vehicle tailpipe. Some of the studies focus more narrowly on specific elements of environmental effects of biofuels such as the effect on water quality or water supplies as a result of increasing biofuel crop production.

The studies focus on a number of important issues, as described below.

Water quality: Several studies consider the effect of increased biofuel production on water quality. One of the main water quality issues relates to eutrophication, meaning the creation of oxygen-starved areas, within water bodies such as the Gulf of Mexico. These oxygen-starved areas appear to be the result of excess nitrogen fertilizer that leaches off farmers’ fields and into waterways.

Greenhouse gas emissions: Studies focus on three greenhouse gases, CO₂, N₂0 and CH₄, typically each translated into CO2 equivalents. Greenhouse gases arise from the production of biofuels – particularly the agricultural machinery used in farmers’ fields, from disturbance of the soil in conventional agricultural practices, from transportation of feedstock from the farmers’ field to the biofuel processing facility, from biofuel processing, and final biofuel transportation. Variations in feedstocks, different agricultural practices such as no-till agriculture and different processing techniques can have a significant impact on greenhouse gas emissions.

Criteria pollutants: Emissions of criteria pollutants come from several stages in the biofuel production and processing process as well as from the vehicle tailpipe. The studies focus in particular on emissions of CO and ozone precursors.

Toxics: Emissions of toxics such as formaldehyde or benzene result from the biofuel production and consumption life cycle.

In general, these studies indicate that the science of life cycle analysis has become much more sophisticated in the last decade. The Canadian GHGenius model, for instance, has been continually updated as it incorporates new knowledge and understanding of the nuance of emissions impacts of different feedstock fuels or co-products that result from the biofuel production process.

The results of these studies vary. General trends are that:

• The feedstock biofuel production is an important consideration because of the emissions impacts of the growth, harvesting and transportation feedstock;
• Greenhouse gas emissions depend a great deal on agricultural practices (the use of conventional or no-till agriculture), process fuels (the use of biomass, natural gas, coal or other fuels as a process fuel), and the use of different types of co-products that result from biofuel production;
• The results from studies of criteria pollutant and toxic emissions vary. All studies show an increase in emissions of nitrogen oxides. Most show decreases in CO and in particulate matter. Results for other pollutants and toxics vary;
• Geography is important; pollutant emissions in non-attainment areas are of particular concern. Although more study is required, it appears that many pollutant emissions occur near ethanol plants in areas that are in attainment for US EPA air quality standards;
• Water quality varies depending on farming practices. Farming practices that use a great deal of nitrogen fertilizer tend to have a negative effect on water quality. Recent farming practices have tended to use less nitrogen fertilizer;
• Water use varies a great deal depending on whether the biofuel is grown on irrigated land or not. In the United States, the vast majority of biofuels are grown on non-irrigated land;
• And, land use issues may be very important but have not been fully explored. A critical issue is what happens when land formerly used for food production is transformed into fuel production. In some cases, this transformation results in new land being brought into agricultural service. If this new land was previously forested, it may increase greenhouse gas emissions.

Biofuel production techniques and farming practices are changing quickly, and becoming more efficient. Thus, studies that rely on old data may need to be updated to account for these greater efficiencies.

This bibliography does not cover a number of important related issues. For instance, it is not focused on the net energy balance of biofuel production – the question of whether the amount of energy used to produce biofuels exceeds the amount of energy contained in the biofuel itself.