based LCA is a bottom-up approach that involves itemization of each step in producing a product and consideration of everything from extraction through production and disposal. Although informative and readily interpretable, it systematically underestimates environmental effects by missing key secondary and “ripple” effects (Majeau-Bettez et al. 2011). Data are often inadequate, and strategies to figure out the best way of drawing system boundaries need attention. In addition, although the life-cycle inventory can be constructed in many situations, determining the health or ecologic effects can be challenging given the array of pollutants, the broad scope, and the resulting lack of site specificity of emissions or effects. Researchers have developed approaches to integrating health risk-assessment concepts into process-based LCA, taking account of such factors as pollutant partition coefficients, stack height, and population density to refine the characterization of effects (Humbert et al. 2011), but more work clearly is needed. The second approach involves conducting input—output LCA, in which large matrices of transfers between economic sectors are constructed. That allows consideration of the full ripple effects of actions that are influencing a specific sector (Majeau-Bettez et al. 2011) but with even greater challenges in linking outputs of economic-sector activity with defined health and environmental effects.

EPA has some internal capacity in LCA, has been required to conduct LCA of fuels in the Energy Independence and Security Act of 2007, and has developed tools such as the Tool for Reduction and Assessment of Chemical and Other Environmental Impacts (Bare 2011); but LCA has not been systematically applied to the agency’s mission. LCA tools and inventories have been much further developed and applied in other regions, such as Europe (Finnveden et al. 2009). Nonetheless, even without undertaking a formal quantitative LCA, complex systems-level challenges require that the agency at least apply “life-cycle

BOX 4-3 The Need for and Challenges of Life-Cycle Assessment: The Biofuels Case

The need for and challenges of LCA are seen in the case of biofuels. Some analyses suggest that regulatory requirements regarding the use of such fuels may not reduce carbon dioxide emissions and indeed might even increase them (NRC 2010). Those analyses suggest that such mandates could result in a loss of US crop lands available for food production because of the use of the land to produce fuel. That, in turn, could result in pressures to clear forest land in other parts of the world (which is an example of indirect land-use effects) (Searchinger et al. 2008). In addition, the fertilizer to grow such fuel crops in the midwestern United States may contribute to runoff that exacerbates the anoxic zone in the Gulf of Mexico (Rabalais 2010). Thoughtful analysis and interpretation of the results of LCA for biofuels are necessary because some of its methods and assumptions remain controversial (Khosla 2008; Kline and Dale 2008).

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