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identified by the prefix EN), the International Standards Organization (identified by the prefix ISO) and the United Kingdom (identified by the prefix IP and the prefix BS) – these test methods are not referenced in this encyclopedia but are available through the use of an internet search engine to which the reader is referred for further details and comparison of the test methods.

      Following nomenclature and definitions presented in the United States Energy Policy Act of 1992 (Section 301), in the context of the present book, alternate fuels (alternative fuels) are defined as

      Methanol, denatured ethanol, and other alcohols; mixtures containing 85 percent or more (or such other percentage, but not less than 70 percent, as determined by the Secretary, by rule, to provide for requirements relating to cold start, safety, or vehicle functions) by volume of methanol, denatured ethanol, and other alcohols with gasoline or other fuels; natural gas; liquefied petroleum gas; hydrogen; coal-derived liquid fuels; fuels (other than alcohol) derived from biological materials; electricity (including electricity from solar energy); and any other fuel the Secretary determines, by rule, is substantially not natural gas or crude oil and would yield substantial energy security benefits and substantial environmental benefits.

      It is this definition that is used to guide the contents of this book and show that sources that are “substantially not petroleum” are available as sources of fuels.

      However, it must be recognized that the forms of energy from renewable sources vary according to the source. For example, biomass and waste can be combusted directly or they can be converted to gaseous fuels and liquid fuels by conversion and refining of the gases and the liquids. The encyclopedia would be missing important articles if there was not some mention of the methods and processes by which gases and liquid products from renewable sources can be prepared for sales. Accordingly, the technologies for refining the gases and liquids into usable fuels and other (petrochemical-type) products are derived from the current natural gas industry and the crude oil industry. Hence the reason for inserting the relevant refining-related articles into the encyclopedia.

      In addition, there is a fundamental attractiveness about harnessing such forces in an age which is very conscious of the environmental effects of burning fossil fuels, and where sustainability is an ethical norm. Currently, the focus of many countries is on both adequacy of energy supply long term and also the environmental implications of particular sources. In that regard the near certainty of costs being imposed on carbon dioxide emissions in developed countries at least has profoundly changed the economic outlook of clean energy sources.

However, there is the need to understand that all energy sources have some impact on the environment. Renewable energy sources do substantially less harm to the environment than do fossil fuels (coal, natural gas, and crude oil) by most measures, including air and water pollution, damage to public health, wildlife and habitat loss, water use, land use, and global warming emissions. However, renewables such as biomass as well as sources such as wind, solar, geothermal, and hydropower also have environmental impacts, some of which are significant and must not be ignored. This encyclopedia also presents information related to those aspects of environmental science and engineering that are susceptible to changes caused by renewable energy sources in addition to the environmental effects caused by the use of fossil fuels. It is for these reasons that articles related to the discharge of pollutants into the environment are included.

      In fact, when the benefits of developing renewable energy sources are considered, it is equally important to acknowledge that there can also be disadvantages. While all renewable energy sources – wind, solar, geothermal, hydroelectric, and biomass – can provide substantial benefits for the climate and the economy, all energy sources have some impact on the environment and even renewable sources such as biomass, wind, solar, geothermal, biomass, and hydropower also have environmental impacts, some of which are significant. The exact type and intensity of environmental impacts varies depending on the specific technology used, the geographic location, and a number of other factors. By understanding the current and potential environmental issues associated with each renewable energy source, effective measures can be taken to avoid or minimize these impacts as they become a larger portion of the electric supply.

      However, there is a variety of environmental impacts associated with the use of alternative energy sources which can include land use and habitat loss, water use that should be recognized and mitigated. They include land use issues and challenges to wildlife and habitat. The exact type and intensity of environmental impacts varies depending on the specific technology used, the geographic location, and a number of other factors. For example, sources of biomass resources for producing energy are diverse, ranging from energy crops (like switchgrass), to agricultural waste, manure, forest products and waste, and urban waste. Both the type of feedstock and the manner in which it is developed and harvested significantly affect land use and life-cycle global warming emissions impacts of producing power from biomass.

      It must be realized that the transfer from non-renewable energy source to renewable energy sources is not without some risk. Just as chemicals from non-renewable energy sources can enter the environment, chemicals from renewable energy sources can also enter the air, water, and soil when they are produced, used, or disposed. The impact of these chemicals on the environment is determined by the amount of the chemical that is released, the type and concentration of the chemical, and where it is found. Some chemicals can be harmful if released to the environment even when there is not an immediate, visible impact. On the other hand, some chemicals are of concern as they can work their way into the food chain and accumulate and/or persist in the environment for many years.

      The final concentration of a chemical (or a mixture of chemicals) in various environmental systems (such as the atmosphere, water, and the land) depends on environmental emission rates and environmental distribution and fate of the chemical. Thus the first step in environmental risk assessment is always to quantify the emissions of a chemical into the atmosphere, the water, and the land.

      Many chemicals, in fact all chemicals, that enter the environment should be categorized and ranked using hazard assessment criteria. This would not only ensure that truly pressing environmental issues are identified and prioritized, but would also maximize the use of limited resources. In the case of soluble chemicals, surrogate data such as persistence and bioaccumulation have been used, in combination with toxicity, for the purpose of hazard categorization. However, for insoluble or sparingly soluble chemicals such as metals and metal compounds, persistence and bioaccumulation are neither appropriate nor useful. Unfortunately, this is not always recognized by regulators or even by scientists.

The use of persistent, bioaccumulative and toxic (PBT) criteria for chemicals was developed to address the hazards posed by synthetic organic chemicals. In fact, the criteria and test methods to evaluate persistence (i.e., the lack of degradability of a chemical) and bioaccumulation (the dispersion of a chemical through knowledge of the water-octanol partition coefficient) were developed to be used in combination with toxicity in order to reduce the importance given to the use of toxicity data alone. These test methods were based on an understanding of the chemistry of chemicals of concern at the time and of the biological interactions that the chemicals would have with the surrounding biota. Specifically, it was realized that if some chemicals exerted high intrinsic toxicity under standardized laboratory test conditions but did not persist or bioaccumulate, the environmental hazard of such chemicals would be lower.

      As mentioned above, persistence is measured by determining the lack of degradability of a substance from a form that is biologically available and active to a form that is less available. This applies to many substances – metals and metal compounds tend to be in forms that are not bioavailable. Only under specific conditions would metals or metal compounds transform into a bioavailable form. Thus, rather than persistence, the key criterion for classifying metals and metal compounds should be their capacity to transform into bioavailable form(s). Furthermore, although bioavailability is a necessary precursor to toxicity, it does not inevitably lead to toxicity. Although metals and metal compounds stay in the environment for long periods of time, the risk they may pose generally decreases over time. For example, metals introduced into the aquatic environment are subject to removal/immobilization processes (e.g., precipitation, complexation and absorption).

      Similarly,

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