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An understanding of the factors influencing the isotopic composition of body water is important to determine the isotopic composition of tissues that are used to reconstruct movement patterns of humans. The δ2H and δ18O values of body water (δ2Hbw and δ18Obw) are related to the δ2H and δ18O values of drinking water (δ2Hdw and δ18Odw), but clearly distinct because of other factors including the composition of food. Here, we develop a mechanistic geographical information system (GIS) model to produce spatial projections of δ2Hbw and δ18Obw values for the USA. We investigate the influence of gender, food, and drinking water on the predicted values by comparing them with the published values. The strongest influence on the predicted values was related to the source of δ2Hdw and δ18Odw values. We combine the model with equations that describe the rate of turnover to produce estimates for the time required for a non-resident to reach an isotopic equilibrium with a resident population. [ABSTRACT FROM AUTHOR]

The recent controversy over the use of MTBE within gasoline to boost oxygen content and decrease carbon monoxide emissions to the atmosphere has led to a proposed phase-out of this compound by 2002. This paper is a preliminary investigation into the use of gas chromatography isotope-ratio mass spectrometry (GCIRMS) to determine both carbon and hydrogen isotopic compositions of MTBE as a means of differentiating sources of MTBE. Three pure MTBE samples were purchased from chemical distributors. Little variation of the δ 13 C values were observed although the samples had isotopically distinct δ-D values. Four different methods of obtaining carbon isotope ratios of neat MTBE, MTBE in gasoline, and MTBE in water are described, and the precision and accuracy of each is discussed. The carbon isotopic compositions of MTBE within 10 gasoline samples from three different areas of the United States show a wide range of carbon isotope compositions. This novel method of MTBE analysis could be valuable in forensic investigations. [ABSTRACT FROM AUTHOR]