ABSTRACT
Isotopologues? ..................................................................................................6 1.4 Natural Abundance of Stable Isotopes .............................................................8 1.5 Stable Isotopes: Delta-Notation and International Standards ......................... 10 1.6 Notations Used in Tracer Studies ................................................................... 13 1.7 Radioisotopes .................................................................................................. 13 1.8 Why Should One Use Isotopes in Biodegradation and Bioremediation? ....... 15 1.9 Type of Information Obtained by Isotopes ..................................................... 17 Acknowledgment ..................................................................................................... 19 References ................................................................................................................ 19
This chapter explains what isotopes are, what their average occurrence in nature is, how isotope measurements are reported with respect to international standards, and how isotope data can be used in biodegradation. The focus is on environmental isotopes, a loosely dened class of primary isotopes in biological and hydrological systems. Because hydrogen, carbon, oxygen, nitrogen, and sulfur are the major elements that make up organic matter, biologists are most interested in the isotopes of these elements. All of these elements are relatively light and, therefore, their isotopes have relatively large mass differences and are subject to fractionation by biochemical or physical processes-which makes them interesting tracers. However, the isotopes of chlorine, calcium, iron, and others are relevant to microbial processes and are candidates to gure among the environmental isotopes. The notion of environmental isotopes has been used in other textbooks (Fritz and Fontes 1980; Clark and Fritz
1997; Mook and De Vries 2000) that focus on tracing the hydrological cycle and its associated biogeochemical processes. It should be noted, however, that environmental isotopes does not signify that these isotopes were all produced by natural reactions (see 14C as an example of an isotope that is of natural and anthropogenic origin). Also, some of the heavier isotopes that are used in geology for dating of rocks or tracing rock-forming processes may be called environmental isotopes. Therefore, there is no exact denition of what environmental isotopes are and this book does not make any attempt to put forward such a denition. We will focus on stable and radioactive isotopes of the elements: hydrogen, carbon, nitrogen, oxygen, sulfur, silica, and chlorine. Chapter 12 will give supplementary information on lithium, chlorine, calcium, selenium, chromium, and iron.
