Isotopes track contaminant breakdown

A new study uses nitrogen isotope ratios to learn more about the way common contaminants degrade in the environment (Environ. Sci. Technol., DOI: 10.1021/es200743t). Nitrogen’s most abundant isotope is ¹⁴N. In recent years, scientists have begun to use its rarer, stable isotope, ¹⁵N, in a method called compound-specific isotope analysis (CSIA) to track degradation processes of nitrogen-containing contaminants, since various reactions enhance or deplete ¹⁵N to different degrees. Many common environmental contaminants, such as biocides, pharmaceuticals, and triazine herbicides, begin their breakdown via oxidation of a primary aromatic amino group. Environmental chemist Thomas B. Hofstetter, at the Swiss Federal Institute of Aquatic Science & Technology, and colleagues, studied ¹⁵N kinetic isotope effects of various components in the oxidation of substituted anilines by manganese oxide, a common environmental reaction. Using CSIA, the researchers detected small differences in ¹⁵N/¹⁴N ratios in different reactants and found that these ratios change with variations in the pH of the reaction conditions. These changes in isotope ratios could help scientists better understand processes that occur in the environment and the reactants’ sources and quantities.