Stable Isotopes as Environmental Tracers




Parker PL
Caughey ME

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Predictable trends in stable isotope ratios, which can facilitate tracing sources, distribution patterns, and eventual fates of a wide variety of environmentally important chemicals, are discussed. Many of the products and by-products of industrial activities in and around the Gulf of Mexico have characteristic stable isotope ratios. The carbon isotope ratio of feedstock, natural gas comprised mostly of methane, is reflected in dissolved organic carbon of the first stage effluent as well as in the products of a Gulf Coast petrochemical plant. Comparing results from a 1986 follow-up study, the overall level of petrochemical pollution in the Houston Ship Channel appears to have decreased. The average value in the original 1968 study was strongly influenced by petrochemicals while the 1986 average suggests a greater proportion of the organic matter came from one or more isotopically heavier sources. Lavaca Bay is not heavily industrialized and so offers a possible control to estimate natural background values. The river mouth and up river values reflect terrestrial dominance and may represent a theoretical, unpolluted Houston Ship Channel. One possible means of distinguishing marine organic matter from terrestrial, or pollution from natural organic matter, is to find a second element to use as an isotopic label. Sulfur from seawater sulfate has delta34S values which are distinctly positive compared with sulfur from continental runoff or from marsh environments. Shrimp tissue analyzed for both carbon and sulfur carries the isotopic signature of its environment allowing classification as estuarine, offshore or migratory. In the case of industrialized studies, if the feedstock sulfur for tracing the effects of both the plant and its products on the environment. Household detergents, as well as certain dispersants used by the oil companies, contain organic sulfates and sulfonates which might be traced using stable isotope measurements. As with the shrimp, correlation diagrams plotting delta13C versus delta15N classify organic matter in marine sediments as to source much more reliably than could be done using either parameter by itself. Three-dimensional plots of delta13C, delta15N and delta34S may permit even more accurate classification of a wide variety of environmental samples. (See also W89-07234) (Miller-PTT)




Carbon isotopes, Environmental tracers, Fate of pollutants, Gulf of Mexico, Houston, Industrial pollution, Isotopic tracers, Path of pollutants, Sediments, Sulfur isotopes, SW 3020 Sources and fate of pollution, SW 5040 Data acquisition, Texas, Tracers