ANTHROPOGENIC OSMIUM IN COASTAL DEPOSITS

We have determined the isotopic composition and concentration of Os, a platinum group metal, in estuarine sediments from New Haven Harbor and adjacent Long Island Sound. Anthropogenic Os is present in recent sediments and is isotopically distinct from natural Os. Preindustrial sediment from the Long Island Sound FOAM core has approximately 40 pg of Os/g and Os-187/Os-186 = 8.8. Surface sediments from the same site and from New Haven Harbor have 64-774 pg of Os/g and Os-187/Os-186 = 1.8-5.0. The Os-187/Os-186 ratio is inversely correlated with Os concentration (ng of Os/g of dry sediment), suggesting simple mixing between more radiogenic natural Os and less radiogenic anthropogenic Os. A possible carrier of anthropogenic Os is sewage sludge-a sample of New Haven Harbor sewage outfall had the lowest Os-187/Os-186 ratio measured in this study. The primary source of anthropogenic Os may be fixative solutions used to stain tissue for electron microscopy in medical laboratories. If the medical industry is the predominant source of Os to the coastal environment, the Os isotopic composition of coastal sediments may be used to track medical waste transport and burial.