Osmium Isotopes Demonstrate Distal Transport of Contaminated Sediments in Chesapeake Bay

Abstract

Because the isotopic composition of anthropogenic Os is normally distinctive in comparison to continental crust and is precisely measurable, this platinum-group element is attractive as a tracer of transport pathways for contaminated sediments in estuaries. Evidence herein and elsewhere suggest that biomedical research institutions are the chief source of anthropogenic Os. In the Chesapeake Bay region, uncontaminated sediments bear a crustal 187Os/188Os signature of 0.73 ± 0.10. Slightly higher 187Os/188Os ratios occur in Re-rich Coastal Plain deposits due to post-Miocene 187Re decay. The upper Susquehanna Basin yields sediments also with higher 187Os/188Os. Beginning in the late 1970s, this signal was overprinted by a low 187Os/188Os (anthropogenic) source in the lower Susquehanna Basin. In the vicinity of Baltimore, which is a major center of heavy industry as well as biomedical research, anthropogenic Os has been found only in sediments impacted by the principal wastewater treatment plant. Surprisingly, a mid-Bay site distant from anthropogenic sources contains the strongest anthropogenic Os signal in the data set, having received anthropogenic Os sporadically since the mid-20th Century. Transport of particles to this site overrode the northward flowing bottom currents. Finding anthropogenic Os at this site cautions that other particle-borne substances, including hazardous ones, could be dispersed broadly in this estuary.

Osmium concentrations and 187Os/188Os ratios of three sediment reference materials

“…This material was collected from Tokyo Bay where both river water and seawater mix with tidal circulation. Some proportion of Os in this reference material may be derived from an anthropogenic source, as described in the United States by Esser and Turekian (1993) in New Haven harbor and by Helz et al (2000) in Chesapeake Bay. Anthropogenic Os has a low isotopic ratio of about 0.14 (Esser and Turekian, 1993;Ravizza and Bothner, 1996), because Osbearing materials used for industry and vehicles originate from ore deposits with low 187 Os/ 188 Os.…”

Anthropogenic Osmium in Macroalgae from Tokyo Bay Reveals Widespread Contamination from Municipal Solid Waste

“…1). Point sources of anthropogenic Os include sewage outflow [17][18][19][20]22 incinerators 17,18,23 and smelters [24][25][26] , whereas automobile catalytic converter exhaust in densely populated regions can impart a significant regional influence 21,27,28 . On a global scale, the refining of PGE ores, coupled to the widespread use of catalytic converters, has driven the 187 Os/ 188 Os of precipitation and oceanic surface waters to more unradiogenic values 7 .…”

Mixing and Transport

“…Using laboratory analyses of sixteen different pesticides, they found that chlorothalonil had the highest concentration in the air, while wet deposition fluxes were highest for methyl parathion, malathion, metolachlor, and atrazine. Helz et al (2000) also investigated the Chesapeake Bay, concentrating on the use of osmium isotopes to investigate distal transport of contaminated sediment in the bay. A Mid-Bay sampling site showed the highest osmium levels, despite the long distance between this sampling location and the anthropogenic contamination sources as well as the northerly bottom currents with flows opposing the direction of transport.…”