Because the isotopic composition of anthropogenic Os is normally distinctiv
e in comparison to continental crust and is precisely measurable, this plat
inum-group element is attractive as a tracer of transport pathways for cont
aminated 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 Os-1
87/ Os-188 signature of 0.73 +/- 0.10. Slightly higher Os-187/Os-188 ratios
occur in Re-rich Coastal Plain deposits due to post-Miocene Re-187 decay.
The upper Susquehanna Basin yields sediments also with higher Os-187/Os-188
. Beginning in the late 1970s, this signal was overprinted by a low Os-187/
Os-188 (anthropogenic) source in the lower Susquehanna Basin. In the vicin
ity of Baltimore, which is a major center of heavy industry as well as biom
edical 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 nor
thward flowing bottom currents. Finding anthropogenic Os at this site cauti
ons that other particle-borne substances, including hazardous ones, could b
e dispersed broadly in this estuary.