BEWARE of pollution that comes unseen from the sea. Fallout from old nuclear weapons tests and traces of river-borne plutonium from the Savannah River (plutonium production) Plant have highlighted this neglected hazard. Radioactivity is not the concern here. The fallout and river-carried radioisotopes are present only in minute amounts. But they are easy to detect. They have helped Curtis R. Olsen of Oak Ridge National Laboratory follow the flow of pollutants in the Savannah River estuary.
Pollution experts often assume that what comes down a river is trapped in the estuary or goes on out to sea. And if it does go to sea, it's supposed to stay there. Reporting their work in the journal Environmental Science and Technology, Dr. Olsen and colleagues at Oak Ridge and at Emory University and Skidaway Institute of Oceanography in Georgia, show this isn't necessarily so. What goes out to sea can creep back to haunt us.
This is more subtle than the return of medical waste and other nasty stuff that messes up beaches. Much of that never made it to sea in the first place. This research involves estuaries with what oceanographers call counter-current flow. These estuaries are common along the North American East Coast and in many other parts of the world. The Savannah River flows into one of them.
Oak Ridge geochemist Patrick J. Mulholland, a coauthor of the report, explains that, here, surface water flows out to sea while a return flow comes back along the bottom. This can bring with it particles such as stirred-up sediment - particles that may have picked up various types of organic and inorganic contamination. It can carry significant pollution into the upper estuary and even well up into the river. Moreover, the pollution may not have originated in that river. It can come from general contamination that enters the sea from distant sources.
Dr. Mulholland notes that ``we're not saying this will happen.'' But, he adds, ``It's a possibility that has not been looked into strongly enough.''
He and his colleagues saw this possibility clearly in their study. They used certain easily detectable elements, such as plutonium, to distinguish particulate material washed out by the river from what came in from the sea. For example, the mixture of different forms of plutonium from the Savannah River Plant is different from that in the fallout from old weapons tests that now resides in the ocean. These distinctive plutonium mixtures mark particles as having a riverine or oceanic origin.
The study found that the Savannah River variety accounted for only about 25 percent of the plutonium discovered as far as 18 1/2 miles upstream from the river's mouth. This, the scientists say, ``is conclusive evidence that the plutonium presently enriching esturine particles comes from oceanic sources.''
Such inflow of pollution from the sea seems to be a worldwide phenomenon. Yet, Olsen and his colleagues say, it has ``largely been ignored in models simulating the fate of contaminants in estuaries.'' They add that this new insight has ``extremely important implications for the landward transport and accumulation of chemically reactive substances disposed of in oceanic waters off coastlines affected by a rising sea level.''
Here is another example of an important environmental factor that experts have vaguely known about but have not yet taken into account. We need to step up research to understand this effect so that pollution creeping in from the sea doesn't surprise us.