Estuaries awash in contaminants.

Estuaries awash in contaminants

Oceanographers have long realized that nutrients and pollutants from land sources travel downriver and collect in the waters of estuaries -- the ecologically critical zone where river meets ocean. But new research suggests pollutants from the ocean also concentrate in estuaries -- a finding that helps explain coastal pollution and may have implications for dumping practices in the ocean, says Curtis R. Olsen, a researcher at the Oak Ridge (Tenn.) National Laboratory who has studied the Savannah River estuary on the Georgia-South Carolina border with colleagues from Oak Ridge and the Skidaway Institute of Oceanography in Savannah.

The researchers measured the estuarian concentration of several different isotopes of plutonium (Pu), which binds to small particles in the water. One isotope, Pu-238, is released upriver in minuscule amounts by the Department of Energy's Savannah River Plant, a nuclear facility. On the other hand, Pu-239 and Pu-240 are fallout from above-ground testing of nuclear weapons and therefore come predominantly from the ocean. When they measured the concentration of the three isotopes, the researchers found the estuaries enriched in the oceanic plutonium -- meaning particles in the ocean must gradually migrate landward and concentrate whatever pollutants they carry within the estuaries, says Olsen. While people who study ocean sediments have known of such landward motion, he says, those who study contaminants in estuaries have not considered this process before.

This finding is not limited to plutonium, Olsen says, because particles also can bind and carry other pollutants such as heavy metals, the insecticide DDT and PCBs (polychlorinated biphenyls). As well, he adds, this transportation process may carry contaminants landward into such coastal environments as bays and fjords.