Hudson River Cleaning Itself, But Still Needs Help
BOSTON, Massachusetts, November 7, 2001 (ENS) - Nature may be slowly scrubbing the lower portion of the Hudson River free of pollution. Researchers have found that dangerous toxins in polluted sediments are being stirred up and gradually washed out to sea as part of the river's natural cycle.
In a yearlong study of the lower Hudson River estuary - the portion of the river where salt water and fresh water mingle from its mouth to the Tappan Zee Bridge about 40 miles upstream - scientists from the Rutgers' Institute of Marine and Coastal Sciences found that dangerous organic and inorganic pollutants are not lying immobile in sediment on the river bottom.
Instead, tidal forces, storms, rain and spring runoff are powering a cycle in which polluted sediment is stirred up and suspended in the water column, then redeposited on the river floor.
Repeated over and over again, the process ultimately releases out of the sediment many dangerous contaminants and moves them out to sea, the scientists said. Contaminants in the Hudson include mercury, zinc, chromium, cadmium, lead and oil based chemicals such as polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs).
"In some regions of the river, there's been, on average, about a 10 fold cut in pollutants over 30 years: the sediments are approaching the levels where they were 30 years ago," said Rutgers professor of marine sciences Yair Rosenthal, a principal investigator in the study. "They are still not clean, but they are getting clean."
Rosenthal and fellow principal investigators Professor Rob Sherrell and researcher Paul Field, both of Rutgers, say that the long term decrease in contaminant levels is due mainly to a number of control measures mandated by the federal Clean Water Act.
They cited in particular a strict permitting system for discharging into the river chemicals from factories, sewage treatment plants and other facilities near the Hudson River drainage basin. But the cleanup is significantly aided, the scientists said, by the river's self washing system.
But they do not stay that way. The pollutants end up back in the sediment either in their original form, or combined with other metals or minerals. There, microscopic organisms drive processes that tend to transform the metals into less toxic forms.
When storms, spring runoff and tidal forces stir up the sediment and suspend it in the river's water column, the already altered pollutants are again dissolved, and the process starts over.
Unfortunately, said the scientist, this natural cleanup is efficient only in the lower part of the river, in the mixing zone between the salty tides and fresh water outflow, and its effect on the contaminated sediments upstream is substantially smaller.
"How safe do we want to be and how much are we willing to pay for it?" asked Fields. "Is it better to leave sediments as is, and let them leak slowly and ultimately clean themselves, or should we intervene and dredge to remove contaminated sediments?"
The answers to those questions could have bearing on the ongoing discussions regarding the best way to clean decades of toxic pollutants out of the Hudson. Last year, the U.S. Environmental Protection Agency (EPA) released a pair of studies indicating that contamination with toxic PCBs in the Upper Hudson River poses a serious risk to human health and the environment even far downstream of their source.
Those studies, along with other data, prompted the EPA last December to order General Electric Corporation (GE) to spend more than $500 million to dredge as much as 2.65 million cubic yards of contaminated sediments from the Hudson River.
Most of the Hudson River is now a federal Superfund site, and fishers are warned against eating fish caught anywhere in the river.
The next step for the Rutgers researchers will be determining how fast the river is cleaning itself.
The two year research program was financed through a $225,000 grant from the Hudson River Foundation, which supports scientific and public policy research, education, and projects to enhance public access to the Hudson River. Their researchers' findings were presented today at the 113th annual meeting of the Geological Society of America in Boston.