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.

plant

General Electric's Hudson Falls Plant and Bakers Falls on the Hudson River (Three photos courtesy EPA)
But on the way, these toxins reenter the food chain, contaminating fish, turtles, and other river inhabitants, as well as those who eat them.

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).

river

Two PCB deposits are shown here, one indicated by the trees in the river, and the second by the yellow area on the bank.
The sediment continues to leak some pollutants back into the river each time it gets stirred up, but over the long term, say the researchers, the river may slowly clean itself.

"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.

pool

The calm surface of this Hudson River pool conceals what the EPA designates as Hot Spot 8 because of its high concentration of PCBs.
The researchers took samples of sediment and water at two points in the river during the year. Their findings suggest that when pollutants get into the water, they dissolve.

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.

boats

Commercial fishing on the Hudson has nearly vanished, and private fishers are warned of the health effects of eating Hudson River fish (Three photos courtesy GE)
Field said that their findings pose a number of policy questions for local, state and national government agencies charged with environmental protection, as well as the general public.

"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.

dredge

Dredging contaminated river sediments
The Bush administration has decided to uphold that plan, despite heavy lobbying by GE. Decades ago, GE used PCBs to manufacturer insulators for electrical equipment at two plants on the Hudson, legally dumping more than a million pounds of PCBs into the river before the chemical was banned in 1976.

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.

remediation

A network of 239 recovery and monitoring wells has been installed around GE's plants to monitor PCBs in the groundwater, prevent movement of PCBs to the river and recover PCB oils from the bedrock
"How many cycles does this giant laundry machine need to get the sediments clean?" asked Rosenthal. "When we know that, we'll be able to give the EPA and the public clearer choices."

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.