U.S. Water News Online
HOUSTON -- Levels of dioxins and other toxins in the Houston Ship Channel haven't diminished under an intensive cleanup that included closing industrial plants, leaving scientists puzzled about other sources of the pollution.
Results from University of Houston researchers show that dioxin, a group of 75 related chemicals that may cause cancer, exceeded standards in more than 80 percent of the water samples. Tests for the chemicals in sediment found it above normal 83 percent of the time.
Researchers who tested fish, blue crabs, sediment and water in 2002 and 2003 presented the results to a group of state, local and company officials.
Particularly alarming to researchers was that levels in fish had not changed, or were higher, than a decade ago. Eating fish is the primary way humans are exposed to dioxin.
``We have exceedances just about everywhere,'' Hanadi Rifai, an associate professor of civil and environmental engineering at the university which is conducting the research for the state, told the Houston Chronicle.
Formerly regarded as one of the nation's most polluted waterways, the channel section most tainted with dioxin was a stretch of several miles between Greens and Carpenter bayous, which are home to numerous refineries and chemical plants, researchers found.
``The fact that there is so much of an exceedance means we are looking at a pervasive issue, instead of a historic problem,'' said Rifai.
The research's goal was to determine how much dioxin can continue to enter the Ship Channel while making fish safe to eat. The state health department first warned in 1990 against eating more than 8 ounces a month of certain species of fish in the waterway to Upper Galveston Bay.
Environmental laws since then have clamped down on air and water pollution, and paper pulp mills, which generated massive amounts of dioxin in the paper bleaching process, also closed.
``The trend is no change. There should have been changes,'' Lial Tischler, an environmental engineer who represents the East Harris County Manufacturer's Association, said. ``The theory was that the pulp mills were the big sources, and those were corrected in the 1990s.''
Shutting down pulp and paper mills has worked in other state waterways polluted with dioxin. Levels of the chemical in fish on the Neches and Brazos rivers dipped to safe levels in two years, Tischler said.
Rifai, who has tested all of the obvious sources, will hunt for more over the next two years. The research isn't expected to end until September 2005.
Burning trash and medical waste are other sources, along with rain and dust laced with dioxin from smokestacks. Tainted runoff is also a big contributor, the study found.
``It boils down to how do the fish get the dioxin,'' she said. ``That pathway is real critical to our understanding.''
Routine channel dredging could be contributing to the dioxin problem, some researchers believe.
``A concern of ours is how much dredging has impacted this study,'' said Jack Wahlstrom, who manages the Washburn Tunnel facility for the Gulf Coast Waste Disposal Authority.
The agency, which treats industrial waste, was blamed in the 1990s for the levels of dioxins it was discharging.
Rifai was urged by other advisers to examine groundwater, ship emissions and the mud-laden dump sites along the channel where dredged material is placed.
``Dredging operations do not create or generate dioxin; any dioxins in the disposal areas are not the result of port operations. We have no evidence that dredge disposal sites are a source of dioxin,'' said Tom Kornegay, executive director of the Port of Houston Authority.
The state is required by the Clean Water Act to develop total maximum daily loads for the 200 to 300 waterways that are too polluted to support fishing, swimming and other uses. Scientists are planning or working on 83 waterways, according to the Texas Commission on Environmental Quality. The five-year study is expected to cost $5 million.
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