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Levels of dioxins and other toxins in the Houston Ship Channel have not diminished despite an intensive cleanup that included closing industrial plants, leaving scientists puzzled about the pollution's source.
Results from University of Houston research shows that dioxins 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 presented the results last week to a group of state, local and company officials. The scientists tested fish, blue crabs, sediment, and water over the past two years.
Researchers were perplexed to find that levels in fish had not changed, or were higher, than a decade ago. And eating fish, of course, is the primary way humans are exposed to dioxin.
Formerly regarded as one of the nation's most polluted waterways, the channel section most tainted with dioxins was a stretch of several miles between Greens and Carpenter bayous home to many refineries and chemical plants, researchers found.
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 become tougher on air and water pollution. Paper pulp mills, which generated massive amounts of dioxin in the paper bleaching process, also were closed. Shutting down pulp and paper mills has worked in other state waterways polluted with dioxins.
Hanadi Rifai, an associate professor of civil and environmental engineering at the university which is conducting the research for the state, has tested all of the obvious potential pollution sources and reportedly will hunt for more over the next two years.
The research is expected to continue through 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.
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," Jack Wahlstrom, who manages the Washburn Tunnel facility for the Gulf Coast Waste Disposal Authority, told the Associated Press.
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.
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.