A major scientific study under way in Texas may help clarify how toxic chemicals are transported through the environment.
Since last summer, University of Houston environmental engineers have been taking hundreds of water, fish and sediment samples from the Houston Ship Channel to determine what levels of dioxins, if any, are present. The scientists will use that data, and more gathered through spring 2003, to develop new computer models to find out where such contaminants originate and to track how they move through the environment, possibly ending up in crab and fish that travel to fishing regions.
"This aspect of the study is quite interesting because such a comprehensive model has never been attempted before," says Hanadi Rifai, associate professor of environmental engineering at UH and principal investigator on the Ship Channel project. "I think this project will set the trend for a lot of national studies looking at these compounds and we'll have many people looking at our results."
In the spring of 2002, Rifai received a $3.2 million grant from the Texas Natural Resource and Conservation Commission (now called the Texas Commission on Environmental Quality) to fund her project in the Houston Ship Channel, home to one of the world's largest industrial complexes. Results from the study will be used by regulatory agencies to help craft implementation plans for reducing pollutants and achieving minimum water quality standards.
The Environmental Protection Agency currently is preparing a comprehensive reassessment of the scientific consensus on dioxin, including its sources, its fate and transport, levels of human exposure, and its toxic effects on humans and other animals. EPA information on dioxins is available on the Web at http://www.epa.gov/.
"Dioxins are a family of contaminants that are very tough to understand in terms of their behavior, toxicity, and how they distribute themselves in the environment," Rifai says. "Although there have been health advisories warning people not to eat blue crab and catfish caught in certain areas of Galveston Bay because of dioxin contamination, there has never been such a comprehensive study of the Houston Ship Channel to determine where contaminants might be."
Rifai says the regulatory limits for acceptable dioxin concentrations are extremely small, and until recently the technology did not exist to detect such minute quantities in water. "Because of the lack of sampling technologies, we don't actually know what the dioxin concentrations are in the water. We'll be the first ones to do this."
There are approximately 200 compounds in the family of chemicals collectively called dioxins, which are released into the air from burning chlorine-based chemical compounds with hydrocarbons, such as in commercial or municipal waste incineration, and from uncontrolled combustion sources such as accidental fires and open burning of wastes. Chlorine bleaching of pulp and paper, certain types of chemical manufacturing and processing, and other industrial processes also can create dioxins.
Dioxins are broken down in the environment very slowly, and can be deposited on plants and taken up by animals and aquatic organisms. Within animals, dioxins tend to accumulate in fatty tissue.
Animal studies have demonstrated a wide range of effects associated with dioxin exposure including increased risk of cancer and reproductive effects. Although the long-term impact of dioxin exposure in humans remains a focal point for research, studies suggest exposure to dioxins may alter immune function and produce developmental effects.
"Dioxins are a potential environmental pollutant and a hazard to human health," says Dr. Donald A. Fox, a professor in the UH College of Optometry with a Ph.D. in environmental toxicology. Fox, an active member of the Society of Toxicology and an expert in developmental toxicology and neurotoxicology, notes that the effects of dioxins depend on a variety of factors, including the level of exposure, the age at time of exposure, and the duration and frequency of exposure.
Rifai says that while the EPA considers air pollution to be a major source of dioxins in water bodies around the country, the Houston area is somewhat unusual.
"The Houston Ship Channel is home to one of the largest industrial complexes in the world, so we receive a lot of industrial waste water discharge," Rifai says. "Because of that, Houston may not be the typical setting the EPA had in mind. Houston may be different from other areas of the country, such as the Great Lakes, where particles from air pollution deposit over the water or land and then wash into the water bodies. Houston may be different not only because of the nature of its air quality, but also because there may be a greater contribution from industrial water discharges."
Rifai is working with state and regional agencies to provide industrial stakeholders with periodic updates and reports on the project, and she works with industry to obtain samples from company sites.
Sampling techniques have moved far beyond dipping a test tube into the water.
Rifai's research group will use a method called high water volume sampling, where a large amount of Ship Channel water will be systematically concentrated down to a very small sample from which lab technicians can then determine the actual levels of dioxins. The group also will collect samples from fish and crab tissue, sediments, from the air at established monitoring stations, and from water run-off at various locations.
Because so many samples will be collected during the study, Rifai will send them to several labs around the country for analysis. It's a very expensive and time-consuming process, taking about eight hours on the boat to acquire a sample and about $5,000 per sample to analyze.