Home Programs Toxics Initiative Dioxin Listing Demystified
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Dioxin Listing Demystified

What is dioxin and where does it come from?

Dioxins are a family of chemicals that are some of the most toxic substances known. Dioxin forms as a by-product during the heating of mixtures of chlorine and organic compounds in industrial processes, such as the bleaching of paper pulp or the manufacturing of vinyl plastics (PVC). Unfortunately, dioxin is extremely toxic and very slow to break down, resulting in a very dangerous, although unintended, consequence of modern industry.

Why is dioxin a problem in Humboldt Bay?

Until the 1980s, many Humboldt County lumber mills used a chemical called pentachlorophenol, or "penta," as a wood preservative. The production of penta creates dioxin, leaving the wood preservative laden with dioxin. Lumber mills using penta employed large dip tanks and spray booths to apply penta - and dioxin - not only to lumber but also to the coastal environment.

Although the EPA banned the use of penta in 1984, spills, leaks, and even deliberate dumping had already polluted soils and groundwater at many sites. Since dioxin takes generations to break down, contamination remains at former industrial sites and continues to impact the Bay through runoff, erosion, and underground water exchange.

What does dioxin do to people and the environment?

Dioxin has a wide range of negative impacts for people and other species. Cancer, birth defects, and neurological problems can result from very low levels of exposure. Additionally, parents can pass on toxic impacts to their children, resulting in significant nervous system problems and developmental disorders. Dioxin has also been linked to learning disabilities, immune system disorders, diabetes, lung problems, and skin disorders.

The EPA considers there to be no safe level of dioxin exposure - the average U.S. resident is already over-exposed and further contact with this chemical is to be avoided when possible.

Beyond humans, research has demonstrated that fish, marine mammals, and birds are highly sensitive to dioxin. The effects on these critters are principally reproductive and developmental but may also include problems with metabolism and immune system function. Bird eggs have been shown to suffer from increased mortality at dioxin levels as low as two parts per trillion (2ppt). Coho salmon have been found to be particularly sensitive to dioxin; juveniles can spend up to 2 years in Humboldt Bay before heading out to sea.

What does it mean for Humboldt Bay to be "listed" for dioxin?

The Environmental Protection Agency monitors U.S. waters for contamination in order to protect our health and environment. In California, the State Water Resources Control Board does the preliminary analysis for the EPA and recommends a list of "impaired" water bodies every two years. This process is required by section 303(d) of the Clean Water Act and the list is often called the 303(d) list.

Once a waterbody is listed as impaired by a particular pollutant, the agencies are required to further research the problem and eventually set standards for preventing further pollution. The listing itself, however, does not impose any additional regulations or restrictions on local businesses or municipalities. It affirms the need for clean-up, enabling local agencies to seek funding for site remediation and restoration that would otherwise be unavailable.

How did the Water Board decide that Humboldt Bay should be listed? 

The listing was based on data collected on behalf of the U.S. Army Corps of Engineers, Sierra Pacific Industries, the Center for Ethics and Toxics, the City of Eureka and the Humboldt Bay Harbor, Recreation, and Conservation District. Specific samples within these data sets showed dioxin in the Humboldt Bay food chain exceeding the "screening" level set by California's Office of Environmental Health Hazard Assessment.

Where do we go from here?

Humboldt Baykeeper intends to work with our environmental agencies in identifying dioxin "hot spots" in the Humboldt Bay watershed. Once sites are identified, they must be characterized to determine the extent of contamination and to develop plans for cleaning them up. Stopping the sources is the first priority.



 
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