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Dioxin Developments

Ever since birds, cats, dogs and even horses began dropping dead in Times Beach, Missouri, 25 years ago, the word "dioxin" has set off alarm bells. Now, after Bay Area studies found dioxin in water and fish tissues, the S.F. Regional Board is starting to take a hard look at dioxin in our waterways. A workshop to brief Board members on the latest dioxin information is planned for this spring. In the meantime, Board staff are designing a study to address some of the many questions about dioxin. Part of the work will be done through the S.F. Estuary Institute's Regional Monitoring Program, which has allocated $7,000 of its 1997 budget to launch a dioxin study program for Bay waters.

Most scientists agree that dioxin - the term refers to a family of chemical compounds with more than 75 variants-has been linked to a range of cancers, endocrine effects, and other disorders. S.F. Estuary Institute scientist Jay Davis says "there is considerable debate over the risk dioxin poses to people," but notes that "in laboratory studies dioxin is extremely toxic to animals. On the basis of these studies, dioxin is considered one of the most toxic chemicals known." The final version of the most comprehensive document on the subject, a U.S. EPA dioxin reassessment, is due to be released this summer. The most recent draft of the assessment called dioxin a "probable" human carcinogen.

"At the national level there are a lot of questions about dioxin," says the Board's Kim Taylor "How prevalent is it? What is the post industrial background level? What are the sources? Are these sources controllable? We want to take a close look at dioxin to try and develop more informed policy alternatives." During the 1995-96 wet season, the Board tested stormwater runoff from oil refineries and municipalities throughout the Bay and found dioxin in almost all samples.

"There is a landslide of new evidence that dioxins are a much greater threat than anyone thought," says Greg Karras of Communities for a Better Environment, who also notes that thousands of people regularly consume fish caught in the Bay. One of the Board's goals is to determine "who is affected and how to communicate the risks to subsistence fishermen," says Taylor.

In a 1994 Board study of fish tissues, 16 of 19 samples exceeded screening values established by the study using U.S. EPA methodologies. The findings indicated a potential health risk to humans. However, the Board's Karen Taberski says all the dioxin measurements were within background levels found nationwide by the EPA.

Another major goal of the new Board study is to identify sources and pathways. Taylor and others believe that most dioxin enters the Bay through the "atmospheric deposition". Each type of dioxin has a specific chemical "fingerprint," which the Board hopes will allow specific sources to be traced. "We're going to test Bay water and try to identify the sources that way," says Taylor.

At the Board's request, the Bay Area Air Quality Management District compiled an inventory of regional sources of airborne dioxin. The District's Brian Bateman estimates that 85 percent of the Bay Area's dioxin emissions are from vehicles and residential wood combustion.

But according to Karras, "We already know exactly what dozens of dioxin sources are." Karras cites oil refineries, medical waste incinerators, diesel emissions and sewage plants as examples. "The Board is still being timid about this issue. The real question is, what are we going to do to eliminate dioxin production and release?" Refineries declined to comment.

A question also remains as to whether there's anything to be done about the dioxin already in our sediments and soils, which Bateman says can persist for up to 100 years. "Dioxin can be reintroduced from these reservoirs into the environmental media by dredging, storms, fires or other events," he says. "A major area of uncertainty is how much of the dioxin we see is from current emissions and how much is historic. Even if we shut off all emissions we may still have dioxin in the environment for many, many years."

EPA Draft Reassessment: http://www.epa.gov/docs/SAB/Reports/Dioxin/dioxin.txt.html

Contact: Kim Taylor (510) 286-3821

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