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Releases Of Dioxins

Analysis that combines amount and potency puts primary metals industry ahead of chemical manufacturing as the main source of dioxin toxicity

by Cheryl Hogue
February 6, 2012 | A version of this story appeared in Volume 90, Issue 6

For years, chemical manufacturers have been the main industrial source of highly toxic chlorinated dioxins and furans released in the U.S., according to the Environmental Protection Agency’s Toxics Release Inventory (TRI) data. Now, because of changes in how EPA analyzes these data, a different pattern is emerging: When both the quantity and toxicity of releases are considered, the primary metals industry emerges as the main source of dioxin toxicity.

In TRI terms, “release” has a broad definition: It could mean disposing of dioxin-contaminated waste in a hazardous landfill; emitting it to air; or discharging it in a flow of wastewater to a river, lake, or stream. And the category of dioxin and dioxin-like compounds consists of the most toxic congener—2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)—as well as six other chlorinated dioxins and 10 chlorinated furans.

“These related chemicals act via the same toxicity pathway and produce similar health effects: increasing the risk of cancer, causing effects on the immune system and early development, among others,” says Olga Naidenko, a senior scientist with the Environmental Working Group, an activist group. Though they pose the same kind of health hazards, each of the 17 compounds exerts a different level of potency.

In analyzing TRI data, EPA now combines the quantity and toxicity of each compound into a single value called toxicity weight, which is expressed in grams of TCDD. These values allow comparison of the chemicals’ relative hazards, and the picture they paint about industry releases of dioxins is different from that based on looking at just the amounts released.

To calculate toxicity weights, EPA uses toxicity equivalency factors to account for the differences in the toxicities of TCDD, other dioxins, and furans (C&EN, Jan. 31, 2011, page 42). TCDD is assigned a factor of one. The other chemicals are assigned a fraction. Multiplying the total grams of each congener released by its toxicity equivalency factor yields its toxicity weight expressed in grams of TCDD, according to EPA. The agency then adds all the toxicity weights for all the congeners by a particular industry to yield a value for that sector.

“Analyzing dioxins in [terms of toxicity weight in grams of TCDD] is useful when comparing disposal or other releases of dioxin from different sources, or different time periods, where the mix of congeners may vary,” EPA explains in its analysis of 2010 TRI data. This approach provides a comprehensive picture to state and federal regulators and the general public of which industries are still releasing dioxins into the environment, Naidenko says.

When applied to 2010 data—the most recent year for which TRI information is available—the method ranks the primary metals sector as the main source of dioxin toxicity, and the chemical industry drops to second place nationwide. The primary metals sector smelts and refines metals from ore, scrap, or pig iron and rolls, draws, and alloys metals.

Specifically, chemical manufacturers were responsible for 64% of the 120 lb of dioxins reported by weight to TRI in 2010, while the primary metals industry accounted for only 19%. But when the toxicity of the various congeners released by the different industries is factored in, the industry contributions change. The 120 lb of all dioxins released in 2010 have a toxicity weight of about 536 g (1.2 lb) TCDD, and of this amount, 42% is due to the primary metals sector and 25% comes from chemical manufacturing, according to EPA.

Also in 2010, most of the dioxins and furans reported as released ended up either in landfills or in surface impoundments—a term that applies to disposal ponds, lagoons, or pits. TRI data show that most chemical plants dispose of dioxin-containing waste in hazardous waste landfills, whereas the primary metals sector disposes or releases dioxins to surface impoundments.

Overall, the amount of the 17 dioxin and dioxin-like compounds disposed of or released by industry fell 65% between 2001 and 2010, according to EPA’s analysis. This reflects efforts by companies in many sectors, including the chemical industry, to ratchet down their releases of the compounds.

That said, the amount of dioxins released rose 18% from 2009 to 2010, the agency says. A number of environmental groups view this as disturbing because it reverses the trend of industries reducing their releases of dioxins.

The increase in releases might in part be due to a reporting error by a single chemical plant. In its analysis, EPA points out that discharges of dioxins and furans to rivers, lakes, and streams—which for years have been relatively small—saw a big jump starting in 2009. This was due mainly to increased releases of dioxins reported by the Westlake Vinyls plant in Calvert City, Ky., according to TRI data.

In both 2009 and 2010, the Westlake plant discharged 31 lb of dioxins into the Tennessee River, 18 miles from its confluence with the Ohio River, TRI data show. This release accounted for most of the 35 lb of discharges of dioxins to rivers, lakes, or other bodies of water by all industries nationwide in 2010, as well as the 34 lb in 2009. During 2008, in contrast, all chemical plants reported releasing a combined 2 lb of dioxins to waterways, TRI data show.

The dioxin water discharge figures for the plant are wrong, David R. Hansen, senior vice president for administration at Westlake Chemical, the Kentucky facility’s owner, tells C&EN. “The original numbers submitted were overstated due to a calculation error,” he says. In late January, the Houston-based company filed revised TRI numbers for the facility’s releases of dioxins with EPA, Hansen says.

Hansen did not respond to requests for the corrected numbers for the Calvert City plant by C&EN’s deadline. An EPA spokeswoman confirmed to C&EN in late January that the agency has received the company’s revised figures. Next, EPA will process them and will update numbers in the public TRI database in the coming months, she says.

Chlor-vinyl manufacturers such as Westlake Chemical have taken steps over the past decade to lower their releases of dioxins, says Allen Blakey, vice president of industry and government affairs for the Vinyl Institute. Westlake Chemical is a member of that industry association.

Typically, producers of chlor-vinyl release a large total amount of the chemicals EPA classifies as dioxins, Blakey says. Most of the congeners they release are polychlorinated furans, which have toxicities that are significantly lower than TCDD’s, he says. According to the World Health Organization, these furans’ toxicities are one-tenth to three-ten thousandths that of TCDD’s, depending on the particular congener. The bottom line is that although chlor-vinyl plants may release a large amount of these substances, the toxicity of these substances is significantly lower than an equivalent quantity of TCDD, Blakey says.


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