GULF SPILL: EPA reports that surface-
slick burns produced very low levels of cancer-causing dioxins
W
HEN OIL GUSHED FROM BP’s Macondo well
in the Gulf of Mexico this spring and summer, cleanup crews burned surface slicks to limit its environmental impact. Now researchers from the Environmental Protection Agency report in two studies that the fires’ health risks were small because the burns released only low levels of cancer-causing polychlorinated dibenzodioxins and polychlorinated dibenzofurans, which belong to the family of compounds called dioxins. Gulf cleanup crews removed as much as 310,000 barrels of oil through in situ burns, according to the U.S. Coast Guard. Burns can produce these dioxins through incomplete combustion of oil. Very little data already existed on the emissions of such dioxins from oil fires at sea. So Brian K. Gullett, an EPA researcher, and colleagues collected smoke samples from 27 oil fire plumes over a four-day period in July. They calculated that the total dioxin emission levels
BLAST AT CHINESE PLANT KILLS FOUR COAL CHEMICALS: Facility made polyvinyl chloride via the acetylene process
A
NOV. 20 EXPLOSION at a polyvinyl chloride
plant in northern China killed four people and injured dozens of others, according to government reports. The Yushe Chemical Industry complex where the accident took place uses acetylene as a feedstock to produce the polymer. Owned by the local government of Yushe, a county in coal-rich Shanxi province, Yushe Chemical employs 2,700 people. The firm has been in operation since the 1970s and, according to its website, can make 400,000 metric tons of PVC per year from coal-derived acetylene. The acetylene is generated by hydrolysis of calcium carbide, which is in turn produced from lime and coal-derived coke. After the explosion, firefighters spent more than 14 hours extinguishing a blaze that raged at the plant site. The government of Yushe later said its initial priority was to take care of the seriously injured. An investigation into the cause of the accident is under way. No haz-
from all 27 fires were more than two orders of magnitude lower than those produced by open burning of residential waste, a common dioxin source (Environ. Sci. Technol., DOI: 10.1021/es103554y). In addition, EPA scientist John Schaum and colleagues collaborated with researchers at the National Oceanic & Atmospheric Administration to calculate the worst-case scenario for health risks to people who breathed in the released dioxins or ate dioxin-tainted fish. For residents along the Gulf Coast, the health risk was an additional six cancer cases for every 1 trillion people; for oil cleanup workers, it was six in 100 million (Environ. Sci. Technol., DOI: 10.1021/es103559w). These risk levels fall below EPA’s threshold for warranting additional study: one case in 1 million. Barry Dellinger, an environmental chemist at Louisiana State University, praises the researchers for undertaking a difficult task. But he cautions that the study did not account for the burnt oil residue and tar left in the ocean, which could contain dioxins and contaminate the fish that people eat. These additional considerations, he says, “might have increased—perhaps doubled—the estimated risks.”—CATHERINE COONEY, special to C&EN
ardous substances were released into the environment, the Chinese government reported. China produces most of its PVC via the acetylene process because coal is abundant in the country, whereas the oil and gas used in the more common ethylenebased PVC route are not. The acetylene process is controversial: It produces large amounts of waste and requires a mercury-containing catalyst (C&EN, Jan. 18, page 18). Producing PVC from acetylene is not inherently more hazardous than making it from ethylene, says Eddie Kok, director of Asian chlor-alkali and vinyls studies at the market research firm Chemical Market Associates, in Singapore. And the safety record of the acetylene route in China is historically no worse than that of the ethylene process, he notes. A number of Western companies are pursuing production of coal-based chemicals in China, although typically they are exploring coal-to-methanol technology. Dow Chemical and the Chinese coal producer Shenhua are planning a large complex in coal-laden Shaanxi province, and France’s Total recently announced a coal chemicals complex in Inner Mongolia.—JEAN-FRANÇOIS TREMBLAY
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NOV E M BE R 2 9, 20 10
Cleanup crews burned up to 310,000 barrels of oil in the Gulf of Mexico this spring and summer.
OTH K/ REUTERS
BURNING QUESTION
T ECH. SGT. P O L LY BEN N ET T/U.S. A IR FO RCE
NEWS OF THE WEEK
Police stand guard in front of Yushe Chemical’s destroyed PVC plant.
