Wednesday, November 10, 2004
JEREMIAH STETTLERTHE SAGINAW NEWS
Dow Chemical Co. has revealed a potential ace up its sleeve in defending claims that dioxin does not threaten the health of residents downwind and downstream of its Midland plant.
Dow scientists have confirmed that a group of dioxin-exposed workers -- monitored for decades as part of a Dow investigation -- harbors dioxin levels twice as high as the normal population.
Yet the group has exhibited no ill health effects in 17 separate dioxin studies, scientists say.
The findings, released late Tuesday, could heighten the credibility of Dow's own studies on dioxin-exposed workers.
Previously, the company relied on occupational information and incidents of a dioxin-induced skin condition known as chloracne to determine if workers had suffered high dioxin exposure. Scientists could not verify the exposure with blood tests.
It's not that Dow didn't want that information. Rather, it lacked the technology to gather it.
Dow scientists say they now can prove that the same workers who reported no unusual occurrences of cancer, immunodeficiencies or other dioxin-related ailments were exposed to high levels of the toxin.
"We are very confident that our exposure estimates in the mid-1980s do represent dioxin exposures that may have existed in these workers many years ago," said James J. Collins, a Dow epidemiologist. "As a result, we are much more confident in the conclusion of the health studies we did based on those estimates."
The study examined 62 workers who were assigned to the company's chlorophenol plants. The facilities, which manufactured agricultural products such as pesticides until their closure in the early 1980s, produced high levels of dioxin.
Dow officials also selected 36 employees who worked in areas with no known dioxin exposure to serve as a control group.
Using blood samples that were drawn by Dow and analyzed by an independent San Diego, Calif., laboratory, scientists discovered that exposed workers had an average dioxin level of 68 parts per trillion in their blood.
That's more than double the dioxin concentration of 33 parts per trillion in the control group.
The gap widened for employees with chloracne. Those workers had dioxin levels five times higher than colleagues who also were exposed to the toxin.
Dow scientists believe dioxin levels in the exposed population likely have dropped considerably since the company's last chlorophenol plant closed in 1982. At a minimum, employees had a two-decade lapse between the blood test and their most recent dioxin exposure -- a significant gap for a substance that has a half-life of seven to 10 years in most adults.
Despite the high dioxin levels, Dow officials say they do not believe exposed workers face any additional threat of illness.
They echo the same conclusion for residents along the dioxin-tainted Tittabawassee River.
"A key principle in epidemiology is that you always study people with the highest exposure first," said Michael L Carson, medical director for Dow's Midland facility.
"We are studying people with exposure levels many times greater than background in the Midland area, and we don't see any indication of increased health effects."
Dow scientists have submitted their study to a review panel of epidemiologists from various universities in the United States and Greece.
They also have presented it to the state Department of Community Health, state Department of Environmental Quality and to the International Symposium on Epidemiology and Occupational Health in Melbourne, Australia.
Dow's study was released too late Tuesday for The News to seek comment from state health and environmental officials. v
Jeremiah Stettler is a staff writer at the Saginaw News. You may reach him at 776-9685.
© 2004 Saginaw News
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