Dow worker study examines dioxin levels in blood
Kathie Marchlewski, Midland Daily News
A study of Dow Chemical Co.’s employees shows that working in some areas of a chemical manufacturing plant can mean higher levels of dioxin in the blood. Still, the average is within what the U.S. Centers for Disease Control and Prevention considers a background range.
Dow began its study in September of 2003, and released results Tuesday.
The study is similar to a community wide study funded by Dow and under way by the University of Michigan. Sixty-two workers who were exposed to dioxin while working in Dow’s agricultural manufacturing facilities, particularly those that produced chlorophenol, were randomly selected to participate. Their blood dioxin levels were compared with those of 36 workers who did not work in the plants.
People with occupational exposure were found to have levels of dioxin averaging twice their non-exposed counterparts. The average blood serum levels for the exposed population was 68 parts per trillion with a high of 300 ppt., versus 33 ppt and a high of 90 ppt in the non-exposed group. Workers who performed tasks both in and outside of the chlorophenol areas were shown to have levels above the averages.
Because dioxin increases with age and body size, the CDC background criteria vary accordingly. For the Dow study group, which ranged from age 47 to 92, the average background, which could come from diet and a variety of other factors, is .08 ppt to 55.4 ppt for those 45 to 59 years old. The background is 3.4 ppt to 146.4 ppt for those 60 and older.
"Even though some may have levels higher than background, we don’t believe there’s any additional health risk," said Dow Epidemiologist Jim Collins.
The levels found in the exposed workers are likely to be higher than those of local residents in the U-M study, he said. "Since our study examines workers who developed chloracne, we know the blood levels will be much higher than the blood levels in the community study."
Chloracne is a long-lasting acne-type disease that Dow scientists consider the only certain health effect of dioxin exposure.
Those workers, who showed blood dioxin levels averaging five times higher than a comparison group, would seem likeliest to experience health problems caused by dioxin.
But like the U-M study, this exposure study was not intended to determine dioxin-related effects. Previous Dow studies, however, show that those who had experienced chloracne had cancer rates 50 percent lower than non-exposed populations.
Collins said the exposure study is an important one, because it validates previous studies on Dow workers’ health. Dow has been studying a group of 2,187 dioxin-exposed workers since 1940. In a 2003 publication, it reports lower overall cancer rates than a non-exposed population. To conduct the work, it categorized employees into groups based on assumed exposure during work. "This adds a lot of scientific value to our studies," he said.
The results of the exposure analysis are consistent with previous test of exposed populations, including one in 1988 by the National Institute for Occupational Safety and Health and one in 1978, conducted on a population in Seveso, Italy, that was exposed as a result of an industrial accident. Those showed that occupational exposure causes increased levels in blood.
The levels in Dow’s study are substantially lower, because it measured the longest number of years between exposure and tests and dioxin’s half life must be considered.
David Wade, Manager of the Michigan Department of Community Health’s Department of Occupational and Environmental Epidemiology, reviewed Dow’s results and agrees they were interpreted correctly and that the numbers were within the range expected by the CDC.
He said uncertainty surrounds what the results mean for health.
"We don’t know for sure," Wade said. "We don’t have literature we can go to that says ‘People with this level will have this effect."
The International Agency for Research on Cancer and the Agency for Toxic Substances and Disease Registry, along with the Environmental Protection Agency have linked high-level dioxin exposure with cancer and diabetes, birth defects and blood disease. Low-level exposure has been linked to increases in thyroid and immune function, learning disabilities and effects on tooth enamel.
©Midland Daily News 2004
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