CHAPEL HILL -- Sustained elevation of the suicide rate in a North Carolina county may be linked to releases of hydrogen sulfide and other airborne chemicals from a nearby paper mill and possibly other industrial sites, a new study led by a University of North Carolina at Chapel Hill psychiatrist indicates. The findings are being presented today (Nov. 7) to the 18th Annual U.S. Psychiatric and Mental Health Congress in Las Vegas.
This is the second study to propose a possible link between increased suicide rates in a North Carolina community and chemical exposures from nearby industry. Many of the same authors of the new research previously presented a study suggesting a possible link between an increased suicide rate in a community in Salisbury and chronic low-level exposure to hydrogen sulfide and other potential neurotoxins released from nearby asphalt plants and petroleum remediation sites.
From 1994 through 2003, the suicide rate in two Salisbury neighborhoods was found to be 38.4 per 100,000 individuals a year, roughly three times the statewide average. That study was presented to the 17th Annual U.S. Psychiatric and Mental Health Congress in 2004 and at the National Institute of Mental Health New Clinical Drug Evaluation Unit meeting in June 2005.
Pointing to their recent analysis of data from the U.S. Centers for Disease Control and Prevention, the current study's authors said the suicide rate in another N.C. area – rural Haywood County – nearly doubled from an age-adjusted rate of 11.8 per 100,000 residents for 1990-1996 to about 21.1 per 100,000 residents for 1997-2002.
The county's age-adjusted suicide rate has now remained elevated since 1997, peaking at 29.7 per 100,000 in 2000. In contrast, the average age-adjusted suicide rate for North Carolina for 1997-2001 was about 11.4 per 100,000 residents per year. Haywood ranked 46th out of North Carolina's 100 counties for average age-adjusted suicide rate for 1979-1996, but the county was ranked third for 1999-2002, according to CDC data.
The study's lead author is Dr. Richard H. Weisler, adjunct professor of psychiatry at UNC's School of Medicine, adjunct assistant professor of psychiatry at Duke University Medical Center and volunteer with the Blue Ridge Environmental Defense League, or BREDL.
"We clearly know there have been increases in suicides during this time period when there were also operational changes at the paper mill," said Weisler. "The 1997 spike in suicides in Haywood County corresponded to a switch to Bleach Filtrate Recycle in late 1996. Whether there is a connection between the increased suicides and operational changes has yet to be determined."
The Haywood County mill uses Bleach Filtrate Recycle, or BFR, to help remove chlorine and other toxins from the waste discharged into the Pigeon River. But Weisler and co-authors said they questioned whether or not a cleaner river comes at the cost of dirtier air.
"The burning of chlorinated compounds that BFR potentially entails, as well as a possible increase in plant volume, may have led to increased releases of dioxins and other harmful compounds into the air," Weisler said. "The switch to BFR, which involves burning of black liquor, may have resulted in an increase in air quality problems."
"Black liquor" is chemical and wood waste produced when turning wood into paper pulp. Some paper mills, including the Haywood County mill, burn black liquor to produce electricity.
The Haywood County mill has reported releases of many chemicals, including more than 93,000 pounds of hydrogen sulfide in 2003. Studies of industries such as asphalt plants, paper mills and sewage treatment plants have shown that exposure to occupational levels of hydrogen sulfide (10 parts per million for a 10-minute ceiling) can result in nervousness, mania, dementia and violence, Weisler said.
It is unknown whether levels lower than those to which nearby residents are exposed also would influence brain chemistry. "I think it has to be explored," Weisler added.
In animal studies, hydrogen sulfide has been shown to be a neurotoxin, altering levels of brain chemicals such as serotonin, norepinephrine, dopamine, aspartate, GABA and glutamate, the authors reported. "We speculate that hydrogen sulfide may serve as a marker for other potentially neurotoxic compounds being released in this mountain valley," Weisler said.
Other chemical releases reported by the paper mill include carbon disulfide, dimethyl disulfide, dimethyl sulfide and methyl mercaptan.
Haywood County is situated in a series of mountainous valleys that experience frequent temperature inversions, in which colder, dense air is trapped in the valley, potentially preventing pollutants from dispersing, and increasing air quality problems, the authors said. As the authors saw in their Salisbury study, many Haywood County residents complained of odor and air quality problems.
Formal studies are needed to model the flow of air pollution from the plant and to monitor the exact levels of particular chemicals released by the mill, the authors said.
"We hope there will be relevant and sensitive air monitoring, as well as a whole reassessment of whether or not burning the black liquor and using Bleach Filtrate Recycle is really the best approach to clean up the Pigeon River," Weisler said.
Co-author Dr. Jonathan R.T. Davidson, professor of psychiatry at Duke University Medical Center, said that the most important point for people to remember is that effective treatments exist for suicidal depression.
"Given that suicide can be a tragic consequence to depression, people who are experiencing persistent symptoms of depression should contact their health-care provider for a professional evaluation," he said. "The findings of this study may suggest another potential risk factor for suicide, but this needs to be confirmed in future studies."