Increased suicide rate possibly linked to chemicals released from nearby asphalt plants.

Exposure to low levels of hydrogen sulfide and possibly other airborne chemicals from nearby asphalt plants may have contributed to an increased suicide rate in a North Carolina community, a study has suggested for the first time.

The study's lead author is Dr. Richard H. Weisler, adjunct professor of psychiatry at the University of North Carolina at Chapel Hill School of Medicine, adjunct assistant professor of psychiatry at Duke University Medical Center, and a volunteer with the Blue Ridge Environmental Defense League.

The affected neighborhoods, comprising two U.S. census tract block groups with a total of 1,561 residents, were immediately downwind from

* a liquid asphalt terminal;

* an asphalt hot-mix plant that also contained a former North Carolina Department of Transportation (NCDOT) solvent-contaminated cleanup site, at which NCDOT had previously dumped solvents used for testing asphalt; and

* a contaminated former petroleum tank farm.

In 2003, the suicide rate in two Salisbury, North Carolina, neighborhoods was found to be 192 per 100,000 individuals a year, roughly 16 times the statewide average. Between 1994 and 2003, death certificate evaluations for the two Salisbury neighborhoods showed a 3.5-fold, statistically significant, increase in the suicide rate. Only two deaths by suicide would be expected for this population over a 10-year period, but seven suicides were observed.

In 2001, the North Carolina Department of Environment and Natural Resources (NCDENR) estimated the average maximum hydrogen sulfide level in a large part of the affected area to be 215 parts per billion (ppb), although in some sections of the neighborhoods levels were reported to be as low as 30 ppb. Based on its own air-modeling study, NCDENR estimated that historical releases of hydrogen sulfide reached average maximum levels of 860 ppb in a few residences very near the asphalt facilities.

By comparison, the World Health Organization has a 10-minute exposure standard of five ppb. The California one-hour standard is 30 ppb. The newly revised, but not yet implemented. North Carolina 24-hour hydrogen sulfide standard is 86.2 ppb.

The exposures accompanied 574 formal complaints to the city of Salisbury from March 11, 1999, to October 15, 2004, for noxious odors and associated respiratory problems, which are still occurring--though at a reduced rate--said Weisler.

In addition to suggestions of an increased suicide rate, the incidence rate of primary brain cancers in these neighborhoods from 1995 to 2000 showed an increase about 6.4 times greater than expected for the population, possibly as a result of benzene and other solvent exposures, Weisler said.

Several studies have shown increased rates of lung and brain cancer among workers with long-term exposure to asphalt emissions, the researchers said.

Weisler and his study team made a hypothetical link between hydrogen sulfide and suicides on the basis of biological plausibility. They noted that hydrogen sulfide affects brain neurochemistry as a direct gaseous neuromodulator that potentially affects mood states and the psychological stress response. In animal studies, it has been shown to alter the levels of the neurotransmitters serotonin, norepinephrine, dopamine, aspartate, and glutamate.

Hydrogen sulfide also affects the hypothalamic pituitary adrenal axis and the corticotropin-releasing factor in animal studies, the report said.

"This is the part of the brain involved in the stress response, and we think it's also involved in psychological resiliency, how people deal with stressors," Weisler said. "It's frequently associated with mood disorders, and there are suggestions that resiliency is impaired when people are suicidal."

The study team reported that additional neurotoxic compounds such as benzene, chlorinated solvents, and carbon disulfide, among others, were released in unknown quantities by the asphalt terminal and hot-mix asphalt plant. Carbon disulfide, also a neurotoxin, has been linked to personality changes, mood disorders, and suicides in occupational settings, the researchers said.

Weisler presented the findings on November 19, 2004, at the 17th Annual U.S. Psychiatric and Mental Health Congress in San Diego.

Formal health studies of the two neighborhoods and other potential sites with chemical exposures are being planned in further collaboration with CDC and UNC's School of Public Health.