Rotorua smell no danger to cognitive functions
The gas that gives Rotorua its rotten-egg smell has been cleared of messing with the heads of the town's residents.
An extensive study involving 1637 Rotorua residents aged between 18 and 65, who had lived in the town for at least three years, found no association between hydrogen sulfide (H2S) exposure and cognition. Some evidence even suggested the exposure might have been slightly helpful.
Rotorua was probably the largest town in the world with long-term exposure to ambient levels of H2S as high as that found in the area, a report on the study said.
The research was the largest epidemiologic study to investigate cognitive effects of ambient H2S concentrations.
Exposures at homes and workplaces of participants were estimated from data collected by summer and winter H2S monitoring networks across Rotorua in 2010 and 2011. Exposure rates were also calculated for the previous 30 years.
The median H2S concentration for current residences was 20.3 parts per billion, while for current workplaces the median was 26.4ppb. The range for both residences and workplaces was 0-64ppb.
Participants went to a study clinic where they answered a questionnaire and did a series of neuropsychological tests, the report said.
"Tests assessed attention, psychomotor speed, fine motor function, memory, and mood - important cognitive functions that are sensitive to adverse effects of a wide variety of injuries and diseases."
The predominant finding was that H2S exposure was not associated with cognitive function.
"Further, higher levels of H2S were sometimes associated with slightly better performance. This was most evident with tests of psychomotor speed where, for both current and long-term exposures, persons in the higher exposure quartiles had faster average reaction times compared to the lowest exposure group."
Those results were most likely due to random variation, but an emerging literature provided some plausibility to the idea that low-level H2S might have beneficial effects on central nervous system function, the report said.
H2S had been found to regulate blood pressure and inflammation, and play a role in metabolic disease. A protective role for H2S in neurodegenerative and cerebral ischaemic disease had been proposed.
"Most importantly, we found no evidence of harmful effects in any cognitive function, regardless of how exposure was quantified and modelled.
"These results provide reassurance about the cognitive effects of chronic exposure to H2S, at least up to the levels found in Rotorua, which are comparable with or higher than other reported ambient H2S concentrations in Iceland, Finland, and the United States."
The study was carried out by researchers from the University of California, Davis, the University of Otago, Auckland University of Technology, Veterans' Administration Northern California Health Care System, and the University of California, Berkeley.
Results were published in Neurotoxicology and Teratology.
The research was part of a larger study into possible health effects of H2S on the Rotorua population.
The report said H2S was reported to cause eye and respiratory irritation at concentrations of about 20 to 50 parts per million and death at concentrations of about 500ppm.
Most human exposure to the gas was from industrial processes, such as sewage treatment plants, paper mills, oil and gas refineries, and concentrated animal farming operations.
There had been reports of cognitive impairment in workers who were exposed to H2S but never lost consciousness, and in people living downwind from industrial H2S sources.