Hidden risks of centuries-old attraction

By SIMON COLLINS

Hundreds of years before Europeans arrived in Aotearoa, people sought the comfort of Rotorua's hot pools.

Bay of Plenty medical officer of health Phil Shoemack says the pools and geysers have never had a tradition of causing ill health.

"The Maori leaders talk of their ancestors going to Rotorua because of the geothermal activity and living right on top of the geothermal field, using it for heating and cooking," he says.

"I would have thought they wouldn't have continued to do that if they were aware of the health impact."

With the coming of the British, Rotorua became a health spa.

Wealthy people came from Europe, North America and Australia to "take the waters" in the grand Tudor-style Bath House.

Today the "geyserland" attracts more than 1.3 million visitors a year. Tourism accounts for 18 per cent of Rotorua's jobs.

But, just as there are risks in bungy jumping or swimming with whales, so the hydrogen sulphide gas that comes with the hot springs and geysers can be treacherous.

Dr Mike Durand, of Canterbury University's Natural Hazards Research Centre, says 11 people have died since 1946 from overexposure to the gas in Rotorua.

Coroners' reports found that three of these, including the latest three years ago, Austrian actress Ellen Umlauf-Rueprecht, probably died from staying in hot pools too long.

Three workers in the early years died in sewers, septic tanks or sump holes.

Rotorua bylaws now ban anyone going into a trench or manhole in high hydrogen sulphide areas without a respirator and a safety harness with a recovery rope, with at least two people at the top of the rope.

The other five victims died in buildings, apparently when hydrogen sulphide got in through the plumbing. The gas is heavier than air and can be lethal if it seeps in above a person in bed.

Hydrogen sulphide occurs naturally in swamps and decaying organic matter, and comes up through the ground in volcanoes and geothermal areas.

It is also produced in industrial processes such as oil refining, mining and making wood pulp.

In most of the world, hydrogen sulphide is present at microscopic levels of less than 1 microgram (millionth of a gram) per cubic metre of air.

In Rotorua's Fenton St and Ti St, Environment Bay of Plenty has found that the gas is commonly about 100 to 500mcg, and occasionally over 1000mcg.

Eye irritation normally develops about 15,000mcg. At 480,000mcg the lungs start to fill with fluid, and about 1.5 million micrograms cause death.

In last month's Australasian Science, Dr Durand wrote that hydrogen sulphide seeping through Rotorua's soil "would not normally be a significant problem if gases could leave the soil unencumbered by tarseal, pavements and buildings".

"Instead, the ground is virtually sealed in some parts of the city, so, taking the easiest route, gases escape where they can."

By crawling along floors and sniffing in corners, Dr Durand found that most gas came in through cracks in floors or vents in walls.

It seeped in even where building owners had put down "gas-proof" membranes made of rubberised fluids such as butanol under concrete floors. "They don't work," he says.

Although deaths have been rare, Dr Durand found many lesser health effects.

Some people said they had dry, itching or irritated eyes, wheezing, headaches, a sore or dry throat and tiredness and fatigue nearly every day they were in an affected building.

Last year, Rotorua's central zone was found to have between 1.5 and 2.7 times the national average rate for diseases ranging from migraines to bronchitis.