Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Kilauea Eruption Producing Heavy Sulfur Dioxide Emissions

Dear Doctor: Our 68-year-old father moved to Hilo on the Big Island of Hawaii two years ago. He's not that great about using sunscreen, so my siblings and I always figured skin cancer would be the biggest health threat. But now with the Kilauea volcano, we're way more worried about the toxic fumes. What are they, and are they really as dangerous as the news stories say?

Dear Reader: When your father relocated to the Big Island, he moved to the youngest of the chain of Hawaiian Islands. It's home to Kilauea, which, despite its outwardly quiet demeanor over recent decades, is considered to be one of the most active volcanoes in the world. In fact, according to the U.S. Geological Survey, Kilauea has been in the process of erupting since 1983. This occurs when magma, the mixture of molten or semimolten rock found beneath the earth's crust, makes its way to the surface.

As this happens, ash, steam and various gases dissolved in the magma are released. Among the emissions is sulfur dioxide, or SO2. It's a noxious gas that in certain concentrations is toxic and potentially deadly. Scientists monitoring the current stage of Kilauea's eruption, which as we've seen from news reports is extremely active, report that significant amounts of the gas are emerging from the volcano's various vents and fissures.

Sulfur dioxide is a colorless, nonflammable gas with the acrid odor of a just-struck match. It's a byproduct of the burning of coal and oil at power plants, of smelting copper and, as Kilauea now reminds us, of volcanic eruptions. In small quantities, SO2 is used as a food preservative, as in dried fruit. It's also used to sanitize food containers and fermentation equipment, and as a moisture control agent.

People exposed to the gas near the volcano may experience eye irritation that can become severe, sneezing, coughing and choking, and a burning sensation or even a rash on the skin. Prolonged exposure to SO2 can cause bronchitis and swelling of the upper airways to the point that breathing becomes difficult or impossible. That's because the gas is highly soluble in water and is easily absorbed by the moist environment of the respiratory tract. SO2 gas is bad news for anyone, but the young, elderly and those with breathing issues are at greater risk of serious side effects. This is why residents have been evacuated from the immediate area and have been allowed to return to fetch pets and valuables only when it has been determined that SO2 is at acceptable levels.

Living in Hilo, a safe distance away from the volcanic activity, your father isn't at direct risk from SO2 gas. However, falling ash, as well as a mixture of SO2 and water vapor from fog or rain, known as "vog," can affect air quality across a wide radius. If your dad has any breathing issues, it's possible that they may flare up as the present eruption continues to affect air quality in a wider area. Staying indoors and avoiding exertion can help protect him from the worst of it.

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