Burning incense exposes people to dangerous levels of smoke laden with cancer-causing chemicals.

	Photo: Stone

The practice is a popular meditative and medicinal aid often used by Buddhists, Hindus and Christians in their homes and places of worship.

Levels of one chemical believed to cause lung cancer were 40 times higher in a badly ventilated temple in Taiwan than in houses where people smoke tobacco. Incense burning also creates more pollution than road traffic at a local intersection.

"We truly hope that incense burning brings only spiritual comfort, without any physical discomfort," says Ta Chang Lin at the National Cheng Kung University in Tainan. But "there is a potential cancer risk. We just cannot say how serious it is."

Burnt offering

Lin's team collected air samples from inside and outside a temple in Tainan City and compared them to samples at a traffic intersection. Inside the temple, they found very high concentrations of polycyclic aromatic hydrocarbons (PAHs), a large group of highly carcinogenic chemicals that are released when certain substances are burnt.

Total levels of PAHs inside the temple were 19 times higher than outside and slightly higher than at the intersection. "Due to poor ventilation in the temples and accumulation from non-stop incense burning, we were not surprised by these results," says Lin.

A PAH called benzopyrene, which is thought to cause lung cancer in smokers, was found in very high quantities inside the temple. The researchers compared benzopyrene levels inside the temple with other indoor areas, and found they were up to 45 times higher than in homes where residents smoked tobacco, and up to 118 times higher than in areas with no indoor source of combustion, such as cooking fires.

"The concentrations of PAHs inside the temple depends on how many visitors come to worship that day. During some major ceremonies, hundreds or even more than a thousand sticks are burnt at the same time," says Lin. "Sometimes the visibility is so low you can't see clearly across the room. We are concerned for the health of workers or keepers in the temples."

In suspension

Lin's team also tested for pollutants known as total suspended particles - a range of similarly sized particles that make up most of the emissions from human activity.

They found that concentrations of TSPs inside the temple were three times higher than at the traffic intersection and 11 times higher than outside the temple. These concentrations exceed the standard "safe" levels for ambient air set in Taiwan.

Lin now hopes to work with public health experts to see how much of the carcinogens reach the lungs of people in the temples. He plans to study the relationship between PAH concentrations in the air and PAH metabolites in temple keepers' urine.

Journal reference: Bulletin of Environmental Contamination and Toxicology (vol 67, p 332)