A Dutch study has found that burning candles and incense inside a poorly ventilated church can produce high levels of fine airborne particles (PM10s).The Maastricht University researchers found the levels reached inside churches were up to 20 times above European air- pollution limits and on a par with the pollution recorded along roads used by 45,000 vehicles a day.The problem was as true in a large basilica as in a small church, reported the study, published in the European Respiratory Journal's December edition.Lead researcher Theo de Kok said the results were "very worrying".Churchgoers exposed to the pollution for only short periods were unlikely to be affected, but the health of priests or devout worshippers inside churches for several hours a day could suffer."It cannot be excluded that regular exposure to candle or incense- derived particulate matter results in increased risk of lung cancer or other pulmonary diseases," wrote de Kok.As well as high levels of PM10s -- the main pollutant in Christchurch air -- the researchers found carcinogenic aromatic hydrocarbons and various free radicals known to aggravate asthma and chronic bronchitis.Catholic Church communications director Lyndsay Freer said New Zealand churches were well ventilated and less likely to be closed against the cold than European churches.She said candles and incense were not heavily used, with some churches even removing candle racks, fearing they were a fire hazard. "The amount of candles used would hardly be a problem."Christchurch Cathedral's Dean Peter Beck said "a lot of candles" were used in the Anglican cathedral, but good ventilation meant it was unlikely to have high pollution levels.Clean Air Society president Gavin Fisher said indoor air pollution was a growing concern and he could "quite believe" that churches were affected."Anything that burns -- candles or open fires -- produces lots of fine particles (PM10s) and if it's not ventilated it builds up."He believed the real health risks from indoor air pollution were in houses or vehicles where people were exposed for long periods. The most vulnerable were young children or those with asthma.New Zealand had a particular problem with portable gas heaters, used in the tens of thousands but which released damaging nitrogen dioxide and carbon monoxide chemicals into the air, Fisher said.An Asthma and Respiratory Foundation board member and Christchurch School of Medicine Dean, Professor Ian Town, said research was under way on lungs and indoor environments.