A medical professor yesterday appealed for Hong Kong owners of factories in the Pearl River Delta to stop using cheap, dirty fuel, saying it risked the health of their own children. Anthony Hedley, chair professor in community medicine at the University of Hong Kong, said the use of so-called 'Bunker C' oil must be stopped immediately. This is a dense, viscous oil made from blending oils rich in sulfur and metals. It is cheap and readily available but also extremely dirty, he said. On average, such oils have 4.5 per cent sulfur content and contain metals like nickel. 'If Hong Kong businessmen continue to use it, it might affect the growth of their next generation in Hong Kong,' he told the 'Living Under Blue Skies' luncheon conference at the Marco Polo Hongkong Hotel in Tsim Sha Tsui. Professor Hedley said the oil was illegal in Hong Kong but it was believed to be widely used by factories across the border. He also called for a review of Hong Kong's air quality objectives, which had been in place for more than a decade. The objectives were far less stringent than those of some advanced nations and the public should change its perception that health problems caused by air pollution were related only to high-level exposure to pollutants. 'The harm to health is caused by average daily levels, not just by very high levels,' he said, adding that air pollution resulted in a direct cost of $148 million for hospital admissions annually. Describing a decision to lift the standard as potentially 'politically unacceptable' to the government, Professor Hedley suspected that some top officials and the tourism sector might be unhappy to set a higher standard that might give the city the image of having pollution problems. He said it would be wiser for the government to set clear objectives to reduce levels of pollution.