Pollutants in the Pearl River Delta are more dangerous than those choking the capital because they contain higher levels of hazardous nitrogenous organic compounds, an expert said yesterday. Wu Dui, an expert in dust haze and researcher at the China Academy of Meteorological Sciences, said health-threatening PM2.5 particles in the delta region contained more nitrogenous organic compounds than in central and eastern parts of China and the Yangtze River Delta. The volatile organic compounds were mainly emitted during the manufacture of shoes and cosmetics and were the main components of photochemical smog. Wu said the problem was identified a decade ago but had been given scant attention. His claim came as a British study concluded that exposure to higher levels of fine particulates - the airborne pollution that plagues many Asian cities including Beijing and Hong Kong - causes a sharp rise in deaths from heart attacks. Researchers from the London School of Hygiene and Tropical Medicine established a clear link between exposure to PM2.5 pollutants and early death after following 154,000 patients in England and Wales who had been taken to hospital with heart attacks between 2004 and 2007. In Hong Kong, we are being disastrously poisoned on a daily basis About 30 times thinner than a human hair, PM2.5 particles have long been identified as a respiratory problem, as their size enables them to lodge deep in the lungs. The average PM2.5 level in Hong Kong is around 30 to 35 microgrammes per cubic metre. The World Health Organisation has set guidelines of a maximum of 10 microgrammes of PM2.5 per cubic metre as an annual average exposure. "We found that for every 10 microgrammes per cubic metre in PM2.5, there was a 20 per cent increase in the death rate," said Cathryn Tonne, who led the research. They followed the patients for more than three years after their release from hospital. Nearly 40,000 died in that period. If PM2.5 levels had been reduced to their natural background rate, they calculated the number of deaths would have fallen by 4,873, or 12 per cent. In Beijing last month, PM2.5 levels reached 993 microgrammes per cubic metre, almost 40 times the WHO's recommended safe limit of 25 microgrammes over a 24-hour period, triggering a public outcry. Anthony Hedley, honorary clinical professor of community medicine at the University of Hong Kong, said the association between air pollution and heart disease had long been established, but the new study quantified the relationship and strengthened knowledge in the area. In the region where the study was conducted, pollution levels were a quarter to a third of that in Hong Kong, yet they were proven to be causing deaths from heart diseases. "In Hong Kong, we are being disastrously poisoned on a daily basis," Hedley said.