Tests on leftover ash reveal carcinogens, but companies say fears are unfounded Environmentalists have called on Hong Kong's two power suppliers, CLP Power and Hong Kong Electric, to report their toxic emissions from coal-burning. Greenpeace made the plea after finding toxins such as mercury and arsenic in six samples it collected in July and August this year from CLP Power's ash lagoon at Lung Kwu Tan in Tuen Mun and from a cement manufacturer that uses ash. When coal is burned, ash falls to the bottom of the combustions unit, while some rises through the stacks, which are equipped with filters. The ash residue is stored in a lagoon or sold to recyclers. Tests by a British laboratory revealed 4 to 38 micrograms of arsenic per kilogram of ash and up to 0.1 microgram of mercury per kg. Arsenic is carcinogenic and mercury can cause brain damage. Based on these findings, Greenpeace estimated CLP Power produced up to 13 tonnes of arsenic and 36kg of mercury each year. The green group said that although this was lower than similar coal-burning power stations in countries such as Greece, Britain, Spain and the mainland, the emissions remained a health hazard. The Environmental Protection Department said the power companies' emissions were strictly controlled. CLP said its ash only had a minor environmental impact. No similar data was available for Hong Kong Electric as Greenpeace could not access the company's ash. 'It is less an issue about immediate danger or exceeding standards than the continuous emissions of the toxic heavy metals,' Greenpeace assistant campaigner Chow Sze-chung said. 'Even though they are below the standards, they are still a health hazard if the public is exposed to it in the long term.' Mr Chow said some of the heavy metals, most of which were very fine particulates that could penetrate the lungs directly, might have spread from the lagoon into the water or soil, or even blown away. CLP Power, which generated about 360,000 tonnes of ash last year, does not publish the volume of toxins it releases. An Environmental Protection Department spokeswoman said a specific process licence helped to regulate the emission of heavy metals by power plants. She also said the heavy metal levels in Hong Kong's air were well below American standards. She said a test carried out last year on CLP Power's coal generation units found the mercury emissions were below the latest United States standard of 19.1 micrograms for every megawatt hour of electricity generated. CLP Power also said its anti-pollution devices could filter out 99 per cent of ash and heavy metals emitted, while a stringent monitoring programme on the ash lagoon indicated there was minimal environmental impact.