High concentrations of potentially deadly parasites and a small amount of cancer-causing dioxin have been found in water and sediment from the Dongjiang river - the source of most of Hong Kong's drinking water.
The findings by the Open University follow the disclosure last week by the Water Supplies Department that low levels of two parasites - giardia and cryptosporidium - had been found in three samples of treated Hong Kong water over the past three years.
Tests by the university found the parasites were present in 40 per cent of raw water samples taken from the Dongjiang and three local reservoirs. The bugs can cause serious intestinal diseases and even kill people with weak immune systems. Small quantities of dioxin were also found for the first time in Dongjiang sediment.
Researchers found up to one million cryptosporidium and 10,000 giardia specimens per litre of water in the most polluted Dongjiang tributary in Sima, Guangdong. At Plover Cove and Shek Pik reservoirs, up to 100,000 cryptosporidium and 10,000 giardia per litre were discovered.
Research team leader Dr Ho Kin-chung said the results had worrying long-term health implications, despite the team's failure to detect the parasites in treated water samples.
'The findings raise concern over the long-term health risk to people as we have found the parasites existing almost everywhere along the tributary,' he said. 'We cannot always rely on the treatment plants to deal with this rising problem. It cannot be reliable all the time.'