More than half of the mainland's thousands of chemical plants are located along its main rivers, posing serious threats to water supplies, the environmental chief says. Zhou Shengxian, director of the State Environmental Protection Administration, yesterday warned of inconceivable consequences if similar accidents like the massive contamination of the Songhua River last year occurred again. 'According to a recent nationwide survey, China has about 21,000 chemical plants, with more than 50 per cent of them located along the Yangtze or the Yellow River,' he said at a briefing. While many plants were built in inappropriate locations without the environmental impact assessments required by a national environmental law, more than 100 chemical plants have 'obvious safety risks', according to the survey. Mr Zhou said the details of the survey, triggered by the country's worst chemical spill caused by a Jilin chemical plant explosion in November, would be made public after the Lunar New Year. He blamed the blind pursuit of economic development among local cadres over environmental protection for the problem. 'In the first decades of the new People's Republic, we have achieved economic growth at the cost of damaging the environment,' he said. 'The Chinese government has made some necessary adjustments to the guiding policies of environmental protection and put an end to a conventional approach which could be characterised as 'pollution and destruction first, treatment later',' Mr Zhou said. He said ensuring the safety of drinking water had topped the government's mounting battle against environmental degradation. Mr Zhou assumed the post more than a month ago, when his predecessor, Xie Zhenhua, was sacked over the chemical spill in the Songhua River, which affected millions of people in Jilin and Heilongjiang, and strained relations between China and Russia. Quoting an interim assessment of the state of the polluted waterway, Mr Zhou said although quite small amounts of nitrobenzene had been frozen in the ice or entrapped in the sediment, it was safe to eat fish from the river and livestock along the banks. A full assessment would not be completed until the end of October, although a preliminary report would be available in March. Chen Jining , from Tsinghua University's Institute of Environmental Science and Engineering, said although the nitrobenzene concentration in the river would rise when the ice thawed, 'it will not exceed national standards on a large scale'. 'Even in the rare cases where levels are beyond standards in some places, we have the technology in place to ensure safe drinking water,' he said. But Mr Zhou admitted the restoration of the damaged ecological system would be a more complicated and expensive task. Meanwhile, he said an investigation into the chemical spill was still under way. It has so far resulted in the removal of the general manager of the Jilin petrochemical plant and two workers. A vice-mayor of Jilin in charge of the much-criticised rescue efforts after the explosion is believed to have committed suicide last month.