Industrial chemicals that leaked into a river, leading to water supplies being cut last week to 30,000 residents in suburban Shanghai, exposed faults in the supervision of chemicals' production and transportation, an expert said.

The leak, caused when a valve being used to control discharge from a tanker to another vessel was left open, also highlighted low access to the chemical manufacturing industry, the expert added.

"It should not be as easy as a company paying some money, and then getting a plot in a chemical enterprise park and starting production," said Dai Xingyi, a professor at the Department of Environmental Science and Engineering at Fudan University in Shanghai.

"Proper supervision should be put in place in the key points of chemicals' production and transportation," he said.

Large amounts of styrene - a chemical hazardous to the intestines, kidneys and respiratory systems if ingested - leaked into a river on Thursday in Jinshan district, home to the city's chemical industry park.

The leak led to operations being suspended at two water plants in the nearby Songjiang district, prompting the authorities to offer emergency supplies to residents.

A total of 23 residents became ill after inhaling the chemical, with five of them still in a hospital on Monday, Xinhua News Agency reported.

By early Monday, the water supply resumed after efforts by the environmental department to deal with the pollution, involving 175 vessels and nearly 700 people.

Residents were told water is only safe to use after they let taps run for 15 to 30 minutes the first time they use it. Households have also been told their water bills for January will be halved.

Four suspects have been detained, with three others released on bail. Suspect Liu Langjian told police the leak was caused by his oversight but denied acting intentionally. He said he regretted the seriousness of the aftermath.

Police also found the three companies involved are not qualified to sell, transport or load the chemicals; the owners of the vessel involved are suspected of installing the discharge valve without approval; and the port is not allowed to load dangerous chemicals.

Dai said: "It showed the government's supervision of the entire process of chemical production and transportation is inadequate."

He said it also showed the government intervened after a pollution incident, rather than acting earlier.

"The government should clear the danger from the source and raise the threshold for companies entering chemical-related sectors."

Dai added that there should be an overall evaluation of a company's ability to manage and deal with emergencies and pollution control before it is allowed to engage in related business.

Experts have called for severe penalties for violators.

wangzhenghua@chinadaily.com.cn

(China Daily 01/15/2013 page4)