The area has a long history of lead mining, and produces precious metals like gold and silver. Many small factories were closed in the 1990s because of pollution concerns, but have reopened recently because of rising metals prices.

Heqing authorities have cracked down on illegal mining. They have cleared up 4,300 tonnes of smelting wastes and shut down more than 200 illegal, fumes-producing, waste-generating workshops that used cyanide to extract gold. However, the situation appears compromised.

Lead poisoning, which often builds up slowly as a result of repeated exposure to small amounts of the metal, can damage various parts of the body including the nervous and reproductive systems and the kidneys. It can cause high blood pressure and anaemia.

It is especially harmful to the developing brains of young children, and can cause learning difficulties and behaviour problems.

Last year, more than 4,000 people were poisoned by lead in China, the Ministry of Environmental Protection (MEP) reported, including more than 2,000 children. For many years now, the Ministry has also tried to put in place tighter controls against heavy metals poisoning.

However, popular unrest due to a rising number of incidents is becoming a problem. In one case last August, protesters broke into a smelting plant they blamed for the lead poisoning of more than 600 children, smashing trucks and tearing down fences.

More recently, a toxic spill scandal involving  the Zijin Mining Co, China’s leading gold and copper producer, continues to reverberate across the nation.

In early July, one of the company’s plants "accidentally" dumped more than 9,000 m3 of copper-tainted waste when heavy rains caused a containment pond to spill its content into the Ting River, killing 1,500 tonnes of fish.

Local residents had already complained about collusion between local authorities and the company when they saw the former cover up pollution incidents rather than carry out necessary controls.

The fact is, according to a report released last year, the company's biggest shareholder is none other than the State-Owned Assets Supervision and Administration Commission's county branch in Shanghang, which holds a stake of nearly 30 per cent. In addition, not only have retired central government and provincial cadres been offered lucrative sinecures, incumbent officials and civil servants have also taken up well-paid senior positions in the company.

Previously, smaller spills had already badly contaminated the river. Fish was killed in early June and reputable local fish farms suffered major losses. In all these cases, local authorities simply covered up the incidents.

On 23 June, fishermen from the five villages organised a demonstration, blocking the gates of the county government headquarters with two tonnes of dead fish. But that was not sufficient.

For some time, the central government has had a zero tolerance policy towards corruption. Under the law, public officials are not allowed to own stocks or have other interests in companies, or accept corporate appointments for three years after retirement.

However, supervision and monitoring are lax and many private companies are actually owned by public agencies.

The rights of ordinary citizens are too often undermined by cosy relationships between corporate groups and local authorities. For this reason, the only means people have at their disposal to defend their rights is to take to the streets in protest.