Environmental group Greenpeace on Tuesday criticized 18 leading companies from both home and abroad for concealing polluting information - a violation of Chinese regulations.

Eight of the world's top 500 companies including Shell, Samsung and Nestle, and 10 major Chinese companies, including industry leaders such as PetroChina and Shenhua, failed to publish pollution details after they were found guilty of irregularities in discharging sewage, Greenpeace reported.

The list also includes a smelting company - owned by Hunan Nonferrous Metals - that discharged excessive toxic chemicals including lead, cadmium and arsenic, without disclosing the information.

"It is shocking that these industrial leaders did not manage to obey the most basic environmental regulation in China," said Ma Tianjie, senior campaigner for Greenpeace China.

China's rules on environmental information disclosure, which took effect in May 2008, mandate that companies must reveal details of pollution to the public within 30 days of environmental authorities finding that these companies broke pollution laws.

They were required to reveal the name and amount of the pollutants, and come up with an emergency plan to rectify the problem. Local governments are also obliged to provide information upon demand by the public.

"The public has the right to know what these corporations are discharging in the rivers and lakes around their communities and what risks they face," Ma said.

The report comes at a time when China is facing an increasing number of major heavy metal pollution incidents.

Nearly 1,000 children in Henan province tested positive for excessive lead in their blood this week, in the latest of several lead poisoning cases involving thousands of children across the country.

The Ministry of Environmental Protection is working on a comprehensive prevention and treatment plan for heavy metal pollution, according to minister Zhou Shengxian.

"An environmental information disclosure system that is free and easy to access for the public ... is essential to safeguard citizens from industry-induced risks," Greenpeace said.

A similar toxic release inventory system in the United States helped reduce pollution by 61 percent in 20 years, it said.

China lacks a sound environmental information disclosure system, said Ma Jun, director of the Institute of Public and Environmental Affairs. Some local governments are protecting polluting companies out of concern for losing economic benefits, Ma said.

In July, Ma's organization launched China's first Pollution Information Transparency Index and published its first annual assessment of pollution information from 113 Chinese cities for 2008. But only 27 cities provided full information such as the polluters' environmental rule violations, and their subsequent improvement and rectification.

Ambiguities in the information disclosure regulations also cause problems, said Greenpeace officials, who are pressing the Chinese government to specify which enterprises and which pollutants must be revealed.