Beijing — Strict law enforcement is needed to prevent heavy metal pollution, which already poses a threat to the country's soil and water, a leading environmental researcher said.

According to China's policy on the disclosure of environmental information, which was implemented in May 2008, companies that exceed their emission limits are required to publish details of their pollution discharge in local media within 30 days of their being blacklisted.

However, few companies have adhered to the policy, said Ma Jun, director of the Institute of Public and Environmental Affairs, a Beijing-based NGO.

Citing a report published by the institute on Wednesday on heavy metal pollution by IT supply chains, Ma said six of the 29 largest IT enterprises, including Sony, Nokia, Apple, Sing Tel, Ericsson and LG, remained silent over pollution in China.

The report, based on 60,000 records of standard violations committed by polluting companies since 2004, found that a number of suppliers of the 29 largest IT companies, whose operations are predominantly located in the Pearl River Delta, have exceeded heavy metal discharge standards and become heavy polluters.

"We sent letters to the companies in April, questioning their supply chain's heavy metal pollution. However, up to now, only eight of them have given firm responses that they will improve their environmental management," he said.

Most companies showed an indifferent attitude, he said, quoting a response from one of the companies: "We have as many as 5,000 suppliers. It is troublesome to check whether they have problems on environmental management."

Currently, printed circuit boards and battery production are regarded as the two main sources of heavy metal pollution, leaving deposits of copper, nickel, chrome and lead.

According to the Annual Report of the Marine Environment of Guangdong for the year 2008, produced by the province's oceanic and fishery bureau, the Pearl and Shenzhen rivers, along with smaller rivers, discharged more than 12,000 tons of heavy metal and arsenic into the sea.

Large amounts of heavy metal were also deposited in the soil across the country, according to the Ministry of Environmental Protection.

China's environment is paying a great price, said Ma, who followed 12 cases of heavy metal pollution in 2009, which left 4,035 people with excessive lead in their blood and 182 with excessive cadmium.

"Current techniques are good enough to prevent heavy metal pollution, but most companies lack the motivation to abide by the law due to weak law enforcement by the government," he said.