Polluters in China are operating in a "black box" of secrecy, the Ministry of Environmental Protection has warned amid a rash of violent protests related to industrial poisoning.

Offenders are protected by the vast majority of local authorities defying Beijing and violating state law by refusing to disclose information about pollution, with a study showing just 4 out of 113 local governments complied.

The ministry said this lack of transparency was partly to blame for recent riots over lead and manganese poisoning in Shaanxi, Hunan and Fujian, which has affected thousands of children.

"Environmental impact assessment was meant to prevent these kinds of harm, but EIA has repeatedly failed to carry out its duties," the ministry noted on its website after the riots. "In the battle between illegal polluters and their opponents, the disparity in power is too great for the public interest to be effectively protected."

An information transparency law introduced in May 2008 was supposed to ease public concerns about the environment and to hold polluters to account.

But more than a year after it came into effect, a survey by leading NGOs and academics found that only four local governments provided comprehensive details about pollution violations as they were obliged to do.

Eighty-six failed to respond beyond claiming the information was secret or an inappropriate subject to raise in an economic downturn. Others simply ignored the request.

Ma Jun, who founded the Institute of Public and Environmental Affairs which carried out the survey with support from the US-based National Resources Defence Council, said local government transparency was at a very basic level. But he emphasised the success of the four who met the targets first year around – Ningbo, Hefei, Fuzhou and Wuhan – and claimed progress should be put in a historical perspective.

"China has never had a tradition of opening up government information before," said Ma, a winner earlier this week of the coveted Ramon Magsaysay Award for integrity in government. "The conclusion from our survey is that this is doable. If the local governments share best practice they can easily improve."

The environment ministry was less guarded in its criticism of local governments. Citing the results of the survey and the recent pollution disturbances, it said more information was vital.

"The absence of comprehensive, timely environmental data has given polluting companies and local authorities the chance to operate in a 'black box'. To break this practice, we need to bring everything out into the sunlight," it said.