BEIJING, June 29 -- The national hotline for public reports of polluting enterprises received 332 tip-offs in the first quarter of this year, said the Ministry of Environmental Protection (MEP) on Monday.

The most common target of the complaints was the chemical industry, which had 82 reports filed against it. Metal smelting and mineral processing were also frequently complained about.

Eighty-two of the reports came from central China's Henan Province, which had the largest concentration of whistleblowers, followed by the coastal Guangdong and Jiangsu provinces.

The MEP transferred these tip-offs to local authorities for investigations which found pollutants, improper operations and equipment failure are the three major causes of environmental hazards.

The polluting companies have mainly affected air quality, said the MEP.

It ordered the violators to rectify the identified problems or face fines, suspended production or revocation of their licenses.