HANGZHOU, Dec. 18 -- Police have arrested 12 suspects and are continuing the search for another after their company was found dumping untreated waste containing heavy metals into a river in east China's Zhejiang Province.

Zhongjinlingnan Environmental Technology Company, which recycles metals in electroplating sludge and other solid wastes from factories, was found to have dumped nearly 10,000 tons of untreated waste into Oujiang River in Wenzhou City, local police told Xinhua on Thursday.

Investigations found the company, despite being overcapacity since April, still accepted hazardous waste from nearby plants manufacturing stainless steel tubing.

It costs the company nearly 500 yuan (about 81 U.S. dollars) per tonne to dispose of industrial wastes safely and 100 yuan to dump it directly into the river. Police found that in May of this year, the company's legal representative, surnamed Jiang, directed workers to dispose of nearly 6,000 tonnes of pollutants sludge into the Oujiang River.

In early June, Jiang and his workers poured another 3,800 tonnes of untreated wastes into the river, police said.

Currently, the local environmental protection department is monitoring the water quality of Oujiang River.