Officials say thousands of fish found on riverbank near site of deadly explosions had died from lack of oxygen.
Chinese police have arrested 12 people over a series of giant explosions that killed 139 people and devastated a large section of the Chinese port city of Tianjin, state media said.
The official Xinhua news agency on Thursday said those arrested include the chairman and senior managers of the firm whose chemical storage facility exploded in Tianjin two weeks ago.
Separately, the Supreme People’s Procuratorate said on its website that prosecutors in the city were also probing 11 officials for “abuse of power” and “dereliction of duty” over the blasts, which also injured hundreds of people.
In China, a formal arrest normally comes after some time in police detention and sees the case handed to prosecutors, with trial and conviction almost guaranteed.
The 12 arrested include owners of Rui Hai International Logistics, who were shown on state television last week when they were already being held by police, “confessing” to using government connections to obtain safety permits.
More than 500 people remain in hospital and dozens are still missing after the huge explosions, which left a trail of mangled buildings and burned out cars in their wake.
Al Jazeera’s Adrian Brown, reporting from Beijing, said the the blasts continued to affect the surrounding environment.
“Tests in the area and the nearby river show levels of toxins in the soil and the water are still very high indeed … in one case, 356 times more than the accepted levels,” Brown said.
“Many people have been affected by what’s happened, some 30,000, many of them living in temporary accommodation and haggling with the government over compensation.”
The incident sparked widespread outrage over alleged safety violations by the firm and possible official collusion, and fears of pollutants contaminating the air and water of Tianjin, home to about 15 million people.
Communist authorities and state-run media have sought to pin blame for the disaster on local individuals and officials, rather than systemic factors.
Prosecutors said the officials they were investigating came from several government departments including transportation management, customs and work safety, and the president of a state-owned port company in Tianjin.
Industrial accidents are common in China, with corruption thought to be a key factor behind lax enforcement of safety regulations.