The Ministry of Environmental Protection is investigating a chemical company’s alleged dumping of carcinogenic industrial chemicals into water systems in Yunnan province. Pollution has been detected in the Chachong Reservoir in the town of Yuezhou and the Nanpan River, a tributary of the Pearl River.

In addition to checking on the human health and environmental impacts, investigators will assess the safety of all 29 heavy industrial plants in Luliang county, according to a local official quoted by China Daily.

The newspaper said that, since April, more than 5,000 tons of chromium waste from Yunnan Luliang Chemical Industry has been illegally dumped near the Nanpan River.

The plant has suspended production, but about 148,000 tons of unprocessed chromium waste was dumped along the Nanpan River, the city said. In June rain washed some of the waste into the water supply, according to the Pearl River Water Conservancy Committee under the Ministry of Water Resources.

The committee has found excessive hexavalent chromium, a carcinogen, at the company’s dumping sites. “Hexavalent chromium poses great health dangers. Drinking water polluted with it could cause acute poisoning symptoms,” said Liu Xiaoduan, a researcher with the Chinese Academy of Geological Sciences.

Two truck drivers who dumped the waste near the river have been arrested.