Procurators in north China's Hebei Province have filed lawsuits against 20 people for discharging toxic waste and causing the death of a restaurant owner.

The suspects from two gangs dumped more than 3,400 tonnes of waste acid and alkali in Hebei's Lixian County, according to the regional people's procuratorate.

On May 18, 2015, Li, owner of a restaurant in the county died after inhaling poisonous gas from his kitchen sewer. Investigations found that a nearby parking lot was used as a dumping ground, with a tank specifically for that purpose.

The police found that from February to May of 2015, more than 2,800 tonnes of waste alkali was dumped into the tank, which then passed into the county's sewerage system. The waste came from a Beijing petrochemical company.

On the day when Li died, another gang introduced 30 tonnes of waste acid into the tank. The ensuing reaction of acid and alkali generated the highly toxic gas, hydrogen sulfide.

The parking lot operator confessed that he charged the gangs 40 yuan (6.2 U.S. dollars) for disposing of one tonne of waste and an additional 10,000 yuan for the use of the tank per year.