Five metal finishing companies in South California have been fined $223,700 (£140,931) for polluting the environment.
The US Environmental Protection Agency (EPA) said the firms violated the Clean water Act, some of which failed to treat pollutants such as nickel and zinc in their industrial wastewater.
It was revealed during inspections at its facilities in Compton, Paramount, Ontario and Sun Valley.
Metal finishers use a process to coat industrial metal which generates dangerous wastes and three of these facilities are in areas where the pollution effects on local residents are higher, the EPA said.
Jared Blumenfeld, EPA’s Regional Administrator for the Pacific Southwest said: “Metal plating facilities, often located close to neighbourhoods, must ensure they comply with federal laws to prevent harm to the community and the environment.”
The five companies have agreed to pay the penalty collectively.