A system and method treat oilfield produced water by two-stages of hazardous sulfide treatments. In an embodiment, a two-stage oil and gas field produced water treatment system includes an oil removal vessel. The oilfield produced water is introduced to the oil removal vessel. The oil removal vessel removes a portion of the hydrocarbons from the oilfield produced water to provide a reduced oil produced water. In addition, the system includes an iron sponge. The reduced oil produced water is introduced to the iron sponge, and the iron sponge removes a portion of the hazardous sulfides from the reduced oil produced water to provide a reduced sulfide produced water. The system also includes a stabilized sodium percarbonate solution. The stabilized sodium percarbonate solution is mixed with the reduced sulfide produced water to remove a portion of the hazardous sulfides from the reduced sulfide produced water to provide a treated produced water.