an aqueous liquid composition containing dihydrogen phosphate salt , sulfur containing surfactant , and preferably a small amount of phosphoric acid cleans soiled metal surfaces without damaging any plastic parts that come into contact with the composition with the composition and without supporting the growth of bacteria that cause unpleasant odors . the composition is particularly useful for cleaning unpainted aluminum sided rail transport cars that have polycarbonate housings insulating electrical contact points that provide motive electric power to the cars ; many conventional aqueous alkaline and acid cleaners promote stress cracking of polycarbonate plastics .