an aqueous liquid composition containing dihydrogen phosphate salt , surfactant , and a dual coordinate bonding agent for iron cleans soiled metal surfaces without damaging any plastic parts that come into contact with the composition , supporting the growth of bacteria that cause unpleasant odors , or obscuring the transparency of any transparent window that it contacts . 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 .