Evidence that Monochloramine Disinfectant Could Lead to Elevated Pb Levels in Drinking Water

摘要

Many water districts have recently shifted from free chlorine (in the form of HOCI/OCI~-)to monochloramine (NH_2-Cl)as a disinfectant for drinking water to lower the concentration of chlorinated hydrocarbon byproducts in the water.There is concern thatthe use of NH_2CI disinfectant may lead to higher Pb levels in drinking water.In this study,the electrochemical quartz crystal microbalance is used to compare the effects of these two disinfectants on the dissolution of Pb films.A 0.5 mu m thick Pb film nearly completely dissolves in a NH_2CI solution,but it is passivated in a HOCI/OCI~-solution.X-ray diffraction analysis shows that the NH_2CI oxidizes Pb to Pb(ll)species such as Pb_3-(0H)_2(C0_3)_2,whereas the stronger oxidant,HOCI/OCl~-,oxidizes Pb to Pb(IV)as an insoluble PbO_2 conversion coating.Although NH_2CI may produce less halogenated organic byproducts than HOCl/OCl~-when used as a disinfectant,it may lead to increased Pb levels in drinking water.