Web Release Date: April 12,
Evidence that Monochloramine Disinfectant Could Lead to Elevated Pb Levels in Drinking Water
Department of Chemistry and Graduate Center for Materials Research, University of Missouri, Rolla, Missouri 65409-1170
Received for review November 30, 2005
Revised manuscript received February 27, 2006
Accepted March 10, 2006
Abstract:
Many water districts have recently shifted from free
chlorine (in the form of HOCl/OCl-) to monochloramine (NH2Cl) as a disinfectant for drinking water to lower the
concentration of chlorinated hydrocarbon byproducts in
the water. There is concern that the use of NH2Cl 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 
m thick Pb film nearly
completely dissolves in a NH2Cl solution, but it is passivated
in a HOCl/OCl- solution. X-ray diffraction analysis shows
that the NH2Cl oxidizes Pb to Pb(II) species such as Pb3(OH)2(CO3)2, whereas the stronger oxidant, HOCl/OCl-, oxidizes
Pb to Pb(IV) as an insoluble PbO2 conversion coating.
Although NH2Cl may produce less halogenated organic
byproducts than HOCl/OCl- when used as a disinfectant,
it may lead to increased Pb levels in drinking water.
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