Investigation of the reduction of lead dioxide by natural organic matter.

Experiments with immobilized lead dioxide showed that this solid was reduced by natural organic matter (NOM) isolated from Potomac River water. Kinetically, the process was slow and occurred throughout many weeks of exposure. The amount of mobilized lead was affected by the concentration of NOM and exposure time but not significantly influenced by the type of NOM used in the experiments. The interactions of NOM with PbO2 were quantified using differential absorbance spectroscopy. It showed that the oxidation of chromophoric groups in NOM was strongly correlated with lead release. Because lead release yields were higher thatthose predicted based on the depletion of the aromatic groups, it is hypothesized that NOM moieties otherthan aromatic functionalities are engaged in the reduction of PbO2 by NOM and/or lead mobilization involves the formation of mixed Pb(II)/Pb(IV) soluble and colloidal species.