The Effect of Natural Organic Matter and Aquatic Humic Substances on the Occurrence of Lead in a Canadian Drinking Water System

摘要

Homes with lead service lines in the City of Brandon, Manitoba, Canada, were found to exceed the provincial standard of 0.01 mg/L for lead in drinking water. The only solids identified in a scale analysis of an excavated lead service line were lead(IV) oxides (PbO2). It is well-established that natural organic matter (NOM) can reduce PbO2 within a few hours. It is believed that the aquatic humic substances (AHS) fraction is responsible for the majority of the reductant potential of NOM. Brandon treated water has relatively high levels of NOM at approx. 5 to 7.6 mg/L as DOC, of which AHS accounts for 50.5%. It is suggested that as water stagnates in the lead service line during periods of no water use, the free chlorine residual is depleted, permitting PbO2 to oxidize NOM and be released as reduced Pb(II) species. It is also possible that microorganisms are assisting this process, directly or indirectly.