Manganese Increases Lead Release to Drinking Water.

Lead and manganese are regulated in drinking water due to their neurotoxicity. These elements have been reported to co-occur in drinking water systems, in accordance with the metal-scavenging properties of MnO. To the extent that manganese is a driver of lead release, controlling it during water treatment may reduce lead levels. We investigated transport of lead and manganese at the tap in a full-scale distribution system: consistent with a cotransport phenomenon, the two metals were detected in the same colloidal size fraction by size-exclusion chromatography with multielement detection. We also studied the effect of manganese on lead release using a model distribution system: increasing manganese from 4 to 215 μg L nearly doubled lead release. This effect was attributed primarily to deposition corrosion of lead by oxidized phases of manganese, and we used 16S rRNA sequencing to identify bacteria that may be relevant to this process. We explored the deposition corrosion mechanism by coupling pure lead with either MnO-coated lead or pure lead exposed to MnO in suspension; we observed galvanic currents in both cases. We attributed these to reduction of Mn(IV) under anaerobic conditions, and we attributed the additional current under aerobic conditions to oxygen reduction catalyzed by MnO.