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Mineralogical and Molecular Microbial Characterization of a Lead Pipe Removed from a Drinking Water Distribution System
Citation:
WHITE, C. P., M. Tancos, AND D. A. LYTLE. Mineralogical and Molecular Microbial Characterization of a Lead Pipe Removed from a Drinking Water Distribution System. Presented at AWWA Annual Conference and Exposition, Washington, DC, June 12 - 16, 2011.
Impact/Purpose:
To inform the public.
Description:
The U.S. Environmental Protection Agency's (US EPA) Lead and Copper Rule established an action level for lead of 0.0 15 mg/L in a 1 liter first draw sample at the consumer's tap. Lead corrosion and solubility in drinking water distribution systems are largely controlled by the formation of lead-based solids (passivating solids) on lead materials. The most important passivating Pb(II) minerals include Pb3(CO3)2(OH)2 (hydrocerussite), PbCO3 (cerussite), and Pb10(CO3)6(OH6)O (plumbonacrite). Biofilms have been shown to influence the corrosion behavior of metals including those used in drinking water pipes. Although researchers acknowledge that biofilm can impact metal release from drinking water distribution system materials, the conclusions are largely based on bench or pilot scale studies or speculation about the impact of microbial activity on metal release. Furthermore, studies that identify the make-up of biofilm using molecular approaches are limited or non-existent for some materials. In this study, a water utility in Illinois observed elevated lead levels in consumers' tap water following a relatively recent change in disinfection practice. The system historically maintained a free chlorine residual despite having elevated ammonia levels (0.6 mg/L) in the finished water; however, the utility recently reduced the chlorine feed to the point of having no free chlorine residual in the distribution system. The utility noted that a dramatic increase in lead levels in the distribution system coincided with the change in chlorine feed. In this study, we characterized lead pipe scale removed from a drinking water distribution system using solids and molecular microbial methods. Specifically, pipe scale cross sections and solids were analyzed using electron microscopy, energy dispersive X-ray analysis, X-ray diffraction and inductively coupled plasma mass spectrometry. The pipe scale consisted of at least 5 layers that contained Pb(II) and Pb(IV) minerals, magnesium, aluminum, manganese, iron, and silicon solids. Significant amounts of trace contaminant vanadium, likely in the form of vanadinite, and copper accumulated in the scale as well. The microbial community was profiled using 16S rDNA techniques. This is the first report of the characterization of biofilm on a surface of a corroded lead drinking water pipe. The majority of identified operational taxonomic units have been linked to heavy-metal contaminated environments. Sequence analysis of the clone library show Massilia and Paenibacillus are the dominantly detected genera accounting for over 66% of sequences. Results will discuss the role biofilms play in lead dissolution and the formation and breakdown of lead passivating films following treatment changes.
