Low Contribution of PbO2-Coated Lead Service Lines to Water Lead

Feb 18, 2015 - To determine if residential water sampling corroborates the expectation that formation of stable PbO2 coatings on lead service lines (L...
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Low Contribution of PbO2‑Coated Lead Service Lines to Water Lead Contamination at the Tap Simoni Triantafyllidou,† Michael R. Schock,*,‡ Michael K. DeSantis,† and Colin White§ †

Oak Ridge Institute for Science and Education (ORISE), c/o U.S. Environmental Protection Agency, Cincinnati, Ohio 45268, United States ‡ Water Supply & Water Resources Division, National Risk Management Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268, United States § Department of Biomedical, Chemical, and Environmental Engineering, College of Engineering & Applied Science, University of Cincinnati, Cincinnati, Ohio 45221, United States S Supporting Information *

ABSTRACT: To determine if residential water sampling corroborates the expectation that formation of stable PbO2 coatings on lead service lines (LSLs) provides an effective lead release control strategy, lead profile sampling was evaluated for eight home kitchen taps in three U.S. cities with observed PbO2-coated LSLs (Newport, Rhode Island; Cincinnati and Oakwood, Ohio). After various water standing times, these LSLs typically released similar or lower peak lead levels (1 to 18 μg/L) than the lead levels from the respective kitchen faucets (1 to 130 μg/L), and frequently 50−80% lower than the lead levels typically reported from Pb(II)-coated LSLs in comparable published sampling studies. Prolonged stagnation (10−101 h) at the Cincinnati sites produced varying results. One site showed minimal (0−4 μg/L) increase in lead release from the PbO2-coated LSL, and persistence of free chlorine residual. However, the other site showed up to a 3-fold increase proportional to standing time, with essentially full depletion of the chlorine residual. Overall, lead release was consistently much lower than that reported in studies of Pb(II)-coated LSL scales, suggesting that natural formation of PbO2 in LSLs is an effective lead “corrosion” control strategy.

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INTRODUCTION Water Lead Profiles in Systems with Pb(II)-Coated LSLs Attribute Much of the Water Contamination to the LSLs. Multiple studies in the United States (U.S.)1−6 and Canada2,7−12 have presented profiles of water lead levels from tap to main through lead service lines (LSLs). In those studies, the LSLs were either presumed to be coated with common Pb(II) corrosion solids (e.g., cerussite, hydrocerussite, hydroxypyromorphite), by inference from water chemistry/treatment/ conventional wisdom, or rarely, verified from scale analysis. These studies suggested that when lead levels in the service lines are controlled by Pb(II) chemistry, peak lead levels in tap water are usually attributable to the LSL and often range from 2 to 8 times higher than near-equilibrium lead levels representing some combination from the kitchen faucet, water meter, interior pipe scale, or other in-line leaded plumbing component. Consequently, peak lead levels from the LSL obtained through nonregulatory profile sampling can be many times higher than the first L first-draw lead results obtained through regulatory sampling in the US,13 Canada and other countries. Water Lead Profiles Identify the Location and Relative Contributions of Lead Sources. A “full profile” consists of This article not subject to U.S. Copyright. Published 2015 by the American Chemical Society

collecting the full volume of water between the kitchen faucet and the water main in small increments. This allows quantification of lead (or other metals) in water representing extended contact with upstream individual plumbing components, such as with the faucet, household piping, soldered joints, inline valves and devices, service line, gooseneck, and the water main.2−6,14−19 The volumes of the successive incremental samples can be individually varied (e.g., 30, 60, 125, 250, 500, or 1000 mL) to improve the precision of detection of sources of lead contamination. A “partial profile” isolates a specific area of plumbing by selectively wasting an appropriate volume of water at the sampling tap, in order to eventually reach the water parcel in previous contact with the plumbing component of interest.5,15,17,18 Investigators have also used a water temperature change protocol to attempt to separate warmer water within interior plumbing from cooler water within the LSL or the water main.20,21 Further evolution of the sampling protocol Received: Revised: Accepted: Published: 3746

December 3, 2014 February 13, 2015 February 18, 2015 February 18, 2015 DOI: 10.1021/es505886h Environ. Sci. Technol. 2015, 49, 3746−3754

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Figure 1. Visual distinction between Pb(IV)-coated LSLs and Pb(II)-coated LSLs. Cross sections of Pb(IV) scales from Newport, RI (A), Oakwood, OH (B), and Cincinnati, OH (C) appear dark reddish brown, and were verified to mostly consist of plattnerite (β-PbO2) at the scale/water interface. Representative Pb(II) scales from three other unnamed locations consisted of either a beige/pale brown mixture of cerussite/hydrocerussite (Pb(II)D and Pb(II)-E), or a white mixture of hydrocerussite/plumbonacrite (Pb(II)-F with the exception of brown spots corresponding to iron solids).

Table 1. Drinking Water Quality in the Three Studied Locations during Each Study’S Timeframea location pH alkalinity (mg/L as CaCO3) TIC (mg/L as C) disinfectant type free Cl2 residual (mg/L) ClO2 Residual (mg/L) scale or corrosion inhibitor (mg/L as P) Al3+ (mg/L) Ca2+ (mg/L) Mg2+ (mg/L) FeT (mg/L) MnT (mg/L) Na+ (mg/L) K+ (mg/L) Cl− (mg/L) F− (mg/L) NO3−-N (mg/L) SO42− (mg/L) SiO2 (mg/L)

NE - Newport, RIb treated surface water

CI - Cincinnati, OHc treated surface water

OK-Oakwood, OHd treated ground water

9.1 (8.7−9.5) 26 (19−37) 6 (4.4−7.5)e free chlorine + ClO2 1.4 (1.0−1.9) 0.3 (0.04−0.7) no

8.6 (8.3−8.9) 74 (44−109) 17 (10−26)f free chlorine 1.26 (0.94−1.62) NA sodium hexametaphosphate 0.23 (0.18−0.30)

7.1 (7.0−7.1) 341 (285−362) 91 (81−102)f free chlorine − NA no

0.06 (0.02−0.1) 19 (9−27) 3.2 (2.3−3.6) 0.01 (0.00−0.02) 0.01 (0.00−0.02) 35 (24−53) 3 (2−3) 61 (37−83) 0.9 (0.4−1.4) 0.3 (0.0−1.3) 31 (22−36) 1 (0.6−3)

0.08 (0.0−0.3) 36 (31−40) 8 (4−11) − 0.01 (0.00−0.01) 26 (13−51) − 27 (18−34) 0.98 (−) 0.8 (0.5−1.1) 70 (46−115) 0.18 (−)

− 101 (73−141) 41 (32−52) 0.1 (0.0−0.3) 0.1 (0.0−0.4) 77 (47−98) 3 (2.5−2.6) 148 (127−160) − − 59 (52−66) 14 (12−15)

Average value and range (within parentheses) are reported. NA, Not Applicable; −, Not analyzed. bEPA/CDM corrosion study plant effluent and field pH analyses, 2008−2009 (N = 23). cR. W. Miller Plant, 2009−2012 (courtesy of Greater Cincinnati Water Works). dEPA field analyses during specific study in 1989 (N = 10), except single values are single results of finished water. eCoulometric analysis using ASTM D513. fComputed using average pH and alkalinity assuming 15 °C and ionic strength of 0.001 (Cincinnati) or 0.01 (Oakwood). a

includes high flow rate, which can identify vulnerability to scale instability under scouring conditions.4,14−16 Occurrence of PbO2-Coated LSLs Necessitates Direct Water Lead Observations in Those Systems. No study has presented water lead profiles in water distribution systems where the LSLs were coated with Pb(IV) corrosion solids (i.e., α-PbO2 or β-PbO2), which are much less soluble than most known Pb(II) drinking water corrosion byproduct solids.5,22−25 The presence of Pb(IV) solids in many water distribution systems has been confirmed by EPA corrosion research since 1989. As of this writing, over 310 corrosion scales from lead or lead-lined service lines and goosenecks have been analyzed using an array of analytical techniques described elsewhere.5,26−29 These pipe samples were obtained from 52

medium to large13 water distribution systems in 17 U.S. states and 4 Canadian provinces. Two-thirds of those systems, some representing previously published lead profiling studies, have scales in which Pb is only present in the divalent form. But over one-third of the sampled LSL systems (19 of 52) have PbO2 scale phases of varying morphology, identified in one or more of the pipes sampled.26,29 Thus, the occurrence of at least some PbO2 solid phase on LSLs in medium to large public water systems is fairly common in North America. Recent research has indicated that in the absence of interfering mechanisms, substantial conversion of Pb(II) carbonate and hydroxycarbonate scales to PbO2-controlled scales in actual LSLs can take place in only months to a few years.5,30 3747

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disinfection with no corrosion or scale inhibitor added. Oakwood used free chlorine as the secondary disinfectant with no corrosion or scale inhibitor added, preceded by greensand filtration to remove source water iron and manganese, and has a water pH, hardness and alkalinity widely considered to be noncorrosive to iron.35 Historically, there were some occasions where limited areas of the Oakwood system were thought to have been briefly subjected to exposure of a lime-softened water with polyphosphate scale inhibitor, through a controlled system interconnection. Lead Pipe Scale Characteristics Confirm PbO2 Dominance. LSL samples were collected from the three cities at about the same time frames as the water lead profiles, and were analyzed at EPA. It was not possible to collect LSLs from the specific houses profiled herein, but LSL analyses from other houses in each city still allow for general observations. In Cincinnati, 15 LSL scale samples were exhumed from homes in the same water quality zone as the Cincinnati water sampling sites, over the time period of 2000 to 2014. The scale in all cases consisted of a nearly pure β-PbO2 (plattnerite) layer at the scale/water contact, underlain by a thin layer of tetragonal PbO (α-PbO, litharge) adjoining the lead pipe. This suggested that the low level of polyphosphate chemical added to Cincinnati tap water (see Table 1) was not the controlling mechanism of lead pipe scale formation at the scale/water contact, since plattnerite (and not lead phosphate compounds) dominated the top scale layer of the sampled LSLs (see Supporting Information (SI) Figure S1). In Newport, 28 LSL scale samples were collected in 2006 to 2007. Almost all of the Newport samples showed a similar structure to the Cincinnati pipe scales, with mostly pure β-PbO2 overlaying a thin tetragonal PbO layer at the pipe/scale contact. Some samples also contained small amounts of α-PbO2 or Pb(II) compounds above the litharge zone (and below the top plattnerite zone). These compounds were mainly Pb3(CO3)2(OH)2 (hydrocerussite) and orthorhombic β-PbO (massicot), and could possibly get exposed to the water if small sections of the top plattnerite zone were disturbed (e.g., see Figure 1A). It is practically impossible to obtain a completely uniform top scale layer in LSLs, but the dominant identified compound at the scale/water contact was always plattnerite. Elemental analyses using a multiacid digestion and sintering techniques,36,37 and confirmatory Pb speciation via X-ray absorption near-edge spectroscopy (XANES), were used to supplement the powder XRD phase identifications, as described elsewhere.29,38 A total of nine LSL scales were obtained from Oakwood from 1989 to 2002, with the last six samples having unknown locations within the distribution system. The powder diffraction analyses were initially performed with an early methodology of a composite scale scraping. The initial two scale samples showed several comingled Pb(II) phases (hydroxycarbonates and orthophosphates) and non-Pb phases, with a large fraction of β-PbO2. None of the six most recent scale samples processed with more advanced subsampling techniques were known to have come from the proximity of the houses profiled for lead, though they could have. Seven of the nine scale samples were almost entirely comprised of β-PbO2 on top of varying amounts of PbCO3 (cerussite) and hydrocerussite on top of a tetragonal PbO scale base. The overall lead pipe scale characteristics differ more widely than either Cincinnati or Newport, and the purity and exact positioning of the PbO2 layer in the scale in the sampling locations cannot be projected to be as consistent and uniform as in the Newport and Cincinnati samples. As a result,

While solubility modeling has largely been successful in predicting trends of soluble lead release with water chemistry and orthophosphate dosing for systems governed by Pb(II) scale mineralogy, the modeling of Pb(IV) solubility is problematic. In addition to sparse information on aqueous speciation and the unreliability of formation and solubility constants for plausible drinking water species, lead levels in the presence of PbO2 mineral scales can be a complex function of kinetic, oxidant and background water chemistry factors, mixes of PbO2 phases, as well as the electronic structure of the scale itself.5,25,29,31 Therefore, this study was initiated to help fill data gaps that will incrementally inform future regulatory/guideline development, human exposure estimation, optimization of lead release or corrosion control, and further the understanding of in situ behavior of lead pipes in drinking water systems. The principal objectives were to (1) Obtain direct observations of “PbO2controlled” drinking water lead levels under typical household stagnation conditions in LSLs with presumed long-term stable uniform PbO2 passivating films; (2) investigate whether there might be a significant variation in lead release from PbO2 scales with major differences in pH and alkalinity; and (3) infer whether intentional formation and stabilization of uniform PbO2 scales in lead pipes would provide at least equivalent “corrosion” and lead release control compared to other wellestablished Pb(II)-based treatment approaches (pH/DIC/ alkalinity adjustment and orthophosphate dosing). To achieve these objectives, water lead concentration data from two historical studies with relevant water sampling protocols, scale and water chemistry characterization, were combined with new and specific lead-in-water profiling from a third water system having established, widespread PbO2-coated LSLs.

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MATERIALS AND METHODS System Selection and Water Quality Information. EPA corrosion research studies have included three cities where LSL scales were comprised nearly entirely of reddish-brown PbO2, distinctly different in color than typical Pb(II) corrosion scales identified elsewhere (Figure 1), and for which there was opportunity for sequential sampling in verified LSL-containing sites. Specifically, (A) Newport, RI, (B) Cincinnati, OH, and (C) Oakwood, OH represent water distribution systems with documented PbO2-coated LSLs,22,23,29,32−34 formed and maintained under the influence of water chemistries with widely different pH (ranging 7.1−9.1) and alkalinity (ranging 26 to 341 mg/L as CaCO3) (Table 1). Water Treatment History. An important commonality across the three chlorinating water systems is that their full suite of treatment processes reduces oxidant demand of the water, oxidant demand of iron mains, or both, and that the fundamental corrosion-controlling water chemistry characteristics of the finished water were essentially stable for years to decades. Presumably, the resulting water chemistry facilitates a high and stable oxidation reduction potential and surface corrosion potential that is favorable for the development and stability of PbO2 corrosion scales in most LSLs.5,24,29 Cincinnati used a combination of elevated pH, moderate alkalinity, and conventional treatment, followed by granular activated carbon filtration, chlorination and post-2002, polyphosphate scale inhibitor addition. Newport used similar elevated pH and moderate alkalinity. But in addition to conventional coagulation and filtration, Newport used chlorine dioxide preoxidation, followed by free chlorine for secondary 3748

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water lead profiling in Oakwood should be conservatively considered to represent essentially an “upper limit” to the lead release from stable β-PbO2 LSL scales. Calcite (CaCO3) was not identified in the LSLs from the three cities, with only a few pipe exceptions where it was a minor phase (see illustrative Supporting Information (SI) Figure S1 for Cincinnati LSLs). Site Selection. Two houses in Newport (NE-1 and NE-2), two houses in Cincinnati (CI-1 and CI-2), and four houses in Oakwood (OK-1, OK-2, OK-3 and OK-4) with documented full LSLs (NE-1, NE-2, OK-1, OK-2, OK-3, and OK-4) or partial LSLs (CI-1 and CI-2) were selected. All houses were built between 1884 and 1928, and were internally plumbed with a mix of copper and galvanized piping; a mix of copper and brass piping; only copper piping; or only galvanized piping. In addition to LSLs, houses with copper plumbing had leaded solder connections, and all houses had other leaded brass components (e.g., water meters and kitchen faucets). Plumbing Information. Because each house was plumbed differently (materials, piping diameter/length, in-line plumbing components type/size), inspection of the plumbing at each site helped tailor the individual sampling protocols. Specifically, approximate measurements of each pipe and in-line component length and diameter allowed calculating the overall water volume to be sampled at each site, from the kitchen faucet to the water main. This also allowed identifying the sequential water volumes needed to capture water in contact with individual plumbing components in each case. Plumbing was inspected and measured by EPA contractors at the two Cincinnati sites, by engineering staff of Camp, Dresser & McKee (CDM, Cambridge, MA) at the two Newport sites, and by engineering staff of LJB Engineers, Inc. (Kettering, Ohio) at the four Oakwood sites.13,33 Water Profile Sampling. Full water lead profiles (CI-1 and CI-2), or partial profiles of water mainly targeting the LSL (NE1, NE-2, OK-1, OK-2, OK-3, OK-4) were obtained. The specifics of profile sampling varied between the sampling sites, depending on different initial goals at each location, and even on practical considerations such as accessibility to the sites (when not sampled by the residents) and availability of the persons conducting the sampling. Synthesis of the information from the distinct case studies necessitates a detailed explanation of the different sampling specifics in each: (A) NE-1 and NE-2 sites were sampled once in 2009 by residents under the direction of CDM engineering staff. Residents flushed the cold water faucet for 10 min before a stagnation time of 6 h (NE-1) or 9 h (NE-2), after which they collected sequential water volumes at the kitchen faucet. Variable sequential water volumes of 250 mL, 500 or 1000 mL were collected, adding up to a cumulative water volume of 4.25 L (NE-1) and 7.75 L (NE-2) that reflected the respective water volumes from tap to main. Due to resource limitations, only the water samples associated with the faucet or the LSL were analyzed, yielding a partial profile of lead concentration. The flow rate was not measured. (B) The CI-1 site was sampled multiple times during 2009 to 2013 by EPA contractors. A detailed profiling approach was initially followed to carefully characterize the plumbing line (see SI Figures S2 and S3). Increasing water volumes of 30 mL, 250 mL, 500 mL, and 1000 mL were sequentially collected, adding up to 8.06 L overall after a stagnation time of 10 h. Insights from this initial

effort led to a subsequent simplified protocol targeting primarily the LSL, with collection of four 1000 mL samples, adding up to 4.0 L overall from tap to main. This simplified protocol was repeated after four different water stagnation times of 2, 10, 91, and 101 h. The 500 and 1000 mL bottles were wide-mouth bottles, permitting the flow rate to approximate that common in normal household use (high but not fully open). For consistency, the 5 min water flush that preceded all of the stagnation periods had a flow rate approximately the same as the maximum flow rate during the sampling events. The CI-2 site was sampled in 2012 by EPA contractors, by collecting two 250 mL samples and then consistently 1000 mL adding up to 10.5 L overall, from tap to main. This protocol was followed three times, to reflect water stagnation times of 11, 27, and 74 h following a preflush of 12 min. Longer stagnation times (10−101 h) than those for the NE and OK sampling sites were included at the Cincinnati sites, to investigate whether lead in water would possibly increase due to hypothesized reduction and dissolution of the PbO2 under typical household use conditions. Increases in lead contamination when free chlorine residual was depleted in water contacting PbO2coated lead pipe have been reported,22,39−41 as well as observed in unpublished EPA pipe studies. (C) The OK-1, OK-2, OK-3, and OK-4 sites were sampled in July and August 1989 by residents as part of a prior EPA study with different objectives,13,33 which was revisited for the needs of this paper. Initially, 1.0 L of water was collected from each kitchen tap, followed by wasting a site-specific volume of water reflecting home plumbing, and then isolating three 250 mL increments (750 mL overall) to capture the LSL.33 Samples were collected after a minimum stagnation time of 6 h. There was no flushing of the line before stagnation, and the water was turned off and then back on as each sequential bottle (or waste volume container) was placed under the tap for sample collection, similar to a protocol discussed elsewhere.42 Water Sample Analyses. At NE and CI sites, total lead in unfiltered water samples was quantified via ICP-MS43 and other metals were analyzed by ICP-AES.44 Graphite Furnace Atomic Absorption was used to measure total lead in unfiltered water samples for OK sites.44 Free chlorine residual was quantified at the two CI sites only, with a portable spectrophotometer using the equivalent to U.S. Environmental Protection Agency Method 330.5.45

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RESULTS AND DISCUSSION Low Contribution of PbO2-Coated LSLs to Water Lead Contamination. Across all eight sampling sites in the three cities, relatively low levels of total lead ranging from 1 to 18 μg/ L were released from the PbO2-coated LSLs into drinking water, even after prolonged water stagnation of 101 h at site CI1, and 74 h at site CI-2 (Figure 2). LSLs in the four OK sites released the highest lead in water (ranging 6−18 μg/L) presumably from the less pure PbO2 scales discussed earlier, followed by CI sites (lead ranging 2−8 μg/L) and NE sites (lead ranging 1−2 μg/L). Overall, these lead levels are considerably lower than reported lead concentrations in contact 3749

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sampling sites appears to corroborate the research suggesting that in water chemistry conditions conducive to forming PbO2 lead pipe scales, the lead pipe becomes cathodic to copper or brass to which it is galvanically connected.27,39 Or, alternatively, that a galvanic effect for either lead or copper was not significant at the time the sites were sampled (≥8 years since partial replacement in both). In addition to the seemingly insignificant galvanic corrosion of lead in the partially replaced LSLs, any physical disturbances (from the partial replacement in this case) appear to have subsided, unlike the experience with disturbed Chicago LSL pipe scales, which had a substantially different Pb(II)-dominated physical and chemical nature.1 Water Profiling Indicates That the Highest Lead in Water Is Not Necessarily Associated with the PbO2Coated LSL. Identification of the plumbing sequence corresponding to the cumulative water sample volume helped determine the relative contribution of LSLs to water lead, as opposed to other leaded plumbing materials (Figure 3A, B, C). Levels of lead from the PbO2-coated LSLs were either lower (NE-1, NE-2, OK-2, OK-3, OK-4 sites), the same (CI-1) or only slightly above the levels found in the kitchen faucet (OK1) and other interior plumbing (CI-2) (Figure 3) for stagnation approximating “overnight.” In three out of four OK sites, the kitchen faucet released 4−13 times more lead (depending on specific site) than the three water samples (LSL1, LSL2, and LSL3) in contact with the LSL (Figure 3C). The highest lead in

Figure 2. Peak lead concentration of water in contact with the lead service line in the studied locations, sampled after various water stagnation times. If available, error bars represent the standard deviation over multiple (≥3) sampling dates.

with LSLs or lead goosenecks from communities with known or presumed Pb(II)-coatings over comparable stagnation times.1−5,7−12,14,19−21,28,30 The two Cincinnati sites had partially replaced LSLs with copper, as opposed to full LSLs in the other locations. Lead release at these two sites could conceivably be enhanced by galvanic corrosion phenomena between lead and copper. But the low observed total lead release from these Cincinnati

Figure 3. Drinking water lead (Pb) profiles at two sampled homes in Newport, RI (A), at two sampled homes in Cincinnati, OH (B) and four sampled homes in Oakwood, OH (C). If available, error bars represent the standard deviation over multiple sampling dates (C). The insets depict the plumbing sequence as it corresponds to the water sample volume (A and B) or to the sample type (C). Home plumbing in (C) refers to the faucet and galvanized pipe (for sites OK 1−4). The plumbing configurations also include brass fittings and/or solder at junctions, which are not depicted on the insets for simplicity reasons (A, B, and C). M at the inset represents the water meter (A, B) but was likely part of the waste volume in (C). LSL: lead service line; CSL: copper service line; Cu: copper pipe. 3750

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water attributable to the LSL among all sections of plumbing was found at site CI-2 only, and even then that contribution was only 3 μg/L of lead above the 1 μg/L contribution of other home plumbing after 11 h of water stagnation (Figure 3B). Very different results are typically reported from profile sampling at Pb(II) systems cited previously, where the contribution of the LSL to lead in water was frequently observed to be four to eight times that of the first draw first liter sample. A “spike” of 8 μg/L lead detected at site CI-1 after 10 h of water stagnation (Figure 3B) is likely attributable to a randomly released microparticle (from leaded brass or lead−tin solder), because this spike was not observed during other sampling events for this site. Even with the very low and relatively consistent behavior of released lead within and across these sampling sites, residences with LSLs or premise plumbing that can accumulate lead will always be vulnerable to sporadic release and potential ingestion of lead-containing particles. Determination of the Plumbing Length/Sequence Indicates That the LSL Is Not Captured by a Fixed Water Volume Across All Sites. As expected, the identified peak positions and/or length of zone of elevated lead within the LSL varied considerably from site to site (for NE-1:3.75 to 4.25 L, for NE-2:6.5 to 7.5 L, for CI-1:3.0 to 4.0 L, for CI-2:6.5 L). With the low lead release levels, the LSL was often difficult to differentiate from interior premise plumbing. The in-depth plumbing knowledge at those sites, and analysis of additional metal profiles in the water samples (e.g., Zn, Fe and/or Cu see SI Figures S3, S4, and S5) was frequently helpful to distinguish LSL-related Pb from contributions of non-LSL materials. This study corroborates the previously- cited studies in finding profiling at each site necessary to identify peak lead levels and contributions of lead from different plumbing components. Effect of Long Water Stagnation on Lead Profiles. Repeated sampling at site CI-1 indicated that longer water stagnation times of 91 and 101 h did not substantially increase the contribution of the LSL to water lead at the tap (reflected by the third and fourth liter of water), compared to shorter stagnation times of 2 and 10 h (Figure 4A). Interestingly, it was the contribution of the kitchen faucet to water lead at the tap (reflected within the first liter of water) that relatively increased after 101 and 91 h of stagnation (Figure 4A). Aside from the different water stagnation times, sampling events at site CI-1 were undertaken in different years and seasons, so seasonal effects on water quality and peak lead levels are possibly present. Even so, three sampling events undertaken at site CI-1 after a constant stagnation time of 10 h but at three different dates resulted in similar total lead profiles (Figure 4A). Since there are inadequate thermodynamic or experimental data from which to predict temperature or seasonality effects on lead release from PbO2, any such impacts remain to be determined, but appear to be small in this study. Repeated sampling at site CI-2 indicated that a longer water stagnation time of 74 h increased the peak contribution of the LSL to water lead at the tap by 3-fold to 12 μg/L lead, compared to a shorter stagnation time of 11 h (Figure 4B). Effect of Long Water Stagnation on Chlorine Profiles. At site CI-1, a longer water stagnation of 101 h resulted in a similar chlorine disinfectant level within the LSL, compared to a shorter stagnation of 10 h. Chlorine residual within the LSL was maintained at both occasions between 0.6 to 0.7 mg/L (Figure 4A). This was apparently a sufficient disinfectant level

Figure 4. Impact of stagnation time on drinking water lead profiles and corresponding chlorine profiles (when available) at Cincinnati, OH sampling sites CI-1 (A) and CI-2 (B). The location of the lead service line (LSL) relevant to the collected water volumes is depicted for each sampling site.

to keep PbO2 scales stable and intact, thereby releasing only minimal levels of lead into the water even after prolonged stagnation (Figure 4A). Conversely, chlorine residual within the LSL of site CI-2 was completely depleted, after 27 and 74 h of water stagnation (Figure 4B). This information, coupled with the lead release data, suggests that PbO2-coated scale was perhaps not as stable in this location. Even so, the maximum lead level of 12 μg/L attributable to the LSL after 74 h of stagnation, is still lower than most levels of lead observed within LSLs in the previously cited studies of systems with Pb(II)-based scales. Implications for Corrosion Control and Water Lead Exposure. Overall, water profile sampling in three PbO2coated LSL systems suggests that with water standing times of several hours to several days, leaded brass plumbing device(s) or interior galvanized pipe can sometimes release a higher level of lead than the LSL. Even when levels of lead from the LSL were above levels found in the interior plumbing, they were typically only slightly higher. In the sites and water systems studied, the position of the peak lead value within the existing LSL (if such a peak was observed) remained consistent, when the same site was sampled multiple times (e.g., site CI-2). Ironically, because the contribution of lead to the water from brass fittings exceeded the lead release peak level from the LSLs in some of the sites, and the composition of such fittings is highly variable in practice, drinking water utilities with PbO2-coated LSL scales 3751

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lead release control strategy, PbO2 scale formation and stabilization equals or exceeds the effectiveness of well-known Pb(II)-based treatment strategies (e.g., orthophosphate or blended phosphate addition or pH/carbonate adjustment).

are faced with the opposite case from water systems having Pb(II)-dominated LSL scales. The PbO2-coated LSL scale systems must make sure their corrosion control treatment effectively controls lead release from interior premise plumbing, while simultaneously maintaining the distribution system water quality conditions that stabilize the beneficial low release levels from the lead lines. As with any corrosion control strategy in the presence of lead pipes, there may be locally variable physical or chemical conditions that compromise PbO2 scale integrity and create a potential for elevated lead release in certain parts of the distribution system. This is illustrated by the compilation of XRD results for the Cincinnati pipe scales in Supporting Information Figure S1. As such, the low lead results presented herein from specific LSL sites should not be generalized to predict negligible lead release and ingestion at every other unsampled LSL site in the 3 cities, though the average overall system-wide LSL lead in the water may be low. In addition, because pipe scales are dynamic, currently stable PbO2-coated scale systems face a potential future risk of scale destabilization/ reduction to Pb(II), depending on treatment changes at the plant, or in fluctuation of key water quality parameters in parts of the distribution system. Further, the combination of important water quality factors that promote PbO2 scale formation and stability in the first place, likely require control of disinfection byproduct precursor material, residence time, overall distribution system ORP, oxidant demand by pipe walls/biofilms, and absence of interfering inorganic deposition that may be beyond the present treatment capability of many water utilities.5,24,28−30 These conditions appear to have been met by the three water systems examined herein, since review of the three different chlorinating water treatment processes (see Water Treatment History section) and the three resulting water chemistries of variable pH, alkalinity and other important parameters (see Table 1) all led to the development of confirmable PbO2 on the LSLs that were analyzed, and to observations of low water lead levels at the sites that were sampled. This currently suggests that different water chemistry conditions can achieve PbO2 formation on LSLs, as long as the high/stable ORP and high surface corrosion potential requirement is met. The sequential sampling results presented herein closely approximate the concentration of lead in prolonged contact with different sections of plumbing. But like all sampling protocols, they cannot be entirely without bias, depending on but not limited to sampling volume; flow rate and velocity; flow regime (laminar, turbulent, or plug flow); flow pattern (on/off or continuous between samples); preflushing and stagnation time prior to sample collection; configuration of plumbing (length, number/location/severity of bends, changes in ID or wall material); adherence of scale material; concentration of the contaminant in the exposed metal surface or in the scale; and corrosivity of the water.2,5,6,14,15,17,46−50 In addition, triplicate profiles for a given stagnation time were obtained for some sites but not others due to practical restrictions, including but not limited to resident availability/participation (if sampled by residents) or accessibility to the site (if not sampled by residents). This is the very first empirical investigation of water lead profiles in three drinking water systems with PbO2-coated LSLs, bound by the inherent complexities and uncertainties of the real-word. Despite any sampling biases and other acknowledged limitations, this study demonstrates that as a

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ASSOCIATED CONTENT

S Supporting Information *

A summary of surface scale layer XRD results for Cincinnati pipes, detailed schematic of the premise plumbing at site CI-1, an explanation of the initial detailed profiling approach at site CI-1, and some multimetal profiles at sites CI-1 and CI-2 are available. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: 513-569-7412; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. John Eastman (LJB Engineers, Inc.), and Barbara Wysock (formerly USEPA Office of Drinking Water) for the Oakwood study, as well as Carol Rego and Kathy Mello (CDM) for the Newport study. Norb Klopsch (City of Oakwood), Jeff Swertfeger and Dawn Webb (Greater Cincinnati Water Works) provided pipe specimens. Keith Kelty, Maily Pham, and Bill Kaylor (USEPA Office of Research and Development) conducted water metals analyses. All pipe scale elemental analyses were conducted by the USGS Mineral Resource Surveys Program under the direction of Dr. Stephen A. Wilson. All XANES analyses were supported by the US DOE Office of Science Grant No. DEFG03-97ER45628 and were conducted in the PNC-CAT facilities at the Advanced Photon Source, Argonne National Laboratory, Argonne, IL. A.P.S. is supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31-109-Eng-38. This project was supported in part by an appointment to the Research Participation Program at the Office of research and Development, USEPA, administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and USEPA. Any opinions expressed in this paper are those of the authors and do not necessarily reflect the official position and policies of the USEPA.

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NOTE ADDED AFTER ASAP PUBLICATION There were errors in the author affiliations in the version published ASAP on February 27, 2015. The corrected version was published ASAP on March 5, 2015.

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