Dissolved Lead Concentrations Research Articles

Reduction in water consumption in premise plumbing systems: Impacts on lead concentration under different water qualities

Water conservation measures are increasing in response to regulatory requirements addressing the need for lower environmental footprint and in response to water shortages. In households with lead service lines (LSLs), lowering consumption can adversely impact lead release as it will increase stagnation. Using a lead dissolution model and data from extensive pilot studies on excavated LSLs, the impact of adaptation to different water conservation strategies on dissolved lead contamination at the kitchen tap is assessed under three water qualities and three LSL lengths (3, 14 and 30 m) using hydraulic and water quality modelling. Consumers' behavioural variability is also assessed based on integration of EPANET and results of the stochastic water demand model SIMDEUM. Demand reduction increased the dissolved lead concentrations (Pbdiss) at the end of the LSL with mean values ranging from 28.4 to 63.3 μg/L (without corrosion control) and from 4.6 to 9.9 μg/L with corrosion control (addition of orthophosphate and pH adjustment). Adding orthophosphate (1 mg P/L) to the water reduces the mean Pbdiss values at the kitchen tap from 7.1 μg/L to 1.2 μg/L for a high water demand scenario and from 31.2 to 4.9 μg/L for a low water demand scenario. Finally, the Integrated Exposure Uptake Biokinetic (IEUBK) model is used to predict the potential blood lead levels (BLLs) for children aged 0–84 months. Results showed that the orthophosphate addition of only 1 mg P/L can significantly decrease the proportion of children with a BLL >5 μg/dL, from 82 % to 17 %, under the most extreme water conservation scenario studied, using the 90th percentile of Pbdiss concentrations during usage at kitchen tap. Wide variations of Pbdiss concentrations at the kitchen tap were calculated at times of use over a week (up to 155 μg/L in lower demand scenarios, without corrosion control) showing evident limitations of single random daytime sampling.

Control of Lead Contamination in Water Distribution Networks: A Dynamic Optimization Framework

This study investigates the optimization of free chlorine-based disinfectant dosage for controlling the dissolution of lead (Pb) while limiting disinfection by-products (DBPs) formation in water distribution networks. A dynamic optimization framework is developed in this study to account for the impact of spatial and temporal variations of network hydraulics and water chemistry on dissolved lead concentrations. Accordingly, a dynamic schedule of disinfectant dosage is proposed to minimize water lead levels and two-point chlorine residual violations in the network. The results suggest that optimization of water chemistry parameters such as pH and orthophosphate dosage provide an additional degree of freedom to be explored in the problem of optimizing disinfectant dosage for compliance with conflicting mandates regulating lead levels and DBPs concentration in drinking water.

Role of Manganese in Accelerating the Oxidation of Pb(II) Carbonate Solids to Pb(IV) Oxide at Drinking Water Conditions.

Pb(II) carbonate solids are corrosion products that form on the inner surfaces of lead service lines (LSLs) and can be oxidized by free chlorine to form Pb(IV) oxide (PbO2). The formation of PbO2 can maintain low dissolved lead concentrations in drinking water, but PbO2 can dissolve if a free chlorine residual is not maintained. Experiments demonstrated that the oxidation of Pb(II) carbonate by free chlorine was faster with manganese (Mn). Without Mn(II), the oxidation of Pb(II) carbonate was an autocatalytic process. With Mn(II), the overall oxidation rate was 2 orders of magnitude faster than without Mn(II). X-ray diffraction and free chlorine consumption profiles indicated that δ-MnO2 was formed within several minutes of the reaction of Mn(II) with free chlorine, and δ-MnO2 catalyzed the oxidation of Pb(II) carbonate by free chlorine. Free chlorine consumption profiles for Pb(II) carbonate with and without Mn(II) were interpreted based on the kinetics and stoichiometry of the underlying chemical reactions. These findings highlight the importance of Mn in accelerating the formation of PbO2 in water with Pb(II) carbonate solids and free chlorine, and it may help explain why PbO2 is observed on LSLs of some but not all water systems that use free chlorine.

Formation and Aggregation of Lead Phosphate Particles: Implications for Lead Immobilization in Water Supply Systems.

Phosphate is commonly added to drinking water to inhibit lead release from lead service lines and lead-containing materials in premise plumbing. Phosphate addition promotes the formation of lead phosphate particles, and their aggregation behaviors may affect their transport in pipes. Here, lead phosphate formation and aggregation were studied under varied aqueous conditions typical of water supply systems. Under high aqueous PO4/Pb molar ratios (>1), phosphate adsorption made the particles more negatively charged. Therefore, enhanced stability of lead phosphate particles was observed, suggesting that although addition of excess phosphate can lower the dissolved lead concentrations in tap water, it may increase concentrations of particulate lead. Adsorption of divalent cations (Ca2+ and Mg2+) onto lead phosphate particles neutralized their negative surface charges and promoted their aggregation at pH 7, indicating that phosphate addition for lead immobilization may be more efficient in harder waters. The presence of natural organic matter (NOM, ≥ 0.05 mg C/L humic acid and ≥ 0.5 mg C/L fulvic acid) retarded particle aggregation at pH 7. Consequently, removal of organic carbon during water treatment to lower the formation of disinfection-byproducts (DBPs) may have the additional benefit of minimizing the mobility of lead-containing particles. This study provided insight into fundamental mechanisms controlling lead phosphate aggregation. Such understanding is helpful to understand the observed trends of total lead in water after phosphate addition in both field and pilot-scale lead pipe studies. Also, it can help optimize lead immobilization by better controlling the water chemistry during phosphate addition.

Effect of total organic carbon and aquatic humic substances on the occurrence of lead at the tap

Homes with lead service lines (LSLs) in the City of Brandon, Manitoba, Canada, were found to exceed the provincial standard of 10 μg/L for lead in drinking water. Solids identified by X-ray diffraction of LSL scale were Pb5O8 and PbO2, indicating that lead(II) solids in the LSL scale have been oxidized to lead(IV) solids by free chlorine residuals. Natural organic matter (NOM) can reduce PbO2 within a few hours, and Brandon treated water has high levels of NOM at approximately 5–7.6 mg/L as total organic carbon (TOC). As water stagnates in the LSL during periods of no water use the free chlorine residual is depleted, permitting PbO2 to oxidize NOM and be reduced to more soluble lead(II) species, resulting in an increase in dissolved lead concentrations. Although it is generally believed that aquatic humic substances (AHS) are primarily responsible for the reductant capacity of NOM, removal of AHS from the treated water resulted in a 6% decrease in lead release from PbO2, while removal of 50% of total NOM resulted in a 75% decrease in lead release. AHS and TOC were not found to play a significant role in the reduction of PbO2 in this water.

Comparison Between the Calibration and the Standard Addition Methods in Determining Dissolved Lead in Borobudur's Control Tanks Water by Flame Atomic Absorption Spectrophotometry (F-AAS)

The use of the calibration and of the standard addition methods in determining dissolved lead in Borobudur's control tanks water were compared. The aim of the study was to develop the standard addition method to determine very low concentrations of dissolved lead using Flame Absorbtion Spectrophotometry (F-AAS). Sampling was executed from five points: a point at the south side, a point at the south west, and three points at the north of the Borobudur Temple. The linearities of both curves were compared. The linearity of the calibration curve was found to be 0.957092, while of the standard addition had a linearity of ≥ 0. 995 (except sample AS). Both methods gave different dissolved lead concentrations. The result of the calibration method was higher than that of the standard addition method.

Role of Pb(II) defects in the mechanism of dissolution of plattnerite (β-PbO2) in water under depleting chlorine conditions.

Destabilization of lead corrosion scales present in plumbing materials used in water distribution systems results in elevated lead concentrations in drinking water. Soluble lead release caused by changes in water chemistry has been linked to dissolution of lead carbonate and/or lead oxide solid phases. Although prior studies have examined the effects of varying water chemistry on the dissolution of plattnerite (β-PbO2), β-PbO2 dissolution under depleting chlorine conditions is poorly understood. This paper reports results obtained for long-term batch dissolution experiments for solid phase β-PbO2 under depleting chlorine conditions. Results indicate that the initial availability of free chlorine effectively depresses dissolved lead concentrations released from β-PbO2. However, the dissolved lead levels remained low (∼4 μg/L) even after free chlorine was depleted. Detailed spectroscopic characterization of solid samples collected during the β-PbO2 experiments indicates that changes in the electronic structure of PbO2 occurred during the dissolution. This further points out that Pb2+ defects present in crystalline β-PbO2 play a dominant role in the dissolution of this solid phase.

Kinetics of the Reductive Dissolution of Lead(IV) Oxide by Iodide

Lead(IV) oxide (PbO(2)) is a corrosion product found in lead service lines used to convey drinking water. The presence of reductants can accelerate PbO(2) dissolution and enhance lead release to drinking water. The dissolution rate rather than the equilibrium solubility of PbO(2) can control the dissolved lead concentrations in water distributed through pipes containing PbO(2). Iodide, a known reductant for PbO(2), was selected as a model reductant for investigating the kinetics and mechanisms of the reductive dissolution of PbO(2). The dissolution rate of plattnerite (β-PbO(2)) was determined as a function of pH, iodide concentration, and dissolved inorganic carbon (DIC) concentration using continuously stirred tank reactors. The dissolution rate of plattnerite increased with decreasing pH and increasing iodide concentrations. The presence of 10 mg C/L DIC accelerated plattnerite dissolution, but further increases in DIC concentration did not affect the dissolution rate. The reductive dissolution of PbO(2) can be interpreted as a coupled process involving chemical reduction of Pb(IV) to Pb(II) at the PbO(2) surface followed by detachment of Pb(II) to solution. The data suggest that chemical reduction is the rate-limiting step for PbO(2) dissolution in the presence of iodide.

Effects of pH and Carbonate Concentration on Dissolution Rates of the Lead Corrosion Product PbO2

Lead(IV) oxide is a corrosion product that can develop on lead pipes and affect lead concentrations in drinking water. Continuously stirred flow-though reactors were used to quantify the dissolution rates of plattnerite (beta-PbO(2)) at different pH values and dissolved inorganic carbon (DIC) concentrations. Organic pH buffers were not used, because several were found to be reductants for PbO(2) that accelerated its dissolution. Most plattnerite dissolution rates were on the order of 10(-10) mol/min-m(2). The rate of dissolution increased with decreasing pH and with increasing DIC. The effect of DIC is consistent with a reductive dissolution mechanism that involves the reduction of Pb(IV) to Pb(II) at the plattnerite surface followed by the formation of soluble Pb(II)-carbonate complexes that accelerate Pb(II) release from the surface. Under the experimental conditions, dissolved lead concentrations were controlled by the dissolution rate of plattnerite and not by its equilibrium solubility. A dissolution rate model was developed and can be used to predict dissolution rates of plattnerite as a function of pH and DIC.

Wintertime trace metal (Zn, Cu, Ni, Cd, Pb and Co) and nutrient distributions in the Subantarctic Zone between 40–52°S; 155–160°E

In high nitrate low chlorophyll (HNLC) oceanic regions, trace metals play a key role in regulating phytoplankton productivity; however large knowledge gaps remain in the biogeochecmical cycling of trace metals in these areas. Here I present the first comprehensive winter dataset (0–1000 m depth) for dissolved zinc, cadmium, copper, nickel, cobalt, and lead along with the macronutrinets phosphate and silicon, between 40°S–52°S, which traverses the Subantarctic zone (SAZ), east of Australia. Dissolved lead concentrations were conservative with depth with values ranging between 12 and 33 pmol kg − 1 . Surface dissolved concentrations for cadmium, copper, nickel, cobalt and phosphate showed large north–south gradients, with lower concentrations at the Subtropical Front (∼ 43°S) and higher concentrations at the Subantarctic Front (∼ 51°S). Profiles of dissolved cadmium, copper, nickel and cobalt concentration increased with depth in a manner similar to that of phosphate. Dissolved cadmium was strongly correlated to phosphate at concentrations greater than 0.74 µmol kg − 1 ; below this concentration cadmium was depleted (< 40 pmol kg − 1 ). The depletion of cadmium before that of phosphate is consistent with the hypothesis that the ‘kink’ in the cadmium–phosphate relationship is linked to iron limitation in Southern Ocean waters. For zinc and silicon, surface dissolved concentrations were low across the transect. Profiles of dissolved zinc and silicon concentration increased with depth and were similar in nature, indicating a close coupling between these two elements. The coupling of zinc and silicon implies that diatoms may control the global zinc–silicon relationship. These results also suggest that mode water and intermediate waters, which are important conduits for the export of silicon depleted waters to low latitudes, play major roles in regulating the concentration of zinc in the main thermocline outside of the Southern Ocean.

Immobilization of Lead with Nanocrystalline Carbonated Apatite Present in Fish Bone

Reactions of lead with phosphate can immobilize lead in situ in contaminated soils. We investigated reactions between dissolved lead and fish bones, which are an environmentally useful phosphate source for lead immobilization. Fish bones contain biogenic nanocrystalline apatite [Ca5(PO4)3OH(s)] that is carbonated and hydroxyl-deficient. Experiments compared the lead removal upon reaction with unheated fish bones, fish bones that had been heated to char the organic phase, and a synthetic hydroxylapatite solid. The investigation combined analyses of the aqueous phase with direct characterization of the solid phase by laser Raman microprobe spectroscopy to determine the identity and location of any lead phosphate precipitates. Dissolved lead concentrations decreased by several orders of magnitude after reaction with all of the solid phosphates studied. The immobilization of lead had a slight but measurable effect on the continuing release of calcium and phosphate from the solid phase to solution. The fish bones were more soluble than the synthetic hydroxylapatite, and both phases were more soluble than was predicted from available equilibrium constants for hydroxylapatite. At high lead loading relative to the surface area of the phosphate solid, homogeneous nucleation of the lead phosphate pyromorphite [Pb5(PO4)3(OH,Cl)(s)] was observed in suspension. At lower dissolved lead concentrations relative to surface area, immobilization may be dominated by adsorption of lead onto bone phases with high surface area rather than by precipitation of pyromorphite.

Sediment–Water Interactions in an Eroded and Heavy Metal Contaminated Peatland Catchment, Southern Pennines, UK

Atmospherically deposited lead in the upper layer of the heavily eroded peatlands of the Peak District, southern Pennines, UK, reaches concentrations in excess of 1,000 mg kg−1. Erosion of the upper peat layer in this region is releasing lead, associated with eroded peat particles, into the fluvial system. Understanding the process mechanisms that control dissolved lead concentrations in contaminated peatland streams is vital for understanding lead cycling and transport in peatland streams. Many headwater streams of the southern Pennines recharge drinking water reservoirs. Measurements in the Upper North Grain (UNG) study catchment show that mean sediment-associated and dissolved lead concentrations are 102±39.4 mg kg−1 and 5.73±2.16 µg l−1, respectively. Experimental evidence demonstrates that lead can desorb from suspended sediments, composed of contaminated peat, into stream waters. In-stream processing could therefore account for the elevated dissolved lead concentrations in the fluvial system of UNG.

Lead and copper speciation in remote mountain lakes

We determined the chemical speciation of lead and copper in remote mountain and high‐latitude lakes at different times of the year, providing background data for regions in Europe least affected by anthropogenic effects. The lakes are characterized by low ionic strength, clear waters, and oligotrophic conditions; are fed predominantly by atmospheric precipitation; and are ice‐covered during a large part of the year. Lead—and copper‐complexing ligands were determined by cathodic stripping voltammetry with ligand competition using Calcein blue and salicylaldoxime, respectively. Water column averages of the dissolved lead concentrations ranged from 0.2 to 0.9 nmol L−1, with generally lowest levels during the prolonged winter ice cover, whereas dissolved copper concentrations, varying from 1 to 1.7 (±0.1) nmol L−1, showed no significant seasonal variations. The lead speciation was controlled by complexation with ligands at concentrations mostly below 2 nmol L−1, with values for the stability constant (log K’PbL) of 12.5‐13.7; calculated 9PbL ionic lead concentrations (‐log[Pb2+] values) were 11.9‐14.5. Copper complexation was controlled by ligands at concentrations of 12—21 nmol L−1, with values for log K’CuL of 13.5‐14.0 and—log[Cu2+] values of 14.4‐15.1. The concentration of the copper‐binding ligands, but not those for lead, varied seasonally, with about 50% higher concentrations during open water conditions compared to periods of ice cover. The data were consistent with the presence of only one class of ligands for copper and lead. The stability constant of the ligands is similar to that of fulvic acid; however, evidence regarding the actual nature of the ligands is still lacking. The lake data show that (1) competition between calcium and lead causes a reduction in the stability constant of approximately one log‐unit for each order of magnitude of Ca2+, and (2) lead scavenging in the lakes is moderated by complexation.

Stable lead isotopes reveal a natural source of high lead concentrations to gasoline-contaminated groundwater

Concentrations of total lead as high as 1,600 μg/L were detected in gasoline-contaminated and uncontaminated groundwater at three gasoline-release sites in South Carolina. Total lead concentrations were highest in turbid groundwater samples from gasoline-contaminated and uncontaminated wells, whereas lower turbidity groundwater samples (collected using low-flow methods) had lower total lead concentrations. Dissolved lead concentrations in all wells sampled, however, were less than 15 μg total lead/L, the current United States Environmental Protection Agency (US EPA) maximum contaminant level (MCL). Because many total lead concentrations exceeded the MCL, the source of lead to the groundwater system at two of the three sites was investigated using a stable lead isotope ratio approach. Plots of the stable isotope ratios of lead (Pb) in groundwater as 207Pb/206Pb versus 208Pb/206Pb, and 208Pb/204Pb versus 206Pb/204Pb were similar to ratios characteristic of lead-based minerals in local rocks of the southeastern US, and were not similar to the stable lead isotopes ratios characteristic of distant lead ore deposits such as Broken Hill, Australia, used to produce tetraethyl lead in gasoline products prior to its phase-out and ban in the United States. Moreover, the isotopic composition of dissolved lead was equivalent to the isotopic composition of total lead in turbid samples collected from the same well, suggesting that the majority of the lead detected in the groundwater samples was associated with sediment particulates of indigenous aquifer material, rather than lead associated with spilled leaded gasoline. The results of this investigation indicate that (1) lead detected at some gasoline-release sites may be derived from the local aquifer material, rather than the gasoline release, and consequently may affect site-specific remediation goals; (2) non-low flow groundwater sampling methods, such as a disposable bailer, may result in turbid groundwater samples and high total lead concentrations, and; (3) stable lead isotopes can be used to clarify the source of lead detected above permissible levels in gasoline-contaminated groundwater systems.

Toxic Metals in Urban Runoff: Physico-Chemical Mobility Assessment Using Speciation Schemes

Physico-chemical characterization of lead, zinc and cadmium has been carried out on eight samples from both separate and combined sewers. Dissolved and paniculate total metal levels have been determined. A speciation scheme has been used to further divide these phases in two dissolved fractions, bioavailable and stable, and five paniculate fractions, ion-exchangeable, acid-soluble, reducible, oxidizable and residual. Total dissolved lead concentrations were found to be largely below European Community (EC) directives for drinking water production. Lead was represented by stable forms while zinc and cadmium were mainly bioavailable. Paniculate concentrations were higher than natural levels found in the Seine-Normandie basin. Zinc was characteristic for municipal effluents, and lead and cadmium were more concentrated in separate sewers. Correlations have been observed between paniculate heavy metals and volatile matter on the ring highway, or with iron at the Savigny site. The paniculate metal speciation scheme has demonstrated the important dependence of heavy metal distribution on the sampling site, as well as the potentially more mobile nature of zinc and cadmium, compared to that of lead. The structural modifications undergone by solids during their transport along the sewer networks had a significant impact on paniculate metal mobility. This has been clearly noted for lead, whose mobility decreased from upstream to downstream in the studied system.

Influence of the Loire River on Dissolved Lead and Cadmium Concentrations in Coastal Waters of Brittany

Two surveys have revealed a significant solubilization of particulate cadmium in the Loire estuary (France). This enrichment of the solution, which does not appear to be linked to any intra-estuarine anthropogenic source, is notable along the entire southern Brittany coastline where mean dissolved cadmium concentrations (0·16 nM) are slightly higher than those observed in northern Brittany (0·12 nM). Lead distribution in the Loire estuary seems to be largely governed by a significant anthropogenic input which completely masks the natural geochemical behaviour of this element. However, the high dissolved lead concentrations (up to 1·7 nM) remain confined to the estuarine zone itself, while the coastal zone presents markedly lower concentrations (0·16 to 0·39 nM). Unlike what may be observed for cadmium, and despite a significant anthropogenic input to the estuary, dissolved lead enrichment in the coastal waters of Brittany therefore seems very confined.

Lead speciation in surface waters of the eastern North Pacific

Titrations using differential pulse anodic stripping voltammetry (DPASV) to detect electroactive lead were carried out on fresh seawater samples and on samples stored acidified to determine the extent of lead complexation in the eastern North Pacific. Results of these analyses on surface water samples indicate total dissolved lead concentrations between 17 and 49 pM. The inorganic or DPASV labile fraction is 30–50%. Titration with lead yielded data consistent with one class of organic ligand(s), present at low concentration (between 0.2 and 0.5 nM) with a mean value for a conditional stability constant with respect to inorganic lead of log K′ cond=9.7. The presence of this ligand, together with the various inorganic ligands in seawater, gives rise to a concentration of free ionic lead of ∼ 0.4 pM.

TRENDS IN LEAD CONCENTRATIONS IN MAJOR U.S. RIVERS AND THEIR RELATION TO HISTORICAL CHANGES IN GASOLINE‐LEAD CONSUMPTION1

ABSTRACT: Declines in concentrations of dissolved lead occurred at nearly two‐thirds of 306 locations on major U.S. rivers from 1974 to 1985. Declines in dissolved lead concentrations are statistically significant (p &lt; 0.10) at approximately one‐third of the sampling locations. Statistically significant increases in dissolved lead concentrations occurred at only 6 percent of the sites, but are clustered in the Texas‐Gulf and Lower Mississippi regions. Possible explanations for the observed trends in lead concentrations are tested through comparisons with (1) records of lead discharges from major sources including leaded‐gasoline consumption and municipal‐ and industrial‐point source discharges, (2) trends in various water‐quality constituents such as pH and total alkalinity, and (3) basin characteristics such as drainage area. Statistically significant declines in lead concentrations in streams and gasoline lead (i.e., the largest source of lead at these sites) are highly coincident for the 1979 to 1980 period at most sampling locations. The greatest amount of decline in gasoline lead occurred at sites showing statistically significant downtrends in stream concentrations of lead from 1974 to 1985. No more than 5 percent of the trends in stream lead are influenced by municipal‐ and industrial‐point sources of lead. Factors that affect the transport of dissolved lead, including lead solubility, suspended sediment, and basin characteristics such as drainage basin size, are not significantly related to trends in dissolved lead. Trends in streamflow explain no more than 7 percent of the downtrends in concentrations of lead and may partly explain the frequent increases in lead concentrations in the Texas‐Gulf and Lower Mississippi regions.

Deposition of metallic and organic pollutants alongside the M6 motorway

The deposition rates of lead, cadmium, copper and selected organic pollutants (polynuclear aromatic hydrocarbons and phenols) have been determined in the vicinity of the M6 motorway near Lancaster, and at background locations remote from the motorway. A major fraction of all motorway-derived pollutants measured is deposited within 15 m of the carriageway; metal deposition rates in the vicinity of the motorway approach background levels at distances of approximately 200 m from the carriageway. Samples of total deposition collected within 10 m of the carriageway had the highest concentrations of particulate-associated lead, the lowest dissolved lead concentrations and the highest pH.

The influence of lead in components of a freshwater ecosystem on molluscan tissue lead concentrations

Two sites wilh elevated levels of lead (Pb) were selected at Weston's Mill Pond and Farrington Lake in central New Jersey, U.S.A. Lead concentrations in surficial sediments and overlying waters were significantly higher in Weston's Mill Pond than in Farrington Lake. Concentrations of lead in molluscs reflected the degree of lead contamination in the two sites. The gastropods, Physa integra, Pseudosuccinea columella, Helisoma trivolis and Idropoma malleata had the highest lead concentrations. The changes in lead concentration over time in the grazing snails ( P. integra, P. columella and H trivolis) appeared to be more strongly correlated to dissolved lead concentrations in water than concentrations in the ‘aufwuchs’, macrophytes, or various sediment fractions. Campeloma decisum had the lowest lead concentrations despite its close association with the contaminated sediments. No strong correlations were noted between lead concentrations in this burrowing prosobranch and those in deriving waters, interstitial waters, or various sediment fractions. The extent of habitat contamination only partially determined the lead concentrations in the species studied.