Free Pb Research Articles

Lead pollution of Dhanmondi Lake in Dhaka

Dhanmondi Lake, which is located in densely populated central Dhaka, has been found to be heavily contaminated with lead. The average lead concentration in the lake water was found to vary from 151 to 210 μg/L during the dry period, and from 30 to 120 μg/L during the wet period. Increased rainfall and surface runoff appears to be responsible for reduced lead concentrations during the wet period. The lead concentration in the bottom sediment was found to vary from 10.7 to 44.7 mg/kg (dry weight), with sediment samples collected from locations in close proximity to major inlet points showing higher levels of contamination. The lead concentration in Dhanmondi Lake exceeds the values set for drinking, fishing, livestock, industrial and irrigation use in the environmental quality standards set out for Bangladesh. The determination of lead concentration in various parts of a fish of the Nilotica species revealed maximum bio-accumulation in the fins (4.90 mg/kg wet weight) and gills (4.78 mg/kg). Contaminated fish from the lake are becoming a local public health concern. Speciation calculations revealed that the major soluble lead species in Dhanmondi Lake are PbCO3(aq), Pb2+ and PbOH+, with PbCO3(aq) being the most dominant, while PbHCO3+, PbCl+ and PbSO4(aq) are minor species. Although the concentration of free ionic Pb2+, apparently the more toxic form, was found to be relatively low, any drop in pH would result in an increase in this species. With rapid industrialisation and an increasing number of motorised vehicles using leaded gasoline, lead pollution is likely to get worse unless appropriate remedial and regulatory measures are taken.

Low levels of inorganic lead noncompetitively inhibit μ-calpain

Calpain is a ubiquitous calcium-dependent cysteine protease, whose cytoskeletal protein substrates suggest that it may be important in neuronal differentiation. Lead (Pb 2+) is known to substitute for Ca 2+ in a variety of intracellular processes, and interferes with the development of hippocampal neurons in vitro. We found that free Pb 2+ at 1 nM does not activate calpain in the absence of Ca 2+. Pb 2+ inhibited the activity of calpain; the degree of calpain inhibition was dependent on an interaction between concentrations of both Ca 2+ and Pb 2+. In the presence of 1 μM free Ca 2+, 10 pM free Pb 2+ reduced calpain activity, but in the presence of 100 μM free Ca 2+, 1 nM free Pb 2+ failed to inhibit calpain. This provides evidence that Pb 2+ competes for the Ca 2+ binding sites on calpain. In the presence of 40 μM free Ca 2+, 1 nM free Pb 2+ significantly reduces V max without altering K m, suggesting that Pb 2+ acts as a noncompetitive inhibitor of calpain. Inhibition of calpain is one mechanism by which Pb 2+ may interfere with neuronal development.

Trace Metal Speciation in Three Unbuffered Salt Solutions Used to Assess their Bioavailability in Soil

AbstractThree unbuffered salt solutions used to estimate soil trace metal bioavailability were compared. The objective was to evaluate chemical speciation of Cd, Cu, Pb, and Zn in 0.01 M CaCl2, 0.1 M NaNO3, and 1 M NH4NO3 extracts. The metal in each extract were speciated with a model that was optimized experimentally using an exchange resin. In NH4NO3, Cd, Cu, and Zn were completely complexed by NH3. In extracts of pH lower than 6.5, Pb was essentially present as free Pb2+ and metal‐organic complexes. In extracts of higher pH, PbCO3 and free Pb2+ were dominant. In CaCl2, Cu and Zn were mainly present as organic complexes and free Zn2+, respectively. In all extracts, 50% of Cd was free Cd2+ and 50% CdCl+. As pH increased, the proportions of free Pb2+ and organic complexes decreased while those of inorganic complexes increased. In NaNO3, Cd, Cu, and Zn were, respectively, mainly present as free Cd2+, organic complexes and free Zn2+. Speciation of Pb changed with pH as in NH4NO3. Similarities were expected between the qualitative composition of the extracts and the soil solution, justifying the use of unbuffered salt solutions, particularly NaNO3 and CaCl2, in the evaluation of soil trace metal availability.

Soil Solution Speciation of Lead(II): Effects of Organic Matter and pH

AbstractThe effects of adjusting the levels of soil organic matter in a Pb‐contaminated soil on the solubility and free Pb2+ speciation were studied within the pH range 3 to 8. A contaminated orchard soil containing 284 mg Pb kg−1 was treated with leaf compost to increase soil organic matter and with H2O2 to decrease it, yielding six soil organic matter levels between 25.6 and 83.7 g C kg−1. The equilibrated solutions were then analyzed for total dissolved Pb by graphite furnace atomic absorption spectrometry and for labile Pb by differential pulse anodic stripping voltammetry (DPASV). The labile Pb values were used to calculate the free Pb2+ activity based on the assumption that organo‐Pb complexes are not DPASV‐labile. The data showed that 30 to 50% of dissolved Pb is present as soluble OM complexes at low pH and up to 80 to 99% at near‐neutral pH. The solubility of Pb shows a linear decrease from pH 3 to 6.5 and is independent of soil organic matter in that pH range. From pH 6.5 to 8, higher pH promotes the formation and dissolution of organo‐Pb complexes, which increase Pb solubility. In this pH range, higher organic matter content results in higher concentrations of dissolved and labile Pb.

Lead Phosphate Solubility in Water and Soil Suspensions

The widespread occurrence of soil Pb contamination requires a good understanding of the factors controlling Pb solubility. Pb solubility will often be controlled by phosphates, which are used to reduce environmental risks of Pb-contaminated soils. The solubility equilibria of two different synthetic lead phosphate minerals were determined electrochemically across a wide range of pH and Pb and phosphate concentrations. The resulting chemical equilibrium data could not be explained by standard solubility equations, although a simple empirical regression explained the data very well. The same lead phosphate mineral was then added to two different soils which were equilibrated across a pH range 4−8. Differential pulse anodic stripping voltammetry was used to determine the ASV-labile Pb in the extracted soil solutions, and the free Pb2+ ion activity was calculated. The free Pb2+ activity in the soil solutions followed the expected pH relationship, highest solubility at low pH and gradual decrease with increasi...

Speciation of Lead in Contaminated Soils

Lead contaminated soils from various origins were sampled and analyzed for total Pb content, dissolved Pb, soil pH, soil organic matter content and Mo-reactive phosphate in solution. The concentration of free Pb 2+ ionic species in solution was determined using differential pulse anodic stripping voltammetry (ASV), assuming that ASV-labile Pb excludes organo–Pb complexes. The dataset shows the solubility relationships between the various soil characteristics for 84 soils covering a wide range of soil properties; pH (3.5 to 8.1), total Pb (10 to 15 000 mg Pb kg −1), dissolved Pb (0.6 to 124 μg Pb litre −1), free Pb 2+ activity (10 −10.4 to 10 −6.8 m) and soil organic matter (4.5 to 108 g C kg -1). Non-linear regression analysis shows that free Pb 2+ in soil solution can be predicted simply using the log of total soil Pb and pH with no significant contributions from the soil organic matter content or the concentration of phosphate in solution. In the case of dissolved Pb, log of total Pb, soil pH and solution phosphate are significant parameters, but soil organic matter does not contribute to the regression. About ∼60–80% of the dissolved Pb is present as organo–Pb complexes, this percentage is lower in soils with low pH or high total Pb content.

Adsorption of Pb(II), NTA, and Pb(II)–NTA onto TiO2

Nitrilotriacetic acid (NTA) is extensively used in different industries because of its excellent chelating properties. Introduction of NTA into the natural environment is a concern because of mobilization of heavy metal species that may be otherwise bound to natural particulate matter. The present study investigates the adsorption behavior of Pb(II) and NTA, both as individual species and as complex species onto titanium dioxide. This adsorption information is important in considering the TiO2-assisted photocatalytic treatment of these metal–organic complexes. Pb(II) shows a typical cationic type of adsorption behavior, whereas NTA demonstrates an anionic type of adsorption trend. Results from stoichiometric ternary systems show a gradual increase in Pb(II) adsorption and a decrease in NTA removal with an increase in pH. However, for the cases of Pb(II) > NTA, increased NTA adsorption as compared to pure NTA systems was noted even at higher pH. Model predictions employing MINTEQA2 software followed the experimental trends. Experimental and model results from ternary systems suggest adsorption of free Pb(II) and NTA, as well as ternaryTi–NTA–Pb(II) andTi–O–Pb(II)–NTA2−species. The cationic-type complexation, i.e.,Ti–O–Pb(II)–NTA2−, was essential for the successful NTA adsorption modeling, especially at higher pH and for Pb > NTA systems, where significant NTA adsorption was noted even at very high pH values. Most of the previous metal–ligand adsorption studies did not consider such a surface complexation. However, the present results indicate that any groundwater transport modeling of such pollutants will require the inclusion of cationic-type surface complexation, in addition to other surface species.

Physico-chemical Speciation of Lead in South San Francisco Bay

The speciation of lead at a site in the South San Francisco Bay was determined using a combination of physical size fractionation and electrochemical analyses. The ‘total dissolvable’ Pb was 8·1nM from analysis of an acidified unfiltered sample. The ‘dissolved’ Pb was equal to 0·20nM (41ng l−1), only 2·5% of the ‘total dissolvable’ Pb. The difference yielded the ‘particulate’ Pb equal to 7·9nM (1·6μg l−1). Results from crossflow ultrafiltration indicated that almost all (0·19nM) of the dissolved Pb was ‘in solution’ [<10K nominal molecular weight (MW)] and that colloidal Pb (10K MW to 0·2μm)accounted for onlyc.1% of the dissolved Pb at this station. This small concentration (0·01nM) of colloidal Pb may be attributed to the low amount of organic carbon associated with colloid size fraction as determined by dissolved organic carbon analyses.The chemical speciation of lead was determined in the dissolved sample and ultrafiltered sub-sample. Differential pulse anodic stripping voltammetry (DPASV) on a thin mercury film (TMF) rotating glassy carbon disk electrode (RGCDE) was used to distinguish the kinetically labile inorganic species (Pb′) from the Pb-chelated by organic ligands (PbLi). Lead titration results were similar for both samples revealing that Pb′, PbLiand excess unbound ligands were present primarily in the ultrafiltrate, rather than in the colloidal phase. The titration data can be interpreted as dissolved Pb being influenced by two classes of Pb-binding ligands. In the dissolved sample, the concentration of the stronger class of ligands was [L1]=0·89±0·35nM, with a conditional stability constant ofKcondL1,Pb′=3±1×1010M−1. The weaker class was [L2]=12·8±1·9nM, withKcondL1,Pb′=4±1×108 M−1. The presence of these ligands, in excess of the dissolved Pb, resulted in [Pb′]=7±2pM and [Pb2+]=0·3pM (62pg l−1). While less than 2·4% of the ambient Pb was ‘in solution’, it existed chiefly in the form of organic complexes with [PbL1]=0·15nM and [PbL2]=0·03nM. More significantly, there were large concentrations of unchelated Pb-binding ligands, (Li′), available to buffer the free Pb2+concentration in the event of perturbations in dissolved Pb.

Extracellular inhibition and intracellular enhancement of Ca2+ currents by Pb2+ in bovine adrenal chromaffin cells.

1. Effects of highly neurotoxic, inorganic lead ions (Pb2+) on voltage-dependent calcium channels were investigated with the use of the whole cell patch-clamp technique in bovine adrenal chromaffin cells maintained in short-term primary culture (1-5 days). 2. Extracellularly applied Pb2+ induced a concentration-dependent, reversible inhibition of Ca2+ currents, with an estimated IC50 approximately equal to 3.0 x 10(-7) M free Pb2+. 3. Elevation of the intracellular free Ca2+ concentration above 10(-8) M dose-dependently reduced the amplitude of the initial Ca2+ current and increased the exponential rate of current rundown. 4. Intracellularly applied Pb2+ prevented the Ca(2+)-dependent reduction of the initial Ca2+ current amplitude and altered the current rundown kinetics from exponential to linear. The effect was dose dependent and saturable, with an estimated EC50 approximately equal to 2.0 x 10(-10) M free Pb2+. 5. These results indicate that in contrast to extracellular blockade, intracellular Pb2+ promotes Ca2+ currents by attenuating the Ca(2+)-dependent, steady-state inactivation of calcium channels. This provides a novel mechanism through which Pb2+ may disrupt calcium signaling in chronically lead-exposed cells.

Lead inhibits Ca 2+-stimulated nitric oxide synthase activity from rat cerebellum

Pb 2+ is reported to cause cognitive dysfunctions in children and to inhibit long-term potentiation (UP), a model form of synaptic plasticity that involves nitric oxide (NO). Since Pb 2+ interacts with Ca 2+-calmodulin, and brain nitric oxide synthase (NOS) is Ca 2+-calmodulin regulated, we examined the effects of Pb 2+ on NOS activity prepared from rat cerebellum. NOS required NADPH and was inhibited by monomethylarginine. Full NOS activity required 0.6μM free Ca 2+ and was inhibited 50% by 17 nM and 100% by 80 nM free Pb 2+. NOS inhibition by Pb 2+ was reversible by increasing free Ca 2+ concentrations. Evaluation of other divalent cations resulted in the following ranked order of potencies: Cu 2+ > Pb2+ ⪢ Zn 2+; Fe 2+, Ba 2+, Mg 2+, Mn 2+, and Sr 2+ were ineffective. These results suggest that Pb 2+ inhibition of brain NOS activity may account for some of the effects of Pb 2+ on the CNS.

Lead activation of protein kinase C from rat brain. Determination of free calcium, lead, and zinc by 19F NMR.

Lead (Pb2+) has been reported to activate calcium/phospholipid-dependent protein kinase C (PKC) at subnanomolar concentrations (Markovac, J., and Goldstein, G. W. (1988) Nature 334, 732-734); however, others have failed to find any Pb(2+)-induced activation of PKC (Murakami, K., Feng, G., and Chen, S. G. (1993) J. Pharmacol. Exp. Ther. 264, 757-761). In neither of these studies was the actual free Pb2+ or Ca2+ concentration measured. In this study, 1,2-bis(2-amino-5-fluorophenoxy)ethane N,N,N',N'-tetraacetic acid (5F-BAPTA) was used to buffer Pb2+ and Ca2+ concentrations in the PKC reaction mixture. The specific free ion concentrations of Pb2+ and Ca2+, as well as Zn2+ and other divalent cations contained in the PKC reaction mixtures, were determined by 19F NMR spectroscopy. Using this approach to set and confirm the free Pb2+ and Ca2+ concentrations, we measured the Pb(2+)-dependent and the Ca(2+)-dependent activation of phosphotydylserine/diolein-dependent incorporation of 32P from ATP into histone and endogenous acid precipitable proteins in the 100,000 x g supernatant from homogenized rat brain cortex. We found that free Pb2+ activates PKC in the range from 10(-11) to 10(-8) M, Kact = 5.5 x 10(-11) M, while Ca2+ activates PKC in the range from 10(-8) to 10(-5) M, Kact = 2.56 x 10(-7) M. These findings clearly resolve the activation of PKC by subnanomolar concentrations of free Pb2+ from activation induced by Ca2+ or other divalent cations. Furthermore, it documents the utility of 5F-BAPTA as buffer and indicator when resolving the contributions of multiple divalent cations in biochemical processes.

Clay adsorption of lead from landfill leachate

Abstract This paper examines clay adsorption of lead from leachates originating in controlled landfills for municipal solid wastes. Special attention has been given to determining the extent to which Freundlich and Langmuir‐derived isotherms may represent the system in various experimental conditions (metal concentration and pH). Lead adsorption is satisfactory described at constant pH by using the Langmuir/Freundlich isotherm over the entire pH range examined (4.0–8.5). By using theoretical speciation, adsorption related to free Pb (Pb2+) in solution makes the results more generalizable than in terms of total Pb. Theoretical speciation also allows for interpreting the pH effect on adsorption: as pH increases, adsorption of free Pb increases but at the same time free Pb decreases. Depending on which effect is prevailing, adsorption at a fixed total Pb concentration can increase or decrease, as pH changes. As an environmental implication, an increase of pH does not always entail stronger attenuation of pol...

Observations on the chemical nature of lead in human blood serum.

1. The binding of lead to human blood serum, and components of serum, was studied by titration with the addition of Pb(NO3)2 solution, monitoring the free Pb2+ concentration with a Pb2+ electrode, and by equilibrium dialysis. 2. In fresh serum, about 4999 out of 5000 parts of added lead were bound. This suggests that the free Pb2+ concentration is around 1/5000th of the total lead concentration in the serum of normal subjects, i.e. about 1 x 10(-12) mol/l. 3. About 60% of the binding of lead in serum is abolished by standing in air, by dialysis or by treatment with N-ethylmaleimide. This appears to be due to the presence of thiol compounds, mainly cysteine. The remaining 40% appears to be due to protein, mainly albumin.

Ca2+‐Surrogate Action of Pb2+ on Acetylcholine Release from Rat Brain Synaptosomes

The effect of lead ions on the release of acetylcholine (ACh) was investigated in intact and digitonin-permeabilized rat cerebrocortical synaptosomes that had been prelabeled with [3H]choline. Release of ACh was inferred from the release of total 3H label or by determination of [3H]ACh. Application of 1 microM Pb2+ to intact synaptosomes in Ca2(+)-deficient medium induced 3H release, which was enhanced by K+ depolarization. This suggests that entry of Pb2+ into synaptosomes and Pb2(+)-induced ACh release can be augmented by activation of the voltage-gated Ca2+ channels in nerve terminals. The lead-induced release of [3H]ACh was blocked by treatment of synaptosomes with vesamicol, which prevents uptake of ACh into synaptic vesicles without affecting its synthesis in the synaptoplasm. This indicates that Pb2+ selectively activates the release of a vesicular fraction of the transmitter with little or no effect on the leakage of cytoplasmic ACh. Application of 1-50 nM (EC50 congruent to 4 nM) free Pb2+ to digitonin-permeabilized synaptosomes elicited release of 3H label that was comparable with the release induced by 0.2-5 microM (EC50 congruent to 0.5 microM) free Ca2+. This suggests that Pb2+ triggers transmitter exocytosis directly and that it is a some 100 times more effective activator of exocytosis than is the natural agonist Ca2+.

Inhibition of Sarcoplasmic Reticulum Ca2+-ATPase Activity by Cadmium, Lead and Mercury

The effect of Cd2+, Pb2+ and Hg2+ on the Ca(2+)-ATPase activity of sarcoplasmic reticulum from rabbit muscle was studied. The concentration of relevant free and complex species for the assay conditions have been computed. As a result, ATP hydrolysis was found to be inhibited with an IC50 value of 950 nmol/l free Cd2+ or 95 nmol/l free Pb2+. Although calculation of the free Hg2+ was not possible, the comparison of the IC50 values for total metal ions show that Hg2+ is the strongest inhibitor of enzyme activity. The inhibition by Cd2+ seems to be independent of substrate concentration, whereas the inhibitory effect of Pb2+ is lowered in the presence of higher MgATP concentrations. Our data illustrate that the three heavy metals are potent inhibitors of the Ca2+ pump. Therefore low concentrations of these metal ions may disturb intracellular Ca2+ homeostasis and act on Ca(2+)-mediated cell functions.

Development of 19F NMR for measurement of [Ca2+]i and [Pb2+]i in cultured osteoblastic bone cells.

Lead (Pb) has been shown to perturb cellular calcium (Ca) homeostasis, altering sizes and flux rates of cellular pools of exchangeable Ca and impairing Ca-mediated cell processes. To date, however, a direct effect of Pb on intracellular-free Ca2+ has not yet been demonstrated. Heavy metals bind to the commonly used fluorescent Ca ion indicators with greater affinity than does Ca and thereby interfere with the expected Ca-dependent fluorescence. In this study, the fluorinated Ca ion indicator, 1,2-bis(2-amino-5-fluorophenoxy)ethane N,N,N',N'-tetraacetic acid (5F-BAPTA), and 19F NMR were used to measure the free intracellular Ca ion concentration ([Ca2+]i) in the rat osteoblastic bone cell line, ROS 17/2.8. Both Pb and Ca bind to 5F-BAPTA with high affinity, but the Pb-5F-BAPTA comple produces a 19F NMR signal at a chemical shift distinct from 5F-BAPTA and the Ca-5F-BAPTA complex. The apparent dissociation constants for Pb-5F-BAPTA and Ca-5F-BAPTA are 2 X 10(-10) M and 5 X 10(-7) M, respectively, at 30 degrees C, pH 7.1, and Mg2+ (0.5 mM). Thus, this methodology allows for the simultaneous identification and quantification of free Pb and free Ca ion concentrations. Determinations of [Ca2+]i were based on 19F NMR measurements of 5F-BAPTA-loaded ROS 17/2.8 osteoblastic bone cells that were attached to collagen-coated microcarrier beads. Cells were continuously superfused with freshly oxygenated medium at 30 degrees C. Under these conditions, the [Ca2+]i of ROS 17/2.8 cells was observed to be 128 +/- 14 nM.(ABSTRACT TRUNCATED AT 250 WORDS)

Spin-resolved core and valence electron photoemission from non-epitaxially grown Pb layers on Pt(111)

The core and valence levels of Pb adsorbates on Pt(111) have been studied by means of spin, angle and energy-resolved photoemission with circularly polarized synchrotron radiation of BESSY. For an eight layer Stranski-Krastanov grown Pb adsorbate (which is thus non-epitaxial) the d core level peaks show a spin-orbit splitting of 2.7 eV and no shift with photon energy. Spin-resolved photoemission for normal light incidence and normal electron emisson from the 5 d 5 2 level reveals a m j splitting in addition to the spin-orbit splitting and in addition to the core level shifts known. The valence levels were studied with photon energies of about 12 eV. Two peaks corresponding to the 6 p 3 2 and 6 p 1 2 -derived levels could be detected for the highly symmetrical setup of normal light incidence and normal electron emission. Off normal electron emission from the 6 p 3 2 - derived level yields the opposite sign polarization component parallel to the photon spin when compared to the normal electron emission results. This is in agreement with earlier photoionization studies of free Pb atoms.

Organic and inogranic lead inhibit neurite growth in vertebrate and invertebrate neurons in culture

Neurons from brains of chick embryos and pond snails (Lymnaea stagnalis) were cultured for 3 to 4 d in the presence of no toxins, inorganic lead (PbCl2), or organic lead (triethyl lead chloride). In chick neurons, inorganic lead reduced the percentage of cells that grew neurites (IC50 = 270 microM total lead, approximately 70 nM free Pb2+) but did not reduce the number of neurites per cell or the mean neurite length. Triethyl lead reduced the percentage of cells that grew neurites (IC50 = 0.24 microM) and the mean neurite length (extrapolated IC50 = 3.6 microM) but did not reduce the number of neurites per cell. In Lymnaea neurons, inorganic lead reduced the percentage of cells that grew neurites (IC50 = 13 microM total lead; approximately 10 nM free Pb2+). Triethyl lead reduced the percentage of cells that grew neurites (IC50 = 0.4 microM) and exerted significant toxicity at 0.2 microM. The two forms of lead affected neurite growth in qualitatively different ways, which suggests that their mechanisms of action are different.

Effect of lead on intracellular free calcium ion concentration in a presynaptic neuronal model: 19F-NMR study of NG108-15 cells

The intracellular free calcium ion concentration ([Ca 2+] i) of the neuroblastoma × glioma hybrid cell line, NG108-15, was measured using the 19F-nuclear magnetic resonance divalent cation indicator, 1,2- bis(2-amino-5-fluorophenoxy)ethane- N, N, N′, N′-tetra-acetic acid (5F-BAPTA). The basal [Ca 2+] i was measured to be 106 ± 14 nM. Treatment with 5 μM lead (Pb) for 2 h produced a 2-fold increase in [Ca 2+] i to 200 ± 24 nM and a measurable intracellular free Pb 2+ concentration ([Pb 2+] i) of 30 ± 10 pM. Intracellular free Zn 2+ concentrations ([Zn 2+] i) were also observed in the presence of Pb. This represents the first direct demonstration that Pb elevates the [Ca 2+] i in neurons, thus providing evidence for a role of [Ca 2+] i in mediating the neurotoxicity of Pb.

Lead increases free Ca2+ concentration in cultured osteoblastic bone cells: simultaneous detection of intracellular free Pb2+ by 19F NMR.

Lead (Pb) has been shown to perturb Ca-mediated cellular processes. However, to date, a direct effect of Pb on intracellular free Ca2+ concentration ([Ca2+]i) has not been demonstrated. 19F NMR in combination with 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (5F-BAPTA) was used to simultaneously measure [Ca2+]i and intracellular free Pb2+ concentration ([Pb2+]i) in the rat osteoblastic bone cell line ROS 17/2.8. The basal concentration of [Ca2+]i in ROS 17/2.8 cells was measured to be 128 +/- 24 nM. Treatment with Pb2+ at 5 and 25 microM produced sustained 50% and 120% increases in [Ca2+]i, respectively, over a time course of 5 hr. At a medium Pb2+ concentration of 25 microM, the entry of Pb2+ into ROS 17/2.8 cells yielded measurable [Pb2+]i in cultured cells. Collectively, these findings advance the hypothesis that Pb toxicity is mediated, in part, through perturbations in [Ca2+]i.