Free Lead Ions Research Articles

Facile synthesis of iminated lignin for enhanced free radical and lead ion scavenging capabilities

Kraft lignin (KL) holds significant potential as a renewable resource for the development of innovative materials that are currently not fully utilized. In this study, a novel iminated lignin (IL) was synthesized by grafting primary amine lignin (N−KL) onto salicylaldehyde. The effects of the dosage and reaction temperature on the nitrogen content of N-KL were evaluated. The maximum nitrogen content in N-KL reached to 3.32 %. Characterization by spectroscopy techniques (FT-IR, XPS, and NMR), elemental analysis, and gel permeation chromatography confirmed the imination of lignin. Additionally, the antioxidant activity of the lignin samples was investigated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability. Moreover, the DPPH radical scavenging capacity of IL-6 (IC50 = 38.6 ± 3.9 μg/mL) was close to that of commercial antioxidant butylated hydroxytoluene (BHT) (IC50 = 37.7 ± 4.5 μg/mL). Furthermore, the adsorption equilibrium results indicated that IL-6 had a maximum uptake of 115.6 mg/g Pb2+, which was 3.2-fold higher than that of KL. Kinetic adsorption experiments suggested that IL-6 adsorption follows a pseudo-second-order model. Therefore, the synthesized iminated lignin is a promising candidate for the development of environmentally friendly materials with applications as an antioxidant and lead-ion adsorbent.

Multi-Functional Regulation on Buried Interface for Achieving Efficient Triple-Cation Perovskite Solar Cells.

Mixed-cation perovskite solar cells (PSCs) have attracted much attention because of the advantages of suitable bandgap and stability. It is still a challenge to rationally design and modify the perovskite/tin oxide (SnO2) heterogeneous interface for achieving highly efficient and stable PSCs. Herein, a strategy of one-stone-for-three-birds is proposed to achieve multi-functional interface regulation via introducing N-Chlorosuccinimide (NCS) into the solution of SnO2: i) C═O functional group in NCS can induces strong binding affinity to uncoordinated defects (oxygen vacancies, free lead ions, etc) at the buried interface and passivate them; ii) incomplete in situ hydrolysis reactions can occur spontaneously and adjust the pH value of the SnO2 solution to achieve a more matchable energy level; iii) effectively releasing the residual stress of the underlying perovskite. As a result, a champion power conversion efficiency (PCE) of 24.74% is achieved with a device structure of ITO/SnO2/Perovskite/Spiro-OMeTAD/Ag, which is one of the highest values for cesium-formamidinium-methylammonium (CsFAMA) triple cation PSCs. Furthermore, the device without encapsulation can sustain 94.6% of its initial PCE after the storage at room temperature and relative humidity (RH) of 20% for 40 days. The research provides a versatile way to manipulate buried interface for achieving efficient and stable PSCs.

Structure and photoluminescence properties of PbO–Bi2O3–Ga2O3 glass-ceramics containing silver nanoparticles, free lead and bismuth ions

We report the synthesis, structural characterization, and optical properties of PbO–Bi2O3–Ga2O3 glass-ceramics (GCs) containing PbO and Bi2O3 crystallites, free lead (Pb2+) and bismuth (Bi3+) ions, and silver nanoparticles (Ag-NPs). The samples were prepared by applying the melt-quenching method followed by suitable heat-treatment of the samples. Transmission Electron Microscopy, X-ray diffraction, linear optical absorption, and photoluminescence (PL) were the techniques applied to characterize the samples. When the samples were excited at 330 nm a large PL intensity, due to the Pb2+ and Bi3+, is observed. Moreover, large PL intensity enhancement of about 1000% for the samples containing Ag-NPs is observed in comparison with the PL intensity from the samples without Ag-NPs. This is the first time that this behavior is reported for a GCs based on heavy-metal oxides. The potential of this class of materials for photonic applications is discussed.

Efficient resource treatment of hexavalent chromium wastewater based on lead carbonate (cerussite)-induced precipitation separation

Recycling treatment of wastewater containing hexavalent chromium [Cr (VI)] has always been an important environmental issue. In this paper, taking advantage of the natural affinity of CrO42− and lead ions, lead carbonate was selected as a precipitant to recover Cr (VI) in the form of chrome yellow (PbCrO4). Firstly, the variation of Cr (VI) and lead species in K+-CrO42−-Pb2+-CO32− solution system with pH and PbCO3 dosage was calculated by Visual MINTEQ. The results show that the treatment effect is better under acidic conditions. Then, the effects of parameters on the removal rate of Cr, including the initial pH of solution, reaction time, reaction temperature, and the dosage of lead carbonate, were studied by batch experiments. Results show that the initial pH of solution, reaction time, and the dosage of lead carbonate have great influence, whereas reaction temperature has slight influence. And the concentration of Cr (VI) could be reduced from 100 mg/L to 0.043 mg/L at an initial pH of 3, a reaction time of 45 min, and the dosage of lead carbonate as n(PbCO3)/n(K2CrO4) = 2. The precipitates are analyzed by XRD, SEM, and EDS，and the results are consistent with the predictions of Visual MINTEQ, that is, the newly produced substance is only PbCrO4. The reaction mechanism of Cr (VI) on the surface of lead carbonate was studied by the adsorption kinetic model, and the results showed that the reaction was more fit with the pseudo-second-order kinetic model. Density functional theory (DFT) calculations show that CrO42− could effectively react with lead atoms with unsaturated coordination bonds on the surface of lead carbonate and free lead ions leached from the surface of lead carbonate to form lead chromate. Under acidic conditions, the removal of Cr (VI) by PbCO3 may involve two main mechanisms: the mineralization and precipitation of lead and chromate ions dissolved from the surface of cerussite and the chemical adsorption of chromate ions on the surface of cerussite. This study provides a new and efficient strategy for the resource treatment of Cr (VI)-containing wastewater.

Sulfation on coated carbon related to lead ion and its effect on the performance of advanced ultra-battery at high rate

The ultra-battery is a kind of advanced power type lead-carbon battery, which is adept in cycling under high rate and partial state of charge. The sulfation in the lead paste of the negative electrode is considered as a key factor which affects the performance of the ultra-battery. Meanwhile, because the free lead ions would contact with the coated carbon and the working potential of the coated carbon is close to the lead paste, the sulfation also occurs in the coated carbon, which in turn affects the performance of carbon materials. However, there has been limited work to explore the sulfation on the coated carbon. In this paper, a variety of physical characterizations and electrochemical research methods are used to study the sulfation process on the coated carbon. The results show that the reduction potential of lead ions on the coated carbon is more negative than that on the lead paste during high-rate cycling, resulting in more serious sulfation occurred on the coated carbon. And the sulfation is more likely to occur in the place where coated carbon is adjacent to the lead paste. This side reaction has a great influence on the performance of the ultra-battery at high-rate. When the PVA gel obtained by the sol-gel method is used to inhibit the sulfation on the coated carbon, the energy retention rate of the ultra-battery is increased from 76.01% to 83.75% after 2000 cycles at 1 A g−1 under 100% DOD, and the charge and discharge efficiency of the ultra-battery is increased from 44.12% to 97.45%.

Lead ion selective electrodes from dibenzo-18-crown-6 derivatives: An exploratory study

Dibenzo-18-crown-6 (DB18C6) and three of its derivatives (-COCH3, -Br, -NO2), are investigated via Density Functional Theoretical (DFT) modelling, Fourier Transform Infrared (FT-IR) and absorption spectroscopies, Differential Pulse Anodic Stripping (DPASV), Cyclic (CV) and Square Wave (SWV) voltammetries, as possible materials for preparing plasticiser free lead(II) ion selective electrodes. The spontaneous, entropy driven, interactions between lead(II) ions and DB18C6 derivatives are such that they form 1:1 complexes via coordination with the high electron density open ether cavity, except for the brominated derivative where the metal: ligand stoichiometry is 2:1 due to exo-cavity coordination via the high electron density bromine atoms. Monolayers resulting from electropolymerization of some derivatives (-H, -COCH3, -Br) and chemisorption of the -NO2 derivative, allows quantification of lead(II) ions at concentrations below 10 mg L−1 with minimal interference from other metal ions except Hg2+ and Al3+.

Activation Mechanism of Lead(II) to Ilmenite Flotation Using Salicylhydroxamic Acid as Collector

In this study, salicylhydroxamic acid (SHA), which exhibits superior flotation performance to conventional collector benzohydroxamic acid (BHA), was first introduced in ilmenite flotation. The addition of lead(II) can significantly increase the recovery of ilmenite using SHA as collector. Thus, the adsorption mechanism of SHA on lead(II)-activated ilmenite surface was systematically studied using micro-flotation tests, adsorption analysis, zeta potential measurements, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Micro-flotation results revealed that SHA had stronger collecting ability than BHA, and ilmenite floatability could be activated by lead ions with either SHA or BHA as collector. Ilmenite showed good floatability at pH 6–8 (over 90% recovery) in the presence of Pb2+ and SHA. In such conditions, the main lead species of Pb(OH)+ and Pb2+ acted as active sites and caused positive surface potential shifts, thereby increasing the adsorbed amounts of negatively charged SHA on the surface of the mineral. FTIR and XPS analyses suggested that the lead species was chemically adsorbed on the surface of ilmenite to form active sites chelated by SHA. Moreover, the free lead ions in solution might form the Pb–SHA complexes to adsorb on the mineral surface, thereby increasing the floatability of ilmenite.

Dual-functional chemical sensor for sensitive detection and bioimaging of Zn2+ and Pb2+ based on a water-soluble polymer

Free lead and zinc ions are toxic to living cells and environment, we develop a multi-responsive fluorescence probe based on water-soluble double hydrophilic block copolymer. The polymer sensor with Schiff moiety can sensitively, selectively and simultaneously fluorescence probe Zn2+ (green) and Pb2+ (blue) through the different fluorescence color. The linear concentration ranges for Pd2+ and Zn2+ were 0.8–10.0 μM and 0–10.0 μM with the detection limits of 0.7 μM and 0.2 μM, respectively. The probe responding to Na+, Mn2+, Fe2+, Fe3+, Cu2+, Zn2+, Cd2+, Al3+, Cr3+, Co2+, Ni2+, Ag+, Ca2+, K+, Mg2+, Ba2+, Hg2+, and Pb2+ displays almost no significant interference with the assay process. The sensing mechanism of the PSAM probe to Pb2+ and Zn2+ was investigated by Job's plot experiment, 1H NMR analysis and density functional theory (DFT), the results show that the nitrogen atom of CHN and oxygen atom of OH may recognize with ions and the Job's plots for the PSAM complexes demonstrate 1:1 complexation, respectively. To achieve its application, the chemosensor is successfully applied to monitor Pd2+and Zn2+ in tap and lake water samples, its ability to monitor free Pd2+ and Zn2+ ions in living cells or in vivo is also validated by the intracellular imaging.

Flotability of laurionite and its response to sulfidization flotation

Laurionite is the main highly hazardous lead bearing waste in iron ore sintering dust due to its poor stability and high content, while its flotability and flotation separation have not been adequately investigated. In this study, the flotation behavior of laurionite and its interaction with Na2S were investigated in detail to find an economic and promising way for the separation of lead from sintering dust. The flotability and sulfidization flotation of laurionite were examined by micro-flotation experiments, zeta potential measurement, Fourier transform infrared spectroscopy (FT-IR) analysis and X-ray photoelectron spectroscopy (XPS) studies and solution chemistry calculation. The micro-flotation experiments results indicated that Na2S would improve the flotability of laurionite within a moderate dosage, otherwise decrease its float. The negativity of zeta potential observably increased when adding an appreciate amount of Na2S prior to NaBX, indicating a better adsorption of BX− on mineral surface, which would increase the flotation recovery. To figure out the mechanism behind that, the laurionite surface was analyzed by XPS, which found the formation of PbS films after adding Na2S. The FT-IR analysis showed the BX− absorbance on laurionite significantly decreased after treating with high concentration of Na2S. Moreover, the solution chemistry calculations demonstrated that the proper dosage of Na2S could enhance the flotation of laurionite by reduce free lead ion in solution and covered some part of lead mineral surface, which sharply reduced the demand of collectors in flotation. However, the excess S2− would inhibited the adsorption of BX− on laurionite surface since the formation Pb(BX)2 was weaker than PbS. These results did not only expose that the addition of appropriate amount of Na2S could enhance laurionite’s sulfidization flotation, but also provide an effective way to separate laurionite from iron ore sintering dust.

Efficient and rapid removal of EDTA-chelated Pb(II) by the Fe(III)/flue gas desulfurization gypsum (FGDG) system

This study introduces the application of the Fe(III)/flue gas desulfurization gypsum (FGDG) system to remove EDTA-chelated Pb(II). Systematic experiments were conducted to explore the possibility of removing EDTA-chelated Pb(II) and the crucial factors of the removal process, as well as to determine the underlying removal mechanism. The results showed that the removal reaction was a quick process, with the removal rate exceeding 90% after 1 min. The system removed 97.35% of EDTA-chelated Pb(II), reducing its concentration from 700 mg/L to 18.81 mg/L. EDTA-chelated Pb(II) can be most effectively removed at pH 2. This system had a high removal rate from 50 mg/L to 1000 mg/L of EDTA-chelated Pb(II), particularly at 700 mg/L when the removal rate reached 97.35%. When the molar ratio of Fe(III)/Pb(II) was greater or smaller than 1:1, an inhibitory effect on removal was observed. TOC and UV–Vis analyses indicated that ferric ions replaced lead ions, resulting in the conversion of the EDTA-chelated Pb(II) to EDTA-chelated Fe(III). Surface structure, crystalline phase and elemental distribution were analyzed to explore the transformation of substances. The results indicated that FGDG coprecipitated with free lead ions to form lead sulfate. Overall, the rapid and efficient removal performance with cost-effective characteristics makes the Fe(III)/FGDG system a potentially attractive method for the removal of EDTA-chelated Pb(II)in wastewater.

Labile lead phytochelatin complex could enhance transport of lead ions across biological membrane

In connection with studies of transport of hazardous metals across model phospholipid membranes (PLMs), behavior of complexes of lead with phytochelatin PC2 has been examined. Using differential potentiometric stripping analysis (PSA, Chronopotentiometry) with different values of constant negative current, the release of free lead ions confirmed their labile behavior. Similar conclusion resulted from voltammetry on silica gel modified carbon paste electrode. Diffusion controlled transport across a PLMs containing ionophore calcimycin (A23187) revealed 26 times more lead ions transported in case of Pb-phytochelatin complexes than in case of free lead ions. For labile behavior, complex with two Pb atoms at phytochelatin molecule is responsible.

ISIDORE, a probe for in situ trace metal speciation based on Donnan membrane technique with related electrochemical detection part 1: Equilibrium measurements

This work presents the development of a new probe (ISIDORE probe) based on the hyphenation of a Donnan Membrane Technique device (DMT) to a screen-printed electrode through a flow-cell to determine the free zinc, cadmium and lead ion concentration in natural samples, such as a freshwater river. The probe displays many advantages namely: (i) the detection can be performed on-site, which avoids all problems inherent to sampling, transport and storage; (ii) the low volume of the acceptor solution implies shorter equilibration times; (ii) the electrochemical detection system allows monitoring the free ion concentration in the acceptor solution without sampling.

Lead toxicity to Lemna minor predicted using a metal speciation chemistry approach.

In the present study, predictive measures for Pb toxicity and Lemna minor were developed from bioassays with 7 surface waters having varied chemistries (0.5-12.5 mg/L dissolved organic carbon, pH of 5.4-8.3, and water hardness of 8-266 mg/L CaCO3 ). As expected based on water quality, 10%, 20%, and 50% inhibitory concentration (IC10, IC20, and IC50, respectively) values expressed as percent net root elongation (%NRE) varied widely (e.g., IC20s ranging from 306 nM to >6920 nM total dissolved Pb), with unbounded values limited by Pb solubility. In considering chemical speciation, %NRE variability was better explained when both Pb hydroxides and the free lead ion were defined as bioavailable (i.e., f{OH} ) and colloidal Fe(III)(OH)3 precipitates were permitted to form and sorb metals (using FeOx as the binding phase). Although cause and effect could not be established because of covariance with alkalinity (p = 0.08), water hardness correlated strongly (r(2) = 0.998, p < 0.0001) with the concentration of total Pb in true solution ([Pb]T_True solution ). Using these correlations as the basis for predictions (i.e., [Pb]T_True solution vs water hardness and %NRE vs f{OH} ), IC20 and IC50 values produced were within a factor of 2.9 times and 2.2 times those measured, respectively. The results provide much needed effect data for L. minor and highlight the importance of chemical speciation in Pb-based risk assessments for aquatic macrophytes.

Lead Ions Encapsulated in Liposomes and Their Effect on Staphylococcus aureus

The aim of the study was the preparation of a liposome complex with encapsulated lead ions, which were electrochemically detected. In particular, experiments were focused on the potential of using an electrochemical method for the determination of free and liposome-encapsulated lead and determination of the encapsulation efficiency preventing the lead toxicity. Primarily, encapsulation of lead ions in liposomes and confirmation of successful encapsulation by electrochemical methods was done. Further, the reduction effect of the liposome matrix on the detected electrochemical signal was monitored. Besides encapsulation itself, comparison of toxicity of free lead ions and lead ions encapsulated in liposome was tested. The calculated IC50 values for evaluating the lead cytotoxicity showed significant differences between the lead enclosed in liposomes (28 µM) and free lead ions (237 µM). From the cytotoxicity studies on the bacterial strain of S. aureus it was observed that the free lead ions are less toxic in comparison with lead encapsulated in liposomes. Liposomes appear to be a suitable carrier of various substances through the inner cavity. Due to the liposome structure the lead enclosed in the liposome is more easily accepted into the cell structure and the toxicity of the enclosed lead is higher in comparison to free lead ions.

Selective BODIPY® based fluorescent chemosensor for imaging Pb2+ ion in living cells

A new fluorescent probe has been designed and synthesized by linking dicarboxylate pseudocrown ether to the BODIPY® (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophore. The probe allows determination of free lead ions in living cells.

Novel approach for generation of low calcium reagents for investigations of heavy metal effects on calcium signaling

Introduction: Lead exposure can cause learning disabilities, memory loss and severe damage to the nervous system. However, the exact mechanism by which lead causes learning disabilities is not fully understood. The effects of lead on calcium-regulated signaling pathways are difficult to study biochemically; with the traditional method of controlling the free calcium concentration with EGTA, the exact concentrations of free lead and calcium ions in solution are interdependent and prone to error because EGTA also buffers lead. Methods and Results: In our approach, we first reduced the free calcium concentration in the solution using calcium-binding resins before adding lead to buffers. The solution was sequentially treated with Chelex-100 ion exchange resin, followed by immobilized BAPTA resin. The final concentration of free calcium in the solution was measured with Fluo-3 indicator. Our protocol successfully produced buffers with free calcium levels below 15nM, which is substantially below threshold for activation of calcium-dependent enzymes in signaling pathways (which is typically a few hundred nanomolar calcium, when determined in vitro). Conclusion: This method provides an improved approach to study the effect of heavy metals on calcium-stimulated signaling pathways.

Effect of Humic Substance Photoalteration on Lead Bioavailability to Freshwater Microalgae

The present study provides results on the influence of humic substance (HS) photoalteration on lead availability to the freshwater microalga Chlorella kesslerii . The evolution of the free lead-ion concentrations measured by the ion exchange technique [Pb](IET) and intracellular lead contents was explored in the presence of Suwannee River humic (SRHA) and fulvic (SRFA) acids, as well as Aldrich humic acid (AHA) exposed at increasing radiance doses under a solar simulator. Modifications of HS characteristics highly relevant to Pb complexation and accumulation of HS to algal surfaces, including Fourier transform infrared spectroscopy, were followed. It was demonstrated that simulated sunlight exposure of HS increased [Pb](IET) in the medium for SRFA and SRHA, but had no effect for AHA. No clear relationship was observed between the changes in free lead-ion concentrations and intracellular content in alga for all studied HS, suggesting that HS photodegradation products also exhibit Pb complexation properties, and that direct interactions between HS and alga are affected. Indeed, photoalteration of humic substances reduced the adsorption of HS to the algal surface; the effect was more pronounced for SRFA and AHA and less significant for SRHA. The bioavailability results were consistent with the characterization of the phototransformation of humic substances: Pb speciation changes followed the modification of the relative abundance of the carboxylic groups and their molecular environment, while the reduced HS adsorption to the alga correlated with losses of the double bond abundance and aromaticity.

Effect of Humic Acid on Cd(II), Cu(II), and Pb(II) Uptake by Freshwater Algae: Kinetic and Cell Wall Speciation Considerations

Thepresent study examines the effect of humic acid on the uptake kinetics of Cd(II), Cu(II), and Pb(II) by the freshwater alga Chlorella kesslerii. The results demonstrated that the relative proportion of Pb in the cell wall layer is greater than that of the internalized Pb, while internalized Cd and Cu were comparable or greater than the adsorbed metal concentration. In the presence of 10 mg L(-1) humic acid (HA), Cd and Cu uptake kinetics were consistent with that predicted by measured free metal concentrations. For Pb, the uptake flux and amount of lead bound to internalization and adsorption sites were an order of magnitude higher than those found at the same free lead ion concentrations in the presence of citric acid. Chemodynamic modeling suggested that the enhancement of the Pb uptake flux in the presence of HA originates from an increasing amount of Pb bound to the internalization sites through a ternary complex formation between lead-humic acid complex and internalization sites. Cell wall speciation calculations indicated that the lead-humic acid complex is the predominant species in the cell wall layer, while for Cu(II) and Cd(II) metal bound to the internalization (Cu) and adsorption (Cd) sites significantly dominated over the M-HA complex. The findings of the work show the relevance of the cell wall layer concentration and speciation and its key role in defining the local equilibrium conditions between metal and internalizations sites. The results of the present kinetic study have important consequences for improvement of the mechanistic understanding of the role of dissolved organic matter in metal uptake in phytoplankton and biogeochemical cycling of metals in the surface waters.

Pb uptake by the freshwater alga Chlorella kesslerii in the presence of dissolved organic matter of variable composition

Environmental context. Dissolved organic matter (DOM) is of utmost importance for a toxic metal’s fate and ecotoxicity in the aquatic system, but the complex nature and variable composition of DOM makes the quantitative understanding of DOM’s role in the environment very difficult. We have demonstrated that the assumption that the properties of a DOM mixture are the sum of the properties of its individual fractions can capture the main trends characterising the role of DOM in lead speciation and adsorption by freshwater microalgae. This was done by mixing the isolated, well-characterised fractions of DOM and measuring levels of free lead ion and Pb adsorbed and internalised by algae. Abstract. Dissolved organic matter (DOM) is a complex mixture of ill-defined components, which makes the quantitative understanding of DOM functions in aquatic systems a challenging task. The traditional approach for studying such complex mixtures involves their separation into groups of different components, while assuming minimal or no alteration of their properties. By mixing the pre-isolated and well-characterised individual fractions of the DOM, including humic, fulvic and alginic acids, we have demonstrated that the free Pb ion concentrations and the adsorbed Pb plus Pb internalised by the alga Chlorella kesslerii in the presence of DOM samples of different compositions can be predicted on the basis of the experiments performed in the presence of the individual DOM fractions. An additivity model assuming that the properties of the mixture can be considered as the sum of the properties of the individual components captured the Pb speciation and adsorption behaviour in the presence of DOM of variable compositions. Similarly to the results with the individual DOM fractions, internalised Pb concentrations in the presence of the reconstituted DOM were greater than that predicted by the corresponding free lead ion concentration. An improved fit between experimental observations and the model predictions of adsorbed plus internalised Pb in the presence of DOM of different compositions was observed by assuming that each individual component adsorbed by the algae gave access to additional binding sites for Pb. Furthermore, the contribution of the Pb–DOM complex to total cellular Pb was dominated by the humic and fulvic acids, whereas the contribution of alginate was minimal.

Predicting Pb bioavailability to freshwater microalgae in the presence of fulvic acid: Algal cell density as a variable

In order to better understand the relationship between lead speciation and its bioavailability in natural waters, the interactions between Pb(II), fulvic acid and the freshwater alga, Chlorella kesslerii were studied at various algal cell densities. An increase in cellular lead or fulvic acid adsorbed to algae was observed with decrease of the cell density from ca. 10 7 to 10 5 cells ml −1. In the presence of fulvic acid, cellular Pb was greater than that expected for the same free lead ion concentrations in the absence of fulvic acid in agreement to our previous study. This effect was found to be more pronounced at lower cell density, in accordance with increased fulvic acid adsorption to algae. Good fit between experimental observations and model predictions of cellular Pb at various cell densities, was observed by assuming that fulvic acid adsorbed to algae give rise to additional binding sites for Pb(II). The findings of this study indicate that a further extension of the biotic ligand model which includes the formation of a ternary complex and cell density (or concentration) as an input parameter is needed to improve its site-specific predictive capacity, especially in the case of dissolved organic matter-rich surface waters. This extension of predictive capacity would allow to reduce the deviations from the BLM model predictions for microalgae in the presence of dissolved organic matter and hence will serve as a mechanistic tool for establishing ambient site-specific water quality criteria.