The complexation of protons, aluminium and calcium by aquatic humic substances: A model incorporating binding-site heterogeneity and macroionic effects

A model is presented that describes the competitive binding of protons and metal ions (Al³⁺, AlOH²⁺, Ca²⁺) by humic substances (HS) in the pH range 3–6 and at different ionic strengths, and allows the net humic charge to be calculated. The HS are treated in terms of two types of carboxyl group, together with other more weakly-acidic groups, and the influence of humic (macroionic) charge is taken into account. Eight parameters are involved: total humic acidity, which can be measured directly, content of COOH groups, 4 intrinsic equilibrium constants (2 for H⁺ binding, 2 for metal binding), and 2 parameters accounting for charge effects at different ionic strengths. The model was applied to 4 aquatic humic samples, parameters being estimated from acid-base titration data. The equilibrium contents did not vary greatly among the humic samples, which is consistent with the idea that the functional groups in each sample are chemically the same. The effect of humic charge on complexation varies considerably among the samples. The model was reasonably successful at predicting humic-bound Al in laboratory-prepared solutions and field samples. Calculations based on the model suggest that, (1) Ca²⁺ does not compete significantly with Al for binding to HS under natural acid conditions, and (2) that there is a direct relationship between humic solubility and net humic charge.     

Conditions required for the precipitation of aluminium in acidic natural waters

Laboratory and field studies were carried out in order to define the conditions necessary for the precipitation of Al in natural waters of pH 4–6. It is concluded that if precipitation does occur it involves the formation of Al(oxy)hydroxide, not aluminosilicates or basic aluminium sulphates. The solubility product of the Al(oxy)hydroxide is highly temperature dependent (ΔH = −30.5 kcal⁻¹). It is also sensitive to concentrations of SO₄²⁻ and, more markedly, humic substances (HS); both of these decrease solubility, HS by more than an order of magnitude at a concentration of approx. 5 mg l⁻¹ (equivalent to approx. 2.5 mg l⁻¹ dissolved organic carbon). A semi-empirical equation is proposed that allows the prediction of the effective solubility product at different temperatures and at humic concentrations in the range 0–7 mg l⁻¹. Of the 113 natural water samples analysed, only one was calculated to be oversaturated with respect to Al(oxy)hydroxide.     

Aluminium speciation in streams and lakes of the UK Acid Waters Monitoring Network, modelled with WHAM

The Windermere Humic Aqueous Model (WHAM) incorporating Humic Ion-Binding Model VI was applied to analytical data from the United Kingdom Acid Waters Monitoring Network, collected for 22 streams and lakes over the period 1988-2007, to calculate the chemical speciation of monomeric aluminium (Al_mon) in 3087 water samples. Model outputs were compared with analytical measurements of labile and non-labile Al_mon concentrations, the former being equated with inorganic forms of Al_mon and the latter with organically-complexed metal. Raw analytical data were used, and also data produced by applying a correction for the possible dissociation of organically-complexed Al_mon, and therefore its underestimation, during passage through the analytical cation-exchange column. Model calibration was performed by finding the conversion factor, F_FADOC, between the concentration of isolated fulvic acid, with default ion-binding properties, required by the model, and the measured concentration of dissolved organic carbon, [DOC]. For both uncorrected and corrected data, the value of F_FADOC for streams was greater than for lakes, indicating greater binding activity towards aluminium. Model fits were better using uncorrected analytical data, but the values of F_FADOC obtained from corrected data agreed more closely with previous estimates. The model provided reasonably good explanations of differences in aluminium speciation between sampling sites, and of temporal variations at individual sites. With total monomeric concentration as input, WHAM calculations might substitute for analytical speciation measurements, or aid analytical quality control. Calculated Al³⁺ activities, a_Al3+, showed a pH-dependence similar to that previously found for other surface waters, and the modelling exercise identified differences between waters of up to two orders of magnitude in the value of a_Al3+ at a given pH. The model gives the net charge of dissolved organic matter, which is calculated to have risen significantly at 15 of the AWMN sites, due to increases in pH and decreases in aluminium concentration.     

The effects of a whole-watershed calcium addition on the chemistry of stream storm events at the Hubbard Brook Experimental Forest in NH, USA

Patterns of storm runoff chemistry from a wollastonite (calcium-silicate mineral, CaSiO₃) treated watershed (W1) were compared with a reference watershed (W6) at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire (NH), USA to investigate the role of Ca²⁺ supply in the acid–base status of stream chemistry. In the summer of 2003, six storm events were studied in W1 and W6 to evaluate the effects of the wollastonite treatment on the episodic acidification of stream waters. Although mean values of Ca²⁺ concentrations decreased slightly from 33.8 to 31.7 μmol/L with increasing stream discharge in W1 during the events, the mean value of acid neutralizing capacity (ANC) was positive (1.2 μeq/L) during storm events, compared to negative values (− 0.2 μeq/L) in W6. This pattern is presumably due to enhanced Ca²⁺ supply in W1 (20.7 to 29.0% of dissolved Ca²⁺ derived from the added wollastonite) to stream water as a result of interflow along shallow flowpaths. In addition, the application of wollastonite increased pH and dissolved silica (H₄SiO₄) concentrations, and decreased the concentration of inorganic monomeric Al (Al_i) in W1 in comparison with W6 during storm events. Despite an increase in SO₄²⁻ concentration, likely due to desorption of sulfate from soil after the treatment, the watershed showed an increase in ANC compared to the reference watershed, serving to mitigate episodic acidification.     

Complexation analysis of fresh waters by equilibrium diafiltration

Equilibrium ultrafiltration has been employed to determine the extent of Cu, Ni, Co, Fe, Mn and Zu chelation in oxic waters from mineralized terrains. Concentrations of Cu, Ni and Co were determined in different organic fractions separated by various Amicon ultrafilters. Titrations of fresh water samples with metal ions were made, and “free” metal concentration measured by equilibrium diafiltration. Experiments were made at concentrations and pH at which metals and ligands occur in natural waters. Conditional stability functions ranged from 10^6.72 at pH 6.5 to 10^7.07 at pH 7.6 for Ni and 10^6.85 at pH 6.8 to 10^6.97 at pH 7.6 for Co. At low metal concentrations (8 × 10⁻⁷ M) only one complexing class of major importance for natural water environments was observed. The order of metal complexing ability was found to be Cu > Ni > Co > Zn > Mn with Cu showing a preference towards the higher MW organic fractions.     

Defluorination of natural waters by filtration through glauconite treated with aluminum salts

It is shown that the use of glauconite modified by the aluminum layers makes it possible to reduce the content of fluoride-ions to the MAC level. Optimal conditions of modification have been established: pH 4–5, C_Al ³⁺-0.15–0.2 mg/dm³. For obtaining high-quality water from underground waters a mixed medium of natural and modified forms of glauconite may be used.     

Note on a rapid and sensitive method for the determination of anionic detergents in natural waters at the ppb level

A rapid and sensitive method for the determination of anionic detergents in natural waters is developed using atomic absorption spectrophotometry and his (ethylenediamine) copper(II) ion. The method is suitable for a concentration range of 0–50 μg1⁻¹ (ppb), but its applicability can be extended up to 15 μg ml⁻¹. The limit of detection is 0.3 μg l⁻¹.     

Batch metal removal by peat. Kinetics and thermodynamics

Peat moss, a natural inexpensive material, is able to play an important rôle in treatment processes of metal-bearing industrial effluents since it adsorbs, complexes or exchanges various metal cations. This paper presents kinetics and thermodynamics of batch metal removal reactions by 50 g l⁻¹ (dry wt) eutrophic or oligotrophic peat particles using Cu²⁺, Cd²⁺, Zn²⁺ and Ni²⁺ concentrations ranging from 0.01 to 100 mM.Metal cation removal reactions are moderately rapid in 10 mM metal unbuffered solutions: the forward kinetic constant ranges between 0.005 and 0.17 M⁻¹s⁻¹, and equilibrium is reached within about 1 h. Under these conditions of pH (2.2–4.2) and concentrations, apparent binding equilibrium constants were found to range between 2 and 3150 M⁻¹ depending upon the peat origin and the metal cation.In 0–6.5 pH-buffered metal cation solutions, the four cations binding reactions behaved differently demonstrating that metal binding equilibrium constant decrease in the order Ni²⁺ > Cu²⁺ > Cd²⁺ = Zn²⁺. When pH is higher than 6.7, more than 90% of a 10 mM metal cation solution is removed by 50 g 1⁻¹ peat particles and metal binding capacities equal 200 mmol kg⁻¹ dry wt, whatever the metal nature and the peat origin. Except for nickel cation which is very strongly bound to peat, all metal cations are completely released when pH is fixed below 1.5.     

A comprehensive study on the biological treatabilities of phenol and methanol—III Treatment system design

The effects of temperature, pH, salinity, and nutrients on bacterial activities were investigated and evaluated using a statistical method. The substrate utilization rate coefficient (k) decreased as pH deviated from neutral and as salinity increased, and the unfavorable pH and salinity alleviated the temperature effect on k. The modified Arrhenius equation, k_T2 = k_T1 θ(^T2−T1), was not effective in describing the temperature effect on k: the temperature coefficient (θ) ranged between 1.0–1.4 depending on the temperature range, pH, salinity, and substance (phenol or methanol). The endogeneous respiration activity was affected by various environmental factors such as pH, temperature, and salinity; however, the cell decay coefficient (k_d) turned out to be correlated to a single parameter, k. Thus, k_d = 0.066 k^0.87 and k_d = 0.0115 k^0.634, where k and k_d are based on the unit of h⁻¹, were proposed for the prediction of cell decay coefficient for phenol and methanol acclimated activated sludge, respectively. In batch treatment of 770 mg l⁻¹ of phenol and 1000 mg l⁻¹ of methanol as TOC, nitrogen and phosphorus did not have any recognizable effect on k, while trace elements such as Fe²⁺, Mg²⁺, Mn²⁺, Ca²⁺, and Zn²⁺, etc. showed a slightly perceptible effect on it. The absence of extra-cellular nitrogen and phosphorus resulted in a greater cell yield; however, the cells in this condition decayed more rapidly than normal cells. The primary factor affecting the substrate decomposition rate in natural systems was pH: phenol decomposition resulted in a considerable decrease in pH so that the buffering capacity of the water was the most important factor, and methanol decomposition did not affect pH significantly so that the initial pH of the water was the most important factor. An initial lag phase was observed in 8 out of 115 phenol batch tests and 31 out of 66 methanol batch tests.     

Copper lethality to rainbow trout in waters of various hardness and pH

The 96 h median lethal concentration (LC₅₀) of total dissolved copper varied from 20 μg 1⁻¹ in soft acid water to 520 μg l⁻¹ in hard alkaline water, in tests with hardness ranging from 30 to 360 mg l⁻¹ as CaCO₃ and pH from 5 to 9. The 3-dimensional response surface was complex, although an increase in hardness usually made copper less toxic. A good prediction of copper LC₅₀ at usual combinations of hardness and pH was given by the equation: LC₅₀ = antilog (1.933 + 0.0592 P_T + 0.4912 H_T + 0.4035 P_TH_T + 0.4813 P²_T + 0.1403 H²_TThe transformed variables are and A somewhat less accurate equation is provided for extreme combinations of hardness and pH.Trout of 10 g weight were 2.5 times more resistant than 0.7 g trout. Effect of size was apparently the same at different combinations of hardness and pH, and was predictable by an equation of the form LC₅₀ = Constant × Weight ^0.348.Ionic copper (Cu²⁺) and two ionized hydroxides (CuOH⁺ and Cu₂OH²⁺₂) seemed to be the toxic species of copper, since they yielded the smoothest response surface with the best fit to measured LC₅₀'s. The sum of these ions produced LC₅₀'s ranging from 0.09 μg l⁻¹ copper in soft alkaline water to 230 μg l⁻¹ in hard acid water. The ions were different in relative toxicity, or became more toxic at high pH, or both.     

An improved method for the determination of adenosinetriphosphate in environmental samples

An improved method has been developed for the analysis of the adenosinetriphosphate (ATP) content of environmental samples with the luciferin-luciferase assay. Factors affecting the recovery and stability of the ATP as well as the enzymatic reaction were optimized. The most versitile method utilizes procedure which can be used for natural waters, sediments and sludges. This involves homogenization at room temperature in 10⁻² M trisodium phosphate, pH 11.7, containing 23% chloroform. This method is more effective than other methods tested and results in minimal interference with the enzymatic reaction. It also provides improved ATP recovery and long term stability of extracted ATP. Another method that can be used on natural waters and sludges is by boiling for 5 min in 10⁻² M glycine buffer, 5 × 10⁻³ M Mg-EDTA, pH 10, which resulted in complete extraction and no hydrolytic loss of ATP. However, it is not satisfactory for sediments containing high humic acid substances as well as high metal loadings.In addition to the direct comparison of endogenous ATP extraction by various methods, actual recoveries of spiked radioactive ATP was measured. ATP adsorption, hydrolysis and recoveries in each method were determined by the use of [8-¹⁴C] ATP and [γ-³²P] ATP.     

Potential hazards of nitrate and fluoride in underground waters

Underground waters of the semi-arid tract of Agra region (India) were examined for their nitrate and fluoride concentration along with other chemical constituents. The results indicated that 40 and 49% of the waters contained injurious concentrations of nitrate and fluoride respectively for drinking water. Only 28.4% of the waters were useful for some crops because of excessively high nitrate concentrations (> 100 mg l⁻¹) and 23.1% were harmful for common crops with respect to fluoride concentration (> 10 mg l⁻¹). Generally, high salinity waters had a high nitrate and fluoride content.     

Addition of NaOH, limestone slurry and finegrained limestone to acidified lake water and the effects on smolts of atlantic salmon (Salmo salar L.)

A neutralization experiment comparing NaOH, limestone slurry and finegrained limestone was performed using smolts of Atlantic salmon as testfish. Smolts were raised on chronically acid Lake Liervatn (pH = 4.9–5.4, conductivity = 55 μ S cm⁻¹, Ca = 1.3 mg l⁻¹, labile Al = 40 μg l⁻¹). As a result testfish were sublethally stressed prior to the experiment, as indicated by low levels of plasma chloride. During the experiment, smolts were held in keepnets in the middle of large plastic enclosures without sediment contact. Rapid changes in pH and Al-speciation were recorded after addition of the neutralizing agents. No mortality of fish occurred during the 3 days exposure. Plasma chloride levels in fish exposed to limestone slurry, limestone and the lowest concentration of NaOH (pH = 5.9) did not differ significantly from levels in fish from the reference group. Fish exposed to the highest concentration of NaOH (pH > 7.45), however, experienced a significant decrease in plasma chloride levels. Increased sublethal stress in treatments with NaOH was presumably caused by the presence of aluminate ions [Al(OH)₄⁻] at high pH and by low concentrations of Ca. The importance of maintaining pH below 7 when using bases with monovalent cations is emphasized. Adding inorganic aluminium to the lake water induced loss of plasma chloride within 48 h at 70 μg labile Al l⁻¹ at pH 5.1 and 1.2 mgCa l⁻¹.     

On the presence of iron(II) in oxygenated surface waters: analytical implications

Iron(II) analyses using bathophenanthroline are shown to be characterized by an inherent, small positive interference when the pH of analysis is below 6.5 and iron(III) is present. The interference, which is due to a colored complex formed in the presence of FeOH²⁺ and bathophenanthroline, varies in magnitude according to the presence or generation of FeOH²⁺ during analysis. This interference necessitates reconsideration of published claims that low levels of stable iron(II) exist in oxygenated natural waters, particularly the surface layers of lakes.     

Investigation on the river water polluted with acidic hot spring water

Tamagawa hot spring in Akita Prefecture gushes hot water of 1 pH hydrochloric acid at some 140 1 s⁻¹. This quantity flows into the River Tama with the result that the river has been denied use for any significant hydropower development thus far. For the purpose of mitigating the acidity of the river water, the hot spring water is carried away through channels and infiltrated into the soil of a mountainside for chemical neutralizing through seepage before flowing into the river.The following facts have been obtained by field geochemical investigation (1951–1963). The neutralization effect following the injection of hot-spring water into the soil is about 80 per cent, the larger part of which effect is due to the function of dissolution of Al³⁺; the pH values of the water in the reservoir of Yoroibata dam to be constructed downstream of the river do not exceed 5; and even in the absence of hot-spring water injection treatment there is acidity reduction due to the alkalinity of the tributary waters as well as due to the dissolution of river-bed components by the acid during seepage.     

Laboratory study on the adsorption of Mn²⁺ on suspended and deposited amorphous Al(OH)₃ in drinking water distribution systems

Manganese (II) is commonly present in drinking water. This paper mainly focuses on the adsorption of manganese on suspended and deposited amorphous Al(OH)₃ solids. The effects of water flow rate and water quality parameters, including solution pH and the concentrations of Mn²⁺, humic acid, and co-existing cations on adsorption were investigated. It was found that chemical adsorption mainly took place in drinking water with pHs above 7.5; suspended Al(OH)₃ showed strong adsorption capacity for Mn²⁺. When the total Mn²⁺ input was 3 mg/L, 1.0 g solid could accumulate approximately 24.0 mg of Mn²⁺ at 15 °C. In drinking water with pHs below 7.5, because of H⁺ inhibition, active reaction sites on amorphous Al(OH)₃ surface were much less. The adsorption of Mn²⁺ on Al(OH)₃ changed gradually from chemical coordination to physical adsorption. In drinking water with high concentrations of Ca²⁺, Mg²⁺, Fe³⁺, and HA, the removal of Mn²⁺ was enhanced due to the effects of co-precipitation and adsorption. In solution with 1.0 mg/L HA, the residual concentration of Mn²⁺ was below 0.005 mg/L, much lower than the limit value required by the Chinese Standard for Drinking Water Quality. Unlike suspended Al(OH)₃, deposited Al(OH)₃ had a much lower adsorption capacity of 0.85 mg/g, and the variation in flow rate and major water quality parameters had little effect on it. Improved managements of water age, pipe flushing and mechanical cleaning were suggested to control residual Mn²⁺.     

Comparative study on organic constituents in polluted and unpolluted inland aquatic environments-I features of hydrocarbons for polluted and unpolluted waters

The constituents of hydrocarbons between highly polluted river waters collected from the Tokyo area and unpolluted river, brook, reservoir and pond waters obtained from the Ogasawara (Bonin) Islands were compared to characterize their features for polluted and unpolluted waters. n-Alkanes between the carbon chain length of C₁₂ and C₃₆, squalane and unresolved complex mixture of hydrocarbons (UCMH) were found in most of the river waters of the Tokyo area at the contents ranging from 0.026 to 14 μg 1⁻¹, from 0.004 to 1.7 μg 1⁻¹ and from less than 5 to 290 μg 1⁻¹, respectively, whereas in the waters of the Ogasawara Islands, only n-alkanes ranging from C₁₃ to C₃₇ were found with the great predominance of odd-carbon numbers at the contents varying from 0.042 to 4.0 μg 1⁻¹.It was indicated that the presence of squalane, UCMH and even-carbon numbered n-alkanes as the major constituents are intimately correlated with artificial hydrocarbon sources (fossil fuels and their products and both combustion products, and industrial products), while the great predominance of odd-carbon numbered n-alkanes for the unpolluted areas are mainly due to algae and higher plants. Besides, the major portion of n-alkanes, squalane and UCMH are thought to be present in polluted and unpolluted waters associated with particulate materials.     

Anodic stripping voltammetric study of the lability of Cd, Pb, Cu ions sorbed on humic acid particles

The sorption of Cd, Pb and Cu by humic acid particles has been studied at μg l⁻¹ levels using A.S.V. on a Hg film electrode as the measuring technique. The variables examined included amount of solid present (0.01–0.2% w/v), initial metal ion concn (10–100 μg l⁻¹), systems pH (5.3, 6.35, 8.15) and base electrolyte composition. The calculated capacity for specific adsorption of the metal ions was a few mmol M²⁺ kg⁻¹, or less. The apparent lability of part of the sorbed material was examined by analysing the base solution before and after filtering, and by adding Chelex 100 particles to the suspension. Some sorbed Cd²⁺ was A.S.V. labile, another fraction transferred to the resin. The effect of solution reactions on uptake was studied by making the 1 M CH₃COONa base solution 0.2 M in a range of Na⁺ salts (8 different anions), or in carboxylic acid content (5 acids) or in compounds having S-type bonding groups. Formation of complex ions in solution altered the extent of metal ion uptake, and in the case of Cu A.S.V. peak size, shape and position were varied. It is suggested that natural waters containing suspended matter should be analysed by A.S.V. “as received”, as well as after filtration since response differences provide guidance in respect to the lability of sorbed ions.     

Flameless atomic absorption analyses of mercury in model aquatic systems

Chemical models of freshwater and seawater (34‰ S) have been used to examine the effect of humic material on the analysis of mercury by flameless atomic absorption spectrometry. Solutions containing mercuric chloride (1 μg Hg 1⁻¹) and various concentrations of humic material were allowed to attain equilibrium under carefully controlled conditions. In both media, association between the inorganic and organic entities took place within 90 min at pH ≥ 7 and the organically bound mercury was not detected by an analytical method designed for inorganic mercury. The amount of detectable mercury was related to the quantity of humic material added to the solutions.In experiments involving changes of pH the model solutions showed three characteristics: (1) a flat response in the neutral and alkaline pH range, where the humates are apparently stable; (2) a minima in the pH range 2–4 where the formation of an acid flocculent appears to remove additional mercury from solution: (3) at pH = 1, some release of mercury occurs from the organic precipitate.Photolysis studies using the model freshwater solutions showed that total mercury measurements could be made after 2 h irradiation at pH = 1. Using the same technique methylmercury chloride and diphenylmercury decomposed within 1 h. These results are relevant to routine and analyses of total mercury in natural waters.     

Effect of temperature and dissolved oxygen on biodegradation of nitrilotriacetate

The effect of temperature and dissolved oxygen on the rate of biodegradation of nitrilotriacetate (NTA) was examined in water samples collected from the Rur River. Biodegradation of NTA was first order with respect to NTA concentration over a concentration range of 50–1000 μg l⁻¹. First order rate constants showed a typical temperature dependency (temperature coefficient, Q₁₀ = 2) and biodegradation of NTA was observed over a temperature range of 2–24°C. The effect of temperature on the rate of NTA biodegradation was described by the Arrhenius equation, with calculated activation energies in the range reported for ordinary enzyme reactions. Biodegradation of NTA was also observed at low dissolved oxygen concentrations (0.3 mg l⁻¹), although at reduced rates compared to high oxygen concentrations (13 mg l⁻¹). Biodegradation of NTA was oxygen-dependent, suggesting an obligate oxygen requirement for the initial steps in NTA metabolism by natural microbial communities in surface waters. In general, our results indicate that NTA biodegradation will occur in natural waters under conditions of low temperature and low dissolved oxygen and also at low NTA concentrations.