Levels of heavy metals in blue whiting caught from the eastern Black Sea area of Turkey

This paper presents data on the concentrations of 5 metals, copper (Cu), cadmium (Cd), iron (Fe), zinc (Zn) and lead (Pb) in Blue Whiting sampled from the Eastern Black Sea coast of Turkey. The highest metal concentrations of Cu, Cd, Fe, Zn and Pb were recorded in Blue Whiting with the values of 2.71, 0.601, 14.137, 15.322 and 1.078 μg g^‐1 dry weight, respectively. On average the metal concentrations in Blue Whiting followed the order of Zn > Fe > Cu > Pb > Cd. Temporal differences of concentrations of these metals were significant (p < 0.05). Spatial fluctuations of Cu, Cd, Fe, Zn and Pb concentrations in Blue Whiting were also significant (p < 0.01). It was found that the concentrations of Cu, Cd, Fe, Zn and Pb in the muscle in Blue Whiting were below the limit of Public Health Regulation in Turkey.     

Spatial and temporal characterization of trace elements and nutrients in the Rawal Lake Reservoir,Pakistan using multivariate analysis techniques

Rawal Lake Reservoir is renowned for its ecological significance and is the sole source of drinking water of the third largest city of Pakistan. However, fish kill in recent years and anthropogenic impacts from human-related activities in its catchment area have resulted in deterioration of its surface water quality. This study aims to characterize spatial and temporal variations in surface water quality, identify contaminant sources, and compare their levels with quality guidelines. Surface water samples were collected from 10 sites and analyzed for 27 physicochemical parameters for a period of 2 years on a seasonal basis. Concentration of metals in surface water in pre-monsoon were in the order: Fe > Mg > Ca > Mn > Zn > Ni > Cr > Cu > Co > Pb, whereas in post-monsoon, the order of elemental concentrations was: Ca > Mg > Na > Fe > K > Zn > Cr > Li > Pb > Co > Ni > Cu > Mn > Cd. Metals (Ni, Fe, Zn, and Ca), pH, electrical conductivity (EC), dissolved oxygen (DO), chemical oxygen demand (COD), and nutrients (PO₄³⁻, NO₃–N, and SO₄²⁻) were measured higher in pre-monsoon, whereas concentration of Cu, Mn, Cr, Co, Pb, Cd, K, Na, Mg, Li, Cl⁻, and NH₄–N were recorded higher in post-monsoon. Results highlighted serious metal pollution of surface water. Mean concentration of Zn, Cd, Ni, Cu, Fe, Cr, and Pb in both seasons and Mn in post-monsoon were well above the permissible level of surface water quality criteria. Results stress the dire need to reduce heavy-metal input into the lake basin and suggest that heavy-metal contamination should be considered as an integral part of future planning and management strategies for restoration of water quality of the lake reservoir.     

Speciation study of trace elements in surface sediment of Winam Gulf,Lake Victoria,by sequential extraction,aqua-regia acid digestion,and ICP-OES

The speciation of trace metals in surface sediment in Kisumu Carwash area of Winam Gulf, was studied and results compared with those found at Usoma beach which was found to be several orders of magnitude less polluted. High proportions of the metals were bioavailable (fractions 1–6) with BA% ranging from 21.7% (Al) to 94.5% (Pb) at Carwash and 19.6% (Al) to ～100% (for Cd and Pb) at Usoma beach. The readily mobilizable fraction (fractions 1–4) decreased in the order: Pb > Mn > Sn > Cu > Co > Zn > Mg > Cd > Mo > Ni > Cr > Fe > Al at Carwash and Mn > Mo > Sn > Pb > Cd > Mg > Cu > Zn > Co > Ni > Fe > Cr > Al at Usoma beach. The total Zn, Cd, Cr, and Cu sediment concentrations at Carwash were higher than the threshold effect concentrations (TECs), although their bioavailable concentrations were lower than these limits. Both the total and bioavailable concentrations of Pb in surface sediment at Kisumu Carwash area were higher than the TEC threshold limit indicating significant contamination from this heavy metal. Although there was a general good agreement on data obtained by sequential extraction as compared with those obtained by direct aqua-regia digestion, there were large discrepancies for some specific metal analytes which could be accounted for in terms of analytical variations and lack of uniformity in physical and chemical composition of the sediment samples analyzed.     

Effects of Cadmium on Nutrient Uptake and Translocation by Indian Mustard

Plants that hyperaccumulate metals are ideal subjects for studying the mechanisms of metal and mineral nutrient uptake in the plant kingdom. Indian Mustard (Brassica juncea) has been shown to accumulate moderate levels of Cd, Pb, Cr, Ni, Zn, and Cu. In this experiment, 10 levels of Cd concentration treatments were imposed by adding 10–190 mg Cd kg^–1 to the soils as cadmium nitrate [Cd(NO₃)₂]. The effect of Cd on phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and the micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in B. juncea was studied. Plant growth was affected negatively by Cd, root biomass decreased significantly at 170 mg Cd kg^–1 dry weight soils treatment. Cadmium accumulation both in shoots and roots increased with increasing soil Cd treatments. The highest concentration of Cd was up to 300 mg kg^–1 d.w. in the roots and 160 mg kg^–1 d.w. in the shoots. The nutrients mainly affected by Cd were P, K, Ca, Fe, and Zn in the roots, and P, K, Ca, and Cu in the shoots. K and P concentrations in roots increased significantly when Cd was added at 170 mg kg^–1, and this was almost the same level at which root growth was inhibited. Zn concentrations in roots decreased significantly when added Cd concentration was increased from 50 to 110 mg kg^–1, then remained constant with Cd treatments from 110 to 190 mg kg^–1. However, Zn concentrations in the shoots seemed less affected by Cd. It is possible that Zn uptake was affected by the Cd but not the translocation of Zn within the plant. Ca and Mg accumulation in roots and shoots showed similar trends. This result indicates that Ca and Mg uptake is a non-specific process.     

Multivariate optimization of Cd(II) biosorption onto Ulmus tree leaves from aqueous waste

Ulmus tree leaves were successfully used as a novel and efficient biosorbent for removing cadmium, (Cd(II)), from aqueous solutions in a batch system. A multivariate strategy for optimization of removal efficiency conditions of Cd(II) was carried out. A 2³ full factorial design with three center points (9 runs) was performed for screening the main variables and reducing the large number of experimental runs. Initial concentration of metal ion (C _m), amount of sorbent (m), and pH were considered as the three main variables at two different levels. The maximum removal efficiency of Cd(II) was achieved within 1 h contact time. It was found that all the main factors and their interactions were significant at p < 0.05. Doehlert response surface methodology was utilized (13 runs) for finding a suitable mathematical model. The analysis of variance and some statistical tests such as lack-of-fit, coefficient of determination (R ²), and residual distribution plot confirmed the validity of the model. The optimum conditions for maximum removal of Cd(II) by Ulmus tree leaves were found as pH = 3.4, m (amount of sorbent) = 0.128 g, C _m (initial concentration of metal ion) = 12.1 mg L^?1.     

Utilization of aluminum hydroxide waste generated in fluoride adsorption and coagulation processes for adsorptive removal of cadmium ion

Although Al-based coagulation and adsorption processes have been proved highly efficient for fluoride (F) removal, the two processes both generate large amount of Al(OH)₃ solid waste containing F (Al(OH)₃-F). This study aimed to investigate the feasibility of utilizing Al(OH)₃-F generated in Al(OH)₃ adsorption (Al(OH)₃-F_ads) and coagulation (Al(OH)₃-F_coag) for the adsorption of cadmium ion (Cd(II)). The adsorption capacity of Al(OH)₃-F_ads and Al(OH)₃-F_coag for Cd(II) was similar as that of pristine aluminum hydroxide (Al(OH)₃), being of 24.39 and 19.90 mg·g^–1, respectively. The adsorption of Cd(II) onto Al(OH)₃-F_ads and Al(OH)₃-F_coag was identified to be dominated by ion-exchange with sodium ion (Na⁺) or hydrogen ion (H⁺), surface microprecitation, and electrostatic attraction. The maximum concentration of the leached fluoride from Al(OH)₃-F_ads and Al(OH)₃-F_coag is below the Chinese Class-I IndustrialWastewater Discharge Standard for fluoride (<10 mg·L^–1). This study demonstrates that the Al(OH)₃ solid wastes generated in fluoride removal process could be potentially utilized as a adsorbent for Cd(II) removal.     

Interaction between cadmium,lead and potassium fertilizer (K<Subscript>2</Subscript>SO<Subscript>4</Subscript>) in a soil-plant system

A pot experiment was conducted to examine the influence of potassium (K) fertilizer (K₂SO₄) application on the phytoavailability and speciation distribution of cadmium (Cd) and lead (Pb) in soil. Spring wheat (Triticum aestivum L.) was selected as the test plant. There were seven treatments including single and combined contamination of Cd and Pb. CdCl₂·2.5 H₂O and Pb(NO₃)₂ were added to the soil at the following dosages: Cd + Pb = 0.00 + 0.00, 5.00 + 0.00, 25.0 + 0.00, 0.00 + 500, 0.00 + 1000, 5.00 + 500 and 25.0 + 1000 mg kg⁻¹, denoted by CK, T1, T2, T3, T4, T5 and T6, respectively. The K fertilizer had five levels: 0.00, 50.0, 100, 200 and 400 mg K₂O kg⁻¹ soil, denoted by K0, K1, K2, K3 and K4, respectively. The results showed that the K fertilizer promoted the dry weight (DW) of wheat in all treatments and alleviated the contamination by Cd and Pb. The application of K₂SO₄ reduced the uptake of Cd in different parts including roots, haulms and grains of wheat; the optimum dosage was the K2 level. K supply resulted in a significant (P < 0.05) decrease in the soluble plus exchangeable (SE) fraction of Cd and there was a negative correlation (not significant, P > 0.05) between the levels of K and the SE fraction of Cd in soil. The application of the K fertilizer could obviously restrain the uptake of Pb by wheat and there were significant (P < 0.05) negative correlations between the concentrations of Pb in grains and the levels of K in soil. K supply resulted in a decrease in the SE fraction of Pb (except the K1 level) from the K0 to K4 levels. At the same time, the application of the K fertilizer induced a significant (P < 0.05) decrease in the weakly specifically adsorbed (WSA) fraction of Pb and a significant (P < 0.05) increase in the bound to Fe–Mn oxides (OX) fraction of Pb. At different K levels, the concentration of Pb in the roots, haulms and grains had a positive correlation with the SE (not significant, P > 0.05) and WSA (significant, P < 0.05) fractions of Pb in the soil. All the K application levels in this experiment reduced the phytoavailability of Cd and Pb. Thus, it is feasible to apply K fertilizer (K₂SO₄) to alleviate contamination by Cd and/or Pb in soil. Moreover, the level of K application should be considered to obtain an optimal effect with the minimum dosage.     

The acidobasic and complexation properties of Humic acids

Complexation of Humic Acids (HA) of different origin, like Fluka, and especially those extracted from bohemian brown coal, with cadmium(II) and lead(II) was studied at pH 5.0 using differential pulse anodic stripping voltammetry. Conditions close to those present in the environment were chosen with 3‐ 10^‐4 moll^‐4 for HAs and 2. 10^‐8‐l . 10^‐5 moll^‐1 for Cd(II) and Pb(II). Stability constants evaluation was done assuming the electrode process is diffusion controlled and the complexes are labile. Obtained log K values were in the range 4.49–5.25 for Cd(II) and as expected the higher log K values 6.05–6.60 were found for Pb(II). There was no significant difference between complexation properties of HA extracted from bohemian brown coal and that of Fluka. The results obtained are in good agreement with the literature and those obtained by ISE in our laboratory.     

Metals and metalloids in PM10 in Nandan County,Guangxi, China,and the health risks posed

Intense mining, smelting, and tailing activities of polymetallic ore deposits have affected the environment in Nandan County, Guangxi, China. Samples of particulates with aerodynamic diameters low or equal 10 μm (PM₁₀) were collected in Nandan County to investigate the concentrations of and health risks posed by 17 metals and metalloids in the PM₁₀. The metal and metalloid concentrations were lower than those found in other industrial cities. The mean Cr concentration was 7.48 ng/m³. Significant higher metal and metalloid concentrations were found in PM₁₀ from mining areas (Dachang and Chehe) than from the control area (Liuzhai) (p < 0.05). Principal component analysis indicated that the main sources of Ba, Co, Cr, Fe, K, Mg, Mo, Na, and Sr were resuspension of the soil produced through mineral erosion, the main sources of As, Cd, Cu, Pb, Sb, and Zn were smelting and mining activities, and the main source of Ni was fossil fuel combustion. Higher non-carcinogenic and carcinogenic risks were posed in Dachang and Chehe than in Liuzhai. The non-carcinogenic risks posed to adults and children by individual metals and metalloids in PM₁₀ at all the sites were low, but the non-carcinogenic risks posed to children by all the metals and metalloids together exceeded the safe level (i.e., risk value > 1). The carcinogenic risks posed by Cd, Ni, and Pb were negligible at all sites, while As, Co, and Cr posed potential carcinogenic risks to the residents.

     

Sperm morphology in the marine gastropodArchitectonica perspectiva (Mollusca): Unique features and systematic relevance

The marine amphipodAllorchestes compressa Dana, fed on the seagrassHeterozostera tasmanica, was exposed to sublethal concentrations of Cd, Cr, Cu and Zn for 4 wk in flowing sea water, and the concentrations producing the minimum detectable decreases (the minimum effect concentrations, MECs) in average weight, survival and biomass (average weight × survival proportion) were estimated by interpolation from regression models. Survival and biomass were more sensitive than average weight as indicators of sublethal effects. The lowest values of MEC for Cd, Cr, Cu and Zn were 11, >250, 3.7 and 99µg 1^–1, respectively. For Cu, this value fell below the minimum risk concentration (MRC) calculated from acute toxicity tests (LC₅₀) and application factors (AF); for Cd, the MEC was similar to the MRC; for Cr and Zn, the MECs were well above the MRCs. The metal concentrations in the amphipods at the MECs were 46, >46, 364 and 139µg g^–1 dry wt for Cd, Cr, Cu and Zn, respectively. Accumulation of the nutrient metals (Cr, Cu and Zn) showed some evidence of metabolic regulation, but the non-nutrient Cd was accumulated without regulation until the amphipods died. In general, those metals that were more highly accumulated by the amphipods were the more toxic.     

Influence of sex and age on the feeding habits of the common soleSolea solea

The lethal concentration of cadmium was determined for the mysidLeptomysis lingvura G.O. Sars, a Mediterranean species from surface coastal waters, and the effect of sublethal doses on respiration, ammonia excretion, and feeding efficiency at different temperatures, and on activities of 19 hydrolases was tested. Experiments were carried out on individuals collected in spring 1987 near Marseille. At 18°C, respiration rate was significantly affected only by concentrations >0.05 mg Cd l^–1. At 0.1 mg Cd l^–1, respiration rate was more significantly depressed at 20°C than at 10°C. There was a concomitant decrease in the Q₁₀ rate (by 23 to 59%, according to the particular experiment), indicating a strong synergistic effect of temperature. Ammonia excretion was likewise affected by cadmium, also with a concomitant decrease in the Q₁₀ rate (by 34%). Daily faecal pellet production was maximum at 18°C; it was inhibited by cadmium at temperatures between 14 and 20°C, and enhanced at extreme temperatures (10 and 22°C). The assimilation efficiency of contaminated individuals was reduced by 9%. These decreases in faecal pellet production and assimilation efficiency reflect a significant decrease in energy (by about 43%) which could rapidly lead to an unbalanced energy budget with a consecutive lowering of the reproductive potential. Generally, hydrolase activities usually increased initially in the presence of 0.2 mg Cd l^–1, but after 48 h they declined, reaching very low values at 72 h. Most physiological processes are therefore affected by exposure to cadmium and the unbalanced energy budget arises from the inability to utilize environmental food. These results are consistent with the literature data on cadmium contamination in marine organisms. Physiological and biochemical changes appear to be very informative in studies of in vitro sublethal effects of micropollutants and in situ environmental modifications.     

Distribution and mobility of metals in agricultural soils near a copper smelter in South China

The distribution and mobility of heavy metals in the paddy soils surrounding a copper smelting plant in south China was investigated. We assessed the degree of metal contamination using an index of geoaccumulation. The metals were divided into two groups: (1) Cu, Zn, Pb and Cd, whose concentrations were heavily affected by anthropogenic inputs, and (2) Ni, Co and Cr, which were mainly of geochemical origin. Concentrations of Cu, Cd, Zn, and Pb in the polluted soils were higher than the Chinese soil quality criteria. The chemical partitioning patterns of Pb, Zn and Cu indicated that Pb was largely associated with the residual and NH₂OH HCl extractable fractions. In contrast, Cd was predominantly associated with the MgCl₂ extractable fraction. A large proportion of Cu was bound to the acidic H₂O₂ extractable fractions, while Zn was predominantly found in the residual phase. The fraction of mobile species, which potentially is the most harmful to the environment, was found to be elevated compared to unpolluted soils in which heavy metals are more strongly bound to the matrix. The mobility of the metals was studied by water extraction using a modification of Tessier’s procedure, and the order of mobility was Zn > Cd > Cu  > Pb.     

Biosorption of cadmium and nickel ions using marine macrophyte,Cymodocea nodosa

ABSTRACT

Seagrass (Cymodocea nodosa) ability to remove cadmium and nickel ions from single metal solutions was investigated in the present study. Metal ions were measured in the solution using an atomic absorption spectrophotometer. Various operational parameters (initial pH, biomass dose, metal ion concentration, and contact time) were tested and found to affect the uptake capacity of Cd (II) and Ni (II). More than 70% of biosorption capacity occurred in the first few minutes for both metal ions. The pseudo-second-order kinetic model and the Langmuir model were found to best fit the experimental data of Cd (II) and Ni (II) biosorption. The maximum uptake capacity (q_max) was 11.6 and 16.7?mg.g^?1 for Cd (II) and Ni (II), respectively. The biosorbent was characterised using Fourier transform infrared spectrometry (FTIR), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX). The infrared spectrum demonstrated that hydroxyl, carboxyl, and phenolic functional groups are the major binding sites for Cd (II) and Ni (II) metals. The ion exchange mechanism plays an important role during biosorption process as shown in EDX analysis. Our results conclude that marine macrophyte C. nodosa can be used as a low-cost biosorbent for the removal of Cd (II) and Ni (II) in wastewater.     

Kinetic and mechanism studies of the adsorption of lead onto waste cow bone powder (WCBP) surfaces

This study examines the adsorption isotherms, kinetics and mechanisms of Pb²⁺ sorption onto waste cow bone powder (WCBP) surfaces. The concentrations of Pb²⁺ in the study range from 10 to 90 mg/L. Although the sorption data follow the Langmuir and Freundlich isotherm, a detailed examination reveals that surface sorption or complexation and co-precipitation are the most important mechanisms, along with possibly ion exchange and solid diffusion also contributing to the overall sorption process. The co-precipitation of Pb²⁺ with the calcium hydroxyapatite (Ca-HAP) is implied by significant changes in Ca²⁺ and PO₄ ^3? concentrations during the metal sorption processes. The Pb²⁺ sorption onto the WCBP surface by metal complexation with surface functional groups such as ≡ POH. The major metal surface species are likely to be ≡ POPb⁺. The sorption isotherm results indicated that Pb²⁺ sorption onto the Langmuir and Freundlich constant q _max and K _F is 9.52 and 8.18 mg g^?1, respectively. Sorption kinetics results indicated that Pb²⁺ sorption onto WCBP was pseudo-second-order rate constants K ₂ was 1.12 g mg^?1 h^?1. The main mechanism is adsorption or surface complexation (≡POPb⁺: 61.6%), co-precipitation or ion exchange [Ca_3.93 Pb_1.07 (PO₄)₃ (OH): 21.4%] and other precipitation [Pb 50 mg L^?1 and natural pH: 17%). Sorption isotherms showed that WCBP has a much higher Pb²⁺ removal rate in an aqueous solution; the greater capability of WCBP to remove aqueous Pb²⁺ indicates its potential as another promising way to remediate Pb²⁺-contaminated media.     

Cadmium removal mechanistic comparison of three Fe-based nanomaterials: Water-chemistry and roles of Fe dissolution

● nZVI, S-nZVI, and nFeS were systematically compared for Cd(II) removal. ● Cd(II) removal by nZVI involved coprecipitation, complexation, and reduction. ● The predominant reaction for Cd(II) removal by S-nZVI and nFeS was replacement. ● A simple pseudo-second-order kinetic can adequately fit Fe(II) dissolution. Cadmium (Cd) is a common toxic heavy metal in the environment. Taking Cd(II) as a target contaminant, we systematically compared the performances of three Fe-based nanomaterials (nano zero valent iron, nZVI; sulfidated nZVI, S-nZVI; and nano FeS, nFeS) for Cd immobilization under anaerobic conditions. Effects of nanomaterials doses, initial pH, co-existing ions, and humic acid (HA) were examined. Under identical conditions, at varied doses or initial pH, Cd(II) removal by three materials followed the order of S-nZVI > nFeS > nZVI. At pH 6, the Cd(II) removal within 24 hours for S-nZVI, nFeS, and nZVI (dose of 20 mg/L) were 93.50%, 89.12% and 4.10%, respectively. The fast initial reaction rate of nZVI did not lead to a high removal capacity. The Cd removal was slightly impacted or even improved with co-existing ions (at 50 mg/L or 200 mg/L) or HA (at 2 mg/L or 20 mg/L). Characterization results revealed that nZVI immobilized Cd through coprecipitation, surface complexation, and reduction, whereas the mechanisms for sulfidated materials involved replacement, coprecipitation, and surface complexation, with replacement as the predominant reaction. A strong linear correlation between Cd(II) removal and Fe(II) dissolution was observed, and we proposed a novel pseudo-second-order kinetic model to simulate Fe(II) dissolution.     

Influence of uraniferous black shales on cadmium,molybdenum and selenium in soils and crop plants in the Deog-Pyoun-g area of Korea

The influence of naturally occurring uraniferous black shales on cadmium, molybdenum and selenium concentrations in soils and plants is examined. The possible implications of element concentrations to animal and human health are considered for the Deog-Pyoung area. Geochemical surveys have been undertaken within 13 river tributary valleys in the area underlain by uraniferous black shales and black slates or grey chlorite schists. Sampling of rocks, soils and plants has been carried out along transect lines within each valley. Samples were analysed for trace elements by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and for uranium by Neutron Activation Analysis (NAA). Soil pH, cation exchange capacity, loss on ignition and particle size distribution have been measured for selected samples. Average trace element concentrations of the Okchon uraniferous black shales were 6.3 μg g⁻¹ Cd, 136 μg g⁻¹ Mo and 8.6 μg g⁻¹ Se. Soils derived from these rocks tend to reflect their extreme geochemical composition. Trace element concentrations in alluvial soils derived in part from these black shales averaged 1.2 μg g⁻¹ Cd, 20 μg g⁻¹ Mo and 1.5 μg g⁻¹ Se. Trace element concentrations in plants were found to be influenced by those of soils. Cadmium accumulated in tobacco leaves up to 46 μg g⁻¹ (D.M.) and leafy plants such as lettuce contain up to 0.5 μg g⁻¹ Se (D.M.). In addition to total concentrations in soils, soil pH is a major factor influencing uptake of Mo into crop plants and soil texture for Se. Concentrations of trace elements in plants also varied between plant species. The relative concentrations of Cd were found to vary in the order tobacco > lettuce > red pepper > rice grain. Elevated concentrations of Cd in crop plants and in tobacco may possibly have deleterious effects on human health in this area. The low Cu:Mo ratio in rice stalk of 2.65:1 may be associated with disturbed Cu metabolism in ruminant animals which regularly consume this material.     

Contamination characteristics of trace metals in dust from different levels of roads of a heavily air-polluted city in north China

Concentrations of eight trace metals (TMs) in road dust (RD) (particles?<?25 μm) from urban areas of Xinxiang, China, were determined by inductively coupled plasma mass spectrometry. The geometric mean concentrations of Zn, Mn, Pb, As, Cu, Cr, Ni and Cd were 489, 350, 114, 101, 60.0, 39.7, 31.6, and 5.1 mg kg^?1, respectively. When compared with TM levels in background soil, the samples generally display elevated TM concentrations, except for Cr and Mn, and for Cd the enrichment value was 69.6. Spatial variations indicated TMs in RD from park path would have similar sources with main roads, collector streets and bypasses. Average daily exposure doses of the studied TMs were about three orders of magnitude higher for hand-to-mouth ingestion than dermal contact, and the exposure doses for children were 9.33 times higher than that for adults. The decreasing trend of calculated hazard indexes (HI) for the eight elements was As?>?Pb?>?Cr?>?Mn?>?Cd?>?Zn?>?Ni?>?Cu for both children and adults.     

Modelling of leachates from dolomitic mine tailings

The REDEQL.EPAK computer model was used to study speciation of Pb, Cd, Zn, and Ca in leachates from dolomitic Pb mine tailings. By allowing or disallowing precipitation of solids and equilibration of the modelled leachate with atmospheric C0₂, comparison of fresh and aged leachates was made. The effects of treatment of the tailings with phosphate containing fertilizer were studied through addition of P0₄ ^3– to the modelled solution. Equilibrium constants pertaining to metal ion-humic acid complexation were added to the thermodynamic data base of the model in order to study the effects of decaying plant material on tailings leachate.Initial leachate of the tailings is found to be supersaturated with Cd and Zn. Non-complexed (free) Cd²⁺ and Zn²⁺ is predicted to comprise most of the soluble form of these metals in the leachate; Pb is predicted to be present largely as PbCO₃ ion pair. Equilibration of the leachate with the atmosphere is predicted to lead to extensive precipitation of CdCO₃ and ZnSiO₃. Precipitation of Pb₅(PO₄)₃Cl is predicted at high PO₄ ^3– concentration and at low pH. Complexation by the humic acid is predicted to compete effectively with other ligands in the leachate for the metal ions. The results are compared with experimental findings.     

Metal remediation potential of naturally occurring plants growing on barren fly ash dumps

The present study aimed to elucidate the remediation potential of visibly dominant, naturally growing plants obtained from an early colonized fly ash dump near a coal-based thermal power station. The vegetation comprised of grasses like Saccharum spontaneum L., Cynodon dactylon (L.) Pers., herbs such as Tephrosia purpurea (L.) Pers., Sida rhombifolia L., Dysphania ambrosioides (L.) Mosyakin & Clemants, Chromolaena odorata (L.) King & H.E. Robins along with tree saplings Butea monosperma (Lam.) Taub. The growth of the vegetation improved the N and P content of the ash. Average metal concentrations (mg kg^?1) in the ash samples and plants were in order Mn (345.1)?>?Zn (63.7)?>?Ni (29.3)?>?Cu (16.8)?>?Cr (9.9)?>?Pb (1.7)?>?Cd (0.41) and Cr (58.58)?>?Zn (52.74)?>?Mn (39.09)?>?Cu (10.71)?>?Ni (7.45)?>?Pb (5.52)?>?Cd (0.14), respectively. The plants showed fly ash dump phytostabilization potential and accumulated Cr (80.19–178.11 mg kg^?1) above maximum allowable concentrations for plant tissues. Positive correlations were also obtained for metal concentration in plant roots versus fly ash. Saccharum spontaneum showed highest biomass and is the most efficient plant which can be used for the restoration of ash dumps.

     

Kinetics of hexavalent chromium reduction by iron metal

The kinetics of Cr(VI) reduction to Cr(III) by metallic iron (Fe⁰) was studied in batch reactors for a range of reactant concentrations, pH and temperatures. Nearly 86.8% removal efficiency for Cr(VI) was achieved when Fe⁰ concentration was 6 g/L (using commercial iron powder (< 200 mesh) in 120 min). The reduction of hexavalent chromium took place on the surface of the iron particles following pseudo-first order kinetics. The rate of Cr(VI) reduction increased with increasing Fe⁰ addition and temperature but inversely with initial pH. The pseudo-first-order rate coefficients (k _obs) were determined as 0.0024, 0.010, 0.0268 and 0.062 8 min^?1 when iron powder dosages were 2, 6, 10 and 14 g/L at 25°C and pH 5.5, respectively. According to the Arrehenius equation, the apparent activation energy of 26.5 kJ/mol and pre-exponential factor of 3 330 min^?1 were obtained at the temperature range of 288–308 K. Different Fe⁰ types were compared in this study. The reactivity was in the order starch-stabilized Fe⁰ nanoparticles > Fe⁰ nanoparticles > Fe⁰ powder > Fe⁰ filings. Electrochemical analysis of the reaction process showed that Cr(III) and Fe(III) hydroxides should be the dominant final products.