Two Experimental Methods to Determine the Speciation of Cadmium in Sediment from the River Neckar

The binding forms of Cd to an anaerobic sediment of low sulfide content from Lauffen reservoir (River Neckar, Germany) were studied using two different approaches, i. e. sequential extraction (modified from published protocols) and titrimetric study of the pH-dependent Cd release. Thermodynamic equilibrium calculations were applied to calculate both the release pattern of Cd during the titrations and the speciation of Cd within the single fractions of the extraction protocol. The calculations were based on measured sediment parameters such as hydrous ferric oxide (HFO), acid volatile sulfide, carbonate content and total Cd content, and the extractants (oxalate, acid etc.) used. The results of the two independent approaches coincided well in that they both assigned more than two thirds of the total Cd content to be adsorbed to organic matter. Cd bound as CdS is of little importance. Sequential extraction after a 3-month oxidation period at pH 7 revealed a shift of Cd from being mainly bound in stronger surface complexes with organic matter to being mainly bound in weaker surface complexes with organic matter and HFO, and thus becoming more bioavailable. This study suggests that the use of sequential extraction although being frequently criticized due to its operational character can be used to determine binding forms of metal ions if they are accompanied by 1) careful supporting experiments, 2) analysis of important sediment parameters, and 3) the use of thermodynamic equlibrium models which can help to understand Cd speciation within the extraction fractions.     

Eliminierung und Rückgewinnung von Metallionen aus Abwässern — eine Übersicht

The present state and the trends of the recovery of heavy metals from wastewaters are presented. The classical precipitation techniques are insatisfactory due to increases of solubility in the presence of impurity ions and/or complexing agents. At present, ion-exchange processes constitute the most frequently used method of metal recycling with an effective enrichment of metal ions. For the effective separation of metals from solutions of a low concentration the electrolytic reduction demands large electrode surface areas. In cells with fixed-bed or fluidized cathodes one can obtain specific electrode surface areas of some 10³ m²/m^m3. For the future, processes of extraction and especially membrane separation will gain in importance. In the past few years, a large number of highly selective metal extracting agents as well as the liquid membrane permeation with suitable carriers were developed. Combinations of membrane separation processes with chemical reactions may attain the same importance, as e.g. ultrafiltration in connection with the fixation of metal ions to watersoluble polymers. In the long run, especially techniques will prevail which will not only result in metal enrichment but also in the recovery of the raw material water.     

Distribution of trace metals in the Odra River system: Water–suspended matter–sediments

Extensive investigations of trace metals concentrations in water, suspended particulate matter (SPM) and bottom sediments of the whole Odra River system were carried out over the years 1997–2000. The vertical distribution of selected metals and their mobility were also studied in the sediment cores from upper and middle river sections. Significant levels of metal contamination were found. Median concentrations (Cd, Pb, Cu, Zn and As) in the SPM and sediments were (mg kg⁻¹) 7.1 and 8.9 Cd, 128 and 146 Pb, 81 and 119 Cu, 1198 and 1204 Zn, 48 and 54 As, respectively. The highest metal pollution of the Odra River solids was found with cadmium, zinc, lead and arsenic, showing high similarity in their frequency distributions in both SPM and sediments. Cd, Zn and As appear to be of particular concern because of the high levels, that appear to be bioavailable, and their high mobility. The exchangeable and carbonate chemical forms of Cd and Zn reached up to 50% of their total amount. Besides the determination of total metal concentration, the metal chemical forms in river solids were investigated. The results of very wide studies of the Odra River system through 4 years suggest that metal pollution decreased, especially for Zn, Pb and Cu. Among all metals studied in the Odra River sediments, substantial reductions of Cd contamination were observed neither in the period after ’97 flood, nor if compared with the earlier results obtained before ’97. No essential differences of the metal contents were observed among the samples for the same river compartment, from the same locality, taken within the five sampling campaigns. The pattern of spatial and vertical metal distributions in the river solids indicates that a variety of sources might be responsible for the contamination; very intensive, historical and current mining and smelting activities probably are the most important ones.     

Distribution and temporal variation of cadmium in the St. Lawrence river basin

Samples of raw water were collected at regular intevals at two transects in the St. Lawremce River and four of its tributaries from March to November 1991 and from April to June 1992. Water samples were analyzed for both the dissolved and the particulate phase for cadmium (Cd), organic carbon, iron and manganese. Mean dissolved Cd concentration was 10±5 ng/L and no spatial variability was observed. Higher concentrations were found during high flow periods, suggesting an uptake of cadmium by phytoplankton during summer. In addition, dissolved cadmium did not appear to be associated with either DOC, dissolved Fe or dissolved Mn. The mean particulate Cd concentration was 1.3±1.1 μg/g, with almost all stations presenting the same concentration except the Yamaska River, which had a concentration of 0.5±0.2 μg/g. Particulate Cd showed a negative correlation with suspended particulate matter and a positive correlation with particulate organic carbon and particulare manganese. Fifty-nine percent of the cadmium was found to be in the particulate phase. Partition coefficients for cadmium (Kd), organic carbon (Kc), iron (KdFe) and manganese (KdMn) were calculated for each sample. Log Kd varied from 3.9 to 5.9, with an average of 5.0±0.4. Log Kd decreased with increasing particulate, matter as did Log Kc and Log KdMn. No significant correlation was found between Log Kd and Log Kc, suggesting that the distribution of cadmium between the dissolved and the particulate phase is not influenced by the distribution of organic carbon. In contrast, positive correlations were observed between Log Kd, Log KdFe and Log KdMn. Cadmium distribution appears to be influenced by Fe and Mn distribution.     

Effects of Lime‐Based Waste Materials on Immobilization and Phytoavailability of Cadmium and Lead in Contaminated Soil

Low cost lime‐based waste materials have recently been used to immobilize metals in contaminated soils. This study was conducted to evaluate the effects of oyster shells and eggshells as lime‐based waste materials on immobilization of cadmium (Cd) and lead (Pb) in contaminated soil, as well as their effects on metal availability to maize plants (Zea mays L.). Oyster shells and eggshells were applied to soils at 1 and 5% w/w, after which they were subject to 420 days of incubation. The toxicity characteristic leaching procedure (TCLP) test was employed to determine the mobility of Cd and Pb in soils. The results showed that the addition of waste materials effectively reduced the metal mobility as indicated by the decrease in the concentration of TCLP‐extractable Cd and Pb, and this was mainly due to significant increases in soil pH (from 6.74 in untreated soil to 7.85–8.13 in treated soil). A sequential extraction indicated that the addition of such alkaline wastes induced a significant decline in the concentration of Cd in the exchangeable fraction (from 23.64% in untreated soil to 1.90–3.81% in treated soil), but it increased the concentration of Cd in the carbonate fraction (from 19.59% in untreated soil to 36.66–46.36% in treated soil). In the case of Pb, the exchangeable fraction was also reduced (from 0.67% in untreated soil to 0.00–0.01% in treated soil), and the fraction of Pb bound to carbonate was slightly increased (from 16.61% in untreated soil to 16.41–18.25% in treated soil). Phytoavailability tests indicated that the metal concentrations in the shoots of maize plant were reduced by 63.39–77.29% for Cd and by 47.34–75.95% for Pb in the amended soils, with no significant differences being observed for the amendment types and the application rates. Overall, these results indicate that oyster shells and eggshells can be used as low cost lime‐based amendments for immobilizing Cd and Pb in contaminated soils.     

Interaction of trace metals with natural particle surfaces: Comparison between adsorption experiments and field measurements

The distribution of the metal ions Zn and Pb between particulate and dissolved phase in river Glatt was studied by field measurements and compared with calculated simulations, using parameters obtained by adsorption experiments with natural suspended particulate material. Differences in distribution coefficients obtained from field data are observed in function of the sampling locations and of the composition of the particulate matter.Experiments in which metal ion solutions are titrated with a suspension of natural particles and analyzed by anodic stripping voltammetry, are interpreted in terms of binding capacities and conditional stability constants of Zn and Pb with the surface sites. Binding constants of a particular metal ion varied very little for all samples. We obtained mean values for the conditional average complex formation constants at pH 8 of: log^cond K _Pb = 9.44 ± 0.18 and log^cond K _Zn = 8.17 ± 0.20. At this pH, binding capacities of 5 10^–3 – 1.7 10^–2 mol/kg of particles were obtained for samples collected at different locations and times; organic material, iron and manganese oxides are considered to be the main components that control the adsorption to the particles.Distribution coefficients are calculated from the experimentally obtained binding capacities and conditional stability constants. Calculated distribution coefficients for Zn agree with those obtained from the field data and are not very sensitive to changes in the composition of the solution. Good agreement was obtained for lead as well; for some samples it was important to take two types of sites with different affinity into consideration.     

Reduktive Dehalogenierung von Chlorkohlenwasserstoffen während der anaeroben Stabilisierung von Hausmüll

Reductive Dehalogenation of Chlorinated Hydrocarbons during Anaerobic Stabilization of Municipal Wastes During sequential anaerobic digestion of municipal wastes, distinct biogeochemical phases exist which show different capabilities to transform halogenated hydrocarbons. Chlorophenols, tetrachloroethylene, and chloroanilines codisposed together with organic-rich waste substrates are reductively dehalogenated during methanogenic conditions. Lindane is degraded during acidogenesis as well as during methanogenesis. However, degradation in methanogenic leachates is faster by a factor of 10. The poor transformation potential during acidogenesis compared to subsequent transient methanogenic and stabile methanogenic phases cannot be explained by inadequate acclimation of prevailing microorganisms to the codisposed organochlorines. Thus, observed transformation capabilities are a pertinent feature of methanogenic leachates, probably due to prevailing low redox potential and/or presence of suitable microbial activities (not necessarily methanogenis). Dehalogenation of 2,3,4,6-tetrachlorophenol as a model compound is hampered in methanogenic leachate by addition of a surplus of sulfate and is completely suppressed by addition of molybdate which selectively inhibits sulfate reducing microorganisms. Competition for common electron donators (e.g. H₂) is discussed as an explanation of these results. The results point to sulfate reducing microorganisms being involved in reductive dehalogenation of chlorophenols.     

Reuse of Drinking Water Treatment Waste for Remediation of Heavy Metal Contaminated Groundwater

Lime softening produces an estimated 10,000 metric tons of dry drinking water treatment wastes (DWTW) per year, costing an estimated one billion dollars annually for disposal worldwide. Lime softening wastes have been investigated for reuse as internal curing agents or supplementary cementitious materials in concrete as well as a high-capacity sorbent for heavy metal removal. Lead, cadmium, and zinc are common heavy metals in groundwater contaminated by mine tailings. Cement-based filter media (CBFM) are a novel material-class for heavy metal remediation in groundwater. This study investigated the incorporation of DWTW as a recycled, low-cost additive to CBFM for the removal of lead, cadmium, and zinc. Jar testing at three different metal concentrations and breakthrough column testing using synthetic groundwater were performed to measure removal capacity and reaction kinetics. Jar testing results show as DWTW content increases at low concentrations, removal approaches 100% but at high metal concentrations removal decreases due to saturation or exhaustion of the removal mechanisms. Removal occurs through the formation of metal carbonate precipitates, surface sorption, and ion exchange with calcium according to the preferential series Pb⁺² > Zn⁺² > Cd²⁺. Removal kinetics were also measured through column testing and exceeded estimated calculations derived from batch jar testing isotherms due to the large formation of oolitic metal carbonates. Lead, cadmium, and zinc was concentrated in the column precipitates from 0.29, 0.23, and 20.0 μg/g in the influent solution to approximately 200, 130, 14,000 μg/g in the reacted DWTW-CBFM. The control and DWTW-CBFM columns had statically similar removal for zinc and lead. In the DWTW-CBFM, cadmium had decreased removal of approximately 25% due to proportionately decreased hydroxide content from cement replacement with 25% DWTW. This study shows the potential for DWTW as an enhancement to CBFM, thereby valorizing an otherwise waste material. Furthermore, the concentrative abilities of CBFM through precipitate and oolitic mineral formation could provide a minable waste product and close the waste-product cycle for DWTW.     

Cd, Cr, Cu, Ni and Pb in the water column and sediments of the Ob-Irtysh Rivers, Russia

Concentrations of Cd, Cr, Cu, Ni and Pb were determined in filtered water, suspended particulate matter, and bottom sediments from a 2000 km section of the Ob and Irtysh Rivers. Dissolved Cd, Cr, Cu and Ni concentrations are similar to, or higher than, results from other Russian Arctic and large world river-estuaries. Concentrations of Cd, Cr, Cu, Ni and Pb in suspended particulate matter are generally comparable to results from other Russian Arctic and large world rivers and estuaries. Comparison of trace metal ratios in crustal material and suspended particulate matter and bottom sediment suggests that the source of Cr, Cu and Ni is continental weathering. Particulate Cd and Pb are elevated relative to their crustal abundance, suggesting a source of these metals to the Ob-Irtysh in addition to continental weathering.     

Trace metal solubility in an anoxic fjord

Intermittent anoxia in the Saanich Inlet water column provides an easily accessible marine O₂/H₂S interface to study the response of metals to both a steep redox gradient and the availability of reactive reduced sulfur species. Our study indicates a strong anoxic zone sink for copper and cadmium and the characteristically enhanced solubility of manganese and iron. Thiosulfate and sulfite are below detection limits (1 μM and 0.1 μM, respectively) and thus not important in metal complexation. Elemental sulfur concentrations are high at the oxic/anoxic interface and throughout the anoxic zone, indicating the potential for metal complexation by polysulfides. A thermodynamic approach employing metal sulfide formation and class specific sulfidic ligand complexation to generate equilibrium profiles adequately describes the solubility of iron, copper, and cadmium. The extension of this scheme to other transition and class B metals in other marine environments with redox fronts is suggested.     

Effects of organic mineral fertiliser on heavy metal migration and potential carbon sink in soils in a karst region

Heavy metal pollution in karst mountainous area of Guizhou has spread due to the long-term exploitation of mineral resources and the improper disposal of environmentally hazardous waste. Heavy metals are characterised by non-degradation, strong toxicity, and constant accumulation, posing a grave threat to karst mountain fragile soil ecosystem. To reduce the harm caused by heavy metal pollution and damage to agricultural products, research was undertaken on the basis of previous work by simulating pot experiments on pak choi cabbage(Brassica rapa chinensis)planted in Cd-contaminated soil: different amounts of organic mineral fertilisers(OMF) compared with chemical fertiliser(CF) were used and by detecting the amount of heavy metal in the mature vegetable, a better fertilisation strategy was developed. The results showed that the Cd content in vegetables grown with CF was 23.70 mg/kg,while that of vegetables grown with OMF and bacterial inoculant was the lowest at 15.13 mg/kg. This suggests that the use of OMF and microbes in karst areas not only promotes plant growth but also hinders plant absorption of heavy metal ions in the soil. In addition, through the collection of pot leachate, the detection of water chemistrycharacteristics, and the calculation of the calcite saturation index, it was found that the OMF method also induces certain carbon sink effects. The results provide a new way in which rationalise the use of OMFs in karst areas to alleviate soil heavy metal pollution and increase soil carbon sequestration.     

Some aspects of vanadium and chromium chemistry in the English Channel

Dissolved and particulate vanadium and chromium concentrations along a transect between Cherbourg and the Isle of Wight were investigated in the English Channel. Seawater samples were collected at two different depths (surface and bottom) at five sampling stations during five cruises carried out between September 1994 and September 1995. Calculated mass flows through this Channel section were 7600 T yr⁻¹ for vanadium (about 66% was in the dissolved phase) and 1650 T yr⁻¹ for chromium (about 50% was in the dissolved phase). Dissolved chromium concentrations do not vary significantly along the transect. Seasonal variations in chromium distribution linked to biotic parameters were noted during the September 1994 cruise, when a significant relationship between particulate chromium and algal organic carbon was found. In addition, dissolved Cr (III) and Cr (VI) were well correlated with both algal and terrestrial organic matter. In the May cruise, during phytoplanktonic decay, particulate chromium was correlated with the detritic and bacterial organic fractions. These observations suggest interactions between chromium and biotic material. During the winter period, no relationship between chromium and POC was found. Dissolved and particulate vanadium concentrations varied, respectively, between 15 and 28 nmol l⁻¹ and 2–32 nmol l⁻¹. Values of dissolved vanadium showed depletion in the Channel with respect to oceanic waters. This loss in dissolved vanadium was higher near the English coast, but was compensated for by the increase in the particulate vanadium. There was no clear relationship between dissolved vanadium and algal organic carbon and it is inferred that the vanadium transfer cannot be explained by trapping with biotic material. On the other hand, the dissolved vanadium depletion could be attributed to the presence of ferric oxyhydroxide phases in particles, which have strong adsorbing properties for a range of dissolved metal ions.     

Heavy metal inflow into the floodplains at the mouth of the river Weiße Elster (Central Germany)

From 1998 to 2002 investigations were carried out to estimate both the quantity and quality (heavy metal contents) of suspended matter loads discharged into a floodplain area measuring approx. 5 km² of the Central German river Weiße Elster, a tributary of the river Saale in the Elbe river basin. Flood sediments, suspended particulate matter, and floodplain soils were investigated especially for the main pollutants Cd, Zn, Cu, Pb, Cr, and Hg. Supplementary gamma spectroscopy examinations were performed to help to identify the age of deposits in order to estimate sedimentation rates for last decades. The recent flood sediments are contaminated by up to 33 times the geogenic background (Cd). Up to 55% of the total annual SPM load of the river Weiße Elster is relocated into the investigated retention area in the flood‐stricken year 2002. The sedimentation rates for the last 50 years vary between 0.5 mm/a and 1 mm/a in far away and rarely flooded parts and between 1 mm/a and 2 mm/a in the frequently flooded parts of the inflow of the retention area.     

Spatial and Temporal Distribution of Dust‐Bound Trace Metal Elements around Kuhdasht Watershed Area in Iran

Dust, as a source of trace metal elements, affects the health of society. The spatial and temporal concentrations of dust‐bound trace metals (Cd, Pb, Ni, Zn, Cu, and Mn) in Kuhdasht watershed (456 km²), Lorestan Province, Iran, is investigated. Dust is collected using glass traps placed in ten research stations in the region. The spatial and temporal distribution of dust trace metals are plotted using ARC‐GIS. The highest and the lowest concentrations of Zn (9751150 mg kg^?1), Pb (46.352.9 mg kg^?1), and Cd (2.443.30 mg kg^?1) are obtained in winter, of Ni (98110 mg kg^?1) and Cu in autumn (16.053.5 mg kg^?1), and of Mn in summer (385505 mg kg^?1). The spatial concentrations of dust‐bound trace metals indicate all, except Cu, show a decreasing trend from the mountains toward the plains, similar to that of soil and of dust, except for Zn, which shows higher concentrations in dust than in soil. The potential sources of dust‐bound trace metals and their rate of contamination are also investigated using the enrichment and contamination factors. The major sources of Cd and Zn in the dust of watershed are due to anthropogenic activities or from activities outside the borders.     

Chemical forms of heavy metal contaminants in sediments of Miyun reservoir

The chemical forms, spatial distribution and sources of As, Hg, Cd, Pb and Zn in sediments of the Miyun reservoir were studied. The results of sequential extraction demonstrate that most of As, Pb and Zn were bound to the residual fraction, Hg was associated with the sulfide fraction while Cd was associated with the carbonate fraction and the residual fraction. On the vertical profiles the concentrations of the heavy metals in total and each fractions mostly decreased with increasing depths in sediments, suggesting that the heavy metals input from the upstream watershed increases yearly. Summation of the residual fraction, the sulfide fraction and the carbonate fraction accounts for 60.03%―85.60% of the total heavy metal contents in the sediments, which represent the geochemical background values of the elements and relate closely to soil erosion. Results of the main factor analysis show that most sediments of the reservoir come from the upstream soil erosion, the point source pollution and domestic waste. Moreover, the microbial activities taking place on the sediment-water interface are also one of the major factors to cause the increasing content of the organic matter fraction and the iron-manganese oxide fraction. Environmental change of the reservoir water could make the removability of the heavy metals increase, leading to the increase of their concentrations in pore water in sediments, and imperiling water quality of the reservoir.     

Transformation of Tobacco with ScMTII Gene‐Enhanced Cadmium and Zinc Accumulation

Genetic transformation is gaining importance for developing plant types suitable to metal accumulate and/or hyperaccumulate. In this study, the transgenic tobacco plant which transferred the ScMTII gene from Saccharomyces cerevisiae to wild type tobacco cultivar Petite Havana (SR1) was grown on soils with low and high cadmium (Cd) and zinc (Zn) concentrations in a growth chamber for 6 weeks and compared to wild type tobacco for Cd and Zn accumulation. Cadmium and Zn accumulations in the transgenic and wild type tobacco plants were increased with the increasing Cd and Zn concentrations. Unlike Zn, the transgenic plant accumulated significantly higher amount of Cd compared to the wild type control plants. Shoot Cd concentrations of transgenic tobacco in higher Cd dosages reached the above the hyperaccumulation threshold value of 100 mg Cd kg^?1 in the dry weight (DW). Transgenic tobacco accumulated 354, 400, 372, and 457 mg Cd kg^?1 DW, for 10, 20, 40, and 80 mg Cd kg^?1 soil treatments, respectively. These values are 3.5–4.5‐fold higher than that of Cd hyperaccumulation threshold value. With 10 mg kg^?1 Cd treatment, the bioconcentration factor (BCF) of transgenic tobacco plants for Cd reached up to 35 in which the threshold value for BCF should be at least 10. Our results showed that the transgenic tobacco may be used as a good Cd hyperaccumulator plant and for phytoextraction of Cd contaminated soils, but not for Zn.     

Hysteresis‐based analysis of overland metal transport

Introducing a concept of equivalent mass depth of flow, this study describes the phenomenon of non‐point source pollutant (metal) transport for pavement (or overland) flow in analogy with wave propagation in wide open channels. Hysteretic and normal mass rating curves are developed for runoff rate and mass of 12 dissolved and particulate‐bound metal elements (pollutants) using the rainfall‐runoff and water quality data of the 15 × 20 m² instrumented pavement in Cincinnati, USA. Normal mass rating curves developed for easy computation of pollutant load are found to be of a form similar to Manning's, which is valid for open channel flows. Based on the hysteresis analysis, wave types for dissolution and mixing of particulate‐bound metals are identified. The analysis finds that the second‐order partial‐differential equation normally used for metal transport does not have the efficacy to describe fully the strong non‐linear phenomena such as is described for various metal elements by dynamic waves. In addition, the proportionality concept of the popular SCS‐CN concept is extended for determining the potential maximum metal mass M_p of all the 12 elements transported by a rain storm and related to the antecedent dry period (ADP). For the primary metal zinc element, M_p is found to increase with the ADP and vice versa. Copyright © 2003 John Wiley & Sons, Ltd.     

Effects of FPOM size and quality on aquatic heterotrophic bacteria

Mechanical and biological processing in aquatic systems converts coarse particulate organic matter (CPOM) into fine particulate organic matter (FPOM). Other sources of particles with different size classes include flocculated dissolved matter, algae and soil particles. The relative magnitudes of these inputs are influenced by the degree of allochthony of a lake or stream. The size-reactivity hypothesis, formulated for dissolved organic matter, postulates that bacterial degradation rates are higher with high-molecular-weight fractions than with low-molecular-weight fractions. In this study, we investigated the effect of particle size on degradation of POM and on freshwater bacterial communities. We generated leaf-derived particle size classes of the same age (same diagenesis status) but differing in quality (maple and beech leaves). Contrary to our expectations, we found a strong effect of particle size and no significant effect of substrate quality on community respiration which decreased at smaller particle size, on C:N ratios which declined with particle size, and on δ¹⁵ N which showed a decreasing trend (though not significant) at smaller particle size in beech leaves. By contrast, bacterial community structure and ∂¹³C values responded mainly to particle quality. Bacterial biomass, estimated by qPCR, was affected by complex interactions between particle size and quality. These findings open an unanticipated perspective on the size-reactivity hypothesis for particulate organic matter.     

Acute toxicity of cadmium to Channa punctatus (BLOCH)

Effects of acute cadmium poisoning on survival, its residual values and histopathology in certain organs of a freshwater airbreathing fish, Channa punctatus (BLOCH ) were investigated. The threshold concentration, MATC and LC₅₀ values obtained from 96 h static bioassay, revealed that Channa is more susceptible to cadmium ions at higher temperature. The atomic absorption spectrophotometric determination of cadmium residues differed significantly in organs of specimens having survived and died after 96 h of exposure. The gill accumulate the highest amount of cadmium, the liver accumulated a slightly smaller amount than the gill, while the kidney accumulated the least. The histopathological lesions subjected to sublethal (5.2 mg/l Cd) and lethal (8.4 mg/l Cd) concentrations of cadmium were: detachment and rupture of lamellar epithelium, collapse of pillar cells and hypertrophy in mucus producing gland cells in the gill; vacuolization and coagulative necrosis in hepatic cells of the liver; and expansion, necrosis and accumulation of cellular debris in renal tubules of the kidney. The probable causes for death of fish due to cadmium ions have been discussed.     

Utilizing Natural Liner Materials for Heavy Metal Removal in Simulated Landfill Conditions

Inorganic industrial waste landfills have the potential to contaminate subsurface groundwater supplies through migration of leachates down to the water table and into groundwater aquifers, despite the use of compacted low permeability clay or polyethene liners. This paper aims the removal of Cu²⁺ and Zn²⁺ in the leachate from an industrial waste landfill using natural materials (natural zeolite, expanded vermiculite, pumice, illite, kaolinite, and bentonite) as a liner material. Cu²⁺ and Zn²⁺ concentrations for all treatments decreased during the process. Of all the different natural materials, natural zeolite, expanded vermiculite and pumice, with bentonite, were effective in removing Cu²⁺ and Zn²⁺ present in the leachate. However, the use of illite and kaolinite with bentonite as liner materials could be of disadvantage in Cu²⁺ and Zn²⁺ removal from leachate. The adsorption kinetic models were also tested for the validity. The second order kinetics with the high correlation coefficients best described adsorption kinetic data.