Enhancement of phenanthrene adsorption on a clayey soil and clay minerals by coexisting lead or cadmium

Phenanthrene is commonly present together with heavy metals at many contaminated sites. This study investigated the influence of coexisting lead (Pb²⁺) or cadmium (Cd²⁺) on phenanthrene adsorption on soils. Batch experiments were conducted under different geochemical conditions including pH, mineral structure, organic matter content, and varying amounts of heavy metals. The results showed that the presence of heavy metals in solution at a fixed pH of 5.8 ± 0.1 enhanced phenanthrene adsorption, the extent of which was closely related to the concentrations and the electro-negativity of the metals. The enhancement on phenanthrene adsorption was positively correlated to the amount of adsorbed metals. Although Cd²⁺ is a softer Lewis acid, Pb²⁺ displayed a more significant effect as it was adsorbed to a greater extent on the soil surfaces. Thus, density of cation accumulation appears to be more influential than metal softness in enhancing phenanthrene adsorption. Moreover, with a portion of organic matter removed by heating at 550 °C, there was a stronger enhancement of phenanthrene adsorption by coexisting Pb²⁺, indicating an increasingly dominant mechanisms associated with Pb²⁺ at a lower organic matter content. Similar enhancement phenomenon was observed on bentonite and kaolinite, probably resulting from the cation-π bonding between the adsorbed soft metal cations and the aromatic ring of phenanthrene in solution. The desorption experiments further suggested that the bonding of phenanthrene adsorption was strengthened in the presence of Pb²⁺ and that a larger proportion of adsorbed phenanthrene remained on the soils (residual fraction) even after sequential methanol extractions. Further spectroscopic analyses and surface characterization are required to provide direct evidence of the formation and relative significance of cation-π bond for phenanthrene adsorption.     

Quantitative assessment of the toxic effects of heavy metals on 1,2-dichloroethane biodegradation in co-contaminated soil under aerobic condition

1,2-Dichloroethane (1,2-DCA) is one of the most hazardous pollutant of soil and groundwater, and is produced in excess of 5.44 × 10⁹ kg annually. Owing to their toxicity, persistence and potential for bioaccumulation, there is a growing interest in technologies for their removal. Heavy metals are known to be toxic to soil microorganisms at high concentrations and can hinder the biodegradation of organic contaminants. In this study, the inhibitory effect of heavy metals, namely; arsenic, cadmium, mercury and lead, on the aerobic biodegradation of 1,2-DCA by autochthonous microorganisms was evaluated in soil microcosm setting. The presence of heavy metals was observed to have a negative impact on the biodegradation of 1,2-DCA in both soil samples tested, with the toxic effect being more pronounced in loam soil, than in clay soil. Generally, 75 ppm As³⁺, 840 ppm Hg²⁺, and 420 ppm Pb²⁺ resulted in 34.24%, 40.64%, and 45.94% increase in the half live (t_½) of 1,2-DCA, respectively, in loam soil, while concentrations above 127.5 ppm Cd²⁺, 840 ppm Hg²⁺ and 420 ppm of Pb²⁺ and less than 75 ppm As³⁺ was required to cause a >10% increase in the t_½ of 1,2-DCA in clay soil. A dose-dependent relationship between degradation rate constant (k₁) of 1,2-DCA and metal ion concentrations was observed for all the heavy metals tested, except for Hg²⁺. This study demonstrated that different heavy metals have different impacts on the degree of 1,2-DCA degradation. Results also suggest that the degree of inhibition is metal specific and is also dependent on several factors including; soil type, pH, moisture content and available nutrients.     

Interactions of copper and pyrene on phytoremediation potential of Brassica juncea in copper–pyrene co-contaminated soil

Phytoremediation which is a plant based remediation process is an emerging technology for treating inorganic (heavy metals) as well as organic pollutants. It may also be suitable for remediation of sites co-contaminated with heavy metals and organics which have become more prevalent. A glasshouse experiment was carried out to investigate the effect of 50 and 100 mg kg^?1 of copper or 250 and 500 mg kg^?1 of pyrene and the combined effect of copper and pyrene on the growth of Brassica juncea together with the uptake and accumulation of copper as well as dissipation of pyrene. Results showed a negative effect of copper–pyrene co-contamination on shoot and root dry matter and an inhibition of copper phytoextraction. Pyrene was significantly decreased in planted and non-planted soils accounting for 90–94% of initial extractable concentration in soil planted with B. juncea and 79–84% in non-planted soil which shows that the dissipation of pyrene was enhanced with planting. The occurrence of copper tended to increase the residual pyrene in planted soil, however in the presence of high concentration of Cu (100 mg kg^?1), the residual pyrene concentration in soil were similar to those in unplanted soil. This may suggest that changes in the root physiology or rhizospheric microbial activity resulting from Cu stress could be an impediment to pyrene dissipation. The inhibition of Cu phytoextraction and degradation of pyrene by B. juncea under co-contamination may reduce the viability of phytoremediation in sites containing multiple pollutants.     

Influence of Phenanthrene on Cadmium Toxicity to Soil Enzymes and Microbial Growth (5 pp)

Background Many contaminated sites contain a variety of toxicants. Risk assessment and the development of soil quality criteria therefore require information on the interaction among toxicants. Interactions between heavy metals are relatively well studied, but little is known about those between heavy metals and polycyclic aromatic hydrocarbons (PAHs). Methods 0.1 mg/kg dry soil phenanthrene alone or phenanthrene plus 10 mg/kg cadmium (Cd) were added to soil to determine the influence of phenanthrene on Cd toxicity to soil enzymes (invertase, urease, dehydrogenase and phosphatase) and microorganisms (fungi, bacteria and actinomycete) in paddy soil. Results and Discussion 0.1 mg/kg phenanthrene did not reduce the number of microorganisms. However, the addition of phenanthrene to soil with Cd enhanced the Cd toxicity to soil enzymes and microorganisms. This deleterious effect was seen to mainly affect the growth of fungi and the activity of invertase, urease and dehydrogenase. The order of combined inhibition of Cd and phenanthrene was fungi>bacteria>actinomycete. Conclusion The presence of phenanthrene might enhance the toxicity of Cd to soil microorganisms. Phenanthrene can easily be used by the soil actinomycetes as a source of carbon and energy and the finding may be supportive to the development of bioremediation techniques.     

高岭土模拟铜污染土壤电动力学修复

采用电动力学方法修复重金属污染土壤。研究中采用高岭土模拟铜污染土壤，结合电动力学修复理论，考察了不同电压、添加络合剂条件下铜的修复效果。结果表明，当电压强度为0．5V／cm时，最靠近阴极部分的土壤中Cu^2＋的C／C。为1．596，当电压强度为1V／cm时，C／C0为2．245，说明适当提高电压强度能够有效的增加Cu^2＋的迁移效果；土壤中未加入络合剂时，Cu^2＋大部分集中在第5段土壤中，C／C0为1．339，在土壤中加入络合剂以后Cu^2＋大部分集中在靠近阴极部分的土壤中，C／C。为1．716，说明在污染土壤中加入一定量的络合剂可以与Cu^2＋结合生成螯合物，提高Cu^2＋的迁移效果。     

Heavy metal speciation and mobility assessment of arid soils in the vicinity of Al Ain landfill, United Arab Emirates

Sixty-four surface soil samples taken in the vicinity of Al Ain landfill were analysed for cadmium, chromium, copper, nickel, lead and zinc by inductively coupled plasma spectroscopy. Extraction techniques were used to establish the association of the total concentrations of the six metals in the soil samples with their contents in the exchangeable, carbonate, iron/manganese oxides, and residual fractions. In the investigated soils, the recorded concentrations were as follows: 0.043 mg kg^-1 for cadmium, 19.1 mg kg^-1 for chromium, 53.3 mg kg^-1 for copper, 60 mg kg^-1 for nickel, 13.7 mg kg^-1 for lead, and 117 mg kg^-1 for zinc. Cadmium, chromium, nickel, lead and zinc concentrations in the investigated soil samples reflect the natural background values in shale, whereas copper is slightly enriched. I-geo (geoaccumulation index) values of the metals in the soils under study indicate that they are uncontaminated with cadmium, chromium, nickel, lead and zinc, but contaminated to moderately contaminated with copper. Heavy metal contents in the sediments were found to be significantly influenced by different physico-chemical parameters. The effect of these parameters can be arranged in the following order: clay fraction > carbonate fraction > silt fraction > organic matter fractions. A sequential extraction procedure showed that the total concentrations of the heavy metals are largely bound to the residual phase (retained 71.4% of cadmium, 77.8% of chromium, 75% of copper, 47% of nickel, 62.8% of lead, and 75.8% of zinc). A likely sequence of mobility in the investigated soils is as follows: chromium > lead > nickel > cadmium > zinc > copper.     

Efficiency of lipopeptide biosurfactants in removal of petroleum hydrocarbons and heavy metals from contaminated soil

This study describes the potential application of lipopeptide biosurfactants in removal of petroleum hydrocarbons and heavy metals from the soil samples collected from industrial dumping site. High concentrations of heavy metals (like iron, lead, nickel, cadmium, copper, cobalt and zinc) and petroleum hydrocarbons were present in the contaminated soil samples. Lipopeptide biosurfactant, consisting of surfactin and fengycin was obtained from Bacillus subtilis A21. Soil washing with biosurfactant solution removed significant amount of petroleum hydrocarbon (64.5 %) and metals namely cadmium (44.2 %), cobalt (35.4 %), lead (40.3 %), nickel (32.2 %), copper (26.2 %) and zinc (32.07 %). Parameters like surfactant concentration, temperature, agitation condition and pH of the washing solution influenced the pollutant removing ability of biosurfactant mixture. Biosurfactant exhibited substantial hydrocarbon solubility above its critical micelle concentration. During washing, 50 % of biosurfactant was sorbed to the soil particles decreasing effective concentration during washing process. Biosurfactant washed soil exhibited 100 % mustard seed germination contradictory to water washed soil where no germination was observed. The results indicate that the soil washing with mixture of lipopeptide biosurfactants at concentrations above its critical micelle concentration can be an efficient and environment friendly approach for removing pollutants (petroleum hydrocarbon and heavy metals) from contaminated soil.     

Mitigation effects of silicon rich amendments on heavy metal accumulation in rice (Oryza sativa L.) planted on multi-metal contaminated acidic soil

The mechanisms of stabilization by silicon-rich amendments of cadmium, zinc, copper and lead in a multi-metal contaminated acidic soil and the mitigation of metal accumulation in rice were investigated in this study. The results from a pot experiment indicated that the application of fly ash (20 and 40 g kg⁻¹) and steel slag (3 and 6 g kg⁻¹) increased soil pH from 4.0 to 5.0-6.4, decreased the phytoavailability of heavy metals by at least 60%, and further suppressed metal uptake by rice. Diffusion gradient in thin-film measurement showed the heavy metal diffusion fluxes from soil to solution decreased by greater than 84% after remediation. X-ray diffraction analysis indicated the mobile metals were mainly deposited as their silicates, phosphates and hydroxides in amended treatments. Moreover, it was found metal translocation from stem to leaf was dramatically restrained by adding amendments, which might be due to the increase of silicon concentration and co-precipitation with heavy metals in stem. Finally, a field experiment showed the trace element concentrations in polished rice treated with amendments complied with the food safety standards of China. These results demonstrated fly ash and steel slag could be effective in mitigating heavy metal accumulation in rice grown on multi-metal contaminated acidic soils.     

Computational spectroscopic study of copper, cadmium, lead and zinc interactions in the environment

Molecular modelling has been used to investigate the interactions of various heavy metals, in order to understand and possibly to control the nature and behaviour of metals, especially in the aquatic environment. The interactions of copper, cadmium, lead and zinc with organic acids were studied using density functional theory (DFT) calculations. Carboxylic acid was used as a model molecule. The structure of each metal carboxylate was optimized and the vibrational spectrum calculated. The results indicate that there is a shift in the calculated v_S(C=O) of metal carboxylates compared with that of carboxylic acid. It was also found that hexaaqua structures of both cadmium and zinc are stable whereas those of copper and lead are not. Furthermore, dipole moment calculations indicate that cadmium carboxylate dihydrate is more representative of cadmium interactions in the aquatic environment. Moreover, hexaaquo cadmium could further interact with surrounding molecules in the aquatic environment.     

Cadmium and lead bioavailability and their effects on polycyclic aromatic hydrocarbons biodegradation by spent mushroom substrate

Bioremediation of mixed metal–organic soil pollution constitutes a difficult task in different ecosystems all around the world. The aims of this work are to determine the capacity of two spent mushroom substrates (Agaricus bisporus and Pleurotus ostreatus) to immobilize Cd and Pb, to assess the effect of these metals on laccase activity, and to determine the potential of spent A. bisporus substrate to biodegrade four polycyclic aromatic hydrocarbons (PAH): fluorene, phenanthrene, anthracene, and pyrene, when those toxic heavy metals Cd and Pb are present. According to adsorption isotherms, spent P. ostreatus and A. bisporus substrates showed a high Pb and Cd adsorption capacity. Pb and Cd interactions with crude laccase enzyme extracts from spent P. ostreatus and A. bisporus substrates showed Cd and Pb enzyme inhibition; however, laccase activity of A. bisporus presented lower inhibition. Spent A. bisporus substrate polluted with PAH and Cd or Pb was able to biodegrade PAH, although both metals decrease the biodegradation rate. Spent A. bisporus substrate contained a microbiological consortium able to oxidize PAH with high ionization potential. Cd and Pb were immobilized during the bioremediation process by spent A. bisporus substrate. Consequently, spent A. bisporus substrate was adequate as a multi-polluted soil bioremediator.     

Influence of clay on the adsorption of heavy metals like copper and cadmium on chitosan

The influence of clay on the adsorption of heavy metals like copper and cadmium on chitosan from simulated industrial wastewater is evaluated. Chitosan–clay blend with ratio of (1:1), (1:2), and (2:1) have been prepared, and these were used as membranes to remove copper and cadmium ions from synthetic industrial wastewater. The chemical parameters for quantities of adsorption of heavy metal contamination have been done, and the kinetics of adsorption has also been carried out. Clay provides enough absorbable sites to overcome mass transfer limitations. The number of absorbable sites for cadmium is more compared to copper, and thus the rate of recovery of cadmium is faster than copper, and the percentage removal of cadmium is more than copper at all times on clay over nylon 6. This difference indicates the influence of clay in the adsorption of heavy metals in comparison to synthetic polymer nylon 6. Rate constant for first-order kinetics of adsorption, k ₁, for copper and cadmium is less than that of clay, which clearly indicates that clay, which is a natural polymer, is more kinetically favored compared to synthetic polymer. The difference in the intraparticle diffusion in both the natural and synthetic polymer is not much, and it suggests that the particle diffusion mechanism is the same in both cases. Copper and cadmium recovery is parallel at all times. The percentage of removal of copper increased with an increase in pH from 3 to 5. In the case of cadmium containing wastewater, the maximum removal of metal occurred at pH 5. The uptake amount of Cu²⁺ ions on chitosan increased rapidly with increasing the contact time from 0 to 360 min and then reaches equilibrium after 360 min, and the equilibrium constant for copper and cadmium ions are more or less the same for the adsorption reaction. There are more adsorption sites for cadmium in the presence of clay and mass transfer limitation is avoided without resorting to rotation, which is the highlight of the present work. And more so, this is pronounced in the case of natural polymer compared to synthetic polymer.     

Copper and cadmium removal from synthetic industrial wastewater using chitosan and nylon 6

Purpose

Chitosan with nylon 6 membranes was evaluated as adsorbents to remove copper and cadmium ions from synthetic industrial wastewater.

Methods

Chitosan and nylon 6 with glutaraldehyde blend ratio with (1:1+Glu, 1:2+Glu, and 2:1+Glu) have been prepared and these were used as membranes to remove copper and cadmium ions from synthetic industrial wastewater. Characterization of the synthesized membrane has been done with FTIR, XRD, TGA/DTA, DSC, and SEM. Chemical parameters for quantities of adsorption of heavy metal contamination have been done and the kinetics of adsorption has also been carried out.

Results

The optimal pH for the removal of Cd(II) and Cu(II) using chitosan with nylon 6. Maximum removal of the metals was observed at pH 5 for both the metals. The effect of adsorbent dose also has a pronounced effect on the percentage of removal of the metals. Maximum removal of both the metals was observed at 5 g/100 ml of the adsorbent.

Conclusion

Copper and cadmium recovery is parallel at all time. The percentage of removal of copper increased with increase in the pH from 3 to 5. In the case of cadmium containing wastewater, the maximum removal of metal occurred at pH 5. The uptake amount of Cu²⁺ ions on chitosan increased rapidly with increasing contact time from 0 to 360 min and then reaches equilibrium after 360 min; the equilibrium constant for copper and cadmium ions is more or less the same for the adsorption reaction.     

Phenanthrene degradation in Arthrobacter sp. P1-1: initial 1,2-, 3,4- and 9,10-dioxygenation, and meta- and ortho-cleavages of naphthalene-1,2-diol after its formation from naphthalene-1,2-dicarboxylic acid and hydroxyl naphthoic acids

Arthrobacter sp. P1-1, isolated from a polycyclic aromatic hydrocarbon (PAH)-contaminated site in Hilo, HI, USA, can decompose phenanthrene (40 mg l⁻¹) completely within 7 days. A detailed phenanthrene metabolism map was constructed based on metabolite analysis and replacement cultures. Initial dioxygenation occurs on 1,2-, 3,4-, and 9,10-C of phenanthrene, dominantly on 3,4-C positions. Rapid accumulation of 5,6- and 7,8-benzocoumarin suggests that phenanthrene-1,2- and -3,4-diols mainly undergo meta-cleavage. However, a trace amount of o-carboxyvinylnaphthoates and diphenic acid indicates a limited extent of ortho-cleavage of the diols. Naphthalene-1,2-diol, as a common and converged metabolite, was formed from 1-[(E)-2-carboxyvinyl]-2-naphthoic acid, naphthalene-1,2-dicarboxylic acid, and 1-hydroxy-2-naphthoic acid in separate culture tests. Naphthalene-1,2-diol is then degraded in a dominant phthalic acid pathway and a minor salicylic acid pathway. Several metabolites of phthalic acid were found, while no salicylic acid metabolites were detected. The strain P1-1 likely has a very diverse set of PAH-degrading enzymes or the enzymes having relaxed substrate-specificity.     

Study of metabolites from the degradation of polycyclic aromatic hydrocarbons (PAHs) by bacterial consortium enriched from mangrove sediments

The PAH metabolites produced during degradation of fluorene, phenanthrene and pyrene by a bacterial consortium enriched from mangrove sediments were analyzed using the on-fiber silylation solid-phase microextraction (SPME) combining with gas chromatography–mass spectrometry (GC–MS) method. Seventeen metabolites at trace levels were identified in different PAH degradation cultures based on the full scan mass spectra. In fluorene degradation cultures, 1-, 2-, 3- and 9-hydroxyfluorene, fluorenone, and phthalic acid were detected. In phenanthrene and pyrene degradation cultures, various common metabolites such as phenanthrene and pyrene dihydrodiols, mono-hydroxy phenanthrene, dihydroxy pyrene, lactone and 4-hydroxyphenanthrene, methyl ester, and phthalic acid were found. The detection of various common and novel metabolites demonstrates that SPME combining with GC–MS is a quick and convenient method for identification as well as monitoring the real time changes of metabolite concentrations throughout the degradation processes. The knowledge of PAH metabolic pathways and kinetics within indigenous bacterial consortium enriched from mangrove sediments contributes to enhance the bioremediation efficiency of PAH in real environment.     

Long-term effects of heavy metals on aouatic plants

In long-term experiments lasting up to 73 days the effect of rather low levels of zinc, copper, lead and cadmium on the growth and metal uptake was studied by investigating four aquatic plant species: Elodea nuttallii, Callitriche plataycarpa, Spirodela polyrhiza and Lemma gibba. Except Elodea, which was already very sensitive to 5 μmol Cu 1^?1, no differentiation in growth or mortality could be detected depending on species or elements. There was a clear differentiation between the uptake levels of the heavy metals with regard to the plant species, resulting in a higher heavy metal content in de submerged species in comparison to the floating ones. For zinc, lead and cadmium, an equal ratio was detected between the concentration in the medium and in the plant tissue independent of the plant species. The involvement of roots in element absorption by aquatic plants and the possibility of using aquatic plants as indicators of heavy metal pollution in Dutch waters are discussed.     

共存物质对重金属絮凝剂 MCC 除镉性能的影响简

为进一步拓展天然高分子絮凝剂壳聚糖的应用范围，以壳聚糖、L-半胱氨酸为原料，通过酰胺化反应制备一种具有重金属捕集功能的高分子重金属絮凝剂-2-氨基-3-巯基丙酰壳聚糖（MCC），研究了水体中常见的阴阳离子、有机配位剂及浊度对MCC除镉性能的影响，探讨了絮体形貌与絮体分形维数及絮凝除镉效果间的关系。结果表明，Na⁺、Cl^-、NO₃^-、F^-、SO₄^2-的存在对MCC除Cd²⁺均有促进作用，Ca²⁺表现为明显的抑制作用；低浓度的EDTA对除镉有促进作用，随着EDTA浓度的增大，逐渐转为抑制作用；低浓度的腐殖酸对MCC去除Cd²⁺有显著的促进作用；在一定范围内，浊度可促进 MCC对Cd²⁺的去除；絮体间空隙越多，絮体分形维数越小，除镉效果越好。     

Simultaneous removal of organic compounds and heavy metals from soils by electrokinetic remediation with a modified cyclodextrin

Thousands of sites are contaminated with both heavy metals and organic compounds and these sites pose a major threat to public health and the environment. Previous studies have shown that electrokinetic remediation has potential to remove heavy metals and organic compounds when they exist individually in low permeability soils. This paper presents the feasibility of using cyclodextrins in electrokinetic remediation for the simultaneous removal of heavy metals and polycyclic aromatic hydrocarbons (PAHs) from low permeability soils. Kaolin was selected as a model low permeability soil and it was spiked with phenanthrene as well as nickel at concentrations of 500 mg kg-1 each to simulate typical mixed field contamination. Bench-scale electrokinetic experiments were conducted using hydroxypropyl beta-cyclodextrin (HPCD) at low (1%) and high (10%) concentrations and using deionized water in control test. A periodic voltage gradient of 2VDC cm-1 (with 5 d on and 2 d off) was applied to all the tests, and 0.01 M NaOH was added during the experiments to maintain neutral pH conditions at anode. In all tests, nickel migrated as Ni2+ ions towards the cathode and most of it was precipitated as Ni(OH)2 within the soil close to the cathode due to high pH condition generated by electrolysis reaction. The solubility of phenanthrene in the flushing solution and the amount of electroosmotic flow controlled the migration and removal of phenanthrene in all the tests. Even though high flow was generated in tests using deionized water and 1% HPCD, migration and removal of phenanthrene was low due to low solubility of phenanthrene in these solutions. The test with 10% HPCD solution showed higher solubility of phenanthrene which caused it migrate towards the cathode, but further migration and removal was retarded due to reduced electric current and electroosmotic flow. Approximately one pore volume of flushing resulted in approximately 50% removal of phenanthrene from the soil near the anode. Sustained higher electroosmotic flow with higher concentration cyclodextrin and maintaining low soil pH near cathode should be investigated to increase removal efficiency of both phenanthrene and nickel.     

Simultaneous removal of phenanthrene and cadmium from contaminated soils by saponin, a plant-derived biosurfactant

Batch experiments were conducted to evaluate the performance of saponin, a plant-derived biosurfactant, for simultaneously removing phenanthrene and cadmium from the combined contaminated soils. Results showed that phenanthrene was desorbed from the contaminated soils by saponin with the partition of phenanthrene into surfactant micelle, meanwhile cadmium was effectively removed from the contaminated soils by the complexation of cadmium with the external carboxyl groups of saponin micelle. The efficiencies of saponin for the removal of phenanthrene and cadmium from the contaminated soils were greater than that of Triton X100 and citric acid, respectively. At concentration of 3750 mg/L, saponin has a removal rate of 87.7% and 76.2% of cadmium and phenanthrene, respectively, from the combined contaminated soil. The removals of cadmium and phenanthrene from the soils were not obviously constrained each other. Thus, saponin has the potential for the removal of heavy metal and PAHs from the combined contaminated soils.     

Body metal concentrations and glycogen reserves in earthworms (Dendrobaena octaedra) from contaminated and uncontaminated forest soil

Stress originating from toxicants such as heavy metals can induce compensatory changes in the energy metabolism of organisms due to increased energy expenses associated with detoxification and excretion processes. These energy expenses may be reflected in the available energy reserves such as glycogen. In a field study the earthworm, Dendrobaena octaedra, was collected from polluted areas, and from unpolluted reference areas. If present in the environment, cadmium, lead and copper accumulated to high concentrations in D. octaedra. In contrast, other toxic metals such as aluminium, nickel and zinc appeared to be regulated and kept at low internal concentrations compared to soil concentrations. Lead, cadmium and copper accumulation did not correlate with glycogen reserves of individual worms. In contrast, aluminium, nickel and zinc were negatively correlated with glycogen reserves. These results suggest that coping with different metals in earthworms is associated with differential energy demands depending on the associated detoxification strategy.     

Effect of cadmium and zinc on intestinal absorption of xylose and tryptophan in the fresh water teleost fish, Heteropneustesfossilis

The effect of cadmium and of zinc on the rate of uptake of a pentose sugar xylose and an aminoacid tryptophan by the intestine of a teleost fish, $\text{Heteropneustes}$$\text{fossilis}$ was studied under two experimental conditions. In the first, four concentrations of cadmium or zinc (1.0 mM, 0.1 mM, 0.01 mM and 0.001 mM) mixed with the nutrient solution were filled in the intestinal sacs, and the rate of absorption was recorded after 1 h at 23°C. In the second experiment fish were exposed by bath to a sublethal concentration of cadmium (0.26 mg/1) or zinc (4 mg/1) for 15 and 30 days and the rate of absorption of the two nutrients was measured. The activity of intestinal Na⁺, K⁺ activated adenosine triphosphatase was also assayed. The two heavy metals at all the four concentrations decreased the rate of intestinal transport of nutrients. Increase in the concentration of each of the heavy metals decreased the uptake of nutrients, but the decreases were not linear. The rate of intestinal absorption of the two nutrients was also reduced by exposure of fish to the heavy metals $\text{in}$$\text{vivo}$. The activity of Na⁺, K⁺ ATPase decreased $\text{in}$$\text{vitro}$ with all four concentrations of cadmium and zinc and was diminished in fish exposed for 15 and 30 days. Of the two heavy metals, cadmium was more effective in reducing the rate of transport of xylose and tryptophan.