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PubMed2003

[Content and extractability of heavy metals in cultivated soil in Fujian province].

The total and extractable contents of 7 heavy metals in cultivated soil in Fujian Province were determined. Statistical results indicated that the cultivated soil in Fujian Province was polluted by heavy metals, but different heavy metals caused different pollution levels. The extractable contents of heavy metals accounted for 10.0 to 52.2% of total contents, varying with different heavy metals. There was a significantly positive correlation between total and extractable content of Cu, Zn, Cd, Pb, and Ni. Besides, Zn, Cd, Pb and As had a significantly positive correlation to each other, while only Zn had a significantly positive correlation to Ni, and Cu and Hg were not significantly correlated to any of other heavy metals.

Metals, Heavy↗

PubMed2004

The importance of exogenous contamination on heavy metal levels in bird feathers. A field experiment with free-living great tits, Parus major.

Feathers have been used extensively as non-destructive biomonitors for heavy metal pollution. Birds excrete heavy metals into growing feathers during moult. After feather formation, the feathers become isolated from the rest of the body, suggesting that the feathers contain information of circulating heavy metal concentrations in the blood at the time of their development. However, heavy metal levels may change due to exogenous contamination, resulting in higher concentrations in feathers that are exposed most to exogenous conditions. We studied the effect of exogenous contamination in free-living adult great tits (Parus major) by measuring--within the same individual--the concentrations of twelve heavy metals (Ag, Al, As, Cd, Co, Cu, Fe, Hg, Mn, Pb, Tl and Zn) in three outermost tail feathers that were exposed to exogenous contamination for different periods of time. In particular, for each individual heavy metal levels in the removed left outermost tail feather were compared with levels in the regrown left and the right outermost tail feather, that were both removed 40 days after removal of the original left feather. This study revealed that, with the exception of mercury, the concentration of all heavy metals was significantly different among the three outermost tail feathers. Our results suggest that concentrations of most heavy metals build up with increasing age of the feather, indicating that exogenous contamination may be an important source of heavy metals in feathers. However, we found no significant differences in Hg concentrations and we found only small differences in Zn concentrations among tail feathers. Consequently, the concentrations of zinc and mercury in feathers are probably primarily due to endogenous deposition.

Animals↗

PubMed2006

Heavy metal contamination of soil and vegetables in suburban areas of Varanasi, India.

Heavy metal contamination of soil resulting from wastewater irrigation is a cause of serious concern due to the potential health impacts of consuming contaminated produce. In this study an assessment is made of the impact of wastewater irrigation on heavy metal contamination of Beta vulgaris (palak); this is a highly nutritious leafy vegetable that is widely cultivated and consumed in urban India, particularly by the poor. A field study was conducted at three major sites that were irrigated by either treated or untreated wastewater in the suburban areas of Varanasi, India according to normal practice. Samples of irrigation water, soil, and the edible portion of the palak (Beta vulgaris L. var All green H1) were collected monthly during the summer and winter seasons and were analyzed for Cd, Cu, Zn, Pb, Cr, Mn, and Ni. Heavy metals in irrigation water were below the internationally recommended (WHO) maximum permissible limits set for agricultural use for all heavy metals except Cd at all the sites. Similarly, the mean heavy metal concentrations in soil were below the Indian standards for all heavy metals, but the maximum value of Cd recorded during January was higher than the standard. However, in the edible portion of B. vulgaris, the Cd concentration was higher than the permissible limits of the Indian standard during summer, whereas Pb and Ni concentrations were higher in both summer and winter seasons. Results of linear regression analysis computed to assess the relationship between individual heavy metal concentration in the vegetable samples and in soil showed that Zn in soil had a positive significant relationship with vegetable contamination during winter. Concentrations of Cd, Cu, and Mn in soil and plant showed significant positive relationships only during summer. Concentration of Cr and Pb during winter season and Zn and Ni during summer season showed significant negative relationships between soil and plant contamination. The study concludes that the use of treated and untreated wastewater for irrigation has increased the contamination of Cd, Pb, and Ni in edible portion of vegetables causing potential health risk in the long term from this practice. The study also points to the fact that adherence to standards for heavy metal contamination of soil and irrigation water does not ensure safe food.

Agriculture↗

PubMed2001

Response of mosses to the heavy metal deposition in Poland--an overview.

Concentrations of heavy metals (Cd, Cr, Cu, Fe, Ni, Pb, Zn) in Pleurozium schreberi (Brid.) Mitt., a common moss species, were used to indicate relative levels of atmospheric deposition in Poland in the years 1975-1998. Spatial and temporal differences in the heavy metal concentrations in mosses were found. The highest concentration of heavy metals was recorded in the moss samples from the southern, most industrialised part of the country, and the lowest from north-eastern Poland. A significant decrease of heavy metals over 20 years (1975-1998) was found.

Air Pollutants↗

PubMed1995

Immunotoxicity of heavy metals in relation to Great Lakes.

Heavy metals including mercury, lead, and cadmium are present throughout the ecosystem and are detectable in small amounts in the Great Lakes water and fish. The main route of exposure of humans to these metals is via the ingestion of contaminated food, especially fish. Extensive experimental investigations indicated that heavy metals alter a number of parameters of the host's immune system and lead to increased susceptibility to infections, autoimmune diseases, and allergic manifestations. The existing limited epidemiologic data and data derived from in vitro systems in which human peripheral blood leukocytes were used suggested that the human immune system may also be at increased risk following exposure to these metals. The magnitude of the risk that the presence of such metals in the Great Lakes may pose to the human immune system, and consequently to their health, is not known. In this review, the available data with respect to potential adverse effects of heavy metals on the immune system of humans and experimental animals are discussed, and additional data requirements are suggested.

Adolescent↗

PubMed2004

Phytotoxicity and heavy metals speciation of stabilised sewage sludges.

The presence of heavy metals in the sludges produced in wastewater treatment restricts plants growth and hence their use for agricultural purposes. This study looks at different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) and compares the distribution of the heavy metals that they contain according to the treatment that they have undergone. The sewage sludges were subjected to chemical characterisation and phytotoxicity testing (in absence of substrate) to provide a preliminary assessment of their suitability for land application. In addition, the total quantity of metals (Cd, Cr, Cu, Ca, K, Fe, Mg, Ni, Na, Pb and Zn) was determined. The Community Bureau of Reference (BCR) method for heavy metal speciation was followed. It was confirmed that the total concentration of heavy metals did not exceed the limits set out by European legislation and that the stabilisation treatment undergone by the sludges strongly influenced the heavy metal distribution and the phases to which they were associated. The sludge extracts did not exert any significant adverse effect on the relative seed germination (RSG) of barley (Hordeum vulgare L.) or cress (Lepidium sativum L.), although the reduction in germination index (GI) indicates that some characteristics existed did have an adverse effect on root growth.

Biological Assay↗

PubMed2005

Enhanced phytoextraction: II. Effect of EDTA and citric acid on heavy metal uptake by Helianthus annuus from a calcareous soil.

High biomass producing plant species, such as Helianthus annuus, have potential for removing large amounts of trace metals by harvesting the aboveground biomass if sufficient metal concentrations in their biomass can be achieved However, the low bioavailability of heavy metals in soils and the limited translocation of heavy metals to the shoots by most high biomass producing plant species limit the efficiency of the phytoextraction process. Amendment of a contaminated soil with ethylene diamine tetraacetic acid (EDTA) or citric acid increases soluble heavy metal concentrations, potentially rendering them more available for plant uptake. This article discusses the effects of EDTA and citric acid on the uptake of heavy metals and translocation to aboveground harvestable plant parts in Helianthus annuus. EDTA was included in the research for comparison purposes in our quest for less persistent alternatives, suitable for enhanced phytoextraction. Plants were grown in a calcareous soil moderately contaminated with Cu, Pb, Zn, and Cd and treated with increasing concentrations of EDTA (0.1, 1, 3, 5, 7, and 10 mmol kg(-1) soil) or citric acid (0.01, 0.05, 0.25, 0.442, and 0.5 mol kg(-1) soil). Heavy metal concentrations in harvested shoots increased with EDTA concentration but the actual amount of phytoextracted heavy metals decreased at high EDTA concentrations, due to severe growth depression. Helianthus annuus suffered heavy metal stress due to the significantly increased bioavailable metal fraction in the soil. The rapid mineralization of citric acid and the high buffering capacity of the soil made citric acid inefficient in increasing the phytoextracted amounts of heavy metals. Treatments that did not exceed the buffering capacity of the soil (< 0.442 mol kg(-1) soil) did not result in any significant increase in shoot heavy metal concentrations. Treatments with high concentrations resulted in a dissolution of the carbonates and compaction of the soil. These physicochemical changes caused growth depression of Helianthus annuus. EDTA and citric acid added before sowing of Helianthus annuus did not appear to be efficient amendments when phytoextraction of heavy metals from calcareous soils is considered.

Biodegradation, Environmental↗

PubMed2005

[Assessment of toxicity of heavy metal contaminated soils by toxicity characteristic leaching procedure].

The contents of heavy metals (Cu, Zn, Pb and Cd) in soils from a lead-zinc mine in Shangyu, Zhejiang Province, China, were analyzed and their toxicity was assessed by toxicity characteristic leaching procedure (TCLP), which was developed by US EPA. The TCLP method is a currently recognized international method for evaluation of heavy metal pollution in soils. The available levels of Cu, Zn, Pb and Cd were 8.2-36 mg x kg(-1), 23-143 mg x kg(-1), 6.4-1367 mg x kg(-1) and 0.41-2.2 mg x kg(-1), respectively, while the international standard were 15 mg x kg(-1), 25 mg x kg(-1), 5 mg x kg(-1) and 0.5 mg x kg(-1), respectively. The results show that soils around the mine are polluted with heavy metals Cu, Zn, Pb and Cd, especially polluted by Zn and Pb, followed by Cd and Cu. Moreover, the heavy metals in the soils extracted by TCLP indicate that fluid 2 is more effective than fluid 1 in extracting the heavy metals from the polluted soils and there is a positive correlation between fluid 1 and fluid 2. The contents of available heavy metals by TCLP are correlated with contents of total heavy metals.

Cadmium↗

PubMed2002

Olive mill solid residues as heavy metal sorbent material: a preliminary study.

Biosorption of heavy metals is an innovative and alternative technology to remove these pollutants from aqueous solutions using inactive and dead biomasses such as agricultural and industrial wastes, algae and bacteria. In this study olive mill solid residue was used as heavy metal adsorbent material for its wide availability as agricultural waste and also for its cellulosic matrix, rich of potential metal binding active sites. Preliminary studies concerned with the removal of different heavy metals (Hg, Pb, Cu, Zn and Cd), the effect of pre-treatments by water and n-hexane and the regeneration possibility. Olive mill solid residue resulted able to remove heavy metals from aqueous solutions with an affinity series reflecting the hydrolytic properties of the metallic ions, but also a particular affinity for copper. It can be supposed that biosorption phenomenon occur by a general ion exchange mechanism combined with a specific complexation reaction for copper ions. Water pre-treatment is sufficient to reduce COD release in the effluent according to the law limit, while n-hexane pre-treatment strongly reduces also the adsorption properties of this material. Experimental isotherms obtained under different operating conditions were fitted using a non linear regression method for the estimation of the Langmuir parameters. Moreover a simple Scatchard plot analysis was performed for a preliminary investigation of the active sites, showing the presence of two different site affinities depending on the metal concentration, according to the previous hypothesis of two kinds of uptake mechanisms for copper biosorption. Regeneration tests gave good results in terms of yield of regeneration and also concentration ratios.

Adsorption↗

PubMed2006

Heavy metals removal from automobile shredder residues (ASR).

The fate of heavy metals during a separation process for automobile shredder residues (ASR) was investigated. A washing method to remove heavy metals from the ASR was also investigated. Although the separation process was not designed for removal of heavy metals, but for the recovery of reusable materials, the heavy metal content in the ASR was efficiently decreased. The concentrations of Pb, Cr and Cd in ASR were effectively reduced by a nonferrous metals removal process, and the As concentration was reduced by the removal of light dusts during the separation process. Five heavy metals (As, Se, Pb, Cr, Cd) remaining in the ASR after the separation process satisfied the content criteria of the Environmental Quality Standards for Soil (EQSS), while the concentrations of As, Se, Pb in the leachate from the remaining ASR did not satisfy the elution criteria of the EQSS. After additional washing of the remaining ASR with a pH 1 acid buffer solution, the As, Se, and Pb concentrations satisfied the EQSS for elution. These results indicate that an ASR residue can be safely recycled after a separation process, followed by washing at acidic pH.

Automobiles↗

PubMed2006

Electrokinetic enhancement removal of heavy metals from industrial wastewater sludge.

An enhanced electrokinetic process for removal of metals (Cr, Cu, Fe, Ni, Pb, Zn) from an industrial wastewater sludge was performed. The electrokinetic experiments were conducted under a constant potential gradient (1.25 V cm(-1)) with processing fluids of tap water (TW), sodium dodecylsulfate (SDS) and citric acid (CA) for 5 days. Results showed that metal removal efficiency of heavy metals for EK-TW, EK-SDS and EK-CA systems are 11.2-60.0%, 37.2-76.5%, and 43.4-78.0%, respectively. A highest metal removal performance was found in EK-CA system. The removal priority of investigated metals from sludge by EK process was found as: Cu > Pb > Ni > Fe > Zn > Cr. The results of sequential extraction analysis revealed that the binding forms of heavy metals with sludge after electrokinetic process were highly depend upon the processing fluid operated. It was found that the binding forms of metals with sludge were changed from the more difficult extraction type (residual and sulfate fractions) to easier extraction types (exchangeable, sorbed, and organic fraction) after treatment by electrokinetic process. Results imply that if a proper treatment technology is followed by this EK process to remove metals more effectively, this treated sludge will be more beneficial for sludge utilization afterwards. Before it was reused, the risk associated with metals of more mobile forms to the environment need to be further investigated. The cost analysis was also evaluated for the investigated electrokinetic systems.

Electrochemistry↗

PubMed2003

Effects of heavy metals on plants and resistance mechanisms. A state-of-the-art report with special reference to literature published in Chinese journals.

GOAL, SCOPE AND BACKGROUND: As one of the consequences of heavy metal pollution in soil, water and air, plants are contaminated by heavy metals in some parts of China. To understand the effects of heavy metals upon plants and the resistance mechanisms, would make it possible to use plants for cleaning and remediating heavy metal-polluted sites. METHODS: The research results on the effects of heavy metals on plants and resistant mechanisms are compiled from Chinese publications from scientific journals and university journals, mostly published during the last decade. RESULTS AND DISCUSSION: Effects of heavy metals on plants result in growth inhibition, structure damage, a decline of physiological and biochemical activities as well as of the function of plants. The effects and bioavailability of heavy metals depend on many factors, such as environmental conditions, pH, species of element, organic substances of the media and fertilization, plant species. But, there are also studies on plant resistance mechanisms to protect plants against the toxic effects of heavy metals such as combining heavy metals by proteins and expressing of detoxifying enzyme and nucleic acid, these mechanisms are integrated to protect the plants against injury by heavy metals. CONCLUSIONS: There are two aspects on the interaction of plants and heavy metals. On one hand, heavy metals show negative effects on plants. On the other hand, plants have their own resistance mechanisms against toxic effects and for detoxifying heavy metal pollution. RECOMMENDATIONS AND OUTLOOK: To study the effects of heavy metals on plants and mechanisms of resistance, one must select crop cultivars and/or plants for removing heavy metals from soil and water. More highly resistant plants can be selected especially for a remediation of the pollution site. The molecular mechanisms of resistance of plants to heavy metals should be studied further to develop the actual resistance of these plants to heavy metals. Understanding the bioavailability of heavy metals is advantageous for plant cultivation and phytoremediation. Decrease in the bioavailability to farmlands would reduce the accumulation of heavy metals in food. Alternatively, one could increase the bioavailability of plants to extract more heavy metals.

Biodegradation, Environmental↗

PubMed1999

Cement for stabilisation of industrial residues containing heavy metals.

A method aimed at decreasing the toxicity of heavy metals [namely, Zn(II) and Cr(III)] in real polluted residues by immobilisation has been developed. The residues were processed either with two cement-type stabilisers or lime. The cement-type stabilisers were Portland cement and Depocrete SM/2 at the self-generated pH (ca. 11) which afforded physical as well as chemical potential for the immobilisation of heavy metals. The other stabiliser, lime, reduced organic compounds, thus favouring the decrease of the chemical oxygen demand (COD) and endowing the residue with better mechanical properties for transport. After leaching the stabilised residues using the standard leaching test [Order 13/10/89, Boletín Oficial del Estado (BOE) 270 10/11/89], three ways for establishing the toxicity of the treated residues were used, namely: (1) the ecotoxicity test using Photobacterium phosphoreum (DIN 38 412); (2) determination of the concentration of heavy metals by atomic absorption spectrometry (AAS); (3) determination of the COD or oxygen required for complete chemical oxidation of a water sample. Portland cement (20%) blended with Depocrete SM/2 (3%) acted as an effective stabiliser for residues containing heavy metals as it increased the ecotoxicity index (EC50) by more than five times. Thus the heavy metal concentration in the leaching liquid was lowered to less than 0.1 mg l-1. The addition of 5% of lime afforded a residue easily transportable from the place of treatment to the landfill. The precision of the method was studied in terms of both repeatability and reproducibility. The values found with respect to EC50 and expressed as the relative standard deviation (RSD) were 1.6% and 5.1%, respectively.

Environmental Pollution↗

PubMed1980

Interactions of heavy metals with bacteria.

The toxicity of heavy metals to bacteria, with particular reference to metal forms and species, has been reviewed. Factors which influence metal forms and thus their potential toxicity, such as pH, chelation and competitive interactions have been discussed. The mechanisms whereby bacteria may influence the forms of heavy metals to which they are exposed have been discussed with reference to the importance of the role of bacteria in immobilisation and environmental cycling of metals. Bacterial resistance to metal toxicity is an environmentally important phenomenon. It may occur from non-specific mechanisms, such as impermeability of the cell, or it may be due to specific resistance transfer factors. The coincidence and co-selection of resistance factors for antibiotics and heavy metals in bacterial populations and the clinical implications of this have been described.

Anti-Bacterial Agents↗

PubMed2000

Phytochelatin biosynthesis and function in heavy-metal detoxification.

Plants respond to heavy-metal toxicity via a number of mechanisms. One such mechanism involves the chelation of heavy metals by a family of peptide ligands, the phytochelatins. Molecular genetic approaches have resulted in important advances in our understanding of phytochelatin biosynthesis. In particular, genes encoding the enzyme phytochelatin synthase have been isolated from plant and yeast species. Unexpectedly, genes with similar sequences to those encoding phytochelatin synthase have been identified in some animal species.

Aminoacyltransferases↗

PubMed2006

In situ distributions and characteristics of heavy metals in full-scale landfill layers.

The leachate from methanogenic landfill normally contains low concentrations of heavy metals. Little samples had ever been collected from the full-scale landfill piles owing to technical difficulty for well drilling. We drilled two wells in Hangzhou Tianziling landfill, 20 m and 32 m in depth each, and collected solid samples of waste age of 1-4 years from both wells. The total amounts, the sequentially extracted amounts, and the chemical binding forms of heavy metals of the samples collected at different depths were measured. With the correlation between leachate production amount and the yearly rainfall amount, the leached ratio of the heavy metals were estimated only 0.13%, 1.8%, 0.15%, and 0.19% of Cu, Cd, Pb, and Zn, respectively. The heavy metals amounts in the main compositions of MSW, like glass, food waste, paper, coal cinders, were measured using fresh MSW samples. Afterward, the contents of heavy metals initially landfilled were estimated. A positive correlation was noted between the measured and the estimated initial contents of heavy metals, indicating that the low migration of heavy metals in landfill layers. However, among the metals investigated, Zn has shown better mobility inside landfill layers. Acid volatile sulfide (AVS) and the simultaneously extracted metals (SEM) were measured for all collected samples with optimal reaction conditions identified to yield nearly perfect sulfide recovery as follows: 100 g wet samples, 80 mL min(-1) N(2) flow rate, reaction time of 150 min. The SEM/AVS ratios ranged 25-45, indicating that the AVS was insufficient to immobilize the SEM. Sequential extraction using six-fraction scheme revealed that the sum of exchangeable and the avid soluble fractions of heavy metals follow: Zn>Cd>Cu, Ni, Pb>Cr. The insoluble fraction of heavy metals in MSW was high, for instance, over 80% for Cr and Pb high insoluble fractions of heavy metals in the landfilled MSW and the sorption capability of the methanogenic landfill layers should be responsible to the low concentrations of heavy metals found in leachate.

Metals, Heavy↗

PubMed2005

Remediation of soil contaminated with the heavy metal (Cd2+).

Soil contamination by heavy metals is increasing. The biosorption process for removal of the heavy metal Cd(2+) from contaminated soil is chosen for this study due to its economy, commercial applications, and because it acts without destroying soil structure. The study is divided into four parts (1) soil leaching: the relationships between the soil leaching effect and agitation rates, solvent concentrations, ratios of soil to solvent, leaching time and pH were studied to identify their optimum conditions; (2) adsorption Cd(2+) tests of immobilized Saccharomycetes pombe beads: different weight percentages of chitosan and polyvinyl alcohol (PVAL) were added to alginate (10 wt.%) and then blended or cross-linked by epichlorohydrin (ECH) to increase their mechanical strength. Next, before blending or cross-linking, different weight percentages of S. pombe 806 or S. pombe ATCC 2476 were added to increase Cd(2+) adsorption. Thus, the optimum beads (blending or cross-linking, the percentages of chitosan, PVAL and S. pombe 806 or S. pombe ATCC 2476) and the optimum adsorption conditions (agitation rate, equilibrium adsorption time, and pH in the aqueous solution) were ascertained; (3) regeneration tests of the optimum beads: the optimum beads adsorbing Cd(2+) were regenerated by various concentrations of aqueous HCl solutions. The results indicate that the reuse of immobilized pombe beads was feasible; and (4) adsorption model/kinetic model/thermodynamic property: the equilibrium adsorption, kinetics, change in Gibbs free energy of adsorption of Cd(2+) on optimum beads were also investigated.

Adsorption↗

PubMed2003

Multivariate statistical study of heavy metal enrichment in sediments of the Pearl River Estuary.

The concentrations and chemical partitioning of heavy metals in the sediment cores of the Pearl River Estuary were studied. Based on Pearson correlation coefficients and principal component analysis results, Al was selected as the concentration normalizer for Pb, while Fe was used as the normalizing element for Co, Cu, Ni and Zn. In each profile, sections with metal concentrations exceeding the upper 95% prediction interval of the linear regression model were regarded as metal enrichment layers. The heavy metal accumulation mainly occurred at sites in the western shallow water areas and east channel, which reflected the hydraulic conditions and influence from riparian anthropogenic activities. Heavy metals in the enrichment sections were evaluated by a sequential extraction method for possible chemical forms in sediments. Since the residual, Fe/Mn oxides and organic/sulfide fractions were dominant geochemical phases in the enriched sections, the bioavailability of heavy metals in sediments was generally low. The 206Pb/207Pb ratios in the metal-enriched sediment sections also revealed the influence of anthropogenic sources. The spatial distribution of cumulative heavy metals in the sediments suggested that the Zn and Cu mainly originated from point sources, while the Pb probably came from non-point sources in the estuary.

China↗