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PubMed2005

Biological effects of heavy metals: an overview.

Heavy metals constitute a very heterogeneous group of elements widely varied in their chemical properties and biological functions. Heavy metals are kept under environmental pollutant category due to their toxic effects on plants, animals and human being. Heavy metal contamination of soil results from anthropogenic as well as natural activities. Anthropogenic activities such as mining, smelting operation and agriculture have locally increased the levels of heavy metals such as Cd, Co, Cr, Pb, As and Ni in soil up to dangerous levels. Heavy metals are persistent in nature, therefore get accumulated in soils and plants. Heavy metals interfere with physiological activities of plants such as photosynthesis, gaseous exchange and nutrient absorption, and cause reductions in plant growth, dry matter accumulation and yield. Heavy metals also interfere with the levels of antioxidants in plants, and reduce the nutritive value of the produce. Dietary intake of many heavy metals through consumption of plants has long term detrimental effects on human health.

Agriculture↗
PubMed2004

Seasonal dynamics of shallow-hyporheic-zone microbial community structure along a heavy-metal contamination gradient.

Heavy metals contaminate numerous freshwater streams and rivers worldwide. Previous work by this group demonstrated a relationship between the structure of hyporheic microbial communities and the fluvial deposition of heavy metals along a contamination gradient during the fall season. Seasonal variation has been documented in microbial communities in numerous terrestrial and aquatic environments, including the hyporheic zone. The current study was designed to assess whether relationships between hyporheic microbial community structure and heavy-metal contamination vary seasonally by monitoring community structure along a heavy-metal contamination gradient for more than a year. No relationship between total bacterial abundance and heavy metals was observed (R(2) = 0.02, P = 0.83). However, denaturing gradient gel electrophoresis pattern analysis indicated a strong and consistent linear relationship between the difference in microbial community composition (populations present) and the difference in the heavy metal content of hyporheic sediments throughout the year (R(2) = 0.58, P < 0.001). Correlations between heavy-metal contamination and the abundance of four specific phylogenetic groups (most closely related to the alpha, beta, and gamma-proteobacteria and cyanobacteria) were apparent only during the fall and early winter, when the majority of organic matter is deposited into regional streams. These seasonal data suggest that the abundance of susceptible populations responds to heavy metals primarily during seasons when the potential for growth is highest.

Base Sequence↗
PubMed1982

Heavy metal ion interactions with Callinectes sapidus hemocyanin: structural and functional changes induced by a variety of heavy metal ions.

Hemocyanins are oligomeric proteins that reversibly bind oxygen. The oxygen binding site is a binuclear copper center bound to the protein by amino acid side chains. The hemocyanin of the blue crab, Callinectes sapidus, occurs in vivo as a mixture of 25S dodecamers and 16S hexamers, whose oxygen binding properties are identical. Four heavy metals have been used as probes of structure and function in this hemocyanin system. Divalent cations of cadmium, copper, mercury, and zinc induced an indefinite self-association of the hemocyanin molecule. These higher ordered association states can be dissociated by ethylenediaminetetraacetic acid. Callinectes oxyhemocyanin possesses at least three mercury binding sites: (1) a sulfhydryl group which forms a mercaptide bond with a single mercuric ion, (2) a tryptophanyl side chain which forms a noncovalent 1:1 complex with mercuric ions with an association constant of 5.7 X 10(15) M-1, and (3) lower affinity site(s) involved in the self-association process also observed with cadmium, copper, and zinc. Sites 1 and 2 are most likely also involved in the binding of cadmium. Upon removal of oxygen from the active site of hemocyanin, an additional binding site becomes available for the reaction with mercury. Binding of mercury to this site leads to loss of one of the coppers from the binuclear oxygen binding site. Both the binuclear copper center and allosteric sites on the hemocyanin are affected by heavy metal binding. Cadmium and zinc ions increase the oxygen affinity; mercury and copper ions have the opposite effect. All four heavy metal ions decrease the degree of cooperative oxygen binding. The mercury-induced changes in oxygen binding by 25S Callinectes hemocyanin appear to be the result of that metal's interaction with the high-affinity tryptophan binding site. Mercury binding to the available sulfhydryl group in oxyhemocyanin occurs without functional consequences. Heavy metal, hydrogen, and chloride ions affect the affinity of the first or last oxygen molecules bound to the hemocyanin, which results in the appearance of multiple T (low oxygen affinity) and R (high oxygen affinity) states. Additionally, these ions shift the equilibrium between the low and high oxygen affinity states. The appearance of additional R states at high pH is accompanied by the cleavage of a tyrosine hydrogen bond.

Allosteric Site↗
PubMed1998

Heavy metals and fertility.

Heavy metals have been identified as factors affecting human fertility. This study was designed to investigate whether the urinary heavy metal excretion is associated with different factors of infertility. The urinary heavy metal excretion was determined in 501 infertile women after oral administration of the chelating agent 2,3-dimercaptopropane-1-sulfonic acid (DMPS). Furthermore, the influence of trace element and vitamin administration on metal excretion was investigated. Significant correlations were found between different heavy metals and clinical parameters (age, body mass index, nationality) as well as gynecological conditions (uterine fibroids, miscarriages, hormonal disorders). Diagnosis and reduction of an increased heavy metal body load improved the spontaneous conception chances of infertile women. The DMPS test was a useful and complementary diagnostic method. Adequate treatment provides successful alternatives to conventional hormonal therapy.

Adult↗
PubMed1997

[Effects of heavy metals on snail development. Use of snails as bio-indicators of heavy metal pollution for the preservation of human health].

The use of snails as biological indicators is particularly appropriate for metals, which they accumulate in their organs. The aim of the present experiment was to carry out a rigorous experimentation in the laboratory and in the wild in order to develop a methodology for the use of snails at a known stage of growth that would give precise information on the toxicity of heavy metals for different concentrations and durations of exposure. We have developed a test of toxicity based on the effects of a noxious and carcinogenic element, cadmium, on the land-snail Helix aspersa aspersa (H.a.a) of one month of age. Five concentrations (50 to 800 micrograms/g), were selected to estimate the concentrations causing 50% inhibition of growth (EC 50) at 14 days: 190 micrograms/g and at 28 days: 180 micrograms/g. A soil matrix contaminated with metals (soil including 800 micrograms/g Cr, 20 micrograms/g Cd, 800 micrograms/g Pb and 2000 micrograms/g Zn) was incorporated into the food at 50 and 75%, it too inhibited the growth of juvenile snails compared to incorporation of control soil. An accurate and rapid (2 to 4 weeks) method is therefore available for the evaluation of the toxicity of pollutants by ingestion. The first trials of this method in the wild consisted of placing batches of 2-month-old snails, identical to those used in the first lab tests, in locations that were either polluted or not. Differences in growth were observed depending on the locations; analysis of the levels of metal in the organs of the snails should enable us to check if there is a correlation between these levels and the growth rates. The results obtained with cadmium compared to those of other authors working with earthworms and soil arthropods show that snails give responses to concentrations comparable to those of earthworms and much more rapidly and with more sensitivity than those of collembolla for example. The ease of handling snails and the perfect control of their breeding are essential factors in carrying out reliable bioassays in toxicology and in ecotoxicology.

Animals↗
PubMed2004

Effects of extracting reagents and metal speciation on the removal of heavy metal contaminated soils by chemical extraction.

Chelating agents and acids were evaluated for removing heavy metals from contaminated soils. Two soils, latosols soil and sandatone-shale alluvial soil, artificially contaminated with Cu, Zn, and Pb were investigated. The removal efficiencies of Cu, Zn, and Pb from both soils for various chelating agents and acids followed the descending order EDTA > DTPA > Citric Acid > HCl. Heavy metals were associated in latosols soil with 34, 40, and 33% in the exchangeable fraction for Cu, Zn, and Pb, respectively. However, heavy metals were associated in sandatone-shale alluvial soil in stronger adsorbed forms with 40, 55, and 42% in the Fe-Mn oxides fraction for Cu, Zn, and Pb, respectively. Effect of EDTA concentration on the removal efficiency of heavy metals was examined for a wide range of 1 x 10(-4) to 5 x 10(-2) M. When EDTA concentration was low in the range from 1 x 10(-4) to 1 x 10(-3) M, the removal efficiencies of all the heavy metals from latosols soil were higher than those from sandatone-shale alluvial soil. The higher removal efficiencies of heavy metals observed in latosols soil than those in sandatone-shale alluvial soil is proved due to that the heavy metals in latosols soil were associated in weaker adsorption forms than heavy metals associated in sandatone-shale alluvial soil.

Acids↗
PubMed1975

Epidemiology of antibiotic and heavy metal resistance in bacteria: resistance patterns in staphylococci isolated from populations in Iraq exposed and not exposed to heavy metals or antibiotics.

Staphylococci were isolated from rural and urban populations in Iraq, which were not known to be exposed to either heavy metals or antibiotics. The antibiotic and heavy metal resistance patterns of these strains were analyzed in both mannitol-fermenting and nonfermenting strains. Over 90% of the strains were resistant to at least one of the following antibiotics: penicillin, chloramphenicol, erythromycin, tetracycline, cephalothin, lincomycin, or methicillin. In general, mannitol-fermenting strains were resistant to penicillin and cupric ions. Mannitol-negative strains were more frequently associated with mercuric ion and tetracycline resistance. Although resistance to penicillin and tetracycline can coexist, the combination of penicillin resistance and tetracycline resistance usually occurred in mannitol-negative strains. The possibility of selection of heavy metal-resistant strains due to exposure to toxic levels of methylmercury was examined. No significant increase in mercuric ion-resistant strains of staphylococci or Escherichia coli were detected in exposed populations as compared to control groups. The possible reasons for this result are discussed.

Anti-Bacterial Agents↗
PubMed1985

Levels of heavy metals in the tidal Elbe and its estuary and the heavy metal input into the sea.

Surface water samples were collected during missions in 1977, 1978, 1980 and 1983 at different sampling stations along the tidal Elbe, from river km 632 downstream from Hamburg to the outer end of the estuary. Special care was taken to minimize contamination during sampling, handling and analysis. Within the tidal Elbe five distinct zones of substantial anthropogenic heavy metal pollution inputs can be detected. An attempt is made to define anthropogenic background levels, which are extremely low for the dissolved trace metals Cd and Pb; 35 and 65 ng/kg, respectively. The level of dissolved Cu is 2200 ng/kg. Total baseline levels of Cd, Pb and Cu are, respectively, 120, 2500 and 4200 ng/kg. In the five river zones affected by anthropogenic trace metal inputs, distinctly larger maximum levels can occur. They decrease to the background values after mixing with the main water body. More elevated levels caused by re-suspension in the mixing zone with maximum turbidity can be assumed. Nickel and Co data are from one mission only. The order of magnitude of the trace metal input from the Elbe into the sea is evaluated.

Cadmium↗
PubMed2005

Thermal treatment of metal-enriched biomass produced from heavy metal phytoextraction.

Phytoextraction is an environmentally sound method for cleaning up sites that are contaminated with toxic heavy metals. However, the method has been questioned because it produces a biomass-rich secondary waste containing the extracted metals. Therefore, further treatment of this biomass is necessary. In this study, we investigated whether thermal treatment could be a feasible option for evaporatively separating metals from the plant residues. We used a laboratory scale reactor designed to simulate the volatilization behavior of heavy metals in a grate furnace. The evaporation of alkali and heavy metals from plant samples was investigated online, using a thermo-desorption spectrometer (TDS). Experiments were performed in the temperature range of 25-950 degrees C with leaves of the Cd and Zn hyperaccumulator Thlaspi caerulescens and of the high biomass plant Salix viminalis (willow), both grown on contaminated soils. Gasification (i.e., pyrolysis), which occurs under reducing conditions, was a better method than incineration under oxidizing conditions to increase volatilization and, hence subsequently recovery, of Cd and Zn from plants. It would also allow the recycling of the bottom ash as fertilizer. Thus, our investigations confirmed that incineration (or co-incineration) is a viable option for the treatment of the heavy metal-enriched plants.

Biodegradation, Environmental↗
PubMed2005

Optimizing cell preparation technique to enhance adsorption capacity of pseudomonas putida 5-x to heavy metal ions.

A heavy metal accumulation bacterium Pseudomonas putida 5-x isolated from electroplating effluent was used as biosorbent for heavy metal removal from wastewater. In order to compete with physical adsorbent, the optimization of the cell preparation technique for further improving its heavy metal adsorption capacity was conducted. Experimental results showed that the variation of medium compositions and cell growth age, and different cell pre-treating technique would result in the variation of the cell surface components and structural, hence the variation of adsorption capacity of the cell to heavy metal ions. With optimum cell culture conditions and pretreatment technique, the Cu2+ adsorption capacity of the cell was obviously increased from 51.2 mg g-1 to 89.6 mg g-1. The optimised P. putida 5-x cell could be reused at least five cycles to remove heavy metal ions from electroplating effluent with about 95% removal efficiency.

Adsorption↗
PubMed1975

Epidemiology of antibiotic and heavy metal resistance in bacteria: resistance patterns in staphylococci isolated from populations not known to be exposed to heavy metals.

Staphylococci were isolated from clinical specimens obtained from patients not known to be exposed to abnormal levels of heavy metals. The antibiotic and heavy metal resistance patterns of these strains were determined by using a disk diffusion test and computer sorting. Though not absolute, an association of resistance to mercury and tetracycline in coagulase-negative strains was found, in contrast to resistance to copper and penicillin in coagulase-producing strains. A high degree of correlation was observed between the resistance to phenyl mercury and inorganic mercury, but no correlation was obtained between resistance to methylmercury and other metals. In general, strains resistant to many agents were usually coagulase negative. A possible mechanism and implications of these associations are considered.

Anti-Bacterial Agents↗
PubMed2005

Joint effects of dimethoate and heavy metals on metabolic responses in a grasshopper (Chorthippus brunneus) from a heavy metals pollution gradient.

We studied how an exposure to an additional stressing factor-dimethoate, might affect detoxifying ability of grasshoppers collected at 5 meadow sites located along a heavy metal pollution gradient. Activities of esterases and enzymes linked with glutathione (GSH) metabolism were assayed 24 h after topical treatment with 0.32 microg dimethoate per insect. Inhibition of acetylcholinesterase (AChE) reaches nearly 50% of the value stated in untreated insects, without significant site-dependent differences. The pesticide also caused a significant decrease in activities of glutathione peroxidase (GPx) followed by a decrease in GSH levels in grasshoppers from all assayed groups, demonstrating high sensitivity of glutathione-dependent metabolism to the additional stressing factor. In the case of glutathione reductase (GR) and carboxylesterases (CarE) the fall of activity was shown especially in insects from less polluted meadows and the reference site. Glutathione reductase (GR) activity in individuals treated with dimethoate did not decrease only in insects from the most contaminated site I. This might suggest the trade-off mechanisms adapting grasshoppers to life in seriously polluted environments.

Acetylcholinesterase↗
PubMed1995

Comparison of microbial tests for the detection of heavy metal genotoxicity.

Heavy metal genotoxicity was evaluated by using different microbial tests. Four genotoxicity assays were employed: the Ames test, the E. coli WP2 test, the Mutatox test detecting mutagenicity, and the SOS assay with E. coli-detecting enzyme induction. All the metals tested (cadmium, chromium, copper, mercury, nickel, and zinc) were detected as genotoxic by the Mutatox and the SOS tests. The Ames test and the E. coli WP2 assay only detected chromium as genotoxic, causing a mutagenic effect. The sensitivity to metals of all the assays used was maintained when they were dissolved in sewage, although there was a slight increase in the sensitivity thresholds.

Environmental Exposure↗
PubMed1976

Lake sediments as indicators of heavy-metal pollution.

Heavy metals are one of the most toxic forms of environmental pollutants, constituting a threat both to aquatic life and the quality of drinking water. By analyzing lake sediments, it is possible to determine the provenance, distribution, extent, and also the possible hazards of metal contamination. Sedimentary cores, in particular, provide the means for evaluating the different influences from natural and civilizational sources; they represent a historical record of the metal accumulations which have taken place during the past decades as a result of population growth and industrial development.

Arsenic↗
PubMed2001

Stabilization of an elevated heavy metal contaminated site.

Heavy metal contamination is a common problem that is encountered at many uncontrolled sites. Immobilization is seen as a promising technology for heavy metal remediation. Here, we report a remediation case study of an elevated and multi-metal contaminated site containing Cd, Cu, Ni, Pb, and Zn. In a laboratory test, when the soil was stabilized with reagent grade stabilizers (CaHPO(4) and CaCO(3)), the toxicity characteristic leaching procedure (TCLP) extractable concentrations of Cd, Cu, Pb, and Zn were reduced by more than 87%. The greatest reduction was shown with Pb (99.8%). In the field, Ca(H(2)PO(4))(2) due to lower cost and higher solubility replaced CaHPO(4). The TCLP results of the field treatment showed that the extractable concentrations of Cd, Cu, Pb, and Zn were significantly reduced after 30 days of stabilization. The reduction ratios were 98% (Cd), 97% (Cu), 99% (Pb), and 96% (Zn). Although, the reduction ratio of Ni was only 65%, the average extractable concentration was still less than 4.0mg/l. The percent reduction can, therefore, be considered reasonable. The significant reduction of extractable metal concentrations showed that the stabilizers, a combination of Ca(H(2)PO(4))(2) and CaCO(3), successfully immobilized heavy metals on the site.

Carbonates↗
PubMedDate not supplied

Uncertainty and sensitivity analysis of spatial predictions of heavy metals in wheat.

Heavy metals seriously threaten the health of human beings when they enter the food chain. Therefore, policymakers require precise predictions of heavy metal concentrations in agricultural crops. In this paper we quantify the uncertainty of regression predictions of Cd and Pb in wheat (Triticum aestivum L.) and the contributions to the uncertainties in these predictions associated with inputs to the regression model. For each node of the 500- x 500-m grid covering the arable soils in The Netherlands, a latin hypercube sample size of 1000 is constructed from the uncertainty distributions of the explanatory variables (pH, soil organic matter [SOM], and heavy metal concentration in soil), the regression coefficients, and the random term of the regression model. This sample is used as input for the regression model to obtain 1000 values from the uncertainty distributions of the log(Cd) and log(Pb) concentration in wheat. There were no nodes where the recent EU quality standards for Cd and Pb (0.2 mg kg(-1) fresh wt.) in wheat were almost certain to be exceeded. For most nodes with clay soils, the quality standard for Cd in wheat almost certainly will not be exceeded; for Pb this is much less certain. The uncertainty in the Cd concentration in soil contributes most to the uncertainty in the predicted Cd concentrations in wheat (36% on the average), followed by the random term of the regression model (23%). For Pb the contribution of the random term is by far the largest (52%).

Agriculture↗