Toxic Effects Of Heavy Metals Research Articles

Toxic effects of zinc on anaerobic microbiota from Zimapán Reservoir (Mexico)

The toxic effects of heavy metals have been extensively documented in different organisms. Nevertheless, a lack of information exists with regard to this topic in the case of autochthonous microorganism communities. The aim of this study was to evaluate the toxic effects of zinc on the anaerobic microorganisms present in the sediment and anoxic water of Zimapán Reservoir (Mexico), with particular focus on dissimilatory sulphate reducing bacteria. In the laboratory, a system of enrichment microcosms was set up with sediment and water from the reservoir. ATP, protein, carbohydrates and lactate and alcohol dehydrogenase activity were determined. The physicochemical parameters of the reservoir were evaluated over the course of one year. Sulphate reduction occurred in the reservoir throughout the year, but was most pronounced at the end of the wet season and during winter. In the field, increases in the rate of sulphate reduction coincided with the lowest levels of total phosphorus and hydrosoluble organic carbon. Zinc enrichment was observed to modify protein and carbohydrate content as well as to affect lactate and alcohol dehydrogenase activity. All responses followed a zinc concentration–response relationship and were dependent on reservoir physicochemical parameters. ATP content was used as a biomarker to evaluate the sublethal toxic effects of zinc. The acceptable threshold concentration of zinc in the aquatic and sediment enrichment microcosms was determined to be 0.06 mg Zn/L and 711.1 mg Zn/kg, respectively.

Sublethal toxicity of trace metals to larvae of the blacklip abalone, Haliotis rubra

The availability of literature regarding sublethal and chronic toxicity of heavy metals to early life stages of marine species is restricted to a few species of invertebrate mollusks. The early life stage of abalone, an important gastropod both environmentally and commercially, has been involved in limited research investigating the effects of heavy metal toxicity. Fertilized eggs of Haliotis rubra were exposed to a range of dissolved nominal concentrations of cadmium, copper, iron, lead, mercury, and zinc in individual solutions for 48 h. After 48 h of exposure, the test was completed by recording survival success and morphological abnormalities of veliger larvae in each heavy metal treatment. The mean 48-h median effective concentrations affecting normal morphological development of veliger larvae determined in this test shows a decreasing order of toxicity of copper (7 mg/L), mercury (21 mg/L), zinc (35 mg/L), iron (4102 mg/L), cadmium (4515 mg/L), and lead (5111 mg/L).

Cellular response of mouse splenocytes to heavy metals exposure

Among the environmental contaminants recognised for their toxicity and their global presence, heavy metals are certainly a major concern. They can elicit a number of immunomodulatory effects leading ultimately to an enhanced susceptibility (sensitivity) of immune cells to microbial agents and the appearance of neoplastic diseases and autoimmune phenomena. Heavy metals also provoke changes in the function(s) of immune cells. A striking biological effect of heavy metals is the induction of intracellular thiols (cysteine, glutathione, metallothioneins). Thiols are involved in many physiological processes, including protection from free radical damage and detoxification of chemicals. The purpose of this study was to assess the differences of susceptibility (sensitivity) in both pre-activated (concanavalin A was used) and non-pre-activated cells in the presence of heavy metals. Five were evaluated on murine splenocytes. The lymphoblastic proliferation test was performed for lymphocytes and a phagocytosis test for macrophages. Data showed that the levels of thiols in the pre-activated cells are greater than non-pre-activated cells following exposure to various heavy metals; macrophages were more resistant than lymphocytes to the toxic effects of heavy metals, and pre-activated cells were more resistant than cells at rest. One possible explanation is that macrophages produce more thiols than lymphocytes and this provides an increased protection from the deleterious effects of heavy metals.

Effects of heavy metals on sea urchin embryo development. Part 2. Interactive toxic effects of heavy metals in synthetic mine effluents

Interactive toxic effects between heavy metals were investigated using a sea urchin ( Anthocidaris crassispina) bioassay. An effluent from an abandoned mine showed significant inhibitory effects on embryo development as well as producing specific malformations. The effects on the embryos were reproduced by synthetic polluted seawater consisting of eight metals (manganese, lead, cadmium, nickel, zinc, chromium, iron, and copper) at the concentrations detected in the mine effluent. This indicated that the heavy metals were responsible for the effects observed. Five heavy metals were ranked in decreasing order of toxicity as follows: Cu > Zn > Pb > Fe > Mn. Among these, zinc and manganese could cause malformation of the embryos. From bioassay results using 27 combinations of heavy metals, 16 combinations including zinc could produce specific malformations, such as radialized, exo-gastrulal, and spaceship Apollo-like gastrulal embryos. Zinc was one of the elements responsible for causing malformations and its effects were intensified by the presence of the other metals, such as manganese, lead, iron, and copper.

Elemental changes in the brain, muscle, and gut cells of the housefly, Musca domestica, exposed to heavy metals

The toxic effects of heavy metals on organisms are well established. However, their specific action at the cellular level in different tissues is mostly unknown. We have used the housefly, Musca domestica, as a model organism to study the toxicity of four heavy metals: copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb). These have been fed to larvae at low and high, semi-lethal concentrations, and their accumulation in the head, thorax, and abdomen was subsequently measured in adult flies. In addition, their impact on the cellular concentration of several elements important for cell metabolism-sodium (Na+), magnesium (Mg++), phosphorous (P), sulphur (S), chloride (Cl-) and potassium (K+)-were measured in neural cells, muscle fibers, and midgut epithelial cells. Our study showed that the heavy metals accumulate mainly in the abdomen, in which the concentrations of two of the xenobiotic metals, Cd and Pb, were 213 and 23 times more concentrated, respectively, than in controls. All the heavy metals affected the cellular concentration of light elements in all cell types, but the changes observed were dependent on tissue type and were specific for each heavy metal, and its concentration.

Production of Catalases by Aspergillus niger Isolates as a Response to Pollutant Stress by Heavy Metals

Isolates of Aspergillus niger, selected from the coal dust of a mine containing arsenic (As; 400 mg/kg) and from the river sediment of mine surroundings (As, 1651 mg/kg, Sb, 362 mg/kg), growing in minimal nitrate medium in the phase of hyphal development and spore formation, exhibited much higher levels of total catalase activity than the same species from the culture collection or a culture adapted to soil contaminated with As (5 mg/L). Electrophoretic resolution of catalases in cell-free extracts revealed three isozymes of catalases and production of individual isozymes was not significantly affected by stress environments. Exogenously added stressors (As(5+), Cd(2+), Cu(2+)) at final concentrations of 25 and 50 mg/L and H(2)O(2) (20 or 40 mM) mostly stimulated production of catalases only in isolates from mines surroundings, and H(2)O(2) and Hg(2+) caused the disappearance of the smallest catalase I. Isolates exhibited a higher tolerance of the toxic effects of heavy metals and H(2)O(2), as monitored by growth, than did the strain from the culture collection.

Attenuation of Zinc-Induced Acute Pancreatitis by Zinc Pretreatment: Dependence on Induction of Metallothionein Synthesis

Pretreatment with zinc (Zn) is known to produce tolerance to several of the toxic effects of heavy metals and pro-oxidants with or without the induction of metallothionein (MT) synthesis. We found previously that injection of high-dose Zn caused acute pancreatitis in mice. An injection of Zn (50-75 mg/kg) resulted in a significant increase in the plasma activities of exocrine enzymes, indicating acute pancreatitis, and no greater increase in Zn concentration in the pancreatic MT fraction with Zn doses. To clarify the role of MT in the pancreatic toxicity of Zn, we examined the effects of pretreatment with nontoxic doses of Zn on the induction of acute pancreatitis by Zn challenge. Pretreatment with Zn (10 mg/kg) 24 hr before Zn challenge attenuated Zn-induced acute pancreatitis. However, pretreatment with Zn only 2 hr before challenge was ineffective. Pretreatment with Zn 24 hr before resulted in more Zn in the MT fraction of pancreatic cytosol and less Zn in the low-molecular-weight fraction compared with pretreatment 2 hr before. These data indicate that pancreatic MT may diminish the toxicity of Zn by sequestering excess Zn. Moreover, Zn-induced acute pancreatitis also was attenuated by treatment with aprotinin, a trypsin inhibitor. Our findings suggest that the Zn ion — either free or bound to small molecules — is involved in the development of acute pancreatitis that includes intrapancreatic trypsinogen activation.

Toxicity of metals and metal mixtures: analysis of concentration and time dependence for zinc and copper

The toxic effects of heavy metals, zinc and copper, in unary and binary solutions were studied using the Microtox® acute toxicity test which relies upon the attenuation of light intensity emitted by Vibrio fischeri. The toxic effect Γ (ratio of the light intensity lost at time t to the light intensity remaining at time t) of zinc could be related to its concentration [X] by a two-parameter equation Γ=a(1-exp(-b[X])), where parameter a was a function of time and b equal to 0.88L/mg. The toxic effect of zinc asymptotically approached a maximum with respect of to concentration at all times. The toxic effect of copper was fundamentally different from that of zinc, and increased exponentially with concentration without any limiting maximum value. It could also be described by a two-parameter equation, however, the equation had the form Γ=aexp(b[X]), where parameter a was a constant and b a function of time. The different functional dependencies (of the toxic effect on the metal concentration) of zinc and copper indicate that different toxicity/inhibition mechanisms were possibly responsible for the attenuation of light intensity for the two metals. The toxic effects of binary mixtures were substantially higher than those expected on the basis of additivity of individual metals. No simple correlations were obtained that could relate the toxic effect of binary mixture to those of individual metals. A better understanding of metal–microbe interactions is needed for achieving predictive capability for toxic effect of mixtures.

Metal toxicity affects fungal and bacterial activities in soil differently.

Although the toxic effect of heavy metals on soil microorganism activity is well known, little is known about the effects on different organism groups. The influence of heavy metal addition on total, bacterial, and fungal activities was therefore studied for up to 60 days in a laboratory experiment using forest soil contaminated with different concentrations of Zn or Cu. The effects of the metals differed between the different activity measurements. During the first week after metal addition, the total activity (respiration rate) decreased by 30% at the highest level of contamination and then remained stable during the 60 days of incubation. The bacterial activity (thymidine incorporation rate) decreased during the first days with the level of metal contamination, resulting in a 90% decrease at the highest level of contamination. Bacterial activity then slowly recovered to values similar to those of the control soil. The recovery was faster when soil pH, which had decreased due to metal addition, was restored to control values by liming. Fungal activity (acetate-in-ergosterol incorporation rate) initially increased with the level of metal contamination, being up to 3 and 7 times higher than that in the control samples during the first week at the highest levels of Zn and Cu addition, respectively. The positive effect of metal addition on fungal activity then decreased, but fungal activity was still higher in contaminated than in control soil after 35 days. This is the first direct evidence that fungal and bacterial activities in soil are differently affected by heavy metals. The different responses of bacteria and fungi to heavy metals were reflected in an increase in the relative fungal/bacterial ratio (estimated using phospholipid fatty acid analysis) with increased metal load.

A survey of symbiotic nitrogen fixation by white clover grown on metal contaminated soils

There is conflicting evidence about toxic effects of heavy metals in soil on symbiotic nitrogen fixation. This study was set-up to assess the general occurrence of such effects. Soils with metal concentration gradients were sampled from six established field trials, where sewage sludge or metal salts have been applied, or from a transect in a sludge treated soil. Additional contaminated soils were sampled near metal smelters, in floodplains, in sludge amended arable land and in a metalliferous area. Symbiotic nitrogen fixation was measured with 15N isotope dilution in white clover ( Trifolium repens L.) grown in potted soil that was not re-inoculated, and using ryegrass ( Lolium perenne L.) as reference crop. The fraction nitrogen in clover derived from fixation (N dff) varied from 0 to 88% depending on soil. Pronounced metal toxicity on N dff was only confirmed in a sludge treated soil where nitrogen fixation was halved from the control value at soil total metal concentration of 737 mg Zn kg −1, 428 mg Cu kg −1 and 10 mg Cd kg −1. The N dff was significantly reduced by increasing metal concentration in soils from two other sites where N dff was low throughout and where these effects might be attributed to confounding factors. No significant effects of metals on N dff were identified in all other gradients even up to elevated total metal concentration (e.g. 55 mg Cd kg −1). The variation of N dff among all soils ( n=48), is mainly explained by the number of rhizobia in the soil (log MPN, log (cells g −1 soil)), whereas correlations with total or soil solution metal concentrations were weak ( R 2<0.25). The log MPN is significantly affected by the presence or absence of the host plant at the sampling site. No effects of metals were identified at log MPN>3, even at total Zn concentrations of about 2000 mg Zn kg −1, whereas metal toxicity could be identified at lower most probable number (MPN) values. This survey shows that the metal toxicity on symbiotic nitrogen fixation cannot be generalized and that survival of a healthy population of the microsymbiont is probably the critical factor.

HEAVY METAL–INDUCED OXIDATIVE STRESS IN ALGAE1

Heavy metals, depending on their oxidation states, can be highly reactive and, as a consequence, toxic to most organisms. They are produced by an expanding variety of anthropogenic sources suggesting an increasingly important role for this form of pollution. The toxic effect of heavy metals appears to be related to production of reactive oxygen species (ROS) and the resulting unbalanced cellular redox status. Algae respond to heavy metals by induction of several antioxidants, including diverse enzymes such as superoxide dismutase, catalase, glutathione peroxidase and ascorbate peroxidase, and the synthesis of low molecular weight compounds such as carotenoids and glutathione. At high, or acute, levels of metal pollutants, damage to algal cells occurs because ROS levels exceed the capacity of the cell to cope. At lower, or chronic, levels algae accumulate heavy metals and can pass them on to organisms of other trophic levels such as mollusks, crustaceans, and fishes. We review here the evidence linking metal accumulation, cellular toxicity, and the generation of ROS in aquatic environments.

Toxicity of heavy metals for microorganisms isolated from slow sand filter schmutzdecke

This paper describes the susceptibility of three species of environmental bacteria isolated from the schmutzdecke of biologically active slow sand filters to cadmium, chromium and lead. The microorganisms, all identified as members of the genus Pseudomonas, were grown in tryptic soy broth with various concentrations of the selected heavy metals. The mean generation times (MGT) of the bacteria were compared to evaluate the toxic effects of the heavy metals. All three species tolerated high doses of heavy metals and the MGTs increased exponentially as the heavy metal concentrations increased; 12 mg I‐1 was die highest dose tested and the bacteria continued to grow albeit at very slow rates. In dilute media, the toxic effects of heavy metals were enhanced, illustrating the protection effect of organic matter and heavy metal complex formation. Growth studies of the isolated microorganisms on half‐strength tryptic soy agar containing 6 mg I‐1 heavy metals also proved useful in determining toxidty.

Responses of Niphargus montellianus and Gammarus balcanicus (Crustacea, Amphipoda) from karst waters to heavy metal exposure

The response to some heavy metals (Cd, Cu, and Zn) was examined in two amphipods, Niphargus montellianus and Gammarus balcanicus, living in karst waters and endowed with different ecological characteristics. Exposure experiments were made, in the controlled conditions of a biospeleology laboratory, to increasing concentrations of metals in the range 0.1-10 μg ml -1 for up to 10 days. Hypogean and epigean amphipods differed in their responses, G. balcanicus being more sensitive to the toxic effects of heavy metals than the hypogean N. montellionus. The degree of tolerance was Cu<Cd<Zn in both organisms. Metal contents were checked in amphipods in natural conditions and after metal exposure; differences in accumulation rates suggest the potential use of Niphargus as a biological indicator for monitoring groundwater heavy metal pollution.

Differential sensitivity of Anabaena doliolum to Cu and Zn in batch and semicontinuous cultures

Elevated concentrations of Cu and Zn inhibited Anabaena doliolum more severely in semicontinuous culture than in batch culture with growth and protein, chlorophyll a, and carotenoid contents generally more than two-fold more sensitive in the former culture system. The greater sensitivity of A. doliolum to test metals in semicontinuous culture was associated with their greater accumulation. The level of inhibition of various parameters of the test organism remained almost constant in semicontinuous culture, but considerable alleviation of the inhibitory effect occurred in batch culture with time concomitant with a regular decline in metal content of cells. However, metal content of cells in semicontinuous culture remained more or less constant with time, thereby causing no change in the level of inhibition. Unlike semicontinuous culture, batch culture showed considerable depletion of phosphate from the medium and a rise in pH (from 7 to 7.8). In conclusion, batch culture is not appropriate for long-term assessment of metal toxicity as it might substantially underestimate toxic effects of heavy metals.

Bioavailability and toxicity of cadmium to microorganisms and their activities in soil: a review

Significant quantities of cadmium (Cd) have been added to the soils globally due to various anthropogenic activities, raising concerns for environmental health. Microorganisms play a unique role in the soil ecosystem, because of their contributions to soil fertility. Contrasting trends, reported on the toxic effects of heavy metals including Cd on soil microorganisms and their activities, are attributable to short-term studies often limited to a single soil type and conducted under controlled laboratory conditions. There is a paucity of reliable field data on Cd alone, since most field studies on Cd-microorganism interactions in soils are based on sewage sludge containing multimetals and organic substances. No single parameter can be used to generalize Cd toxicity and different parameters can provide contrasting results. A battery of relevant tests, rather than just one single assay, involving important microbial activities should therefore be included in ecotoxicity studies. The bioavailability of Cd and associated toxicity to soil biota vary with time, soil type, speciation, ageing, Cd-source, organisms and the environmental factors. The available fraction or soil solution Cd, and not the total concentration of Cd, seems to correlate well with the toxicity parameters.

Early toxic effect of zinc, cobalt, and cadmium on photosynthetic activity of green alga Chlorella pyrenoidosa Chick S-39

Early toxic effects of heavy metals (HMs) Zn, Co, and Cd in concentration from 0.01 to 100 mM on photosynthetic activity of the green alga Chlorella pyrenoidosa Chick S-39 were studied. The early effect of HMs was manifested as a rapid (0.5-2 h) reduction of photoinduced oxygen release by the algal cells. The suppressed relative yield of variable chlorophyll fluorescence ratio (Fv/Fm) by the metals as well as its dynamics in C. pyrenoidosa demonstrated rapid inactivation of photosystem II (PS II). Analysis of the induction curve of delayed chlorophyll fluorescence in Chlorella cells suggested that the early toxic effects of the tested concentrations of Zn, Co, and Cd included both reduced electron transport in PS II and decreased photosynthetic membrane energization. Hence, the early toxic effect of Zn, Co, and Cd was primarily related to the decreased efficiency of the light reactions of photosynthesis which further reduced the alga productivity later.

Effect of heavy metals and PAH on soil assessed via dehydrogenase assay

Dehydrogenase enzyme activity (DHA) assay method using resazurin was accommodated for measuring of toxicity of compound contaminants on uncharacterized microbial communities present in any given soil. The method was used to compare the toxic effect of heavy metal and polycyclic aromatic hydrocarbon (PAH) contaminant mixture (Cr, Pb, Cu, Cd, Pyrene) on four typical Estonian soils covering a range of compositions. The method proved to be useable on all soils; the sensitivity of soil microbiology to toxic effect of contaminants was found to have a negative correlation with Ca and organic matter (OM) content and a positive correlation with amorphous phase content of soils.

Saucing of tobacco-cut so as to increase microelement content in the cigarette smoke

Tobacco plant is known to easily absorb heavy metals from soil and accumulate them in leaves. Part of these metals is transferred by the smoke into the human body, where they accumulate, damage the organs (mainly kidney and liver) and act as promoters in conjunction with carcinogens. Application of the essential elements can be effective in the prevention of toxicity and curative manner against the negative effects of toxic heavy metals. Reducing the harmful health effects of tobacco smoke is one of the major tasks of our research. Essential elements, first of all Zn and Fe, were added in an artificial way on tobacco-cut so that these elements should pass by the smoke to the smokers' bodies. The toxic metal content of our tobacco-sample was consistent with other data published in international literature (Cd: 1.55 mg g –1; Pb: 1.51 mg g –1). The transfer rates of these metals from tobacco-cut to smoke were significant (Cd: 15–34%; Pb: 8–20%). Twenty-thirty percent of the artificially added Zn and 10–23% o...

Toxicity Assessment of Environmental Complex Mixtures in and around Roadways

The aim of this study was to evaluate the toxic effect of heavy metals to bacteria and plant. A spiderwort (Tradescantis clone BNL 4430) and coliform bacteria (Esherichea coli strain MV1184 and Comamonas testosteroni strain TK102) were used in this study. The growth of C. testosteroni strain TK102 was inhibited by copper, lead, and cadmium. Cadmium shows the strongest growth inhibition among these three metals. In an assay of Tradescantis, zinc reduced the amount of chlorophiles in leaves. Copper inhibited flowering and had a fatal effect on Tradescantia.

Toxic metals and oxidative stress part I: mechanisms involved in metal-induced oxidative damage.

Toxic metals (lead, cadmium, mercury and arsenic) are widely found in our environment. Humans are exposed to these metals from numerous sources, including contaminated air, water, soil and food. Recent studies indicate that transition metals act as catalysts in the oxidative reactions of biological macromolecules therefore the toxicities associated with these metals might be due to oxidative tissue damage. Redox-active metals, such as iron, copper and chromium, undergo redox cycling whereas redox-inactive metals, such as lead, cadmium, mercury and others deplete cells' major antioxidants, particularly thiol-containing antioxidants and enzymes. Either redox-active or redox-inactive metals may cause an increase in production of reactive oxygen species (ROS) such as hydroxyl radical (HO.), superoxide radical (O2.-) or hydrogen peroxide (H2O2). Enhanced generation of ROS can overwhelm cells' intrinsic antioxidant defenses, and result in a condition known as "oxidative stress". Cells under oxidative stress display various dysfunctions due to lesions caused by ROS to lipids, proteins and DNA. Consequently, it is suggested that metal-induced oxidative stress in cells can be partially responsible for the toxic effects of heavy metals. Several studies are underway to determine the effect of antioxidant supplementation following heavy metal exposure. Data suggest that antioxidants may play an important role in abating some hazards of heavy metals. In order to prove the importance of using antioxidants in heavy metal poisoning, pertinent biochemical mechanisms for metal-induced oxidative stress should be reviewed.