Showing papers on "Zinc toxicity published in 2011"

Interactions of zinc and cadmium toxicity in their effects on growth and in antioxidative systems in tomato plants (Solarium lycopersicum)

Abstract: The interaction between zinc and cadmium was investigated in tomato plants (Solanum lycopersicum). Ten-day-old seedlings were treated with 10 micromol/L CdCl2 associated to different concentrations of ZnCl2 (10, 50, 100, and 150 micromol/L). Zn supply clearly reduced Cd accumulation in leaves and simultaneously increased Zn concentration. Cd induced oxidative stress in leaves as indicated by an increase in thiobarbituric acid-reactive substances (TBARS) level and chlorophyll breakdown. Furthermore, compared with control, Cd-treated plants had significantly higher activities of superoxide dismutase (SOD, EC 1.15.1.1), whereas, catalase (CAT, EC 1.111.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) activities were significantly suppressed by Cd addition. Zn supplementation, at low level, restored and enhanced the functional activity of these enzymes (SOD, CAT, APX and GR) as compared to Cd-alone-treated plants. The beneficial effect of adequate Zn level on Cd toxicity was confirmed by a significant decrease in TBARS level and restoration of chlorophyll content. However, when Zn was added at high level in combination with Cd there was an accumulation of oxidative stress, which was higher than that for Cd or excess Zn alone treatments. These results suggested that higher Zn concentrations and Cd are synergistic in their effect on plant growth parameters and oxidative stress.

The alleviation of zinc toxicity by silicon is related to zinc transport and antioxidative reactions in rice

Abstract: The objective of this study is to elucidate the roles of silicon (Si) in enhancing tolerance to excess zinc (Zn) in two contrasting rice (Oryza sativa L.) cultivars: i.e. cv. TY-167 (Zn-resistant) and cv. FYY-326 (Zn-sensitive). Root morphology, antioxidant defense reactions and lipid peroxidation, and histochemical staining were examined in rice plants grown in the nutrient solutions with normal (0.15 μM) and high (2 mM) Zn supply, without or with 1.5 mM Si. Significant inhibitory effects of high Zn treatment on plant growth were observed. Total root length (TRL), total root surface area (TRSA) and total root tip amount (TRTA) of both cultivars were decreased significantly in plants treated with high Zn, whereas these root parameters were significantly increased when Zn-stressed plants were supplied with 1.5 mM Si. Supply of Si also significantly decreased Zn concentration in shoots of both cultivars, indicating lower root-to-shoot translocation of Zn. Moreover, superoxide dismutase (SOD), catalase (CAT), and asorbate peroxidase (APX) activities were increased, whereas malondialdehyde (MDA) and hydrogen peroxide (H2O2) concentrations were decreased in Si-supplied plants of both Zn-sensitive and Zn-resistant rice cultivars exposed to Zn stress. These alleviative effects of Si, further confirmed by the histochemical staining methods, were more prominent in the Zn-resistant cultivar than in the Zn-sensitive one. Taken together, all these results suggest that Si-mediated alleviation of Zn toxicity is mainly attributed to Si-mediated antioxidant defense capacity and membrane integrity. The possible role of Si in reduction of root-to-shoot translocation of Zn can also be considered.

Zinc Toxicity in Humans

Abstract: Zinc excess and insufficiency can moderate a cascade of metabolic processes that adversely affect the health of human beings and other organisms. Exposure to elevated levels of zinc and zinc-containing compounds can result in a variety of adverse effects in the gastrointestinal, hematological, and respiratory systems along with alterations in the cardiovascular and neurological systems of humans. In spite of the thousands of papers that have been published on biological effects of zinc, the challenge of quantifying the range of exposure doses that constitute zinc deficiency versus excess remains unresolved and some recent studies have pointed to a considerable overlap between what has generally been considered to be the essential dose and toxic dose, suggesting that the dose–response curve for zinc may not be a ‘U’ but a ‘V’. The limited margin of safety should be of some concern since millions of people are currently being exposed to various levels of zinc through food supplements and additives, medicines, disinfectants, antiseptic and deodorant preparations, and dental cement.

A novel approach reveals that zinc oxide nanoparticles are bioavailable and toxic after dietary exposures

Abstract: If engineered nanomaterials are released into the environment, some are likely to end up associated with the food of animals due to aggregation and sorption processes. However, few studies have considered dietary exposure of nanomaterials. Here we show that zinc (Zn) from isotopically modified 67ZnO particles is efficiently assimilated by freshwater snails when ingested with food. The 67Zn from nano-sized 67ZnO appears as bioavailable as 67Zn internalized by diatoms. Apparent agglomeration of the zinc oxide (ZnO) particles did not reduce bioavailability, nor preclude toxicity. In the diet, ZnO nanoparticles damage digestion: snails ate less, defecated less and inefficiently processed the ingested food when exposed to high concentrations of ZnO. It was not clear whether the toxicity was due to the high Zn dose achieved with nanoparticles or to the ZnO nanoparticles themselves. Further study of exposure from nanoparticles in food would greatly benefit assessment of ecological and human health risks.

Effect of zinc toxicity on liver histology of Nile tilapia, Oreochromis niloticus

Abstract: In the present study the toxic effects of zinc (Zn) on the liver structure of Nile tilapia,Oreochromis niloticus were investigated. Additionally, we estimated whether Zn concentration and exposure period influence the degree and nature of histological changes in the liver of exposed fish. Two hundred and forty fish (the average weight was 24.30± 2.85 g) were distributed randomly in twenty four glass aquaria (80 L) with stocking density of 10 fish for each. The aquaria were divided into two groups: the first group was exposed to 2, 4 and 6 mg/L of ZnCl2 which represent 0.25, 0.50 and 0.75 of Zn LC50 respectively for one week (short exposure period); while the second group was exposed to the same concentrations of ZnCl2 with the same replicates for 4 weeks (long exposure period). In addition, control group were not exposed fish to ZnCl2 (0.00 LC50) were stocked with three replicates for each period. Fish mortality was significantly increased in a dose-dependent manner, without any significant effect of the exposure duration. Histological changes in the liver included hepatocyte degeneration, nuclear pycnosis, cellular swelling, and congestion of blood vessels. There was a marked difference in these changes among the different treatments of Zn concentrations in addition to the intensity of histological changes were however influenced by the extent of exposure period. Key words: Nile tilapia, Oreochromis niloticus, liver, histological changes, LC50 of Zinc.

Impact of manganese, copper and zinc ions on the transcriptome of the nosocomial pathogen Enterococcus faecalis V583.

Abstract: Mechanisms that enable Enterococcus to cope with different environmental stresses and their contribution to the switch from commensalism to pathogenicity of this organism are still poorly understood. Maintenance of intracellular homeostasis of metal ions is crucial for survival of these bacteria. In particular Zn(2+), Mn(2+) and Cu(2+) are very important metal ions as they are co-factors of many enzymes, are involved in oxidative stress defense and have a role in the immune system of the host. Their concentrations inside the human body vary hugely, which makes it imperative for Enterococcus to fine-tune metal ion homeostasis in order to survive inside the host and colonize it. Little is known about metal regulation in Enterococcus faecalis. Here we present the first genome-wide description of gene expression of E. faecalis V583 growing in the presence of high concentrations of zinc, manganese or copper ions. The DNA microarray experiments revealed that mostly transporters are involved in the responses of E. faecalis to prolonged exposure to high metal concentrations although genes involved in cellular processes, in energy and amino acid metabolisms and genes related to the cell envelope also seem to play important roles.

Histidine Protects Against Zinc and Nickel Toxicity in Caenorhabditis elegans

Abstract: Zinc is an essential trace element involved in a wide range of biological processes and human diseases. Zinc excess is deleterious, and animals require mechanisms to protect against zinc toxicity. To identify genes that modulate zinc tolerance, we performed a forward genetic screen for Caenorhabditis elegans mutants that were resistant to zinc toxicity. Here we demonstrate that mutations of the C. elegans histidine ammonia lyase (haly-1) gene promote zinc tolerance. C. elegans haly-1 encodes a protein that is homologous to vertebrate HAL, an enzyme that converts histidine to urocanic acid. haly-1 mutant animals displayed elevated levels of histidine, indicating that C. elegans HALY-1 protein is an enzyme involved in histidine catabolism. These results suggest the model that elevated histidine chelates zinc and thereby reduces zinc toxicity. Supporting this hypothesis, we demonstrated that dietary histidine promotes zinc tolerance. Nickel is another metal that binds histidine with high affinity. We demonstrated that haly-1 mutant animals are resistant to nickel toxicity and dietary histidine promotes nickel tolerance in wild-type animals. These studies identify a novel role for haly-1 and histidine in zinc metabolism and may be relevant for other animals.

Interactions of cadmium and zinc impact their toxicity to the earthworm Aporrectodea caliginosa

Abstract: Individual and binary mixture effects of Cd and Zn on mortality of the earthworm Aporrectodea caliginosa were investigated in one soil type. Mutual, systemic interactions of Cd and Zn were assessed over a broad range of concentration combinations. Exposures were expressed as measured total concentrations in soil, porewater concentrations, and CaCl(2)-extractable concentrations. The Cd-Zn and Zn-Cd interactions in soil were estimated by comparing partition coefficients (K(d)) of one metal in the presence and absence of the second metal. Simple patterns of mixture toxicity (additive, antagonistic, or synergistic) were evaluated by the toxic unit approach. The more complex patterns (dose ratio dependent or dose level dependent) were quantified by the MIXTOX model. The partitioning of Cd and Zn between soil and pore water was affected neither by their concentration nor presence of the other metal, and metal partitioning remained linear at all exposure levels tested. The effect of the Cd and Zn mixtures on mortality of A. caliginosa was mainly antagonistic, and the magnitude of antagonism (1.1- 2.7 toxic units) was dependent upon both the relative concentrations of Cd and Zn and the concentration magnitudes. Interactions of both metals occurred at the organism level and were manifested in terms of effects (28-d median lethal concentrations). The present study highlights the importance of identifying the relative influence of various interactions from external exposure to internal assimilation in evaluating mixture toxicity.

Adsorption Studies of Zn (II) Ions from wastewater using Calotropis procera as an adsorbent

Abstract: Increased industrialization and human activities have impacted on the environment through disposal waste containing heavy metals. The presence of heavy metals in the environment can be detrimental to a variety of living species. Metals can be distinguished from other toxic pollutants, because these are non biodegradable, may undergo transformation, and can have a large environmental, public health, and economic impact. The presence of toxic heavy metal contaminants in aqueous streams, arising from the discharge of untreated metal containing effluents into water bodies, is one of the most important environmental issues. Zinc is an essential mineral, but too much is not beneficial. Symptoms of zinc toxicity include nausea/vomiting, fever, cough, diarrhea, fatigue, neuropathy and dehydration. Adsorption technique is one of the most important technologies for the treatment of polluted water from zinc, but seeking for the low-cost adsorbent is the target of this study. Removal of zinc studied using adsorbent prepared from poly vinyl activated charcoal of calotropis procera leaves (PVAC-CP). Batch adsorption experiments performed by varying adsorbent dose, pH of the metal ion solution and contact time. Adsorption of zinc is highly pH dependent and the results indicate that the maximum removal (85.8%) took place at dose 15gm/l in the pH range of 6 and initial concentration of 60 ppm. Kinetic experiments reveal that the dilute zinc solution reached equilibrium within 105 min. the adsorbent capacity was also studied the zinc adsorption followed both the Langmuir and Freundlich equation isotherms. Comprehensive characterization of parameters indicates that PVAC-CP to be an excellent material for adsorption of zinc ion to treat wastewater containing low concentration of the metal.

Luteolin protects against reactive oxygen species-mediated cell death induced by zinc toxicity via the PI3K-Akt-NF-κB-ERK-dependent pathway.

Abstract: Zinc ion elevation contributes to acute excitotoxic brain injury and correlates with the severity of dementia in chronic neurodegenerative diseases. Downstream control of zinc-triggered signals is believed to be an efficient countermeasure. In the current study, we examined whether the flavonoid luteolin (Lu) could protect human neuroblastoma SH-SY5Y cells against zinc toxicity. We found that Lu suppressed overproduction of reactive oxygen species and protected against apoptotic cell death induced by zinc. By using specific inhibitors, we found that zinc strongly triggered Akt and ERK1/2 activation via a PI3K–Akt–NF-κB–ERK1/2-dependent pathway. Furthermore, Lu completely blocked this activation. Our study strongly supports the hypothesis that Lu might protect SH-SY5Y cells against ROS-mediated apoptotic cell death induced by zinc in part by inhibiting the PI3K–Akt–NF-κB–ERKs pathway. © 2011 Wiley-Liss, Inc.

Effect of selected heavy metals on the histopathology of different tissues of earthworm Eudrillus eugeniae.

Abstract: Laboratory-scale experiments were conducted to determine the effect of heavy metals viz. copper (Cu), cadmium (Cd), chromium (Cr), lead (Pb), and zinc (Zn) on the different vital tissues of earthworm Eudrillus eugeniae such as head, gizzard, clitellum, and intestine after the worms were placed in municipal solid waste (MSW) substrate spiked with heavy metals in the concentration range of 0.05 g/kg to 1.0 g/kg of the waste for Cu, Cr, PB, and Zn and 0.05 g/kg for Cd. The experiments were conducted for 100 days with periodic observations and sample collection for investigation after every 10th day. Copper and lead metals were found to cause more deleterious effect in head, gizzard, and intestine. Chromium metal caused cellular damage to the intestinal region. In comparison, cadmium metal severity was more than copper, lead, and chromium metal. Zinc metal did not show deleterious effect on tissues. In general, earthworms can be used as biomarkers in toxicity studies related to heavy metals at cellular levels.

Effects of lead and zinc mining contamination on bacterial community diversity and enzyme activities of vicinal cropland

Abstract: In the process of mining activity, many kinds of heavy metals enter into soils with dust, causing serious contamination to the environment. In this study, six soils were sampled from cropland at different distances from a lead/zinc mine in Heilongjiang Province, China. The total contents of lead and zinc in the vicinal cropland exceeded the third level of environmental quality standard for soil in China, which indicated that soils in this area were moderately contaminated. Bacterial community diversity and population were greatly decreased when the concentrations of lead and zinc were beyond 1,500 and 995 mg kg − 1, respectively, as analyzed by plate counting and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The bands of DGGE patterns varied with the degree of contamination. The activities of soil urease, phosphatase, and dehydrogenase were negatively correlated with the concentrations of lead and zinc. The highest inhibitory effect of heavy metals on soil enzyme activities was observed in urease. It was noted that PCR-DGGE patterns combined with soil enzyme activity analysis can be indices for the soil quality assessment by heavy metal contamination.

Uptake and partitioning of zinc in Lemnaceae.

Abstract: Macrophytes provide food and shelter for aquatic invertebrates and fish, while also acting as reservoirs for nutrients and trace elements. Zinc accumulation has been reported for various Lemnaceae species. However, comparative accumulation across species and the link between zinc accumulation and toxicity are poorly understood. Morphological distribution and cellular storage, in either bound or soluble form, are important for zinc tolerance. This study shows differences in the uptake and accumulation of zinc by three duckweed species. Landoltia punctata and Lemna minor generally accumulated more zinc than Lemna gibba. L. minor, but not L. gibba or L. punctata, accumulated greater concentrations of zinc in roots compared to fronds when exposed to high levels of zinc. The proportion of zinc stored in the bound form relative to the soluble-form was higher in L. minor. L. punctata accumulated greater concentrations of zinc in fronds compared to roots and increased the proportion of zinc it stored in the soluble form, when exposed to high zinc levels. L. gibba is the only species that significantly accumulated zinc at low concentrations, and was zinc-sensitive. Overall, internal zinc concentrations showed no consistent correlation with toxic effect. We conclude that relationships between zinc toxicity and uptake and accumulation are species specific reflecting, among others, zinc distribution and storage. Differences in zinc distribution and storage are also likely to have implications for zinc bioavailability and trophic mobility.

V-ATPase dysfunction under excess zinc inhibits Arabidopsis cell expansion

Abstract: Although zinc is an essential micronutrient for all living organisms, zinc is harmful to cells at high levels. In the presence of excess zinc, plants exhibit several major symptoms, including root growth inhibition, abnormal root hair morphology and chlorosis. To dissect the molecular mechanisms underlying the effects of excess zinc on plant cells, we used aniTRA Q-based quantitative proteomics approach to analyze the microsomal protein profiles of Arabidopsis roots from wild-type (WT) plants and de-etiolated 3-1 (det3-1), a vacuolar H+ -AT Pase (V-AT Pase) subunit C-defective mutant. A comparative analysis of the iTRA Q data from WT and det3-1 plants exposed to excess zinc suggests that the reduction in V-AT Pase subunit levels and its activity are the cause of the symptoms of zinc toxicity, including the inhibition of cell expansion. Provided that reduced V-AT Pase activity in the trans-Golgi network (TGN) alone can inhibit cell expansion, it is possible that the det3-1 mutant phenotype is caused mainly by a defect in TGN acidification, leading to reduced cell wall component trafficking and cell expansion in the presence of excess zinc. To evaluate the contribution of V-AT Pase activity to vacuolar acidification under excess zinc, the vacuolar pH was measured. Our results indicate clear alkalinization of deep cell vacuoles treated with 300 μM ZnSO4.

Investigation of zinc, copper, lead and cadmium accumulation in the tissues of Sander lucioperca (L., 1758) living in Hirfanlı Dam Lake, Turkey.

Abstract: This study, some metals (zinc, copper, lead and cadmium) were analyzed in liver, muscle and gills of Sander lucioperca (Linnaeus, 1758) caught from the Hirfanli Dam Lake in December 2007. The highest concentrations were found in liver (zinc:32.5 μg/g, lead:10.73 μg/g, copper:5.85 μg/g, cadmium:0.76 μg/g) of Sander lucioperca. It was seen that the accumulation of zinc, lead and cadmium primarily took place in liver followed by muscles and gills. It was observed that copper is mainly accumulated in liver followed by gill and mucsles.

Effect Of Copper And Zinc Toxicity On Physiological And Biochemical Parameters In Vigna Mungo (L.) Hepper

Abstract: The present study aimed at investigating the effects of copper and zinc in Vigna mungo (L.) growth and metabolism. Physiological parameters decrease consequently with increasing copper and zinc concentration in nutrient medium. Copper at 0.2mM concentration led to 32.12% and 47.82% reduction in fresh weight and dry weight respectively whereas, zinc at 1.50mM concentration resulted in 23.83% and 70.56% decrease in fresh weight and dry weight of seedlings with respect to control. The combined effect of copper and zinc on seedling growth was antagonistic at low concentration but showed additive effect at high concentrations. The results demonstrated an increase in DNA content/mg fr. Wt. of seedlings up to 124.45% at 0.2mM Cu + 1.50mM Zn and RNA content was adversely affected in all treatment conditions. Moreover, seedlings exposed to copper and zinc metal ions have shown significant variations in phosphate hydrolysis and mobilization from source to sink and specific activity of acid phosphatase.

Dietary Taurine Reduces Zinc-Induced Toxicity in Male Wistar Rats

Abstract: Taurine is an agent for treating the heavy metal intoxication and presence of metals such as zinc, copper, and iron may have a role in heavy metal toxicity, a study was undertaken to investigate the effect of taurine on the toxicity of zinc in male Wistar rats. The rats were divided into 8 groups and fed different diets with or without supplement of 5% taurine and 150 to 600 ppm zinc for 2 mo. It was found that the body weight of rats, the ratios of liver and kidney weight to body weight, and the level of glutathione in the liver were decreased with increasing the dose of zinc. The levels of zinc in the liver, kidney, and plasma, the levels of malondialdehyde in the plasma, the levels of thiobarbiture acid-reactive substances in the liver, the activities of aspartate transaminase, alanine transaminase in the plasma, the levels of blood urea nitrogen and creatinine in the plasma of rats were increased with the increasing dose of zinc. Hence, symptoms of zinc toxicity in rats included loss of body weight, hepatotoxicity, and nephrotoxicity. However, these toxic effects of zinc were significantly reduced when the rats fed diet with supplement of taurine. Furthermore, the level of zinc in the feces of rats treated with taurine and zinc was higher than that of rats treated with zinc alone. It indicated that taurine thereby leading to a decreased absorption of dietary zinc and promoted excretion.

Hair zinc levels in pet and feral cats (felis catus)

Abstract: Zinc is an essential element for maintaining proper functions of animal bodies. It is a component of many hormones and enzymes and a participant in the metabolism of carbohydrates or the synthesis of nucleic acids and proteins. Animal tissues typically contain 10-200 mg of zinc kg–1. Most of this amount (98%) can be found inside the cells. Zinc toxicity is associated mainly with the secondary copper deficit. The aim of the present investigation has been to assess zinc contamination of the environment with coats of domestic and feral cats being the indicator. Urban feral cats are synantrophic animals, living in an urbanized environment and scavenging on human food waste. Thus, they can be treated as a bioindicator of the presence of certain elements in the environment. Analyses of the zinc content in cats’ hair have been performed to check whether the zinc level is connected with cats’ coat colour, living conditions and gender. The coat samples were collected from the middle abdominal region. Then they were degreased and mineralized in a microwave apparatus, in concentrated nitric acid under increased pressure. The zinc content was determined by the ICP-OES method. The mean zinc content in the investigated coat samples was 238.9 mg kg –1 . The lowest zinc content was observed in white hair and the highest – in tortoiseshell hair. The results have confirmed that the content of zinc depends on the hair saturation with melanin. Statistical analysis has shown significant differences between the group of female cats living in the wild (268.09 mg kg–1) and the group of breeding female cats (214.49 mg kg–1) at p=0.05. A higher zinc content was observed in the group of older cats. The mean values did not differ from mean values of the zinc content in the coat and hair of other mammals. Considering the living conditions of the animals, the highest zinc content was noted in the group of animals living in the wild (feral ones).

Foraging, feeding, and reproduction on silica substrate: Increased waterborne zinc toxicity to the estuarine epibenthic amphipod Melita plumulosa.

Abstract: Artificial substrates consisting of fine milled silica with or without α-cellulose were evaluated for their capacity to support survival, growth, and fecundity in the amphipod Melita plumulosa. There were no significant differences in the survival and fecundity of adult amphipods maintained for up to 13 d on natural sediment, silica-only, or silica/α-cellulose substrate when fed two algal foods, Sera micron and Rotiselco-ALG. However, growth among juveniles maintained on the silica/α-cellulose mixture was significantly inhibited over 14 d compared with natural sediment. Addition of a microencapsulated shrimp feed, Frippak, to the algal foods improved juvenile growth over 28 d but still did not match the nutritive value of natural sediment. Fine silica without cellulose was subsequently used in acute and reproductive toxicity tests with waterborne zinc. With food, a 10-d median lethal concentration (LC50) of 140 µg Zn/L and a 10-d no-effect concentration (NEC) of 80 µg Zn/L were obtained for juvenile survival on silica. In contrast, a 10-d LC50 of 200 µg Zn/L and a 10-d NEC of 180 µg Zn/L were obtained for juveniles in water-only exposures. Similarly, exposure of adult females to Zn without food on silica compared with water-only exposures gave 10-d LC50s of 380 and 490 µg Zn/L and 10-d NECs of 130 and 370 µg Zn/L, respectively. The reproduction toxicity test indicated significant adult mortality at 92 µg Zn/L and significantly reduced fecundity at 22 µg Zn/L. We surmised that the toxicity of waterborne zinc to M. plumulosa increased when maintained on nutrient-depleted silica compared with water-only exposure because of increased energy expended through foraging, in concert with the likely increased exposure to Zn via the digestive tract and the gills.

Oxidative stress in newly-hatched Chorthippus brunneus--the effects of zinc treatment during diapause, depending on the female's age and its origins.

Abstract: The responses of glutathione, glutathione S-transferases (GSTs), and catalase (CAT) were determined in 1-day-old larvae of Chorthippus brunneus Thunberg, 1815, a grasshopper exposed to zinc during diapause, from unpolluted (Pilica) or polluted (Olkusz, Szopienice) sites. The aim of the work was to search for differences among populations of the insects as a result of various multistress pressures in their habitats. The question of zinc toxicity in the context of energy allocation was also considered. Zinc caused a decrease in glutathione concentration in the body of zinc-treated larvae. Significant differences between control and zinc-treated groups were confirmed for young females' progeny from Pilica and Olkusz as well as old females' progeny from Olkusz. GSTs activity was generally not influenced by zinc. It is possible that GSTs were not the most important target of zinc action. On the contrary, the influence of zinc on CAT activity was found. The increase in CAT activity after zinc treatment was similar for all studied populations. An increase in CAT activity after zinc exposure seems to be the most universal reaction. CAT activity in zinc-treated grasshoppers may explain the mechanism of zinc toxicity based on reactive oxygen forms generation.