Showing papers on "Zinc toxicity published in 2002"

Bioavailability and toxicity of dietborne copper and zinc to fish

Abstract: To date, most researchers have used dietborne metal concentrations rather than daily doses to define metal exposure and this has resulted in contradictory data within and between fish species. It has also resulted in the impression that high concentrations of dietborne Cu and Zn (e.g. > 900 mg kg(-1) dry diet) are relatively non-toxic to fish. We re-analyzed existing data using rations and dietborne metal concentrations and used daily dose, species and life stage to define the toxicity of dietborne Cu and Zn to fish. Partly because of insufficient information we were unable to find consistent relationships between metal toxicity in laboratory-prepared diets and any other factor including, supplemented metal compound (e.g. CuSO(4) or CuCl(2)), duration of metal exposure, diet type (i.e. practical, purified or live diets), or water quality (flow rates, temperature, hardness, pH, alkalinity). For laboratory-prepared diets, dietborne Cu toxicity occurred at daily doses of > 1 mg kg(-1) body weight d(-1) for channel catfish (Ictalurus punctatus), 1-15 mg kg(-1) body weight d(-1) (depending on life stage) for Atlantic salmon (Salmo salar) and 35-45 mg kg(-1) body weight d(-1) for rainbow trout (Oncorhynchus mykiss). We found that dietborne Zn toxicity has not yet been demonstrated in rainbow trout or turbot (Scophthalmus maximus) probably because these species have been exposed to relatively low doses of metal ( < 90 mg kg(-1) body weight d(-1)) and effects on growth and reproduction have not been analyzed. However, daily doses of 9-12 mg Zn kg(-1) body weight d(-1) in laboratory-prepared diets were toxic to three other species, carp Cyprinus carpio, Nile tilapia Oreochromis niloticus, and guppy Poecilia reticulata. Limited research indicates that biological incorporation of Cu or Zn into a natural diet can either increase or decrease metal bioavailability, and the relationship between bioavailability and toxicity remains unclear. We have resolved the contradictory data surrounding the effect of organic chelation on metal bioavailability. Increased bioavailability of dietborne Cu and Zn is detectable when the metal is both organically chelated and provided in very low daily doses. We have summarized the information available on the effect of phosphates, phytate and calcium on dietborne Zn bioavailability. We also explored a rationale to understand the relative importance of exposure to waterborne or dietborne Cu and Zn with a view to finding an approach useful to regulatory agencies. Contrary to popular belief, the relative efficiency of Cu uptake from water and diet is very similar when daily doses are compared rather than Cu concentrations in each media. The ratio of dietborne dose:waterborne dose is a good discriminator of the relative importance of exposure to dietborne or waterborne Zn. We discuss gaps in existing data, suggest improvements for experimental design, and indicate directions for future research.

Toxicity of metal mixtures to a tropical freshwater alga (Chlorella sp): the effect of interactions between copper, cadmium, and zinc on metal cell binding and uptake.

Abstract: The individual and combined effects of copper, cadmium, and zinc on the cell division rate of the tropical freshwater alga Chlorella sp. were determined over 48 to 72 h. Metal mixtures were prepared based on multiples of their single-metal median effective concentration (EC50) values, i.e., toxic units (TU) using a triangular mixture design with five toxicant levels (0, 0.75, 1.0, 1.25, and 1.5 TU). Single-metal EC50 values after a 72-h exposure were 0.11, 0.85, and 1.4 microM for copper, cadmium, and zinc, respectively. Significant interactions were observed for all metal combinations after 48 and 72 h. An equitoxic mixture of Cu + Cd was more than concentration additive (synergistic) to the growth of Chlorella sp., while combinations of Cu + Zn, Cd + Zn, and Cu + Cd + Zn were all less than concentration additive or were antagonistic. To determine the effect of each metal on the uptake of the other, extracellular (membrane-bound) and intracellular metal concentrations, both alone and in mixtures, were compared. The increased growth inhibition observed for mixtures of Cu + Cd was due to higher concentrations of cell-bound and intracellular copper in the presence of cadmium compared with copper alone (i.e., cadmium-enhanced copper uptake). In contrast, both extra- and intracellular cadmium concentrations were reduced in the presence of copper. In mixtures of Cu + Zn, copper also inhibited the binding and cellular uptake of zinc, which resulted in decreased toxicity. Zinc had no appreciable effect on the uptake of copper by Chlorella sp. Our results suggest that all three metals share some common uptake and transport sites on Chlorella cells and that copper out competes both cadmium and zinc for cell binding. Determination of metal cell distribution coefficients (K(d)) confirmed that K(d) values for cadmium and zinc in single-metal exposures decreased in the presence of copper.

Predicting acute zinc toxicity for Daphnia magna as a function of key water chemistry characteristics: Development and validation of a biotic ligand model

Abstract: The individual effect of different major cations(Ca2+, Mg2+, Na+, K+, and H+) on the acute toxicity of zinc to the waterflea Daphnia magna was investigated. The 48-h median effective concentration (EC50) in the baseline test medium (i.e., a standard medium with very low ion concentrations) was about 6 μM (Zn2+). An increase of Ca2+ (from 0.25 mM to 3 mM), Mg2+ (from 0.25 mM to 2 mM), and Na+ activity (from 0.077 mM to 13 mM) reduced zinc toxicity by a factor of 6.3, 2.1, and 3.1, respectively. No further toxicity reduction was observed when Ca2+ and Mg2+ activities exceeded 3.0 and 2.0 mM, respectively. Both K+ and H+ did not significantly alter zinc toxicity (expressed as Zn2+ activity). From these data, conditional stability constants for Ca2+ (log K = 3.24), Mg2+ (log K = 2.97), Na2+ (log K = 2.16), and Zn2+ (log K = 5.31) were derived and incorporated into a biotic ligand model (BLM) predicting acute zinc toxicity to D. magna in surface waters with different water quality characteristics. Validation of the developed BLM using 17 media with different pH, hardness, and dissolved organic carbon (DOC) content resulted in a significant correlation coefficient (R2 = 0.76) between predicted and observed 48-h EC50. Eighty-eight percent of the predictions were within a factor of 1.3 of the observed 48-h EC50.

Application of the biotic ligand model to predicting zinc toxicity to rainbow trout, fathead minnow, and Daphnia magna.

Abstract: The Biotic Ligand Model has been previously developed to explain and predict the effects of water chemistry on the toxicity of copper, silver, and cadmium. In this paper, we describe the development and application of a biotic ligand model for zinc (Zn BLM). The data used in the development of the Zn BLM includes acute zinc LC50 data for several aquatic organisms including rainbow trout, fathead minnow, and Daphnia magna. Important chemical effects were observed that influenced the measured zinc toxicity for these organisms including the effects of hardness and pH. A significant amount of the historical toxicity data for zinc includes concentrations that exceeded zinc solubility. These data exhibited very different responses to chemical adjustment than data that were within solubility limits. Toxicity data that were within solubility limits showed evidence of both zinc complexation, and zinc-proton competition and could be well described by a chemical equilibrium approach such as that used by the Zn BLM.

Comparative pulmonary toxicity of various soluble metals found in urban particulate dusts.

Abstract: The potential toxicity of an atmospheric dust sample EHC-93 has been attributed to the soluble fraction and, more specifically, to the zinc component. The concentration of Zn is the highest among the metals present in the soluble EHC-93 fraction. We now determine whether other metal components of this dust could cause similar lung injury if present at the same concentration as Zn (4.8 mg/g dust). Solutions of Zn, Cu, V, Ni, Fe, and Pb salts in 0.1 mL water were instilled to mouse lung and animals were killed at intervals up to 2 weeks later; each mouse received tritiated thymidine 1 hour before death. Solutions containing Zn and to a lesser degree Cu induced lung injury; in addition, increased numbers of alveolar macrophages and polymorphonuclear leukocytes were found in the lavage fluid, which also contained increased protein levels up to 1 week later. The magnitude of response was similar to that seen after administering EHC-93 dust at 1 mg in 0.1 mL water, whereas the response to other metal solutions containing Ni, Fe, Pb, and V was minimal. Morphologic evidence of lung injury and inflammation was also seen after EHC dust and the Zn or Cu solutions only. Reparative cell proliferation was measured after thymidine uptake and autoradiographs showed increased labeling of lung cells, particularly at 3 and 7 days. Labeling was confined to bronchiolar and type 2 alveolar epithelial cells, indicating previous epithelial cell necrosis in response to Zn or Cu. The results indicate that atmospheric contaminant metals Zn and Cu are most likely to cause lung injury and inflammation as compared to metals such as Ni, Fe, Pb, and V at the same concentrations. It appears that similar toxicity occurs when both redox (Cu) and nonredox (Zn) reactions are involved.

Biotic ligand model development predicting Zn toxicity to the alga Pseudokirchneriella subcapitata: possibilities and limitations.

Abstract: Biotic ligand models have been developed for various metals (e.g. Cu, Ag, Zn) and different aquatic species. These models incorporate the effect of physico-chemical water characteristics (major cations, pH, dissolved organic carbon) on the bioavailability and toxicity of the metal. In this study, the individual effects of calcium, magnesium, potassium, sodium and pH on zinc toxicity to the green alga Pseudokirchneriella subcapitata (formerly and better known as Selenastrum capricornutum and Raphidocelis subcapitata) were investigated. Stability constants for binding to algal cells (KBL) were derived for those cations affecting zinc toxicity, using the mathematical approach proposed by De Schamphelaere and Janssen [Environ. Sci. Technol. 63, (2002) 48–54]. Potassium proved to be the only cation tested that did not alter zinc toxicity to algae significantly. Log (KBL) values for Ca, Mg and Na, derived at pH 7.5, were 3.2, 3.9 and 2.8, respectively. Toxicity tests performed at different pH values (5.5–8.0) indicated that competition between H+ and Zn2+ reduces zinc toxicity. However, the observed relationship between (H+) and the 72h-EbC50 [expressed as μM (Zn2+)] is not linear and suggests that pH affects the physiology of the biotic ligand. Although, in general, our findings seem to suggest that zinc toxicity to algae can be modelled as a function of key water characteristics, the results also demonstrate that the part of the conventional BLM-hypothesis—i.e. that the binding characteristics of the biotic ligand are independent of the test medium characteristics—is not valid for algae. The observed pH-dependent change of stability constants should therefore be further investigated and incorporated in future BL-modelling efforts with algae.

Effects of zinc contamination on a natural nematode community in outdoor soil mesocosms.

Abstract: The effect of zinc on the indigenous nematode fauna of a sandy soil was determined in an experimentally contaminated outdoor field plot. The aims of the study were to describe and quantify the changes in density of separate nematode taxa and total nematodes, and the changes in the number of taxa, species diversity, community maturation, and species composition in response to zinc exposure with time, and to compare the observed responses with benchmark concentrations for soil as derived from the species sensitivity distribution (SSD) for zinc toxicity. Speciation of zinc in pore water was considered and CaCl2-exchangeable zinc concentrations were used as a measure of the bioavailable zinc fraction. After contamination, a reduction of total zinc and an increase of labile sorbed zinc over time occurred, concurrent with various changes in soil and biological characteristics. Data analyses on the nematode species revealed different sensitivity levels for several population and community endpoints to zinc exposure. Based on no observed effect concentration (NOEC) values, the most sensitive community-level response was obtained with principal response curve (PRC) analysis, which incorporates all density data in a single analysis. The PRC-based community NOECs were 56, 100, and 100 mg total Zn/kg dry soil after 3, 10, and 22 months of exposure, respectively. Based on 0.01 M CaCl2-exchangeable zinc, the community response appeared to increase, as NOECs were 4.9, 4.4, and 0.67 mg exchangeable Zn/kg dry weight. Total density was least sensitive, followed by diversity of taxa and the Shannon-Wiener index. NOECs for separate species covered a broad range from sensitive to tolerant species. This range of sensitivities was similar to the one found for other species groups tested in the field plot soil. A comparison was made between benchmark concentrations HC5 and HC50 derived from the general SSD of soil organisms for zinc and the nematode response data. These comparisons roughly confirm the predictions of the SSD model, that is, the community NOEC is in agreement with the benchmark that should protect the soil ecosystem's integrity, and large adverse effects were found at the benchmark derived for setting remediation urgency.

Cellular transporters for zinc.

Abstract: Nutritionally essential metals such as zinc are moved into and out of cells by a series of transport proteins or transporters. Their tri-fold purpose is to procure zinc from the environment, to protect cells against zinc toxicity, and maintain ample supplies of zinc for metabolic purposes. Two families of zinc transporters are known: the ZIP family that imports zinc and the ZnT family that functions in releasing zinc or sequestering zinc internally.

Pyruvate blocks zinc-induced neurotoxicity in immortalized hypothalamic neurons.

Abstract: Zinc is an essential trace element and present at high concentrations in the central nervous system. Recent studies have revealed that excess amount of extracellular zinc is neurotoxic, and that the disruption of zinc homeostasis may be related to various neurodegenerative diseases. Zinc (25-100 microM) caused significant death of immortalized hypothalamic neuronal cells (GT1-7 cells) in a dose- and time-dependent manner. LD50 was estimated to be 34 microM. The degenerated cells were TUNEL-positive and exhibited apoptosis-like characteristics. Preadministration of sodium pyruvate (1-2 mM), a downstream energy substrate, inhibited the zinc-induced neurotoxicity in GT1-7 cells. GT1-7 cells can be used as a good tool for the investigation of zinc neurotoxicity in the hypothalamus.

Acute and chronic toxicity of zinc to the mottled sculpin Cottus bairdi

Abstract: The acute and chronic toxicity of zinc to wild mottled sculpin (Cottus bairdi) was measured with 13-d and 30-d flow-through toxicity tests, respectively. Exposure water hardness was 48.6 mg/L as CaCO3 and 46.3 mg/L as CaCO3 in the acute and chronic tests, respectively; pH was slightly above neutral; and temperature near 12 degrees C. The median lethal concentration (LC50) after 96 h was 156 microg Zn/L, but decreased with exposure duration to a median incipient lethal level (ILL50) of 38 microg Zn/L after 9 d, the lowest zinc LC50 reported for any fish species. The 30-d chronic no-effect and lowest-effect concentrations were 16 microg Zn/L (no mortality) and 27 microg Zn/L (32% mortality), respectively. The ILL50 was 32 microg Zn/L. No sublethal growth differences were observed during the chronic test. Analysis of the results from these tests suggested that mottled sculpin may experience acute and chronic toxicity at zinc concentrations lower than any other fish species tested to date. Protection of aquatic communities in stream reaches contaminated by metals seem to require determination of zinc toxicity to lotic species other than trout and other species amenable to aquaculture.

Toxicity of cadmium and zinc to cercarial tail loss in Diplostomum spathaceum (Trematoda: Diplostomidae).

Abstract: The effect of cadmium and zinc at concentrations ranging from 0.1 to 10,000 microg/l on tail loss in cercariae of Diplostomum spathaceum was investigated at 3 temperatures (12, 20 and 25 degrees C) and 3 levels of water hardness (distilled water, soft water and hard water). Increasing tail loss over time was found to be linked with a parallel decrease in cercarial survival in controls. Exposure to the heavy metals induced, especially at high concentrations, a change in the relationship between cercarial tail loss and survival, causing either stimulation or inhibition of tail loss dependent on the individual toxic exposure. Under most environmental conditions the rate of tail loss over time was reduced by increasing metal concentrations. Inhibition of tail loss occurred in a limited number of both control and metal-exposed cercariae, with a number of low metal concentrations inducing greater inhibition than in controls. Stimulation of tail loss causing an increased tail loss rate above controls also occurred at certain high metal concentrations. Increasing water hardness and decreasing water temperature caused a reduced tail loss rate over time in both control and metal-exposed cercariae. However, with decreasing temperature a reduced rate of tail loss over time in metal-exposed cercariae compared to controls occurred at some low metal concentrations. When tail loss was compared against cercarial death of the experimental population toxic exposure induced changes in the parallel relationship of these parameters, dependent on individual metal concentration, water temperature and hardness. Differences in the relative effects of cadmium and zinc on cercariae were dependent on the environmental conditions of exposure. Both metals showed limited effects during the period of maximum cercarial infectivity (0-5 h). The mechanisms and importance of metal toxicity to cercarial tail loss are discussed.

Cadmium and zinc toxicity to soil microbial biomass and activity.

Abstract: Publisher Summary This chapter focuses on cadmium and zinc toxicity to soil microbial biomass and activity In the study discussed in the chapter, the effects of sewage sludge selectively enriched with zinc at the maximum permitted level and cadmium at concentration four times the current European Union (EU) limits on microbial biomass and activity were tested using soils under different management in a laboratory incubation experiment The microbial biomass and activity and the heavy metal mobility were measured over a period of six months The results showed that neither zinc at the maximum permitted level nor cadmium at concentrations as high as four times the current EU limits may have adverse effects on the microbial biomass and respiration of soils However, a better understanding of the synergistic interactions among heavy metals will enable to use the responses of the soil microbial biomass as a reliable index of the environmental impact of the incorporation into soils of heavy metal-contaminated wastes

Effect of low level zinc pretreatment on zinc-mediated toxicity in different lung cell lines

Abstract: Reduced toxicity of high zinc exposure was observed after pretreatment of various lung cells with nonlethal zinc concentrations. This effect became significant when various parameters of cytotoxicity were assessed (e.g., inhibition of protein synthesis, depletion of reduced glutathione [GSH], increase of oxidized glutathione [GSSG], release of lactate dehydrogenase [LDH]). Similar protective effects by zinc have already been shown by several investigators for a variety of toxicity studies dealing with cadmium, in vitro and in vivo. Zinc-induced toxicity has been linked to glutathione metabolism and cellular GSH contents. Activity of glutathione reductase (GR) and rates of glutathione synthesis were identified as determinants of zinc (cyto)toxicity. However, these variables were virtually unaffected in our adapted cells. Consequently, another variable appears to be crucial for modulating cellular suscepticibility in zinc pretreated cells. Protection in our cells was achieved by pretreatment with 80–120 µmol/L zinc chloride for 24–72 h, roughly 10-fold more zinc in the medium than is normally found in human plasma. Protection was not observed when the cells were concomitantly exposed to cycloheximide, an inhibitor of protein synthesis, or actinomycin D, an inhibitor of RNA synthesis, but it was found in the presence of amanitin, an inhibitor of mRNA synthesis. It is therefore concluded that the altered zinc tolerance of pretreated cells is not attributable to the induction of metallothionein.

[Interaction between fluorine and zinc after long-term oral administration into the digestive system of rats].

Abstract: Drug interactions are the side effect of administration of two or more drugs or a drug-food combination. Although some drug interactions are intentional and beneficial to the patient, the majority are unintentional and associated with a potentially harmful effect. The aim of this study was to search for interactions in rats between fluoride and zinc administered orally for 12 weeks and to elucidate any potential toxicological and therapeutic consequences. 60 male Wistar rats were divided into six groups of ten rats each and exposed to: 1. controls (distilled water); 2. sodium fluoride (NaF); 3. low-dose zinc (Zn); 4. high-dose zinc; 5. NaF + low-dose Zn; 6. NaF + high-dose Zn. At the end of the experiment the content of F- and Zn+ in serum, urine, incisors, femur and mandible was measured and densitometry of femoral bones was performed. Serum alkaline phosphatase, alanine and aspartate aminotransferase activities, as well as bilirubin and creatinine concentrations were determined to confirm non-toxicity of fluoride dose. Animals receiving NaF only demonstrated higher content of fluorine in serum, urine bones and teeth. Zinc concentrations in serum, urine, bones and teeth were elevated in rats receiving zinc with or without NaF. Fluorine accumulation in bones and teeth was reduced by Zn, but in general the effect lacked statistical significance. Zinc slightly reduced the concentrations of fluorine in serum and urine. Sodium fluoride slightly reduced the concentration of zinc in serum and urine. Bone mineral content (BMC) was significantly increased by NaF and was not further increased by co-administration of zinc. No changes in serum alkaline phosphatase, alanine and aspartate aminotransferase activities, bilirubin and creatinine concentrations were detected. In conclusion, simultaneous administration of fluorine and zinc may be beneficial for prevention and treatment of pathologic conditions in bones and teeth and is not accompanied by an increase in fluorine levels which could be responsible for toxicological symptoms.