Doses Of Nickel Research Articles

Effects of selected epigenetic factors on the rabbit ejaculate quality

The aim of our study was to monitor the impact of heavy metals and hyperthermia on the basic rabbit semen characteristics. Rabbit males (n=31) of New Zealand White line were exposed to different doses of nickel and zinc administered to feed mixture (P1 group - 17.5 mg NiCl2/kg, P2 group - 35.0 mg NiCl2/kg, P3 group - 17.5 mg NiCl2/kg + 30.0 mg ZnCl2/kg and P4 group - 35.0 mg NiCl2/kg + 30.0 mg ZnCl2/kg; experiment I) and to high ambient temperature (36 ± 3ºC; experiment II), and then compared to control C. Semen samples collected from each buck were analyzed using CASA system in order to evaluate the concentration and motility parameters of rabbit spermatozoa. In the first experiment, highly significant differences were observed in the motility of spermatozoa between P3 and P1, P4 groups and C (p<0.001). P3 group had the lowest progressive motility of spermatozoa in comparison to groups P1, P4 and C (p<0.001). In the second experiment, the lowest motility was noted in the last experimental collection in comparison to the 1st collection (p<0.01). The highest progressive motility was found in the 1st collection comparing to the control collection and the 3rd collection (p<0.05). In conclusion, our study showed that the quality of rabbits semen and subsequently also fertility may be potentially negatively affected by exposure to heavy metals and hyperthermia.

Oral Hyposensitization to Nickel Induces Clinical Improvement and a Decrease in TH1 and TH2 Cytokines in Patients with Systemic Nickel Allergy Syndrome

Some patients with nickel (Ni) allergic contact dermatitis suffer from systemic (intestinal or cutaneous) symptoms after ingestion of Ni-rich foods and experience symptoms reduction with low-Ni diet, a condition termed Systemic Ni Allergy Syndrome (SNAS). We aimed at evaluating whether oral administration of low nickel doses improved clinical conditions and modulated immunological aspects of SNAS, without significant side effects. Thirty-six SNAS patients were enrolled. Treatment started after 1-month of low-Ni diet and consisted in an incremental oral NiOH dose phase (0.3ng to 1.5 microg/week) followed by a 12-months maintenance phase (1.5 microg/week). Randomly, twenty-four patients added Ni therapy to low-Ni diet and 12 remained with diet alone. All patients were allowed rescue medications (antihistamines and topical steroids). After 4 months, Ni-rich foods were gradually reintroduced. In vitro allergen-driven IL13, IL5 and IFN-gamma release by peripheral blood mononuclear cells was evaluated before and after treatment. Twenty-three patients receiving NiOH and the 12 control patients completed the study. Evaluation of SNAS clinical severity (by VAS and drug consumption) showed a significant difference in favor of NiOH-treated patients compared to controls. Twenty of 23 patients in the NiOH group and none in the control group tolerated Ni-rich food reintroduction. Release of all studied cytokines in culture supernatants was significantly lower after NiOH treatment. In conclusion NiOH is effective in reducing symptoms and drug consumption in SNAS and is able to modulate inflammatory parameters.

Allergy to Nickel: First Results on Patients Administered with an Oral Hyposensitization Therapy

Nickel sulphate allergy is the most common contact allergy. In fact, nickel sulphate is an ubiquitous element, contained in various objects and food; it occurs in igneous rocks, as a free metal and together with iron, but it is also a component of living organism, mainly vegetables. We carried out a clinical trial of oral hyposensitization therapy with low doses of nickel in a group of 67 patients affected by systemic allergy to this sensitizer element. We obtained good results on consequent tolerance to nickel in treated patients.

XAFS studies of the short-range order in Ni nanoparticles embedded in carbonacoues matrix

X-ray absorption fine structure (XAFS) studies of Ni nanograins embedded in carbonaceous films were performed basing on the K edge spectra of nickel. A series of samples containing various doses of Ni doped to the film during the deposition was studied. The crystalline structure and chemical constitution of formed nanograins were found dependent on the nickel dose. They change along the series from those similar to bulk structure of metallic Ni towards amorphous form of NiO. The Fourier transform fitting analysis based on Ni fcc and NiO rock salt models showed for all samples a significant reduction of the range of atomic order around Ni as compared to appropriate bulk materials. The changes in an oxide content rate in the nanograins were evaluated by fitting the coefficients of the linear combination spanned on two the most distinct measured XAFS spectra. We have found that low oxygen inflow resulted in formation of amorphous NiO, but saved the metallic core of grains. High oxygen uptake resulted in thorough grain oxidation.

Is the variability of nickel patch test reactivity over time associated with fluctuations in the systemic T-cell reactivity to nickel?

Patch test reactivity to nickel varies over time. To what extent this variation is associated with fluctuations in the T-cell reactivity to nickel is not known. Our aim was to investigate the relationship between variation over time in the patch test and the systemic T-cell reactivity to nickel. Patients (n = 15) with a history of contact allergy to nickel were subjected to three consecutive patch tests at 3-month intervals, utilizing NiSO4 at 10 concentrations ranging from 0.0032% to 12.5%. Prior to each patch test, blood mononuclear cells were analysed for T-cell reactivity to nickel by interleukin (IL)-4 and IL-13 enzyme-linked immunospot assay. Eleven patients reacted positively in all three patch tests, two patients reacted in one or two tests and two remained negative. All 13 positive patients displayed variability over time, in terms of the lowest dose of nickel to which they responded. Also the cytokine response to nickel varied over time but the patients' mean cytokine response was positively correlated with their mean patch test reactivity (r(s) = 0.70, P < 0.01 for IL-4; r(s) = 0.78, P < 0.001 for IL-13). However, although the changes over time in patch test reactivity and the cytokine responses to nickel displayed a similar pattern in many patients, there was no significant correlation between the individuals' variation over time in vivo and in vitro. The overall magnitude of the T-cell reactivity to nickel and the patch test reactivity are closely associated but fluctuations in the systemic T-cell reactivity cannot be singled out as the major cause of longitudinal variability in nickel patch test reactivity.

Effects of dietary nickel on detoxification enzyme activities in the midgut of Spodoptera litura Fabricius larvae

Nickel accumulated in midugt of Spodoptera litura Fabricius could induce the expression of metallothionein, one of the most important detoxification proteins in organisms. In the present study, the effects of dietary nickel on the activities of detoxification enzymes, such as carboxylesterase (CarE) and glutathione S-transferase (GST) in the midgut of S. litura larvae have been studied to get an understanding of the detoxification mechanisms of S. litura larvae to excessive nickel. Results showed that CarE activities in the midgut of the 5th instar larvae decreased at lower levels of nickel (⩽5 mg/kg), while increased with increasing nickel doses at higher levels of nickel (⩾10 mg/kg) exposure in successive 3 generations. CarE activities of the 6th instar larvae were also characterized as inhibited at low levels of nickel exposure, and improved at higher levels in the 1st generation. CarE activities of 6th instar larvae in the 2nd and 3rd generations were all lower than that in control. However, GST activities in the midgut of the 5th and 6th instar larvae all increased with increasing nickel doses (1–20 mg/kg) in diets.

Effect of short‐time exposures to nickel and lead on brain monoamine oxidase from Danio rerio and Poecilia reticulata

The aim of this work was to verify, in two small size freshwater teleosts Danio rerio and Poecilia reticulata, the effects of short-time exposures (24 and 72 h) to a sublethal dose (500 microg/L) of nickel and lead, on brain monoamine oxidase (MAO), an important neural enzyme. The 24-h treatment using both metals caused a strong reduction of MAO activity in D. rerio brain, whereas causing a slight MAO activity stimulation in P. reticulata brain. The same treatment in both species did not affect the brain MAO mRNA production as showed by RT-PCR. Extending the duration of treatment as far as 72 h, partly (D. rerio) or completely (P. reticulata) reversed the metal effects on brain MAO activity suggesting that mechanisms to neutralize the metals had been activated.

Development of a Young’s modulus model for Gilsocarbon graphites irradiated in inert environments

Dimensional and material property changes caused by fast neutron damage, radiolytic oxidation or a combination of both have been measured over many years on the Gilsocarbon graphites. The data have been gathered together in a comprehensive database and are being used to develop dose–damage relationships of irradiated graphite material properties for use in irradiated graphite component stress analyses up to a fast neutron dose of ∼200 × 10 20 n/cm 2 equivalent DIDO nickel dose (EDND) in the temperature range ∼300–650 °C. This paper covers development and validation of an empirical model for Young’s modulus of Gilsocarbon graphite when irradiated in an inert environment. The new model provides a good fit over the range of the primary modelling variables: dose, irradiation temperature, and graphite group. The proposed model is convenient to use in component stress analysis, as it features an analytic function of temperature and dose that eliminates the need in the existing model for interpolation on those variables.

Nitrate reductase activity of two leafy vegetables as affected by nickel and different nitrogen forms

The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO3 −–N, NH4 +–N, NH4NO3). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in lettuce plants supplied with nitrate nitrogen (NO3 −–N) or mixed (NH4NO3) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants. At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with NO3 −–N or NH4NO3. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the enzyme activity in the roots of NO3 −-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution contained ammonium nitrogen (NH4 +–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs, especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated with NH4 +–N the enzyme activity in roots was even higher than in those supplied with NO3 −–N.

Metallothionein expression induced by nickel accumulation in the midgut of Spodoptera litura Fabricius larvae exposed to nickel

Metallothionein expression induced by nickel accumulation in the midgut of Spodoptera litura Fabricius larvae was investigated by exposing S. litura larvae to the artificial diets amended with different doses of nickel for 3 generations. Nickel accumulations in the midgut of 6th instar larvae were detected by Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES), and the induced metallothionein expression in the midgut of 5th and 6th instar larvae in 120 h were quantified using cadmium-hemoglobin total saturation methods. The accumulated nickel in the midgut of the 6th instar larvae within a generation increased with the increase of the nickel doses in the treated diets and showed significant dose-dependence with the nickel doses in diets. Metallothioneins induced by nickel accumulated in the larval midgut also increased with nickel doses in diets and with the increasing stressing time in a generation. Results also suggested that the metallothionein expression was different with the time of S. litura larvae stressed by nickel.

Effects of Increasing Levels of Nickel Contamination on Structure of Offshore Nematode Communities in Experimental Microcosms

A microcosm experiment was used to examine the effects of nickel on offshore nematode communities of a Tunisian coastal zone (Southwestern Mediterranean Sea). Sediments were contaminated with three nickel concentrations [low (250 ppm), medium (550 ppm) and high (900 ppm)], and effects were examined after 30 days. Results showed significant differences between nematode assemblages from undisturbed controls and those from nickel treatments. Most univariates measures, including diversity and species richness, decreased significantly with increasing level of Ni contamination. Results from multivariate analyses of the species abundance data demonstrated that responses of nematode species to the nickel treatments were varied: Leptonemella aphanothecae was eliminated at all the nickel doses tested and seemed to be intolerant species to nickel contamination; Daptonema normandicum, Neochromadora trichophora and Odontophora armata which significantly increased at 550 ppm nickel concentration appeared to be "opportunistic" species at this dose whereas Oncholaimus campylocercoides and Bathylaimus capacosus which increased at all doses tested (250, 550 and 900 ppm) seemed to be "nickel-resistant" species.

Nickel accumulation and its effects on the survival rate of Spodoptera litura fabricius under continuous nickel stress

The artificial diets mixed with various concentrations of nickel were offered to the larvae of the phytophagous insect Spodoptera litura Fabricius for 3 generations. Nickel accumulations in the 6th instar larvae, pupae and newly emerged adults of the corresponding generations of S. litura were investigated by inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES), and the effects of nickel accumulations on the survival rate of S. litura were also evaluated by individual rearing. The results showed that nickel accumulated in the 6th instar larvae, pupae and adults of S. litura, and the accumulated nickel in all the tested developmental stages within a generation increased with the increase of the nickel doses in the treated diets and showed significant dose-dependent relationship with the nickel doses in the artificial diets. The results also indicated that the nickel accumulations in the 6th instar larvae, pupae, and newly emerged adults from the 3rd generation were higher than those from the 2nd generation, which were also higher than those from the 1st generation. Nickel concentrations in pupae and adults were significantly lower than those in larvae, which indicated that the excessive nickel might be excreted during metamorphosis. Furthermore, larval survival rate, pupation rate and eclosion rate of S. litura in the tested three generations all decreased with the increase of the nickel doses in the treated diets.

Phenotypic heterogeneity can enhance rare‐cell survival in ‘stress‐sensitive’ yeast populations

Individual cells within isogenic microbial cultures exhibit phenotypic heterogeneity, an issue that is attracting intense interest. Heterogeneity could confer benefits, in generating variant subpopulations that may be better equipped to persist during perturbation. We tested this hypothesis by comparing the survival of wild-type Saccharomyces cerevisiae with that of mutants which are considered stress-sensitive but which, we demonstrate, also have increased heterogeneity. The mutants (e.g. vma3, ctr1, sod1) exhibited the anticipated sensitivities to intermediate doses of nickel, copper, alkaline pH, menadione or paraquat. However, enhanced heterogeneity meant that the resistances of individual mutant cells spanned a broad range, and at high stress occasional-cell survival in most of these populations overtook that of the wild type. Green fluorescent protein (GFP) reporter studies showed that this heterogeneity-dependent advantage was not related to perturbation of buffered gene expression. Deletion strain screens combined with other approaches revealed that vacuolar alkalinization resulting from loss of Vma-dependent vacuolar H(+)-ATPase activity was not the cause of vma mutants' net stress sensitivities. An alternative Vma-dependent resistance mechanism was found to suppress an influence of variable vacuolar pH on the metal resistances of individual wild-type cells. In addition to revealing new mechanisms of heterogeneity generation, the results demonstrate experimentally a benefit under adverse conditions that arises specifically from heterogeneity, and in populations conventionally considered to be disadvantaged.

The Validity of the Use of Equivalent DIDO Nickel Dose for Graphite Dosimetry

Abstract Fast neutron dose recommendations for the graphite moderators of Magnox power plant are expressed in terms of Equivalent DIDO Nickel Dose (EDND). EDND is a calculated property that relates the damage rate in graphite at a given location to the fast neutron fluence experienced by graphite test samples irradiated in the DIDO reactor. This paper describes a study undertaken to determine the sensitivity of EDND recommendations to assumptions made in the modeling of neutron damage in graphite. These include different scattering cross sections and damage weighting functions. It is concluded that, although apparently significant differences exist between the available graphite damage response functions, their net effect is not significant in determining EDND. Therefore, confidence in past calculations has been improved and continued use of existing methods is supported.

Systemic contact dermatitis after oral exposure to nickel: a review with a modified meta‐analysis

Systemic contact dermatitis can be elicited experimentally in nickel-sensitive individuals by oral nickel exposure. A crucial point interpreting such experiments has been the relevance of nickel exposure from drinking water and diet. The aim of this meta-analysis study on former nickel-exposure investigations was to provide the best possible estimation of threshold values of nickel doses that may cause systemic contact dermatitis in nickel-sensitive patients. 17 relevant investigations were identified, and statistical analyses were performed in a stepwise procedure. 9 studies were included in the final dose-response analysis, which divided the studies into a homogenous middle group of 5 studies and 2 groups of 2 studies with a higher and lower response frequency, respectively, described by logistic dose-response curves shifted in parallel. On the basis of these curves, calculations were made of the doses that, theoretically, would cause systemic contact dermatitis in exposed nickel-sensitive patients. The results from the 2 most sensitive groups show that 1% of these individuals may react with systemic contact dermatitis at normal daily nickel exposure from drinking water and diet, i.e. 0.22-0.35 mg nickel.

Disponibilidade de níquel em solo tratado com lodo de esgoto e cultivado com sorgo

A presença do metal pesado níquel no lodo de esgoto pode se constituir em entrave para sua aplicação em solos agrícolas. Nesse contexto, o presente trabalho teve como objetivo avaliar o efeito da aplicação do lodo de esgoto contaminado com doses crescentes de níquel, em um solo, sobre a disponibilidade e a absorção desse metal pelas plantas de sorgo. O experimento foi desenvolvido em casa de vegetação, em vasos, usando Latossolo Vermelho distrófico. As amostras de solo foram coletadas aos 0 e 128 dias após a instalação do experimento. O delineamento utilizado foi o inteiramente casualizado, com cinco tratamentos (4 doses de níquel no lodo de esgoto e 1 tratamento testemunha, sem adição de lodo de esgoto e com fertilização mineral) em quatro repetições. A aplicação de lodo de esgoto contaminado com doses crescentes de níquel resultou em aumentos proporcionais nos teores "total" e disponíveis de níquel no solo. Os extratores Mehlich-1 e Mehlich-3 extraíram os maiores teores de níquel do solo. O Mehlich-3 foi o extrator que obteve a maior correlação com as quantidades de níquel presentes nas plantas de sorgo. A partir do aumento dos teores de níquel no solo, ocorreu também aumento na absorção desse metal pesado, de 39,93; 101,16; 152,58 e 171,38 %, pelas plantas de sorgo.

Effects of cadmium and nickel exposure on haematological parameters of common carp, Cyprinus carpio L.

Introduction. Single intraperitoneal injections of sublethal doses of cadmium (10&nbsp;&micro;g&nbsp;Cd&#183;kg-1 body weight) and nickel (60 &micro;g Cd&#183;kg-1 body weight) were administered to carp, Cyprinus carpio L., to determine detoxification potential of the fish affected after transfer to a clean milieu, as revealed by haematological parameters. Observation of haematological parameters allows the most rapid detection of changes in fish after cadmium and nickel injection Disrupted haematological patterns appear very quickly and precede changes in fish behaviour and visible lesions. The rapidity of toxic effects exerted by xenobiotics is related to the blood&#8217;s transport function, with the blood distributing the metals to all the body parts. Materials and methods. Each experiment took 60 days and was divided into 8 stages during which blood was collected for assays. At each stage, blood samples were assayed for selected haematological parameters (RBC, WBC, Hb, Hct, MCV, MCHC, MCH). Results. Cadmium and nickel exposure-related changes in haematological parameters were detected. Immediately after injection, the haematological parameters were seen to change, a return to the normal values being observed after some time. The study allowed following the changes in the haematological parameters of cadmium- and nickel-injected carp during the process ofdetoxification. Conclusion. Within the 60 days following injection of sublethal doses of cadmium and nickel, haematological parameters were observed to revert to the levels close to those in the control.

Nickel-induced oxidative stress in testis of mice: evidence of DNA damage and genotoxic effects.

Oxidative stress (OS) mechanisms are speculated to play a significant role in nickel-induced toxic effects and their carcinogenic potency. Although nickel-induced oxidative damage in somatic tissues is well demonstrated, evidence of the involvement of a similar mechanism(s) in nickel-induced testicular dysfunction and associated genotoxic effects is scarce. Hence, the present study aimed to investigate the nickel-induced OS response in testis and the associated genotoxic implications in vivo. Initially, the toxicity profile of nickel chloride was determined in adult albino mice (CFT-Swiss) following administration (intraperitoneal) of single doses. Subsequently, multiple sublethal doses (1.25, 2.5, and 5.0 micromol/100 g of body weight per day for 3 days) were used to characterize effects on testicular histoarchitecture, lipid peroxidation (LPO) in testis (homogenates, microsomal or mitochondrial fractions) and epididymal sperm, DNA damage, induction of apoptosis in testis, and incidence of sperm head abnormalities. Although short-term doses of nickel induced only a minimal LPO response, multiple doses elicited a moderate (15% to 30%) increase in LPO in whole homogenates and higher dose-related increases in both mitochondrial (20% to 50%) and microsomal fractions (25% to 60%). This was associated with a significant increase in DNA damage in the testis as evidenced by increased single-strand breaks (fluorimetric analysis of DNA unwinding assay). Further, at higher doses, nickel-induced apoptosis was demonstrable in the testis biochemically. Although caudal sperm counts determined at all sampling weeks showed no alterations, analysis for head abnormalities revealed a nearly 3- to 4-fold increase in the percentage of abnormal sperms among the nickel-treated males during the first 3 weeks. Furthermore, mating of nickel-treated (2.5 micromol/100 g of body weight per day for 5 days) males sequentially for a period of 5 weeks with untreated females resulted in a significant increase in male-mediated dominant lethal-type mutations (the frequency of dead implantations) during the first 3 weeks, suggesting a stage-specific effect on postmeiotic germ cells. These findings suggest that testicular toxicity of nickel compounds may be related to enhanced production of reactive oxygen species, probably mediated through oxidative damage to macromolecules, including damage to DNA.

Experimental systemic contact dermatitis from nickel: a dose–response study

Systemic contact dermatitis is usually seen as flare-up of previous dermatitis or de novo dermatitis similar to allergic contact dermatitis. Although systemic contact dermatitis from medicaments is a well-established entity, the existence of clinically relevant systemic reactions to oral nickel exposure, in particular systemic reactions to nickel in the daily diet, remains controversial. Several studies have shown that oral exposure to nickel can induce systemic contact dermatitis in nickel-sensitive individuals. In most of these studies, however, the exposure dose of nickel used has been considerably higher than the nickel content in the normal daily diet. The aim of the current investigation was to study dose-response dependency of oral exposure to nickel. In a double-blind, placebo-controlled oral exposure trial, 40 nickel-sensitive persons and 20 healthy (non-nickel-sensitive) controls were given nickel sulfate hexahydrate in doses similar to and greater than the amount of nickel ingested in the normal Danish daily diet. The nickel content in urine and serum before and after oral exposure was measured to determine nickel uptake and excretion. The influence of the amount of nickel ingested on the clinical reactions to oral exposure and on nickel concentrations in serum and urine was evaluated. Among nickel-sensitive individuals, a definite dose-response dependency was seen, following oral exposure to nickel. 7 of 10 nickel-sensitive individuals had cutaneous reactions to oral exposure to 4.0 mg nickel, an amount approximately 10 times greater than the estimated normal daily dietary intake of nickel. 4 of 10 nickel-sensitive individuals had cutaneous reactions to 1.0 mg nickel, a dose which is close to the estimated maximum amount of nickel contained in the daily diet. 4 of 10 nickel-sensitive individuals reacted to 0.3 mg nickel or to the amount equivalent to that contained in a normal daily diet, and 1 of 10 reacted to a placebo. None of the 20 healthy controls had cutaneous reactions to 4.0 mg nickel or to a placebo. Prior to oral exposure, there was no measurable difference in the amount of nickel in the urine or serum of nickel-sensitive persons and healthy controls. Following the oral challenge, the nickel content in the urine and serum of both nickel-sensitive and healthy control individuals was directly related to the dose of nickel ingested.

The Ecological Dose of Nickel in a Semiarid Soil Amended with Sewage Sludge Related to the Unamended Soil

Nickel pollution may affect microbial communitydevelopment and its activity in soil and, therefore, itsfertility, while organic amendment may affect Ni mobilityand bioavailability. The aim of this research was toascertain the extent to which the addition of sewage sludgeto soil may affect Ni toxicity and to establish theecological dose of this heavy metal. Unamended and amendedsoils with sewage sludge were spiked with differentconcentrations of Ni (0–8000 mg kg-1) and then incubatedfor 3 hours, 12 days and 40 days. Soil dehydrogenaseactivity, ATP content, microbial respiration and microbialbiomass C were measured in the samples containing differentNi concentrations. A mathematical model which describe theinhibition of these soil parameters were used to calculatethe ecological dose of Ni: ED50. Soil microbialbiomass C measurements of all treatments better fitted themodel (r2 = 0.95–0.69 with p < 0.05) than the otherparameters studied; but the ED50 values predicted by the modelhad a high coefficient of variation. For both ATP contentand microbial biomass C, the ED50 values calculatedfor the amended soil were higher than for the unamendedsoil and so that the effect of Ni toxicity on theseparameters of microbial activity may be considered lower inthe former. In this study, an increase in ED50 valueswith the time elapsed was also observed.