Inhibition of H+ efflux and K+ uptake,and induction of K+ efflux in yeast by heavy metals

Energy and cell membrane ATPase-dependent H⁺ efflux from yeast cells was inhibited by heavy metals, which also inhibited energy-dependent K⁺ uptake by the cells. Heavy metals also induced K⁺ efflux from metabolizing cells in two phases: reversibly at low concentrations and irreversibly at high concentrations. The concentration dependence of all of these effects varied considerably between metals. The effect of in vivo inhibition of H⁺ transporting ATPases on cell membrane polarization and thus on cellular transport processes, including heavy metal uptake, are discussed. It is proposed that the inhibition of H⁺ efflux and the appearance of irreversible K⁺ efflux in yeast are potentially useful indicators of heavy metal toxicity toward yeast and possibly other fungi.     

6种内生菌对发酵人参茎叶农药残留降解和皂苷转化的影响

目的 研究6种内生菌对人参茎叶中5种农药残留降解和20种皂苷单体转化的影响。方法 在同一培养条件下,通过GC、HPLC分别对6种人参内生芽孢杆菌处理前后人参茎叶中农药残留及人参皂苷含量进行测定,计算6种内生菌对人参茎叶中农药残留率和皂苷转化率,评价内生菌对人参茎叶转化产物质量的影响,优选出降农残和转化皂苷效果好的菌株。结果 6种人参内生菌对人参茎叶中的5种农药残留均有降解作用,其中,多黏类芽孢杆菌对农药残留降解作用最强,氟啶胺、六六六、五氯硝基苯、毒死蜱、滴滴涕的降解率分别为86.90%,88.89%,79.88%,86.12%和86.67%(P<0.05);对20种单体皂苷均有转化作用,其中,赖氨酸芽孢杆菌和蜡样芽孢杆菌转化人参茎叶皂苷作用最强,20种单体皂苷加和值分别为5.84%和5.85%(P<0.05)。结论 6种内生菌对人参茎叶农药残留降解和皂苷转化的影响不同,多黏类芽孢杆菌降解农药残留效果最好,赖氨酸芽孢杆菌和蜡样芽孢杆菌转化人参皂苷效果最好,为提高人参茎叶总皂苷提供理论依据。     

Essential metal (Cu,Zn) exposures alter the activity of ATPases in gill,kidney and muscle of tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

An acute (96 h—0.1, 0.5, 1.0, 1.5 μg/ml) and chronic (up to 30 days—0.05 μg/ml) protocols of Cu and Zn were applied to freshwater fish Oreochromis niloticus to investigate these essential metal effects on the activities of gill, kidney and muscle Na⁺/K⁺-ATPase, Mg²⁺-ATPase and Ca²⁺-ATPase. In vitro effects of both metals (20 min—0.1, 0.5, 1.0, 1.5 μg/ml) were also measured to be able to compare both exposure routes. Data showed that ATPase activities, in general, decreased following all the exposure conditions, though there were some increases especially in Mg²⁺-ATPase activity. Among the enzymes, Na⁺/K⁺-ATPase and Ca²⁺-ATPase appeared to be more sensitive than Mg²⁺-ATPase to the metals. The data also indicated that effects of Cu on ATPase activity in the tissues of O. niloticus were stronger than the effects of Zn, possibly due to higher toxic effects of Cu. In vivo and in vitro exposures of metals showed similar trends with a few exceptions, especially in the gill. Variability of ATPase activity is determined by tissue type, metal species, concentration and duration. This work showed that even essential metals can alter significantly activities of ATPases in fish and thus suggests using them as a sensitive biomarker in metal contaminated waters.     

Alterations of valve closing behavior in juvenile Catarina scallops (Argopecten ventricosus Sowerby, 1842) exposed to toxic metals

We conducted an evaluation of alterations produced in the valve closing speed of juvenile Argopecten ventricosus (Catarina scallop) exposed to the metals cadmium, chromium and lead, because of the connection of this response to the state of health of the mollusk. Bioassays were conducted with 50 juveniles (length 3 ± 0.5 cm) exposed to 0.02, 0.1, 0.2 mg Cd l⁻¹; 0.1, 0.5, 1.0 mg Cr l⁻¹; 0.04, 0.2, 0.4 mg Pb l⁻¹ and 0.8 and 1.6 mg Cd + Cr + Pb l⁻¹ for 480 h. The average valve closing speed at the end of the experiment was under 1 s in the control group, from 2 to 3.6 s in the bioassays with cadmium, from 1.4 to 3.4 s with chromium, from 3 to 12 s with lead, and from 12 to 15 s with the metal mixtures. It was found that there are significant differences between the values recorded in assays with metals and the control (P < 0.05). The retardation of valve closing in the organisms exposed to toxic substances is probably caused by damage to the sensory cilia located on the edge of the mantle.     

Uptake pathways and subcellular fractionation of Cd in the polychaete Nereis diversicolor

Polychaetes have often been utilized as indicator species to investigate the impacts of pollutants, such as heavy metals. The uptake of Cd by the polychaete Nereis diversicolor was determined at varying Ca concentrations and with pre-exposure to Ca ion channel blockers and metabolic inhibitors in simulated sea water over 1 week period. The supply of Ca in simulated sea water inhibited Cd uptake and increased Ca concentration in N. diversicolor after 10 μM Cd exposure. Pre-exposure to a Ca-channel blocker (Lanthanum) significantly inhibited Cd uptake, suggesting that the uptake of Cd was exerted at a Ca channel. N-ethylmaleimide, which specifically binds to sulfhydryl groups, inhibited Cd uptake at 10 μM, implying that the transport of Cd is carrier-mediated by proteins or other SH-containing compounds. Subcellular Cd distribution analysis showed that more than 60% of the total Cd associated with the cytosolic fraction. The presence of higher concentration of Ca in simulated sea water did not impact the proportional subcellular distribution of Cd in N. diversicolor. Nevertheless, the supply of Ca could significantly lower Cd concentration in cytosol and cellular debris. The present study provides evidence that Cd transport by N. diversicolor was mediated mainly through lanthanum- sensitive Ca ion channels and accumulated by SH-containing compounds. These results help to understand the uptake mechanism and subcellular distribution of Cd in polychaetes.     

Synthesis, characterization and evaluation of thiolated quaternary ammonium-chitosan conjugates for enhanced intestinal drug permeation

In a previous report quaternary ammonium-chitosan conjugates (N⁺-Chs) endowed with intestinal drug permeability-enhancing properties were described. They are characterized by short pendant chains of n adjacent diethyl-dimethylene-ammonium groups substituted onto the primary amino group of the chitosan (Ch) repeating units. In the present work two N⁺-Chs, one having DS (degree of substitution) = 59.2 ± 4.5%, n = 1.7 ± 0.1 (N⁺(60)-Ch), the other one having DS = 40.6 ± 1.3%, n = 3.0 ± 0.2 (N⁺(40)-Ch) were used to synthesize novel multifunctional non-cytotoxic Ch derivatives, each carrying thiol along with quaternary ammonium groups (N⁺-Ch–SH), with increased potential to enhance transepithelial drug transport. They have been obtained by transforming the residual free amino groups of N⁺(60)-Ch and N⁺(40)-Ch into 3-mercaptopropionamide moieties. The former yielded 4.5 ± 0.7% thiol-bearing groups, the latter, 5.2 ± 1.1% of such groups, on a Ch repeating unit basis. The multifunctional derivatives have improved the ability of the parent N⁺-Chs to enhance the permeability of the water-soluble macromolecular fluorescein isothiocyanate dextran, MW 4400 Da (FD4) and that of the lipophilic dexamethasone (DMS) across the excised rat intestinal mucosa and Caco-2 cell monolayer, respectively. The data from the present work altogether point to a synergism of quaternary ammonium and thiol groups to improve the intestinal drug absorption enhancing properties of the multifunctional Ch derivatives.     

Comparative study on elemental composition and DNA damage in leaves of a weedy plant species, Cassia occidentalis, growing wild on weathered fly ash and soil

Open dumping of fly ash in fly ash basins has significant adverse environmental impacts due to its elevated trace element content. In situ biomonitoring of genotoxicity is of practical value in realistic hazard identification of fly ash. Genotoxicity of openly disposed fly ash to natural plant populations inhabiting fly ash basins has not been investigated. DNA damage, and concentrations of As, Co, Cr, Cu and Ni in the leaves of natural populations of Cassia occidentalis growing at two contrasting sites—one having weathered fly ash (fly ash basin) and the other having soil (reference site) as plant growth substrates—were assessed. The foliar concentrations of As, Ni and Cr were two to eight fold higher in plants growing on fly ash as compared to the plants growing on soil, whereas foliar concentrations of Cu and Co were similar. We report, for the first time, based upon comet assay results, higher levels of DNA damage in leaf tissues of Cassia occidentalis growing wild on fly ash basin compared to C. occidentalis growing on soil. Correlation analysis between foliar DNA damage and foliar concentrations of trace elements suggests that DNA damage may perhaps be associated with foliar concentrations of As and Ni. Our observations suggest that (1) fly ash triggers genotoxic responses in plants growing naturally on fly ash basins; and (2) plant comet assay is useful for in situ biomonitoring of genotoxicity of fly ash.     

Antioxidant activities, metal contents, total phenolics and flavonoids of seven Morchella species

Seven Morchella species were analyzed for their antioxidant activities in different test systems namely β-carotene/linoleic acid, DPPH, reducing power, chelating effect and scavenging effect (%) on the stable ABTS⁺, in addition to their heavy metals, total phenolic and flavonoid contents. In β-carotene/linoleic acid system, the most active mushrooms were M. esculenta var. umbrina and M. angusticeps. In the case of DPPH, methanol extract of M. conica showed high antioxidant activity. The reducing power of the methanol extracts of mushrooms increased with concentration. Chelating capacity of the extracts was also increased with the concentration. On the other hand, in 40 μg ml⁻¹ concentration, methanol extract of M. conica, exhibited the highest radical scavenging activity (78.66 ± 2.07%) when reacted with the ABTS⁺ radical. Amounts of seven elements (Cu, Mn, Co, Zn, Fe, Ca, and Mg) and five heavy metals (Ni, Pb, Cd, Cr, and Al) were also determined in all species. M. conica was found to have the highest phenolic content among the samples. Flavonoid content of M. rotunda was also found superior (0.59 ± 0.01 μg QEs/mg extract).     

Growth,morphology, ammonium uptake and nutrient allocation of Myriophyllum brasiliense Cambess. under high NH4 + concentrations

The effects of high NH₄ ⁺ concentration on growth, morphology, NH₄ ⁺ uptake and nutrient allocation of Myriophyllum brasiliense were investigated in hydroponic culture. The plants were grown under greenhouse conditions for 4 weeks using four levels of NH₄ ⁺ concentration: 1, 5, 10 and 15 mM. M. brasiliense grew well with a relative growth rate of c.0.03 day⁻¹ at NH₄ ⁺ concentration up to 5 mM. At the higher NH₄ ⁺ concentrations the growth of the plants was stunted and the plants had short roots and few new buds, especially when grown in 15 mM NH₄ ⁺ where the submerged leaves were lost and there were rotten roots and submerged stems. To avoid NH₄ ⁺ toxicity, the plants may have a mechanism to prevent cytoplasmic NH₄ ⁺ accumulation in plant cells. The net uptake of NH₄ ⁺ significantly decreased and the total N significantly increased in the plants treated with 10 and 15 mM NH₄ ⁺, respectively. The plant may employ NH₄ ⁺ assimilation and extrusion as a mechanism to compensate for the high NH₄ ⁺ concentrations. However, the plants may show nutrient deficiency symptoms, especially K deficiency symptoms, after they were exposed to NH₄ ⁺ concentration higher than 10 mM. The present study provides a basic ecophysiology of M. brasiliense that it can grow in NH₄ ⁺ enriched water up to concentrations as high as 5 mM.     

Assessment of toxic metals in raw and processed milk samples using electrothermal atomic absorption spectrophotometer

Milk and dairy products have been recognized all over the world for their beneficial influence on human health. The levels of toxic metals (TMs) are an important component of safety and quality of milk. A simple and efficient microwave assisted extraction (MAE) method has been developed for the determination of TMs (Al, Cd, Ni and Pb), in raw and processed milk samples. A Plackett–Burman experimental design and 2³ + star central composite design, were applied in order to determine the optimum conditions for MAE. Concentrations of TMs were measured by electrothermal atomic absorption spectrometry. The accuracy of the optimized procedure was evaluated by standard addition method and conventional wet acid digestion method (CDM), for comparative purpose. No significant differences were observed (P > 0.05), when comparing the values obtained by the proposed MAE method and CDM (paired t-test). The average relative standard deviation of the MAE method varied between 4.3% and 7.6% based on analyte (n = 6). The proposed method was successfully applied for the determination of understudy TMs in milk samples. The results of raw and processed milk indicated that environmental conditions and manufacturing processes play a key role in the distribution of toxic metals in raw and processed milk.     

Genome sequencing reveals mechanisms for heavy metal resistance and polycyclic aromatic hydrocarbon degradation in Delftia lacustris strain LZ-C

Strain LZ-C, isolated from a petrochemical wastewater discharge site, was found to be resistant to heavy metals and to degrade various aromatic compounds, including naphenol, naphthalene, 2-methylnaphthalene and toluene. Data obtained from 16S rRNA gene sequencing showed that this strain was closely related to Delftia lacustris. The 5,889,360 bp genome of strain LZ-C was assembled into 239 contigs and 197 scaffolds containing 5855 predicted open reading frames (ORFs). Among these predicted ORFs, 464 were different from the type strain of Delftia. The minimal inhibitory concentrations were 4 mM, 30 µM, 2 mM and 1 mM for Cr(VI), Hg(II), Cd(II) and Pb(II), respectively. Both genome sequencing and quantitative real-time PCR data revealed that genes related to Chr, Czc and Mer family genes play important roles in heavy metal resistance in strain LZ-C. In addition, the Na⁺/H⁺ antiporter NhaA is important for adaptation to high salinity resistance (2.5 M NaCl). The complete pathways of benzene and benzoate degradation were identified through KEGG analysis. Interestingly, strain LZ-C also degrades naphthalene but lacks the key naphthalene degradation gene NahA. Thus, we propose that strain LZ-C exhibits a novel protein with a function similar to NahA. This study is the first to reveal the mechanisms of heavy metal resistance and salinity tolerance in D. lacustris and to identify a potential 2-methylnaphthalene degradation protein in this strain. Through whole-genome sequencing analysis, strain LZ-C might be a good candidate for the bioremediation of heavy metals and polycyclic aromatic hydrocarbons.

     

Using chemical fractionation to evaluate the phytoextraction of cadmium by switchgrass from Cd-contaminated soils

The purpose of this study is to evaluate the phytoextraction of cadmium (Cd) from contaminated soils by switchgrass (Panicum virgatum L.), which is a promising energy crop with high biomass. Two ecotypes of switchgrass cultivars, Alamo and Blackwell, were investigated in a pot experiment. Dry weight and plant Cd concentration of the switchgrass plants growing on Cd-spiked soils (0, 20, and 60 mg Cd kg⁻¹ soil) with chelating agent amendments (1 g kg⁻¹ citric acid [CA] and 0.1 g kg⁻¹ ethylene diaminetetraacetic acid [EDTA]) were measured to examine the phytotoxicity and accumulation of Cd in the switchgrass. Fractions of Cd (F1, exchangeable; F2, carbonate; F3, Fe–Mn oxide; F4, organic matter; F5, residual) for the soils sampled at the time of harvesting were also determined using chemically sequential extractions. In the results, the dry weight of the switchgrass decreased with increasing Cd, with a significant dry weight reduction when Cd exceeded 20 mg kg⁻¹. However, the high Cd spike of 60 mg kg⁻¹ was not lethal to Alamo and Blackwell, which suggests that switchgrass plants can tolerate Cd and grow in contaminated soils. Compared with the control, the CA and EDTA amendments had no adverse effect on the growth of switchgrass plants. With regard to Cd accumulation, higher plant Cd concentrations were frequently found after CA amendment in Alamo; however, the Cd concentrations of Blackwell plants may increase when amended with EDTA. On the basis of the fractionation of soil Cd, dry weight and plant Cd concentration could be expressed as a function of Cd fractionation to predict the phytoextraction of Cd. Thus, the fractionation of Cd is a useful approach for evaluating the phytoextraction of Cd by switchgrass in contaminated soils. According to the comparison of phytoextractions of Cd between Alamo and Blackwell, Alamo plants removed substantially more Cd from Cd-spiked soils than Blackwell. Therefore, Alamo is better suited for the phytoextraction of Cd from contaminated soils.     

One-pot synthesis and <Emphasis Type="Italic">in vitro</Emphasis> microbiological evaluation of pyrimidinyl thiazolidinones catalyzed by activated fly ash in dry media

Novel bioactive 2-phenyl-3-(4,6-diarylpyrimidin-2-yl)thiazolidin-4-ones 12–22 were synthesized with good yields in a short reaction time by the “one-pot” multicomponent reaction of the appropriate 2-amino-4,6diarylpyrimidines, benzaldehyde and thioglycolic acid under microwave irradiation in the presence of an activated fly ash catalyst in dry medium. The characterization of these compounds was confirmed by melting point, elemental analysis, mass spectrometry, FT-IR spectroscopy, and one-dimensional NMR (¹H and ¹³C) spectroscopic data. In search for new leads toward potent antimicrobial agents, all the synthesized compounds have been tested in vitro for their antibacterial activity against Bacillus subtilis and Micrococcus luteus and antifungal activity against Aspergillus niger, Candida albicans, Candida 6 and Candida 51, and the results are discussed.     

Cadmium and lead uptake by <Emphasis Type="Italic">Salix viminalis</Emphasis> under modified Ca/Mg ratio

The studies were focused on the influence of mutual changes in the ratio of calcium and magnesium in soil on the efficiency of cadmium and lead uptake and accumulation by Salix viminalis. In the environmental experiment the soil was modified according to the natural Ca/Mg ratio with the experimental groups 4:1 (physiological ratio), 20:1, and 1:10, and was characterized by the amounts of the most important elements (including heavy metals) and selected soil parameters. Efficiency of lead and cadmium accumulation was in the order of Ca/Mg ratios 1:10 > 4:1 > 20:1, and was higher in the shoots at 0.5 m height when compared to 0.1 m above the ground. Under Cd and Pb supplementation the level of both metals was 2-fold higher, while bioaccumulation factor values according to selected literature indicated weak accumulation. When the seasonal metal uptake was analysed (from April to October), the highest accumulation efficiency was observed in the first two periods (April to August) and was Ca/Mg ratio independent. Salix growth was restrained under 1:10 Ca/Mg ratio while it was stimulated under 20:1 ratio, which was opposite to the metal sorption. Summing up, increased calcium level in soil (20:1 Ca/Mg) resulted in limited sorption of heavy metals and stimulated biomass productivity. Under increased magnesium concentration (1:10 Ca/Mg) in relation to the natural 4:1 ratio the accumulation efficiency was the greatest but plant growth was inhibited.     

Selective adsorption for Ag (I) from wastewater by carbon-magnetic fly ash beads modified with polydopamine and thiourea

A magnetic adsorbent was prepared by polydopamine coating and thiourea grafting on carbon-modified discarded fly ash magnetic beads (TPCMFA). The successfully preparation of the TPCMFA was supported by SEM image, XRD, FT-IR and Raman spectroscopy. Batch adsorption experiments reveal that the adsorption of silver ions on this magnetic sorbent TPCMFA agreed with the Langmuir isotherm model, with a maximum absorbability of 94.94 mg g^-1. Kinetics data revealed that the adsorption of silver ions on TPCMFA conform to a pseudo-second-order. The TPCMFA achieved remarkable selectivity for Ag (I) that was almost five times higher than that for ions of copper, zinc and nickel. After three cycles, the adsorption capacity of TPCMFA remained at 93.5% of the adsorption capacity of the initial material. These results show that this new magnetic adsorbent prepared from discarded fly ash magnetic beads has promising commercial prospects.     

Subacute inhalation toxicity assessment of fly ash from industrial waste incinerators

Fly ash from industrial waste incinerators has been a significant concern because of their constituent toxic heavy metals and organic compounds. The objective of this study was to identify the subacute inhalation toxicity of fly ash from industrial waste incinerators, using whole body inhalation exposure chambers. Male and female groups of Sprague-Dawley rats were exposed to fly ash by inhalation of concentrations of 0, 50, 100, 200?mg/m³, for 6?h/day, 5 days/week for 4 weeks. There was no significant difference in body weight, and relative organ weight to body weight, between the exposure groups and the control group. Hematological examinations revealed a significant increase of monocyte counts in fly ash exposed rats and brown pigment laden macrophage was found in the lungs of rats exposed to high concentration of fly ash. A decrease of blood glucose levels and an increase in glutamate oxaloacetate transaminase activity were observed in fly ash treated rats. There was also a significant increase of lactate dehydrogenase levels in rat blood exposed fly ash. A significant dose-dependent increase of DNA damage was found in lymphocytes, spleen, bronchoalveolar lavage, liver, lung, and thymus of rats exposed to fly ash. In addition, the level of lipid peroxidation was increased in the plasma of rats exposed to a high concentration of fly ash. These results suggest that inhalation of fly ash from industrial waste incinerators can induce histopathologic, hematological, and serum biochemical changes and oxidative damage.     

HIV infection confers distinct mechanisms in severe drug eruption: Endogenous virus activation with aberrant Th2/Th1 and CD8+ T cells function

Severe drug eruption (SDE), a common skin disease, becomes dangerous when it occurs in patients with human immunodeficiency virus (HIV). However, the molecular mechanisms are poorly understood. Forty patients including HIV⁺ SDE⁺ (n = 15), HIV⁻ SDE⁺ (n = 15) and HIV⁺ SDE⁻ (n = 10) subjects were enrolled in our study. All HIV⁺ patients were at acquired immune deficiency syndrome (AIDS) stage. Serum levels of TNF-α, IFN-γ, IL-4, IL-13, IL-6, CXCL9, and CCL17 were quantified by ELISA. Epstein–Barr virus (EBV) and cytomegalovirus (CMV) loads were quantified by RT-qPCR. CD4, CD8, Th1, Th2, TNF-α-CD8, and IFN-γ-CD8 T cell populations were measured by flow cytometry. Levels of biochemical indexes in HIV⁺ SDE⁺ patients were significantly different from in HIV⁻ SDE⁺ patients (P < .05). EBV and CMV viral loads were significantly higher in HIV⁺ SDE⁺ patients, but not in HIV⁻ SDE⁺ patients (P < .05). Inflammatory cytokines TNF-α and IFN-γ were significantly elevated in HIV⁺ SDE⁺ patients (P < .05). Th2/Th1 populations and TNF-α secreting or IFN-γ secreting CD8⁺ T cells, were significantly up-regulated in HIV⁺ SDE⁺ patients compared to HIV⁻ SDE⁺ patients (P < .05). Conversely, the CD4/CD8 ratio was significantly down-regulated in HIV⁺ SDE⁺ patients compared to HIV⁻ SDE⁺ patients (P < .05). HIV infection confers distinct clinical phenotypes and immune inflammatory mechanisms in SDE. Sustained EBV and CMV activation, unbalanced Th2/Th1 and overactive CD8⁺ T cells mediating a pro-inflammatory response could act as distinct mechanisms in the aggravation of SDE in HIV⁺ SDE⁺ patients.     

Air pollution-related metals induce differential cytokine responses in bronchial epithelial cells

Different transition metals have been shown to induce inflammatory responses in lung. We have compared eight different metal ions with regard to cytokine responses, cytotoxicity and signalling mechanisms in a human lung epithelial cell model (BEAS-2B). Among the metal ions tested, there were large differences with respect to pro-inflammatory potential. Exposure to Cd^2 +, Zn^2 + and As^3 + induced CXCL8 and IL-6 release at concentrations below 100 μM, and Mn^2 + and Ni^2 + at concentrations above 200 μM. In contrast, VO₄^3 −, Cu^2 + and Fe^2 + did not induce any significant increase of these cytokines. An expression array of 20 inflammatory relevant genes also showed a marked up-regulation of CXCL10, IL-10, IL-13 and CSF2 by one or more of the metal ions. The most potent metals, Cd^2 +, Zn^2 + and As^3 + induced highest levels of oxidative activity, and ROS appeared to be central in their CXCL8 and IL-6 responses. Activation of the MAPK p38 seemed to be a critical mediator. However, the NF-κB pathway appeared predominately to be involved only in Zn^2 +- and As^3 +-induced CXCL8 and IL-6 responses. Thus, the most potent metals Cd^2 +, Zn^2 + and As^3 + seemed to induce a similar pattern for the cytokine responses, and with some exceptions, via similar signalling mechanisms.     

Suitability of <Emphasis Type="Italic">Daphnia similis</Emphasis> as an alternative organism in ecotoxicological tests: implications for metal toxicity

The acute toxicity of metals to Daphnia similis was determined and compared to other daphnid species to evaluate the suitability of this organism in ecotoxicology bioassays. To verify the performance D. similis in toxicity tests, we also investigated the effect of Pseudokirchneriella subcapitata at 1 × 10⁵ and 1 × 10⁶ cells ml⁻¹ on Cd and Cr acute toxicity to the cladoceran. Daphnid neonates were exposed to a range of chromium and cadmium concentrations in the absence and presence of the algal cells. Metal speciation calculations using MINEQL⁺ showed that total dissolved metal concentrations in zooplankton culture corresponded to 96.2% free Cd and 100% free Cr concentrations. Initial total dissolved metal concentrations were used for 48 h-LC₅₀ determination. LC₅₀ for D. similis was 5.15 × 10⁻⁷ mol l⁻¹ dissolved Cd without algal cells, whereas with 1 × 10⁵ cells ml⁻¹, it was significantly higher (7.15 × 10⁻⁷ mol l⁻¹ dissolved Cd). For Cr, the 48 h-LC₅₀ value of 9.17 × 10⁻⁷ mol l⁻¹ obtained for the cladoceran in tests with 1 × 10⁶ cells ml⁻¹ of P. subcapitata was also significantly higher than that obtained in tests without algal cells (5.28 × 10⁻⁷ mol l⁻¹ dissolved Cr). The presence of algal cells reduced the toxicity of metals to D. similis, as observed in other studies that investigated the effects of food on metal toxicity to standard cladocerans. Comparing our results to those of literature, we observed that D. similis is as sensitive to metals as other standardized Daphnia species and may serve as a potential test species in ecotoxicological evaluations.