Jiří Machát

Bioaccumulation and toxicity of selenium compounds in the green alga Scenedesmus quadricauda

BackgroundSelenium is a trace element performing important biological functions in many organisms including humans. It usually affects organisms in a strictly dosage-dependent manner being essential at low and toxic at higher concentrations. The impact of selenium on mammalian and land plant cells has been quite extensively studied. Information about algal cells is rare despite of the fact that they could produce selenium enriched biomass for biotechnology purposes.ResultsWe studied the impact of selenium compounds on the green chlorococcal alga Scenedesmus quadricauda. Both the dose and chemical forms of Se were critical factors in the cellular response. Se toxicity increased in cultures grown under sulfur deficient conditions. We selected three strains of Scenedesmus quadricauda specifically resistant to high concentrations of inorganic selenium added as selenite (Na2SeO3) – strain SeIV, selenate (Na2SeO4) – strain SeVI or both – strain SeIV+VI. The total amount of Se and selenomethionine in biomass increased with increasing concentration of Se in the culturing media. The selenomethionine made up 30–40% of the total Se in biomass. In both the wild type and Se-resistant strains, the activity of thioredoxin reductase, increased rapidly in the presence of the form of selenium for which the given algal strain was not resistant.ConclusionThe selenium effect on the green alga Scenedesmus quadricauda was not only dose dependent, but the chemical form of the element was also crucial. With sulfur deficiency, the selenium toxicity increases, indicating interference of Se with sulfur metabolism. The amount of selenium and SeMet in algal biomass was dependent on both the type of compound and its dose. The activity of thioredoxin reductase was affected by selenium treatment in dose-dependent and toxic-dependent manner. The findings implied that the increase in TR activity in algal cells was a stress response to selenium cytotoxicity. Our study provides a new insight into the impact of selenium on green algae, especially with regard to its toxicity and bioaccumulation.

Vapour generation inductively coupled plasma optical emission spectrometry in determination of total iodine in milk

Vapour generation inductively coupled plasma optical emission spectrometry (VG-ICP-OES) was used for the determination of the iodine content in milk samples. Modified alkaline ashing of the milk sample was employed for the total digestion of organic matrix constituents. A mixture of potassium hydroxide (2 mL, 2 mol L−1 in ethanol) and calcium nitrate (2 mL, 0.4 mol L−1 in ethanol) was used in the digestion step as an ashing aid for 2 ml of milk sample (or 200 mg of milk powder). Sample ash was then treated with hydrochloric acid (1.5 mL, 5 mol L−1) and sodium sulfite (1.25 mL, 1 mol L−1) for the elimination of carbonates, which would otherwise cause spectral interference. The vapour of elemental iodine was generated by means of oxidation of iodide by hydrogen peroxide (1 mol L−1) in sulfuric acid (5 mol L−1). Using a gas phase separator, matrix elements were completely eliminated; thus the spectral interference of phosphorus (178.222 nm) was removed and the most intense analytical line of iodine (178.218 nm) could be used for determination. The accuracy of the method was verified by analysis of CRM Non-Fat Milk Powder 1549 from NIST, as well as by the comparative study of VG-ICP-OES and ICP-MS results after alkaline solubilization (TMAH 2.5 mL, 10%). The limit of detection for the VG-ICP-OES method is 20 μg L−1 for original milk samples (based on 3σ of blank value). The concentration of iodine in real milk samples was found in the range 0.2–0.8 mg L−1 with a precision of determination from 0.5 to 3.5% (3 replicates).

Contribution to vapor generation-inductively coupled plasma spectrometric techniques for determination of sulfide in water samples

Vapor generation-inductively coupled plasma-optical emission spectrometry was used for the determination of sulfide in water samples preserved by the addition of a zinc acetate and sodium hydroxide solution. Hydrogen sulfide and acid-volatile sulfides were transformed, by acidification, to a gaseous phase in a vapor generator and subsequently detected by inductively coupled plasma optical emission spectrometry. Compounds interfering with iodometric titration and spectrophotometric determination were examined as potential chemical interferents. The proposed method provides results comparable to iodometric titration in the tested concentration range 0.06-22.0 mg L(-1). Limit of detection for the determination of hydrogen sulfide by this method is 0.03 mg L(-1).

Simultaneous determination of inorganic arsenic, antimony, selenium and tellurium by ICP-MS in environmental waters using SPE preconcentration on modified silica

This paper deals with a simplified multi-element profiling of inorganic arsenic, antimony, selenium and tellurium in the form of 75As, 82Se, 121Sb and 125Te by ICP-MS for amounts less than 10 µg L−1. Internal standards such as 72Ge and 209Bi were successfully used for the suppression of both influence of macro elements Na+, K+, Ca2+, Mg2+ or Al3+, and interference of limited concentrations of heavy metal ions. Modified silica sorbents Separon™ SGX C18, C8, CN, NH2, RPS and Phenyl were tested for the preconcentration of As, Sb, Se and Te (0.25–5 µg L−1) in the form of ion associates with cationic surfactants from 50–250 mL sample volume. 1-etoxycarbonyl-pentadecyltrimethylammonium bromide (Septonex®, 0.005 mol L−1) was suitable for this purpose in the presence of 4-(2-pyridylazo) resorcinol, 2-pyrrolidinecarbodithioate and 8-hydroxyquinoline-5-sulphonic acid. The quantitative retention occurred at pH 7 ± 0.2 and the mixture of acetone with ethanol in ratio 1 : 1 in the presence of 0.1 mol L−1 HCl was used for the quantitative elution. Organic solvents and the excess of acid were removed by evaporation prior to the determination by ICP-MS. The determination of the above trace metalloids in various kinds of water with enrichment factor till 50 times on silica Separon™ SGX C18 and the above reagents were compared with the standard addition method.

Kinetic bacterial bioluminescence assay for contact sediment toxicity testing: Relationships with the matrix composition and contamination

The present study represents the first broader evaluation of the rapid 30-s kinetic bioluminescence assay with Vibrio fisheri (microplate format modification) for contact toxicity testing of whole sediments. The present study focused on river sediments from the Morava River basin, Czech Republic, repeatedly sampled during 2005 to 2006 and analyzed for geological and geochemical parameters, content of toxic metals, major organic pollutants, and toxicity. High natural variation in toxicity (50% inhibitory concentration [IC50] values ranging from 0.8 to >80 mg sediment dry wt/ml) was found (among different sampling periods and years, among sites), and this could be related to the sediment dynamics affected by spring high flows and summer droughts. From the 46 sediment descriptors, exchangeable protons (H(+)) was the only parameter that consistently correlated with toxicity. Three other descriptors (i.e., content of organic carbon plus two parameters from the detailed silicate analysis of sediments: percentage of SO(3) representing total sulfur content, structural water H(2)O+) also significantly correlated with toxicity. There were only minor and variable correlations with contamination. We propose sediment safety guideline categories for the V. fisheri kinetic test with severe toxicity threshold of IC50 < 1 mg dry wt/ml. Although sediments are considered a rather stable matrix in comparison with river water, we confirmed high variability and dynamics that should be reflected in monitoring plans and field studies.

Comparison and Characterization of OECD Artificial Soils

OECD artificial soil is a widely used substrate in soil toxicity tests. Despite its apparent necessity as a defined mixture relevant for solid phase exposure, several problematic issues have been revealed recently which must be considered seriously. It is not clear if the OECD artificial soil is really a standardized reference material omitting the influences of varying natural soil properties or if there is still significant variability present, which may influence toxicity results. Under the auspices of the EU ringtest for the ecotoxicity of wastes, a new project has been started with the aim of addressing the variability of nearly 20 artificial soils. Although the collected soils were declared to have been prepared strictly according to OECD guidelines, they were different even at the first look and the organic carbon content in the artificial soils varied from 1.4 to 6.0%. This indicates the variability in the organic carbon content of peat from different sources, producers and countries. The cadmium sorption experiment on selected soils suggests that the cadmium K d varies among artificial soils over one order of magnitude. It is apparent from our pilot results that there are differences between the OECD artificial soils from various labs in the EU.

Association of minor and trace elements with mineralogical constituents of urinary stones: A hard nut to crack in existing studies of urolithiasis

The role of metals in urinary stone formation has already been studied in several publications. Moreover, urinary calculi can also be used for assessing exposure of humans to minor and trace elements in addition to other biological matrices, for example, blood, urine, or hair. However, using urinary calculi for biomonitoring of trace elements is limited by the association of elements with certain types of minerals. In this work, 614 samples of urinary calculi were subjected to mineralogical and elemental analysis. Inductively coupled plasma mass spectrometry and thermo-oxidation cold vapor atomic absorption spectrometry were used for the determination of major, minor, and trace elements. Infrared spectroscopy was used for mineralogical analysis, and additionally, it was also employed in the calculation of mineralogical composition, based on quantification of major elements and stoichiometry. Results demonstrate the applicability of such an approach in investigating associations of minor and trace elements with mineralogical constituents of stones, especially in low concentrations, where traditional methods of mineralogical analysis are not capable of quantifying mineral content reliably. The main result of this study is the confirmation of association of several elements with struvite (K, Rb) and with calcium phosphate minerals, here calculated as hydroxylapatite (Na, Zn, Sr, Ba, Pb). Phosphates were proved as the most important metal-bearing minerals in urinary calculi. Moreover, a significantly different content was also observed for Fe, Zr, Mo, Cu, Cd, Se, Sn, and Hg in investigated groups of minerals. Examination of such associations is essential, and critical analysis of mineral constituents should precede any comparison of element content among various groups of samples.

Urinary calculi — atypical source of information on mercury in human biomonitoring

AbstractChemical analysis of various biological matrices is routinely used for assessment of human exposure to various toxic metals. In this work, 489 samples of urinary calculi originating from almost the whole of The Czech Republic, were collected and subjected to mineralogical and elemental analysis. This study was aimed at mercury, the content of which was determined using thermo-oxidation — cold vapor — atomic absorption spectrometry. The effects of mineralogical composition, sex, age and region were recorded in order to verify the applicability of urinary calculi for biomonitoring. Relationships with other minor and trace elements were also investigated. Association of mercury with whewellite mineral was observed as well as a remarkable relationship with selenium, confirming the role of selenium in mercury excretion. No statistically significant effect was observed on the mercury content in stones with regard to the sex or region. Median values in age groups follow a trend with the maximum median value 0.365 mg kg−1 in the group of 41–50 year old donors, decreasing to 0.060 mg kg−1 for the oldest group (81–92 years). Our results confirm that urinary calculi can be helpful in providing complementary information on human exposure to mercury and its excretion.

The EPMA, LA-ICP-MS and ICP-OES study of corrosion of structural materials for a nuclear reactor cooling circuit by molten fluoride salt treatment

Electron probe microanalysis (EPMA), inductively coupled plasma atomic emission spectrometry (ICP-OES), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were applied to study the interaction of molten LiF-NaF salt mixtures with candidate structural materials (alloys) for a nuclear reactor-transmutor cooling circuit. The corrosion of test ampoules and inserted test specimens made of structural materials was brought about by the action of molten LiF-NaF coolant at 680 °C and its extent and character were examined in dependence on the time of exposure. The material corrosion changes were studied by mapping the sections of ampoule walls and inserted specimen surfaces with EPMA, whereas LA-ICP-MS was employed for linear scanning the salt/ampoule wall boundary. Corrosion-released structural material, dissolved in solidified molten salt, was analyzed by ICP-OES after the salt dissolution. The melt activity was proved to induce a surficial modification of a structural material up to the depth of 15–50 µm, which was associated with the coolant contamination. The X-ray maps by EPMA with its 1-µm lateral resolution revealed compositional changes in alloys, such as regular depletion of Cr to the depth of 10–25 µm. While the lateral resolution of LA-ICP-MS with the applied laser spot diameter of 25 µm was not exactly adequate to dimensions of the corroded regions and, consequently, yielded less information in comparison with EPMA, this technique was quite sufficient for the monitoring of the presence of alloy constituents in an adhered salt layer. It was concluded that: i) the EPMA study, involving semi-quantitative elemental mapping/content profiling and detailed spot quantitative analyses makes it possible to obtain quantitative assessment of the corrosion process; ii)LA-ICP-MS profiles can be converted from signal domain to elemental contents on a semi-quantitative level when applying signal normalization to the total sum of signals.

The variability of standard artificial soils: cadmium and phenanthrene sorption measured by a batch equilibrium method

Artificial soil (AS) is used in soil ecotoxicology as a test medium or reference matrix. AS is prepared according to standard OECD/ISO protocols and components of local sources are usually used by laboratories. This may result in significant inter-laboratory variations in AS properties and, consequently, in the fate and bioavailability of tested chemicals. In order to reveal the extent and sources of variations, the batch equilibrium method was applied to measure the sorption of 2 model compounds (phenanthrene and cadmium) to 21 artificial soils from different laboratories. The distribution coefficients (Kd) of phenanthrene and cadmium varied over one order of magnitude: from 5.3 to 61.5L/kg for phenanthrene and from 17.9 to 190L/kg for cadmium. Variations in phenanthrene sorption could not be reliably explained by measured soil properties; not even by the total organic carbon (TOC) content which was expected. Cadmium logKd values significantly correlated with cation exchange capacity (CEC), pHH2O and pHKCl, with Pearson correlation coefficients of 0.62, 0.80, and 0.79, respectively. CEC and pHH2O together were able to explain 72% of cadmium logKd variability in the following model: logKd=0.29pHH2O+0.0032 CEC -0.53. Similarly, 66% of cadmium logKd variability could be explained by CEC and pHKCl in the model: logKd=0.27pHKCl+0.0028 CEC -0.23. Variable cadmium sorption in differing ASs could be partially treated with these models. However, considering the unpredictable variability of phenanthrene sorption, a more reliable solution for reducing the variability of ASs from different laboratories would be better harmonization of AS preparation and composition.