Philip H. E. Gardiner

Remediation of chromium(VI) by a methane-oxidizing bacterium

Methane-oxidizing bacteria are ubiquitous in the environment and are globally important in oxidizing the potent greenhouse gas methane. It is also well recognized that they have wide potential for bioremediation of organic and chlorinated organic pollutants, thanks to the wide substrate ranges of the methane monooxygenase enzymes that they produce. Here we have demonstrated that the well characterized model methanotroph Methylococcus capsulatus (Bath) is able to bioremediate chromium(VI) pollution over a wide range of concentrations (1.4-1000 mg L(-1) of Cr(6+)), thus extending the bioremediation potential of this major group of microorganisms to include an important heavy-metal pollutant. The chromium(VI) reduction reaction was dependent on the availability of reducing equivalents from the growth substrate methane and was partially inhibited by the metabolic poison sodium azide. X-ray spectroscopy showed that the cell-associated chromium was predominantly in the +3 oxidation state and associated with cell- or medium-derived moieties that were most likely phosphate groups. The genome sequence of Mc. capsulatus (Bath) suggests at least five candidate genes for the chromium(VI) reductase activity in this organism.

Determination of aluminium in blood plasma or serum by electrothermal atomic absorption spectrometry

Abstract A carbon-furnace atomic absorption method is used to determine aluminium in blood serum or plasma, diluted (1 + 2) with purified water prior to injection (20 μl) into the furnace. Procedures are described to reduce contamination during sample collection, storage and preparation of samples. A study of the interferences of inorganic ions shows that the temperature programme developed minimises these, allowing the use of aqueous standards for calibration. Ashing at 1400°C, prior to atomisation, also removes non-specific background effects, and optical correction is not required. A sample throughput of 50 duplicate analyses per day is possible and the precision (between batch) at 24 μg Al l-1 was 11.2% (n = 10) and at 340 μg Al l-1 was 6.3% (n = 18). Down to 4 μg Al l-1 can be determined. Reference values for a healthy population were 4.1–20 μg Al l-1 (mean 10.2).

The application of gel filtration and electrothermal atomic absorption spectrometry to the speciation of protein-bound zinc and copper in human blood serum

Abstract Gel filtration with Sephadex G-100 is used to partition zinc- and copper-containing proteins in samples of human sera. The zinc and copper content in the fractions collected are determined by electrothermal (carbon furnace) atomic absorption spectrometry without sample pretreatment. Proteins associated with both metals are measured by immunonephelometry. The results confirm the known association of zinc with α 2 -macro-globulin and albumin, but association with other proteins was also found. This combination of techniques provides a method of estimating copper bound to caeruloplasmin and non-caeruloplasmin. Essential clean-up procedures are described.

Simultaneous determination of total nitrogen, phosphorus and sulphur by means of microwave digestion and ion chromatography

A method for the oxidation of nitrogen, phosphorus and sulphur to nitrate, phosphate and sulphate ions using 22% (v/v) hydrogen peroxide and closed-vessel microwave assisted digestion in two stages is described. Solutions of a variety of nitrogen-, phosphorus- and sulphur-containing compounds with formic acid added to prevent hydrolysis were used to test the efficiency of the procedure. The products of oxidation were determined by ion chromatography. Good recoveries of nitrogen, phosphorus and sulphur were obtained. The results for the NIST reference materials, oyster tissue and Buffalo River sediments agree well with the certified values.

The speciation of inorganic and methylmercury in human hair by high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry

Inorganic and methylmercury content in human hair has previously been determined using different analytical techniques for each species. In this study a single method, allowing the separation and determination of mercury species in human hair, is developed. Using a HPLC-ICP-MS system it is possible to separate inorganic and methylmercury in hair, without any modifications to the existing instrumentation. The results showed that in order to determine methylmercury as well as inorganic mercury the hair sample must be cold digested with 2 ml of concentrated nitric acid plus 1 ml of hydrogen peroxide and that a minimum of 0.1 g hair is required. Hair washing procedures are also investigated to remove exogenously bound species. It is seen that when hair is soaked with simulated sweat solution containing both inorganic and methylmercury and then washed with 0.1 M HCl all the methylmercury, both existing and spiked, can be removed from the hair sample. However, only 65% of the spiked inorganic mercury can be removed by washing with 0.1 M HCl, the rest being irreversibly bound to the hair.

Microbial Transformations of Selenium Species of Relevance to Bioremediation

ABSTRACT Selenium species, particularly the oxyanions selenite (SeO3 2−) and selenate (SeO4 2−), are significant pollutants in the environment that leach from rocks and are released by anthropogenic activities. Selenium is also an essential micronutrient for organisms across the tree of life, including microorganisms and human beings, particularly because of its presence in the 21st genetically encoded amino acid, selenocysteine. Environmental microorganisms are known to be capable of a range of transformations of selenium species, including reduction, methylation, oxidation, and demethylation. Assimilatory reduction of selenium species is necessary for the synthesis of selenoproteins. Dissimilatory reduction of selenate is known to support the anaerobic respiration of a number of microorganisms, and the dissimilatory reduction of soluble selenate and selenite to nanoparticulate elemental selenium greatly reduces the toxicity and bioavailability of selenium and has a major role in bioremediation and potentially in the production of selenium nanospheres for technological applications. Also, microbial methylation after reduction of Se oxyanions is another potentially effective detoxification process if limitations with low reaction rates and capture of the volatile methylated selenium species can be overcome. This review discusses microbial transformations of different forms of Se in an environmental context, with special emphasis on bioremediation of Se pollution.

Recent developments in selenium research

Some of the main biochemical features of selenium have emerged only in the last five years, although it has been known to be an essential element for nearly 40 years. The investigations into selenoproteome gene expression and a better understanding of the selenocysteine synthetic pathway have undoubtedly provided the evidence that underpins the biochemical roles of the element. To date, 25 selenium-containing proteins have been identified in humans but the functions of a number of these have yet to be elucidated. The roles of the selenium-containing enyzmes (glutathione peroxidases, thioredoxin reductases and iodothyronine deiodinases) are well established, the first two being linked with antioxidant activity, and the latter involved with thyroid hormone metabolism. Recently, the interaction between sulphur, in the same periodic group and therefore chemically similar, and selenium has been investigated in a bid to understand the role of both elements in disease. There is renewed interest in the anticancer properties of selenium-containing compounds as evidence of their effectiveness in animal models has been demonstrated. Herein, selenium metabolism, gene expression, interaction with sulphur, and role in cancer are reviewed.

Aluminium speciation in soil solutions as studied by size exclusion chromatography

Size exclusion chromatography was used for the fractionation of the aqueous extracts taken from different soil horizons (LOf, Oh, Ah, 15 and 35 cm). The aluminium content in the fractions was determined by graphite furnace atomic absorption spectrometry. In the fractions obtained from the LOf, Oh and Ah horizons, a great part of the total aluminium was bound to organic molecules. Over 90% of the aluminium in mineral soil solutions (15 and 35 cm depth) was of low molecular weight or associated with those species.

µLC–ICP-MS Determinations of Unexposed UK Urinary Arsenic Speciation Reference Values

This study provides background levels for five arsenic species in urine, based on urinary data obtained from 95 nonoccupationally exposed volunteers based in the UK. Using a novel, sensitive, robust and reliable speciation methodology, five species of arsenic (arsenobetaine [AB], arsenite [As(3+)], arsenate [As(5+)], monomethylarsonic acid [MMA(5+)] and dimethylarsinic acid [DMA(5+)]) were determined in urine samples collected from 95 adults. The analytical instrumentation used to analyze the urine samples was a hyphenated micro liquid chromatography (μLC) system coupled to an inductively coupled plasma mass spectrometry (ICP-MS). Separation was achieved using an anion exchange micro-sized column. The results presented give the 95th percentile of concentrations, both uncorrected for creatinine (µg/L) and creatinine corrected (µmol/mol) in urine for the 95 volunteers. Statistical analysis was performed on the dataset using a Bayesian model to determine and quantify effects of gender, smoking and diet. The statistical results show that the consumption of fish, shellfish and red wine has a significant elevating effect on AB, DMA and MMA urinary concentrations; however, no significant effect was observed for smoking. The regression model results indicate that creatinine correction was effective for arsenic species As(3+), MMA, DMA and AB. The background levels established here can be used as reference values to help aid interpretation of arsenic speciation results and better assess exposure.

Chemical speciation in biology and medicine: the role of atomic spectrometric techniques

For the detection, characterisation and identification of trace element containing chemical species in a sample, a wide range of techniques have to be used, and an interdisciplinary approach to the solution of the problems involved is essential. The application of these techniques can produce meaningful results only when particular attention is paid to the choice of methods used for sample collection, pre-treatment and storage, and to the changes that occur during these steps, which can affect the distribution of the chemical species. Some of these changes are identified and suggestions are made as to how they can be kept to a minimum. The detection and determination of metal- and metalloid-containing species by atomic spectrometric techniques are examined, and the potential of the techniques for use in chemical speciation experiments is assessed.