T.M. Florence

Evaluation of some physico-chemical techniques for the determination of the fraction of dissolved copper toxic to the marine diatom nitzschia closterium

The toxicity of copper to the marine diatom Nitzschia closterium was determined by growth rate measurements in the presence of a range of copper complexing agents, both natural and synthetic. The measurements were made in raw, unenriched sea water to avoid the reaction of copper with silicate or colloidal hydrated iron(III) oxide which occurs in standard culture media. The algae remained in exponential growth for at least 72 h in unenriched sea water and, in the presence of copper, produced an exudate which decreased the concentration of labile copper. Labile copper was measured in the algal assay solutions by using anodic stripping voltammetry (a.s.v.) at different deposition potentials, by separation on iminodiacetate (Chelex-100) and thiol resins, and by extraction with hexane/n-butanol (9:1) to simulate lipid solubility. No consistent correlation was observed between the toxic fraction of copper measured by algal assay, and the labile copper determined by the physico-chemical techniques. Although some of the naturally-occurring ligands (e.g., fulvic acid and iron—humic acid colloid) gave reasonable agreement between the toxic fraction and a.s.v.-labile copper, the chelating resins usually grossly overestimated toxicity. Lipid-soluble complexes of copper with synthetic ligands (e.g., 8-quinolinol and diethyldithiocarbamate) were highly toxic; as little as 2 μg Cu l−1 in the presence of 5 × 10−5 M 8-quinolinol caused complete depression of algal growth. It is proposed that the extreme toxicity of lipid-soluble copper complexes results from their ability to catalyse the intercellular formation of highly destructive hydroxyl free radicals (OH.) from molecular oxygen, in a Fenton-type reaction.

Development of physico-chemical speciation procedures to investigate the toxicity of copper, lead, cadmium and zinc towards aquatic biota

Abstract A range of model compounds was studied to test the effect of complexing agents on the adsorption of copper, lead, cadmium and zinc by Chelex-100 resin, oxine porous glass, thiol porous glass and thiol resin, from seawater and distilled water. The thiol materials, while showing behaviour similar to Chelex-100 resin and oxine porous glass for zinc, cadmium and lead, retained copper much more strongly. Methods for measuring lipid-soluble metal complexes in waters were also studied. Bio-Rad SM2 resin was the most suitable extractant, although a citrate buffer of pH 5.7 was needed to prevent the co-adsorption of free metal ions. Seawater and various fresh waters were analyzed for trace metal speciation by using Chelex-100 resin, thiol resin and anodic stripping voltammetry to determine labile metal. Bio-Rad SM2 resin and hexane—butanol extraction were used for the estimation of lipid-soluble metal. The polluted water samples had higher fractions of labile and organic-soluble metal, but it was concluded that some of the waters contained unidentified ligands which caused speciation behaviour different from that of the synthetic solutions with model ligands. The factors involved in the choice of speciation procedures for the measurement of the toxic fraction of a metal in a water sample are discussed in detail.

Platinum in the human diet, blood, hair and excreta.

Baseline levels of platinum in the blood, hair and urine of 21 adults from Sydney, Australia, and three adults from the relatively unpolluted area of Lord Howe Island, Australia, were determined by adsorptive voltammetry. The median concentrations of platinum in samples from residents in Sydney were: whole blood, 0.56 microgram Pt l-1; hair, 3.84 micrograms Pt kg-1; urine, 0.18 microgram Pt l-1 (0.23 microgram Pt g creatinine). Samples from residents of Lord Howe Island had platinum levels that were within the range of values of the corresponding samples from Sydney residents. For faeces samples, the median platinum concentration was 10.5 micrograms kg-1 FW. The excretion of platinum over a 4-day period was measured in one adult male. Urinary excretion of platinum was between 0.76 and 1.07 micrograms Pt day-1 and in faeces it was between 0.61 and 0.73 microgram Pt day-1. The concentrations of platinum in a range of foodstuffs from Sydney were between 8.11 micrograms kg-1 FW for liver and 0.13 microgram kg-1 FW for full-cream milk. This information as well as the amounts of these foods in hypothetical diets for Australians was used to calculate the total dietary intake of platinum. The average diet of a Sydney adult contains 1.44 micrograms of platinum per day (adult male, 1.73 micrograms Pt day-1; adult female, 1.15 micrograms Pt day-1). The uptake of dietary platinum from the gut was estimated to be at least 42% and, therefore, diet appears to make a substantial contribution to total platinum intake.

Percutaneous absorption of inorganic lead compounds

In vivo experiments with the stable lead isotope, 204Pb, have confirmed that inorganic lead compounds can be absorbed through the skin. Three different analytical techniques--thermal ionization mass spectrometry, inductively coupled plasma mass spectrometry and anodic stripping voltammetry--showed that lead, as lead nitrate or lead acetate, was rapidly absorbed through the skin and detectable in sweat, blood and urine within 6 h of skin application. Of the 4.4 mg of lead applied to the skin in one experiment, 1.3 mg was absorbed within 24 h. Initial rapid uptake was probably via sweat glands and hair follicles, followed by slower absorption via the transepidermal route. While increases in 204Pb concentration and abundance were observed, no increase in total lead in blood or urine was found. It is possible that the physicochemical form of skin-absorbed lead partitions strongly into extracellular fluid, but has a low affinity for erythrocytes. There was no significant difference in uptake of lead into erythrocytes (in vitro) from normal saline, synthetic sweat or sauna sweat. Ultrafiltration of sweat showed that up to 70% of lead in sweat was associated with > 30,000 MW particles. It is possible that percutaneous absorption of lead could contribute significantly to lead body burden, particularly from occupational exposure to lead in dust. Moreover, because lead absorbed through the skin was only just detectable in blood, and blood lead is the main criterion by which industry determines exposure, skin-absorbed lead may remain undetected.

Anodic stripping voltammetry with medium exchange in trace element speciation

Abstract The application of medium exchange in anodic stripping voltammetry (ASV) was investigated by determing the fractions of ASV-labile copper, lead, cadmium and zinc in the presence of a variety of natural and sysnthetic ligands in a soft water. Pristin and polluted samples of river water were also tested. Medium exchange, where the test solution is replaced after electrodeposition by a simple electrolyte such as acetate buffer, before the oxidation (stripping) of the deposited metals, can ensure that the ASV-labile metal fraction depends only on the parameters of the electrodeposition step. Significant differences were found for ASV-labile fractons when medium exchange was used for the two river water samples, and for several mertal/ligand combinations such as copper/chloride, copper/humic acid, and zinc/tannic aid. It is recommended that medium exchange be used routinely for ASV-labile determinations.

A novel adsorbent for the determination of the toxic fraction of copper in natural waters

A novel adsorbent for the determination of the toxic fraction of copper in natural waters is described. Aluminium hydroxide adsorbed on a sulfonic acid cation-exchange resin quantitatively retains copper(II) ions in the absence of organic ligands such as fulvic, humic and tannic acids. In the presence of these ligands, a smaller fraction of copper is adsorbed and can be related to the toxic fraction. The toxic fraction determined by this method agreed well with results of algal assay with the marine diatom Nitzschia closterium in seawater and the green alga Chlorella pyrenoidosa in a synthetic soft water. The aluminium hydroxide-coated column also quantitatively adsorbs lipid-soluble copper complexes, which can be leached selectively from the column with methanol. The Al:OH ratio on the resin was 1:2 and the conditional stability constants (log K) of the Cu2+-adsorbent complexes in seawater and synthetic soft water were found to be 9.87 and 11.10, respectively; these values are similar to the equilibrium constatns for the reaction between Cu2+ and algae. The application of this adsorbent in an in-situ instrument for the continuous, unattended determination of the toxic fraction of copper and some other toxic metals in natural waters is outlined.

Comparison of physicochemical speciation procedures with metal toxicity to chlorella pyrenoidosa

Abstract Metal speciation as measured by anodic stripping voltammetry (ASV), adsorption on a resin with adsorbed hydrated aluminium oxide, and dialysis with receiving resins is compared with the toxicity of the metals to the freshwater green alga Chlorella pyrenoidosa Chick. In the presence of natural and synthetic ligands, similar labile fractions of metals were obtained for ASV at three electrodes (hanging mercury drop electrode, mercury film electrode and Nafion-coated mercury film electrode). The toxic fractions determined by ASV and bioassay were in reasonable agreement for zinc, cadmium and copper, and alteration of the analytical conditions provided some measure of agreement for lead. The resin with adsorbed hydrated aluminium oxide correlated well with bioassay for copper, but over-estimated lead toxicity and under-estimated cadmium toxicity. Dialysis with receiving resins under-estimated metal bioaccumulation in the presence of ligands. Metal speciation analysis for water samples gave higher toxic fractions for metals in samples of polluted river water and road runoff samples than those found in pristine river water.

Rapid radiochemical separation in neutron activation analysis : Part 1. The use of C18-bonded silica gel and selective complexation for determinations of manganese, copper and zinc in biological materials

Abstract A rapid radiochemical separation method based on the removal of metal ions by columns of C 18 -bonded silica gel after selective complexation by 8-quinolinol, ammonium pyrolidinedithiocarbamate or cupferron is described for the determination of manganese, copper and zinc in neutron-activated biological materials. The removal of the metal ions, either by adsorption or by a combination of filtration and adsorption on columns of C 18 -bonded silica gel, was investigated to optimise the separation procedure. Analysis of several National Bureau of Standards and International Atomic Energy Agency biological reference materials demonstrated the effectiveness of this technique. The method is simple and reliable and readily adaptable in all radiochemical laboratories. Furthermore, columns of C 18 -bonded silica gel have been successfully recycled a number of times without deterioration.

Fumed silica for the direct determination of lead in urine by differential-pulse anodic stripping voltammetry

Abstract The use of fumed silica for the direct determination of lead in urine by differential-pulse anodic stripping voltammetry was investigated. Fumed silica, added to urine prior to the nitrogen purge step, completely removed sorption interferences by urinary organic constituents. Values for lead in urine from eight unexposed individuals were 3 ± 2 μg l−1 or 3 ± 2 μg g−1 creatinine. This method is a fast, simple and effective means for the accurate determination of lead in undiluted urine without pretreatment.

RAPID DETERMINATION OF SELENIUM IN HUMAN SERUM BY NEUTRON ACTIVATION ANALYSIS

A simple and rapid method was developed for the determination of selenium in human serum using a pre-irradiation separation technique of ultrafiltration followed by neutron activation analysis via the short-lived activation product77mSe. The method was validated using certified reference material.