John R. Dean

Determination of mercury in environmental and biological samples using pyrolysis atomic absorption spectrometry with gold amalgamation

This paper is concerned with a new, rapid technique for the determination of total mercury in environmental and biological samples. This technique features the pyrolysis of the sample in a combustion tube at 750°C under an oxygen atmosphere, collection on a gold amalgamator and subsequent detection by atomic absorption spectrometry (AAS) using a silicon UV diode detector. This technique has the advantage of no sample pre-treatment and is free from matrix interference. Eight certified reference materials (CRMs) have been analysed and were found to give results in good agreement with the certified values. The levels determined ranged from 0.035 to 7.06 mg/kg with an average relative standard deviation of 3.6% (n = 8).

Extraction of polycyclic aromatic hydrocarbons from contaminated soil using Soxhlet extraction, pressurised and atmospheric microwave-assisted extraction, supercritical fluid extraction and accelerated solvent extraction

Soxhlet extraction has been compared with pressurised and atmospheric microwave-assisted extraction, accelerated solvent extraction and supercritical fluid extraction for the extraction of polycyclic aromatic hydrocarbons (PAHs) from native, contaminated soil. The results indicate that the recovery of PAHs is dependent on the extraction technique. The highest recoveries of individual PAHs were consistently obtained by Soxhlet extraction. For the samples investigated here the preferred technique in terms of recoveries is Soxhlet extraction.

Extraction of organic pollutants from environmental matrices: selection of extraction technique

The extraction of organic pollutants from solid environmental matrices has traditionally been done using non-instrumental approaches, e.g. Soxhlet extraction. Recent developments have seen the possibility of extraction using instrumental techniques, namely, supercritical fluid extraction, microwave-assisted extraction and pressurised fluid extraction. This review considers the applications of instrumental techniques for the extraction of polycyclic aromatic hydrocarbons, polychlorinated biphenyls and pesticides from soils/sediments. Then, in order to assist the analyst to select the most appropriate technique (traditional versus instrumental techniques), a comparison of their analytical figures of merit is considered.

Uptake of heavy metals by vegetable plants grown on contaminated soil and their bioavailability in the human gastrointestinal tract

Lettuce, spinach, radish and carrot were grown on compost that had previously been contaminated at different concentrations of Cd, Cu, Mn, Pb and Zn. Control plants of each vegetable were also grown on unadulterated compost. The experiment was carried out under greenhouse conditions. Mature plants were harvested and their roots and leaves collected. Soil samples from each growing pot and plant materials were acid digested and analysed to determine total metal concentration. Flame-Atomic Absorption Spectroscopy (FAAS) was employed to determine metal concentrations in soil and plant samples (Mn and Zn), while Cd, Cu and Pb in plant materials were analysed by Differential Pulse Anodic Stripping Voltammetry (DP-ASV). Soil (BCR 146R and GBW 07310) and plant (tea leaves, INCT-TL-1) certified reference materials were used to assess accuracy and precision. The edible part of plants, i.e. the leaves of lettuce and spinach and the roots of radish and carrot, were also extracted using an in vitro gastrointestinal (GI) extraction to assess metal bioavailability. The results showed that the uptake of Cd, Cu, Mn and Zn by plants corresponded to the increasing level of soil contamination, while the uptake of Pb was low. Soil-to-plant transfer factor (TF) values decreased from Mn ≫ Zn > Cd > Cu > Pb. Moreover, it was observed from this investigation that individual plant types greatly differ in their metal uptake, e.g. spinach accumulated a high content of Mn and Zn, while relatively lower concentrations were found for Cu and Pb in their tissues. From the in vitro gastrointestinal (GI) study, results indicate that metal bioavailability varied widely from element to element and according to different plant types. The greatest extent of metal releasing was found in lettuce (Mn, 63.7%), radish (Cu, 62.5%), radish (Cd, 54.9%), radish (Mn, 45.8%) and in lettuce (Zn, 45.2%).

Extraction of polycyclic aromatic hydrocarbons from highly contaminated soils using microwave energy

Microwave energy, generated in a commercial microwave system designed for extraction of organic samples, has been used for the extraction of polycyclic aromatic hydrocarbons (PAHs) from highly contaminated land samples. Initial studies used a native soil and compared a 20 min microwave extraction with a 6 h conventional Soxhlet extraction (both using dichloromethane) with comparable results. The low concentration of PAHs found in the soil resulted in large relative standard deviation (sr) values for the individual PAHs (maximum of 60.9% for microwave extraction). A second soil, with higher PAH levels, was microwave extracted using both dichloromethane and different compositions of an acetone–hexane mixture and compared with Soxhlet extraction. The results indicate that microwave extraction using pure acetone is a more efficient procedure than other combinations studied. A repeatability study gave an sr value for the total PAHs extracted of 2.4%(n= 6). A central composite experimental design was used to elucidate optimum operating parameters but variations in temperature, extraction time and solvent volume were found to have little effect on recovery. The over-all sr for the design was 5.34% illustrating no statistical significance in recovery. A third, Laboratory of the Government Chemist, test soil was used which indicated that the soil matrix was the greatest factor affecting PAH recovery.

Application of high-performance liquid chromatography-inductively coupled plasma mass spectrometry to the investigation of cadmium speciation in pig kidney following cooking and in vitro gastro-intestinal digestion

The speciation of cadmium in retail pig kidney has been examined by size-exclusion chromatography (SEC) coupled directly to inductively coupled plasma mass spectrometry (ICP-MS). Approximately 35% of the cadmium from uncooked kidney was soluble after aqueous extraction at pH 8 and SEC - ICP-MS revealed three discrete peaks whose retention times corresponded to estimated relative molecular masses of 1.2 x 10(6), 7.0 x 10(4) and 6 x 10(3)-9 x 10(3). In the cooked kidney, 35% of the Cd was soluble and was all associated with a peak of a relative molecular mass (Mr) of 6 x 10(3)-9 x 10(3). After simulated gastric digestion of cooked pig kidney at pH 2.5, 60% of the cadmium was solubilised and associated with a species of Mr less than 1 x 10(3). When the digest was also subjected to simulated intestinal digestion at pH 6.8, a single peak, which corresponded to 20% of the original cadmium, was eluted. This peak co-eluted with the single peak extracted at pH 8.0 from the cooked kidney. It was also of similar estimated Mr to the single broad peak observed after simulated gastro-intestinal digestion of equine renal metallothionein (Mr = 1.1 x 10(4]. The results suggest that the majority of soluble cadmium in retail pig kidney is associated with a metallothionein-like protein that survives both cooking and simulated in vitro gastro-intestinal digestion.

Determination of triazine herbicides in environmental samples

The extraction and subsequent chromatographic analysis of the triazine herbicides from environmental samples is reviewed. Particular emphasis is focused on the extraction of the herbicides from aqueous samples (e.g. natural waters). For completeness, however, an indication of the methods used for extraction from solids (e.g. soils) is also included. The range of chromatographic separation techniques involved in the separation and subsequent detection are described. Advantages and drawbacks of both the extraction and chromatographic analysis are discussed. The characteristics of the extraction methodology and chromatographic techniques involved for the determination of the triazine herbicides are summarised and future developments outlined.

Supercritical fluid extraction of analytes from environmental samples. A review

Supercritical fluid extraction (SFE) has become a prominent sample preparation technique in recent years owing to its reported efficiency and time-saving extraction capabilities. This is particularly so in the field of environmental analysis, where a large amount of SFE research has been undertaken. This paper describes the major areas of environmental SFE research being currently investigated with emphasis on the type of matrix being considered. Typical analytes reported include pesticides, polychlorinated biphenyls, dioxins and polycyclic aromatic hydrocarbons.

Supercritical fluid extraction of Chinese herbal medicines: investigation of extraction kinetics

The extraction kinetics, using supercritical carbon dioxide, of two Chinese herbal medicines, deoxyschisandrin and paeonol from Schisandra chinensis and Paeonia suffruticosa Andr., respectively have been studied. Experimental results have been assessed using the hot-ball approach and by a simple first-order kinetic approach. The extraction of analytes from Chinese herbal medicines was determined to be controlled by the solubility of each analyte in the supercritical carbon dioxide. Extrapolated and experimental extraction yields of the analytes from their respective matrices were compared.

Bioavailability, bioaccessibility and mobility of environmental contaminants

This book covers all aspects of bioavailability, as related to environmental contaminants. After a discussion of the definition of bioavailability and its context, focus is placed on the role of risk assessment and bioavailability. Methods of analysis are then discussed including a range of atomic spectroscopic and electrochemical techniques for metal analysis and chromatographic approaches for persistent organic pollutants (POPs). The occurrence, properties and eco-toxicity of POPs and metals in the soil/sediment environment are discussed. Particular emphasis is placed on the uptake of POPs and metals by plants (phytoextraction). Examples of POPs and metals in the environment are reviewed. Methods to assess the bioavailability of POPs and metals in the environment are discussed. The particular approaches considered are: non-exhaustive extraction techniques; single extraction techniques; sequential extraction techniques; use of cyclodextrin and surfactants; in-vitro gastrointestinal methods including physiological-based extraction test; the use of bioasssays including earthworms. Finally, selected case studies highlight the importance of determining the bioavailability of POPs and metals.