Barry J. Coles

Heavy metal distribution in sediment profiles of the Pearl River estuary, South China

The Pearl River estuary is created by the inflow of freshwater from the largest river system that drains into the South China Sea. In recent years, massive economic growth and development in the region has led to excessive release of waste into the environment. The accumulation of contaminants in sediments is likely to pose serious environmental problems in surrounding areas. The study of sediment profiles can provide much information on the metal contamination history and long term potential environmental impacts. In this project, 21 core samples (up to 3.65 m deep) were collected in the Pearl River estuary. About 15 subsamples from each core were analysed for moisture content, total organic matter (L.O.I.), particle size and heavy metal and major element concentrations. The results show that Pb and Zn contents are elevated in the sediments at most of the sampling sites. Compared with historical monitoring results, the sediment metal contents have increased over the last 20 a, particularly for Pb. The west side of the Pearl River estuary tends to be more contaminated than the east side due to the contaminants inputs from the major tributaries and different sedimentation conditions. There are close associations between Fe, Co, Ni and Cu concentrations in the sediments. Zinc and Pb contents in the sediment profiles reflect a combination of the natural geochemical background, anthropogenic influences and the mixing effects within the estuary. The distribution of Pb in the sediments shows strong influences of atmospheric inputs, probably from the coal burning activities in the region.

Sequential extraction of soils for multielement analysis by ICP-AES

Realistic environmental interpretation of soil contamination depends on an understanding of how metals are bound to the various phases in the soil. A five-step sequential chemical extraction scheme, originally designed for sediment analysis by flame atomic adsorption spectroscopy (FAAS), has been developed for the multielement analysis of soils by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Each of the chemical fractions is operationally defined as follows: (1) exchangeable; (2) bound to carbonates or specifically adsorbed; (3) bound to FeMn-oxides; (4) bound to organic matter and sulphides; and (5) residual. The number of elements determined by ICP-AES has been extended to fifteen (Be, Ca, Co, Cr, Cu, Fe, K, Li, Mn, Ni, P, Pb, Ti, V, Zn), which include most of the major elements, thereby increasing the potential of the sequential extraction method by enabling broader studies of geochemical associations in soils. The precision was estimated to be ∼ 5% (2σ) for each extraction step. The overall recovery rates of international reference materials were between 85 and 110% for most elements, with an average of 92%. There is good agreement between the results for the international reference material (USGS MAG-1) in each extraction step and published values. A wide range of soil reference materials, including SO-1-SO-4 and BCR141-BCR143, were also analysed for future comparison. The application of the method to soils contaminated by past mining and smelting activities showed distinctive partitioning patterns of heavy metals from the two sources. The multielement measurements gave useful information to assist in the interpretation of the possible geochemical forms and sources of the trace elements in soils.

An objective assessment of analytical method precision: comparison of ICP-AES and XRF for the analysis of silicate rocks

Abstract The precision of an analytical method has been evaluated objectively by applying the method of Thompson and Howarth (1976) to the analysis in duplicate of 55 igneous rocks covering a range of silicate matrix types and analyte concentrations. Results were analysed 1.0 characterise the change in precision ( s c ) of the analytical method with concentration ( c ) according to the equation s c = s o + kc , where the k parameter represents the limiting high-level precision and s o , the precision at zero concentration, which is related to the method detection limit (MDL). Test materials were analysed using four analytical methods based on two analytical techniques, inductively coupled plasma-atomic emission spectrometry (ICP-AES) and X-ray fluorescence spectrometry (XRF), as operated under routine working conditions in the two participating laboratories. The two XRF methods were major elements on fused glass discs and trace elements on powder pellets, and the two ICP-AES methods were major elements after a fusion decomposition technique and trace elements together with selected major elements, after an acid attack. Statistical evaluation of the data showed that significant changes in precision as a function of concentration (i.e. the k factor) were determined in 34 cases out of 78 analyte-method combinations. In cases where no significant change in precision could be detected, a grand mean precision, representative of the concentration range analysed was calculated. The s o parameter was found to be significantly different from zero in 36 cases out of 72. To allow evaluation of the detection limit performance of all data, a maximum method detection limit (MMDL) was calculated, which was estimated to be on average 1.62 times greater than the MDL derived from significant values of s o In terms of the four methods studied, median high-level precision of the techniques used to determine major elements were found to be 0.23% relative (XRF/glass discs), 0.43% (ICP-AES/fusion decomposition) and 0.70% (ICP-AES/acid attack). Typical precision values in the determination of trace elements by both techniques was 1.5%, providing elemental concentrations extended over a significant range. MMDLs varied from element to element but for XRF/powder pellet data were found to be approximately equivalent to instrumental detection limits (IDLs) calculated from background count rates. However, for trace elements determined by ICP-AES/acid attack, MMDL were found to be on average three times larger than IDLs measured from repeated analysis of an aqueous blank. As a result of an evaluation of these data, it is proposed that appropriate figures of merit to describe the analytical performance of a technique are: (1) median precision in the determination of major elements; and (2) the number of trace elements that can be determined to MDLs of less than one-tenth the crustal abundance of the element. These factors should then be evaluated in conjunction with logistical factors including the rate at which samples can be analysed and the cost per determination. The influence of these factors on applications of the techniques studied in pure and applied geochemistry are discussed.

The composition of hypersaline, iron-rich granitic fluids based on laser-ICP and Synchrotron-XRF microprobe analysis of individual fluid inclusions in topaz, Mole granite, eastern Australia

Abstract High-temperature (>550°C) hypersaline (>50 wt% salts) fluid inclusions, representative of the earliest hydrothermal fluids associated with the Sn-W-Cu-Pb-Zn-mineralised Mole granite of eastern Australia, are well developed in topaz from the Fielders Hill locality. Methods based on Inductively Coupled Plasma Emission Spectroscopy following laser ablation and on Synchrotron X-Ray Fluorescence microanalysis are described and applied to the semiquantitative point analysis of these inclusions. Crushleach analysis provides further information as well as highlighting the importance of point methods when several generations of inclusions are present. The laser-ICP results confirm the dominance of Fe, K, and Na in these early high-temperature fluids. The mean Fe:K:Na atomic ratios (0.95:0.79:1.00) are entirely in agreement with published experimental data on the composition of chloride brines in equilibrium with synthetic granite at magmatic temperatures and support the view that these fluids are direct products from a cooling granite magma. A number of trace and minor elements have also been detected in the inclusions. These include Ca, Mg, Li, B, Be, Ba, Sr, and several of the ore metals. Order of magnitude estimates of the ore metal contents of these fluids, based on combined XRF-microprobe and laser-ICP analysis, are in the percent range for Fe, Mn, and Zn, in the range from several hundred to several thousand ppm in the case of Sn, Cu, and Pb, and less than 600 ppm for Mo and W. These results have important implications for ore genesis in granitic environments and point to the very high ore-carrying potential of high-temperature, hypersaline, chloride-rich brines exsolved from cooling granite magmas.

Chemical partitioning of the new National Institute of Standards and Technology standard reference materials (SRM 2709–2711) by sequential extraction using inductively coupled plasma atomic emission spectrometry

Three new NIST standard reference materials (2709–2711) have been analysed by a widely-used sequential chemical extraction method to provide analyte levels that are particularly useful for the characterization of contaminated soils. Each chemical fraction is operationally defined as follows: (i) exchangeable; (ii) bound to carbonates or specifically adsorbed; (iii) bound to Fe–Mn oxides; (iv) bound to organic matter and sulfides; and (v) residual. The extraction solutions resulting from the five steps have been analysed for 15 elements (Al, Ca, Cd, Co, Cu, Fe, K, Mn, Ni, P, Pb, Sr, Ti, V, and Zn) using ICP-AES. The over-all recovery rates (the sum concentrations from the five steps/the certified total concentrations) were observed to lie between 90 and 105% for most of the elements. The precision was estimated to be approximately 5%(2s) for most extraction steps. The high concentrations and proportions of trace elements in the exchangeable fraction (step 1) in NIST 2710 suggest that this reference material can be especially appropriate for studies of mobility and bioavailability of heavy metals in contaminated soils. Using sequential extraction methods, the elemental concentrations in these reference materials determined by ICP-AES for some major elements (Al, Ca, Fe, K, Mn, P and Ti) help to indicate the mineralogical compositions actually dissolved in each step.

Measurement of zinc stable isotope ratios in biogeochemical matrices by double-spike MC-ICPMS and determination of the isotope ratio pool available for plants from soil

AbstractAnalysis of naturally occurring isotopic variations is a promising tool for investigating Zn transport and cycling in geological and biological settings. Here, we present the recently installed double-spike (DS) technique at the MAGIC laboratories at Imperial College London. The procedure improves on previous published DS methods in terms of ease of measurement and precisions obtained. The analytical method involves addition of a 64Zn–67Zn double-spike to the samples prior to digestion, separation of Zn from the sample matrix by ion exchange chromatography, and isotopic analysis by multiple-collector inductively coupled plasma mass spectrometry. The accuracy and reproducibility of the method were validated by analyses of several in-house and international elemental reference materials. Multiple analyses of pure Zn standard solutions consistently yielded a reproducibility of about ±0.05‰ (2 SD) for δ66Zn, and comparable precisions were obtained for analyses of geological and biological materials. Highly fractionated Zn standards analyzed by DS and standard sample bracketing yield slightly varying results, which probably originate from repetitive fractionation events during manufacture of the standards. However, the δ66Zn values (all reported relative to JMC Lyon Zn) for two less fractionated in-house Zn standard solutions, Imperial Zn (0.10 ± 0.08‰: 2 SD) and London Zn (0.08 ± 0.04‰), are within uncertainties to data reported with different mass spectrometric techniques and instruments. Two standard reference materials, blend ore BCR 027 and ryegrass BCR 281, were also measured, and the δ66Zn were found to be 0.25 ± 0.06‰ (2 SD) and 0.40 ± 0.09‰, respectively. Taken together, these standard measurements ascertain that the double-spike methodology is suitable for accurate and precise Zn isotope analyses of a wide range of natural samples. The newly installed technique was consequently applied to soil samples and soil leachates to investigate the isotopic signature of plant available Zn. We find that the isotopic composition is heavier than the residual, indicating the presence of loosely bound Zn deposited by atmospheric pollution, which is readily available to plants. FigureZinc isotope ratio pools of bulk soil and the associated acid leach (estimated plant available pool) as measured by double-spike MC-ICPMS. δxZnLyon-JMC=(Rsample/RJMC-Lyon -1)x103, where Rsample and RJMC-Lyon denote the xZn/64Zn isotope ratio of the sample and standard (JMC-Lyon), respectively, and where x denotes either 66 or 68.

A simple combined sample–standard bracketing and inter-element correction procedure for accurate mass bias correction and precise Zn and Cu isotope ratio measurements

The modified sample–standard bracketing method (m-SSB) combines a sample–standard bracketing and an inter-element correction procedure to account for instrumental mass fractionation during multi-collector ICP-MS measurements. Precisions for Cu and Zn isotopes in plant and experimental granite leachate samples are in line with those obtained using other mass bias correction techniques. In addition, the inherent temporal drift of mass bias during the analytical session and the empirical linear relationship between dopant and analyte are used to apply independent correction schemes that rigorously check the accuracy of mass bias correction using m-SSB. Consequently, a very robust isotope data set is obtained. We further suggest the use of a matrix-element spike in inter-element doped standards to increase the mass bias variability. This improves the quality of the empirical relationship between dopant and analyte and enables cross-checking of the m-SSB method when instrumental mass bias is stable.

A new separation procedure for Cu prior to stable isotope analysis by MC-ICP-MS

A novel ion exchange chromatography was developed for the separation of Cu from biological samples prior to stable isotope analyses. In contrast to previous methods, the new technique makes use of the different distribution coefficients of Cu(I) and Cu(II) to anion exchange resin and this helps to significantly improve the purity of the Cu separates obtained from biological samples, whilst maintaining crucial quantitative yields. Careful method validation confirmed that the procedure yields sufficiently pure Cu fractions after a single pass through the anion exchange columns, with a recovery of 100 ± 2%. Subsequent isotopic analyses of the Cu by multi-collector inductively coupled plasma mass spectrometry, using admixed Ni for mass bias correction, produced accurate Cu stable isotope data with a reproducibility of ±0.04‰ for pure standard solutions and of ±0.15‰ for samples of biological origin.

The effect of crude oil on arsenate adsorption on goethite

This study reports the adsorption of arsenate, As(V), on goethite (α-FeO(OH)) and oil-coated goethite at experimental conditions chosen to mimic settings of wastewater from oil fields being released into marine and freshwater bodies. Similarities are evident between the As(V)-goethite and As(V)-oil-goethite systems: i) Adsorption is fast and saturation is achieved within 180 min, ii) Reaction rates approximate to a pseudo second order rate expression and range between 6.5 and 52.3 × 10(-4)g/μmol/min, iii) Adsorption mechanisms are best described with a Langmuir model, and iv) Adsorption capacity rises with decreasing pH reflecting the increase of positive charges on the goethite surface. A difference is discernable in that the adsorption of As(V) is reduced significantly when the goethite is coated with oil. The similar experimental macroscopic observations for both systems, i.e., Langmuir model fits, reaction rates, and the effect of pH and ionic strength (I), suggest that the oil reduces the effective and/or reactive surface area. The zeta potential (ζ) indicates that the oil coating also changes the surface charge of the goethite, shifting the pH point of zero charge from 9.8 to about 3, thus contributing to the reduced As(V) adsorption. FTIR spectra show that As(V) interacts with the carbonyl functional groups of the oil. Our results suggest that oil-covered goethite significantly reduces the adsorption of As(V) and this points to a potentially significant indirect effect of oil on the cycling of As(V) and other oxyanions in oil polluted waters.

Tracing anthropogenic thallium in soil using stable isotope compositions

Thallium stable isotope data are used in this study, for the first time, to apportion Tl contamination in soils. In the late 1970s, a cement plant near Lengerich, Germany, emitted cement kiln dust (CKD) with high Tl contents, due to cocombustion of Tl-enriched pyrite roasting waste. Locally contaminated soil profiles were obtained down to 1 m depth and the samples are in accord with a binary mixing relationship in a diagram of Tl isotope compositions (expressed as ε(205)Tl, the deviation of the (205)Tl/(203)Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 10(4)) versus 1/[Tl]. The inferred mixing endmembers are the geogenic background, as defined by isotopically light soils at depth (ε(205)Tl ≈ -4), and the Tl emissions, which produce Tl-enriched topsoils with ε(205)Tl as high as ±0. The latter interpretation is supported by analyses of the CKD, which is also characterized by ε(205)Tl ≈ ± 0, and the same ε(205)Tl value was found for a pyrite from the deposit that produced the cocombusted pyrite roasting waste. Additional measurements for samples from a locality in China, with outcrops of Tl sulfide mineralization and associated high natural Tl backgrounds, reveal significant isotope fractionation between soils (ε(205)Tl ≈ +0.4) and locally grown green cabbage (ε(205)Tl between -2.5 and -5.4). This demonstrates that biological isotope fractionation cannot explain the isotopically heavy Tl in the Lengerich topsoils and the latter are therefore clearly due to anthropogenic Tl emissions from cement processing. Our results thus establish that isotopic data can reinforce receptor modeling for the toxic trace metal Tl.