Michael H. Ramsey

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.

Objective evaluation of precision requirements for geochemical analysis using robust analysis of variance

Abstract The pursuit of high precision in geochemical analysis has no inherent limit. An appropriate analytical precision requirement can be set, however, by comparing the “analytical variance” with the other sources of variance in geochemical data. The purpose of a geochemical survey is to give a description of the geochemical variation of a region. Numerically this can be expressed in terms of the natural “geochemical variance” of the area. The information content is diminished by the two processes of measurement: the act of taking a sample adds a random error with “sampling variance”; and the act of chemical analysis adds another random error with “analytical variance”. In order to optimise the analytical variance for cost-effectiveness, rather than simply to minimize it, all three variances must be estimated. This requires that traditional analytical quality control be extended to include the total measurement process, rather than only the “analytical” portion. Such a Sampling and Analytical Quality Control Scheme (SAX) requires some duplication of field samples and the duplicate analysis of each field duplicate. A robust Analysis of Variance (ANOVA) is then used to separate the three components of the total variance. Robust statistics can accommodate outlying values that have undue influence on classical ANOVA. For a clear description of the natural geochemical variance, the combined sampling and analytical variances for the data should comprise not more than, say, 20% of the total variance. If this figure is exceeded then these extraneous variances should be reduced. The decision as to whether this reduction requires improved sampling or improved analytical precision can also be based on the ANOVA results. As a general rule, we suggest that the analytical variance should comprise not more than 4% of the total variance. If, on the other hand, the analytical variance is less than 1% of the total variance, then needless expense has probably been incurred and the natural geochemical variation can be adequately described with less precise methods of analysis. Similar arguments can be applied to sampling variance. An application of SAX with robust ANOVA to a stream sediment survey for Cu, Pb and Zn demonstrates the advantages of the technique. For the analytical geochemist it provides a realistic target for analytical precision. For the field geochemist it provides a quantitative tool for the design of geochemical surveys. It facilitates the optimisation of both sampling and chemical analysis for a particular region to reveal geochemical patterns at minimal expense.

Total and exchangeable concentrations of heavy metals in soils near Bytom, an area of Pb/Zn mining and smelting in Upper Silesia, Poland

Abstract High concentrations of several heavy metals were suspected in soils in an area of some contemporary and extensive historical mining and smelting of Pb and Zn near the town of Bytom. In order to investigate the spatial distribution of heavy metals, 152 soil samples were taken at high sampling density in an area of 14 km2 on a regular grid as well as along an 11 km transect. The samples were analysed for total Pb, Zn and Cd content by ICP-AES; a selection of samples were also analysed for total As content. Significant levels of contamination were found. Median topsoil concentrations (0–10 cm) for Pb, Cd, Zn and As were 430 μg g−1, 13 μg g−1, 1245 μg g−1 and 35 μg g−1, respectively. The detected levels of Pb, Zn and Cd were mostly in reasonable agreement with findings from a previous low-density study, but As concentrations were up to 6 times higher than had previously been reported for the area. Additional zones of particularly high concentrations could be identified for all 4 elements by this higher-density survey. Contaminant concentrations were generally found to decrease substantially with increasing depth, on average by a factor of 3.5 for Cd, 3.0 for Zn and 2.6 for Pb. However, significant subsoil contamination (40–50 cm) was also detected, in particular for Zn, Pb and As, which appeared to be enriched at depth in certain locations. To assess the potential availability of the metals to plants, the exchangeable fraction (0.5 M MgCl2) was estimated for Pb, Zn and Cd for 84 samples. Levels were strongly influenced by soil pH and were generally low for Pb (less than 1% of total, max 15.6%), moderate for Zn (less than 10% of total, max 32.4%), and high for Cd (mean 35% of total, max 59.8%). For Zn and Pb, there seemed to be a threshold pH value of about 6, below which a significant increase in the exchangeable fraction was observed. No such threshold value appeared to exist for Cd, which was found to be relatively labile even in slightly alkaline soils (mean of 27.6% exchangeable Cd in pH range 7–8). The detected levels of total metal contamination exceed various national and international thresholds, indicating the need for further investigation and an assessment of the suitability of the land for agricultural use, particularly in view of the high levels of exchangeable Cd.The pattern of spatial variation of the metals in the topsoil indicates that a variety of sources might be responsible for the contamination, historical mining and smelting probably being the most important.

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.

Sampling as a source of measurement uncertainty: techniques for quantification and comparison with analytical sources

A tutorial review is presented of current methods for the estimation of measurement uncertainty due to primary sampling. Current terminology used in the description of uncertainty and analytical data quality is reviewed and explained. One basic method for the estimation of uncertainty in sampling is described in detail with a worked example of its application to a test dataset. This method employs the taking of a proportion of samples in duplicate, with the further duplication of chemical analysis on these samples. Robust analysis of variance (ANOVA) is applied to estimate the total measurement uncertainty and also to quantify the contributions to that uncertainty which arise from the processes of primary sampling and chemical analysis. The ANOVA program and test data are available electronically to enable application of the methodology. The assumptions and limitations of this basic method are discussed, including its inability to estimate sampling bias. More sophisticated methods are discussed that include the estimation of the contributions to uncertainty from systematic errors in both sampling and analysis. Other approaches to the estimation of uncertainty from sampling, from both sampling theory and geostatistics are compared with these methods. The comparison is made between sampling and chemical analysis as the two sources of uncertainty, relative to each other, and relative to the overall variance of the measurements. Fitness-for-purpose criteria are given and discussed for the ideal maximum and minimum values of the proportion of the measurement variance to the total variance, and the relative contributions of the sampling and analytical variances.

Heavy metal contamination of soils around a PbZn smelter in Bukowno, Poland

Abstract An exploratory study of the area surrounding a Pb Zn smelting and mining centre in Bukowno, Poland, detected significant contamination by heavy metals. The median concentrations for field and garden topsoils (0–10 cm depth) were: Pb 545 μg/g, Zn 2175 μg/g, Cd 14.8 μg/g and As 81 μg/g. Close to the smelter area, topsoil concentrations of Pb, Zn and Cd exceeded Dutch “C” and Polish “V” action levels indicating that remediation should be considered. In the nearby village, concentrations of Pb, Zn and Cd in garden topsoils generally exceeded Dutch “B” cutoff levels, indicating a need for further investigation. Significant contamination of subsoils (40–50 cm depth) was also found. Median subsoil concentrations of Pb, Zn and Cd were 339 μg/g, 1860 μg/g and 8.9 μg/g, respectively. These high subsoil concentrations may have resulted from mechanical mixing of soils during previous remediation attempts. Visual inspection of the site suggested that there were three main sources of heavy metals in the soils. Geochemical mapping of the contamination confirmed that the primary source of pollution has been the smelting operations, however, it was not possible to establish the relative importance of airborne dispersion of material from uncovered waste tips versus flue gas particulate dispersion. Mine waste surrounding small-scale historical mine shafts appear to be a second source of contamination, with localised affected areas of less than 1 hectare. Preliminary sequential extraction investigation has been applied to investigate differences between two soil samples and two potential source materials. The mineral phases that hold the heavy metals appear to be significantly different in the source materials compared to contaminated soils. This change in speciation of the metal is probably the result of natural weathering processes.

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.

Rapid and accurate analyses of silicon and phosphorus in plants using a portable X-ray fluorescence spectrometer

The elemental analysis of plant material is a frequently employed tool across biological disciplines, yet accurate, convenient and economical methods for the determination of some important elements are currently lacking. For instance, digestion-based techniques are often hazardous and time-consuming and, particularly in the case of silicon (Si), can suffer from low accuracy due to incomplete solubilization and potential volatilization, whilst other methods may require large, expensive and specialised equipment. Here, we present a rapid, safe and accurate procedure for the simultaneous, nonconsumptive analysis of Si and phosphorus (P) in as little as 0.1 g dried and ground plant material using a portable X-ray fluorescence spectrometer (P-XRF). We used certified reference materials from different plant species to test the analytical performance of P-XRF and show that the analysis suffers from very little bias and that the repeatability precision of the measurements is as good as or better than that of other methods. Using this technique we were able to process and analyse 200 ground samples a day, so P-XRF could provide a particularly valuable tool for plant biologists requiring the simultaneous nonconsumptive analysis of multiple elements, including those known to be difficult to measure such as Si, in large numbers of samples.

Quality concepts and practices applied to sampling—an exploratory study

There is now a self-consistent and almost complete body of concepts and practices relating to the quality of analytical data. The need for quality in sampling is also well recognized but there has been no comparable development of an over-all approach or, in some aspects, even of a basic methodology. This paper discusses the prospects for a complete approach to quality in sampling. It shows that virtually all of the concepts and practices used in analysis can be adapted, with only a slight change of detail, for application to sampling. Topics considered include the sampling analogues of trueness, bias, accuracy error, precision, uncertainty, traceability, fitness for purpose, reference materials, collaborative trials, proficiency tests and internal quality control.

Matrix effects due to calcium in inductively coupled plasma atomic-emission spectrometry: their nature, source and remedy

Matrix effects due to calcium in inductively coupled plasma atomic-emission spectrometry have been characterised for a representative selection of analyte lines. Operating conditions were typical of those widely used for routine analysis. Calcium is among the most potent elements causing matrix effects and is an important geological matrix element. Most analyte sensitivities were suppressed, by as much as 30% in some instances, but lithium could be supressed or enhanced depending on small changes in the conditions. The effects are strongly related to analyte excitation potentials, and were found to be caused by changes in excitation conditions in the plasma. Several effective methods of obviating the matrix problem are demonstrated and compared.