Applied Geochemistry (v.27, #5)
Recent progress in environmental geochemistry – Selected papers from the special session honoring Professor Iain Thornton at the SEGH 2010 conference on environmental quality and human health by Xiang-dong Li (937-938).
Environmental geochemistry: 40 years research at Imperial College, London, UK by Iain Thornton (939-953).
► Widespread occurrence of molybdeniferous black shales and likely Cu deficiency in cattle. ► Intake of trace elements and toxic metals through soil ingestion by cattle and sheep. ► Very high levels of Cd and Zn in soils at Shipham: no apparent human health effects. ► Lead intake by dust ingestion in children in old mining areas: need for further blood Pb studies. ► Human exposure to As in SW England: no evidence of adverse health effects.This paper reviews the development of multi-purpose geochemical mapping and the progress of research in applied environmental geochemistry and health at Imperial College over the past 40 years. With funding from the research councils, UK government, EU, industry and NGOs, research has provided the basis for postgraduate training in areas ranging from the applications of geochemistry to plant, agricultural livestock and wildlife nutrition, to evaluating contamination from metalliferous mining and smelting, understanding the chemical nature of the urban environment and relationships between geochemistry and human health and disease. Examples include (1) the influence of Mo in marine black shales on the Cu nutrition of grazing cattle and sheep, (2) the importance of soil ingestion on trace element intake and metabolism and metal exposure in farm livestock, (3) the impacts of soil contamination from historical metalliferous mining and smelting on agriculture and human exposure to metals, including potential health problems from Cd at Shipham and from As in SW England, (4) the growth of urban geochemistry and the importance of Pb in the urban environment, (5) the health impacts due to Hg losses from the informal sector Au mining in Brazil, and (6) health issues relating to F- excess and Se deficiency in China.
Involuntary soil ingestion and geophagia: A source and sink of mineral nutrients and potentially harmful elements to consumers of earth materials by Peter W. Abrahams (954-968).
► A mineral nutrient deficiency can trigger geophagia in a number of animal species. ► Ingested soils can be an important source of some mineral nutrients to humans. ► Excessive absorption of mineral elements following soil ingestion leads to toxicity. ► Accidentally and deliberately ingested soils can cause nutrient deficiencies. ► In vitro methods simulating the impact of ingested soils continue to be developed.Members of the animal kingdom, including humans, can ingest soil either involuntarily or deliberately, the latter practice being known as geophagy or geophagia. This paper briefly documents the often significant quantities of soil that can be consumed, but discusses in detail the importance of this ingestion in supplying mineral nutrients and potentially harmful elements (PHEs) to consumers of earth materials. Whilst geophagia is recognised as a multi-causal behaviour, a prevalent explanation is the ‘nutritional hypothesis’ where the deliberate consumption of soil is attributed to an attempt to regulate a mineral nutrient imbalance such as sodium deficiency. When soils encounter digestive fluids, chemical elements can be solubilised and are potentially available for absorption, sometimes to an extent where toxicity symptoms are evident. In grassland agricultural systems, two main pathways of chemical elements are recognised, the soil–plant–animal flow being complemented by the more direct soil–animal transfer of mineral nutrients and PHEs. In locations where the pasture herbage absorbs very low concentrations of chemical elements relative to the soil content, ingested soil particles can often be observed to be the major source of mineral nutrients/PHEs consumed by livestock. However, further research is required in quantifying the bioaccessibility – defined as the fraction that is soluble in the gastrointestinal tract and is potentially available for absorption – of soil-elements to animals. In this respect, regarding human nutrition, for more than a decade considerable work has been undertaken on the development of in vitro bioaccessibility tests (IVBA) that can rapidly and inexpensively estimate this portion of chemical elements from ingested soils. Work to date has demonstrated that significant amounts of some mineral nutrients, especially iron, can be bioaccessible to humans, as can quantities of PHEs such as lead. Paradoxically, some ingested soils can also result in mineral nutrient deficiency problems in humans and other members of the animal kingdom attributable, for example, to the adsorptive properties of earth materials that can effectively bind chemical elements.
Can in situ geochemical measurements be more fit-for-purpose than those made ex situ? by Michael H. Ramsey; Katy A. Boon (969-976).
► We compare measurements made without removing a sample (in situ) and those made in a lab (ex situ). ► In situ values are more uncertainty, but reduce overall costs and enable reliable interpretation. ► A field study demonstrates this for the measurement of arsenic concentration in soils. ► The best criterion by which to compare measurement methods is the fitness-for-purpose of the measurements.It is argued that the selection of the most appropriate geochemical measurement technique should be based upon the fitness of its measurement results for any specified purpose, regardless of whether the measurement are made in situ or ex situ. Using this approach, in situ measurements made in the field are shown to have some definite advantages over those made ex situ in a laboratory. A case study is used to show that there are cases where in situ measurements can be more fit-for-purpose than their ex situ equivalents. This is primarily because the uncertainty of both types of measurement is usually limited by the uncertainty arising from the field sampling process. That uncertainty is mainly caused by small-scale heterogeneity (in space or time) in the analyte concentration within the environmental material (e.g. soil, water or air).
A risk management interpretation of a series of studies of exposure to lead by John Watt (977-984).
► Presents risk governance framework approach to lead exposure. ► Interprets earlier studies on children’s exposure undertaken at Imperial College. ► Looks at the relationship between the scientific results and policy development. ► Contribution to Special Session at SEGH 2010 to honour the work of Iain Thornton.The relationship between environmental contamination, human exposure and the risk to health is a complex and fascinating area of research. This paper reviews a number of earlier studies, which focussed on contamination by Pb and sought to address this complexity. It places them within an historical context of different stages of the evolution of the field of risk analysis as applied to environmental research. A risk framework permits these scientific studies to be discussed in relation to the complex social and political environment within which the risks associated with Pb-rich particulate matter were managed (and policy was developed). This paper undertakes this analysis through a risk governance framework, which allows the relationship between the various functions required for management of the risks to be evaluated. It shows ways that values (including stakeholder concerns and risk perceptions) need to be included along with the science that underpins risk analysis in order to make sustainable judgements. It is such judgements that lie at the heart of risk management decision making.
Citywide distribution of lead and other element in soils and indoor dusts in Syracuse, NY by A. Hunt; D.L. Johnson; D.A. Griffith; S. Zitoon (985-994).
► Strong soil Pb and dust Pb associations in Syracuse suggests soil is a major source for indoor dust Pb. ► Differences in Pb in soil vs. Pb in dust is suggestive of an indoor source of Pb in some study homes. ► High soil and dust Pb significantly correlated by census tract with lower socioeconomic status.Associations between Pb, Zn, Fe and Mn in soils and indoor dusts in urban Syracuse, NY have been investigated at different levels of spatial aggregation. The concentrations of these elements of interest (EOI) in 3566 soil samples were mapped across the city to investigate variations in concentration potentially associated with specific city locations. Indoor floor dust loadings for the EOI determined at 433 residences were mapped in a similar fashion. Pearson product correlation coefficients at different levels of soil sample aggregation (individual sampling points, block group averages, and census tract (CT) averages), consistently demonstrated a strong correlation between soil Pb and Zn concentrations. Correlations between Pb and both Fe and Mn soil concentrations were also significant. However, the correlation between the Fe and Mn floor dust loadings was much stronger than that for soil, as were the correlations between the Pb and both the Fe and Mn dust loadings. The correlation between the Fe and Zn floor dust loadings was far less significant. Surprisingly, most of the correlations between the paired EOI in the dusts and soils at the individual homes were mostly not statistically significant. The two correlations of any significance, and these were between the Pb in soil and the Pb in the dust, and between Pb in dust and Zn in soil.The strongest association was between Pb concentration in soil and Pb loading in dust which suggests that Pb in soil is a major source for Pb in indoor dust in urban Syracuse. Differences in the concentrations between the Pb in soil and dust implied the possibility of an indoor source of Pb in a number of the homes. Levels of Pb in dust aggregated at the CT level correlated with a range of socioeconomic variables. Census tracts of lower socioeconomic status also had higher average dust loadings in homes. Not only did soil Pb apparently have a significant influence on indoor dust Pb but socioeconomic status was also a significantly associated.
The mobility, bioavailability, and human bioaccessibility of trace metals in urban soils of Hong Kong by Xiao-san Luo; Shen Yu; Xiang-dong Li (995-1004).
► Four operationally defined fractions of trace metals in urban soils were investigated. ► Available metal concentrations were influenced by total contents and soil properties. Anthropogenic Pb in urban soils tended to be environmentally available. ► Site specific data and environmental availabilities produce more realistic estimation for risk.Trace metals in soils may pose risks to both ecosystem and human health, especially in an urban environment. However, only a fraction of the metal content in soil is mobile and/or available for biota uptake and human ingestion. Various environmental availabilities of trace metals (Cu, Pb and Zn) in topsoil from highly urbanized areas of Hong Kong to plants, organisms, and humans, as well as the leaching potential to groundwater were evaluated in the present study. Forty selected soil samples were extracted with 0.11 M acid acetic, 0.01 M calcium chloride, 0.005 M diethylenetriaminepentaacetic acid, and simplified physiologically based extraction tests (PBET) for the operationally defined mobilizable, effectively bioavailable, potentially bioavailable, and human bioaccessible metal fractions, respectively. The metals were generally in the order of Zn > Cu ∼ Pb for both mobility (24%, 7.6%, 6.7%) and effective bioavailability (2.8%, 0.9%, 0.6%), Pb (18%) > Cu (13%) > Zn (7.4%) for potential bioavailability, and Pb (59%) ∼ Cu (58%) > Zn (38%) for human bioaccessibility. Although the variations in the different available concentrations of metals could mostly be explained by total metal concentrations in soil, the regression model predictions were further improved by the incorporation of soil physicochemical properties (pH, OM, EC). The effectively bioavailable Zn and Pb were mostly related to soil pH. Anthropogenic Pb in urban soils tended to be environmentally available as indicated by Pb isotopic composition analysis. Combining various site-specific environmental availabilities might produce a more realistic estimation for the integrated ecological and human health risks of metal contamination in urban soils.
Comparison of trace metal adsorption onto different solid materials and their chemical components in a natural aquatic environment by Xiuyi Hua; Deming Dong; Liang Liu; Ming Gao; Dapeng Liang (1005-1012).
► Surface coatings were very important to the adsorption of trace metals. ► The importance of organics to metal adsorption was observed. ► Mn oxides have greater specific adsorption capability than other components. ► The specific adsorption capability of organics in the solids varied greatly.Solid materials such as suspended particulate matter (SPM), deposited sediment (DS) and natural surface coatings (NSC, composed of biofilms and associated minerals) are important sinks and potential sources of pollutants in natural aquatic environments. Although these materials can exist in the same water body, few studies have been conducted to compare their ability to adsorb trace metals. In this study, the adsorption of Pb, Cu and Cd by these solids, collected from an urban lake, was investigated. In addition, the metal adsorption properties of the main components of these solids, namely Mn and Fe oxides and organics, were also investigated using the method of selective extraction followed by metal adsorption. The solids that co-existed in water showed similarities and differences in their compositions. For each metal, adsorption to the solids occurred in the same order: NSC > SPM > DS. For Pb and Cd, Fe and Mn oxides and organics contributed to the adsorption by NSC and SPM, and the adsorption by DS was dominated by Fe oxides. For Cu, the organics were the main adsorptive phase. The specific adsorption capability of these components decreases in the following order: Mn oxides > Fe oxides > organics. Overall, the results presented herein indicate that different solids and their components played important roles in the adsorption of trace metals.
Modelled and measured arsenic exposure around a power station in Slovakia by T.J. Keegan; M.J. Nieuwenhuijsen; B. Pesch; U. Ranft; I. Thornton (1013-1019).
► This paper assesses arsenic excretion and absorption as modelled by a USEPA-derived exposure model. ► Modelled urinary arsenic was compared to measured urinary arsenic. ► Median modelled arsenic was lower than median measured arsenic excretion by a factor of 3.5. ► Modelled arsenic absorption and excretion were poor predictors of measured exposure.In 1999–2000 an epidemiological study was carried out to investigate arsenic exposure and risk of non-melanoma skin cancer in the population around a power station in Slovakia. As part of the exposure assessment for that study, markers of physiological exposure to arsenic (urinary arsenic and nail arsenic) and measures of environmental arsenic were taken. Residential history and arsenic emissions were combined in a measure used to classify the study population’s exposure. Here, we take a model designed to estimate the daily arsenic absorption and urinary arsenic excretion developed by the US EPA and compare its output to the values for measured urinary arsenic, measured environmental arsenic and modelled food arsenic used in the previous study. We found that the US EPA model underestimated arsenic exposure in this population. Potential misclassification compared to the exposure used previously was also quantified, with poor agreement between a measured biomarker of current arsenic exposure and modelled estimates of arsenic uptake and excretion.
Arsenic contamination in agricultural soils surrounding mining sites in relation to geology and mineralization types by Ji Cheol Kwon; Jin-Soo Lee; Myung Chae Jung (1020-1026).
► We examined arsenic in soils controlled by geology and mineralization types of mines. ► Weathering process of sulfide minerals influenced arsenic in soils. ► Soils derived by hydrothermal mineralization rocks contain high levels of arsenic. ► Soils underlain by highly altered rocks with igneous and metamorphic processes contain high levels of arsenic.A national-scale survey of the environment in and around mines was conducted to evaluate the status of total As contamination in agricultural soils surrounding numerous abandoned metal mines in Korea. This survey aimed to compare As concentrations in soils in relation to geology and mineralization types of mines. A total of 16,386 surface soil (0–15 cm in depth) samples were taken from agricultural lands near 343 abandoned mines (within 2 km of each mine). These samples were decomposed by aqua regia and analyzed for As by AAS with a hydride-generation (HG) device. To compare As levels in soils meaningfully with geology and mineralization types, three sub-classification criteria were adapted: (1) five mineralization types, (2) four valuable ore mineral types, and (3) four parent rock types. The average concentration of As in all the soils was 11.6 mg kg−1 with a range of 0.01–4230 mg kg−1. Based on the mineralization types, average As concentrations (mg kg−1) in the soils decreased in the order of pegmatite (18.2) > hydrothermal replacement (14.5) > sedimentary deposits (12.4) > hydrothermal vein (10.7) > skarn (4.08). In terms of the valuable ore mineral types, the concentrations decreased in the order of Sn, W, Mo, Fe and Mn mines > Au, Ag, and base metal mines > Au and Ag mines ≈ base metal mines. For parent rock types, soils from metamorphic rocks and heterogeneous rocks exhibited enhanced As levels related to both igneous and sedimentary rocks. Therefore, it can be concluded that soils from highly altered rocks subject to metamorphic and igneous activities contained relatively high concentrations of As in the surface environment.
Optimization of As(V) adsorption on Fe-RH-MCM-41-immobilized GAC using Box–Behnken Design: Effects of pH, loadings, and initial concentrations by Kitirote Wantala; Eakkachai Khongkasem; Nuthakarn Khlongkarnpanich; Suthipong Sthiannopkao; Kyoung-Woong Kim (1027-1034).
► Powdered Fe-RH-MCM-41 was loaded by adhesive on GAC, an innovation increasing area. ► Fe-RH-MCM-41 immobilized on GAC removed more arsenate than GAC alone. ► Granular size of Fe-RH-MCM-41-immobilized GAC suitable for water column adsorption. ► Significant effects of pH, As(V) concentration, and initial loading were found. ► An optimal model was made using these variables with RSM based on BBD, a first.This work focused on the removal from water of arsenate in the 100 to 500 μg/L range using Fe-RH-MCM-41 immobilized on GAC by a colloidal impregnation method. A Response Surface Method (RSM) based on the Box–Behnken Design (BBD) was used to evaluate the effects of pH, adsorbent loading, and initial arsenate concentrations. The thermal stability of Fe-RH-MCM-41/GAC was greater than 460 °C because Fe-RH-MCM-41 and epoxy resin covered the GAC, preventing GAC weight loss. The rate and capacity for arsenate adsorption on Fe-RH-MCM-41/GAC were higher than for GAC. The effects of pH, adsorbent loading, and initial arsenate concentration showed significant effects on efficiency, in terms of percent arsenate removal. Significant interaction occurred as positive effects between arsenate and arsenate concentrations, and pH and arsenate concentrations, and as negative effects between pH and pH, adsorbent loading and adsorbent loading, and adsorbent loading and arsenate concentrations.