Assessing the link between the Geochemistry of Soils and the Bioaccessibility of Arsenic, Chromium and Lead in the Urban Environment

One of the principal pathways for potentially harmful elements (PHE) in soil to enter the human body is through ingestion. The amount of PHE which enters the systemic circulation is governed by the amount of PHE released in the Gastrointestinal Tract, this is the bioaccessible fraction. A geochemical survey of the soils of Northampton, located on ironstone soils with naturally elevated arsenic concentrations, carried out by the BGS G-BASE project showed that 45% of the 275 soils sampled contained total arsenic concentrations exceeding the Environment Agency soil guideline value (SGV) of 32 mg kg-1. A newly validated in-vitro bioaccessibility test was used to measure the bioaccessibility of arsenic and other PHEs on a representative subset of 50 of the soils showed a maximum bioaccessibility value of 10 mg kg-1 arsenic. A systematic study of the relationship between the bioaccessible fraction of arsenic and other PHE with the geochemical make up of the soil, the solid phase distribution of PHE as measured by sequential extraction and the physical properties of the soil( as measured using NIR spectroscopy) showed that the bioaccessibility of different PHEs were governed by the source of the PHE (i.e. anthropogenic or geogenic) and their relative solid phase distribution between iron oxide phases and carbonates. Statistical modelling of the bioaccessible fraction using geochemistry and NIR data also helped to identify the factors controlling the mobility of PHE’s and provided a potential means for predicting bioaccessibility

Development of an in-situ pressurised fluid extraction method for the extraction of PAHs prior to GC-MS analysis

Polycyclic aromatic hydrocarbons (PAHs) are derived from a number of sources including anthropogenic (i.e. industrial processes and combustion of fossil fuels) or natural (i.e. forest fires, volcanic activity and geological sources). The 16 PAH priority pollutants are known for their carcinogenic effect and mutagenic characteristics. Previous studies describe pressurised fluid extraction (PFE) as an effective way to extract components from soils, compared to other extraction methods, such as microwave, ultrasonic and Soxhlet extraction.1 In this study column chromatography has been evaluated for soil clean-up following PFE. The influence of two different absorbents (florisil and alumina) on extract clean-up have been investigated with respect to PAH recovery. This approach has been compared with an in-situ PFE procedure.2 The aim of this work is to establish a robust and effective procedure for the recovery of PAHs from contaminated soil prior to analysis by gas chromatography - mass spectrometry (GC-MS)

Effect of weathering product assemblages on Pb bioaccessibility in mine waste: implications for risk management

General assessments of orebody types and associated mine wastes with regards to their environmental signature and human health hazards are needed to help managing present and historical mine waste facilities. Bioaccessibility tests and mineralogical analysis were carried out on mine waste from a systematic sampling of mine sites from the Central Wales orefield, UK. The bioaccessible Pb widely ranged from 270 to 20300 mg/kg (mean 7250 mg/kg; median 4890 mg/kg) and the bioaccessible fraction from 4.53 % to >100 % (mean 33.2 %; median 32.2 %), with significant (p=0.001) differences among the mine sites. This implies sensitivity of bioaccessibility to site-specific conditions and suggests caution in the use of models to assess human health impacts generalised on the basis of the mineral deposit type. Mineralogical similarities of the oxidation products of primary galena provided a better control over the observed Pb bioaccessibility range. The higher Pb bioaccessibility (%) was related to samples containing cerussite, irrespective of the presence of other Pb minerals in the mineral assemblage; lower Pb bioaccessibility resulted where anglesite was the main Pb mineral phase and cerussite was absent. A solubility diagram for the various Pb minerals in the waste was derived using PHREEQC model and the experimental Pb concentration measured in the simulated gastric solution compared with the equilibrium modelling results. For samples containing cerussite, the model well predicted the soluble Pb concentrations measured in the experimental simulated gastric solution, indicative of the carbonate mineral phase control on the Pb in solution for these samples and little kinetic control on the dissolution of cerussite. On the contrary, most mine waste samples containing dominant anglesite and or plumbojarosite (no cerussite) had lower solution Pb values, falling at or below the anglesite and plumbojarosite solubility equilibrium concentrations, implying kinetic or textural factors hindering the dissolution

Identification of the geochemical signatures of diffuse pollution in the Tellus Border soil data set, using source apportionment

The statistical process of ‘self-modelling mixture resolution’ has been used to identify chemical signatures of diffuse pollution in the topsoil samples of the Tellus Border geochemical survey, Ireland. Seventeen geochemical components were identified, of which nine were derived from underlying geology (high concentrations of trace metals suggest two of these are from mineralised sources), four were from secondary processes (iron oxides and carbonates) and four were associated with peat. One of the peat bog components has high concentrations of certain anthropogenic elements, probably from aerial deposition of anthropogenic particulates derived from modern industrialisation. The spatial extent of the diffuse pollution from aerial deposition in peat bogs has been mapped over the whole region

Linking selective chemical extraction of iron oxyhydroxides to arsenic bioaccessibility in soil

The relationship between As bioaccessibility using the physiologically based extraction test (PBET) and As extracted by hydroxylamine hydrochloride (HH), targeting the dissolution of amorphous Fe oxyhydroxides, is established in soils from the British Geological Survey Geochemical Baseline Survey of SW England, UK, to represent low As background and high As mineralised/mined soils. The HH-extracted As was of the same order of magnitude as the As extracted in the bioaccessibility test and proved to be a better estimate of bioaccessible As than total As (bioaccessible As − total As: r = 0.955; bioaccessible As – HH-extracted As: r = 0.974; p-values = 0.000). These results provide a means of estimating soil As bioaccessibility on the basis of the HH extraction. Further selective extraction data, using hydrochloride acid that seeks to dissolve both amorphous and crystalline Fe oxyhydroxides, indicates a decrease in the As bioaccessible fraction with the increase of the soil Fe oxyhydroxide crystallinit

Stream sediment background concentrations in mineralised catchments in Northern Ireland: assessment of ‘pressures’ on water bodies in fulfilment of Water Framework Directive objectives

An approach for deriving sediment background metal and metalloid element concentrations using systematically collected geochemical survey data is demonstrated in the mineralised area associated with the Ordovician-Silurian rocks in counties Down and Armagh in Northern Ireland. Operationally-defined background ranges can be used for improving the assessment of the environmental pressures posed by historical mining on impacted catchments and establishing feasible catchment restoration goals. Deriving pre-mining baselines provides essential information for any proposed mineral development project, with direct benefit to the mineral sector and industry

Measuring the solid-phase fractionation of lead in urban and rural soils using a combination of geochemical survey data and chemical extractions

The study used 276 urban soils and 447 rural soils collected from in and around the UK town of Northampton and focussed on the fractionation of Pb. The Pb fractionation obtained from total element data was compared to the fractionation of Pb in a subset of 10 urban soils obtained using a sequential extraction method. The fractionation of the Pb from the total element data and from the sequential extractions was estimated using a self-modelling mixture resolution statistical model. The bioaccessibility of Pb in a subset of 50 of the urban soils, as measured using the unified BARGE method, was shown to be quantitatively linked with Pb fractionation from both the total element and the sequential extraction data. Three intrinsic soil components from the regional total element data model and one physico-chemical component from the sequential extraction data model were identified as the sources of bioaccessible Pb. The source of bioaccessible Pb in both rural and urban soils was tentatively identified as a fine-grained pyromorphite mineral

In vitro investigations of human bioaccessibility from reference materials using simulated lung fluids

An investigation for assessing pulmonary bioaccessibility of metals from reference materials is presented using simulated lung fluids. The objective of this paper was to contribute to an enhanced understanding of airborne particulate matter and its toxic potential following inhalation. A large set of metallic elements (Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr, and Zn) was investigated using three lung fluids (phosphate-buffered saline, Gamble’s solution and artificial lysosomal fluid) on three standard reference materials representing different types of particle sources. Composition of the leaching solution and four solid-to-liquid (S/L) ratios were tested. The results showed that bioaccessibility was speciation- (i.e., distribution) and element-dependent, with percentages varying from 0.04% for Pb to 86.0% for Cd. The higher extraction of metallic elements was obtained with the artificial lysosomal fluid, in which a relative stability of bioaccessibility was observed in a large range of S/L ratios from 1/1000 to 1/10,000. For further investigations, it is suggested that this method be used to assess lung bioaccessibility of metals from smelter-impacted dust

Modelling and Mapping Total and Bioaccessible Arsenic and Lead in Stoke-on-Trent and Their Relationships with Industry

This study was based on a geochemical soil survey of Stoke-on-Trent in the UK of 747 surface soil samples analysed for 53 elements. A subset of 50 of these soil samples were analysed for their bioaccessible As and Pb content using the Unified Barge Method. Random Forest modelling, using the total element data as predictor variables, was used to predict bioaccessible As and Pb for all 747 samples. Random Forest modelling, using inverse distance weighed predictors and bedrock and superficial geology, was also used to map both total and bioaccessible As and Pb on a 400 × 400 spatial prediction grid with a 50 m resolution. The predicted bioaccessible As ranged from ca. 1 to 8 mg/kg and the total As ca. 8 to 45 mg/kg. The bioaccessible Pb and the total Pb both covered the range ca. 16–1200 mg/kg, with the highest values for both forms of Pb showing similar spatial distributions. Predictor variable importance and information on past industry suggest that the source of both of these elements is driven by anthropogenic cause