Normal background concentrations (NBCs) of contaminants in English soils : final project report

The British Geological Survey (BGS) has been commissioned by the Department for Environment, Food and Rural Affairs (Defra) to give guidance on what are normal levels of contaminants in English soils in support of the Part 2A Contaminated Land Statutory Guidance. This has initially been done by studying the distribution of four contaminants – arsenic, lead, benzo[a]pyrene (BaP) and asbestos – in topsoils from England. This work was extended to a further four contaminants (cadmium, copper, nickel and mercury) which enabled methodologies developed to be tested on a larger range of contaminants. The first phase of the Project gathered data sets that were: nationally extensive; systematically collected so a broad range of land uses were represented; and collected and analysed to demonstrably and acceptable levels of quality. Information on the soil contaminant concentrations in urban areas was of particular importance as the normal background is considered to be a combination of both natural and diffuse anthropogenic contributions to the soil. Issues of soil quality are most important in areas where these affect most people, namely, the urban environment. The two principal data sets used in this work are the BGS Geochemical Baseline Survey of the Environment (G-BASE) rural and urban topsoils (37,269 samples) and the English NSI (National Soil Inventory) topsoils (4,864 samples) reanalysed at the BGS laboratories by X-ray fluorescence spectrometry (XRFS) so both data sets were highly compatible. These two data sets provide results for most inorganic element contaminants, though results explored for mercury and BaP are drawn from a variety of different and much less extensive data sets

Variation in soil chemistry related to different classes and eras of urbanisation in the London area

Systematic mapping of the chemical environment of urban areas from around the world has demonstrated the strong impact of urbanisation on topsoil geochemical distributions originally controlled by the underlying parent material (PM). The variance of some elements including As, Ba, Ca, Cr, Cu, Mo, P, Pb, Sb, Se, Sn and Zn in urban domains appears to be impacted by a mixture of geogenic and anthropogenic controls. This study evaluates how soil chemistry has been influenced by different eras of urbanisation within London and other UK urban areas using (a) the pre-1940 Dudley Stamp First Land Utilisation Survey data and (b) the modern urban domain principally defined by the aggregate classes of the 2007 Land Cover Map. In the London area, calcium, and possibly a substantial proportion of Cu, Pb, Sn and Zn enrichment observed in soils impacted by pre-1940 urbanisation relative to soils impacted only by post-1940 urbanisation, may be partly related to the destruction of buildings during the period 1940–1941 rather than from the disposal or aerial dispersion of coal ash from domestic fires. Some Pb, Cu, Sb, Sb, Sn and Zn contamination appears to be caused by road traffic (leaded petrol and brake dust). The relationships between pre- and post-1940 urbanised areas in London also characterise most of 20 other urban centres in England and Wales for which BGS holds soil chemistry data

Soil, wheat, cabbage and drinking water iodine in relation to human iodine status and iodine deficiency disorders in Xinjiang Province, China

Iodine is an essential trace element for humans and animals. A lack in the diet can lead to iodine deficiency disorders (IDD) the most common manifestation being goitre, an enlargement of the thyroid gland in the neck. Infants born to severely Ideficient mothers may suffer cretinism and I-deficiency is the world's most common cause of preventable mental retardation. In many countries this problem has been tackled successfully using medical interventions such as the iodination of table salt. Xinjiang Province in northwest China is a remote desert region where goitre and cretinism have been reported for many years. People in this region do not like the taste of iodised salt and prefer to use local rock-salt with very low concentrations of iodine. As an alternative treatment, previous investigators added potassium-iodate to irrigation waters in an attempt to increase the I-concentrations of crops and animals in the food supply and the I-status of the population. Initial successes were reported but the long-term effectiveness of the method had not been tested. The present study aims to assess environmental controls on iodine uptake into the food chain and in Xinjiang had the opportunity to study three contrasting area

Bioaccessibility and human health risk : chromium in Glasgow

The assessment of risk to human health from contaminated land is based on a comparison of predicted human exposure to a contaminant with a Health Criteria Value (HCV) that represents an exposure below which there is thought to be little or no risk to human health. Most assessment tools, such as the Contaminated Land Exposure Assessment Model (CLEA), use estimates of exposure based on intake (consumption rate) rather than on measures of uptake (the amount of contaminant which enters the bloodstream), thus allowing comparison with HCVs, which are also based on intake apposed to uptake. Soil Guideline Values (SGVs) derived using the CLEA model assume that a soil contaminant will be taken up into the body to the same extent as from the medium of exposure used to derive the oral HCV (e.g. soluble salts of Cr(VI)). This is a conservative assumption as contaminants can be tightly bound to other soil components, thus reducing bioavailability (the fraction of a contaminant that can be absorbed by the body)

Anthropogenic and geogenic impacts on arsenic bioaccessibility in UK topsoils

Predictive linear regression (LR) modelling between bioaccessible arsenic (B-As) and a range of total elemental compositions and soil properties was executed in order to assess the potential for developing a national B-As dataset for the UK. LR indicates that total arsenic (As) is the only highly significant independent variable for estimating B-As in urban areas where it explains 75–92% of the variance. The broad compatibility of the London, Glasgow and Swansea regression models suggests that application of these models to estimate bioaccessible As in UK soils impacted by diffuse anthropogenic urban contamination and non-ferrous metal processing should be relatively accurate. In areas dominated by Jurassic ironstones and associated clays and limestones, total As, P and pH are significant, accounting for 53, 14 and 5%, respectively, of the B-As variance. Models based on total As as the sole predictor in the combined Jurassic and Cretaceous sedimentary ironstones datasets explain about 40% of the B-As variance. The median As bioaccessible fraction (%As-BAF) is 19 to 28% in the anthropogenic contamination impacted urban domains, but much lower (5–9%) in geogenic terrains dominated by ironstones. Results of this study can be used as part of a lines of evidence approach to localised risk assessment but should not be used to replace bioaccessibility testing at individual sites where local conditions may vary considerably from the broad overview presented in this study

Using 206/207Pb isotope ratios to estimate phosphorus sources in historical sediments of a lowland river system

Purpose Engineering and dredging strategies to manage sediment, along with river-scouring, can reveal older sediments. These present a unique opportunity to assess past sources of phosphorus (P) inputs into river sediments. We used the sediment concentrations of P, lead (Pb) and 206/207Pb isotopes to produce ‘first-order’ estimates of the source (diffuse agricultural or sewage treatment) of phosphorus. Materials and methods Sediment cores (n = 30) were collected from the length of the non-tidal River Nene, a lowland river in eastern England. Cores were analysed for sediment elemental concentrations and Pb isotopes. Principal component analysis and linear regression modelling were used to assess the relationships between P, Pb and Pb isotopes. Monte-Carlo simulations and boot-strapping were undertaken to estimate, with 95% confidence intervals, the source of P in these sediments. Results and discussion Analysis of the relationships between PTotal, PbTotal and 206/207Pb isotope ratios suggested that sediments were deposited largely prior to the phasing out of tetra-ethyl Pb (PbBHT) from petrol. Regression models showed positive correlations between PTotal and PbTotal (R2 = 0.85). Principal component analysis suggested a strong sewage treatment signal for Pb and P enrichment. In the rural upper three water bodies, little sewage treatment work (STW)-derived P was found in the sediment, a consequence of limited STW input and greater sediment transport. In the more urbanised water bodies 4–6, ‘first-order estimates’ of STW P suggest that median concentrations were 30–40% of PTotal. Conclusions The strong relationships between Pb and P concentrations in river water provided the opportunity to use 206/207Pb isotope ratios to calculate ‘first-order’ estimates of the proportion of P released from STWs in the historical sediment. Understanding the sources of historical sediment P can be used to assess the success of current sediment management strategies and to base further mitigation measures. Results suggest that whilst much recent sediment P is removed, the legacy sediment remains to contribute P to the water body. Thus, options regarding the practical removal of these sediments and the extent to which this would improve water P status need to be assessed and balanced against options such as further decreasing soil P or STW P stripping

Sources, mobility and bioaccessibility of potentially harmful elements in UK soils

Potentially harmful elements (PHE) occur both naturally from geogenic sources and from anthropogenic derived pollution. Anthropogenic sources can be further categorised into those derived from point sources. A point source is a single identifiable source which is confined to a very small area such as that arising from disposal of waste material or from an industrial plant. Diffuse pollution arises where substances are widely used and dispersed over an area as a result of land use activities, often associated with urban development. Examples of diffuse pollution include atmospheric deposition of contaminants arising from industry, domestic coal fires and traffic exhaust, and disposal of domestic coal ash. The total concentration and the chemical form and hence the mobility of the PHE in a soil is highly dependent on the source

Validation of a gravimetric PM2.5 impactor using particle sizing techniques

Particulate matter sampling was conducted at Ballidon Quarry, Ballidon, Derbyshire. The quarry is owned and managed by Tarmac Trading Ltd. (Tarmac). The monitoring station deployed comprised two DS500X gravimetric samplers fitted with PM2.5 impactors, that were placed side by side in the primary crusher shed during February 2016. Monitoring was conducted over three, seven day periods. Particulate matter from six filters and oversize particulate matter collected from the impactor plates were analysed by BGS on behalf of DustScan using Scanning Transmission Electron Microscopy and Laser Diffraction granulometry. The results of the work show that the DS500X fitted with a PM2.5 size selective impactor is capable of separating particles with a projected area diameter of ≤ 2.5 μm from ambient air, retaining themon filter media for subsequent quantification. The overall median particle size recorded on the filters was 0.46 μm, the mean was 0.74 μm and the 95th percentile was 2.15 μm (n = 6343). A number of observations were made during this study and included in the full report which should be considered when interpreting the results

Equal abundance of odd and even n-alkanes from cycad leaves: can the carbon preference index (CPI) faithfully record terrestrial organic matter input at low latitudes?

Long chain n-alkanes from the leaves of thirteen extant cycad species within the Cycadacaea, Stangeriaceae, Zamiaceae families were measured by gas chromatographymass spectrometry (GC-MS). Cycad n-alkane patterns ranged from nC10-nC37, were unimodal in distribution, maximised at nC27-nC33 and gave average chain length (ACL) values of 23.9 to 31.0. Low carbon preference indices (CPI) in the range of 0.88 to 2.70 were observed which is atypical of lipids from the leaves of terrestrial plants. Analysis of variance between the three families of true cycads showed that there were no significant differences between CPI values. The unusually low CPI values (<1.5) in nine of the thirteen cycad species analysed suggests that caution needs to be exercised in the use of n-alkanes distibutions as a chemical marker of terrestrial plant input in sediments from tropical and sub-tropical regions

Determination of stream sediment background concentrations in mineralised catchments impacted by mining using Tellus data from Northern Ireland : final project report

Background metal(loids) concentrations, intended as concentrations of naturally occurring substances rather than anthropogenic, are more often integrated in the assessment of water and sediment quality. This approach allows that ecosystems may be adapted or acclimatised to certain concentrations of metals in surface water and sediments as a result of their natural abundance. Background values of metal(loids) have long been recognised to be higher in mineralised catchments than those in unmineralised, and this is in fact the same as the central precept of geochemical exploration for economic ore deposits. From the environmental perspective, these mineralised zones should be considered as a separate baseline unit from that of the unmineralised formation. Information on the baseline conditions of catchments prior to mining is needed to better understand what restoration goals are achievable in mining impacted catchments. The geochemical baseline data also provide a reference point against which changes can be measured and can be used both by industry and regulators in future mine applications. In this project an approach for deriving pre-mining baseline sediment concentrations using systematically collected survey geochemical data is demonstrated using the mineralised area associated with the Ordovician-Silurian rocks in southern Co. Armagh in Northern Ireland as study area. The Tellus geochemical survey data for sediments were used for this scope. International literature has usefully provided methodologies and examples of deriving ‘background’ concentrations in mineralised catchments. Statistical methods in use to distinguish between anomalous and background concentrations in geochemical exploration of mineral deposits all converge on various methods of discriminating outliers and making estimates of central tendency, spread and identification of upper thresholds of background. The statistical method used in this project is the method of Sinclair (1976a) and applied using the ‘PROBPLOT’ code (Stanley, 1987), reproduced in an ‘R’ script environment. This method chooses threshold values between anomalous and background geochemical data, based on partitioning a cumulative probability plot of the data. Data analysis has primarily focused on elements for which there are sediment quality standards derived in other jurisdictions, which may be adopted in the UK regulatory framework in future. Probability distribution plots of stream sediment lead (Pb) zinc (Zn), arsenic (As), chromium (Cr) and nickel (Ni) concentrations have been partitioned in the respective contributing populations and population statistics derived (mean and standard deviation). Interpretation of the significance of the resulting groupings of data and understanding different background populations has then been achieved through analysis of the spatial distribution of the groups in a GIS framework. Where data exceed environmental quality standards, these populations can assist in identifying where natural background concentrations (due to mineralogical variations in the catchment geology) may contribute to the exceedance. This is designed to aid the decision-making process in relation to why quality standards may have failed, or if there is any merit in ‘remediation’ of a natural ecosystem. Separation of the more widespread, potentially natural, high concentrations from the data populations which reflect very high concentrations (more likely to arise from anthropogenic sources) could also help in targeting key sites for further investigation