B.G. Rawlins

GSUE: urban geochemical mapping in Great Britain

The British Geological Survey is responsible for the national strategic geochemical survey of Great Britain. As part of this programme, the Geochemical Surveys of Urban Environments (GSUE) project was initiated in 1992 and to date, 21 cities have been mapped. Urban sampling is based upon the collection of top (0.05 to 0.20 m) and deeper (0.35 to 0.50 m) soil samples on a 500 m grid across the built environment (one sample per 0.25 km2). Samples are analysed for c. 46 total element concentrations by X-ray fluorescence spectrometry, pH and loss on ignition as an indicator of organic matter content. The data provide an overview of the urban geochemical signature and because they are collected as part of a national baseline programme, can be readily compared with soils in the rural hinterland to assess the extent of urban contamination. The data are of direct relevance to current UK land use planning, urban regeneration and contaminated land legislative regimes. An overview of the project and applications of the data to human health risk assessment, water quality protection and contaminant source identification are presented.

The assessment of point and diffuse metal pollution of soils from an urban geochemical survey of Sheffield, England

A model of soil variability as a continuous background process with superimposed point contamination was applied to 569 measurements of metal concentrations (Cr, Ni and Pb) in the topsoils of Sheffield, England. Robust estimators of the variogram were shown to be required to describe spatial variation of the metal concentrations at most sampled locations. This is diagnostic of the presence of a contaminant process. Values of the standardized kriging error from the cross-validation of each datum were used to identify spatial outliers for each metal. The ordinary kriged estimates of Cr, Ni and Pb were mapped after removing the outliers to estimate the background variation. Each of the 35 spatial outliers that occured in gardens have concentrations exceeding their Soil Guideline Value for residential land use with plant uptake, highlighting a potentially significant exposure pathway. The frequent observation of coal and furnace waste at these sites suggests that their dispersal, following domestic use and industrial processes, respectively, represents a significant point contaminant process. There was no evidence for spatial clustering of the point process. However, the spatial outliers of Cr and Ni showed a significant association with disturbed sites identified from historical land use maps, in part due to their prevalence in areas of historical steel manufacture. The magnitude of diffuse pollution for each metal in the urban soil was estimated by removing the spatial outliers and comparing robust measures of location with those from a survey of soils developed over the same parent materials in adjacent rural and peri-urban environments. The Winsorized mean Pb concentrations in urban topsoil (203 mg kg−1) were twice the value in the rural environment (101 mg kg−1), highlighting a very substantial diffuse Pb load to urban soils. The equivalent estimated diffuse components in urban soils for Cr and Ni were, respectively, 25% and 14% higher than the rural soils.

Review of agricultural pollution in the Caribbean with particular emphasis on small island developing states

Recent studies have attributed the degradation of coastal living resources in the Caribbean to the potential impacts of agricultural pollution. Physical features controlling the delivery, retention and dispersal of pollutants throughout the region are discussed. Information relating to four types of agricultural pollution is presented and assessed: soil erosion leading to siltation, nutrient enrichment, pesticide contamination and agro-industrial pollution. The results of this review have enabled gaps in knowledge to be identified. Areas prone to soil erosion and the reasons for their susceptibility are known. There is a paucity of baseline data on turbidity and on the concentration of nutrients and pesticides in the coastal zone. The increase in the use of agricultural fertilisers and pesticides over the last 20 years suggests a concomitant rise in their loads to coastal waters. Few studies have made direct links between agricultural pollution, reduction in coastal water quality or clarity, and the degradation of coastal living resources.

Potential and pitfalls in establishing the provenance of earth-related samples in forensic investigations

ABSTRACT: Earth scientists are often asked to establish or constrain the likely provenance of very small quantities of earth‐related material as part of a forensic investigation. We tested the independent and collective interpretations of four experts with differing analytical skills in the prediction of sample provenance for three samples from different environmental settings. The methods used were X‐ray diffraction, scanning electron microscopy, the assessment of pollen assemblages, and structural characterization of organic matter at the molecular level. Independent interpretations were less accurate than those where multiple techniques were combined. Collective interpretation was very effective in the assessment of provenance for two of the three sites where the mineralogy and plant communities were distinctive. At the other site, although the mineralogical analysis correctly identified the Triassic mudstone soil parent material, Carboniferous spores from domestic coal were initially interpreted as deriving directly from bedrock. Such an interpretation could be a common pitfall owing to anthropogenic redistribution of material such as coal.

Apportioning sources of organic matter in streambed sediments: an integrated molecular and compound-specific stable isotope approach.

We present a novel application for quantitatively apportioning sources of organic matter in streambed sediments via a coupled molecular and compound-specific isotope analysis (CSIA) of long-chain leaf wax n-alkane biomarkers using a Bayesian mixing model. Leaf wax extracts of 13 plant species were collected from across two environments (aquatic and terrestrial) and four plant functional types (trees, herbaceous perennials, and C3 and C4 graminoids) from the agricultural River Wensum catchment, UK. Seven isotopic (δ13C27, δ13C29, δ13C31, δ13C27-31, δ2H27, δ2H29, and δ2H27-29) and two n-alkane ratio (average chain length (ACL), carbon preference index (CPI)) fingerprints were derived, which successfully differentiated 93% of individual plant specimens by plant functional type. The δ2H values were the strongest discriminators of plants originating from different functional groups, with trees (δ2H27-29=-208‰ to -164‰) and C3 graminoids (δ2H27-29=-259‰ to -221‰) providing the largest contrasts. The δ13C values provided strong discrimination between C3 (δ13C27-31=-37.5‰ to -33.8‰) and C4 (δ13C27-31=-23.5‰ to -23.1‰) plants, but neither δ13C nor δ2H values could uniquely differentiate aquatic and terrestrial species, emphasizing a stronger plant physiological/biochemical rather than environmental control over isotopic differences. ACL and CPI complemented isotopic discrimination, with significantly longer chain lengths recorded for trees and terrestrial plants compared with herbaceous perennials and aquatic species, respectively. Application of a comprehensive Bayesian mixing model for 18 streambed sediments collected between September 2013 and March 2014 revealed considerable temporal variability in the apportionment of organic matter sources. Median organic matter contributions ranged from 22% to 52% for trees, 29% to 50% for herbaceous perennials, 17% to 34% for C3 graminoids and 3% to 7% for C4 graminoids. The results presented here clearly demonstrate the effectiveness of an integrated molecular and stable isotope analysis for quantitatively apportioning, with uncertainty, plant-specific organic matter contributions to streambed sediments via a Bayesian mixing model approach.

Changes in soil pollen assemblages on footwear worn at different sites

Abstract The application of palynology to forensic investigations relies on the similarity of pollen assemblages from forensic items, such as footwear, with control samples from a crime scene. The pollen from material adhering to footwear is likely to reflect some combination of pollen from the locations where the boots/shoes have been worn most recently. This study investigated the changes in pollen assemblages on footwear that had been worn at different sites. Six rural sites in the East Midlands of England, United Kingdom were visited wearing pristine boots (i.e. no mixing), and boots that were previously worn at other localities (i.e. potential mixing). Samples of adherent soil from these items of footwear, and control samples, were analysed palynologically in order to assess the degree and significance of mixing of the pollen assemblages. With the exception of one sample, the pollen adherent to footwear or in the soil samples from each of the six sites (no mixing) had a characteristic signature. This supports the general distinctiveness of pollen from individual sites, the concept of widespread palynological heterogeneity, and the utility of palynology in forensic geoscience. The data from this study show that when mixing occurs from wearing footwear at different sites, the pollen/spore content of the boots etc. dominantly reflects that of the last site. This was evident from a visual examination of the raw data, and was confirmed using detrended correspondence analysis applied to the eleven dominant taxa. These data showed clustering of samples based on the last site visited. The more abundant the pollen/spores, the closer the samples were clustered. The clustering was less convincing at localities that yielded relatively sparse palynomorphs. However, sample material from footwear that was potentially contaminated with soil from previous localities typically exhibited some subtle differences. These were normally slight increases in diversity, and small variations in certain pollen types. The relative insignificance of these differences means that they would be difficult to discern consistently and quantify. It is thus critical that, in relevant forensic investigations, footwear belonging to suspects is seized as soon as possible after a crime is committed.

Temporal and spatial variability of stream waters in wales, the welsh borders and part of the West Midlands, UK-1. Major ion concentrations

Spatial and temporal controls on major ion stream water chemistry are assessed using hydrochemical survey data for Wales and the West Midlands, and time-series data from the intensively studied Plynlimon catchment (mid-Wales). Spatial variations in stream water chemical composition are interpreted in relation to the environmental chemistry of the major ions and controls such as bedrock geology, land-use, anthropogenic activities and atmospheric inputs. Piper diagrams are used to illustrate compositional variation, allowing comparison to be made between samples of widely varying Total Dissolved Solids (TDS). Spatial and temporal data sets are overlaid on Piper plots to determine the relative importance of these two factors in controlling major ion chemistry. Bedrock geology, atmospheric input and land-use can satisfactorily explain compositional variation in the spatial data set. Combined analysis of the spatial and temporal data sets indicated that the variation in cation composition at the Plynlimon site is considerably more constrained than that on the corresponding anion diagram. Time-series data sets for sites of different bedrock geology and at a range of distances from sources of marine derived solute inputs are necessary for further investigation of the relative importance of temporal and spatial controls on major ion stream water chemistry.

Sedimentary transport and fate of polycyclic aromatic hydrocarbons (PAH) from managed burning of moorland vegetation on a blanket peat, South Yorkshire, UK.

This study reports the concentrations of 18 polycyclic aromatic hydrocarbons (PAH) from managed burning of moorland vegetation and compares them to PAH in catchment vegetation, underlying peats, head water suspended sediment (HSS), stream water and reservoir sediment cores. Total PAH ranged from 203 to 11,112 μg/kg in the blanket peats, 101-290 μg/kg in the fresh moorland vegetation, 4186 μg/kg at the burnt site, 17,439 μg/kg in the HSS, 56 ng/L in the stream water and 987 to 7346 μg/kg in the reservoir sediments. No total or individual PAH concentrations exceeded the published sediment quality guidelines. The perylene content of selected moorland vegetation (sphagnum, heather and bilberry) ranged from 10 to 18% as compared to only 2% for the sediment hosted PAH. A comparison of whole and <250 μm fractions from the burnt surface layer revealed a near threefold increase in PAH concentration in the fine fraction and a change in the PAH distribution such that naphthalene>>phenanthrene>2-methylnaphthalene. Elevated total PAH contents were observed close to the blanket peat sediment surface (0-10 cm) and then declined at greater depths. The high PAH content of the HSS was attributed to the high sorption capacity of the organic-rich particles (TOC 25.8% (wt/wt)). The distribution of individual PAH in reservoir cores and HSS was consistent and the results of the principal component analysis and isomeric ratios suggest mainly pyrolytic inputs, from either vegetation burning and coal combustion. A comparison of the reservoir core PAH profiles shows that the source(s) have remained largely unchanged since the reservoir construction in 1929A.D. reflecting consistent moorland management practices.

Microscopic and chemical studies of metal particulates in tree bark and attic dust: evidence for historical atmospheric smelter emissions, Humberside, UK

Tree barks and attic dusts were examined as historical archives of smelter emissions, with the aim of elucidating the pathways of pollution associated with a plume of Sn and Pb contamination in top soils, found close to the former Capper Pass smelter, Humberside, UK. Samples were collected from three villages within the area of the contamination plume. Scanning electron microscopy (SEM) and bulk chemical analyses were used to assess particle type, number and deposition patterns. SEM analysis of dusts and bark revealed that Sn and Pb particles were present in samples from all three villages along with copper, zinc and iron particles. These were almost entirely <10 microm in diameter and occurred mostly as oxides, frequently forming clusters of sub-micron crystals. Samples further from the smelter contained considerably fewer particles. We present images of smelter derived Sn particles. Chemical assays of the barks and attic dusts demonstrated that concentrations of Sn, Pb, Cu, As, Sb and Cd diminished with increasing distance from the source. Strong positive correlations were found between Sn and Pb, As, Sb and Cd in the attic dusts. Enrichment factors (EF) were calculated for these trace elements based on topsoil element concentrations obtained from the soil survey of the study area. Decreases in these trace element concentrations and EF values with distance away from the smelter are consistent with trends found in the soil survey for Sn and Pb and are typical of deposition patterns around smelter stacks. The study demonstrates that tree bark and attic dusts can be effective archives of metal particulates deposited from large static emission sources.

Investigating multi-element soil geochemical signatures and their potential for use in forensic studies

Abstract Data from a regional soil survey in eastern England have been used to determine whether samples over the same parent material can be discriminated on the basis of both individual and multielement geochemistry. Discrimination was based on estimates of measurement uncertainty, which were calculated from the analysis of a series of duplicates and subsamples. In the multivariate analysis we estimated a covariance matrix for the two sources of uncertainty and compared this to Mahalanobis distances calculated for pairs of samples within each parent material group. For 12 of the 19 individual elements, it was possible on average to discriminate between more than 80% of the samples within parent material groups and typically between 15 and 17 of the 19 elements discriminated individual samples. In the multi-element analysis, typically more than 99.8% of samples within the same parent material group were discriminated from one another. Hence, the geochemistry of a natural soil sample, when collected and analysed according to a strict protocol, and compared to a database that adopted the same methods, could be used to help establish provenance within bedrock-derived soil types. However, there are significant differences between the nature of soil samples and the way they are collected or derived in soil surveys and forensic investigations. These questions need to be addressed thoroughly before any practical application to forensic cases in which an investigator is attempting to link a suspect to a location based on soil geochemical signatures.