Ben Klinck

Arsenic and selenium

This chapter outlines the main effects of arsenic and selenium on human and animal health, their abundance and distribution in the environment, sampling and analysis, and the main factors controlling their speciation and cycling. Such information should help identify aquifers, water resources and soils at risk from high concentrations of arsenic and selenium, and areas of selenium deficiency. Human activity has had, and is likely to continue to have, a major role in releasing arsenic and selenium from the geosphere and in perturbing the natural distribution of these and other elements over the Earths surface.

Comparison of five in vitro digestion models to in vivo experimental results: Lead bioaccessibility in the human gastrointestinal tract

This paper presents a multi-laboratory comparison study of in vitro models assessing bioaccessibility of soil-bound lead in the human gastrointestinal tract under simulated fasted and fed conditions. Oral bioavailability data from a previous human in vivo study on the same soil served as a reference point. In general, the bioaccessible lead fraction was significantly (P < 0.05) different between the in vitro methods and ranged for the fasted models from 2% to 33% and for the fed models from 7% to 29%. The in vivo bioavailability data from literature were 26.2 ± 8.1% for fasted conditions, compared to 2.5 ± 1.7% for fed conditions. Under fed conditions, all models returned higher bioaccessibility values than the in vivo bioavailability; whereas three models returned a lower bioaccessibility than bioavailability under fasted conditions. These differences are often due to the methods digestion parameters that need further optimization. An important outcome of this study was the determination that the method for separating the bioaccessible lead from the non-bioaccessible fraction (centrifugation, filtration, ultrafiltration) is crucial for the interpretation of the results. Bioaccessibility values from models that use more stringent separation methods better approximate in vivo bioavailability results, yet at the expense of the level of conservancy. We conclude from this study that more optimization of in vitro digestion models is needed for use in risk assessment. Moreover, attention should be paid to the laboratory separation method since it largely influences what fraction of the contaminant is considered bioaccessible.

Bioaccessibility of arsenic in mine waste-contaminated soils: A case study from an abandoned arsenic mine in SW England (UK)

This study characterises the total As concentrations and As bioaccessibility in 109 soils from Devon Great Consols Mine, an abandoned Cu-As mine in Devon, SW England, UK and discusses the soil and mineralogical factors that influence the bioaccessibility of this element. These data provide the basis for developing more accurate exposure estimates for use in human health risk assessments. The median value of the percent bioaccesible As of 15% for these As rich soils contaminated by mining activities indicated that relatively little of the total As is present in a bioaccessible form. Spatial variability of As bioaccesibility in the soils was also recognised throughout the mine site as a function of mineralogy. Multivariate statistical analysis identified a sulphide component responsible for the reduced As bioaccessibility of one cluster of soils. In the larger cluster of acidic mine soils covered by woodland As is mainly hosted in Fe oxyhydroxides whose partial dissolution is responsible for the bioaccessible As fraction. It was highlighted that the degree of Fe oxyhydroxide crystallinity might represent an important factor influencing arsenic bioaccessibility. Mine soils from Devon Great Consols Mine showed overall higher As bioaccessibility (15%) than other mineralised soils not affected by mining activities and background soils within the Tamar Catchment whose percent bioaccessible As median values were 9%.

The bioaccessibility of lead from Welsh mine waste using a respiratory uptake test

The objective of this study was to develop an in vitro respiratory uptake test to determine the bioaccessibility of lead derived from mining waste tailings and dusts. Samples were collected from an abandoned mining area in mid-Wales, UK, the < 10 μ m fraction was characterized using SEM and the < 100 μ m fraction using XRD techniques. Gambles Solution was employed as the synthetic lung fluid and tests were run for 630 hours in a specially designed water bath. The long test duration was specified because of the long duration of particulates in the lung after inhalation. Bioaccessible lead was determined throughout the test and the final values ranged from 15 to 41% of total lead. The extraction profile of the lead could be modeled by: Pb − extracted (M) = b × ln (time, t) + c, where b and c are sample specific constants, M is the mass extracted in mg and t is the time in hours. However, despite acceptable values of R2, the standardised residuals of simple regression suggest that lead extracted is under predicted at early time and over predicted at later time. Clearly from the regression model presented the dissolution rate is declining with time and the dissolution rate decreases by an order of magnitude for the tailings tested over the duration of the test. The explanation for this is the deposition of an insoluble lead phosphate mineral during the extraction onto lead mineral surfaces that effectively limits dissolution. Based on this finding it is suggested that the in vitro extraction method described can provide a conservative estimate of bioaccessible lead for a shorter duration test of 100 hours.

Soil–plant interactions and the uptake of Pb at abandoned mining sites in the Rookhope catchment of the N. Pennines, UK : a Pb isotope study

This paper examines Pb concentrations and sources in soil, grass and heather from the Rookhope catchment in the North Pennines, UK, an area of historical Pb and Zn mining and smelting. Currently, the area has extensive livestock and sports shooting industries. Risk assessment, using the source-pathway-receptor paradigm, requires the quantification of source terms and an understanding of the many factors determining the concentration of Pb in plants. A paired soil and vegetation (grass and heather) geochemical survey was undertaken. Results showed no direct correlation between soil (total or EDTA extractable Pb) and vegetation Pb concentration. However, regression modelling based on the Free-Ion Activity Model (FIAM) suggested that the underlying mechanism determining grass Pb concentration across the catchment was largely through root uptake. Spatial patterns of (206/207)Pb isotopes suggested greater aerosol deposition of Pb on high moorland and prevailing wind facing slopes. This was evident in the isotopic ratios of the heather plants. Pb isotope analysis showed that new growth heather tips typically had (206/207)Pb values of ~1.14, whilst grass shoots typically had values ~1.16 and bulk soil and peat ~1.18. However, the (206/207)Pb ratio in the top few cm of peat was ~1.16 suggesting that grass was accessing Pb from a historical/recent pool of Pb in soil/peat profiles and consisting of both Pennine ore Pb and long-range Pb deposition. Isotope Dilution assays on the peat showed a lability of between 40 and 60%. A simple source apportionment model applied to samples where the isotope ratios was not within the range of the local Pennine Pb, suggested that grass samples contained up to 31% of non-Pennine Pb. This suggests that the historical/recent reservoir of non-Pennine Pb accessed by roots continues to be a persistent contaminant source despite the principal petrol Pb source being phased out over a decade ago.

Arsenic speciation and mobility in mine wastes from a copper–arsenic mine in Devon, UK: a SEM, XAS, sequential chemical extraction study

Abstract The nature of As speciation is a determining factor for As mobility in mine wastes. In this study, scanning electron microscopy (SEM), X-ray absorption spectroscopy and sequential chemical extraction methods were used for the environmental, mineralogical and genetic characterisation of mine spoil and calciner wastes from Devon Great Consols Mine, an abandoned copper–arsenic mine in Devon, UK. The geochemical control of As-bearing phases on dissolved As during leaching was investigated. Arsenic is mainly present as As(V) co-precipitated or adsorbed with, or on, iron (Fe) oxyhydroxides. The water extracts from the mine spoil and calciner wastes indicated a generally low dissolution of As, especially in sandy tailings (Aswater soluble 0.0004% of total As content). Thermodynamic calculations did not identify a major As phase controlling the composition of the water leachates, which suggests a process of desorption of Fe oxyhydroxide-bound As as the source of As in the solution. A relative higher As mobility (Aswater soluble 3.7% of total As content) was found in the waste material with an alkaline pH in the vicinity of the ore crusher. Available thermodynamic data supported by SEM evidence and chemical extraction data suggest that calcium-arsenate phases such as weillite (CaHAsO4) and calcium–copper arsenates together with scorodite (FeAsO4·2H2O) and Fe oxyhydroxides may all contribute to the higher As content in the alkaline waste leachates. The results indicate the importance of considering the nature of As in mine waste management.

Trihalomethane formation potential: a tool for detecting non-specific organic groundwater contamination

The trihalomethane formation potential (THMFP) was measured in groundwaters affected by infiltration of wastewater or landfill leachate from Mexico, Jordan and Thailand. THMFP was directly related to the concentration of dissolved organic carbon (DOC), except where leachate was produced from burnt waste or where bromide concentrations were unusually high indicating the proportion of brominated derivatives was dependent on the concentration of bromide. It is proposed that the THMFP provides a sensitive measure of low levels of organic contamination and can be used as a surrogate for DOC concentration where there are difficulties in measuring this parameter. A risk assessment model has been used and demonstrates indirect health effects due to the chlorination of leachate contaminated groundwater.