This paper hypothesizes that arsenic in drinking water indirectly contributes to Buruli ulcer (BU), a skin disease caused by Mycobacterium ulcerans (MU) infection. Samples of groundwater and surface water used as drinking water by the population in Ghana's Amansie West district (part of which has a high prevalence of BU), were collected near rural settlements and analysed for arsenic. Arsenic concentration levels per settlement were compared with BU prevalence. A positive exposure-response relationship was obtained between arsenic in surface water and BU (r2 = 0.82). However, there is no significant exposure-response relation between groundwater and BU.

The headwaters of the Río Pilcomayo drain the Cerro Rico de Potosí precious metal-polymetallic tin deposits of southern Bolivia. Mining of these deposits has taken place for around 500 years, leading to severe contamination of the Pilcomayo's waters and sediments for at least 200 km downstream. Communities living downstream of the mines and processing mills rely on the river water for irrigation, washing and occasionally, cooking and drinking, although most communities take their drinking water from springs located in the mountains above their village. This investigation focuses on arsenic exposure in people living in riverside communities up to 150 km downstream of the source. Sampling took place in April–May 2003 (dry season) and was repeated in January–March 2004 (wet season) in five communities: El Molino, Tasapampa, Tuero Chico, Sotomayor and Cota. Cota was the control in 2003 and again in 2004; a nearby city, Sucre, and several locations in the UK were also used as controls in 2004. Drinking, irrigation and river waters, hair and urine samples were collected in each community, digested where appropriate and analysed for As using ICP-MS. Arsenic concentrations in drinking waters ranged 0.2–112 μg 1–1, irrigation water 0.6–329 μg 1–1, river waters 0.9–12,800 μg 1–1, hair 37–2110 μg kg–1 and urine 11–891 μg 1–1. All but one drinking water sample was found to contain As below the World Health Organization recommended guideline of 10 μg 1–1, although a number of irrigation and river water concentrations were above Canadian and Bolivian guidelines. Many As concentrations in the hair and urine samples from this study exceeded published values for non-occupationally exposed subjects. Analysis of mean concentration values for all media types showed that there were no statistically significant differences between the control locations and the communities exposed to known As contamination, suggesting that the source of As may not be mining-related. Arsenic concentration appears to increase as a function of age in hair samples from males and females older than 30 years. Male volunteers over the age of 35 showed increasing urine-As concentrations as a function of age, whereas the opposite was true for the females.

The reactivity of primary Pb metallurgical slags in high-molecular-weight (HMW) organic solutions has been studied in order to determine the processes of release and attenuation of metal and metalloid contaminants (Pb, Zn, Cu, As) in 'soil-like' environments. Slag was submitted to a 112-day batch leaching experiment in Suwannee River fulvic acid solution and peat water (∼50 mg DOC l–1). The leaching was coupled with investigation of the secondary phases (SEM/EDS, Raman microspectrometry) and thermodynamic speciation-solubility modelling using MINTEQA2. Metals and As are released in large amounts during the early stage of the experiment, followed by a decrease in the concentrations in the leachate as a result of adsorption on secondary (hydrous) ferric oxides (HFO/FO), predicted by MINTEQA2 calculations and confirmed on the leached slag surface by SEM and Raman spectrometry. Compared to other contaminants, Zn exhibits more pronounced mobility and is adsorbed on HFO/FO only at pH >7. Such a scavenging process may be predominant during the long-term interaction of slag with an HMW organic solution of real soil. As a result, the soil cover and subsequent re-vegetation of slag dumps may be considered as a possible scenario for slag management.

Here we describe preliminary research into the in situ electrokinetic generation of continuous iron-rich precipitates to act as sub-surface barriers for the containment of contaminated sites. This is achieved using sacrificial iron electrodes emplaced either side of a soil/sediment mass to introduce iron into the system, and their dissolution and re-precipitation under the influence of an applied (DC) electric field. Continuous vertical and horizontal iron-rich bands (up to 2 cm thick) have been generated over a timescale of 300—500 h, at voltages of <5 V with an electrode separation of between 15 and 30 cm. The thickness of the iron-rich band increases as the applied voltage is increased. Geotechnical tests in sand indicate that the iron-rich band produced is practically impervious (coefficient of permeability of 10—9 ms—1 or less), and has significant mechanical strength (unconfined compressive strength of 10.8 N mm—2). By monitoring the current, the integrity of the iron-rich band may be assessed, and by continued application of current, the barrier may 'self heal'. The iron-rich barrier is composed of amorphous iron, goethite, lepidocrocite, maghemite and native iron.

Gully pot sediments and pavement and road gutter dusts have been collected from the city of Coventry in the West Midlands, UK. These samples have been subjected to metallic element analysis and the activity of a number of gamma-emitting radionuclides have been measured in order to assess whether they exceed published trigger or action levels, and whether their disposal or dispersal may have implications for receiving landfills and/or water courses. Results indicate above-background levels of metallic elements in dusts and sediments with Cu and Zn exceeding ICRCL action levels in some cases. The highest activities of some radionuclides are found in road gutter and street dusts and the lowest activities are found in gully pot sediments. Road dusts are more likely to be recirculated into the ambient air by passing traffic and could potentially pose a risk to pedestrians. The effective dose rates calculated for these dusts and sediments indicate that some samples approach and even exceed the 1 mSv y—1 limit to members of the public recommended by ICRP (1991). Some individual nuclides exceed their clearance levels laid down in the revised basic safety standards of the 1993b Radioactive Substances Act, 1993 (DoETR, 1999), by as much as 2.5 times. This is especially true of 210Pbun and 7Be, two fallout nuclides, and also of 40K.

Arsenic(V) removal from aqueous solution following addition of either a mixture of synthetic hydroxylapatite and baryte or bone-char is discussed. Arsenic concentrations of 4, 10 and 100 mg/l were investigated and additions of 0.2—10 g/l of solid (hydroxylapatite, baryte or bone-char) were tested, at an initial pH of either 5 or 7. Although the mixture of hydroxylapatite and baryte had a small influence on arsenic concentrations, bone-char was found to be a very effective sorbing agent for arsenic(V). Packed-column studies to investigate the bone-char capacity, followed by leaching tests were carried out. The capacity of bone-char was found to be superior to that of granular activated carbon. The experiments presented here indicate that the mechanism involved is adsorption rather than co-precipitation.

The solubility of arsenic in anoxic soil and sediment pore waters is strongly influenced by complexation with dissolved sulphide. Despite their importance in arsenic chemistry, thioarsenite complexes have not been well characterized, and considerable questions remain regarding their structure, protonation state, and relative stabilities. Here we use X-ray absorption spectroscopy to examine the type and structure of aqueous arsenic-sulphur complexes in sulphidic solutions under neutral to alkaline pH. Arsenic formed a variety of thioarsenites, including AsS(SH)(OH)—, As(SH)S22—, AsS33—and As(SH)4— complexes. The relative fraction of each species varied strongly with the S:As ratio — with the fraction of AsS(SH)(OH)— greatest at low S:As and trithioarsenites dominating As speciation when S:As ratios exceeded 3 in solution. As much as 40% of the total As also was present as AsS3S3+x(SH)3—x—x in solutions at S:As ratios of 3 or greater. Sulphide complexation was somewhat dependent on pH, with sulphide complexation generally increasing with pH. The speciation observed in these experiments is similar to, though distinct from, speciation predicted based on As2S3 solubility (inferred to contain AsS2— and AsS3S3+x(SH)—x3—x) and chromatographic separation of arsenic species (which does not identify polymeric species). Thus, these data indicate that stability constants for arsenic sulphide complexes must be reappraised.

The water column chemistry of lake St Eloy (St Eloy-les Mines, Allier, France) was monitored over a period of a year. This is a small stratified lake created by subsidence of an underground coal mine. The results show a permanent stratification and the development of two water bodies with contrasting chemistry. The superficial oxic layer (i.e. the upper 5 m) is of high water quality and the water, not affected by seasonal changes, is suitable as a source of drinking water. In contrast, the deeper layer is permanently anoxic and the waters have a conductivity which is six times greater than in the epilimnion. Due to density difference and the small size of the lake, no turn-over occurs and all elements that diffuse from bottom sediments are strongly concentrated in the hypolimnion. Arsenic concentrations are very low in the epilimnion, but they increase quickly with depth below the oxycline, to reach up to 7 μm below 8 m depth. Different solid phases could control the fate of arsenic in this lake such as gypsum for As(V) in the hypolimnion, mackinawite for As(V) and As(III) in the hypolimnion, and close to the oxycline, Fe(III) oxyhydroxides are possible hosts for both As(III) and As(V).

Our recent discovery of hazardous concentrations of arsenic in shallow sedimentary aquifers in Cambodia raises the spectre of future deleterious health impacts on a population that, particularly in non-urban areas, extensively use untreated groundwater as a source of drinking water and, in some instances, as irrigation water. We present here small-scale hazard maps for arsenic in shallow Cambodian groundwaters based on >1000 groundwater samples analysed in the Manchester Analytical Geochemistry Unit and elsewhere. Key indicators for hazardous concentrations of arsenic in Cambodian groundwaters include: (1) well depths greater than 16 m; (2) Holocene host sediments; and (3) proximity to major modern channels of the Mekong (and its distributary the Bassac). However, high-arsenic well waters are also commonly found in wells not exhibiting these key characteristics, notably in some shallower Holocene wells, and in wells drilled into older Quaternary and Neogene sediments.

It is emphasized that the maps and tables presented are most useful for identifying current regional trends in groundwater arsenic hazard and that their use for predicting arsenic concentrations in individual wells, for example for the purposes of well switching, is not recommended, particularly because of the lack of sufficient data (especially at depths >80 m) and because, as in Bangladesh and West Bengal, there is considerable heterogeneity of groundwater arsenic concentrations on a scale of metres to hundreds of metres. We have insufficient data at this time to determine unequivocally whether or not arsenic concentrations are increasing in shallow Cambodian groundwaters as a result of groundwater-abstraction activities.