Margaret E. Farago

Factors influencing metal bioavailability in soils: preliminary investigations for the development of a critical loads approach for metals

The concept of critical loads, previously applied to acidifying substances, is currently being extended, within the Convention on Long Range Transboundary Air Pollution (CLRTAP), to several metals: Cd, Cu, Hg, Pb and Zn. Receptors in the soil, such as plants and microbiota, are directly exposed to these metals via the soil solution and this should ideally be reflected in environmental quality objectives which, presently, are commonly based on ‘total’ rather than bioavailable metal contents of soils. An understanding of the factors influencing the partition of metals between the solid and solution phases of soils is an essential prerequisite of any attempt to apply the critical loads approach in a manner which relates to the effects of metals on soil organisms.

Arsenic enrichment in waters and sediments of the Rio Loa (Second Region, Chile)

The Second Region of Chile (126,500 km2) is extremely arid, with a dramatic scarcity of water. The only water resource for the population (about 420,000 habitants) and the mining industry (the most important economic activity in the region) is the 440 km long Rio Loa. Moreover, this is highly enriched in As. In order to assess As concentrations and sources, and to evaluate the impact of mining activity on the water quality in the Rio Loa basin, water and sediment samples were taken at strategic points along the river and its major tributaries. The water in the whole basin is quite saline (total dissolved solids up to 11 g/l) and heavily enriched in As (average: 1400 μg/l) and B (average: 21,000 μg/l). These values are up to 300 and 100 times higher than the respective guidelines suggested by the WHO for drinking water. The quality of water is extremely poor along the tributary Salado, mainly fed by the El Tatio geothermal waters that are very rich in As (up to 27,000 μg/l) and other components. Sediments from the Rio Loa and its tributaries have As contents in the range of 26–2000 mg/kg (mean value of 60 samples: 320 mg/kg), and reach 11,000 mg/kg at El Tatio. Sequential extraction analyses show the As to be mainly associated with Fe–Mn oxy-hydroxides and residual phases, but part of the As (about 20%) is readily available being extracted from the exchangeable and carbonate phases. This result is in agreement with the correlation observed between As content in sediments and As concentration in waters in the area. The extreme arid conditions, high evaporation, and the lack of low-As tributaries contribute to maintain high concentrations of As and other components in the Rio Loa water to the mouth. Due to the oxidising conditions, neutral to alkaline pH, high salinity and high As concentrations, adsorption of As-species is not favoured. The main As source in the Rio Loa basin is considered to be natural, i.e. linked to the lithologies in the area. Smelter emissions and mining wastes, as well as the As-rich effluents from the water treatment plants, possibly represent additional sources.

Platinum concentrations in urban road dust and soil, and in blood and urine in the United Kingdom †

Increasing Pt concentrations from vehicle catalysts have been reported from a number of countries. Analysis of Pt and Pd in soils and road dusts taken from areas of high and low traffic flows in SE England show concentrations of Pt in the range < 0.30-40.1 ng g-1 and Pd in the range < 2.1-57.9 ng g-1. Higher concentrations of Pt are associated with high traffic densities. Samples taken from streets of lower traffic flows were found to contain the lower concentrations of the ranges. Pilot studies of Pt concentrations in blood and urine using ICP-MS have been carried out. Platinum concentrations in whole blood were: precious metal workers, 780-2170, mean 1263 pmol l-1 (0.152-0.423, mean 0.246 microgram l-1); motorway maintenance workers, 645-810, mean 744 pmol l-1 (0.126-0.158, mean 0.145 microgram l-1); Imperial College staff, 590-713, mean 660 pmol l-1 (0.115-0.139, mean 0.129 microgram l-1). Platinum concentrations in urine in pmol Pt per mmol creatinine were: precious metal workers, 122-682, mean 273 [0.21-1.18, mean 0.47 microgram Pt (g creatinine)-1]; motorway maintenance workers, 13-78, mean 33.7 [0.022-0.135, mean 0.058 microgram Pt (g creatinine)-1]; Imperial College staff, 28-130, mean 65.6 [0.048-0.224, mean 0.113 microgram Pt (g creatinine)-1]. Detection limits were 0.03 microgram l-1 for both blood and urine. The possible health effects of increasing Pt in the environment are discussed. Platinum provides an excellent example of the significance of speciation in metal toxicity. Platinum allergy is confined to a small group of charged compounds that contain reactive ligand systems, the most effective of which are chloride ligand systems. Metallic Pt is considered to be biologically inert and non allergenic and since the emitted Pt is probably in the metallic or oxide form, the sensitising potential is probably very low. Platinum from road dusts, however, can be solubilised, and enter waters, sediments, soils and the food chain. There is at present no evidence for any adverse health effects from Pt in the general environment, particularly allergic reactions.

Heavy metal pollution in the vicinity of a secondary lead smelter in the Czech Republic

Abstract The aim of the study was to determine the major sources and the extent of heavy-metal pollution in a mining and smelting region of the Czech Republic where concern had been expressed over high lead levels. Soils (0–5 and 15–30 cm) were sampled from 200 sites along 2 transects which crossed the mining and smelter areas, the town centre and outlying rural areas. Samples were analysed for levels of Pb, Zn, Cd, Cu, As and Sb, using ICP-AES. Soil concentrations of all the metals peaked in the smelter area with Pb levels of up to 37,300 ppm. Smaller peaks occurred in the mining area and the town centre. Moving away from the smelter, metal concentrations decreased exponentially over the first 1 km with a less steep decrease between 1 and 6 km. In residential areas in the smelter and mining zones, metal concentrations significantly breached the threshold trigger values set in the U.K. by the Interdepartmental Committee on the Reclamation of Contaminated Land (ICRCL). Particulate material from the smelter stack appears to contaminate soils up to at least 6 km. However, high metal levels in the immediate smelter area may be due primarily to fugitive emissions. Metal concentrations were significantly higher in soils sampled from woodland areas relative to other, non-wooded sites along the transects.

Differences in lead bioavailability between a smelting and a mining area.

Soils and housedusts were collected from three areas of Pribram,an historic metal mining and smelting town in the Czech Republic. The main objectives of the study were: (i) to assessthe influence of physico-chemical form, particle size, soilproperties and contaminant source on Pb bioavailability andexposure risk; (ii) compare the Pb bioavailability data obtainedfrom the mining and smelting areas and assess whether anydifferences observed could be attributed to the factors thoughtto exert an influence. Lead concentrations were highest in thesmelter area. Mining area garden soils also contained elevatedPb concentrations. Solubility of housedust Pb in 0.12 M HCl (asurrogate for stomach acid) was similar in all study areas andwas similar to values reported in the literature. However, 0.12M HCl solubility of garden soil Pb was low in the mining areacompared to the other study areas and compared to other urbanareas. Blood Pb concentrations were also relatively low in themining area compared to the other study areas and the reducedsoil Pb solubility observed in this area was suspected as aninfluencing factor. However, exposure pathways may also beimportant in explaining the differences observed.

Impact of Fly Ash from Coal-Fired Power Stations in Delhi, with Particular Reference to Metal Contamination

Indraprastha Power Station (IPP Stn) and Rajghat Power House (RPH), owned by Delhi Electric Supply Undertaking, are both coal-fired power stations located on Ring Road in New Delhi. Ash content of the coal used ranges between 38–47%. The ash is collected in electrostatic precipitators which have an efficiency of 99.3% (IPP station), and 99.7% (RPH). There are instances of major dust pollution around the power stations from fly ash dispersal. The main method of disposal of fly ash from the power stations is by mixing with water, the resultant slurry is pumped through pipes to ash disposal ponds. The supernatant from these ponds is discharged into River Yamuna. Field studies have revealed large quantities of fly ash being deposited into the river. Local populations of Eichhornia crassipes have reduced dramatically between 1987–1995, with a marked reduction in the year 1994–1995. Field studies, conducted in January, 1995 have investigated the impact of fly ash dispersal in the Delhi region with particular reference to metal contamination. Elemental concentrations for a range of elements are determined by ICP-AES in fly ash and top soils along four transects from the power stations up to a distance of 8 km. The effects of fly ash leachates from the ash settling ponds on the river are determined by analyzing river overbank soils and vegetation for their elemental contents. It is concluded that fly ash dispersal from the stacks are a source of alkali, alkaline-earth and to some extent heavy metals in soils in the vicinity of the power stations, and enrichment of elements in river overbank soils are a result of discharge of fly ash leachates from ash disposal ponds. However, the impact from both these sources of metal contamination is not large enough to give cause for concern. Marked reduction in populations of Eichhornia crassipes downstream of the river where it receives leachates from the ash disposal ponds are attributed to turbidity of the ash pond leachates and metal toxicity. Elemental enrichment in the floodplain soils, as a result of fly ash particle deposition during monsoons, may enhance the horticultural value of these soils as is shown by a healthy cultivated crop of Brassica juncea.

The effects of various platinum metal species on the water plant Eichhornia crassipes (Mart.) Solms.

AbstractEichhornia crassipes, the water hyacinth, has been grown in the presence of a number of complexes of the platinum group metals. In general those compounds which are taken up by the plants in larger quantities are the more toxic. The relative order of toxicities determined from visual appraisal and in terms of oxidation states, is Pt(II), Pd(II) > Ru(III) ∼ Ru(II) ∼ Ir(III) > Pt(IV) ∼ Os(IV) >> Rh(III)). In most cases the metals are accumulated in the roots, and where the metal is translocated to the tops and this is associated with toxic symptoms. Root elongation and biomass studies confirm that Eichhornia is more tolerant to Rh(III) and Pt(IV) than to Pt(II). Treatment with a Rh and three Pt complexes produced little differences in the concentrations of Ca, Cu, Fe, Mn and Zn in treated plants compared with controls. Sequential extractions of tissue from plants treated with cis[Pt(NH3)2Cl2] showed that in the leaves and floats almost half the platinum is insoluble and associated with α-cellulose a...

Quantifying the influence of soil properties on the solubility of metals by predictive modelling of secondary data

The concept of critical loads, previously applied to acidifying substances, is currently being extended, within the Convention on Long Range Transboundary Air Pollution (CLRTAP) under the UNECE, to several metals: Cd, Cu, Pb and Zn. Soil organisms such as plants and microbiota are exposed to these metals via the soil solution, and critical loads should therefore be based on metal concentrations in soil solution rather than total concentrations. Whilst such data do not exist on a large scale, empirical models may be able to predict bioavailable metal concentrations from existing data on total metal concentrations and those soil factors thought to influence the partition of metals between the solid and solution phases of soils. In this study we attempt, by undertaking statistical analysis of previously published data, to quantify the influence of soil factors on this partition. A major limitation to the approach is the availability of suitable data. However, analysis shows that, amongst the soil factors investigated, pH alone consistently accounts for a large percentage of the variance in metal extractability. Verification of this finding may enable models to be developed which can use existing and commonly available data on total metal concentrations, and pH, to predict approximations of bioavailable concentrations of metals which can subsequently be used in the derivation of critical loads.

Bioavailability of arsenic in soil and mine wastes of the Tamar valley, SW England

ABSTRACTThe southern part of the Tamar valley area in SW England is highly mineralised and mines in the region were the worlds principal producers of tin, copper and arsenic during the mid nineteenth century. The Devon Great Consols Mine, covering 67.6 ha (167 acres) is situated in this area. Residues from the mining activity resulted in unvegetated spoil tips and local soils highly contaminated with As (range 120–52600 μg/g As). Sequential chemical extraction procedures were conducted on eight surface samples (0–15 cm) taken from a 2.0 km long transect from within the mine site to agricultural grassland. The proportion of water extractable As in agricultural top soils was lower (0.05–0.3%) than the values obtained for mine wastes (0.02–1.2%). Arsenic was found to be concentrated in the Fe-organic and residual fractions, which accounted for up 93 % of the total As in mine spoil and nearby soils.

Heavy Metal Concentrations in and Around Households Near a Secondary Lead Smelter

Housedusts and garden soils were sampled in 14 houses in the vicinity of a secondary Pb smelter and analysed for concentrations of Pb, Zn, Cu, Cd, As, and Hg. Sixty-one topsoil samples were also taken from a 2 km2 grid covering the smelter grounds and surrounding residential areas and analysed for concentrations of Pb, Zn, Cd and Cu. Contour maps generated from the grid data indicate significant contamination in the area (maximum Pb concentration 58 500 μg g-1), particularly down-wind of the smelter grounds. A geometric mean Pb concentration of 2225 μg g-1 was recorded in garden soil and similarly elevated levels were recorded for Zn, Cd, As and Sb. In housedusts, a geometric mean Pb concentration of 1668 μg g-1 was observed. Whilst housedust metal concentrations were generally elevated, compared to other urban or residential areas, there appears to be a large degree of attenuation of the metals between the exterior and interior environments of the homes studied. A significant correlation was not recorded between metal concentrations of garden soils and housedusts. There were significant correlations for: distance from the smelter against garden soil metal concentrations; garden soil metal concentrations against each other; housedust metal concentrations against each other; and house age against garden soil metal concentrations.