Arsenic-contaminated Soil Research Articles

Arsenic-contaminated soils genetically modifiedPseudomonas spp. and their arsemc-phytoremediation potential

Sorghum was inoculated withPseudomonas bacteria, including strains harboring an As-resistance plasmid, pBS3031, to enhance As-extraction by the plants.Pseudomonas strains (P.fluorescens 38a, P.putida 53a, and P.aureofaciens BS1393) were chosen because they are antagonistic to a wide range of phyto-pathogenic fungi and bacteria, and they can stimulate plant growth. The resistance of natural rhizospheric pseudomonads to sodium arsenite was assessed. Genetically modifiedPseudomonas strains resistant to As(III)/As(V) were obtained via conjugation or transformation. The effects of the strains on the growth of sorghum on sodium-arsenite-containing soils were assessed. The conclusions from this study are: (1) It is possible to increase the survivability of sorghum growing in sodium-arsenite-containing soil by using rhizosphere pseudomonads. (2) The presence of pBS3031 offers the strains a certain selective advantage in arsenite-contaminated soil. (3) The presence of pBS3031 impairs plant growth, due to the As-resistance mechanism determined by this plasmid: the transformation of the less toxic arsenate into the more toxic, plant-root-available arsenite by arsenate reductase and the active removal of arsenite from bacterial cells. (4) Such a mechanism makes it possible to develop a bacteria-assisted phytoremediation technology for the cleanup of As-contaminated soils and is the only possible way of removing the soil-sorbed arsenates from the environment.

Effects of Arsenic Concentrations and Forms on Arsenic Uptake by the Hyperaccumulator Ladder Brake

Ladder brake (Pteris vittata L.) is a newly discovered arsenic hyperaccumulator. No information is available about arsenic effects on ladder brake. This study determined the effects of different arsenic concentrations (50 to 1000 mg kg(-1)) or forms (organic vs. inorganic and arsenite vs. arsenate) applied to soils on growth and arsenic uptake by ladder brake. Young plants were grown in a greenhouse for 12 or 18 wk. Ladder brake was highly tolerant of arsenic and survived in soil containing up to 500 mg As kg(-1). The fact that addition of arsenate up to 100 mg As kg(-1) increased fern biomass by 64 to 107%, coupled with higher arsenic concentration in younger fronds at low soil arsenic concentrations and older fronds at high soil arsenic concentrations, implies that arsenic may be beneficial for fern growth. Addition of 50 mg As kg(-1) was best for fern growth and arsenic accumulation, resulting in the highest fern biomass (3.9 g plant(-1)), bioconcentration factor (up to 63), and translocation factor (up to 25). With an exception of FeAsO4 and AlAsO4, which had the lowest effects due to their low solubility, little difference was observed among other arsenic forms mainly because of arsenic conversion in soil. Aboveground biomass was mostly responsible for accumulation of arsenic by plant (75-99%). Up to 26% of the added arsenic was removed by ladder brake, showing the high efficiency of ladder brake in arsenic removal. The results suggest that ladder brake may be a good candidate to remediate arsenic-contaminated soils.

Arsenic species in an arsenic hyperaccumulating fern, Pityrogramma calomelanos: a potential phytoremediator of arsenic-contaminated soils.

The fern Pityrogramma calomelanos is a hyperaccumulator of arsenic that grows readily on arsenic-contaminated soils in the Ron Phibun district of southern Thailand. P. calomelanos accumulates arsenic mostly in the fronds (up to 8350 microg As g(-1) dry mass) while the rhizoids contain the lowest concentrations of arsenic (88-310 microg As g(-1) dry mass). The arsenic species in aqueous extracts of the fern and soil were determined by high performance liquid chromatography coupled to an inductively coupled plasma mass spectrometer (HPLC-ICPMS) which served as an arsenic specific detector. Only a small part of the arsenic (6.1-12%) in soil was extracted into water, and most of this arsenic (> 97%) was present as arsenate. The arsenic in the fern rhizoids was approximately 60% water-extractable, 95% of which was present as arsenate. In contrast, arsenic in the fern fronds was readily extracted into water (86-93%) and was present mainly as arsenite (60-72%) with the remainder being arsenate. Methylarsonate and dimethylarsinate were detected as trace constituents in only two fern samples. Preliminary estimates of phytoremediation potential suggest that P. calomelanos might remove approximately 2% of the soil arsenic load per year. With due consideration to the type of arsenic compounds present in the fern, and their water-solubility, the option of disposing high arsenic ferns at sea is raised for discussion.

Effects of Arsenic Concentrations and Forms on Arsenic Uptake by the Hyperaccumulator Ladder Brake

Ladder brake (Pteris vittata L.) is a newly discovered arsenic hyperaccumulator. No information is available about arsenic effects on ladder brake. This study determined the effects of different arsenic concentrations (50 to 1000 mg kg−1) or forms (organic vs. inorganic and arsenite vs. arsenate) applied to soils on growth and arsenic uptake by ladder brake. Young plants were grown in a greenhouse for 12 or 18 wk. Ladder brake was highly tolerant of arsenic and survived in soil containing up to 500 mg As kg−1 The fact that addition of arsenate up to 100 mg As kg−1 increased fern biomass by 64 to 107%, coupled with higher arsenic concentration in younger fronds at low soil arsenic concentrations and older fronds at high soil arsenic concentrations, implies that arsenic may be beneficial for fern growth. Addition of 50 mg As kg−1 was best for fern growth and arsenic accumulation, resulting in the highest fern biomass (3.9 g plant−1), bioconcentration factor (up to 63), and translocation factor (up to 25). With an exception of FeAsO4 and AlAsO4, which had the lowest effects due to their low solubility, little difference was observed among other arsenic forms mainly because of arsenic conversion in soil. Aboveground biomass was mostly responsible for accumulation of arsenic by plant (75–99%). Up to 26% of the added arsenic was removed by ladder brake, showing the high efficiency of ladder brake in arsenic removal. The results suggest that ladder brake may be a good candidate to remediate arsenic-contaminated soils.

Effect of phosphorus on arsenic accumulation in As-hyper- accumulator Pteris vittata L. and its implication

Pot experiment was conducted to understand the effect of phosphorus on arsenic accumulation in As-hyperaccumulator Chinese brake (Pteris vittata L.). It is shown that arsenic concentrations in the fronds and rhizoids, the arsenic bioaccumulation factor, and the total arsenic in the fronds were not influenced significantly under low levels of phosphorus (≤400 mg/kg) and increased sharply under high levels of phosphorus (>400 mg/ kg). The discovery implies that the efficiency of arsenic removal in phytoremediation using the hyperaccumulating plant can be greatly elevated by the phosphorus addition at high rates. The interaction between the accumulation of phosphorus and that of arsenic in plant was stimulated mutually. The result represents that Chinese brake is a good material for plant physiologist to conduct comparative and mechanism studies on the uptake behaviors of phosphorus and arsenic, and phosphorus is also a potential accelerator for phytoremediation of arsenic-contaminated soils.

Acid washing and stabilization of an artificial arsenic-contaminated soil

An acid-washing process was studied on a laboratory scale to extract the bulk of arsenic(V) from a highly contaminated Kuroboku soil (Andosol) so as to minimize the risk of arsenic to human health and the environment. The sorption and desorption behavior of arsenic in the soil suggested the possibility of arsenic leaching under acidic conditions. Artificially contaminated Kuroboku soil (2830 mg As/kg soil) was washed with different concentrations of hydrogen fluoride, phosphoric acid, sulfuric acid, hydrogen chloride, nitric acid, perchloric acid, hydrogen bromide, acetic acid, hydrogen peroxide, 3:1 hydrogen chloride–nitric acid, or 2:1 nitric acid–perchloric acid. Phosphoric acid proved to be most promising as an extractant, attaining 99.9% arsenic extraction at 9.4% acid concentration in 6 h. Sulfuric acid also attained high percentage extraction. The arsenic extraction by these acids reached equilibrium within 2 h. Elovich-type equation best described most of the kinetic data for dissolution of soil components as well as for extraction of arsenic. Dissolution of the soil components could be minimized by ceasing acid washing in 2 h. The acid-washed soil was further stabilized by the addition of lanthanum, cerium, and iron(III) salts or their oxides or hydroxides which form insoluble complex with arsenic. Both salts and oxides of lanthanum and cerium were effective in immobilizing arsenic in the soil attaining less than 0.01 mg/l As in the leaching test.

Phytoremediation of arsenic‐contaminated soil as affected by the chelating agent CDTA and different levels of soil pH

AbstractElevated levels of arsenic can pose a major threat to both human health and the environment. The phytoremediation of heavy metals from soil is emerging as a cost‐effective technology for the remediation of contaminated soils. The present greenhouse study was undertaken to identify plants capable of tolerating and accumulating high concentrations of arsenic. Asparagus fern and rye grass were found to tolerate and accumulate more than 1,100 ppm of arsenic in plant tissue. Arsenic uptake as affected by different levels of the chelating agent trans‐1, 2‐ cyclohexylenedinitrilotetraacetic acid (CDTA) and soil pH were also studied. The application of 5 mmol kg−1 of CDTA to arsenic‐contaminated medium loam field soil enhanced the accumulation of arsenic by the test plants. Under these conditions, plants accumulated up to 1,400 ppm of arsenic as compared to 950 ppm by the plants grown in soil containing 1,200 ppm of arsenic but without any amendment of the chelating agent. Plants grown in field soil of pH 5 containing 300 ppm of arsenic absorbed higher concentrations of arsenic than at other tested pH levels. Corresponding reductions in arsenic content of soil after plant harvests were observed. © 2001 John Wiley & Sons, Inc.

Extraction of arsenic in a synthetic arsenic-contaminated soil using phosphate

An environment-friendly and cost-effective extraction method has been studied for the removal of arsenic from contaminated soil. A yellow-brown forest soil was contaminated with arsenic(V) and used as a model soil. Among various potassium and sodium salts, potassium phosphate was most effective in extracting arsenic, attaining more than 40% extraction in the pH range of 6–8 with minimum damage to the soil properties. Exchange mechanism is proposed for the extraction of arsenic from soil by phosphate. Sequential extraction shows that phosphate is effective in extracting arsenic of Al- and Fe-bound forms. Arsenic of residual form was not extracted. Arsenic was efficiently extracted by phosphate solution of pH 6.0 at 300 mM phosphate concentration and at 40°C.

Treatment of Arsenic-Contaminated Soils. I: Soil Characterization

Industrial sites frequently have arsenic-contaminated soils as a result of repeated applications of arsenic herbicides. Four such sites were investigated to determine the suitability of cement-based solidification/stabilization (S/S) for in situ soil treatment. Arsenic concentrations ranged up to about 2,000 ppm in the soil, although leachability was relatively low. No toxicity characteristic leaching procedure leachates showed As concentrations as high as 5 mg/L. The low leachability appears to be due, at least in part, to iron present in the soil. Although soils with higher As concentrations generally showed greater leachability, a somewhat stronger relationship existed between the percentage of As in the soil that was leached and the iron concentration in the soil. Another factor working in favor of the success of S/S in the present cases is the sandy character of the soils with little clay or organic content. Thus, the quartz sand will serve as an aggregate and should not offer any interferences to cement hydration. A third favorable circumstance is afforded by the oxidizing character of the soils. The weathered arsenic present in the soils should be in the form of As(V), and arsenate salts present a wider range of possibilities for precipitation of insoluble arsenic species than arsenite salts. A significant variable with the potential to affect S/S is the soil moisture content, which varied greatly among the four sites due to differing water table depth.

Treatment of Arsenic-Contaminated Soils. II: Treatability Study and Remediation

Treatment of sandy soils contaminated with arsenic was investigated at a bench scale and carried through to remediation in the field. The initial treatability study looked at many combinations of cement binders and reagents. Salts of iron, barium, manganese, and magnesium were generally effective at reducing arsenic leachability. The most consistently low potential for leaching [toxicity characteristic leaching procedure (TCLP) and a modified version of the American Nuclear Society's ANS16.1] was observed when the soils were treated with a mixture of Type I portland cement and ferrous sulfate. For instance, the average of arsenic concentrations in TCLP leachates in many treated soil samples from four sites was 0.26 mg/L. Better protection against leaching was observed when the soil was pretreated with FeSO4⋅7H2O, then with portland cement. In addition to chemical containment, the mixture should prevent ground-water leaching by physical entrapment, because the permeabilities of the treated soils were in the range of 10−9–10−10 m/s. Scanning electron microscope micrographs showed a dense mass with minimal void space, and a combination of X-ray diffraction, thermal analysis, and solid-state nuclear magnetic resonance (NMR) spectroscopy indicated the formation of a normal hydrated cement matrix, with some excess ettringite being present due to the extra sulfate being added to the formulation. Results from the bench-scale treatability study were reproduced very faithfully in the field, with permeabilities and compressive strengths being similar to those observed in the laboratory and TCLP leachability being even lower than predicted by the laboratory study.

Assessment of arsenic contamination in soils and waters in some areas of Bangladesh

The soil samples and tubewell waters were collected from 25 locations representing five thanas of four districts of Bangladesh. The soils were collected from three depths viz. 0–15, 15–30 and 30–45 cm and tubewell waters were collected from same locations. The arsenic content of soils and waters were detected by Molybdenum blue method. The arsenic content in soils ranged from 1.27–56.68, 3.18–54.77, 1.27–50.95, 1.27–39.48 and 3.18–35.66 ppm in Chapainawabganj Sadar, Kustia Sadar, Bera, Ishurdi and Sarishabari thanas, respectively. Out of a total of 25 samples arsenic was detectable for 18 samples at 0–15 cm, 17 samples at 15–30 cm and 15 samples at 30–45 cm depth. One sample at 0–15 cm, 7 samples at 15–30 cm and 4 samples at 30–45 cm depth were found to be slightly contaminated. In tubewell water the arsenic content measured from Chapainawabganj Sadar, Kustia Sadar, Bera, Ishurdi and Sarishabari thanas were ranged 0.010–0.056, 0.010–0.071, 0.010–0.056, 0.010–0.056 and 0.025–0.071 ppm, respectively. Out of 25 water samples 17 contained variable amounts of arsenic where 6 sampling sites contained arsenic levels above 0.05 ppm, and these sites are Rajarampur of Chapainawabganj Sadar thana, Jordaha of Bera thana, Courtpara of Kustia Sadar thana, Nalgari of Ishurdi thana and Ijarapara of Sarisabari thana. Arsenic contained in soils was positively correlated with arsenic content in waters.

Reduction and coordination of arsenic in Indian mustard.

The bioaccumulation of arsenic by plants may provide a means of removing this element from contaminated soils and waters. However, to optimize this process it is important to understand the biological mechanisms involved. Using a combination of techniques, including x-ray absorption spectroscopy, we have established the biochemical fate of arsenic taken up by Indian mustard (Brassica juncea). After arsenate uptake by the roots, possibly via the phosphate transport mechanism, a small fraction is exported to the shoot via the xylem as the oxyanions arsenate and arsenite. Once in the shoot, the arsenic is stored as an As(III)-tris-thiolate complex. The majority of the arsenic remains in the roots as an As(III)-tris-thiolate complex, which is indistinguishable from that found in the shoots and from As(III)-tris-glutathione. The thiolate donors are thus probably either glutathione or phytochelatins. The addition of the dithiol arsenic chelator dimercaptosuccinate to the hydroponic culture medium caused a 5-fold-increased arsenic level in the leaves, although the total arsenic accumulation was only marginally increased. This suggests that the addition of dimercaptosuccinate to arsenic-contaminated soils may provide a way to promote arsenic bioaccumulation in plant shoots, a process that will be essential for the development of an efficient phytoremediation strategy for this element.

Determination of arsenic species in water, soils and plants.

Ion chromatographic separation coupled with ICP-MS was used to determine arsenic species in plant and soil extracts. A scheme for growth, harvesting, sample pre-treatment and analysis was developed for the arsenic species to enable determination. Preliminary results obtained with ten herb plants grown on arsenic-contaminated soil compared to non-contaminated soil show a heterogeneous pattern of accumulation rate, metabolization and detoxification mechanisms in monocots and dicots. Arsenite appears to be the major component in plants with good growth. Organic arsenic species were even detected at very low concentrations (< 150 microg kg(-1) (dry mass)).

Arsenic speciation in environmental samples of contaminated soil

A coupled method of high performance liquid chromatography and inductively coupled plasma mass spectrometry was used to determine arsenic compounds, such as arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine and arsenocholine in soils. The technique was successfully applied to analyse environmental samples from an arsenic-contaminated soil; arsenate was found to be the major component. Due to microbial activity, transformation from arsenate to arsenite, resulted in monomethylarsonic acid and dimethylarsinic acid also being present. The measurements showed that the transformations induced by microorganisms in the highly contaminated soil lead to a detoxification. It is thus possible to use microorganisms for phytoremediation of contaminated soils.

Arsenic Enrichment in the Soil of the Salek Valley, Slovenia

Arsenic is distributed rather uniformly in major types of rocks and its common contents in most rocks range from 0.5 to 2.5 p.g/g. Although arsenic minerals and compounds are readily soluble, arsenic migration is greatly limited due to the strong sorption by clays, hydroxides, and organic matter. Strongly adsorbed arsenic in soil is hardly to be desorbed again and generally the retention of arsenic by soil progressed with the years. Arsenic enrichment in agrillaceous sediments as well as in surface soils, as compared to contents in igneous rocks, apparently reflect also some external arsenic sources, such as pollution (Kabata&Pendias and Pendias, 1986). Significant anthropogenic sources of arsenic are related to industrial activities (coal combustion, pyrometallurgical non-ferrous metal production, steel and iron manufacturing, cement production, etc.) (Dobson et al., 1992), in agriculture the use of arsenical pesticides and arsenical sprays. Numerous studies have demonstrated significant arsenic contamination in soil, plants, and animals in the vicinity of combustion sources (Adriano, 1986). In the Salek valley, which is one of the most polluted areas in Slovenia, the coal-fired Sostanj Thermal Power Plant (TPP) is a large regional emission source of SO2, NOx, dust and trace elements. In the Salek valley several environmental pollution studies have been made in which the general effects of industrial activities were investigated. Estimation of soil contamination related to air pollution began recently in the Salek valley. In this work a study of arsenic enrichment in the soil of the Salek valley is presented with the aim of estimating the arsenic contents in three different types of soil in comparison to the background content.

Bioavailability and speciation of arsenic in carrots grown in contaminated soil.

Carrots were grown in seven experimental plots (A-G) containing mixtures of arsenic-contaminated and uncontaminated soil at concentrations ranging from 6.5 to 917 microgram g(-1) (dry mass). The carrots harvested from plots A-D (6.5-338 microgram g(-1) arsenic in the soil mixtures) showed a gradually increasing depression of growth with increasing level of contamination. At the experimental plots E-G with soil arsenic concentrations above 400 microgram g(-1) no carrots developed. Whether this effect was caused by arsenic or the concomitant copper content which ranged from 11 to 810 microgram g(-1) in the soil mixtures is unknown. The arsenic species extracted from the soils and carrots were separated and detected using anion-exchange HPLC coupled with ICP-MS. In the less contaminated soils from plots A and B arsenite (AsIII) was more abundant than arsenate (Asv) in the soil using 1 mmole 1-1 calcium nitrate as extractant. In the soils from plots C and D however, Asv dominated over AsIII whereas in the corresponding carrots Asv and AsIII were found at similar concentrations. Methylated arsenic species were sought after but not detected in any of the samples. The soil-to-carrot uptake rate (bioavailability) of arsenic was 0.47 +/- 0.06% (average +/- one standard deviation) of the arsenic content in the soils from plots A-D. In contrast to arsenic, the increasing copper content in the soils from plot A through D was not available to the carrots as the concentration of this element did not increase with increasing soil copper content. The ingestion of the potentially toxic inorganic arsenic via consumption of carrots grown in soil contaminated at 30 microgram g(-1) in arsenic (plot B) was conservatively estimated at 37 microgram week (-1). This was equivalent to only 4% of the provisional tolerable weekly intake (PTWI) for inorganic arsenic as suggested by the WHO and was therefore toxicologically safe. Consumption of carrots grown in more intensely arsenic-contaminated soils, however, would lead to a higher intake of inorganic arsenic and is therefore not recommended.

Partitioning of Arsenic Species in Fine-Grained Soils

It has been theoretically and experimentally shown that rate-limited sorption/desorption can have a profound effect upon the transport of sorbing contaminants. The advection/dis-persion equation that has been traditionally used to model contaminant transport uses a retardation factor to account for sorption, thereby implicitly assuming local equilibrium between contaminant in the sorbed and aqueous phases. This assumption fails to consider the possibly large effects of rate-limited sorption/desorption. The mass release characteristic of arsenic-contaminated soils at the Crystal Chemical site in Houston, TX, was examined. Soils were collected from beneath two former waste-water ponds that were the source of arsenic in the uppermost aquifer. Samples were typical of those found within the fine-grained components of local alluvial overbank deposits that comprise the bulk of the site. The dynamic test applied a continuing head of water, operating in an upflow mode, through 4-inch-diameter by 12-inch-long soil columns repacked to in-situ density. Three columns were constructed The mass release characteristic of arsenic-contaminated soils at the Crystal Chemical site in Houston, TX, was examined. Soils were collected from beneath two former waste-water ponds that were the source of arsenic in the uppermost aquifer. Samples were typical of those found within the fine-grained components of local alluvial overbank deposits that comprise the bulk of the site. The dynamic test applied a continuing head of water, operating in an upflow mode, through 4-inch-diameter by 12-inch-long soil columns repacked to in-situ density. Three columns were constructed— two containing predominantly clay, and the other containing clayey silt. Leachate from the most permeable column was collected over 42 pore volumes (equivalent to 120 years of extraction). Sharp declines in arsenic concentrations in the leachate were measured after just four pore volumes. A biphasic response was evident, consistent with published research on kinetically limited mass transfer of retarding solutes. The most responsive column was pulsed to elucidate the effects of diffusion and pulsed pumpingtwo containing predominantly clay, and the other containing clayey silt. Leachate from the most permeable column was collected over 42 pore volumes (equivalent to 120 years of extraction). Sharp declines in arsenic concentrations in the leachate were measured after just four pore volumes. A biphasic response was evident, consistent with published research on kinetically limited mass transfer of retarding solutes. The most responsive column was pulsed to elucidate the effects of diffusion and pulsed pumping. Arsenic concentrations returned to baseline levels in less than three pore volumes. These studies ultimately led to a joint assessment between Southern Pacific Lines (SPL) and EPA Region VI, which concluded that extraction and treatment of the shallow aquifer beneath the site was not feasible, in light of the aggressive restoration goal.

Chemical fixation of arsenic in contaminated soils

Arsenic-contaminated soils have been successfully treated using fixation methods whereby chemicals are added to prevent As mobilization. However, the chemistry of the fixation process used in the field is poorly understood. We have examined one process which succeeded in immobilizing 0. I to 0.2 weight % As in soil at a 69 a old dump site through the addition of ferrous sulfate and water followed by Ca(OH) 2, Portland cement and water. The intent of the first step is to form insoluble Fe arsenate, the second to bind the soil. The particle-size distribution of the untreated soil grains containing As is bimodal, with 70% of the As occurring in 2 size fractions: 38% in the 0.25–0.5 mm fraction mostly as the mineral hoernesite (Mg 3(ASO 4) 2 · 8H 2O), and 32% in the size fraction less than 5 pm. From sequential extractions, As in the finest fraction is inferred to be present in an oxyanionic form adsorbed on mineral surfaces. Arsenic may also be associated with Fe or Mn oxide coatings, and may be present as fine grains of hoernesite. Hoernesite, which we infer formed because of the brackish nature of the ground water at this site, represents an example of natural fixation of As. Arsenic is more evenly distributed among grain size fractions in the field-fixed soils. Using X-ray diffraction, electron microscopy, and chemical analysis, we find no direct evidence for the formation of Fe arsenate phases in the fixed soils. Sequential extractions demonstrate that the fixation method reduces exchangeable As in the < 5 μm fraction even when only Fe sulfate is added. While fixation occurs by reaction with FeSO 4, it is unlikely that ferric arsenate forms as an insoluble phase under these conditions, as is generally assumed. Arsenic fixation occurs through precipitation of an unknown As Fe phase or by incorporation during Fe oxide precipitation aided by immobilization by a cement coating.

In situ treatment of arsenic contaminated soil from a hazardous industrial site: Laboratory studies

Some industrial sites have contaminated surface soils with arsenic (As) concentrations significantly above those that can be stabilized through natural soil mechanisms. A review of the chemistry of arsenic in the soil environment indicates that is possible to stabilized this element by reacting it with amorphous iron oxides. The addition of ferrous sulfate proved to be effective in reducing water-soluble As and its leachability in arsenic-contaminated soil from a pesticide manufacturing industrial site. Soil samples containing up to 4.2% total As, and more than 2.5 g L −1 water soluble and readily leachable As, had these As forms significantly reduced after just three 24-hour wet-dry cycles. The efficiency and potential reversibility of this treatment under extreme field conditions remains to be tested.

Arsenic Distribution in Soils Surrounding the Utah Copper Smelter

We investigated the extent of arsenic contamination from a Utah copper smelter as reflected by arsenic residue accumulated in the surface soil. The highest arsenic concentrations occurred within 3 km of the smelter. Arsenic soil contamination was evident up to 10 km from the smelter, with the major transport direction being ESE. Data from the subsurface soil samples indicated that arsenic has also leached through the soil.