Arsenic speciation in arsenic-rich Brazilian soils from gold mining sites under anaerobic incubation

BACKGROUND: Arsenic speciation in environmental samples is essential for studying toxicity, mobility and bio-transformation of As in aquatic and terrestrial environments. Although the inorganic species As(III) and As(V) have been considered dominant in soils and sediments, organisms are able to metabolize inorganic forms of arsenic into organo-arsenic compounds. Arsenosugars and methylated As compounds can be found in terrestrial organisms, but they generally occur only as minor constituents. We investigated the dynamics of arsenic species under anaerobic conditions in soils surrounding gold mining areas from Minas Gerais State, Brazil to elucidate the arsenic biogeochemical cycle and water contamination mechanisms. METHODS: Surface soil samples were collected at those sites, namely Paracatu Formation, Banded Iron Formation and Riacho dos Machados Sequence, and incubated in CaCl2 2.5 mmol L(-1) suspensions under anaerobic conditions for 1, 28, 56 and 112 days. After that, suspensions were centrifuged and supernatants analyzed for soluble As species by IC-ICPMS and HPLC-ICPMS. RESULTS: Easily exchangeable As was mainly arsenite, except when reducible manganese was present. Arsenate was mainly responsible for the increase in soluble arsenic due to the reductive dissolution of either iron or manganese in samples from the Paracatu Formation and Riacho dos Machados Sequence. On the other hand, organic species of As dominated in samples from the Banded Iron Formation during anaerobic incubation. DISCUSSION: Results are contrary to the expectation that, in anaerobic environments, As release due to the reductive dissolution of Fe is followed by As(V) reduction to As(III). The occurrence of organo-arsenic species was also found to be significant to the dynamics of soluble arsenic, mainly in soils from the Banded Iron Formation (BIF), under our experimental conditions. CONCLUSIONS: In general, As(V) and organic As were the dominant species in solution, which is surprising under anaerobic conditions in terrestrial environments. The unexpected occurrence of organic species of As was attributed to enrollment of ternary organic complexes or living organisms such as algae or cyanobacteria. PERSPECTIVES: These findings are believed to be useful for remediation strategies in mine-affected regions, as the organic As species are in general considered to be less toxic than inorganic ones and even As(V) is considered less mobile and toxic than As(III).     

Arsenic speciation in field-collected and laboratory-exposed earthworms Lumbricus terrestris

Mature Lumbricus terrestris were host soils and leaf litter were collected from a former arsenic mine in Devon, UK (Devon Great Consols), a former gold mine in Ontario, Canada (Deloro), and an uncontaminated residential garden in Nottingham, UK. Arsenic concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) in soils were 16-348 mg kg⁻¹, 6.0-239 mg kg⁻¹ in the earthworms and 8.6 mg kg⁻¹ in leaf litter sampled at Deloro (all dry weight). High performance liquid chromatography (HPLC-ICP-MS) analysis revealed arsenite (As^III), arsenate (As^V) and five organoarsenic species; arsenobetaine (AB), methylarsonate (MA^V), dimethylarsinate (DMA^V), arsenosugar 1 (glycerol sugar), arsenosugar 2 (phosphate sugar), and trimethylarsineoxide (TMAO) in field-collected L. terrestris. Differences were observed in the variety of organoarsenic species present between field sites. Several organoarsenic species were observed in the leaf litter (DMA^V, arsenosugar 2 and TMAO) but not AB. Depuration resulted in higher concentrations of inorganic As being detected in the earthworm whereas the concentration or variety of organoarsenic species was unchanged. Commercially sourced L. terrestris were exposed to As contaminated soil in laboratory mesocosms (1.0, 98, 183, 236, 324 and 436 mg kg⁻¹) without leaf litter and were additionally analyzed using X-ray absorption near edge structure (XANES). Only inorganic As^III and As^V was observed. It is proposed that ingestion of leaf litter and symbiotic processes in the natural soil environment are likely sources of organoarsenic compounds in field-collected L. terrestris.     

Arsenic and chromium speciation in an urban contaminated soil

The distribution and speciation of As and Cr in a contaminated soil were studied by synchrotron-based X-ray microfluorescence (μ-XRF), microfocused X-ray absorption spectroscopy (μ-XAS), and bulk extended X-ray absorption fine structure spectroscopy (EXAFS). The soil was taken from a park in Wilmington, DE, which had been an important center for the leather tanning industry along the Atlantic seaboard of the United States, until the early 20th century. Soil concentrations of As, Cr, and Pb measured at certain locations in the park greatly exceeded the background levels of these heavy metals in the State of Delaware. Results show that Cr(III) and As(V) species are mainly present in the soil, with insignificant amounts of Cr(VI) and As(III). Micro-XRF maps show that Cr and Fe are distributed together in regions where their concentrations are diffuse, and at local spots where their concentrations are high. Iron oxides, which can reduce Cr(VI) to Cr(III), are present at some of these hot spots where Cr and Fe are highly concentrated. Arsenic is mainly associated with Al in the soil, and to a minor extent with Fe. Arsenate may be sorbed to aluminum oxides, which might have transformed after a long period of time into an As-Al precipitate phase, having a structure and chemical composition similar to mansfieldite (AlAsO(4)?2H(2)O). The latter hypothesis is supported by the fact that only a small amount of As present in the soil was desorbed using the characteristic toxicity leaching procedure tests. This suggests that As is immobilized in the soil.     

Arsenic leachability and speciation in cement immobilized water treatment sludge

Arsenic leachability and speciation in cement immobilized water treatment sludge were investigated with leaching tests and X-ray absorption near edge structure (XANES) spectroscopy. The As leachability in the sludge determined with the toxicity characteristic leaching procedure (TCLP) and the waste extraction test (WET) was 283 and 7490 microgl(-1), respectively. Extractions with a lower liquid to solid ratio, under anaerobic conditions, and using citric acid buffer solution dramatically increased the leachate As concentration. XANES results showed that the As(III) composition was reduced from 51.1% of the total As content in the sludge to 16.3% in the cement treated sample with 28 days of cure. When the cement treated sample was cured for two years, the As(III) composition was decreased to 7.4%. The cement treatment reduced the As leachability. The leachate As(III) and total As concentrations were of the same order of magnitude in the samples cured for 28 days as for 2yr. However, consistently lower concentrations were detected in samples with longer cure time. The results of this study improve our understanding of arsenic speciation and leachability in the cement matrix after long cure times.     

Arsenic speciation in marine fish and shellfish from American Samoa

We speciated arsenic compounds in marine fish and shellfish from two islands of the United States Territory of American Samoa in the South Pacific, and found that inorganic arsenic occurred as a minor fraction. The proportion of inorganic arsenic was generally far below the levels of prevailing assumptions typically used in human health risk assessments when only total arsenic is analysed. Fish and shellfish were collected from Tutuila and Ofu between May 2001 and March 2002 (n=383 individual specimens, with 117 composites); sites were selected based on habitat type and were representative of those frequented by local fishers. These islands have moderately developed reef fish fisheries among artisanal fishers, are far removed from any industrial or mining sources of arsenic, and presented an opportunity to study arsenic variations in marine biota from un-impacted environments. Target species were from various trophic levels and are among those frequently harvested for human consumption. We found evidence that arsenic concentrated in some marine species, but did not tend to follow classic trophic patterns for biomagnification or bioaccumulation. For the majority of samples, inorganic arsenic was less than 0.5% of total arsenic, with only a few samples in the range of 1-5%, the latter being mollusks which are recognized to have unusually high arsenic levels in general. This work supports the importance of speciation analysis for arsenic, because of the ubiquitous occurrence of arsenic in the environment, and its variable toxicity depending on chemical form.     

Arsenic speciation and accumulation in evapoconcentrating waters of agricultural evaporation basins

To sustain agricultural productivity, evaporation basins (or ponds) have been widely used for the disposal of agricultural drainage in areas requiring subsurface drainage in the San Joaquin Valley of California, USA. The drainage water contains elevated concentration of trace elements including selenium (Se) and arsenic (As). Unlike Se, little information is available about As, a potentially high risk element. The objective of this study was to characterize the chemical behavior of As and acquire data for better understanding of biogeochemical processes and conditions affecting As fate in evaporation ponds. The study site was a 726 ha evaporation basin facility (containing 10 cells with water flowing in series) in the hydrologically closed Tulare Basin of California. We examined water chemistry, As concentration and speciation along the water flow path between cells as well as within the cells. Arsenic concentrations in the water increased linearly with Cl(-), a conservative ion from evapoconcentration. Reduced As species as arsenite [As(III)] and organic arsenic (org-As) also increased with increases in Cl(-) and salinity. Water samples with elevated EC (i.e., towards the end of flow path) had high dissolved organic matter, low dissolved oxygen, and elevated sulfide concentrations, indicating the development of reducing conditions. We hypothesize that such changes could facilitate the reduction of arsenate [As(V)] to As(III) and org-As. Elevated As in sediment profiles indicate a solid phase sink mechanism, but not significant enough to remove and reduce As concentrations in the water columns. These findings help us better define the processes that affect As in drainage facilities and contribute to our understanding of how As behaves in other regions of the world that have similar climatic and hydrogeochemical conditions.     

Arsenic accumulation and speciation in the submerged macrophyte Ceratophyllum demersum L.

Introduction

Ceratophyllum demersum L. is a widespread submerged macrophyte in aquatic environments.

Methods

Simulation experiments were conducted in the laboratory to investigate arsenic (As) accumulation, speciation, and efflux of C. demersum exposed to arsenate and arsenite solutions.

Results

Plant shoots showed a significant accumulation of As with a maximum of 862 and 963???g?As?g^?1 dry weight after 4?days of exposure to 10???M arsenate and arsenite, respectively. Regardless of whether arsenate or arsenite was supplied to the plants, arsenite was the predominant species in plant shoots. Furthermore, a dramatically higher influx rate of arsenate compared with arsenite was observed in C. demersum exposed to As solutions without the addition of phosphate (P). Arsenate uptake was considerably inhibited by P in this study, suggesting that arsenate is taken up by C. demersum via the phosphate transporters. However, arsenite uptake was unaffected by P and markedly reduced in the presence of glycerol and antimonite (Sb), indicating arsenite shares the aquaporin transport pathway. In addition, C. demersum rapidly reduces arsenate to arsenite in the shoot of the plant and extrudes most of them (>60?%) to the external solutions. The efflux of arsenite was much higher than that of arsenate; the former is supposed to be both active and passive processes, and the latter through passive leakage.

Conclusion

C. demersum is a strong As accumulator and an interesting model plant to study As uptake and metabolism due to the lack of a root-to-shoot translocation barrier.     

Effect of applying persulfate on the accumulation of arsenic in rice plants grown in arsenic-contaminated paddy soil

Environmental Science and Pollution Research - Arsenic is known to be a notorious human carcinogen and rice consumption is becoming the primary human exposure route for As, especially in many Asian...     

Comparison of multi-criteria analysis methodologies for the prioritization of arsenic-contaminated sites in the southwest of China

The issue of contaminated sites has been highlighted as an immediate priority in the 13th Five-Year Plan of China. Identification and prioritization of contaminated sites are of key importance for proposing effective strategies for the regional management of contaminated sites. In this study, three advanced multi-attribute methodologies, the risk-based priority methodology, the regional risk assessment methodology, and the dominance-based rough set approach (DRSA), were comparatively employed to screen contaminated sites in, Guangxi, Southwest of China. The results of the three prioritizations show that the highest ranking site identified by the three methods had great agreement. In regard to the screening attributers, while the risk-based prioritization methodology and regional risk assessment methodology allowed a high discrimination in the screening of contaminated sites associated with different attributes, such as farmland, residential areas, contaminant level, number of people, area, storage quality, site service life, and surrounding communities, the DRSA allowed the identification of contamination strength (CS) and contamination potential (CP).

     

Arsenic toxicity and accumulation in radish as affected by arsenic chemical speciation.

Arsenic (As) uptake by Rhapanus sativus L. (radish), cv. Nueva Orleans, growing in soil-less culture conditions was studied in relation to the chemical form and concentration of As. A 4 x 3 factorial experiment was conducted with treatments consisting of four As chemical forms [As(III), As(V), MMAA, DMAA] and three As concentrations (1.0, 2.0, and 5.0 mg As L-1). None of the As treatments were clearly phytotoxic to this radish cultivar. Arsenic phytoavailability was primarily determined by the As chemical form present in the nutrient solution and followed the trend DMAA < or = As(V) < or = As(III) < MMAA. Root and shoot As concentrations significantly increased with increasing As application rates. Monomethyl arsonic acid treatments caused the highest As accumulation in both roots and shoots, and this organic arsenical showed a higher uptake rate than the other As compounds. Inner root As concentrations were, in general, within the normal range for As contents in food crops but root skin As levels were close or above the maximum threshold set for As content in edible fruit, crops and vegetables. The statement that toxicity limits plant As uptake to safe levels was not confirmed in our study. If radish plants are exposed to a large pulse of As, as growth on contaminated nutrient solutions, they may accumulate residues which are unacceptable for animal and human consumption without exhibiting symptoms of phytotoxicity.     

Effect of arsenic-contaminated irrigation water on agricultural land soil and plants in West Bengal, India

Total arsenic withdrawn by the four shallow tubewells, used for agricultural irrigation in the arsenic-affected areas of Murshidabad district per year is 6.79 kg (mean: 1.79 kg, range: 0.56-3.53 kg) and the mean arsenic deposition on land per year is 5.02 kg ha(-1) (range: 2-9.81 kg ha(-1)). Mean soil arsenic concentrations in surface, root of plants, below ground level (0-30 cm) and all the soils, collected from four agricultural lands are 14.2 mg/kg (range: 9.5-19.4 mg/kg, n = 99), 13.7 mg/kg (range: 7.56-20.7 mg/kg, n = 99), 14.8 mg/kg (range: 8.69-21 mg/kg, n = 102) and 14.2 mg/kg (range: 7.56-21 mg/kg, n = 300) respectively. Higher the arsenic in groundwater, higher the arsenic in agricultural land soil and plants has been observed. Mean arsenic concentrations in root, stem, leaf and all parts of plants are 996 ng/g (range: <0.04-4850 ng/g, n = 99), 297 ng/g (range: <0.04-2900 ng/g, n = 99), 246 ng/g (range: <0.04-1600 ng/g, n = 99) and 513 ng/g (range: <0.04-4850 ng/g, n = 297) respectively. Approximately 3.1-13.1, 0.54-4.08 and 0.36-3.45% of arsenic is taken up by the root, stem and leaf respectively, from the soil.     

修复植物热解半焦中重金属形态分布研究

采用欧盟标准物质局(BCR)连续提取法对修复植物长香谷稻秆热解半焦中重金属元素Cd、Pb、Mn和Cu的赋存形态进行研究.结果表明:(1)用BCR连续提取法分析修复植物热解半焦中Cd、Pb、Mn和Cu的赋存形态是可行和有效的.(2)半焦中Pb,Mn和Cu在900℃时的不稳定态比400℃时分别降低了50.8、38.0、28...     

Elemental composition of Marrubium astracanicum Jacq. growing in tungsten-contaminated sites

Environmental Science and Pollution Research - This study evaluates the elemental (W, Mo, Zn, Fe, Cu, Cd, Mn, Pb, Cr, Co, B, and Bi) composition of Marrubium astracanicum Jacq. (Lamiaceae), around...     

Source apportionment of PM2.5 at two Seattle chemical speciation sites

ABSTRACT

Positive Matrix Factorization analysis of PM_2.5 chemical speciation data collected from 2015–2017 at Washington State Department of Ecology’s urban NCore (Beacon Hill) and near-road (10th and Weller) sites found similar PM_2.5 sources at both sites. Identified factors were associated with gasoline exhaust, diesel exhaust, aged and fresh sea salt, crustal, nitrate-rich, sulfur-rich, unidentified urban, zinc-rich, residual fuel oil, and wood smoke. Factors associated with vehicle emissions were the highest contributing sources at both sites. Gasoline exhaust emissions comprised 26% and 21% of identified sources at Beacon Hill and 10th and Weller, respectively. Diesel exhaust emissions comprised 29% of identified sources at 10th and Weller but only 3% of identified sources at Beacon Hill. Correlation of the diesel exhaust factor with measured concentrations of black carbon and nitrogen oxides at 10th and Weller suggests a method to predict PM_2.5 from diesel exhaust without a full chemical speciation analysis. While most PM_2.5 sources exhibit minimal change over time, primary PM_2.5 from gasoline emissions is increasing on average 0.18 µg m^?3 per year in Seattle.     

工业污染场地土壤中汞的化学形态及其环境限值探讨

汞是中国工业污染场地土壤中常见的重金属污染物,汞的常见形态包括单质汞、无机汞和甲基汞。比较了不同形态的汞及其化合物在物化性质、环境行为、毒性效应及致毒机制上的差异,还以美国、英国为例,探讨了针对不同形态的汞分别制定土壤环境限值的方法。最后指出,中国现有的土壤环境质量相关标准以及污染场地风险评估导则中均尚未区分汞的形态,仅给出总汞含量的限值。因此,在未来的相关标准制定中,应考虑按汞的各种形态制定不同的标准,这将更有利于客观准确评价工业污染场地土壤中汞的污染程度和环境风险。     

Heavy metal accumulation in trees growing on contaminated sites in Central Europe

Metal-accumulating woody species have been considered for phytoextraction of metal-contaminated sites. We investigated Zn and Cd accumulation in tissues of adult trees and associated herbaceous species collected from contaminated areas in Central Europe. We found considerable Cd and Zn accumulation in various willow, poplar and birch species with up to 116mgCdkg(-1) and 4680mgZnkg(-1) in leaves of Salix caprea. Annual variation of Cd and Zn concentrations in leaves of Salix caprea were small, indicating that data obtained in different years can be compared. Metal concentrations in leaves were not related to total (aqua regia) or labile (1M NH(4)NO(3) extract) concentrations in soil but the accumulation factors (leaf concentration: soil concentration) for Cd and Zn followed an inverse log type function. Metal partitioning between tissues showed a minimum in the wood, with increasing concentrations of Cd and Zn towards the leaves and fine roots.     

矿化垃圾混配种植介质的盆栽实验研究

矿化垃圾营养成分和有机质含量较高,但含有重金属和盐分.为了解矿化垃圾的施加比例对植物的生长影响以及植物对矿化垃圾混配种植介质中营养成分的吸收和重金属的富集,将矿化垃圾和本地绿化土按照不同比例混配,研究混配种植介质的理化性质的改善条件、矿化垃圾对植物体内的生物量和叶绿素含量的影响、植物对混配种植介质中营养成分的吸收量以及植物体内各种重金属累积浓度,探索矿化垃圾的最佳施用比例.实验结果表明,矿化垃圾可改善上海本地土壤贫瘠的普遍状况,其添加质量分数在50%～75%合适,对植物生长有利.     

Arsenic contamination of soils and agricultural plants through irrigation water in Nepal

This study monitored the influence of arsenic-contaminated irrigation water on alkaline soils and arsenic uptake in agricultural plants at field level. The arsenic concentrations in irrigation water ranges from <0.005 to 1.014 mg L(-1) where the arsenic concentrations in the soils were measured from 6.1 to 16.7 mg As kg(-1). The arsenic content in different parts of plants are found in the order of roots>shoots>leaves>edible parts. The mean arsenic content of edible plant material (dry weight) were found in the order of onion leaves (0.55 mg As kg(-1))>onion bulb (0.45 mg As kg(-1))>cauliflower (0.33 mg As kg(-1))>rice (0.18 mg As kg(-1))>brinjal (0.09 mg As kg(-1))>potato (<0.01 mg As kg(-1)).     

Arsenic speciation of atmospheric particulate matter (PM10) in an industrialised urban site in southwestern Spain

An arsenic speciation study has been performed in PM10 samples collected on a fortnight basis in the city of Huelva (SW Spain) during 2001 and 2002. The arsenic species were extracted from the PM10 filters using a NH2OH x HCl solution and sonication, and determined by HPLC-HG-AFS. The mean bulk As concentration of the samples analyzed during 2001 and 2002 slightly exceed the mean annual 6 ng m(-3) target value proposed by the European Commission for 2013, arsenate [As(V)] being responsible for the high level of arsenic. The speciation analyses showed that As(V) was the main arsenic species found, followed by arsenite [As(III)] (mean 6.5 and 7.8 ng m(-3) for As(V), mean 1.2 and 2.1 ng m(-3) for As(III), in 2001 and 2002, respectively). The high levels of arsenic species found in PM10 in Huelva have a predominant industrial origin, such as the one from a nearby copper smelter, and do not present a seasonal pattern. The highest daily levels of arsenic species correspond to synoptic conditions in which the winds with S and SW components transport the contaminants from the main emission source. The frequent African dust outbreaks over Huelva may result in an increment of mass levels of PM10, but do not represent a significant input of arsenic in comparison to the anthropogenic source. The rural background levels of arsenic around Huelva are rather high, in comparison to other rural or urban areas in Spain, showing a relatively high atmosphere residence time of arsenic. This work shows the importance of arsenic speciation in studies of aerosol chemistry, due to the presence of arsenic species [As(III) and As(V)] with distinct toxicity.     

Arsenic distribution in soils and plants of an arsenic impacted former mining area

A mining area affected by the abandoned exploitation of an arsenical tungsten deposit was studied in order to assess its arsenic pollution level and the feasibility of native plants for being used in phytoremediation approaches. Soil and plant samples were collected at different distances from the polluting sources and analysed for their As content and distribution. Critical soil total concentrations of As were found, with values in the range 70-5330 mg kg⁻¹ in the uppermost layer. The plant community develops As tolerance by exclusion strategies. Of the plant species growing in the most polluted site, the shrubs Salix atrocinerea Brot. and Genista scorpius (L.) DC. exhibit the lowest bioaccumulation factor (BF) values for their aerial parts, suggesting their suitability to be used with revegetation purposes. The species Scirpus holoschoenus L. highlights for its important potential to stabilise As at root level, accumulating As contents up to 3164 mg kg⁻¹.