Earthworms and in vitro physiologically-based extraction tests: complementary tools for a holistic approach towards understanding risk at arsenic-contaminated sites

The relationship of the total arsenic content of a soil and its bioaccumulation by earthworms (Lumbricus rubellus and Dendrodrilus rubidus) to the arsenic fraction bioaccessible to humans, measured using an in vitro physiologically-based extraction test (PBET), was investigated. Soil and earthworm samples were collected at 24 sites at the former arsenic mine at the Devon Great Consols (DGC) in southwest England (UK), along with an uncontaminated site in Nottingham, UK, for comparison. Analysis of soil and earthworm total arsenic via inductively coupled plasma mass spectrometry (ICP-MS) was performed following a mixed acid digestion. Arsenic concentrations in the soil were elevated (204–9,025 mg kg⁻¹) at DGC. The arsenic bioaccumulation factor (BAF) for both earthworm species was found to correlate positively with the human bioaccessible fraction (HBF), although the correlation was only significant (P ≤ 0.05) for L. rubellus. The potential use of both in vitro PBETs and earthworms as complementary tools is explored as a holistic and multidisciplinary approach towards understanding risk at contaminated sites. Arsenic resistant earthworm species such as the L. rubellus populations at DGC are presented as a valuable tool for understanding risk at highly contaminated sites.     

Sediment geochemistry and arsenic mobilization in shallow aquifers of the Datong basin,northern China

Understanding the mechanism of arsenic (As) mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning, such as the Datong basin in northern China. The bulk geochemistry analysis of sediment samples from three 50-m boreholes drilled specifically for this study at As-contaminated aquifers, the groundwaters of which have an As concentration up to 1060 μg/l, revealed that the average bulk concentrations of major and trace elements of the samples are similar to those of the average upper continental crust. The average As content of the sediment samples (18.7 mg/kg) is higher than that of modern unconsolidated sediments (5–10 mg/kg). Moreover, the abundance of elements varied with grain size, with higher concentrations in finer fractions of the sediments, such as silt and clay. The concentration of NH₂OH–HCl-extracted iron (Fe) strongly correlated with that of extracted As, suggesting that Fe oxyhydroxides may be the major sink of As in the aquifer. The results of microcosm experiments showed that As mobilization from sediments to groundwater is probably mainly related to changes in the redox conditions, with moderately reducing conditions being favorable for As release from sediments into groundwater.     

土壤中重金属[S,S]-乙二胺二琥珀酸浸提及其对重金属形态分布的影响

采用螯合剂[S,S]-乙二胺二琥珀酸([S,S]-EDDS)对废弃矿区附近的农田土壤进行浸提,分析浸提前后残留土壤样品中重金属的形态.结果表明,[S,S]-EDDS对重金属元素的提取率在不同土壤之间有较大差异,对Cu的浸提率为13.4%-13.8%,对Pb的浸提率为2.28%-16.3%,对Zn的浸提率为2.73%-11.3%.[S,S]-EDDS在提取重金属的同时也造成了Fe和Mn的明显溶出,其中Fe的溶出率为0.090%-0.291%,Mn的溶出率为2.53%-6.31%,均远高于对照组.[S,S]-EDDS浸提后酸溶/可交换态金属含量的变化倚赖于金属种类,对于Cu和Zn,经[S,S]-EDDS浸提之后,其酸溶/可交换态含量远低于对照组;但对于Pb,经[S,S]-EDDS浸提之后,酸溶/可交换态含量略高于对照组.[S,S]-EDDS对Cu和Zn四种形态均有浸提作用,且对残渣态的影响小于其它形态.[S,S]-EDDS浸提导致土样中Cu和Zn残渣态比例上升,其它形态比例的变化则依赖于金属的种类以及土壤性质.     

土壤酸度对稀土元素在小麦体内的生物可利用性及分馏效应的影响

采用盆栽实验,研究了土壤酸度对稀土元素在小麦体内的生物可利用性及分馏效应的影响.结果表明:小麦体内稀土含量与pH之间呈二次方程的关系,在实验pH范围内,随pH值升高小麦体内稀土含量逐渐降低,每种稀土含量随pH变化程度表现为:Ce>La>Nd>Sm>Gd>Yb>Tb>Eu,表明Ce对pH值更为敏感,Eu最小.土壤中3种稀土形态的含量顺序为B2(NH₂OHHCl提取态)>B3(H₂O₂-NH₄Ac提取态)>B1(HAc提取态),随着酸度的降低,B1有向B2、B3转化的趋势.线性回归和多元逐步回归分析表明不同形态的稀土对小麦吸收的贡献程度因单个稀土元素的不同而不同,但B1态是主要的生物可利用态.小麦体内轻重稀土之间分馏系数与pH值呈负线性相关,土壤酸度越大,分馏系数越大.     

Differentiation in low molecular weight organic acids exudation into rhizosphere and their creation in Ulmus laevis Pall organs treated by As – pot experiment

Two-year old Ulmus laevis Pall (U. laevis) seedlings were cultivated in a three-month hydroponic experiment with inorganic (aresenite – As(III) and arsenate – As(V)) and organic (dimethylarsenic acid – DMA(V)) arsenic forms, at 0.06 and/or 0.6?mM concentrations. Further, the profile and content of total low molecular weight organic acids (LMWOAs) were investigated in the rhizosphere, roots and leaves of U. laevis. Obtained results showed that the addition of As(III) or As(V) individually or in a mixture led to increased LMWOAs concentration in the rhizosphere, especially of oxalic and malonic acids, in comparison to the control, while in roots the overall content of the profiled LMWOAs decreased. In both rhizosphere and roots, addition of the DMA(V) form resulted in the inhibition of LMWOAs exudation into the rhizosphere and their creation in plant roots. Leaves were characterised by a higher content of LMWOAs than in the rhizosphere and roots for all experimental systems, where the profile and content of LMWOAs was strictly correlated with the analysed As forms. Our study indicated that creation of LMWOAs in U. laevis organs and their exudation to the rhizosphere could be responsible for the As toxicity tolerance of the plants.     

Composting in small laboratory pilots: performance and reproducibility

Small-scale reactors (<10 l) have been employed in composting research, but few attempts have assessed the performance of composting considering the transformations of organic matter. Moreover, composting at small scales is often performed by imposing a fixed temperature, thus creating artificial conditions, and the reproducibility of composting has rarely been reported. The objectives of this study are to design an innovative small-scale composting device safeguarding self-heating to drive the composting process and to assess the performance and reproducibility of composting in small-scale pilots. The experimental setup included six 4-l reactors used for composting a mixture of sewage sludge and green wastes. The performance of the process was assessed by monitoring the temperature, O₂ consumption and CO₂ emissions, and characterising the biochemical evolution of organic matter. A good reproducibility was found for the six replicates with coefficients of variation for all parameters generally lower than 19%. An intense self-heating ensured the existence of a spontaneous thermophilic phase in all reactors. The average loss of total organic matter (TOM) was 46% of the initial content. Compared to the initial mixture, the hot water soluble fraction decreased by 62%, the hemicellulose-like fraction by 68%, the cellulose-like fraction by 50% and the lignin-like fractions by 12% in the final compost. The TOM losses, compost stabilisation and evolution of the biochemical fractions were similar to observed in large reactors or on-site experiments, excluding the lignin degradation, which was less important than in full-scale systems. The reproducibility of the process and the quality of the final compost make it possible to propose the use of this experimental device for research requiring a mass reduction of the initial composted waste mixtures.     

Enhanced electrokinetic remediation of chromium-contaminated soil using approaching anodes

As a new technology used for the cleaning of chromium-contaminated soil, worldwide interest in eletrokinetic (EK) remediation has grown considerably in recent times. However, owing to the fact that chromium exists as both cationic and anionic species in the soil, it is not an efficient method. This paper reports upon a study in which a process using approaching anodes (AAs) was used to enhance the removal efficiency of chromium by eletrokinetics. Two bench-scale experiments to remove chromium from contaminated soil were performed, one using a fixed anode (FA) and the other using AAs. In the AAs experiment, the anode moved toward the cathode by 7 cm every three days. After remediation, soil pH, total chromium, and fractionation of chromium in the soil were determined. The average removal efficiency of total chromium was 11.32% and 18.96% in the FA and AAs experiments, respectively. After remediation, acidic soil conditions throughout the soil were generated through the use of AAs, while 80% of the soil remained neutral or alkalic when using the FA approach. The acidic soil environment and high field intensity in the AAs experiment might have favored chromium desorption, dissolution and dissociation from the soil, plus the mobility of chromium in the soil was also enhanced. The results demonstrate that AAs used in the process of EK remediation can enhance the efficiency of chromium removal from soil.     

Comparison of three sequential extraction procedures for trace element partitioning in three contaminated Mediterranean soils

The sequential extraction procedures described by Tessier et al., McGrath and Cegarra, and Gimeno-García et al. were compared to investigate trace element (As, Cr, Cu, Pb, and Zn) partitioning patterns and extraction efficiency in three contaminated soils from Mediterranean regions of Spain. Soils were selected from Onda (Castellón) (S1), Aznalcóllar (Sevilla) (S2), and Silla (Valencia) (S3). S1 was a soil contaminated with Pb and Zn after dumping of wastes from the manufacture of ceramic tiles, S2 was polluted accidentally with a highly acid and As-concentrated sludge from mining activities, and S3 was a soil with a high Cr content from tannery sludge disposal. Trace element distribution in the soils—soluble, exchangeable, organically bound, precipitated with carbonates, bound to iron and manganese oxides, and precipitated with sulfides fractions—varied significantly according to the extraction procedure used. In addition, different extraction efficiencies were found for the three sequential extraction procedures compared. Finally, the trace elements studied showed different and specific distribution patterns between the various soil fractions examined.     

Arsenic and fluoride in the groundwater of Mexico

Concentrations of arsenic and fluoride above Mexican drinking water standards have been detected in aquifers of various areas of Mexico. This contamination has been found to be mainly caused by natural sources. However, the specific processes releasing these toxic elements into groundwater have been determined in a few zones only. Many studies, focused on arsenic-related health effects, have been performed at Comarca Lagunera in northern México. High concentrations of fluoride in water were also found in this area. The origin of the arsenic there is still controversial. Groundwater in active mining areas has been polluted by both natural and anthropogenic sources. Arsenic-rich minerals contaminate the fractured limestone aquifer at Zimapán, Central México. Tailings and deposits smelter-rich fumes polluted the shallow granular aquifer. Arsenic contamination has also been reported in the San Antonio-El Triunfo mining zone, southern Baja California, and Santa María de la Paz, in San Luis Potosí state. Even in the absence of mining activities, hydrogeochemistry and statistical techniques showed that arsenopyrite oxidation may also contaminate water, as in the case of the Independencia aquifer in the Mexican Altiplano. High concentrations of arsenic have also been detected in geothermal areas like Los Azufres, Los Humeros, and Acoculco. Prevalence of dental fluorosis was revealed by epidemiological studies in Aguascalientes and San Luis Potosí states. Presence of fluoride in water results from dissolution of acid-volcanic rocks. In Mexico, groundwater supplies most drinking water. Current knowledge and the geology of Mexico indicate the need to include arsenic and fluoride determinations in groundwater on a routine basis, and to develop interdisciplinary studies to assess the contaminant's sources in all enriched areas.     

STUDIED THE OSCILLOSCOPIC POLAROGRAPHV ANALYSIS OF TRACE ARSENIC IN WATER

本方法叙述了用示波极谱法测定水与污水中的微量砷。水样中的有机砷和无机砷被高锰酸钾氧化生成砷酸,在支持电解质中测定。校准曲线范围为0～10.0μg/10ml,方法的相对标准偏差分别为4.7,2.9和2.1回收率范围为91.67%～105.88%。