Heavy metal bioavailability and chelate mobilization efficiency in an assisted phytoextraction process

The heavy metal bioavailable fraction of a soil is a core parameter to verify the potential risks of contaminant exposure to organisms or plants. The purpose of the present work is to identify the bioavailable metal fraction in soils treated with chelates. This fraction was evaluated directly by analyzing metal concentrations in soil solution and indirectly using sequential extraction procedures. The metal bioavailable fraction was compared with metal accumulated in plant leaves, grown in both untreated and chelate-treated reactors. In order to verify the effect of the readily and slowly biodegradable chelates [S,S]-ethylenediaminedisuccinic acid (EDDS), methylglycine diacetic acid (MGDA), and ethylenediaminetetraacetic acid (EDTA) on metal speciation in soils, a simulation of chelate treatment was made and metal concentrations in different soil compartments before and after the simulation were compared. Lead concentration in the soil solution was positively correlated with metal concentration in the test plants. The soluble fraction showed the best correlation with metal concentration in soil solution. The simulation of the chelate treatment demonstrated that EDTA and EDDS were able to extract part of the organic- and sulfide-bound fraction, which are less available to plants.     

BTP-N_2复合气体配比优化及灭火临界条件研究

为了考察一溴三氟丙烯(简称BTP)与氮气(N2)所形成的复合灭火介质的复合比以及不同复合比下的临界灭火条件,开展了以下工作:首先,基于多组分分压原理,探讨了BTP-N2预混技术的可行性;其次,基于燃烧学和气体运动学理论,提出了BTP与N2复合灭火介质的灭火临界条件预测理论模型;再次,依据卤代烷灭火介质的特点和灭火机理,构建了临界灭火试验平台,对不同BTP和N2复合比下的复合气体灭火介质进行灭火临界条件研究;最后,通过实验结果修正和完善预测理论模型。结论:BTP-N2复合灭火介质的灭火临界条件理论值与实验值吻合性较好,因此该预测模型能很好地对复合卤烃灭火介质的临界灭火条件进行估算,为研究卤烃气体与惰性气体复合灭火介质的灭火机理及研发高效清洁灭火介质奠定了基础。     

3种刺激性化学战剂对藻类的急性毒性研究

采用国际通用的试验藻种斜生栅藻(Scendesmus obliuus)作为试验生物,研究了3种刺激性化学战剂(二苯氰胂、二苯氯胂和苯氯乙酮)对试验藻类的急性毒性.结果表明:二苯氰胂、二苯氯胂和苯氯乙酮对斜生栅藻急性毒性试验的96 h半数生长抑制浓度(EC50)分别为0.14,0.10和0.36mg/L,表明这3种化学战剂均属于极高毒性物质,其毒性依次为二苯氯胂＞二苯氰胂＞苯氯乙酮,但其毒性均在同一数量级上,区分度不强.      

Effect of external iron and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake in rice (Oryza sativa L.)

This study was conducted to investigate the effect of external iron status and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake. Rice seedlings (Oryza sativa L.) were used as model plant, and were grown in artificially contaminated sandy soils irrigated with Murashige and Skoog (MS) culture solution. Arsenate uptake in roots and shoots of rice seedlings were affected significantly (p > 0.05) while dimethylarsinic acid (DMAA) was not by the additional iron and chelating ligand treatments. Regardless of iron concentrations in the soil solution, HIDS increased arsenic uptake for roots more than EDTA and EDDS. Chelating ligands and arsenic species also influenced iron uptake in rice roots. Irrespective of arsenic species, HIDS was found to be more effective in the increase of iron bioavailability and uptake in rice roots compared to other chelants. There was a significant positive correlation (r = 0.78, p < 0.05) between arsenate and iron concentrations in the roots of rice seedlings grown with or without additional iron indicating that arsenate inhibit iron uptake. In contrast, there was no correlation between iron and DMAA uptake in roots. Poor correlation between iron and arsenic in shoots indicated that iron uptake in shoots was neither affected by additional iron nor by arsenic species. Compared to the control, chelating ligands increased iron uptake in shoots of rice seedlings significantly (p < 0.05). Regardless of additional iron and arsenic species, iron uptake in rice shoots did not differed among EDTA, EDDS, and HIDS treatments.     

铅蓄电池厂铅污染土壤清洗剂的筛选及清洗结果研究

为探索不同清洗剂对铅蓄电池厂区内铅污染土壤的去除效果及铅在不同粒径土壤清洗过程中的行为,本研究通过设定清洗剂的浓度梯度,对土样粒径分级、设定清洗时间等方法进行研究。结果显示EDTA和EDDS对铅具有最佳去除率(B点土107.19%和96.49%);盐酸对A点土最佳铅去除率为49.57%,B点、C点土在99.03%和89.93%;柠檬酸对3点位土的铅去除率最大为39.51%;鼠李糖脂对3份土铅去除率均低于10%。EDTA和EDDS在高浓度铅的去除中表现优势;柠檬酸适合去除中低浓度铅;盐酸的使用需考虑土壤本身情况。粗沙粒和细沙粒中的铅去除率高,粉粘粒的铅去除率低;最佳清洗时长为240min。此外,土壤本身理化性质对清洗剂效果的发挥有影响,清洗剂浓度过高可能降低清洗效率。该研究可为铅污染土壤清洗技术提供科学依据。     

Effect of Fe-chelating complexes on a novel M2FC performance with ferric chloride and ferricyanide catholytes

As an effort to better utilize the microbial fuel cell (MFC) technology, we previously proposed an innovative MFC system named M2FC consisting of ferric-based MFC part and ferrous-based fuel cell (FC) part. In this reactor, ferric ion, the catholyte in the MFC part, was efficiently regenerated by the FC part with the generation of additional electricity. When both units were operated separately, the ferric-based MFC part produced approximately 1360 mW m⁻² of power density with FeCl₃ as catholyte and Fe-citrate as anolyte. The ferrous-based FC part with FeCl₃ as catholyte and Fe-EDTA as anolyte displayed the highest power density (1500 mW m⁻²), while that with ferricyanide as catholyte and Fe-noligand as anolyte had the lowest power density (380 mW m⁻²). The types of catholytes and chelating complexes as anolyte were found to play important roles in the reduction of ferric ions and oxidation of ferrous ion. Linear sweep voltammetry results supported that the cathode electrolytes were electrically active and these agreed well with the M2FC reactor performance. These results clearly showed that ligands played critical role in the efficiency and rate for recycling iron ion and thus the M2FC performance.     

纺织品抗拒挥发性有机化合物沾染整理方法的研究

频繁接触挥发性有机化合物的工厂作业岗位上的工人,所穿着的服装容易粘附有害的有机物质分子,进而危害工人的健康。为解决这一问题,本文探索采用变化服装面料的织造工艺、面料织物与聚四氟乙烯微孔薄膜复合以及含氟织物整理剂整理等方法,制作具有一定抗挥发性有机化合物沾染性能的防护服面料。实验中对不同纤维原料的织物,在未经整理和进行覆膜或含氟织物整理剂整理后,分别剪取样品放置在充满有机气体的氛围中熏蒸24小时,用二硫化碳萃取布料上的有机物,并使用气相色谱分析仪分析这些物质的含量。经过比较,发现克重较低、与聚四氟乙烯膜复合以及经含氟织物整理剂整理的布料,其抗拒挥发性有机化学物质沾染的能力均有所增强。综合使用这些处理方法,有望制作出具有理想的抗有机化学物质沾染的防护工作服,用于经常接触这类物质的工厂工人的日常劳动防护。     

Chelant-aided enhancement of lead mobilization in residential soils

Chelation of metals is an important factor in enhancing solubility and hence, availability to plants to promote phytoremediation. We compared the effects of two chelants, namely, ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) in enhancing mobilized lead (Pb) in Pb-based paint contaminated residential soils collected from San Antonio, Texas and Baltimore, Maryland. Batch incubation studies were performed to investigate the effectiveness of the two chelants in enhancing mobilized Pb, at various concentrations and treatment durations. Over a period of 1 month, the mobilized Pb pool in the San Antonio study soils increased from 52 mg kg⁻¹ to 287 and 114 mg kg⁻¹ in the presence of 15 mM kg⁻¹ EDTA and EDDS, respectively. Stepwise linear regression analysis demonstrated that pH and organic matter content significantly affected the mobilized Pb fraction. The regression models explained a large percentage, from 83 to 99%, of the total variation in mobilized Pb concentrations.     

Electrokinetic remediation of concrete: effect of chelating agents

Contamination of concrete at various nuclear power plants and spent nuclear fuel reprocessing facilities by radionuclides represents a significant problem for the world's nuclear power industries and nuclear waste management. The present publication summarizes the most recently published data on Electrokinetic Remediation (EK) of various concrete installations and advantageous effects of the combination of EK with different chelating agents. The specific aspects of decontamination of concrete and mortar surfaces are analyzed, such as: (a) effect of chelating agents (EDTA, citric acid), (b) effect of the zeta-potential (zeta) of concrete surface, (c) effects of sorption and complex formation equilibrium, and (d) specific advantages and problems of the electrokinetic decontamination process. The results of laboratory and in situ tests of chelating agent assisted EK removal of radionuclides are reported. It is demonstrated that the correct combination of EK with specific chelating agents can be effectively employed for decontamination of concrete surfaces.     

Complexing agents in waste waters of finnish electrolytic and chemical surface treatment plants

Goal, Scope and Background  Complexing agents are one of the major environmental concerns in electrolytic and chemical surface treatment (ECST) industry; e.g. the EU reference document on the best available technology (BREF) pays special attention to the usage of EDTA. However, no comprehensive studies are available on usage of EDTA or other complexing agents or their load to the receiving waters from ECST industry. In this study, the concentrations of complexing agents were analyzed to get an overview of their usage and load and also to recognize their relevance in the environmental permitting and compliance monitoring of such facilities. Methods  Complexing agent concentrations of treated waste water samples of 23 ECST plants with vat volume exceeding 30 m³ was studied. HPLC and GC-MS were used to analyze and identify complexing agent concentrations, ICP-AES to analyze metals, and TOC to analyse the organic load. The number of the plants in this study equals around 50% of such installations in Finland subject to environmental permit as the IPPC directive provides. Results  EDTA, DTPA, and NTA were found in 11 samples out of 23 mainly in rather small concentrations. Their annual load to the receiving waters may be estimated to be 0.3 tons and the total load from Finnish ECST industry can be extrapolated to be up to 1 ton. Compared to the estimated use of 5–10 tons in the industry this finding is rather low, even though in Finland cast-off treatment baths are typically delivered to the hazardous waste treatment plants. Discussion  Since the load of complexing agents is rather low, the chemical waste water treatment seems to be either capable of reducing complexing agent concentrations to some extent or their usage is lower than expected. On the other hand, it is possible that not all complexing agents were identified from the samples. The metal concentrations and TOC were well hand in hand with concentrations found in the Finnish environmental database, which proves that the samples were of average quality of the waste water from the facilities. Conclusions  According to the results, complexing agents cannot be considered as an environmental risk in the ECST industry in Finland; EDTA concentrations are clearly below PNEC_aqua (2.2 mg/l) and the total discharge is very marginal compared to the discharge from the pulp and paper industry. However, DPTA seems to be as commonly used as EDTA, but also biodegradable NTA was found. Recommendations and Perspectives  Since EDTA has gained plenty of attention in the BREF, DTPA and other, poorly biodegradable complexing agents should also be taken into account when the BREF is updated within a few years. Also an EU risk assessment report especially for DTPA should be supplied, since its use is obviously increasing.