Impact of chemical leaching on permeability and cadmium removal from fine-grained soils

The aim of this study was to investigate the influence of chemical leaching on permeability and Cd removal from fine-grained polluted soils. Column leaching experiments were conducted using two types of soils (i.e., artificially Cd-polluted loam and historically polluted silty loam). Chemical agents of CaCl₂, FeCl₃, citric acid, EDTA, rhamnolipid, and deionized water were used to leach Cd from the soils. Results showed that organic agents reduced permeability of both soils, and FeCl₃ reduced permeability of loam soil, compared with inorganic agents and deionized water. Entrapment and deposition of colloids generated from the organic agents and FeCl₃ treatments reduced the soil permeability. The peak Cd effluence from the artificially polluted loam columns was retarded. For the artificially polluted soils treated with EDTA and the historically polluted soils with FeCl₃, Cd precipitates were observed at the bottom after chemical leaching. When Cd was associated with large colloid particles, the reduction of soil permeability caused Cd accumulation in deeper soil. In addition, the slow process of disintegration of soil clay during chemical leaching might result in the retardation of peak Cd effluence. These results suggest the need for caution when using chemical-leaching agents for Cd removal in fine-grained soils.

     

The use of ultrasound-assisted anaerobic compost tea washing to remove poly-chlorinated dibenzo-p-dioxins (PCDDs), dibenzo-furans (PCDFs) from highly contaminated field soils

The remediation of dioxin-contaminated soil of a specific coastal area previously employed for the manufacture of pentachlorophenol (PCP) in southern Taiwan’s Tainan City has attracted much attention of researchers there. This work addresses the possibility of providing an effective and environmentally friendly option for removing PCDD/Fs from soil in that field. Soil screening/sieving was first conducted to assess particle distribution. Fine sand was observed to be the major component of the soil, accounting for more than 60% of the total mass. A combination of ultrasonification and mechanical double-blade agitation was used to facilitate the washing of the soil using the biosurfactant anaerobic compost tea. More than 85 and 95% of total removal efficiencies were achieved for moderately and highly contaminated soils after 6 and 10 washing cycles, respectively, under ambient temperature, a soil/liquid ratio 1:2.5, 700 rpm, and over a relatively short duration. These results were achieved through the collision and penetration effects of this combined treatment as well as PCDD/F partitioning between the particles and anaerobic compost tea. This study represents the first to report the use of anaerobic compost tea solvent to wash soil highly contaminated by dioxin. It was concluded that anaerobic compost tea, rich in non-toxic bio-surfactants (e.g., alcohols, humic acids), can be used to improve bioavailability and bioactivity of the soil making bio-attenuation and full remediation more efficient.     

铅和得克隆联合暴露对斑马鱼胚胎的神经毒性作用

以斑马鱼(Danio rerio)为研究对象,探讨铅(Pb)、得克隆(DP)及二者联合急性暴露对斑马鱼胚胎的神经毒性作用。结果表明,Pb(5、20μg·L~(-1))和DP(15、60μg·L~(-1))单独暴露均会引起斑马鱼自主运动频率增加,触摸反应能力和自由游泳活力下降,并且抑制初级运动神经元的生长,加剧尾部细胞凋亡。但与20μg·L~(-1)Pb单独暴露相比,高剂量联合暴露(20μg·L~(-1)Pb+60μg·L~(-1)DP)使斑马鱼的自主运动频率显著降低(P0.05),触摸反应能力和自由游泳活力显著增强(P0.05),初级运动神经元轴突长度显著增加(P0.05),尾部细胞凋亡减少。与5μg·L~(-1)Pb单独暴露相比,低剂量联合暴露(5μg·L~(-1)Pb+15μg·L~(-1)DP)也显著减少斑马鱼尾部的细胞凋亡(P0.05)。上述结果表明,Pb或DP单独暴露对斑马鱼均可引起神经毒性作用;但二者联合暴露对斑马鱼自主运动、触摸反应以及自由游泳活力的影响则表现为拮抗作用。     

赤霉酸暴露对SD大鼠青春期发育的影响

赤霉酸是目前国内外使用极其广泛的一种植物生长调节剂,但是针对其发育毒性的数据依然较少。本文探讨了赤霉酸暴露对SD大鼠青春期发育的影响。参考国内外环境内分泌干扰物危害的评价方法,将144只初断乳SD大鼠按体重随机分为4组,分别为对照组和1、10、100 mg·kg-1bw剂量组,采用经口灌胃方式对雄鼠连续染毒28 d,雌鼠连续染毒21 d。暴露结束后检测大鼠的体重、食物利用率、雄鼠包皮分离时间/雌鼠阴道开口时间、血清生化指标、脏器系数及组织病理学的变化。研究结果表明,与对照组相比,仅10和100 mg·kg-1bw剂量组雄鼠的肌酐水平显著升高(P<0.01),100 mg·kg-1bw剂量组雌鼠谷丙转氨酶水平有显著升高(P<0.01)。而与对照组相比,所有剂量组均未观察到大鼠的体重、食物利用率、雄鼠包皮分离时间/雌鼠阴道开口时间、脏器系数等指标有显著性差异的改变(P>0.05),组织病理学结果亦显示大鼠重要器官无损害性改变。因此,在本试验给予的剂量范围内赤霉酸染毒不会对SD大鼠青春期发育产生显著影响。     

Assessment and potential sources of metals in the surface sediments of the Yellow River Delta,Eastern China

The Yellow River Delta is the most intact estuary wetland in China and suffers from great pressure of metals. Seventy-seven surface sediment samples were collected in the delta, and contents of Cu, Pb, Cd, Cr, Zn, Ni, and Mn were analyzed by inductively coupled plasma spectrometry and those of Hg and As by atomic fluorescence spectrometry. The results showed that means of metal contents (ppm, dry weight) were as follows: Hg, 0.04; Cr, 61.72; Cu, 20.97; Zn, 60.73; As, 9.47; Pb, 21.91; Cd, 0.12; Ni, 27.24; and Mn, 540.48. 43.8% of Hg and 14.3% of Cd were from the allogenic source while others from the authigenic source. The results of the geoaccumulation indexes appeared that 6.5% of sites from the estuarine and the Gudao areas were moderately polluted by Hg. All ecological risk index values of Hg and 37.7% of Cd were more than 40, which were the main factors of strongly and moderately potential ecological risks of 37.7% of sites in the delta. High Cd contents may be due to the alkaline conditions of the delta and the unreasonable management of the farmland, while the abnormal distribution of Hg to the wet or dry deposition and the erosion of the seawater. It was suggested to monitor Hg content in the atmosphere of the Yellow River Delta. The results were expected to update the pollution status of metals in the delta and created awareness of preserving the sound condition of the Yellow River Delta.     

Fe(Ⅱ)EDTA络合吸收-铁粉还原再生脱除NO性能

利用Fe(Ⅱ)EDTA络合吸收-铁粉间歇还原再生脱除NO并回收氨资源的方法,实验研究了铁粉还原再生Fe(Ⅱ)(NO)EDTA的过程及其影响因素。结果表明,以0.015 mol/L的Fe(Ⅱ)EDTA做吸收剂,在起始p H 5.5、温度323K条件下吸收400×10-6~500×10-6的NO,脱除率95%以上;铁粉还原再生Fe(Ⅱ)(NO)EDTA过程可用缩芯模型阐释;铁粉添加量与搅拌强度直接决定了铁粉质点数量,是影响反应的重要因素;实验中Fe(Ⅱ)(NO)EDTA络合液150 m L,氧气含量为5%时,搅拌速度900 r/min、粒径为0.12 mm的铁粉浓度5.3 g/L、温度353 K、p H=6为最适宜再生条件。     

Atmospheric depositional fluxes and sources apportionment of organochlorine pesticides in the Pearl River Delta region, South China

Organochlorine pesticides (OCPs) have variously been phased out in agricultural activities, but they are still widely detected in air, water, and soil systems due to their recalcitrant nature in the environment. The purposes of this study were to assess potential OCP pollution via dry and wet deposition over the fast developing Pearl River Delta area with 41,700 km², where the main effort has been focused on emerging pollutants such as petroleum hydrocarbons and PM2.5. We quantified both the dry and wet deposition fluxes of 19 OCPs including dichlorodiphenyltrichloroethanes (DDTs), endosulfans (Endos), and hexachlorocyclohexanes (HCHs). The results showed that each year about 67.4, 42.0, 15.0, and 8.07 kg of total OCPs, DDTs, Endos, and HCHs were returned to the ground, among which 11.7, 10.4, 0.84, and 0.16 kg were in the dry deposition forms. The large spatial variations in OCP deposition fluxes indicated that OCP pollution in the air is mainly influenced on local scales because evaporation from local soil is likely the major source of the phased out OCPs. Source analysis indicated that DDTs may be still in use as antifouling agent and/or dicofol, but Endos and HCHs were mainly derived from the residual of historical usage. The study suggests that the historical OCP pollutants are persistent at high levels in this area and should not be overlooked, while we tackle emerging pollutants.     

Seasonal variations of monocarbonyl and dicarbonyl in urban and sub-urban sites of Xi’an,China

Seventeen airborne carbonyls including monocarbonyls and dicarbonyls were determined in urban and sub-urban sites of Xi’an, China in three seasons in 2010. In winter, acetone was the most abundant carbonyl in the urban site due to usage of organic solvents in constructions and laboratories and its slower atmospheric removal mechanisms by photolysis and reaction with hydroxyl radical than those of formaldehyde and acetaldehyde. In the sub-urban site, acetaldehyde was the most abundant carbonyl, followed by formaldehyde and acetone. During summer, however, formaldehyde was the most dominant carbonyl in both sites. The photooxidations of a wide range of volatile organic compounds (VOCs) yielded much more formaldehyde than other carbonyls under high solar radiation and temperature. In the urban site, the average concentrations of dicarbonyls (i.e., glyoxal and methyglyoxal) in spring and summer were higher than that in winter. Transformation of aromatic VOCs emitted from fuel evaporation leads to the formation of 1,2-dicarbonyls. A reverse trend was observed in sub-urban sites, as explained by the relatively low abundances and accumulations of VOC precursors in the rural atmosphere during warm seasons. Moreover, cumulative cancer risk based on measured outdoor carbonyls (formaldehyde and acetaldehyde) in Xi’an Jiaotong University and Heihe was estimated (8.82?×?10^?5 and 4.96?×?10^?5, respectively). This study provides a clear map on the abundances of carbonyls and their source interpretation in the largest and the most economic city in Northwestern China.     

Occurrence and dominance of Cylindrospermopsis raciborskii and dissolved cylindrospermopsin in urban reservoirs used for drinking water supply,South China

The tropical cyanobacterium Cylindrospermopsis raciborskii is of particular concern for its invasive characteristics and production of the toxin cylindrospermopsin (CYN). The present study represents the first attempt to determine the distribution of C. raciborskii and CYN in tropical China. The presence of C. raciborskii and CYN, as well as the composition of phytoplankton, was determined from a total of 86 samples from 25 urban reservoirs for drinking water supply in Dongguan City of South China. The presence of C. raciborskii was observed in 21 of the 25 reservoirs and confirmed that this species has been widely distributed in the investigated reservoirs. C. raciborskii accounted for between 0.1 and 90.3 % of the total phytoplankton biomass and contributed to the majority of the phytoplankton in some reservoirs such as Tangkengbian and Xiagongyan. Its biomass was negatively correlated with NO₃ ^?-N concentration and Secchi depth. Dissolved CYN was detected in more than one-half of the reservoirs with concentrations up to 8.25 μg L^?1, and it positively correlated with C. raciborskii biomass. Dissolved microcystins (MCs) were detected in 12 of the 25 reservoirs with a maximum concentration 1.99 μg L^?1. Our data strongly suggest that C. raciborskii and CYN could be important health hazards in urban reservoirs of South China and that more data are needed for further assessment.     

Effect of air-drying and oven-drying treatment on Cr(VI) content and Cr bond forms in soil

Air-drying and oven-drying are pretreatment processes often used before testing and analyzing various soil characteristics in the laboratory. This study selected three kinds of soil, including red soil, entisol, and alluvial soil, and examined the variation of the Cr(VI) content and Cr bond forms in these soils during air-drying and oven-drying. The results show that when the soil is air-dried in natural environment, the Cr(VI) content decreases with air-drying time. On day 10 of air-drying, the Cr(VI) content in these soils is 22.8～47.9 % of the initial value. When the soil is oven-dried, the Cr(VI) concentration decays faster; on day 8, the Cr(VI) is no longer detected in these soil samples. When the Cr(VI)-contaminated soil is treated by air-drying and oven-drying, the Cr bond form converts into a more stable form. After oven-drying, the Cr mainly exists in Fe–Mn oxide form, organic bond form, and residual form. The air-drying and oven-drying pretreatment processes of soil reduce the Cr(VI) content and stabilize the Cr bond form. If the laboratory analytic results are applied to risk analysis or remediation strategy planning for chromium-contaminated soil, the toxicity, bioavailability, and mobility of Cr in soil may be underrated.