湘江株洲段镉污染动态模拟与情景分析

本研究利用美国环境保护局(USEPA)推荐的WASP水质分析模拟软件,对湘江株洲段2009年的镉浓度进行动态模拟,并进行总量控制的情景分析。对水文条件变化和源强变化2种情景下的河道镉浓度进行了预测。结果表明,WASP模型能较好重现镉浓度的时间变化规律。情景分析表明,水文条件和源强条件对镉浓度的影响在霞湾和马家河断面较为明显,且在枯水月份表现得更为明显。     

土壤重金属铅镉形态和有效态的提取方法研究

选择一步提取法(CaCl2法、NaNO3法、NH4NO3法、HCl法)提取土壤铅镉有效态含量,顺序提取法(BCR提取法、Tessier提取法)提取土壤中铅镉各形态含量。结果表明,4种一步提取法对供试土样有效态铅镉的提取效率为HCl法NH4NO3法CaCl2法NaNO3法。当镉质量浓度为0~20、40~90 mg/kg时,BCR法对土壤中镉的总提取率分别为104.9%、105.3%,Tessier法对土壤中镉的总提取率分别为101.7%、98.9%;当镉质量浓度为20~40mg/kg时,两种顺序提取法的提取效果均不佳。BCR法适合铅质量浓度为20 000~45 000 mg/kg时应用,此时BCR法对铅的总提取率为99.8%;Tessier法适合铅质量浓度为0~1 500、9 000~15 000mg/kg时应用,此时Tessier法对土壤铅的总提取率分别为100.7%、90.9%。土壤重金属铅镉各形态的含量受土壤自身pH影响不明显,但在遇到外界酸性环境影响时容易发生重金属铅镉迁移。     

基于WASP模型计算尾水回用河道污染负荷

城市景观河道水质恶化,主要是由于河道两岸污染物质排放进入水体,导致水体水质下降。为了计算下游各区段污染物质日负荷排放量,同时甑别重点排污区段,提出采用WASP水质分析模拟软件计算各段氨氮负荷排放量。模拟过程需先定义河道基本参数:河道长宽、水深,入河流量增加量、水体流速、氨氮循环拟合公式中硝化速率、反硝化速率系数等。模拟结果表明,不同氨氮浓度求得的入河负荷值是相对唯一的。1 g/d负荷的增加会导致模拟浓度改变0.01~0.06mg/L。同心河下游生活区(一~三段)的氨氮排放负荷比上游工业区(四~六段)大,生活区氨氮排放负荷达到河道总排放负荷60%~70%。河道氨氮负荷削减模拟的结果表明:上游氨氮污染负荷量越大,下游削减负荷程度越高,从而使得下游氨氮浓度越低。     

“镉米”生物能源化过程中Cd的迁移途径

镉属于环境中持久性污染物,毒性大,对环境及人类造成严重危害,"镉米"事件已引起了对环境镉污染尤其是土壤镉污染的高度关注。利用镉米生产酒精不但能为企业能源生产提供新的原料来源,而且可解决有害大米的出路问题。通过摇瓶和UASB厌氧反应器实验,重点研究了Cd2+在厌氧处理过程中的迁移途径。结果表明,90%以上的Cd2+主要以微溶的形式富集于厌氧污泥里。厌氧泥离心分离:泥中镉浓度为0.35~0.40 mg/kg,水中镉浓度低于0.025 mg/kg。厌氧出水镉浓度在0.010~0.015 mg/kg,可以实现达标排放。出水VFA基本维持在300~500 mg/L,COD的去除率达65%~80%。实验结果可为镉米能源化利用提供一定的理论依据和技术支撑。     

邛海主要入湖河流氮、磷入湖污染负荷特征研究

针对入湖河流小流域水文资料缺乏的情况，提出了水文比拟法和水文分割法相结合的入湖径流量与入湖污染负荷计算方法，并对邛海主要入湖河流开展总氮、总磷入湖污染负荷量及组成研究。结果表明：2019—2020年，邛海3条主要入湖河流鹅掌河、官坝河和小青河的两年平均入湖径流量分别为2.19×10⁷、5.31×10⁷、2.94×10⁶ m³/a,其中雨季(5—10月)入湖径流量占到约90%。3条河流两年共计向邛海输送总氮、总磷污染负荷量255.99 t和12 447.22 kg,其中面源污染是邛海主要入湖河流污染负荷的首要来源，总氮、总磷面源污染负荷量分别占入湖污染负荷量的74.48%～81.02%、78.78%～84.39%。降雨量、土地利用方式等是影响邛海主要入湖河流入湖径流量与入湖污染负荷的重要因素。研究结果对邛海流域湖泊富营养化治理的精准实施具有重要意义，同时也为其他水文资料缺乏地区的污染负荷估算提供了方法参考。     

镉胁迫对向日葵幼苗生长和生理特性的影响

采用溶液培养方法,研究了不同浓度镉(0、0.05、0.1、0.5和1 mg/L)处理7 d对向日葵幼苗生长和生理特性的影响。结果表明：随着镉处理浓度的增加，向日葵幼苗对镉的吸收显著增加。1 mg/L镉浓度处理时，叶、茎和根中镉浓度分别为0.05 mg/L镉处理时的16.3、19.2和581倍；根中积累的镉含量明显高于叶和茎, 各浓度根部积累的镉分别为叶和茎的37.8～63倍和29.4～41倍。镉胁迫显著抑制向日葵幼苗生长和叶绿素合成，当镉浓度达1 mg/L时，整株植物生物量和总叶绿素含量分别为对照的55.9%和52.6%。镉胁迫下向日葵幼苗游离脯氨酸和丙二醛（MDA）含量显著增加，1 mg/L镉浓度时，根中含量分别为对照的4和5.8倍。向日葵幼苗可溶性蛋白含量和过氧化物酶(POD)活性变化与镉胁迫浓度呈明显的倒U字型关系，可溶性蛋白含量在0.05 mg/L镉浓度时达到最大值，叶、茎、根中的POD活性分别在0.1、0.1和0.05 mg/L镉浓度时达到最大值。     

香蒲根际过滤对水中镉的去除

通过水培实验,研究香蒲根系对水中镉的根际过滤效果及富集量。结果表明:在镉浓度1 mg·L~(-1)的静止水体中,香蒲根际过滤对镉的去除率为66%;在相同镉浓度并且水力停留时间为8 h的流动水体中,镉去除率为52%。香蒲体内富集的镉约90%集中在根部,且第1天镉的去除速率最快,镉浓度以约0.1 mg·h~(-1)速率下降;在静止水体中,香蒲根系7 d对镉的富集量为682.99 mg·kg~(-1)(DW),动态水体中香蒲根系富集量达1 096.94 mg·kg~(-1),可有效去除水中的镉。     

关于水质总量控制中的流量测定

水质总量控制是防治封闭水域水质污染的重要措施,其控制手段是通过限定各污染源的污染负荷,有计划地削减流入控制水域的污染物总量;控制目标是使该水域逐渐达到水质环境基准;而所采用的各项措施的重要技术依据、则为各污染源的污染负荷量的计算和确定。在计算污染负荷量过程中需要直接测定的项目有两项,即污染物浓度和排水流量的测定。其中污染物浓度的测定早已引起普遍的重视,实毋庸赘述,然而对于排水流量的测定,当前却尚存在着不同程度的认识上或技术上的问题。本文就排水流量测定问题谈谈个人浅见。     

添加天然沸石和石灰对土壤镉形态转化的影响

采用土壤培养实验,研究镉污染土壤中添加沸石、石灰及两者配施对土壤pH值和土壤镉形态变化的影响。结果表明,土壤pH值随沸石用量的增加而增加,随培养时间呈现先增加后下降并逐渐趋于稳定的趋势,但均高于对照。高剂量石灰的处理对土壤pH的影响最大,与对照相比土壤pH提高了3.33个单位。在土壤5~50 d培养过程中,石灰处理的土壤交换态镉含量呈现先逐渐降低而后略有升高的趋势,其余处理均呈下降趋势。培养50 d后,高剂量的沸石、石灰及高剂量沸石与石灰配施处理的土壤交换态镉含量从5 d时的67.54、61.95和55.56 mg/kg降低至54.65、49.93和45.96mg/kg。相关分析表明,不同培养时期交换态镉含量与土壤pH值呈负相关关系。在10个处理中,L2Z3(石灰2 g/kg土和沸石60 g/kg土)组合处理效果最好,使土壤交换态镉含量下降了34.68%,碳酸盐结合态镉含量上升了4.30%,铁锰氧化结合态镉含量上升了16.97%,有机结合态镉含量上升了1.31%,残渣态镉含量上升了12.11%。     

高寒地区刺儿菜对重金属镉污染土壤修复效果研究

为探究刺儿菜在不同施肥水平下对土壤重金属的修复作用与效果,对研究区进行了不同尿素水平的施肥试验,并定量分析了其试验结果。结果表明:施用231.5~925.9kg/hm2尿素,刺儿菜地上部分生物量和镉积累量均显著提高,镉提取率与对照组相比升高了15.44%~35.12%,施用694.4kg/hm2尿素时效果最佳。刺儿菜对镉的转移系数和富集系数均大于1,具备超富集植物的基本特征,可作为该污染区土壤修复的乡土植物。     

Nitrilotriacetate- and citric acid-assisted phytoextraction of cadmium by Indian mustard (Brassica juncea (L.) Czernj, Brassicaceae)

In a pot experiment the effects of nitrilotriacetate (NTA) and citric acid applications on Cd extractibility from soil as well as on its uptake and accumulation by Indian mustard (Brassica juncea) were investigated. Plants were grown in a sandy soil with added CdS at four levels ranging from 50 to 200 mg Cd kg(-1) soil. After 30 days of growth, pots were amended with NTA or citric acid at 10 and 20 mmol kg(-1). Control pots were not treated with chelates. Harvest of plants was performed immediately before and one week after chelate addition. Soil water-, NH(4)NO(3)- and EDTA-extractable Cd fractions increased constantly with both increasing soil metal application and chelate concentration. Shoot dry weights did not suffer significant reductions with increasing Cd addition to the soil except for both NTA treatments in which at 200 mg Cd kg(-1) a 30% decrease in dry matter was observed. Generally, following NTA and citric acid amendments, Cd concentration in shoots increased with soil Cd level. However, due to Cd toxicity, at the highest metal application rate both NTA treatments lowered Cd concentration in the above-ground parts. Compared to the control, at 10 mmol kg(-1) citric acid did not change Cd concentration in shoots, whereas NTA-treated plants showed an about 2-fold increase. The addition of chelates at 20 mmol kg(-1) further enhanced Cd concentration in shoots up to 718 and 560 microg g(-1) dry weight in the NTA and citrate treatments, respectively.     

Clonal variation in heavy metal accumulation and biomass production in a poplar coppice culture. II. Vertical distribution and phytoextraction potential

Short rotation coppice cultures (SRC) are intensively managed, high-density plantations of multi-shoot trees. In April 1996, an SRC field trial with 17 different poplar clones was established in Boom (Belgium) on a former waste disposal site. In December 1996 and January 2001, all shoots were cut back to a height of 5 cm to create a coppice culture. For six clones, wood and bark were sampled at the bottom, middle and top of a shoot in August and November 2002. No significant height effect of metal concentration was found, but for wood, metal concentrations generally increased toward the top of the shoot in August, and decreased toward the top of the shoot in November. Phytoextraction potential of a clone was primarily determined by metal concentration and by biomass production. Shoot size and number of shoots per stool were less important, as a high biomass production could be achieved by producing a few large shoots or many smaller shoots. Clone Fritzi Pauley accumulated 1.4 kg ha(-1) of Al over two years; Wolterson and Balsam Spire showed a relatively high accumulation of Cd and Zn, i.e. averaging, respectively 47 and 57 g ha(-1) for Cd and 2.4 and 2.0 kg ha(-1) for Zn over two years.     

Identification of barley genotypes with low grain Cd accumulation and its interaction with four microelements

The variation in grain cadmium (Cd) concentrations was evaluated among 600 barley genotypes grown in the same field condition to select low Cd accumulating genotypes. The results showed that there is considerable genotypic variation in grain Cd concentrations in barley grain samples, with the mean concentration of 0.16 mg kg(-1) DW and the variation of 0 (not detected) to 1.21 mg kg(-1) DW, and 47.2% of the grain samples exceeded the maximum permissible concentration (MPC) for Cd in cereal grains. In addition, differences between genotypes over the two years were fairly consistent, and Beitalys and Shang 98-128 showed the lowest grain Cd concentration, being 97.5% lower than that in the two highest Cd accumulators E-barley 6 and Zhenong 8 in the second harvest year. The great genotypic differences in Cd concentrations indicated that it is possible to lower Cd content of barley through cultivar selection and breeding for use at sites where Cd concentration in grain exceeds the MPC. Significant genotypic difference was also found in microelement concentrations. Correlation analysis showed that only Mn accumulation is synergetic with Cd accumulation, despite slightly positive relationship between Cd and Zn, Cu, or Fe in accumulation in barley grains.     

Symbiotic efficiency of autochthonous arbuscular mycorrhizal fungus (G. mosseae) and Brevibacillus sp. isolated from cadmium polluted soil under increasing cadmium levels

The effect of inoculation with indigenous naturally occurring microorganisms (an arbuscular mycorrhizal (AM) fungus and rhizosphere bacteria) isolated from a Cd polluted soil was assayed on Trifolium repens growing in soil contaminated with a range of Cd. One of the bacterial isolate showed a marked PGPR effect and was identified as a Brevibacillus sp. Mycorrhizal colonization also enhanced Trifolium growth and N, P, Zn and Ni content and the dually inoculated (AM fungus plus Brevibacillus sp.) plants achieved further growth and nutrition and less Cd concentration, particularly at the highest Cd level. Increasing Cd level in the soil decreased Zn and Pb shoot accumulation. Coinoculation of Brevibacillus sp. and AM fungus increased shoot biomass over single mycorrhizal plants by 18% (at 13.6 mg Cd kg(-1)), 26% (at 33.0 mg Cd kg(-1)) and 35% (at 85.1 mg Cd (kg(1)). In contrast, Cd transfer from soil to plants was substantially reduced and at the highest Cd level Brevibacillus sp. lowered this value by 37.5% in AM plants. Increasing Cd level highly reduced plant mycorrhization and nodulation. Strong positive effect of the bacterium on inocula, are important in plant Cd tolerance and development in Cd polluted soils.     

柠檬酸对褐土中DTPA提取态铜、镉含量及对紫花苜蓿吸收铜、镉的影响

为了阐述有机酸对土壤中重金属生物有效性的影响,通过盆栽实验,研究了Cu、Cd复合污染下柠檬酸对褐土中二乙基三胺五乙酸(DTPA)提取态铜和镉含量的影响,并探讨了柠檬酸对植物吸收铜、镉的影响。结果表明,土壤中DT-PA-Cu含量随柠檬酸添加量的增加而减小,添加高浓度铜(Cu 1 000)处理中,DTPA-Cu含量减小更明显。在添加低铜浓度(Cu600)处理下,柠檬酸添加量为2和12 mmol/kg时,土壤DTPA-Cu含量随土壤镉含量的增加而增加,而柠檬酸含量为5mmol/kg时,DTPA-Cu含量在低镉处理(Cd 1)时含量最低。紫花苜蓿中铜含量随柠檬酸添加量的增加明显降低。土壤中DTPA-Cd含量随柠檬酸添加量的增加而减小,且随铜添加量的增加而降低。紫花苜蓿中的镉含量随柠檬酸添加量的增加先增加后减小;在相同柠檬酸添加量处理时,紫花苜蓿中镉的含量随镉含量的增加而增加;在低镉处理下,铜的加入对较低柠檬酸浓度时紫花苜蓿镉含量影响不明显,但柠檬酸浓度为12 mmol/kg时,紫花苜蓿中镉含量随铜添加量的增加而明显增加。     

Cadmium (Cd) distribution and contamination in Chinese paddy soils on national scale

Rice is a staple food by an increasing number of people in China. As more issues have arisen in China due to rice contaminated by cadmium (Cd), Cd contamination in arable soils has become a severe problem. In China, many studies have examined Cd contamination in arable soils on a national scale, but little studies have focused on the distribution of Cd in paddy fields. This study explored the spatial pattern of Cd in paddy soils in China, made a preliminary evaluation of the potential risk, and identified the most critically contaminated regions based on the domestic rough rice trade flow. The results showed that Cd concentrations in paddy soils in China ranged from 0.01 to 5.50 mg/kg, with a median value of 0.23 mg/kg. On average, the highest Cd concentrations were in Hunan (0.73 mg/kg), Guangxi (0.70 mg/kg), and Sichuan (0.46 mg/kg) provinces. Cd concentrations in paddy soils in central and western regions were higher than those in eastern regions, especially the southeastern coastal regions. Of the administrative regions, Cd standard exceedance rate was 33.2 %, and the heavy pollution rate was 8.6 %. Regarding to Cd of paddy soil, soil environmental quality was better in Northeast China Plain than in Yangtze River Basin and southeastern coastal region. Mining activities were the main anthropogenic pollution source of Cd in Chinese paddy soil. Based on rice trade, more of the Chinese population would be exposed to Cd through intake of rice produced in Hunan province. Certain regions that output rice, especially Hunan province, should be given priority in the management and control of Cd contamination in paddy soil.     

Cadmium availability to wheat grain in soils treated with sewage sludge or metal salts

Grain Cd concentrations were determined in wheat (Triticum aestivum L.) grown in 1999, 2001 and 2003, at six sludge cake field experiments. Three of these sites also had comparisons with Cd availability from metal amended liquid sludge and metal salts. Grain Cd concentrations in all years and at all sites were significantly linearly correlated with NH4NO3 extractable Cd and soil total Cd (P<0.001). Soil extractability was greater in the liquid sludge and metal salt experiments than in the cake experiments, as were grain Cd concentrations. Across all the sites, NH4NO3 extractable soil Cd was no better at predicting grain Cd than soil total Cd. Stepwise multiple linear regression analysis showed that soil total Cd, pH and organic carbon were the only significant (P<0.001) variables influencing wheat grain Cd concentrations, explaining 78% of the variance across all field experiments (1408 plots). This regression predicted that the current UK soil total Cd limit of 3 mg kg(-1) was not sufficiently protective against producing grain above the European Union (EU) grain Cd Maximum Permissible Concentration (MPC) of 0.235 mg Cd kg(-1) dry weight, unless the soil pH was > 6.8. Our predictions show that grain would be below the MPC with > 95% confidence with the proposed new EU draft regulations permitting maximum total Cd concentrations in soils receiving sludge of 0.5 mg kg(-1) for soils of pH 5-6, 1 mg kg(-1) for soils of pH 6-7, and 1.5 mg kg(-1) for soils of pH > or = 7.     

Silicon-mediated enhancement of cadmium tolerance in maize (Zea mays L.) grown in cadmium contaminated soil

Pot experiments were performed to study the alleviative effects of exogenous silicon (Si) on cadmium (Cd) phytotoxicity in maize grown in an acid soil experimentally contaminated with Cd. Five treatments were investigated in the first trial consisting of a control (neither Cd nor Si added), Cd added at 20 or 40 mg kg(-1) Cd without or with Si added at 400 mg kg(-1) Si. A following-up trial was conducted with almost the same treatments as in the first trial except that Si was incorporated at 50 mg kg(-1) Si. The results showed that Cd treatment significantly decreased shoot and root dry weight, while addition of Si at both levels significantly enhanced biomass. Addition of Si at 400 mg kg(-1) Si significantly increased soil pH but decreased soil Cd availability, thus reducing Cd concentration in the shoots and roots and total Cd in the shoots. Moreover, more Cd was found to be in the form of specific adsorbed or Fe-Mn oxides-bound fraction in the Si-amended soil. In contrast, soil pH, available Cd and Cd forms were unaffected by addition of Si at 50 mg kg(-1) Si, but shoot Cd concentration in the Si-amended Cd treatments significantly decreased at both Cd levels used compared to the non-Si-amended Cd treatments. Total Cd in the shoots and roots was considerably and significantly higher in the Si-amended Cd treatments than in the non-Si-amended Cd treatments. The xylem sap significantly increased but Cd concentration in the xylem sap significantly decreased in the Si-amended Cd treatments compared with the non-Si-amended Cd treatments irrespective of Cd and Si levels used. The results suggest that Si-enhanced tolerance to Cd can be attributed not only to Cd immobilization caused by silicate-induced pH rise in the soils but also to Si-mediated detoxification of Cd in the plants.     

Promotion effect of graphene on phytoremediation of Cd-contaminated soil

Echinacea purpurea (L.) Moench was selected as a remediation plant in this study, and different concentrations of graphene oxide (GO) were added to Cd-contaminated soil. Through pot experiments, the effect of E. purpurea on Cd-contaminated soil was determined at 60 days, 120 days, and 150 days. A preliminary study on the remediation mechanism of GO was explored through changes in the forms of Cd in the rhizosphere soil, soil pH, and soil functional groups. Results showed that the optimal concentration of GO was 0.4 g/kg, and under the condition, the accumulation of Cd in the roots of E. purpurea was as high as 113.69 ± 23.86 mg/kg, and the maximum EF reached 5.87 ± 1.34. Compared with those of the control group, accumulated Cd concentration and EF in the roots increased by 60.34% and 2.32, respectively. Correlation analysis showed that the absorption and accumulation of Cd was negatively correlated with the exchangeable Cd content at 120 days, and the exchangeable Cd was negatively correlated with the relative content of functional groups in the soil with 0.4 g/kg GO (E2). The artificial application of GO to the soil can be used as an effective way to improve the effect of E. purpurea in the remediation of Cd soil pollution, and it has great application potential in the stabilization of plants and vegetations and restoration of high-concentration Cd-contaminated soil.

Graphical abstract

     

Effect of soil characteristics on Cd uptake by the hyperaccumulator Thlaspi caerulescens

The influence of soil characteristics on the phytoremediation potential of Thlaspi caerulescens is not well understood. We investigated the effect of soil pH and Cd concentration on plant Cd uptake on one soil type, and the variation in Cd uptake using a range of field contaminated soils. On soils with total Cd concentrations of 0.6-3.7 mg kg(-1), T. caerulescens (the Ganges ecotype) produced greater biomass in the pH range 5.1-7.6 than at pH 4.4. The highest plant Cd concentration (236 mg kg(-1)) and Cd uptake (228 microg pot(-1)) were observed at pH 5.1. On soils with total Cd concentrations of 2.6-314.8 mg kg(-1), shoot Cd concentrations were 10.9-1,196 mg kg(-1). Multiple regression analysis indicated that higher Cd in soil, low pH (within the range of >5) and coarser texture were associated with higher Cd concentration and Cd uptake by T. caerulescens.