典型行业再利用土壤重金属含量分布、来源解析及生态风险评价

为深入探究典型行业再利用土壤重金属污染特征及生态风险状况,基于上海市嘉定区49个地块315个不同深度剖面土壤样品数据,采用地累积指数和潜在生态风险指数评估Cd、Pb、Cu、Zn、Ni、Hg和As这7种重金属含量特征和潜在生态风险程度,并利用源解析受体模型（APCS-MLR）和正定矩阵因子分解模型（PMF）解析其污染来源.结果表明：①研究区土壤中除As外,其余重金属均不同程度超过上海市土壤背景值,表层土壤中Cd、Pb、Cu、Zn、Ni和Hg含量分别是背景值的3.54、2.34、2.91、1.20、3.75和4.40倍;7种重金属含量随着土壤垂直剖面深度的增加逐渐降低,重金属在表层土壤中存在一定程度的富集,人类活动影响了重金属在土壤中的分布规律.②研究区内APCS-MLR和PMF两种受体模型均识别出土壤重金属4种主要来源,源1（Cu、Zn和Pb）为金属制品和汽车制造混合源,源2（Ni和Cd）为电镀企业来源,源3（Hg）主要为化工企业来源,源4（As）为自然源,两种受体模型结合运用,进一步提高源解析的精准度和可信度.③地累积指数由大到小表现为：Hg（1.54）>Ni（1.32）>Cd（1.21）>Cu（0.96）>Pb（0.64）>Zn（-0.33）>As（-1.02）;潜在生态风险指数结果显示,研究区综合潜在生态风险指数RI值在32.50~4 910.97,均值为321.40,整体呈现较强潜在生态风险,再开发利用工业场地土壤中重金属Hg、Ni和Cd的污染值得进一步关注.     

滇黔桂岩溶区河漫滩土壤重金属含量、来源及潜在生态风险

利用全国地球化学基准计划在滇黔桂岩溶区35个点位采集的70件河漫滩表、深层土壤样品,分析了As、Cd、Cr、Cu、Hg、Ni、Pb和Zn 8种重金属元素含量特征,探究了重金属来源、污染状况及潜在生态风险.结果表明,8种重金属元素含量大部分均高于全国土壤背景值,在滇东南地区含量最高,桂西北地区最低.表层土壤Cd、Hg明显富集,As、Cr、Cu、Ni与深层土壤含量相当;As、Cd、Hg、Pb、Zn在农田、菜地中明显高于深层土壤,Cr、Cu和Ni在各类土地中与深层土壤相当.因子分析结果显示,表层土壤中Cd、Cr、Cu、Ni受地质背景控制,As、Pb、Zn既与地质背景有关,也受人为活动影响,Hg受人为活动影响较严重;深层土壤中Cd、Cr、Cu、Ni、Cr、Zn继承了区域母岩特征,As、Hg和Pb受地质背景和人为活动双重影响.地累积指数法和富集因子法污染评价结果表明,研究区河漫滩表层土壤中Cd、Hg污染较重,As、Cr、Cu、Ni、Pb、Zn大部分为轻度污染或无污染.各重金属潜在生态风险指数高低顺序依次为Hg > Cd > As > Cu > Ni > Pb > Cr > Zn,Cd和Hg的生态风险指数之和占综合指数的82.43%,生态风险最高;滇东南地区重金属潜在风险综合指数最高,具重度生态风险.     

神木北部矿区重金属污染与生态风险评价

通过测试神木北部矿区及其毗邻地区2种主要土壤类型区(风沙区和黄土区)的8种重金属(As、Cd、Cr、Hg、Pb、Cu、Zn、Ni)元素含量,了解研究区土壤重金属累积污染状况,同时采用生态风险指数法,对土壤重金属单因子和综合潜在生态风险危害进行评价。结果表明:煤矿开采区Hg、Cr、As、Cu、Zn元素较未开发的毗邻地区分别增加了850%、33%、64%、51%、79%,Pb、Ni差异不明显,而Cd降低了65%;除Pb、Cd外其他几种重金属累积污染超标倍数表现为风沙区大于黄土区;Hg元素的单因子潜在生态风险系数为重度生态风险等级,其他7种重金属均为低生态风险等级;风沙区综合潜在生态风险指数等级为严重污染,黄土区表现为重度污染。     

辽东湾表层沉积物重金属污染特征及潜在生态危害评价

为了解辽东湾海域表层沉积物重金属的污染特征,利用原子吸收分光光度法及原子荧光法测定了辽东湾33个站位表层沉积物中Hg、Cu、Pb、Cd、Cr、Zn及As共7种重金属的含量,同时应用地累积指数法及潜在生态风险评价法对辽东湾海域进行了污染程度及潜在生态风险评价。结果表明:（1）重金属相关性及主因子分析表明,辽东湾表层沉积物中Zn、Cu、Pb、Cr、Cd、As和Hg可能具有同一污染源;（2）辽东湾海域表层沉积物中Hg、Cu、Pb、Cd、Cr、Zn、As的平均质量浓度分别为0.09、18.81、20.55、0.35、34.15、52.94、5.84 mg/kg;（3）重金属污染程度由高到低依次为:Cd > Hg > Cu > Pb > Zn > As > Cr;（4）单个重金属生态风险由高到低依次为:Hg > Cd > As > Cu > Pb > Cr > Zn,研究海域除锦州湾13号站位附近具有很高的生态风险外,其他海域生态风险处于轻微或中等生态危害水平。     

闽中某矿区县茶园土壤和茶叶重金属含量及健康风险

以闽中某矿区县茶园表层土壤（0~20cm）为研究对象,采集了25份茶园土壤样品,分析了土壤中重金属Cr、Ni、Cu、Zn、As、Pb、Cd和Co的含量,分别利用地累积指数法和潜在生态风险指数法对土壤重金属的污染现状和潜在生态风险程度进行评价;同时收集矿区茶叶企业23个商品茶样品,利用美国国家环保署（USEPA）推荐的健康风险评价模型进行人体重金属健康风险评价.结果表明：（1）矿区茶园表层土壤Cr、Ni、Cu、Zn、As、Pb、Cd和Co平均含量分别为110、23.5、23.0、107、50.7、78.0、0.23和14.3mg/kg,均明显高于福建省土壤背景值;（2）茶园土壤地累积指数（I_geo）表现为As > Cd > Cr > Pb > Zn > Co > Ni > Cu,As属于重度污染,Cd和Cr属于中度污染,其它5种重金属元素污染风险较低;（3）单项潜在生态风险系数（E）的大小顺序依次为Cd > As > Pb > Co > Ni > Cr > Cu > Zn,土壤Cd属于很强生态风险,土壤As属于较强生态风险,其余属于轻微生态风险.8种重金属综合潜在生态风险指数（RI）平均值为255.74,属于较强风险级别,Cd和As是最主要的潜在生态风险因子.（4）商品茶中重金属Cr和Cd含量均低于限量标准,个别茶样中Cu、As和Pb含量超标,说明茶叶中重金属含量总体处于安全级别;（5）健康风险评价结果表明,茶叶中重金属元素健康个人年风险总和为1.01×10^-4~9.07×10^-5,乌龙茶的个人年风险总和稍高于美国环境保护署（USEPA）推荐的最大可接受风险水平（1.0×10^-4）,红茶和绿茶低于USEPA推荐的最大可接受风险水平;茶叶中重金属元素健康风险以Cr为主,平均贡献率为90.38%,是主要的风险元素,其余重金属元素处于安全范围之内.     

武汉集中式饮用水源地土壤重金属的时空分布特征及生态风险评价

研究了武汉市19个集中式饮用水源地土壤重金属Cd、Hg、As、Pb、Cr、Cu、Ni和Zn的时空分布特征,采用单因子污染指数和综合污染指数分析重金属污染程度,利用潜在生态风险指数评价重金属生态风险,通过相关性和聚类分析重金属的来源.结果表明,武汉市中心城区水源地土壤重金属的含量普遍高于远城区,同时长江干流附近的水源地土壤重金属含量普遍高于长江支流.Hg、As、Pb、Cr、Cu、Ni和Zn的单项潜在生态风险指数平均值均小于40,属于轻微风险程度.Cd的单项潜在生态风险指数平均值在80~160范围内,属于强度风险程度.武汉集中式饮用水源地土壤重金属的综合潜在生态风险指数平均值为142.12,属于轻微风险水平.相关性分析表明,武汉集中式水源地土壤重金属Cu、Pb和Cr来源相似,均与交通有关;Ni、As、Cr和Cu来源相似,均与冶金生产有关;Zn、Hg和Cr来源相似,均与防腐和催化化工有关.武汉白沙洲水厂和堤角水厂周边土壤长期定点监测表明,2017年后武汉集中式水源地土壤各种重金属含量均呈现显著下降趋势,其生态风险在未来将进一步降低.     

兰州市黄河风情线地表积尘及周边绿地土壤重金属污染特征及风险评价

为研究城市滨河公园景区地表积尘和周边绿地土壤重金属污染状况及潜在生态风险和健康风险,选择兰州市黄河风情线沿线的游园、广场和主题公园为研究区,分别采集了27个地表积尘和26个周边绿地表土样品.采用地累积指数(I_geo)、单因子污染指数(P_i)、内梅罗综合污染指数(P_N)和改进的潜在生态风险指数(RI)评估Cr、 Ni、 Cu、 Zn、 As、 Cd、 Hg和Pb这8种重金属污染特征和潜在生态风险程度,并利用暴露风险模型进行健康风险评价.结果表明,研究区地表积尘和周边绿地土壤As含量的平均值略低于甘肃省土壤元素背景值,但地表积尘的其余元素均高于甘肃省和兰州市元素背景值,而周边绿地除Cr和Ni元素略低于甘肃省和兰州市的背景值之外,其余Cu、 Zn、 Cd、 Hg和Pb含量的平均值却高于两者的背景值.地累积指数和单因子污染指数显示,研究区地表积尘受到Cr、 Cu、 Zn、 Cd、 Hg和Pb的污染,沿途绿地土壤存在不同程度的Cu、 Zn、 Cd、 Hg和Pb的污染.内梅罗综合污染指数表明,研究区地表积尘和周边绿地土壤的综合污染程...     

重庆某铁矿区周边耕地土壤重金属污染评价及来源解析

为了解重庆市南部某历史遗留铁矿区周边耕地土壤重金属污染状况及污染来源,在铁矿渣场周边采集了34个耕地表层土壤样品,分析了重金属Cd、Hg、As、Pb、Cr、Cu、Ni和Zn的含量,采用地累积指数和潜在生态风险指数对铁矿渣场周边耕地土壤污染进行评价,并利用主成分分析（PCA）和绝对主成分得分多元线性回归受体模型（APCS-MLR）识别铁矿区周边耕地土壤重金属的污染来源及贡献率.结果表明,研究区土壤除Cr外,其余重金属含量平均值均超过重庆市土壤背景值,且有20.6%的土壤点位Cd以及2.94%的土壤点位Hg、Cu和Ni超过《土壤环境质量农用地土壤污染风险管控标准（试行）》（GB15618-2018）风险筛选值;地累积污染指数评价结果显示研究区土壤主要受Cd和Hg污染,呈现无污染到中度污染等级,并且Cd与Hg对潜在生态污染指数（RI）贡献率分别达到24.47%和60.33%.相关性分析与主成分/绝对主成分（PCA/APCS）受体模型分析结果表明,Cr、Cu、Ni和Zn主要来源于成土母质,Hg和Pb来源主要为化石燃料燃烧及交通运输,Cd和As主要来源于采矿冶炼、施用化肥等采矿工业活动及农业活动...     

海绵城市生物滞留带重金属污染特征及风险评价

生物滞留带作为海绵城市重要的净水和渗水措施,在全国海绵城市建设中得到了广泛的应用.为了探明生物滞留带重金属累积、污染和可能存在的环境风险,以全国首批海绵城市建设示范区重庆市悦来新城生物滞留带为研究对象,探讨其重金属含量与空间分布特征,利用污染系数、地质累积指数和潜在生态风险指数进行污染水平和生态环境风险评价.结果表明,悦来新城生物滞留带中除Mn外,Cu、Zn、Pb、Ni和Cd的含量平均值均超出重庆市土壤背景值的4.14、1.77、4.98、1.23和6.51倍.空间分布上,不同功能区域道路旁的生物滞留带重金属含量呈现出较大差异性,工业区道路生物滞留带中Cu、Zn、Mn、Pb、Ni和Cd的含量均显著高于其他区域生物滞留带中的同种类重金属含量（P<0.05）.污染系数和地质累积指数显示重金属的污染水平排序为：Mn相似文献   

杭州蔬菜基地重金属污染及风险评价

为掌握杭州市蔬菜基地土壤中重金属污染状况,采用野外调查结合室内分析法,就杭州市10个区县30个蔬菜基地中203个土壤样品进行了Cu、Zn、Pb、Cd、Cr、As和Ni含量的分析及评价,并就重金属含量与土壤理化指标进行了相关分析.结果表明,杭州市菜地土壤中Zn、Cr、As、Ni含量均未超标,但部分土壤中Cu、Pb和Cd含量有超标现象.污染指数评价表明,杭州市菜地土壤重金属综合污染等级多为轻度污染,且主要以Cd污染为主.累积评价表明,杭州市菜地土壤重金属多呈中高度累积,亦主要由土壤Cd累积所致.潜在生态风险评价表明,杭州市菜地土壤中Cu、Zn、Pb、Cr、As和Ni的生态风险轻微,综合潜在生态风险处于中等水平,但Cd存在较强的潜在生态风险.相关分析表明,土壤中Cu、Zn、Pb、As、Cd含量受土壤理化性质影响较大.综上,杭州市要做好菜地土壤重金属的污染防治工作,尤其要防范Cd的污染风险.     

Toxic effects of acetochlor, methamidophos and their combination on nifH gene in soil

Toxic effects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel electrophoresis （DGGE） and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene diversity （both in gene richness and diversity index values） and caused changes in the nifH gene composition. The effects of acetochlor on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed that nifH gene composition which had been affected by low concentration of acetochlor （50 mg/kg） recovered firstly. Methamidophos reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos （150 mg/kg） caused the most apparent changes in nifH gene diversity at the first week while the high concentration of methamidophos （250 mg/kg） produced prominent effects on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found at 1 week and maximal changes at 4 weeks. Toxic effects of acetochlor and methamidophos combination on nifH gene were also apparent. Different nifH genes （bands） responded differently to the impact of agrochemicals： four individual bands were eliminated by the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 different nifH sequences, which were used for phylogenetic reconstructions. All sequences were affiliated with the alpha- and beta-proteobacteria, showing higher similarity to eight different diazotrophic genera.     

Arsenic uptake by arbuscular mycorrhizal maize （Zea mays L.） grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment.Non-mycorrhizal and zero-P addition controls were included.Plant biomass and concentrations and uptake of As,P,and other nutrients,AM colonization,root lengths,and hyphal length densities were determined.The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium.Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments,but shoot and root biomass of AM plants was depressed by P application.AM fungal inoculation decreased shoot As concentrations when no P was added,and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition,respectively.Shoot and root uptake of P,Mn,Cu,and Zn increased,but shoot Fe uptake decreased by 44.6%,with inoculation, when P was added.P addition reduced shoot P,Fe,Mn,Cu,and Zn uptake of AM plants,but increased root Fe and Mn uptake of the nonmycorrhizal ones.AM colonization therefore appeared to enhance plant tolerance to As in low P soil,and have some potential for the phytostabilization of As-contaminated soil,however,P application may introduce additional environmental risk by increasing soil As mobility.     

Degradation of metabolites accumulated of benzo[a]pyrene by coupling Penicillium Chrysogenum with KMnO4

Several main metabolites of benzo[a]pyrene （BaP） formed by Penicillium chrysogenum, Benzo[a]pyrene-1,6-quinone （BP 1,6- quinone）, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene （BP 7,8-diol）, 3-hydroxybenzo[a]pyrene （3-OHBP）, were identified by high-performance liquid chromatography （HPLC）. The three metabolites were liable to be accumulated and were hardly further metabolized because of their toxicity to microorganisms. However, their further degradation was essential for the complete degradation of BaP. To enhance their degradation, two methods, degradation by coupling Penicillium chrysogenum with KMnO4 and degradation only by Penicillium chrysogenum, were compared; Meanwhile, the parameters of degradation in the superior method were optimized. The results showed that （1） the method of coupling Penicillium chrysogenum with KMnO4 was better and was the first method to be used in the degradation of BaP and its metabolites; （2） the metabolite, BP 1,6-quinone was the most liable to be accumulated in pure cultures; （3） the effect of degradation was the best when the concentration of KMnO4 in the cultures was 0.01% （w/v）, concentration of the three compounds was 5 mg/L and pH was 6.2. Based on the experimental results, a novel concept with regard to the bioremediation of BaP-contaminated environment was discussed, considering the influence on environmental toxicity of the accumulated metabolites.     

Impact of atrazine and nitrogen fertilizers on the sorption of chlorotoluron in soil and model sorbents

Sorption of chlorotoluron in ammonium sulfate, urea and atrazine multi-solutes system was investigated by batch experiments. The results showed application of nitrogen fertilizers to the soil could affect the behavior of chlorotoluron. At the same concentration of N, sorption of chlorotoluron decreased as the concentration of atrazine increased on the day 0 and 6 in soil, respectively. The sorption of chlorotoluron increased from 0 to 6 d when soils were preincubated with deionized water, ammonium sulfate and urea solution for 6 d. That indicated incubation time was one of the most important factors for the sorption of chlorotoluron in nitrogen fertilizers treatments. The individual sorption isotherms of chlorotoluron in rubbery polymer and silica were strictly linear in single solute system, but there were competition sorption between pesticides or between pesticides and nitrogen fertilizers. That indicated the sorption taken place by concurrent solid-phase dissolution mechanism and sorption on the interface of water-organic matter or water-mineral matter.     

Potential of plant polyphenol oxidases in the decolorization and removal of textile and non-textile dyes

In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.     

Effects of two sludge application on fractionation and phytotoxicity of zinc and copper in the soil

The potential harm of heavy metals is a primary concern in application of sludge to the agricultural land. A pot experiment was conducted to evaluate the effect of two sludges on fractionation of Zn and Cu in soil and their phytotoxicity to pakchoi. The loamy soil was mixed with 0%, 20%, 40%, 60% and 80% (by weight) of digested sewage sludge (SS) and composted sludge (SC). The additions of both sludges caused a significant raise in all fractions, resulting in that exchangeable (EXCH) and organic bound (OM) became predominance of Zn and organic bound Cu occupied the largest portion. There was more available amount of Zn and Cu in SS treatments than SC treatments. During the pot experiment, the concentration of Zn in EXCH, carbonate (CAR) and OM and Cu in EXCH and OM fractions decreased in all treatments, so their bioavailability reduced. Germination rate and plant biomass decreased when the addition rate was high and the best yield appeared in 20% mixtures at the harvest of pakchoi. The two sludges increased tissue contents of Zn and Cu especially in the SS treatments. Zn in pakchoi was not only in relationship to ΔEXCH and ΔCAR forms but also in ΔOM forms in the sludge-soil mixtures. Tissue content of Cu in pakchoi grown on SC-soils could not be predicted by ΔEXCH. These correlation rates between Zn and Cu accumulation in pakchoi and variation of different fractions increased with time, which might indicate that sludges represented stronger impacts on the plant in long-term land application.     

Intraspecific differences in effects of co-contamination of cadmium and

A hydroponic experiment was carried out to study intraspecific differences in the effects of different concentrations of cadmium (Cd)(0-10 mg/L) and arsenate (As(V)) (0-8 mg/L) on the growth parameters and accumulation of Cd and As in six wheat varieties Jing-9428, Duokang-1, Jingdong-11, Jing-411, Jingdong-8 and Zhongmai-8. The endpoints of wheat seedlings, including seed germination,biomass, root length and shoot height, decreased with increasing the Cd and As concentrations. Significant differences in seed germination, biomass, root length, shoot height and the accumulation of Cd and As were observed between the treatments and among the varieties (p ＜ 0.05). The lethal dosage 50% were about 20, 80, 60, 60, 80 and 20 mg As/L for Jing-9428, Duokang-1, Jingdong-11,Jing-411, Jingdong-8 and Zhongmai-8, respectively, and the corresponding values for Cd were about 30, 80, 20, 40, 60 and 10 mg Cd/L, respectively. Among the six varieties, Duokang-1 was found to be the most resistant to Cd and As toxicity, and Zhongmai-8 was the most sensitive to Cd and As co-contamination. The resistance of the six varieties was found dependant on the seedling uptake of Cd and As. Duokang-1 was the most suitable for cultivation in Cd and As co-contaminated soils.     

Removal of heavy metals from sewage sludge by low costing chemical method and recycling in agriculture

ＲｅｍｏｖａｌｏｆｈｅａｖｙｍｅｔａｌｓｆｒｏｍｓｅｗａｇｅｓｌｕｄｇｅｂｙｌｏｗｃｏｓｔｉｎｇｃｈｅｍｉｃａｌｍｅｔｈｏｄａｎｄｒｅｃｙｃｌｉｎｇｉｎａｇｒｉｃｕｌｔｕｒｅＷｕＱｉｔａｎｇ，ＮｙｉｒａｎｄｅｇｅＰａｓｃａｓｉｅ，ＭｏＣｅｈｕｉＦ...     

Isolation and preliminary characterization of a 3-chlorobenzoate degrading bacteria

A study was conducted to compare the diversity of 2-, 3-, and 4-chlorobenzoate degraders in two pristine soils and one contaminated sewage sludge. These samples contained strikingly different populations of mono-chlorobenzoate degraders. Although fewer cultures were isolated in the uncontaminated soils than contaminated one, the ability of microbial populations to mineralize chlorobenzoate was widespread. The 3- and 4-chlorobenzoate degraders were more diverse than the 2-chlorobenzoate degraders. One of the strains isolated from the sewage sludge was obtained. Based on its phenotype, chemotaxonomic properties and 16S rRNA gene, the organism S-7 was classified as Rhodococcus erythropolis. The strain can grow at temperature from 4 to 37℃. It can utilize several （halo）aromatic compounds. Moreover, strain S-7 can grow and use 3-chlorobenzoate as sole carbon source in a temperatures range of 10-30℃ with stoichiometric release of chloride ions. The psychrotolerant ability was significant for bioremediation in low temperature regions. Catechol and chlorocatechol 1,2-dioxygenase activities were present in cell free extracts of the strain, but no （chloro）catechol 2,3- dioxygenase activities was detected. Spectral conversion assays with extracts from R. erythropolis S-7 showed accumulation of a compound with a similar UV spectrum as chloro-cis,cis-muconate from 3-chlorobenzoate. On the basis of these results, we proposed that S-7 degraded 3-chlorobenzoate through the modified ortho-cleave pathway.     

Single and joint effects of pesticides and mercury on soil urease

The influence of two pesticides including chlorimuron-ethyl and furadan and mercury （Hg） on urease activity in 4 soils （meadow burozem and phaeozem） was investigated. The soils were exposed to various concentrations of the two pesticides and Hg individually and simultaneously. Results showed that there was a close relationship between urease activity and organic matter content in soil. Chlorimuron-ethyl and furadan could both activate urease in the 4 soils. The maximum increment of urease activity by chlorimuronethyl was up to 14%-18%. There was almost an equal increase （up to 13%-21%） in the urease activity by furadan. On the contrary, Hg markedly inhibited soil urease activity. A logarithmic equation was used to describe the relationship （P〈0.05） between the concentration of Hg and the activity of soil urease in the 4 tested soils. Semi-effect dose （ED50） values by the stress of Hg based on the inhibition of soil urease in the 4 soils were 88, 5.5, 24 and 20 mg/kg, respectively, according to the calculation of the corresponding equations. The interactive effect of chlorimuron-ethyl or furadan with metal Hg on soil urease was mainly synergic at the highest tested concentrations.