渭南市道路移动源高分辨温室气体排放清单及特征研究

根据渭南市机动车保有量和抽样调查与观测数据,采用MOVES模型计算了渭南市2017—2019年道路移动源CO₂、CH₄、N₂O和CO 4种 温室气体的排放量,分析了机动车车型、燃料和排放标准对温室气体排放量的影响.基于ArcGIS和渭南市道路网信息,建立了高分辨率（1 km× 1 km和1 h×1 h）的温室气体排放清单.结果表明,渭南市2019年道路移动源CO₂、CH₄、N₂O和CO的排放量分别为424.322×10⁴、0.044×10⁴、0.007×10⁴和2.808×10⁴ t,以CO₂当量计,机动车温室气体的总排放量为432.843×10⁴ t. 4种道路移动源温室气体中,CO₂占总温室气体排放量的98.03%.渭南市小型客车对温室气体的贡献率最大,分别排放了43.41%的CO₂、74.78%的N₂O和57.17%的CO.大型客车排放了34.47%的CH₄, 汽油车和天然气汽车是N₂O和CH₄的主要排放源,分别排放了86.76%的N₂O和61.87%的CH₄.渭南市道路移动源温室气体排放强度24 h变化呈“双峰”分布,空间分布呈明显的“线-面”特征,这与道路分布密度高度相关,路网密集的城市中心为机动车温室气体的高排放区.     

中国省域农业源非CO2温室气体排放的影响因素分析与峰值预测

运用IPCC清单方法核算了中国各省(直辖市、自治区)农业源非二氧化碳(非CO₂)温室气体(GHG)的排放,基于Tapio弹性脱钩理论和情景预测法、STIRPAT模型和向量自回归模型(VAR)预测了其达峰时间和规模,并结合对数平均迪氏指数(LMDI)模型、STIRPAT模型和固定效应模型识别了中国农业非CO₂ GHG排放的影响因素.结果表明,高情景和中情景下中国农业非CO₂ GHG排放量整体呈上升趋势,到2050年仍未达峰;2018—2050年低情景下GHG排放量整体呈下降趋势,其中,低情景下已于2018年达峰,峰值为0.73×10⁹ t (以CO₂-eq计,下同);北京市、上海市、江苏省、浙江省、福建省、广东省、海南省、重庆市、四川省和青海省农业生产与其农业非CO₂ GHG排放呈强脱钩状态,其余21个省(直辖市、自治区)呈弱脱钩状态;除天津市和黑龙江省以外的29个省(直辖市、自治区),经济和人口为农业非CO₂ GHG排放的促进因素,效率和结构为其抑制因素.     

螃蟹活动对闽江河口互花米草沼泽湿地土壤温室气体排放通量的影响

于2015年1月（冬季）、4月（春季）、6月（夏季）和9月（秋季）,以闽江河口互花米草沼泽湿地为研究区,采用静态箱与气相色谱结合的方法,研究螃蟹对湿地土壤CO₂、CH₄和N₂O排放通量及综合增温潜势的影响。研究表明：温室气体排放季节变化较为显著,CO₂、CH₄排放通量最大值均出现在夏季,N₂O排放通量最大值出现在秋季,CO₂、CH₄和N₂O排放通量最小值均出现在春季。与无螃蟹组相比,高潮滩和中潮滩螃蟹组CO₂、CH₄和N₂O排放通量均值都增大,其中高潮滩螃蟹组CO₂、CH₄和N₂O排放通量依次增大了46.36%、66.67%和69.66%,中潮滩螃蟹组CO₂、CH₄和N₂O排放通量依次增大了53.57%、142.97%、73.08%。相关性分析结果表明：土壤CO₂排放通量与土壤温度显著正相关（n=96,p＜0.05）,CH₄和N₂O排放通量与土壤温度显著正相关（n=96,p＜0.01）;N₂O排放通量与土壤pH显著正相关（n=96,p＜0.01）,与土壤含水量显著正相关（n=96,p＜0.05）。综上所述,螃蟹活动对闽江河口互花米草沼泽湿地土壤的干扰促进了温室气体的排放,为有效调节湿地碳、氮固持作用和湿地生态系统科学管理提供了参考。     

农垦与放牧对内蒙古草原N2O、CO2排放和CH4吸收的影响

利用优选静态箱/气相色谱法(GC),首次对我国内蒙古草原典型地区进行了人类活动对N₂O、CO₂和CH₄交换通量影响的实验观测结果表明,农垦麦田N₂O平均排放通量比原始草原高出3倍,并改变了草甸草原为CO₂汇的性质,使其季节排放净通量以C计增加14.3 mg·(m²·h).随放牧强度的增加CO₂排放通量呈线性增长,轻牧会引起草原对CH₄吸收的大幅增加,而随着放牧压力的增大,增加值迅速回落.农垦麦田与草甸草原相比地-气间CH₄交换无显著变化,放牧强度对N₂O排放影响无显著规律.土壤湿度和温度是影响草原排放N₂O和CO₂、吸收CH4季节变化形式的关键因子,而人类活动仅影响排放强度.排放和吸收量年际间差异很大,但主要受降水的影响.N₂O和CO₂排放与CH₄吸收峰值相反现象普遍存在.     

小型养殖塘水体中CH4、CO2和N2O浓度的时空变化特征及影响因素

养殖塘作为重要的温室气体排放源,水体中温室气体浓度的变化不仅是准确量化温室气体排放量的基础,还是明确其影响因素的重要依据.基于顶空平衡-气相色谱仪法对长三角一处典型的小型养殖塘水体中CH₄、CO₂和N₂ O浓度的时空变化特征以及影响因素进行了分析.结果表明,除春季外,在水温影响下,CH₄和N₂ O浓度在午间或午后出现高值;受水温和水生植物光合作用影响,CO₂浓度的高值出现在晨间光合作用较弱的时候.养殖塘水体中CH₄和CO₂浓度呈现秋季最高、冬季最低的季节变化特征,c（CH₄）在秋季和冬季的均值分别为176.34 nmol·L^-1和32.75 nmol·L^-1,主要受气温、水温和溶解氧（DO）影响;c（CO₂）秋季和冬季的均值分别为134.37 μmol·L^-1和23.10 μmol·L^-1,主要受水生植物光合作用和pH影响;c（N₂ O）在夏季最高,冬季最低,均值分别为97.05 nmol·L^-1和19.41 nmol·L^-1,主要受气温和水温影响.在空间上,垂直方向上,夏季养殖塘c（CH₄）随水深的加深而降低,表层与底层、中间层的浓度差值为71.28 nmol·L^-1和42.80 nmol·L^-1,秋季随水深的加深而升高,底层与表层的浓度差值为163.94 nmol·L^-1.c（CO₂）在夏季和秋季都表现为随着水深的加深而升高,其底层与表层的浓度差值分别为18.69 μmol·L^-1和29.90 μmol·L^-1.N₂ O浓度在垂直方向上无明显变化规律.水平方向上,夏季饲料及春季鸡粪投放的区域会出现CH₄、CO₂和N₂ O浓度的高值,春季和夏季CH₄浓度约为其他区域的1.34~1.98倍和1.95~2.42倍,春季N₂ O浓度和夏季CO₂浓度约为其他区域的1.13~1.26倍和1.39~1.74倍.     

生物质炭与强还原处理对退化设施蔬菜地土壤温室气体排放的影响

生物质炭和土壤强还原处理（Reductive Soil Disinfestation, RSD）可以有效地修复退化设施蔬菜地土壤,但2种修复技术联用对土壤温室气体（CO₂、N₂O和CH₄）排放的影响研究报道较少.本研究采用室内培养实验,设置未修复土壤（CK）、生物质炭修复（BC）、RSD修复（RSD）和BC与RSD联合修复（BC+RSD）4个处理,35℃条件下培养15 d,研究BC与RSD单独以及联合修复对退化设施蔬菜地土壤温室气体排放和综合温室效应（Global Warming Potential, GWP）的影响.结果表明,与对照CK相比,BC处理土壤N₂O排放量显著下降了50.0%,但CO₂排放量和GWP均显著增加（p<0.05）;RSD和BC+RSD处理土壤CO₂、N₂O、CH₄排放量和GWP均大幅度增加.但与RSD处理相比,BC+RSD处理土壤N₂O排放量和GWP分别下降了71.0%和30.0%.相关分析表明,土壤CO₂、N₂O、CH₄排放量和GWP与可溶性有机碳（DOC）和铵态氮（NH₄⁺-N）显著正相关,与pH和硝态氮（NO₃^--N）显著负相关.可见,生物质炭可以减少退化设施蔬菜地RSD修复引起的GWP.     

淡水沼泽湿地CO2、CH4和N2O排放通量年际变化及其对氮输入的响应

利用静态暗箱-气相色谱法自2002～2004年连续3a观测了三江平原淡水沼泽湿地CO₂、CH₄和N₂O 3种主要温室气体排放特征及外源氮素输入条件下温室气体通量的变化.结果表明,三江平原CO₂、CH₄和N₂O 3种主要温室气体排放具有明显的季节及年际变化规律.其中生态系统呼吸CO₂排放的最大值[779.33～965.40 mg·(m·h)^-1]出现在7、8月份,CH4通量最大值[19.19～30.52 mg·(m·h)^-1]出现在8月,N₂O通量最大值[0.072～0.15 mg·(m·h)^-1]出现在5月和9月,3种温室气体通量最小值CO₂为2.36～18.73 mg·(m·h)^-1;CH₄为-0.35～0.59 mg·(m·h)^-1;N₂O为-0.032～-0.009 mg·(m·h)^-1大都出现在冬季,且冬季淡水沼泽湿地表现为N2O的吸收.对气候因子的分析发现,温度条件是影响淡水沼泽湿地温室气体排放通量季节性变化的主要因子,而降水和积水水位变化是影响其排放年际变化的关键因素,特别是降水对CH₄排放通量的影响较其它2种温室气体更显著,且冬季雪融水对夏季CH₄的排放起重要作用.CO₂和CH4排放与土壤温度(5cm)呈显著的指数相关关系,而N₂O排放通量与土壤温度和水深相关性不显著.氮输入促进了三江平原CO₂、CH₄和N₂O 3种主要温室气体的排放,与对照处理相比,其排放通量分别升高了34%,145%和110%.     

凋落物添加和去除处理对三江平原小叶章湿地生长季温室气体排放的影响

为了解三江平原小叶章湿地温室气体排放对凋落物处理的响应,利用黑龙江省科学院自然与生态研究所三江平原湿地生态定位研究站内的试验平台,采用静态箱-气相色谱法,分别对去除当年凋落物（NL）、去除当年凋落物和草炭层（NL+NH）、添加当年凋落物（DL）、添加当年凋落物和草炭层（DL+DH）以及空白对照（CK）等5个处理的小叶章湿地进行了生长季温室气体排放通量观测,并同步观测相关环境因子.结果表明：（DL+DH、DL）处理分别使CO₂排放通量增加了21.23%和10.86%;使生长季CH₄排放通量增加了21.37%和9.81%;使N₂O排放通量增加了29.62%和12.76%.（NL+NH、NL）处理分别使CO₂排放通量降低了16.13%和9.41%;使CH₄排放通量增加了65.67%和45.92%;使N₂O排放通量降低了14.36%和16.92%.添加和去除凋落物均未改变CO₂、CH₄和N₂O排放的季节动态.CO₂排放通量与土壤温度出现了显著正相关关系,CH₄和N₂O排放通量未与土壤温度出现显著相关关系.CO₂、CH₄和N₂O排放通量均未与土壤含水量出现显著相关关系.     

季节性冻融期沼泽湿地CO2、CH4和N2O排放动态

三江平原季节性冻-融时间长达7～8个月,对沼泽湿地温室气体排放有重要影响.采用静态箱/气相色谱法研究了三江平原冻、融期沼泽湿地温室气体排放特征,表明三江平原不同类型沼泽湿地冬季都有明显的CH₄和CO₂排放,且冬季沼泽湿地CH₄排放量在全年CH₄排放中占有重要份额.融冻期沼泽湿地出现明显的CH₄和CO₂排放峰值,季节性积水沼泽化草甸CH₄和CO₂排放量大于常年积水沼泽湿地,而冬季常年积水沼泽湿地CH₄排放通量大于季节性积水沼泽化草甸.融冻期CO₂排放通量与土壤温度(5cm)呈指数相关关系(R²=0.912,p<0.001),沼泽湿地CO₂排放通量与CH₄通量间也呈显著正相关关系(R²=0.751,p<0.001).冬季三江平原沼泽湿地是N₂O的汇,融冻期随着土壤温度升高逐渐成为N₂O的源,且在5月份沼泽湿地表层土壤(0～20cm)融冻期间N₂O排放通量明显增大.三江平原土壤冻、融期间沼泽湿地温室气体的排放特征,反映了冬季微生物活性的存在及融冻作用对土壤碳矿化和氮硝化、反硝化作用有重要影响.     

施用不同污泥堆肥品对土壤温室气体排放的影响

通过田间试验,分别施加两种不同的污泥堆肥品（A：含生物质炭堆肥品,B：不含生物质炭堆肥品）和不同施肥量,分析土壤CO₂、CH₄和N₂O动态变化特征和排放系数,研究施用污泥堆肥品对土壤温室气体排放的影响.结果表明,土壤CO₂和CH₄排放主要集中在生长期,生物质炭堆肥品低施用量能减少CO₂排放,而高施肥量增加CO₂排放.CH₄排放主要为负值,总体表现为土壤吸收CH₄,对照处理吸收量远高于其他处理（P<0.01）,A组处理CH₄吸收量随施肥量的增加而增加（P<0.05）.N₂O排放集中在发芽期和幼苗期,施肥量越高,排放量越大（P<0.01）.污泥堆肥品农用过程排放的温室气体主要是N₂O,施用A、B两种污泥堆肥品的土壤N₂O排放系数分别为1.02%~1.90%和1.28%~2.93%.生物质炭堆肥品具有显著的碳减排效果,其温室气体排放量比不含生物质炭堆肥品的土壤低19.49%~35.56%,且对于N₂O的减排效果较CH₄更为显著.     

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.     

EDTA-enhanced phytoremediation of lead contaminated soil by Bidens maximowicziana

Phytoremediation is a potential cleanup technology for the removal of heavy metals from contaminated soils.Bidens maximowicziana is a new Pb hyperaccumulator,which not only has remarkable tolerance to Pb but also extraordinary accumulation capacity for Pb.The maximum Pb concentration was 1509.3 mg/kg in roots and 2164.7 mg/kg in overground tissues.The Pb distribution order in the B. maximowicziana was:leaf>stem>root.The effect of amendments on phytoremediation was also studied.The mobility of soil Pb and the Pb concentrations in plants were both increased by EDTA application.Compared with CK(control check),EDTA application promoted translocation of Pb to overground parts of the plant.The Pb concentrations in overground parts of plants was increased from 24.23-680.56 mg/kg to 29.07-1905.57 mg/kg.This research demonstrated that B.maximowicziana appeared to be suitable for phytoremediation of Pb contaminated soil,especially,combination with EDTA.     

Distribution and ecological effect of mercury in Laogang landfill, Shanghai, China

Laogang landfill near Shanghai is the largest landfill in China, and receives about 10000 t of daily garbage per day, Samples of topsoil and plants were analyzed to evaluate mercury pollution from the landfill. For topsoil samples, there were significant correlations among total mercury （HgT）, combinative mercury （Hgc） and gaseous mercury （HgG）, and content of total organic carbon （TOC）, but, no significantly relationship was found between Hg content and filling time. Hg content changes in vertical profiles with time showed that the average Hgv of profiles 1992, 1996, and 2000 was similar, but their average HgG was quite different. HgT was significantly correlated with Hgc in profile 1992 and 2000, and Hgv was significantly correlated with Hg6 in profile 1996. HgG/Hgv ratio in profile samples decreased in the order of （HgG,/HgT）1992〉（HgG/HgT）1996〉〉（HgG/HgT）2000. A simple outline of Hg release in landfill could be drawn： with increasing of filling time, degradation undergoes different biodegradation, accordingly, gaseous mercury goes through small, more, and small proportion to total mercury. Distribution of Hg in plants was inhomogeneous, following the order of leaf〉root〉stem. The highest value of leaf may be associated with higher atmospheric Hg from landfill. Ligneous plants （e.g. Phyllostachys glanca, Prunus salicina and Ligustrum lucidum） are capable of enriching more Hg than herbaceous plants.     

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.     

Enzymatic oxidation of aqueous pentachlorophenol

The influence of the nonionic surfactant Tween 80 on pentachlorophenol （PCP） oxidation catalyzed by horseradish peroxidase was studied. The surfactant was tested at concentrations below and above its critical micelle concentration （CMC）. Enhancement of PCP removal was observed at sub-CMCs. The presence of Tween 80 in the reaction mixture reduced enzyme inactivation which occurred through a combination of free radical attack and sorption by precipitated products. A simple first-order model was able to simulate time profiles for enzyme inactivation in the presence or absence of Tween 80. At supra-CMCs, the surfactant caused noticeable reductions in PCP removal, presumably through micelle partitioning of PCP which precluded the hydrophobic PCP molecule from interacting with the enzyme.     

Decomposition of alachlor by ozonation and its mechanism

Decomposition and corresponding mechanism of alachlor, an endocrine disruptor in water by ozonation were investigated. Results showed that alachlor could not be completely mineralized by ozone alone. Many intermediates and final products were formed during the process, including aromatic compounds, aliphatic carboxylic acids, and inorganic ions. In evoluting these products, some of them with weak polarity were qualitatively identified by GC-MS. The information of inorganic ions suggested that the dechlorination was the first and the fastest step in the ozonation of alachlor.     

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.     

基于综合水质标识指数和对应分析法的校园河道水质评价

以三峡大学的校园河道求索溪为研究对象,利用综合水质标识指数法确定求索溪水质类别,分析其水质时空变化规律,并利用对应分析法得出求索溪中不同监测点的主要污染因子.研究结果表明:求索溪整体的综合水质标识指数为7.423,整体水质为劣V类(地表水环境质量标准GB 3838-2002)且黑臭.从时间变化来看,求索溪4月份的水质最差,5月份次之,4、5月份所有监测点的水质都劣于V类且黑臭;8月份水质最好,水质为Ⅳ类;从空间分布来看,8个监测点综合水质标识指数均超过6.0,水质为劣V类,其中6号监测点的水质相对最好,监测点3号的水质相对最差;对应分析法得出求索溪的整体水体污染程度受总氮因子的影响最大,其次为总磷.该研究拟为求索溪及类似校园河道的水环境治理研究提供基础依据和参考.     

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.