稻草烟尘中正构烷烃和正构脂肪酸的碳同位素

为了查清稻草燃烧烟尘中正构烷烃和正构脂肪酸的碳同位素分馏状况,对我国的6种稻草在明火燃烧和闷烧条件下进行室内模拟试验,并测定了烟尘中两类有机物的单体碳同位素.结果表明,在明火烟尘中,正构烷烃和正构脂肪酸单体的δ13C值分别为-28.6‰～-38.8‰、-29.6‰～-41.9‰;正构烷烃和正构脂肪酸的平均碳同位素组成分别是-32.6‰～-36.4‰、-34.0‰～-36.2‰.在多数稻草的明火烟尘中,正构烷烃总体上比秸秆内同碳数烷烃亏损13C,其δ13C值最大相差4.1‰.大部分正构脂肪酸的单体碳同位素组成比稻草重,二者最大相差6.3‰.在闷烧烟尘中,正构烷烃和正构脂肪酸的单体δ13C值分别为-31.7‰～-39.0‰、-31.3‰～-38.8‰;正构烷烃和正构脂肪酸的平均碳同位素组成分别为-35.1‰～-36.4‰、-34.4‰～-35.6‰.在多数稻草的闷烧烟尘中,正构烷烃的单体碳同位素组成比稻草轻,二者最大相差6.1‰;而正构脂肪酸的单体碳同位素却比稻草重,二者最大相差8.4‰.稻草闷烧时排放的正构烷烃比明火燃烧时排放的更趋向于亏损13C,而高碳数（≥C19）正构脂肪酸的单体碳同位素组成呈现出比明火烟尘偏重的趋势.在稻草烟尘中,正构烷烃和正构脂肪酸的单体碳同位素组成与未燃烧稻草中的对应化合物有显著差别.烟尘中两类有机物相对于稻草而发生了方向相反的碳同位素分馏.     

秸秆烟尘中正构脂肪醇和甾醇的碳同位素组成

选取稻草、麦秸和玉米秸进行室内模拟燃烧试验,用气相色谱/稳定同位素在线分析系统(GC/C/IRMS)测定了烟尘中正构脂肪醇和甾醇的单体碳同位素比值.结果显示:在稻草明火烟尘中,正构脂肪醇(C20~C30)和甾醇(胆固醇、菜油甾醇、豆甾醇、β-谷甾醇)与稻草δ~(13)C值之差(Δ~(13)C)的平均值分别为-1.3‰、+0.7‰.在稻草闷烧烟尘中,两类化合物的Δ~(13)C平均值分别为-1.4‰、+1.1‰.在麦秸明火烟尘中,正构脂肪醇和甾醇单体的Δ~(13)C平均值分别为+2.4‰、+0.5‰.在麦秸的闷烧烟尘中,两类化合物的Δ~(13)C平均值分别为+3.0‰、+1.7‰.在玉米秸的明火烟尘中,两类化合物的Δ~(13)C平均值分别为-2.5‰和+0.7‰.在玉米秸闷烧烟尘中,两类有机物的Δ~(13)C平均值分别为-3.8‰、+1.8‰.3类秸秆烟尘中的正构脂肪醇和甾醇均发生了明显的碳同位素分馏.秸秆闷烧比明火燃烧更有利于烟尘中此两类有机物发生碳同位素分馏.这对识别气溶胶中以秸秆燃烧为来源的这两类有机物有参考意义.     

玉米秸秆烟尘中正构脂肪酸的分子与碳同位素组成

在模拟的明火燃烧和闷烧条件下对4种玉米秸秆进行了焚烧试验,用GC/MS和GC/C/IRMS分别测定烟尘中正构脂肪酸的分子与碳同位素组成.结果表明,在明火烟尘中正构脂肪酸由C7~C_(34)组成,其平均总含量为13 895.0 mg·kg-1.其低碳数(≤C_(16))与高碳数(C_(16))正构脂肪酸的含量比(L/H)平均值为1.1.C_(18)/C_(16)、C_(24)/C_(16)、C_(24)/C_(18)、C_(24)/(C_(22)+C_(26))(CAR)的平均值分别为0.33、0.17、0.50、1.2.正构脂肪酸单体表现出以C_(16)、C_(24)为主、次峰碳数的双峰式分布模式.其碳优势指数(CPI)的平均值为4.5.在闷烧烟尘中正构脂肪酸由C_6~C_(34)组成,其平均总含量为50 183.7 mg·kg-1.L/H、C_(18)/C_(16)、C_(24)/C_(16)、C_(24)/C_(18)、CAR的平均值分别为1.3、0.33、0.20、0.60、1.6.也具有与明火烟尘相同的分布模式.其CPI的平均值为6.1.明火烟尘中C_(14)~C_(26)单体的δ~(13)C平均值在-21.0‰~-24.8‰之间变化,总平均值为-23.5‰.该值与玉米秸秆中对应值之差(Δ~(13)C)达-0.7‰.闷烧烟尘中C_(14)~C_(26)单体δ~(13)C平均值的变化范围为-21.8‰~-25.4‰,总平均值为-23.3‰.其Δ~(13)C值达-0.5‰.与玉米秸秆相比,两种烟尘中正构脂肪酸的分子组成和碳同位素组成均发生了明显的改变.L/H、C_(24)/C_(16)、C_(24)/C_(18)、CAR、δ~(13)C等指标可用于识别大气气溶胶中玉米秸秆燃烧来源的正构脂肪酸.     

秸秆燃烧排放的正构烷烃及其碳同位素组成特征

为了探讨生物质燃烧过程中正构烷烃化学组成及其碳同位素的变化规律,对4种玉米秸秆进行了室内焚烧实验,用GC-MS和GC/C/IRMS方法对燃烧前后的样品进行测定.结果表明,秸秆中正构烷烃的碳数为C13~C35,分布形态为单峰型,主峰碳数为C31.正构烷烃的碳优势指数(CPI)值为1.1~5.3,平均碳链长度(ACL)为25.1~28.8.明火烟尘中正构烷烃的碳数为C14~C35,呈双峰型分布,2个主峰碳数分别是C18和C31.其CPI值为1.0~2.4,ACL值为23.0~26.8.正构烷烃单体碳同位素比值为-20.1‰~-33.5‰.闷烧烟尘中正构烷烃的碳数是C12~C35,CPI值为2.2~4.8,ACL值为26.6~28.9.其含量呈双峰式分布,2个主峰碳数分别是C22/C23、C31.正构烷烃单体碳同位素比值为-21.5‰~-32.5‰.在明火烟尘和闷烧烟尘中,正构烷烃的单体碳同位素组成与原秸秆中同碳数正构烷烃的差值分别为-13.8‰~5.4‰、-6.7‰~ -5.1‰.2种烟尘中正构烷烃的化学组成与碳同位素分布都与原玉米秸秆有着显著的差别.     

稻草和玉米秸秆燃烧烟尘中正构烯烃的组成

在明火燃烧和闷烧条件下对6种稻草和5种玉米秸秆进行了燃烧试验,并对烟尘中的正构烯烃进行了分析.结果表明,在稻草明火烟尘中,正构烯烃由C15~C29组成,其平均总含量为918.7mg/kg,低碳数与高碳数正构烯烃含量比(L/H)的平均值为0.6,碳优势指数(CPI)的平均值为1.2.正构烯烃呈双峰式分布,两个峰碳数主要是C24和C28.在稻草闷烧烟尘中,正构烯烃由C17~C29组成,其总含量、L/H、CPI等的平均值分别是517.0mg/kg、0.7和0.9.正构烯烃同样呈双峰型分布,两个峰碳数主要是C23和C28.在玉米秸秆的明火烟尘中,正构烯烃由C19~C29组成.其总含量、L/H、CPI等的平均值分别为126.0mg/kg、0.7和1.3.正构烯烃呈单峰型分布,主峰碳数主要是C24和C23.在玉米秸秆的闷烧烟尘中,正构烯烃由C17~C29组成,其总含量、L/H、CPI等的平均值分别是198.9mg/kg、1.8和 0.9.正构烯烃呈双峰式分布,其主峰碳数均为C23,次峰碳数主要是C29.在两类秸秆燃烧产生的烟尘之间,正构烯烃的组成存在明显差别.这有助于识别气溶胶中稻草或玉米秆燃烧来源的此类污染物.     

稻草及其烟尘中正构脂肪酸的组成

为了解稻草露天焚烧产生烟尘中正构脂肪酸的组成特征,在明火燃烧和闷烧条件下对6种稻草进行了模拟焚烧试验,采集了排放的烟尘,并用GC/MS进行测定.结果表明,稻草中的正构脂肪酸由C8~C34组成.明火烟尘中含有碳数为C8~C34的正构脂肪酸.其总含量的变化区间是8613.9~27225.0μg/g,平均值为15147.4μg/g.正构脂肪酸呈现以C16、C24为主、次碳峰的双峰式分布,并具有显著的偶碳数优势.其碳优势指数(CPI)的分布区间是3.08~6.41,平均值为4.31.平均碳链长度(ACL)为18.51~21.77,平均值是20.48.C24/C16值分布在0.11~0.41之间.闷烧烟尘中正构脂肪酸的碳数范围是C6~C34.其总含量的分布区间是59112.6~95214.3μg/g,平均值为76934.9 μg/g.呈与明火烟尘类似的双峰式分布,偶碳数优势显著.其CPI为3.88~5.24,平均值为4.38.ACL值分布在17.37~18.91之间,平均值为18.42.C24/C16比值为0.07~0.23.明火烟尘中C24/C16比值比稻草有所下降.闷烧烟尘中C24/C16比值均小于稻草和明火烟尘,正构脂肪酸的ACL也明显小于稻草和明火烟尘.烟尘中正构脂肪酸的组成相比原稻草已发生了明显的改变.     

典型排放源黑碳的稳定碳同位素组成研究

采集了我国主要的黑碳排放源(生物质燃烧、民用燃煤和机动车尾气)的烟尘样品,分析烟尘中黑碳(BC)和总碳(TC)与原始燃料的稳定碳同位素组成(δ13C),对比各种δ13C值之间的关联性,评估运用δ13C技术进行BC源解析的潜力.结果表明:①3种典型排放源烟尘样品的δ13CBC与燃料有较好的一致性,且不同排放源的δ13CBC变化范围之间有比较明显的差别:生物质燃料除玉米秸(C4植物,δ13CBC为-13.62‰)显著不同外,C3植物的δ13CBC平均值为-26.49‰±1.17‰;烟煤的平均值为-23.46‰±0.37‰;机动车尾气(包括柴油车和汽油车)的平均值为-25.17‰±0.40‰.②各种排放源的BC形成过程存在程度各异的碳同位素分馏,C4植物(玉米秸)燃烧过程分馏作用较明显(BC的δ13C相对燃料负偏1.62‰),而C3植物和民用煤燃烧过程的分馏较小(分别正偏0.63‰和0.52‰).③BC的纯化手段(CTO-375方法)对生物质烟尘的δ13C有一定的影响(BC和TC的δ13C相差约为0.50‰),对化石燃料烟尘没有影响.上述典型排放源的δ13C数据库可为BC源解析提供依据.     

麦草及其烟尘中正构烷烃的组成

在明火和闷烧条件下对6种麦草进行焚烧试验,用GC/MS测定了秸秆和烟尘中正构烷烃的组成.结果表明,从麦秆和烟尘中检出的正构烷烃主要是C16~C33.麦秸中正构烷烃的总含量变化范围是19.6~62.3 mg·kg-1,平均值为36.0mg·kg-1.低碳数(碳数相似文献   

麦秸及其烟尘中正构脂肪酸的组成

在不同燃烧条件下对6种麦草进行焚烧,并利用GC/MS对麦秸和烟尘中的正构脂肪酸进行了测定.结果表明,烟尘中含有碳数C8~C32的正构脂肪酸.在明火烟尘中,正构脂肪酸总含量分布于1 509.3~10 543.7 mg·kg-1之间,平均值为5 871.2mg·kg-1.其轻(C8~C16)、重(C17~C32)正构脂肪酸含量之比(L/H)为0.8~5.3,平均值为2.8;C14/C16、C28/C16、C30/C16等比值的平均值分别为16.5%、14.1%、11.4%.正构脂肪酸呈双峰式分布,其主峰碳数是C16,次峰碳数是C28或C30,且具有显著的偶碳数优势.其碳优势指数(CPI)和平均碳链长度(ACL)的平均值分别为19.8和18.2.在闷烧烟尘中,正构脂肪酸的总含量为5 799.3~37 244 mg·kg-1,平均值为15 838.6 mg·kg-1.其L/H值介于1.2~5.6之间,平均为4.2;C14/C16、C28/C16、C30/C16的平均值分别为12.7%、10.1%、6.0%.闷烧烟尘中正构脂肪酸的分布模式与明火烟尘的类似,其CPI和ACL的平均值分别为24.7和17.7.总之,虽然两类烟尘和麦秸中的正构脂肪酸均具有类似的分布模式和偶碳数优势,但三者在组成上仍然存在明显的差别.这有助于识别大气气溶胶中麦秸及其燃烧排放的正构脂肪酸.     

稻草及其燃烧烟尘中正构烷烃的研究

利用气质联用仪测定了中国6种稻草及其明火和闷火燃烧烟尘中正构烷烃的含量.结果表明,稻草中正构烷烃的平均含量为73.0μg/g.碳数分布范围为C12~C37,呈以C29为主峰的单峰型分布.高碳数正构烷烃(>C23)具有明显的奇碳数优势,其平均碳优势指数是2.9.在明火焚烧和闷烧烟尘中正构烷烃的含量均值分别是 1633.1,5458.5μg/g.碳数分布范围为C14~C35,呈以C29或C31为主峰的单峰型分布.碳数在C27以上的正构烷烃具有明显的奇碳数优势,其平均碳优势指数分别是1.5和1.9.稻草烟尘中正构烷烃的组成与原秸秆存在显著的差别.     

Evaluation of phytoextracting cadmium and lead by sunflower, ricinus, alfalfa and mustard in hydroponic culture

Soil contaminated with heavy metals cadmium(Cd)and lead(Pb)is hard to be remediated.Phytoremediation may be a feasible method to remove toxic metals from soil,but there are few suitable plants which can hyperaccumulate metals.In this study,Cd and Pb accumulation by four plants including sunflower(Helianthus annuus L.),mustard(Brassica juncea L.),alfalfa(Medicago sativa L.), ricinus(Ricinus communis L.)in hydroponic cultures was compared.Results showed that these plants could phytocxtract heavy metals, the ability of accumulation differed with species,concentrations and categories of heavy metals.Values of BCF(bioconcentration factor)and TF(translocation factor)indicated that four species had dissimilar abilities of phytoextraction and transportation of heavy metals.Changes on the biomass of plants,pH and Eh at different treatments revealed that these four plants had distinct responses to Cd and Pb in cultures.Measurements should be taken to improve the phytoremediation of sites contaminated with heavy metals,such as pH and Eh regulations,and so forth.     

Oxidation of As(Ⅲ) by potassium permanganate

The oxidation of As(Ⅲ) with potassium permanganate was studied under conditions including pH, initial As(Ⅲ) concentration and dosage of Mn(Ⅶ). The results have shown that potassium permanganate was an effective agent for oxidizing of As(Ⅲ) in a wide pH range. The pH value of tested water was not a significant factor affecting the oxidation of As(Ⅲ) by Mn(Ⅶ). Although theoretical redox analyses suggest that Mn(Ⅶ) should have better performance in oxidization of As(Ⅲ) within lower pH ranges, the experimental results show that the oxidation efficiencies of As(Ⅲ) under basic and acidic conditions were similar, which may be due to the adsorption of As(Ⅲ) on the Mn(OH)2 and MnO2 resulting from the oxidation of As(Ⅲ).     

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.     

Chlorobenzenes in waterweeds from the Xijiang River （Guangdong section） of the Pearl River

The Xijiang River is the major source of water for about 4.5 millions of urban population and 28.7 millions of rural population. The water quality is very important for the health of the rural population. The concentration and distribution of chlorobenzenes (CBs) in both water and waterweeds collected from 4 stations in the Xijiang River (Gangdong section) of the Pearl River in April and November were determined. The result showed that nearly every congener of CBs was detected. The total contents of CBs (∑CBs) in the river water ranged from 111.1 to 360.0 ng/L in April and from 151.9 to 481.7 ng/L in November, respectively. The pollution level of CBs in the water in April was higher than that in November. The contents of ∑ CBs in waterweeds ranged from 13.53×102 μg/g to 38.27×102μg/g dry weight (dw). There was no significant difference between April and November in waterweeds. The distribution of CBs in roots, caulis, and leaves of Vallisneria spiralis L. showed different patterns. The leaves mainly contained low-molecular-weight CBs(DCBs), whereas the roots accumulated more PCBs and HCBs. The average lgBCFlip (bioconcentration factor) of CBs ranged from 0.64 to 3.57 in the waterweeds. The spatial distribution character of CBs in the Xijiang River was: Fengkai County ＜ Yunan County ＜Yun'an County ＜ Gaoyao County according to the ∑CBs, and the pollution deteriorated from the upstream to the downstream of the Xijiang River. Further analysis demonstrated that the discharge of waste containing CBs may be the main source of CBs pollution in the Xijiang River.     

Effect of copper on the degradation of pesticides cypermethrin and cyhalothrin

The influence of coexisting copper (Cu) ion on the degradation of pesticides pyrethroid cypermethrin and cyhalothrin in soil and photodegradation in water system were studied.Serial concentrations of the pesticides with the addition of copper ion were spiked in the soil and incubated for a regular period of time,the analysis of the extracts from the soil was carried out using gas chromatography (GC).The photodegradation of pyrethroids in water system was conducted under UV irradiation.The effect of Cu~(2 ) on the pesticides degradation was measured with half life (t_(0.5)) of degradation.It was found that a negative correlation between the degradation of the pyrethroid pesticides in soil and Cu addition was observed.But Cu~(2 ) could accelerate photodegradation of the pyrethroids in water.The t_(0.5) for cyhalothrin extended from 6.7 to 6.8 d while for cypermethrin extended from 8.1 to 10.9 d with the presence of copper ion in soil.As for photodegradation,t_(0.5) for cyhalothrin reduced from 173.3 to 115.5 rain and for cypermethrin from 115.5 to 99.0 min.The results suggested that copper influenced the degradation of the pesticides in soil by affecting the activity of microorganisms.However, it had catalyst tendency for photodegradation in water system.The difference for the degradation efficiency of pyrethroid isomers in soil was also observed.Copper could obviously accelerate the degradation of some special isomers.     

Degradation of 2,4-dichlorophenol with a novel TiO2/Ti-Fe-graphite felt photoelectrocatalytic oxidation process

Degradation of 2,4-dichlorophenol(2,4-DCP)was studied in a novel three-electrode photoelectrocatalytic(PEC)integrative oxidation process,and the factors influencing the degradation rate,such as applied current,flow speed of O_2,pH,adscititious voltage and initial 2,4-DCP concentration were investigated and optimized.H_2O_2 was produced nearby cathode and Fe~(2 )continuously generated from Fe anode in solution when current and O_2 were applied,so,main reactions,H_2O_2-assisted TiO_2 PEC oxidation and E-Fenton reaction,occurred during degradation of 2,4-DCP in this integrative system.The degradation ratio of 2,4-DCP was 93% in this integrative oxidation process,while it was only 31% in E-Fenton process and 46% in H_2O_2-assisted TiO_2 PEC process.So,it revealed that the degradation of 2,4-DCP was improved greatly by photoelectrical cooperation effect.By the investigation of pH,it showed that this integrative process could work well in a wide pH range from pH 3 to pH 9.     

Effects of arsenic on seed germination and physiological activities in wheat seedlings

The effects of arsenic(As)were investigated on seed germination,root and shoot length and their biomass and some other factors to elucidate the toxicity of As.The results showed low concentrations of As(O-1 mg/kg)stimulated seed germination and the growth of root and shoot,however,these factors all decreased gradually at high concentrations of As(5-20 mg/kg).The contents Of O2-,MDA,soluble protein and peroxidase(POD)activity all increased with increasing As concentrations.Soluble sugar content,ascorbate peroxidase(APX),and superoxide dismutase(SOD)activities decreased at low concentrations of As,and increased at high concentrations of As.While acetylsalicylic acid(ASA)and chlorophyll contents,catalase(CAT)activity displayed increasing trend when the concentrations of As was lower than 1 mg/kg,and then decreasing trend.By polyacrylamide gel electrophoresis(PAGE).As induced the expression of POD isozymes of wheat seedlings.As induced the expression of CAT isozymes but inhibited the expression of SOD isozymes of wheat seedlings at concentrations lower than 1 mg/kg.However,As inhibited the expression of CAT isozymes but induced the expression of SOD isozymes at concentrations higher than 5 mg/kg.The results indicated As could exert harmfulness in the early development stage of wheat at inappropriate concentrations.     

Sustainability： A view from the wind-eroded field

This article explores the assessment of sustainability in fields subject to wind erosion. In the first part, simple sustainability audits are examined, as of soil depth and nutrients. Direct measurement of these characteristics has many problems, largely because of huge variability in space and time at all scales. Modelling still has its problems, but it may be possible to overcome many of them soon. It is true that wind erosion preferentially removes soil nutrients, but there are imponderables even here. The nutrient balance in many of these soils includes considerable input from dust. In West Africa, it has been shown that the amounts of calcium and potassium that are added in dust are sufficient to fertilize dispersed crops. In mildly acidic sandy soils, such as those found on the widespread palaeo- aeolian deposits, much of the phosphorus is fixed and unavailable to plants by the time it is removed by wind erosion, so that erosion has no added downside. Most of the nutrients carried by dust have been shown to travel close to the ground （even when they are attached to dust-sized particles）, and so are trapped in nearby fallow strips, and are thus not lost to the farming system. Second, the sustalnabillty of a whole semi-arid farming system is explored. Wind erosion in semi-arid areas （like China, the Sahel and Norflawestern Europe） generally takes place on aeolian deposits of the recent geological past. Most of these soils are deep enough to withstand centuries of wind erosion before they are totally lost to production, and some of these soils have greater fertility at greater depth （so that wind erosion may even improve the soil）. Finally some remarks are made about environmental change in relation to sustainability.     

Bioconcentration kinetics of PCBs in various parts of the lifecycle of the tadpoles Xenopus laevis

Polychlorinated biphenyls （PCBs） in Xenopus laevis have been reported only for a few congeners. Additionally, there is very little information on the ability of Xenopus laevis to bioconcentrate PCBs. To address these issues, the tadpole Xenopus laevis was exposed to Aroclor 1254 mixtures in water at room temperature for 110 d followed by an additional 110 d of nonspiked PCBs in the water for the control group. During the whole process, bioconcentration factors （BCFs） of PCBs ranged from 1180 to 15670. For most PCB congeners, the highest and lowest bioconcentrations of the kinetic curves were found to be remarkably simultaneous, respectively. All 141 PCB congeners under the same experimental conditions had no linear correlation on the lgBCF versus lgKow relationship. The relationship between lgBCFs and lgKow followed a parabolic pattern indicative of selective bioconcentration, suggesting that the kinetic curves of the PCB congeners observed in the lifecycle of the tadpoles may be concentrated due to the amphibian special species and internal metabolism. In contrast, lgBCFs for PCBs were inversely related to lgKow, suggesting that a metabolism of the higher Kow PCB congeners occurred. These results support the author＇s conclusion that the tadpole Xenopus laevis plays major roles in the bioconcentration of PCB congeners, and demonstrated that the exposure kinetic curves of PCB congeners are complex. Besides the amphibian metamorphous development, the lifecycle of the tadpole Xenopus laevis also may be of importance in determining the bioconcentration of PCB congeners.