Contents of heavy metals, polycyclic aromatic hydrocarbons (PA Hs), dichlorodiphenyltrichloroethanes (DDTs) and hexachlorcy- clohexanes (HCHs) in surface sediments from mangrove areas of the Leizhou Peninsula were analyzed in July and November 2005. Risk assessment criteria applied by Long E R et al. (1995) and Long E D et al. (1995) (effects range low, ERL; effects range mean, ERM) of chemicals in sediments from the gulf or estuary were used to assess the potential ecological risks of heavy metals, PAHs, DDTs and HCHs to aquatic organisms in the studied area. The results indicated that the average contents of zinc, nickel, chromium, lead, copper, arsenic and mercury were (61.97 ± 55.87), (59.99 ± 39.01 ), (47.93 ± 28.37), (26.64± 13.00) , (23.45 ± 41.96), (9.32 ± 3.62), (0.14 ± 0.18) mg/kg in dry weight in the sediment samples col- lected from five studied sites in the Leizhou Peninsula, respectively. Cadmium was not calculated due to its content being below the detection limit ( 〈 0.3 mg,/kg). The average levels of Cr, Cu, Ni, Pb, Zn and Hg exceed their background values. The average contents of Ni were higher than ERM. The contents of PAHs in the sediments from the five studied sites were (79.78 ± 43.70) ng/g in dry weight, far lower than ERL(4 022 ng/g). The contents of DDE, DDD and DDTs in the sediments from five studied sites were (2.60 ± 4.68), ( 17.52 ± 27.25 ), (27.78 ± 46.64) ng/g in dry weight respectively, clearly higher than ERL, and the average contents of DDT were (7.66 ± 15.93) ng/g in dry weight, much higher than ERM. HCHs could be detected in the sediments only from Gaoqiao sampling site, with the average contents (0.07 ± 0.08) ng/g in dry weight. 相似文献
The study by the eddy covariance technique in the alpine shrub meadow of the Qinghai-Tibet Plateau in 2003 and 2004 showed that the net ecosystem carbon dioxide exchange (NEE) exhibited noticeable diurnal and annual variations, with more distinct daily changes during the warmer seasons. The CO2 emission of the shrub ecosystem culminated in April and September while the CO2 absorption capacity reached a maximum in July and August. The absorbed carbon dioxide during the two consecutive years was 231.4 and 274.8 g CO2·m−2 respectively, yielding an average of 253.1 gCO2·m−2 per year: that accounts for a large proportion of absorbed CO2 in the region. Obviously, the diurnal carbon flux was negatively related to temperature, radiation and other atmospheric factors. Still, minute discrepancies in kurtosis and duration of carbon emission/absorption were detected between 2003 and 2004. It was found that the CO2 flux in the daytime was similarly affected by photosynthetic photon flux density in both years. Temperature appears to be the most important determinant of CO2 flux: specifically, the high temperature during the plant growing season inhibits the carbon absorption capacity. One potential explanation is that soil respiration is enhanced under such condition. Analysis of biomass revealed that the annual net carbon fixed capacity of aboveground and belowground biomass was 544.0 in 2003 and 559.4 g C·m−2 in 2004, which coincided with the NEE absorption capacity (63.1 g C·m−2 in 2003 and 74.9 g C·m−2 in 2004) in the corresponding plant growing season.
Plinabulin,a potent microtubule-targeting agent,is derived from marine natural diketopiperazine ‘phenylahistin'.To develop novel plinabulin analogue that could display better pharmacokinetic properties and less side effects,deuterated plinabulin 9 was synthesized and evaluated in vitro and in vivo.In comparison with plinabulin,in vivo pharmacokinetic studies indicated that the deuterated derivative 9 could alter blood circulation behavior obviously,which was proved by increased area under the plasma concentration-time curve(AUC_(0–∞)),reduced clearance(CL),and prolonged total body mean residence time(MRT).The derivative 9 also has higher inhibition rates against Bx PC-3,Jurkat and A-431 tumor cell lines as compared with its prototype plinabulin.Therefore,the deuterated compound 9 might be developed as a potential agent for different cancer treatments. 相似文献
以2000-03到2001-02的辐射观测资料,分析了海北高寒草甸生态系统定位站地区辐射及各分光辐射的变化特征,将为高寒草甸生态系统的物质循环、能量流动、草地生产力形成机制等问题的研究提供科学依据。结果表明:海北站区Eg、Er、UV、PAR、NIR和En具有明显的日、年变化,年内其总量分别达6 278.867 M J/m2、1 515.139 M J/m2、311.242 M J/m2、2 576.777 M J/m2、3 397.404 M J/m2和2 542.950 M J/m2,其中在植物生长期的5~9月分别为3 181.215 M J/m2、698.021 M J/m2、165.955 M J/m2、1 133.965 M J/m2、1 673.871 M J/m2和1 668.805M J/m2。年内Er、UV、PAR、NIR和En占Eg的比例分别为0.242、0.048、0.410、0.540和0.410,在植物生长期分别为0.219、0.052、0.413、0.528和0.527。对Eg和PAR提出了下列形式的模拟求算式:Eg=Eg0(0.0897 0.9768S/S0)和PAR=-3.804 4 0.417 7Eg,模拟效果较好,可利用有关常规气象观测资料进行估算。 相似文献