A Century of Plant Species Loss from an Isolated Fragment of Lowland Tropical Rain Forest

An isolated 4-ha fragment of lowland tropical rain forest has been preserved in the Singapore Botanic Gardens since their founding in 1859. The Botanic Gardens'Jungle has recently had enumerated all woody stems 5 cm diameter at breast height (dbh) and larger and the complete vascular plant flora inventoried. This inventory can be compared with the historic record of the flora of the Gardens'Jungle obtained from the extensive collection of herbarium specimens dating back to the 1890s. Of the 448 historically recorded native species, 220 are still present. Ninety-four native species for which there were no historic records and 80 introduced species were also recorded in the recent inventory. The 50.9% loss of plant species richness over approximately the last century has not been distributed uniformly across plant life-form groups. Tree species have been less likely to go extinct than shrubs, climbers, or epiphytes. But half of the tree species present in 1994 were represented by only one or two individuals ≥ 5 cm dbh and larger. Individual longevity may be the major correlate with persistence of plant species in isolated forest fragments. Shade-tolerant understory shrubs (mostly Rubiaceae ) and rattans ( Palmae ) have been particularly prone to extinction. Some species have probably proliferated during the period of isolation. The tree Calophyllum ferrugineum currently constitutes one quarter of all woody stems. A group of climbers has become very common and covers large areas, probably inhibiting tree regeneration. We conclude that tiny fragments will act as refuges for tropical rain-forest plant species for decades, possibly even centuries after isolation but on their own they will not provide a permanent guarantee of the conservation of tropical biodiversity.     

吸烟与非吸烟肺癌患者中P53基因突变的检测

P53基因定位于人类第17号染色体的短臂,野生型P53基因是肿瘤抑制基因。这一基因正成为研究人类肿瘤DNA的主要目标。作者运用聚合酶链反应－单链构象多态性技术（PCR－SSCP）,研究了45例石蜡包埋的肺癌组织标本中肿瘤抑制基因P53基因突变,结果发现在P53基因的第5～8外显子中共检测到19例P53基因突变的样本,检出率为42.2％,并且发现吸烟的肺癌患者中P53基因突变的检出频率明显高于非吸烟的肺癌患者。     

Effect of pH on transport of Pb（2＋）,Mn（2＋）,Zn（2＋）and Ni（2＋） through lateritic soil： Column experiments and transport modeling

This study investigated the e ects of pH on the transport of Pb2+, Mn2+, Zn2+ and Ni2+ through lateritic soil columns. Model results by fitting the symmetric breakthrough curves (BTCs) of bromide (Br??) with CXTFIT model suggested that physical non-equilibrium processes were absent in the columns. The heavy metal BTCs were, however, asymmetrical and exhibited a tailing phenomenon, indicating the presence of chemical non-equilibrium processes in the columns. The retardation factors of Pb2+ were the largest of the four metal ions at both pH 4.0 (33.3) and pH 5.0 (35.4). The use of Langmuir isotherm parameters from batch studies with HYDRUS-1D did not predict the BTCs well. Rather the two-site model (TSM) described the heavy metal BTCs better than the equilibrium linear/nonlinear Langmuir model. The fraction of instantaneous sorption sites ( f ) of all four metal ions on the lateritic soil was consistently about 30%–44% of the total sorption sites.     

Biotransformation of 17α-methyltestosterone in sediment under different electron acceptor conditions

17α-Methyltestosterone (MT), an anabolic androgenic steroid, is used widely in inducing an all male population in aquaculture farming of fish, such as Nile tilapia (Oreochromis niloticus). Current understanding of the occurrence and fate of MT in the sediments and the surrounding areas of the aquaculture ponds are very limited. Bioassay tests showed that MT was biotransformed under aerobic and sulfate-reducing conditions with a half-life of 3.8 d and 5.3 d, respectively, with complete disappearance of androgenic activity. However, under methanogenic condition, MT was found to biotransform but the androgenic activity continued to persist even after 45 d of incubation. In contrast, MT was found to transform slowly under iron(III)-reducing condition and was hardly transformed under nitrate-reducing condition. A possible reason for the lack of transformation of MT under nitrate-reducing condition is the presence of the methyl group at the C-17 position. The results of this study suggest that MT and its degradation products with androgenic activity may potentially accumulate in the sediments of fish farming ponds under iron(III)-reducing, nitrate-reducing and methanogenic conditions.     

Modeling of air sparging of VOC-contaminated soil columns

Air sparging is a remediation technology currently being applied for the restoration of sites contaminated with volatile organic compounds (VOCs). Attempts have been made by various researchers to model the fate of VOCs in the gas and liquid phase during air sparging. In this study, a radial diffusion model with an air–water mass transfer boundary condition was developed and applied for the prediction of VOC volatilization from air sparging of contaminated soil columns. The approach taken was to use various parameters such as mass transfer coefficients and tortuosity factors determined previously in separate experiments using a single air channel apparatus and applying these parameters to a complex system with many air channels. Incorporated in the model, is the concept of mass transfer zone (MTZ) where diffusion of VOCs in this zone was impacted by the volatilization of VOCs at the air–water interface but with negligible impact outside the zone. The model predicted fairly well the change in the VOC concentrations in the exhaust air, the final average aqueous VOC concentration, and the total mass removed. The predicted mass removal was within 1% to 20% of the actual experimental mass removed. The results of the model seemed to suggest that air-sparged soil columns may be modeled as a composite of individual air channels surrounded by a MTZ. For a given air flow rate and air saturation, the VOC removal was found to be inversely proportional to the radius of the air channel. The approach taken provided conceptual insights on mass transfer processes during air sparging operations.     

Mineralization of PAHs in coal-tar impacted aquifer sediments and associated microbial community structure investigated with FISH

The microbial community structure and mineralization of polycyclic aromatic hydrocarbons (PAHs) in a coal-tar contaminated aquifer were investigated spatially using fluorescence in situ hybridization (FISH) and in laboratory-scale incubations of the aquifer sediments. DAPI-detected microbial populations in the contaminated sediments were three orders of magnitude greater than nearby uncontaminated sediments, suggesting growth on coal-tar constituents in situ. Actinobacteria, beta- and gamma-Proteobacteria, and Flavobacteria dominated the in situ aerobic (>1 mg l(-1) dissolved oxygen) microbial community, whereas sulfate-reducing bacteria comprised 37% of the microbial community in the sulfidogenic region of the aquifer. Rapid mineralization of naphthalene and phenanthrene were observed in aerobic laboratory microcosms and resulted in significant enrichment of beta- and gamma-Proteobacteria potentially explaining their elevated presence in situ. Firmicutes, Flavobacteria, alpha-Proteobacteria, and Actinobacteria were also enriched in the mineralization assays, but to a lesser degree. Nitrate- and sulfate-limited mineralization of naphthalene in laboratory microcosms occurred to a small degree in aquifer sediments from locations where groundwater chemistry indicated nitrate- and sulfate-reduction, respectively. Some iron-limited mineralization of naphthalene and phenanthrene was also observed in sediments originating near groundwater measurements of elevated ferrous iron. The results of this study suggest that FISH may be a useful tool for providing a much needed link between laboratory microcosms and groundwater measurements made in situ necessary to better demonstrate the potential for natural attenuation at complex PAH contaminated sites.     

Treatment of methylene blue-containing wastewater using microorganisms supported on granular activated carbon under packed column operation

We studied the feasibility of using biological granular activated carbon-packed column in treating methylene blue-containing wastewater. The granular activated carbon with immobilized microbes was packed into a column and fed with 3 liter methylene blue-containing wastewater daily. With initial 1350 mg/l of methylene blue and 1550 mg/l of chemical oxygen demand, it was observed that the colour and chemical oxygen demand removal efficiencies were 99 and 78%, respectively. The high treatment performance of the system could be due to the simultaneous adsorption and biodegradation processes and advantages of immobilized microbes compare to suspended cell system.     

Determination of Polycyclic Aromatic Hydrocarbons in Rougan, a Traditional Chinese Barbecued Food, by Capillary Gas Chromatography

Several polycyclic aromatic hydrocarbons (PAHs), including those which are carcinogenic, have been detected in rougan, a traditional Chinese barbecued pork dish. The food samples were cleaned up by caustic digestion, solvent extraction, liquid-liquid partition, and column chromatography. The determination was carried out using capillary gas-chromatography with a flame ionization detector. A 25-m HP-1 capillary column was used. Fluorene, phenanthrene, anthracene, benzo[a]anthracene, chrysene and benzo[k]fluoranthene were detected in three of the five samples within the range of 3-17 ng/g. Fluoranthene and pyrene were detected in only two of the samples at similar levels. Two potent carcinogenic compounds, benzo[a]pyrene and benzo[b,j,k]fluoranthene, were not detected in any of the samples. No detectable PAHs have been found in meat cooked without the direct contact of food with flame and smoke. In barbecuing over an open charcoal fire, animal fat and juices dripping onto the open fire probably enhanced the formation of PAHs.     

Modification of a full-scale sequencing batch reactor operational mode for biological nutrient removal.

Two biological nutrient removal modes, consisting of anaerobic, anoxic, and oxic sequences, were tested in a full-scale sequencing batch reactor. The modes, identified as BNR-S1 and BNR-S2, had average total nitrogen removals of 84 and 89%, respectively, for the months of August to October. Over the same period, total phosphorus removals for BNR-S1 and BNR-S2 were 88 and 87%, respectively. In contrast, total nitrogen and total phosphorus removals for the regular aerobic mode were 54.7 and 44.7%, respectively. When the wastewater temperature changed from approximately 20 to 15 degrees C in the winter months, total nitrogen and total phosphorus removals for BNR-S2 were reduced to 81 and 70%, respectively. Total nitrogen effluent concentrations were between 2.5 and 4 mg-N/L (at approximately 20 degrees C), while the effluent total phosphorus concentrations were between 1 and 2 mg/L. The BNR-S2 mode was found to require less energy per kilogram of soluble chemical oxygen demand removed than the regular and BNR-S1 modes.     

Maternal serum activin A and inhibin A in trisomy 18 pregnancies at 10–14 weeks

In 45 cases of trisomy 18 and 493 control pregnancies at 10–14 weeks of gestation, maternal serum inhibin A, total activin A, free β-hCG and PAPP-A were measured. In the trisomy 18 pregnancies the median values were 0.74 MoM for inhibin A, 1.23 MoM for activin A, 0.38 MoM for free β-hCG and 0.16 MoM for PAPP-A. The degree of deviation from normal in the levels of inhibin and activin is small in comparison with free β-hCG and PAPP-A and they are therefore unlikely to be of value in improving the sensitivity of 90% for a 1% false-positive rate achieved by screening with fetal nuchal translucency and maternal serum free β-hCG and PAPP-A. Copyright © 2001 John Wiley & Sons, Ltd.