Analysis of Toxic Air Contaminant Data Containing Concentrations Below the Limit of Detection

Air quality data often contain several observations reported only as below the analytical limit of detection (LOD), resulting in “censored” data sets. Such censored and/or truncated data sets tend to complicate statistical analysis. This paper discusses various procedures for estimating mean concentration and Its 95 percent confidence bounds from air contaminant data sets which contain values that are reported as below the LOD, A quantitative approach for assessing the uncertainty Inherent In the estimated mean concentration due to (a) presence of values below the LOD In the data set, and (b) natural variability of atmospheric concentration data, is described. The utility of this approach In the analysis and interpretation of ambient pollutant concentration data Is demonstrated for both hypothetical and observed singly-censored data sets, and for a multiply-censored, multi-pollutant observed concentration data set. The methodologies discussed here should be particularly useful In verifying compliance with environmental regulations, and In estimating the risks associated with long-term exposure of populations to toxic air contaminants and assessing the uncertainty associated with these estimates.     

食蚊鱼(Gambusia afinis)cat、gapdh和gst基因的克隆及其在生态毒理学中的应用

根据Ensembl、Genbank登录的鱼类cat、gapdh和gst基因的CDS序列设计普通PCR扩增引物,寻找食蚊鱼的cat、gapdh和gst基因的c DNA片段,并根据定量引物设计要求设计出相应的SYBR Green I荧光定量RT-q PCR引物,建立了食蚊鱼cat、gapdh和gst基因的SYBR Green I荧光定量RT-q PCR方法。该方法在104~108数量级范围内有良好线性关系(R=0.999~1.000);熔解曲线显示扩增产物特异性良好,均为单一峰值;质粒标准品最高浓度与最低浓度的批内试验变异系数与批间试验变异系数均低于2%。利用该方法监测和评价环境污染物对水生生物的影响,选择了水体中常见典型药物污染物——双氯芬酸,研究其对食蚊鱼抗氧化基因表达的影响。结果表明,雌性食蚊鱼暴露在不同浓度双氯芬酸钠(0.005、0.05、0.5和5 mg·L-1)24 h后,其肝脏cat、gapdh和gst的mRNA呈现显著变化,相对于对照组,在低浓度0.005 mg·L-1时,cat与gst mRNA的表达量均有极显著上升(p0.01),而其它浓度均极显著下降(p0.01)。试验表明该方法具有快速、精确、灵敏度高的优点,可为利用该类小型鱼类的原位污染物的生物监测和生态毒理评价提供有力的技术支持。     

Evaluating biotoxicity variations of landfill leachate as penetrating through the soil column

Recent studies of leachate-induced ecotoxicity have focused on crude samples, while little attention has been given to changes in biotoxicity resulting from the environmental behavior of landfill leachate. Therefore, we set up a soil column to simulate the underground penetration of leachate into the soil layer, define the rules of migration and transformation of leachate pollutants, and determine the variation in toxicity of landfill leachate during penetration. The results demonstrated that: (1) landfill leachate inhibited the growth and chlorophyll levels, elevated the levels of lipid peroxidation and protein oxidation, and stimulated the antioxidant enzyme activities of barley seedlings. The effects generally displayed a peak value at 12–24 cm, slowly declined at 36–48 cm, and then rapidly decreased with penetrating distance in the column. (2) Statistical correlation analysis of the properties of leachate and the observed biotoxic effects revealed that COD, conductivity and heavy metals (esp. Ni, Mn, Cd) were positively correlated with variations in biotoxicity. (3) The microbial activity of outflowing leachate sampled from the 48 cm port was significantly higher than the activity from succedent ports, and the types of contaminants increased in the leachate outflowing from the same port, implying that microbial behaviors near the 48 cm port could be used to partially evaluate variations in the composition and biotoxicity of landfill leachate. Taken together, the above results illustrate the polluting characteristics of landfill leachate when penetrating a soil column and provide guidance for pollution control and risk assessment of landfill leachate.     

Mercury removal from aqueous solutions by zinc cementation

The main purpose of this research is to study the addition effect of the surfactant and other operating factors on the treatment of wastewater containing mercury ions in aqueous solution by cementation with sacrificing metal, zinc. The removal of mercury ions from aqueous solutions by cementation of zinc powder was found to be a function of solution pH and temperature, amount of zinc, concentration of mercury ion, contact time and the addition of several organic surfactants. Cementation of mercury was shown to be a feasible process to achieve a very high degree of mercury removal over a broad operational range within a fairly reasonable contact time. The reaction rate is approximately first order with respect to the concentration of mercury ion in aqueous solution. Among the surfactants used in this study, only the presence of SDS, an anionic surfactant, slightly enhanced the cementation rate of mercury. The presence of CTAB and Triton-X100 retarded the cementation of mercury by zinc.     

Decomposition of gas-phase trichloroethene by the UV/TiO2 process in the presence of ozone.

The decomposition of gas-phase trichloroethene (TCE) in air streams by direct photolysis, the UV/TiO2 and UV/O3 processes was studied. The experiments were carried out under various UV light intensities and wavelengths, ozone dosages, and initial concentrations of TCE to investigate and compare the removal efficiency of the pollutant. For UV/TiO2 process, the individual contribution to the decomposition of TCE by direct photolysis and hydroxyl radicals destruction was differentiated to discuss the quantum efficiency with 254 and 365 nm UV lamps. The removal of gaseous TCE was found to reduce by UV/TiO2 process in the presence of ozone possibly because of the ozone molecules could scavenge hydroxyl radicals produced from the excitation of TiO2 by UV radiation to inhibit the decomposition of TCE. A photoreactor design equation for the decomposition of gaseous TCE by the UV/TiO2 process in air streams was developed by combining the continuity equation of the pollutant and the surface catalysis reaction rate expression. By the proposed design scheme, the temporal distribution of TCE at various operation conditions by the UV/TiO2 process can be well modeled.     

Evaluation of oxidation stability of lignite humic substances by DSC induction period measurement

The stability of lignite humic acids and four regenerated humic acids was estimated by employing differential scanning calorimetry. Induction period for the oxidative decomposition of humic matter was calculated from non-isothermal measurements at six different rates of heating. To simulate the gradual evolution history of humic acids, different intensities of oxidation attack by nitric acid on the original lignite was used. Experimental data showed higher stability of natural humic acids in the temperature range where the decomposition step occurred. On the other hand, extrapolation to lower temperatures and calculated kinetic parameters did not correspond to the order observed at higher temperatures. An oscillating trend of calculated parameters of the two proposed parts of stability was observed, which agreed with data concerning regenerated humic acids production. The approach applied in this work represents a rapid and useful method for evaluation of organic matter stability.     

Decomposition of 2-nitrophenol in aqueous solution by ozone and UV/ozone processes.

The decomposition of 2-nitrophenol in aqueous solutions by ozone and UV/ozone processes was found to be technically feasible under adequate experimental conditions. Formation of nitrate ions was observed following the decomposition of 2-nitrophenol by ozone and UV/ ozone processes. Increasing ozone dosage and UV light intensity accelerated the decomposition rate of 2-nitrophenol in an aqueous solution. The species distribution of 2-nitrophenol under various solution conditions plays a significant role in determining decomposition behavior. In most experiments conducted in this study, the decomposition of 2-nitrophenol by ozone and UV/ozone processes was favored to occur in alkaline conditions. The addition of 2-butanol accelerated the rate of gaseous ozone transfer to an aqueous phase by reducing the surface tension of aqueous solution and therefore enhancing the decomposition rate of 2-nitrophenol by ozone and UV/ozone processes.     

The light transmission and distribution in an optical fiber coated with TiO2 particles

The light delivery and distribution phenomena along the optical fiber coated with the P-25 TiO(2) particles by dipping was investigated. The surface properties (coverage, roughness and thickness) of the TiO(2) layer coated on the optical fiber were characterized by SEM micrographs. For TiO(2) layer prepared from solutions containing less than 20 wt.% of TiO(2) slurry, the thickness of layer was increased linearly with the TiO(2) slurry content in solutions. The UV light intensity transmitted along a TiO(2)-coated optical fiber decreased more rapidly than that transmitted along a non-coated fiber. Based on the experimental results, the light intensity distribution around a coated optical fiber was modeled to determine the optimum configuration for the design of optical fiber reactors under various operational conditions.     

An assessment of the emissions inventory processing systems EMS-2001 and SMOKE in grid-based air quality models

In the United States, emission processing models such as Emissions Modeling System-2001 (EMS-2001), Emissions Preprocessor System-Version 2.5 (EPS2.5), and the Sparse Matrix Operator Kernel Emissions (SMOKE) model are currently being used to generate gridded, hourly, speciated emission inputs for urban and regional-scale photochemical models from aggregated pollutant inventories. In this study, two models, EMS-2001 and SMOKE, were applied with their default internal data sets to process a common inventory database for a high ozone (O3) episode over the eastern United States using the Carbon Bond IV (CB4) chemical speciation mechanism. A comparison of the emissions processed by these systems shows differences in all three of the major processing steps performed by the two models (i.e., in temporal allocation, spatial allocation, and chemical speciation). Results from a simulation with a photochemical model using these two sets of emissions indicate differences on the order of +/- 20 ppb in the predicted 1-hr daily maximum O3 concentrations. It is therefore critical to develop and implement more common and synchronized temporal, spatial, and speciation cross-reference systems such that the processes within each emissions model converge toward reasonably similar results. This would also help to increase confidence in the validity of photochemical grid model results by reducing one aspect of modeling uncertainty.