Mixture effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and polychlorinated biphenyl congeners in rats

Concern of the toxic effects and bioaccumulation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls in the environment continues to be a focus of research in persistent organochlorine contaminants. Groups of five adult female S.D. rats were administered by gavage 0, 2.5, 25, 250 or 1000 ng TCDD/kg body weight/day or TCDD in combination with a mixture of PCB congeners (PCBs) at 2 or 20 microg/kg b.w./day for a period of 28 days. Growth suppression, increased absolute and relative liver weights, and decreased thymic weight were observed in either the 1000 ng TCDD group alone, or the groups receiving a mixture of 1000 ng TCDD + 2 microg PCBs. The TCDD induced increases in liver and thymic weights were not altered by co-administration with PCBs, however, growth suppression appeared to be more pronounced in the group receiving 1000 ng TCDD + 2 microg PCBs than with TCDD alone. Treatment with TCDD at 250 ng and 1000 ng/kg resulted in a significant increase in hepatic microsomal methoxy resorufin-O-demethylase and ethoxy resorufin-O-deethylase activities which were antagonized by co-administration with PCBs. Similarly, effects of 250 ng TCDD on serum cholesterol and liver UDP glucuronosyl transferase activity and ascorbic acid were significantly reduced by co-administration with 20 microg PCBs. Other biochemical effects elicited by treatment with 1000 ng TCDD, but not affected by co-administration with PCBs include the following: increased serum albumin, decreased liver vitamin A, and increased kidney vitamin A and liver microsomal glutathione-S-transferase activity. While decreased hemoglobin, platelet, packed cell volume and red cell indices were observed in TCDD treated rats, no interactive effects were seen. The above results indicate that the mixture effects of PCBs and TCDD may be additive or antagonistic depending on the dose level and endpoints measured. For the purpose of predicting mixture effects, knowledge of mechanisms of action and toxicokinetics is required.     

The kinetics of catalytic incineration of dimethyl sulfide and dimethyl disulfide over an MnO/Fe2O3 catalyst

The catalytic incineration of dimethyl sulfide and dimethyl disulfide [(CH3)2S and (CH3)2S2] over an MnO/Fe2O3 catalyst was carried out in a bench-scale catalytic incinerator. Three kinetic models (i.e., the power-rate law, the Mars and Van Krevelen model, and the Langmuir-Hinshelwood model) were used to analyze the results. A differential reactor design was used for best fit of kinetic models in this study. The results show that the Langmuir-Hinshelwood model may be feasible to describe the catalytic incineration of (CH3)2S and (CH3)2S2. This suggests that the chemical adsorption of O2 molecules is important in this incineration.     

Subtropical urban turfs: Carbon and nitrogen pools and the role of enzyme activity

Urban grasslands not only provide a recreational venue for urban residents, but also sequester organic carbon in vegetation and soils through photosynthesis, and release carbon dioxide through respiration, which largely contribute to carbon storage and fluxes at regional and global scales. We investigated organic carbon and nitrogen pools in subtropical turfs and found that dissolved organic carbon(DOC) and dissolved organic nitrogen(DON)were regulated by several factors including microbial activity which is indicated by soil enzymatic activity. We observed a vertical variation and different temporal patterns in both soil DOC, DON and enzyme activities, which decreased significantly with increasing soil depths. We further found that concentration of soil DON was linked with turf age. There were correlations between grass biomass and soil properties, and soil enzyme activities. In particular, soil bulk density was significantly correlated with soil moisture and soil organic carbon(SOC). In addition, DOC correlated significantly with DON. Significant negative correlations were also observed between soil total dissolved nitrogen(TDN) and grass biomass of Axonopus compressus and Zoysia matrella. Specifically, grass biomass was significantly correlated with the soil activity of urease and β-glucosidase. Soil NO3-N concentration also showed negative correlations with the activity of both β-glucosidase and protease but there were no significant correlations between cellulase and soil properties or grass biomass. Our study demonstrated a relationship between soil C and N dynamics and soil enzymes that could be modulated to enhance SOC pools through management and maintenance practices.     

Determining the equilibrium partitioning coefficients of volatile organic compounds at an air-water interface

The single equilibration technique (SET) was adopted to determine the partitioning coefficients (pc) at an air-water interface for volatile organic compounds (VOCs), including ethanol, iso-propanol (IPA), iso-butanol (IBA), methyl ethyl ketone (MEK) and toluene, all extensively used in industrial processes. Standard SET procedures were established. The liquid concentrations (CL) of tested VOCs ranged from 10 to 125 mg l(-1) for alcohols and MEK, and from 0.5 to 20 mg l(-1) for toluene. The temperatures (Tw) of aqueous VOC solutions were maintained at 27, 32, 38 and 42 degrees C to determine the gaseous concentrations at equilibrium (Cg*) and pc of VOCs, using the formula pc=(Cg*/CL). Results reveal that the pc values of all tested components increase slowly with Tw given a constant CL, and that the pc of alcohols and MEK fall as CL increases at a constant Tw. In contrast, the pc of toluene is not significantly impacted by a variation in CL at a constant Tw. However, the effect of CL concentration has seldom been discussed. The heats of liquid and gaseous phase transfer (DeltaHtr) of VOC, and the highly linear regression (with squared correlation coefficients, R2, from 0.901 to 0.999) between lnCg* and Tw(-1) are also evaluated. The experimental results and the VOC mass transfer characteristics are helpful for evaluating the emission of VOC from the water surface of wastewater treatment facilities.     

Sensitivity analysis of ground-level ozone concentration to emission changes in two urban regions of southeast Texas

Air pollutant emission is one of the predominant factors affecting urban air quality such as ground-level ozone formation. This paper assesses the impact of changing emission inventory scenarios, based on combinations of point, mobile, area/non-road and biogenic sources, on the tropospheric ozone concentration in two southeast Texas urban areas, i.e. Houston-Galveston and Beaumont-Port Arthur, during the rapid ozone formation event (ROFE) on August 25, 2000. The EPA's Community Multiscale Air Quality (CMAQ) modeling system with 1999 national emission inventory (NEI99) estimates and updated SAPRC99 chemical mechanism are used in the sensitivity analysis for twelve different emission scenarios. Based on model results, it is found that the point source emission of NOx and VOC contributes the greatest ozone peak in the ROFE. Removing Texas point sources of VOC and NOx emission from the inventory results in a reduction in peak O3 concentration by 128 and 70 ppbv in Houston urban area, respectively. Similar but less drastic impact from point source is also observed in the Beaumont-Port Arthur area. The effect on peak ozone concentration due to mobile, area and non-road sources emissions are less significant compared to that of point source emission. Reducing VOC emission appears to be more effective than reducing NOx emission in lowering peak O3 concentration in the studied region. Although biogenic emission can contribute up to 37 ppbv of peak ozone level over a large area, the affected area is away from the urban region of concern, and should not be the main cause for O3 non-attainment in the two urban areas. Removing CO emission from mobile sources does not lead to significant reduction (< 1 ppbv) in ozone concentrations. The modeled data also show that the transport of O3 precursors from adjacent states can cause a significant ozone plume near Beaumont due to its proximity to the state border based on the conditions during the August 25, 2000 O3 episode.     

WATER QUALITY MODELING FOR THE FEITSUI RESERVOIR IN NORTHERN TAIWAN1

ABSTRACT: Field data collected from the Feitsui Reservoir in Taiwan indicate that the water is at a stage between mesotrophic and eutrophic. Recent measurements such as total phosphorus, chlorophyll a and Secchi depth levels suggest that the water quality has been declining. A two‐dimensional, laterally averaged, finite difference hydrodynamic and water quality model was used to simulate the water quality in the Feitsui Reservoir in an effort to determine sound water quality management strategies. The model was calibrated and verified using data collected in 1996 and 1997. The calibrated model was used to simulate algal biomass (in terms of chlorophyll a) levels under various wasteload reduction scenarios. Model results show that 50 percent reduction of the total phosphorus load will improve the existing water quality, shifting the trophic status from eutrophic/mesotrophic to oligotrophic. The modeling effort has yielded valuable information that can be used by decision makers for the evaluation of different management strategies of reducing watershed nutrient loads.     

依法行政,促进环境执法的完善

环境执法是将环境法规中抽象的权利义务变成环境法中具体的权利义务的过程.环境执法是中国环境法制建设的一个重要组成部分.相关国家环保行政职能部门在行使行政权力时,享有很大的自由裁量权,他们能否合法有效地行使好行政权力,直接关系到国家的环保事业和发展.针对当前中国环境执法的现状及环境依法行政的重要意义,以期为政府制定相关环境执法政策、措施提供科学的决策依据和建议,提出了几点环境依法执法的构思:建立系统的、严谨的环境执法理论,树立崭新的执法理念,运用崭新的执法方式,严格依据法定程序办事,健全依法行政责任制和监督机制,推行政务公开,创建公正有效的执法环境.     

上海市2006～2008年实施燃煤电厂烟气脱硫的综合经济分析

根据上海市新一轮“环境保护和建设三年行动计划”（2006-2008年）提出的未来3年全市将有11家电厂的35台共约650.8万kW燃煤发电机组实施烟气脱硫的目标，结合上海市实际，建立相关假定条件，并考虑SO2减排的作用及脱硫产物的利用等方面因素，从经济、环境等角度对上海市650.8万kw燃煤发电机组实施湿法烟气脱硫的成本、效益进行了综合分析。结果显示，燃煤电厂烟气脱硫的固定资产投资和运行费用均较大，而脱硫产生的直接经济效益相对较小，其效益更多地体现在无法直接以货币形式衡量的环境效益、社会效益上。     

“2+26”城市大气重污染下PM2.5来源解析

基于区域大气环境模拟系统RegAEMS开发了大气污染物来源解析模块APSA，以京津冀及周边"2+26"城市为研究对象，模拟2017年12月26日~2018年1月2日该地区一次PM_2.5重污染过程，对PM_2.5进行区域和行业来源解析.结果表明：本次污染持续时间长、影响范围广、污染程度重，"2+26"城市PM_2.5小时最大值为201~507μg/m³，RegAEMS可较好模拟出PM_2.5时空分布；区域来源解析表现为外围区域对"2+26"边界城市影响较大，贡献为15.3%~57.5%，"2+26"中部城市受外围区域影响较小，贡献为0.3%~8.4%，区域传输特征明显，受近地面风场影响较大；行业来源表现为区域内生活源、工业源贡献较大，分别为26.6%~45.8%、16.4%~37.8%，交通源占比13.0%~35.9%.本文研究表明RegAEMS可以实现重污染过程PM_2.5的数值模拟和来源解析，在大气污染精准管控方面具有较好应用前景.