不同离子对黑土胶体在土壤中运移的影响

黑土样品采自于黑龙江海伦市,提取胶体并对其主要理化性质进行定性定量表征,通过淋滤实验研究胶体在土柱中的运移特征以及不同离子及其强度对胶体运移的影响。结果显示:所提取胶体粒径与理论计算基本吻合,粒径主要分布在2~5μm;当pH由4上升到9时,胶体的zeta电位则由-26.43mV降低到-34.52mV;红外光谱显示胶体颗粒的有机机团主要为-OH、CH-、C=O、多糖;X射线衍射表明其主要矿物组成是石英(56.9%)。不同离子及其强度对胶体的在土壤中的运移有较为明显的影响,当pH由4增加到9时,k值由6.020×10-4降低至3.858×10-4,Ca2+、K+、Na+当离子强度由0.5mmol/L变化到0.001mmol/L时,k值分别由6.087×10-4降低至4.024×10-4、5.518×10-4降低至3.818×10-4、5.401×10-4降低至4.109×10-4。     

地下水中污染物的迁移传输及排泄通量研究

以辽宁某化工污染场地为研究对象,结合场地调查结果,应用地下水模型系统软件(GMS)中的MODFLOW和RT3D模型,建立了地下水中污染物的数值模型,探讨其迁移传输及排泄通量。根据模拟结果,地下水中苯、二氯苯和三氯苯的污染羽约在20年后达到动态平衡,污染羽不再随时间变化,污染物的自然衰减速率与污染源释放速率达到平衡。排泄通量估算表明:地下水向河流排泄的量在20年时达到稳定,地下水中苯、二氯苯和三氯苯向河流的排泄通量分别为每天180 g、6 100 g和5.5 g。由于污染物会导致污染生态环境和健康风险,建议从控制污染源、实施污染源区修复和切断迁移传输途径等多种措施控制风险。     

浅谈黑龙江及乌苏里江流域废水中污染物排放特征

以跨界流域黑龙江和乌苏里江为研究对象,通过合理的流域断面设置,对流域废水中的污染物及农药残留进行分析测定,通过监测结果为以后的污染防治提供依据。     

中国地区二次有机气溶胶的时空分布特征和来源分析

二次有机气溶胶(SOA)由于其在大气污染、气候变化与人体健康方面的影响,是我国大气环境中一种重要的污染物.确定中国SOA分布规律以及产生来源是大气污染防治的前提.利用全球化学传输模型(Model for Ozone and Related Chemical Tracers,Version 4,MOZART4)并集成多相SOA参数化方案,模拟了中国地区SOA的时空分布,并按前体物分区域进行了来源分析.结果表明,受SOA前体物排放分布的影响,中国地区的SOA主要分布在东部和南部地区,并且夏季SOA产量是冬季产量的2.5倍.中国地区分布的SOA由人为源排放产生占55%,高于自然源(45%);并且境内排放贡献了我国SOA产量的77%,主要影响东部近地面大气的浓度分布.境外排放主要影响我国西部地区,尤其是对高空SOA分布影响显著.     

不同季节气象条件对北京城区高黑碳浓度变化的影响

利用2013年至2015年北京城区黑碳气溶胶(下文统称为"BC")和PM2.5观测资料,结合地面气象观测资料、ECMWF边界层高度再分析资料和FNL/NCEP不同高度风速再分析资料,讨论了BC质量浓度及其在PM_(2.5)质量浓度中所占比例(下文统称"黑碳占比")的季节、月、日变化特征,并通过计算北京城区BC浓度与不同高度风速的相关矢量,分析了气象条件和外来输送对北京城区BC浓度变化的影响.结果发现:研究时段内北京城区BC浓度平均值为(4.77±4.49)μg·m~(-3);黑碳占比为8.23%±5.47%.BC浓度和黑碳占比在春、夏季低,秋、冬季高,其日变化特征在4个季节均为"白天低夜间高"的单峰型特征.随着PM_(2.5)浓度的升高,BC浓度增大,黑碳占比减小.当北京地区风向为东北、东北偏东、东南和西南偏西(主风向)时,BC浓度与风速和边界层高度均呈反向变化,即随风速和边界层高度的增大而减小.另外不同季节BC浓度随风速变化的临界值及其变化速率不同.冬季高BC浓度时段,北京城区BC浓度在低层大气的关键影响区分别位于河北南部与山东交界地区以及河北西北部与山西内蒙交界地区;高空关键影响区主要位于北京以西的河北西部、山西北部和内蒙古地区.     

大宝山矿区水体中重金属的行为研究

广东大宝山矿区矿山废水的排放使周边生态环境遭受了严重的破坏。水体中重金属Cu、Zn、Cd和Pb的溶解态浓度分别达到13.82、50.83、0.103和2.91 mg.L-1。Cu、Zn、Cd和Pb的溶解态和悬浮态含量沿河流主干道断面呈相似的空间分布规律,上游都是沿水流方向降低,下游因吸附于悬浮物中的重金属重新释放略有增加。悬浮物中重金属元素的化学形态提取和扫描电镜能谱分析(SEM/EDAX)表明:4种重金属元素都以残渣态为主要存在形态,其次为可还原态,个别断面的Cd可还原态甚至超过了残渣态的含量,说明该水体这4种元素对环境都有一定的潜在威胁性。     

Dioxins,chlorophenols and other chlorinated organic pollutants in colloidal and water fractions of groundwater from a contaminated sawmill site

BACKGROUND, AIM, AND SCOPE: The distribution of chlorinated organic contaminants in groundwater and the importance of colloids were studied in groundwater from a sawmill site contaminated by chlorophenol preservatives. MATERIALS AND METHODS: The groundwater was fractionated into three different size ranges: (1) >0.7 mum, (2) 0.4-0.7 mum and (3) 0.2-0.4 mum and the filtered water phase. The concentrations of chlorophenols (CP), chlorinated phenoxy phenols (PCPP), chlorinated diphenyl ethers (PCDE), chlorinated dibenzofurans (PCDF) and chlorinated dibenzo-p-dioxins (PCDD) were determined in each fraction. The colloids were characterised regarding the chemical composition using X-ray photoelectron spectroscopy (XPS). RESULTS: Chlorophenols were mostly found in the water fraction and PCDD/Fs were found almost exclusively in the particulate fractions. For example, the filtered water phase contained 2,100 mug l(-1) and 0.72 ng l(-1) for CPs and PCDD/Fs, respectively, and the particulate fractions contained 27 mug l(-1) and 32 ng l(-1) for CPs and PCDD/Fs, respectively. XPS evaluation of the particulate phases showed no correlation between the surface chemistry of the particle properties and the distribution of chlorinated compounds. DISCUSSION: The results suggest that groundwater transport of CPs, PCPPs, PCDEs and PCDD/Fs may occur from contaminated sawmill sites and that the colloid-facilitated transport, especially of PCDD/Fs, is substantial. The results correlated well with previous studies of compounds sorbed to dissolved organic carbon, which indicate that dissolved and colloidal organic carbon facilitated the transport of PCDEs, PCDFs and PCDDs particularly. CONCLUSIONS: Several classes of chlorinated compounds were readily detected in the groundwater samples. Due to the differences in their physicochemical properties, CPs, PCPPs, PCDEs and PCDD/Fs vary in their partitioning between colloidal fractions and the filtered groundwater. The proportion of the bound fraction increased with an increasing hydrophobicity of the chlorinated compounds. The groundwater transport of colloid-associated pollutants from the site may be significant. RECOMMENDATIONS AND PERSPECTIVES: The results imply that colloidal particles <0.7 mum are freely mobile in groundwater from this site. The groundwater transport of colloid-associated pollutants may be significant. However, the extent of the problem is not yet known and, thus, further research is needed to evaluate the impact of colloidal transport of hydrophobic organic contaminants. In Sweden alone, 400 to 500 sawmill sites are estimated to be contaminated with PCDD/Fs as a result of the former use of CP-based wood preservatives. The widespread use of CP mixtures for a variety of applications, including wood preservation, indicates that potential colloidal transport will be an issue of concern in many countries.     

Effect of soil moisture dynamics on dense nonaqueous phase liquid (DNAPL) spill zone architecture in heterogeneous porous media

The amount, location, and form of NAPL in contaminated vadose zones are controlled by the spatial distribution of water saturation and soil permeability, the NAPL spill scenario, water infiltration events, and vapor transport. To evaluate the effects of these processes, we used the three-phase flow simulator STOMP, which includes a new permeability-liquid saturation-capillary pressure (k-S-P) constitutive model. This new constitutive model considers three NAPL forms: free, residual, and trapped. A 2-D vertical cross-section with five stratigraphic layers was assumed, and simulations were performed for seven cases. The conceptual model of the soil heterogeneity was based upon the stratigraphy at the Hanford carbon tetrachloride (CT) spill site. Some cases considered co-disposal of NAPL with large volumes of wastewater, as also occurred at the Hanford CT site. In these cases, the form and location of NAPL were most strongly influenced by high water discharge rates and NAPL evaporation to the atmosphere. In order to investigate the impact of heterogeneity, the hydraulic conductivity within the lower permeability layer was modeled as a realization of a random field having three different classes. For six extreme cases of 100 realizations, the CT mass that reached the water table varied by a factor of two, and was primarily controlled by the degree of lateral connectivity of the low conductivity class within the lowest permeability layer. The grid size at the top boundary had a dramatic impact on NAPL diffusive flux just after the spill event when the NAPL was present near the ground surface. NAPL evaporation with a fine grid spacing at the top boundary decreased CT mass that reached the water table by 74%, compared to the case with a coarse grid spacing, while barometric pumping had a marginal effect for the case of a continuous NAPL spill scenario considered in this work. For low water infiltration rate scenarios, the distribution of water content prior to a NAPL spill event decreased CT mass that reached the water table by 98% and had a significant impact on the formation of trapped NAPL. For all cases simulated, use of the new constitutive model that allows the formation of residual NAPL increased the amount of NAPL retained in the vadose zone. Density-driven advective gas flow from the ground surface controlled vapor migration in strongly anisotropic layers, causing NAPL mass flux to the lower layer to be reduced. These simulations indicate that consideration of the formation of residual and trapped NAPLs and dynamic boundary conditions (e.g., areas, rates, and periods of different NAPL and water discharge and fluctuations of atmospheric pressure) in the context of full three-phase flow are needed, especially for NAPL spill events at the ground surface. In addition, NAPL evaporation, density-driven gas advection, and NAPL vertical movement enhanced by water flow must be considered in order to predict NAPL distribution and migration in the vadose zone.     

Transport of simazine in unsaturated sandy soil and predictions of its leaching under hypothetical field conditions

The potential contamination of groundwater by herbicides is often controlled by processes in the vadose zone, through which herbicides travel before entering groundwater. In the vadose zone, both physical and chemical processes affect the fate and transport of herbicides, therefore it is important to represent these processes by mathematical models to predict contaminant movement. To simulate the movement of simazine, a herbicide commonly used in Chilean vineyards, batch and miscible displacement column experiments were performed on a disturbed sandy soil to quantify the primary parameters and processes of simazine transport. Chloride (Cl(-)) was used as a non-reactive tracer, and simazine as the reactive tracer. The Hydrus-1D model was used to estimate the parameters by inversion from the breakthrough curves of the columns and to evaluate the potential groundwater contamination in a sandy soil from the Casablanca Valley, Chile. The two-site, chemical non-equilibrium model was observed to best represent the experimental results of the miscible displacement experiments in laboratory soil columns. Predictions of transport under hypothetical field conditions using the same soil from the column experiments were made for 40 years by applying herbicide during the first 20 years, and then halting the application and considering different rates of groundwater recharge. For recharge rates smaller than 84 mm year(-1), the predicted concentration of simazine at a depth of 1 m is below the U.S. EPA's maximum contaminant levels (4 microg L(-1)). After eight years of application at a groundwater recharge rate of 180 mm year(-1) (approximately 50% of the annual rainfall), simazine was found to reach the groundwater (located at 1 m depth) at a higher concentration (more than 40 microg L(-1)) than the existing guidelines in the USA and Europe.     

Bacteria transport and deposition under unsaturated conditions: the role of the matrix grain size and the bacteria surface protein

Unsaturated (80% water saturated) packed column experiments were conducted to investigate the influence of grain size distribution and bacteria surface macromolecules on bacteria (Rhodococcus rhodochrous) transport and deposition mechanisms. Three sizes of silica sands were used in these transport experiments, and their median grain sizes were 607, 567, and 330 microm. The amount of retained bacteria increased with decreasing sand size, and most of the deposited bacteria were found adjacent to the column inlet. The deposition profiles were not consistent with predictions based on classical filtration theory. The experimental data could be accurately characterized using a mathematical model that accounted for first-order attachment, detachment, and time and depth-dependent straining processes. Visual observations of the bacteria deposition as well as mathematical modelling indicated that straining was the dominant mechanism of deposition in these sands (78-99.6% of the deposited bacteria), which may have been enhanced due to the tendency of this bacterium to form aggregates. An additional unsaturated experiment was conducted to better deduce the role of bacteria surface macromolecules on attachment and straining processes. In this case, the bacteria surface was treated using a proteolitic enzyme. This technique was assessed by examining the Fourier-transform infrared spectrum and hydrophobicity of untreated and enzyme treated cells. Both of these analytical procedures demonstrated that this enzymatic treatment removed the surface proteins and/or associated macromolecules. Transport and modelling studies conducted with the enzyme treated bacteria, revealed a decrease in attachment, but that straining was not significantly affected by this treatment.