Structural and optical characterization of dissolved organic matter from the lower Athabasca River, Canada

Dissolved organic matter (DOM) is a ubiquitous constituent of natural waters and is comprised of a variety of chemically heterogeneous molecular structures and functional groups. DOM is often considered to be a major ligand for metals in most natural waters and its reactivity is thought to be strongly dependent on its chemical composition and structure. In this study, a combination of UV/visible, emission excitation matrix fluorescence (EEM) and ¹H NMR spectroscopies were used to characterize DOM from the Athabasca River (Alberta, Canada). The chemical characterization of river DOM showed that the most upstream samples located in agricultural areas were blue-shifted and less aromatic and contained more hydrogens connected with oxygen functional groups than those in the wetland dominated area in the Athabasca oil sand deposit region. The presence of paramagnetic ions (Fe and Al) was not found to significantly affect the structural composition of DOM as revealed by ¹H NMR. Such change in the quality of DOM may have a profound impact on metal binding in the Athabasca River watershed.     

Investigating the effect of landfill leachates on the characteristics of dissolved organic matter in groundwater using excitation–emission matrix fluorescence spectra coupled with fluorescence regional integration and self-organizing map

For the purpose of investigating the effect of landfill leachate on the characteristics of organic matter in groundwater, groundwater samples were collected near and in a landfill site, and dissolved organic matter (DOM) was extracted from the groundwater samples and characterized by excitation–emission matrix (EEM) fluorescence spectra combined with fluorescence regional integration (FRI) and self-organizing map (SOM). The results showed that the groundwater DOM comprised humic-, fulvic-, and protein-like substances. The concentration of humic-like matter showed no obvious variation for all groundwater except the sample collected in the landfill site. Fulvic-like substance content decreased when the groundwater was polluted by landfill leachates. There were two kinds of protein-like matter in the groundwater. One kind was bound to humic-like substances, and its content did not change along with groundwater pollution. However, the other kind was present as “free” molecules or else bound in proteins, and its concentration increased significantly when the groundwater was polluted by landfill leachates. The FRI and SOM methods both can characterize the composition and evolution of DOM in the groundwater. However, the SOM analysis can identify whether protein-like moieties was bound to humic-like matter.     

Dissolved organic matter effects on the performance of a barrier to polycyclic aromatic hydrocarbon transport by groundwater

In order to contain the movement of organic contaminants in groundwater, a subsurface sorption barrier consisting of sand or clay minerals coated with a cationic surfactant has been proposed. The effectiveness of such a sorption barrier might be affected by the presence of dissolved organic matter (DOM) in the groundwater. To study the impact of DOM on barrier performance, a series of batch experiments were performed by measuring naphthalene and phenanthrene sorption onto sand coated with cetylpyridinium chloride (CPC) and bentonite coated with hexadecyltrimethylammonium bromide (HDTMA) in the presence of various concentrations of DOM. The overall soil-water distribution coefficient (K*) of naphthalene and phenanthrene onto CPC-coated sand decreased with increasing DOM concentration, whereas the K* of the compounds onto HDTMA-coated bentonite slightly increased with increasing DOM concentration. To describe the overall distribution of polycyclic aromatic hydrocarbons (PAHs) in the systems, a competitive multiphase sorption (CMS) model was developed and compared with an overall mechanistic sorption (OMS) model. The modeling studies showed that while the OMS model did not explain the CPC-coated sand experimental results, a model that included competitive sorption between DOM and PAH did. The experimental results and the modeling study indicated that there was no apparent competition between DOM and PAH in the HDTMA-coated bentonite system, and indicated that in groundwater systems with high DOM, a barrier using HDTMA-coated bentonite might be more effective.     

Effect of organic fertilizers derived dissolved organic matter on pesticide sorption and leaching

Incorporation of organic fertilizers/amendments has been, and continues to be, a popular strategy for golf course turfgrass management. Dissolved organic matter (DOM) derived from these organic materials may, however, facilitate organic chemical movement through soils. A batch equilibrium technique was used to evaluate the effects of organic fertilizer-derived DOM on sorption of three organic chemicals (2,4-D, naphthalene and chlorpyrifos) in USGA (United States Golf Association) sand, a mixed soil (70% USGA sand and 30% native soil) and a silt loam soil (Typic Fragiochrept). DOM was extracted from two commercial organic fertilizers. Column leaching experiments were also performed using USGA sand. Sorption experiments showed that sorption capacity was significantly reduced with increasing DOM concentration in solution for all three chemicals. Column experimental results were consistent with batch equilibrium data. These results suggest that organic fertilizer-derived DOM might lead to enhanced transport of applied chemicals in turf soils.     

城市生活垃圾填埋初期有机质演化规律研究

为阐明生活垃圾填埋初期有机质演化规律,于填埋场打井采集填埋1～3年3个不同时期垃圾样品,用水浸提制备水溶性有机物(DOM)。采用红外光谱、同步荧光光谱及紫外光谱,对浸提液中DOM的结构和演化特征进行了研究。结果显示,生活垃圾中含有脂肪类、蛋白类、糖类及木质素类物质,在填埋初期,有机质中的脂肪类、蛋白质类、糖类及木质素类物质均发生了降解,羧基、氨类及水溶性芳香结构物质减少,DOM分子量降低。研究结果表明,垃圾填埋初期有机质以降解为主。     

Mobility of chloroaromatic compounds in soil: case studies of Swedish chlorophenol-contaminated sawmill sites

This paper summarizes recent studies on the environmental fate of chloroaromatic compounds in chlorophenol (CP)-contaminated soil and groundwater at Swedish sawmill sites. Relative proportions of CPs, polychlorinated phenoxy phenols (PCPPs), polychlorinated diphenyl ethers (PCDEs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) were determined in preservatives, particulate organic matter (POM), dissolved organic matter (DOM), groundwater, and particles filtered from groundwater. All compound classes were found in the different compartments. The fraction of PCPPs, PCDEs, PCDDs, and PCDFs had increased in the soil samples relative to the proportions in the preservatives. This increase showed correlation with the hydrophobicity, that is, PCDDs had the largest increase. Similar correlation was found between hydrophobicity and the importance of partitioning to POM over DOM. The more water soluble compound group, CP, was found equally distributed between POM and DOM. For PCPPs, PCDEs, PCDDs, and PCDFs, the relative partitioning to POM increased with increased hydrophobicity. Despite the relative partitioning towards POM, compared with DOM, cotransport with DOM and suspended colloidal fractions was found to substantially increase the transport of these compounds in the groundwater samples.     

Characterization of dissolved organic matter in fogwater by excitation–emission matrix fluorescence spectroscopy

Dissolved organic matter (DOM) present in fogwater samples collected in southeastern Louisiana and central-eastern China has been characterized using excitation–emission matrix fluorescence spectroscopy. The goal of the study was to illustrate the utility of fluorescence for obtaining information on the large fraction of organic carbon in fogwaters (typically >40% by weight) that defies characterization in terms of specific chemical compounds without the difficulty inherent in obtaining sufficient fogwater volume to isolate DOM for assessment using other spectroscopic and chemical analyses. Based on the findings of previous studies using other characterization methods, it was anticipated that the unidentified organic carbon fraction would have characteristic peaks associated with humic substances and fluorescent amino acids. Both humic- and protein-like fluorophores were observed in the fogwater spectra and fluorescence-derived indices for the fogwater had similar values to those of soil and sediment porewater. Greater biological character was observed in samples with higher organic carbon concentrations. Fogwaters are shown to contain a mixture of terrestrially- and microbially-derived fluorescent organic material, which is expected to be derived from an array of different sources, such as suspended soil and dust particles, biogenic emissions and organic substances generated by atmospheric processes. The fluorescence results indicate that much of the unidentified organic carbon present in fogwater can be represented by humic-like and biologically-derived substances similar to those present in other aquatic systems, though it should be noted that fluorescent signatures representative of DOM produced by atmospheric processing of organic aerosols may be contributing to or masked by humic-like fluorophores.     

Investigations on the binding mechanism of the herbicide simazine to dissolved organic matter in leachates of compost

14C-labelled simazine was composted together with biowaste on a pilot (m3) scale. The herbicide was quickly bound to the compost matrix. By aqueous extraction of 29 and 200 days old compost (equivalent to thermophilic and mesophilic phase of composting) only 4.2% and 3.1% respectively of the radioactivity in the compost samples could be extracted with water. Analysis of the extracts using high-performance size exclusion chromatography (HPSEC) revealed that the dissolved organic matter (DOM) had molecular weights ranging between 2 and 28 kDa. The amount of DOM-associated radioactivity increased from 53% (day 29) to 65% (day 200) of total extractable radioactivity. The type of binding of the 14C-labelled residues and the DOM was elucidated by silylation of humic matter and subsequent HPSEC. The data demonstrated that besides polar metabolites also intact simazine was bound to the DOM. A distinct shift from rather weak interactions to strong covalent linkages of simazine and its metabolites with increasing age of the compost was observed. The results showed that only low amounts of free simazine and its degradates can be extracted with water. We concluded that the shift towards stable covalent linkages is equivalent to a detoxification of the contaminant in aged compost. Consequently, the use of the analysed compost in its mature stage should not pose an environmental risk to the groundwater or the subsoil.     

Effects of sewage sludge amendments on pesticide sorption and leaching through undisturbed Mediterranean soils

The Gharb region in Morocco is an important agricultural zone where soils receive pesticide treatments and organic amendments to increase yields. The groundwater aquifer in the Gharb region is relatively shallow and thus vulnerable. The objective of this work was to study the influence of organic amendments on diuron, cyhalofop-butyl and procymidone leaching through undisturbed soil columns. Two soils were sampled from the Gharb region, a Dehs (sandy soil) and a R'mel (loamy clay soil). Following elution (124.5 mm), the amount of pesticide residues in the leachates of the sandy soil (0.06-0.21 %) was lower than in those of the loamy clay soil (0.20-0.36 %), which was probably due to preferential flow through the loamy clay soil. The amount of procymidone leached through the amended soil columns was greater than the control for the sandy soil only. The organic amendments did not significantly influence diuron and cyhalofop-butyl leaching in either of the soils. The application of organic amendments affected the amounts of dissolved organic matter (DOM) eluted and thus pesticide leaching as a function of soil-type. Nevertheless, in some case, the formation of pesticide-DOM complexes appeared to promote pesticide leaching, thus increasing groundwater contamination risks.     

Effects of sewage sludge amendments on pesticide sorption and leaching through undisturbed Mediterranean soils

The Gharb region in Morocco is an important agricultural zone where soils receive pesticide treatments and organic amendments to increase yields. The groundwater aquifer in the Gharb region is relatively shallow and thus vulnerable. The objective of this work was to study the influence of organic amendments on diuron, cyhalofop-butyl and procymidone leaching through undisturbed soil columns. Two soils were sampled from the Gharb region, a Dehs (sandy soil) and a R’mel (loamy clay soil). Following elution (124.5 mm), the amount of pesticide residues in the leachates of the sandy soil (0.06–0.21 %) was lower than in those of the loamy clay soil (0.20–0.36 %), which was probably due to preferential flow through the loamy clay soil. The amount of procymidone leached through the amended soil columns was greater than the control for the sandy soil only. The organic amendments did not significantly influence diuron and cyhalofop-butyl leaching in either of the soils. The application of organic amendments affected the amounts of dissolved organic matter (DOM) eluted and thus pesticide leaching as a function of soil-type. Nevertheless, in some case, the formation of pesticide-DOM complexes appeared to promote pesticide leaching, thus increasing groundwater contamination risks.     

光催化氧化降解垃圾渗滤液中溶解性有机物

研究了UV-TiO2光催化氧化降解垃圾渗滤液过程中溶解性有机物(DOM)的变化特征。结果表明:在适宜条件下,UV-TiO2光催化氧化降解垃圾渗滤液的色度、COD和DOC的去除率分别可达97%、72%和60%;紫外光谱分析说明渗滤液DOM中包括多种含有共轭双键、羰基的大分子有机物及多环芳香类化合物,不同光催化处理液中DOM具有基本一致的结构单元和官能团;红外光谱分析说明渗滤液DOM中含有大量包括羟基、羧基、氨基和苯环的芳香族化合物,在光催化处理液中这几种官能团都能被有效降解;GC/MS分析结果表明,渗滤液DOM中含有72种有机污染物,醇类、羧酸和酮类分别为25、14和12种;在光催化72 h处理液中,有机物减少为44种;酯类和醇类较多,分别为12种和16种;酮类8种,羧酸没有检出。     

Determination of the origin of groundwater nitrate at an air weapons range using the dual isotope approach

Nitrate is one of the most common contaminants in shallow groundwater, and many sources may contribute to the nitrate load within an aquifer. Groundwater nitrate plumes have been detected at several ammunition production sites. However, the presence of multiple potential sources and the lack of existing isotopic data concerning explosive degradation-induced nitrate constitute a limitation when it comes to linking both types of contaminants. On military training ranges, high nitrate concentrations in groundwater were reported for the first time as part of the hydrogeological characterization of the Cold Lake Air Weapons Range (CLAWR), Alberta, Canada. Explosives degradation is thought to be the main source of nitrate contamination at CLAWR, as no other major source is present. Isotopic analyses of N and O in nitrate were performed on groundwater samples from the unconfined and confined aquifers; the dual isotopic analysis approach was used in order to increase the chances of identifying the source of nitrate. The isotopic ratios for the groundwater samples with low nitrate concentration suggested a natural origin with a strong contribution of anthropogenic atmospheric NOx. For the samples with nitrate concentration above the expected background level the isotopic ratios did not correspond to any source documented in the literature. Dissolved RDX samples were degraded in the laboratory and results showed that all reproduced degradation processes released nitrate with a strong fractionation. Laboratory isotopic values for RDX-derived NO(3)(-) produced a trend of high delta(18)O-low delta(15)N to low delta(18)O-high delta(15)N, and groundwater samples with nitrate concentrations above the expected background level appeared along this trend. Our results thus point toward a characteristic field of isotopic ratios for nitrate being derived from the degradation of RDX.     

Characterizing sources of nitrate leaching from an irrigated dairy farm in Merced County, California

Dairy farms comprise a complex landscape of groundwater pollution sources. The objective of our work is to develop a method to quantify nitrate leaching to shallow groundwater from different management units at dairy farms. Total nitrate loads are determined by the sequential calibration of a sub-regional scale and a farm-scale three-dimensional groundwater flow and transport model using observations at different spatial scales. These observations include local measurements of groundwater heads and nitrate concentrations in an extensive monitoring well network, providing data at a scale of a few meters and measurements of discharge rates and nitrate concentrations in a tile-drain network, providing data integrated across multiple farms. The various measurement scales are different from the spatial scales of the calibration parameters, which are the recharge and nitrogen leaching rates from individual management units. The calibration procedure offers a conceptual framework for using field measurements at different spatial scales to estimate recharge N concentrations at the management unit scale. It provides a map of spatially varying dairy farming impact on groundwater nitrogen. The method is applied to a dairy farm located in a relatively vulnerable hydrogeologic region in California. Potential sources within the dairy farm are divided into three categories, representing different manure management units: animal exercise yards and feeding areas (corrals), liquid manure holding ponds, and manure irrigated forage fields. Estimated average nitrogen leaching is 872 kg/ha/year, 807 kg/ha/year and 486 kg/ha/year for corrals, ponds and fields respectively. Results are applied to evaluate the accuracy of nitrogen mass balances often used by regulatory agencies to assess groundwater impacts. Calibrated leaching rates compare favorably to field and farm scale nitrogen mass balances. These data and interpretations provide a basis for developing improved management strategies.     

Transformation of dissolved organic matter in a novel groundwater recharge system with reclaimed water

A novel process, enhanced direct injection-well recharge system (EnDir), can overcome the technical difficulties during the application of conventional surface spreading and has been developed to recharge groundwater with reclaimed water. In this study, removal and transformation of dissolved organic matter (DOM) in the system were investigated in laboratory-scale experiments. Results demonstrated that dissolved organic carbon and trihalomethane formation potential values could be reduced from 6.54 +/- 1.30 mg/L and 267.9 +/- 24.3 microg/L to 1.59 +/- 0.64 mg/L and 104.5 +/- 10.2 microg/L, respectively, as a result of DOM biodegradation in the aerobic short-term vadose soil treatment. Fluorescence spectra showed that aromatic protein-like substances and soluble microbial byproducts could be removed, to a great extent, in the soil system. Despite different removal efficiencies of DOM in different molecular weight fractions, the residual DOM was composed mainly of fulvic acid-like and humic acid-like substances, with molecular weights of 500 Da to 1 kDa.     

Predicting groundwater nitrate concentrations in a region of mixed agricultural land use: a comparison of three approaches.

We investigated whether nitrate-N (NO3(-)-N) concentrations of shallow groundwater (< 30 m from the land surface) in a region of intensive agriculture could be predicted on the basis of land use information, topsoil properties that affect the ability of topsoil to generate nitrate at a site, or the 'leaching risk' at different sites. Groundwater NO3(-)-N concentrations were collected biannually for 3 years at 88 sites within the Waikato Region of New Zealand. The land use was classed as either the predominant land use of the farm where the well or bore was located, or the dominant land use within a 500 m radius of the well or bore. Topsoil properties that affect the ability of soil to generate nitrate were also measured at all the sites, and a leaching risk assessment model 'DRASTIC' was used to assess the risk of NO3(-)-N leaching to groundwater at each site. The concentration of NO3(-)-N in shallow groundwater in the Waikato Region varied considerably, both temporally and spatially. Nine percent of sites surveyed had groundwater NO3(-)-N concentrations exceeding maximum allowable concentrations of 11.3 ppm recommended by the World Health Organisation for potable drinking water which is accepted as a public health standard in New Zealand. Over half (56%) of the sites had concentrations that exceeded 3 ppm, indicating effects of human activities (commonly referred to as a human activity value). Very few trends in NO3(-)-N concentration that could be attributed to land use were identified, although market garden sites had higher concentrations of NO3(-)-N in underlying groundwater than drystock/sheep sites when the land use within 500 m radius of a sampling site was used to define the land use. There was also some evidence that within a district, NO3(-)-N concentrations in groundwater increased as the proportion of area used for dairy farming increased. Compared to pastoral land, market gardens had lower total C and N, potentially mineralisable N and denitrifying enzyme assay. However, none of these soil properties were directly related to groundwater NO3(-)-N concentrations. Instead, the DRASTIC index (which ranks sites according to their risk of solute leaching) gave the best correlation with groundwater NO3(-)-N concentrations. The permeability of the vadose zone was the most important parameter. The three approaches used were all considered unsuitable for assessing nitrate concentrations of groundwater, although a best-fit combination of parameters measured was able to account for nearly half the variance in groundwater NO3(-)-N concentrations. We suggest that non-point source groundwater NO3(-)-N contamination in the region reflects the intensive agricultural practices, and that localised, site-specific, factors may affect NO3(-)-N concentrations in shallow groundwaters as much as the general land use in the surrounding area.     

硅藻土强化混凝去除微污染原水中的有机物

研究了联用硅藻土与聚合氯化铝（PAC）强化混凝对有机微污染原水中不同性质溶解性有机物的去除效果。采用超滤膜和XAD系列树脂对微污染原水中溶解性有机物进行分级表征,物理分级表明分子量〈4 kD的溶解性有机物占50%以上,化学分级表明原水中以憎水酸（HoA）和亲水物质（HiM）为主。硅藻土助凝去除溶解性有机物,实验结果表明,当PAC投加量30 mg/L,硅藻土投加量0.5 g/L时,溶解性有机碳去除率由22.5%提高到26.3%。     

Oxidative biodegradation of dissolved organic matter during composting

Dissolved organic matter (DOM) plays an important role in the microbial degradation of compost since it represents the most active organic fraction, both biologically and chemically. The detailed evaluation of the changes in the chemical and biochemical characteristics of DOM induced by oxidative biodegradation, presented in this work highlights the mechanisms involved in the degradation of soluble organic matter during composting. In fact, the results show that during the initial stages of composting, DOM is highly degradable under aerobic conditions, particularly due to the predominance of labile, hydrophilic compounds such as carbohydrates, amino acids and proteins. As such compounds are degraded more resistant aromatic moieties accumulate in solution resulting in a reduction in the degradability of DOM with composting time. This decrease in degradability was found to be highly correlated with microbial oxygen demand, and could have important implications in the evaluation of the composting process.     

An independent prediction of the effect of dissolved organic matter on the transport of polycyclic aromatic hydrocarbons

The transport of polycyclic aromatic hydrocarbons (PAH) in porous media in the presence of dissolved organic matter (DOM) was predicted with a transport bicontinuum model using independently obtained relationships to derive transport parameters for describing the effect of PAH binding to the DOM. The sorption constants of PAHs to soil and their binding constants to DOM were derived from basic correlations with K(ow) (indicator of hydrophobicity). The kinetic (rate) constants were derived from previously published correlations with K(p) (sorption constant). The independently obtained sorption and rate constants were corrected for binding to DOM and were used to predict the breakthrough curves (BTC) of contaminants in the presence and the absence of DOM. Column results confirmed the independently predicted BTC of PAHs in the presence of DOM that did not sorb to the solid phase, as well as the effect of DOM on the rate of the sorption and desorption processes. These findings confirm the ability to quantitatively describe how DOM facilitates transport of contaminants in the subsurface using independently derived parameters.     

Effects of photodegradation of dissolved organic matter on the binding of benzo(a)pyrene

Dissolved organic matter (DOM) in natural waters can bind various organic pollutants, and the affinity of this binding is strongly influenced by the chemical characteristics of the DOM and water pH. This study examined the effects of photochemically induced alteration of the DOM's chemical properties and water pH on the binding of benzo(a)pyrene (BaP). Time- and pH-series of solar-simulated irradiations were performed on a natural water sample and aqueous DOM solutions prepared from aquatic and soil humic substances. The binding affinity of BaP, expressed as a partition coefficient of a compound to DOM, decreased substantially after the DOM samples were irradiated over environmentally relevant radiation doses and pH ranges. The lowering of the pH due to the photoproduction of acidic products often partly offsets the reduction of the binding affinity caused by direct photoalteration of the DOM's chemical structure. The decrease of the binding affinity, after correction for the photoinduced pH change, was positively correlated with the decrease in the molecular weight and the aromaticity of the DOM in the course of irradiation. Increasing O(2) abundance accelerated the decrease of the binding affinity as a result of enhanced DOM photodegradation. Visible light played a more important role in reducing the molecular weight and aromaticity of the DOM than in reducing the content of dissolved organic carbon (DOC) via photoremineralization while the reverse was true for UV radiation, indicating that photochemical reduction of the binding affinity may occur in natural waters at depths greater than UV radiation can reach. A decrease of the affinity of DOM for binding BaP will increase the free dissolved fraction of BaP and thus its availability and toxicity to aquatic organisms. The results from this study may have similar implications for organic pollutants other than BaP.     

Transport and fate of organic wastes in groundwater at the Stringfellow hazardous waste disposal site, southern California

In January 1999, wastewater influent and effluent from the pretreatment plant at the Stringfellow hazardous waste disposal site were sampled along with groundwater at six locations along the groundwater contaminant plume. The objectives of this sampling and study were to identify at the compound class level the unidentified 40-60% of wastewater organic contaminants, and to determine what organic compound classes were being removed by the wastewater pretreatment plant, and what organic compound classes persisted during subsurface waste migration. The unidentified organic wastes are primarily chlorinated aromatic sulfonic acids derived from wastes from DDT manufacture. Trace amounts of EDTA and NTA organic complexing agents were discovered along with carboxylate metabolites of the common alkylphenolpolyethoxylate plasticizers and nonionic surfactants. The wastewater pretreatment plant removed most of the aromatic chlorinated sulfonic acids that have hydrophobic neutral properties, but the p-chlorobenzene-sulfonic acid which is the primary waste constituent passed through the pretreatment plant and was discharged in the treated wastewaters transported to an industrial sewer. During migration in groundwater, p-chlorobenzenesulfonic acid is removed by natural remediation processes. Wastewater organic contaminants have decreased 3- to 45-fold in the groundwater from 1985 to 1999 as a result of site remediation and natural remediation processes. The chlorinated aromatic sulfonic acids with hydrophobic neutral properties persist and have migrated into groundwater that underlies the adjacent residential community.