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1.
The aim of this work is to investigate the influence of pH and the metal:humic substances (HS) ratio on HS complexing capacity and the stability and solubility of metal–HS complexes in solution. We selected four HS with different physicochemical properties and studied their interaction with Cu(II), Zn(II) and Fe(II) at different pH and metal:HS ratios. The selected HS were a humic acid and a whole humic extract (containing the humic and fulvic acids) extracted from black peat, and a fulvic acid and a whole humic extract extracted from a compost of grape solid wastes.Our results showed that HS complexing capacity significantly varied as a function of pH, thus indicating the influence of both functional group ionisation and molecular conformation on this property. As was expected, total acidity affected the complexing capacity of the selected HS.The results related to stability and complexing capacity indicated the possible presence of two binding patterns, one at acid-neutral pH probably involving carboxylates, and another at alkaline pH probably involving carboxylates and phenolic groups. The relationship between these binding patterns and the strength of the binding process varied according to the complexed metal.Complex solubility was greatly affected by the ratio between the concentration of free ionised functional groups and the molecular weight in the HS studied.  相似文献   

2.
The effects of photoirradiation of dissolved organic matter (DOM) on its subsequent adsorption to the Fe(III)oxyhydroxide mineral goethite were investigated at 22°C in 0.10 mol L−1 NaClO4 solutions at pH 3.5 and 5.5, Photoirradiation of DOM decreased the abundance of high molecular-weight components and formed new lower molecular-weight components, including low molecular weight carboxylic acids (i.e., formic, malonic, and acetic acids). Adsorption of non-irradiated DOM decreased from pH 3.5 to 5.5 and was dominated by the intermediate molecular weight (1251-3750 Da) fraction, although the 451-1250 and 3751-11350 Da fractions also contributed to adsorption at pH 3.5. Irradiation resulted in a substantial decrease in DOM adsorption affinity at pH 3.5, primarily due to loss of components in the 1251-3750 and 3751-11350 Da fractions. Irradiation resulted in only a small decrease in DOM adsorption affinity at pH 5.5; the loss of components in the 3751-11350 Da fraction upon irradiation had little effect on adsorption because they played little or no role in the non-irradiated sample at this pH. Irradiation of DOM also affected its interactions with Fe in solution and the solution iron(II)/iron(III) speciation. The combined effects of irradiation followed by adsorption produced DOM that was lower in molecular weight and had a decreased UV-Vis absorptivity than either process, alone. Together, these two processes are likely to have important environmental consequences in terms of UV penetration of surface waters, contaminant mobility, and DOM bioavailability.  相似文献   

3.
《Applied Geochemistry》1999,14(6):807-816
A rapid procedure is described to evaluate the significance of inorganic and organic pollutants in fine-grained sediments. The air- (<30°C) or freeze-dried samples are screened within 30 min. in stainless steel sieves (<0.04 mm) prior to chemical analysis. This procedure is also suitable for analysis of such elements as Hg and many non-volatile organic pollutants. The sediment size fraction of <0.04 mm was chosen in order to separate the smallest grain-size obtainable by rapid dry-screening techniques; this is representative of the grain-size of suspended matter transported at low and medium river discharge (0.1–0.7 m/s). The screened fraction (<0.04 mm) of aquatic sediments is more homogeneous in grain-size and distribution, and the fine particles are more capable of adsorbing pollutants than coarser fractions. However, large differences are observed in grain-size distribution and adsorbable phases from one sample to another, even in the smallest size fractions (<0.04, <0.02, <0.002 mm). Clay minerals, Fe- and Mn-(oxy)hydrates, amorphous silica and humic substances all adsorb water at normal humidity. In order to estimate and standardise the adsorption capacity of the surface of these screened sediment fractions, the weight loss after heating at 105°C is used, instead of tedious quantification of all the above mentioned sediment phases. In addition, this procedure allows the rejection of sediment samples, unsuitable for monitoring purposes, which have very low adsorption capacities. In order to correct for the variable adsorption capacity of different sediment samples or size fractions, the weight loss (WL) at 105°C can be inserted in the widely used GeoIndex formula (Igeo105°=log2 (Cmeasured/Cbackground1WL105°C). This improves the evaluation of pollution in aquatic environments.  相似文献   

4.
天然有机质与矿物间的吸附及其环境效应的研究进展   总被引：18，自引：0，他引：18  
本文综述了天然有机质与矿物间吸附行为的研究进展.具体介绍了天然有机质与矿物间的吸附机理,包括配位交换、范德华力、静电引力、疏水作用、离子交换及阳离子桥;阐述了不同分子大小及亲疏水性组分的天然有机质在矿物上的吸附行为;讨论了影响吸附行为的环境条件（pH,离子强度）及天然有机-矿物体系对全球碳循环、重金属和有机污染物产生的环境效应,并提出了研究展望.  相似文献   

5.
Pharmaceuticals have gained significant attention in recent years due to the environmental risks posed by their versatile application and occurrence in the natural aquatic environment. The transportation and distribution of pharmaceuticals in the environmental media mainly depends on their sorption behavior in soils, sediment?Cwater systems and waste water treatment plants, which varies widely across pharmaceuticals. Sorption of ibuprofen, a non-steroidal anti-inflammatory drug, onto various soil minerals, viz., kaolinite, montmorillonite, goethite, and activated carbon, as a function of pH (3?C11), ionic strength (NaCl concentration: 0.001?C0.5?M), and the humic acid concentration (0?C1,000?mg/L) was investigated through batch experiments. Experimental results showed that the sorption of ibuprofen onto all sorbents was highest at pH 3, with highest sorption capacity for activated carbon (28.5?mg/g). Among the minerals, montmorillonite sorbed more ibuprofen than kaolinite and goethite, with sorption capacity increasing in the order goethite (2.2?mg/g)?<?kaolinite (3.1?mg/g)?<?montmorillonite (6.1?mg/g). The sorption capacity of the selected minerals increased with increase in ionic strength of the solution in acidic pH condition indicating that the effect of pH was predominant compared to that of ionic strength. An increase in humic acid concentration from low to high values made the sorption phenomena very complex in the soil minerals. Based on the experimental observations, montmorillonite, among the selected soil minerals, could serve as a good candidate to remove high concentrations of ibuprofen from aqueous solution.  相似文献   

6.
在痕量元素的海洋生物地球化学循环过程中,有机配体直接控制痕量元素在不同形态及粒径范围内的分配,进而影响痕量元素的迁移转化过程和生物可利用性。深入研究海水中痕量元素-有机配体的配分特征及影响因素,明确有机配体分子量组分及其对痕量元素的配合作用差异,对于了解痕量元素的生物地球化学行为,评估痕量元素的生物可利用性和毒性效应均具有十分重要的意义。对海水中痕量元素-有机配体的分布规律、配分特征及盐度、pH、氧化还原条件和生物活动对配体的影响进行了系统总结。海水中的有机配体一般以低分子量部分为主体,配合能力因元素性质差异存在随分子量增加而提高或降低的不同趋势。除此之外,有机配体的结构、配合能力及分子量分布随水体各物理化学参数的变化而改变。盐度的增加会降低有机配体相邻官能团的静电排斥力从而降低配体的配合能力,还会导致高分子量金属有机配合物发生絮凝和降解而去除。pH的增加不仅可以促使有机配体离子化,还能促进部分痕量元素水解为与有机配体亲和力更高的形式,提高有机配体配合率。氧化还原环境同时影响了痕量元素的价态和有机配体的浓度,间接影响痕量元素-有机配体的配合率。浮游植物利用及微生物分解可以增加低分子量有机配体的比例,从而提高其配合能力,但当生物遭受过量金属离子的毒性胁迫时,其细胞内会释放胞内配体,将致毒元素转化为配合物并排出体外,从而增加水体中痕量元素高分子量有机配体的浓度。未来应结合有机物结构分析技术及痕量元素分离检测技术,系统研究海洋环境中不同分子量有机配体的结构及与痕量元素配合强度的相互关系,进一步揭示痕量元素的迁移转化过程与生态学意义。  相似文献   

7.
Organic metal-binding ligands represent an essential role in the bioavailability of trace elements since they govern the species and sizes of those elements in seawater. The distribution and properties of organic ligands in seawater as well as the factors influencing their complexation abilities were summarized in this paper. Most organic ligands exist in the low molecular weight fraction, and their concentration nearshore is often higher than that of open ocean while the vertical distribution varies in different areas. The complexation of trace elements and organic ligands is influenced by several factors such as molecular weight of organic ligands, salinity, pH, biological activities and redox conditions. Ligand with a lower molecular weight usually represents stronger complexation ability, whereas the opposite seems to be true sometimes due to the specific affinity between some elements and ligands. Increasing salinity lowers the electrostatic repulsion among adjacent functional groups of ligands and thus decreases their complexing rate, yet increasing pH promotes the ionization of organic ligands and results in the formation of more complexes. The utilization of phytoplankton and degradation of microorganism release more low molecular weight organic ligands while more high molecular weight ligands are released from marine organisms under heavy metal stress. Therefore, sufficient significance should be attached to characterizing the structure and molecular weight of organic ligands and exploring the interaction between trace elements and organic ligands and the influence of related marine factors on their behaviors, which will certainly help us to understand the global biogeochemical cycles and ecological significance of trace elements.  相似文献   

8.
The effect of temperature on the sorption of cations onto a dioctahedral smectite was investigated by running batch experiments at 25, 40, 80 and 150°C. We measured the distribution coefficient (Kd) of Cs+, Ni2+ and 14 lanthanides (Ln3+) between solutions and the montmorillonite fraction of the MX80 bentonite at various pH and ionic strengths. Up to 80°C we used a conventional experimental protocol derived from Coppin et al. (2002). At 150°C, the experiments were conducted in a PTFE reactor equipped with an internal filter allowing the sampling of clear aliquots of solution.The results show a weak but measurable influence of the temperature on the elements sorption. Kd’s for Ni2+ and Ln3+ increase by a factor 2 to 5 whereas temperature raises from 25 to 150°C. This effect seems higher at high ionic strength. The estimated apparent endothermic sorption enthalpies are 33 ± 10 kJ.mol−1 and 39 ± 15 kJ.mol−1 for Ni2+ and Eu3+, respectively. On the other hand, the temperature effect on Cs+ sorption is only evidenced at low ionic strength and under neutral conditions where the Kd decreases by a factor 3 between 25 and 150°C. Apparent exothermic sorption enthalpy for Cs+ on the montmorillonite is −19 ± 5 kJ.mol−1.Experiments conducted at the four temperatures with the coexistence of all of the cations in the reacting solution (100 ppb of each element in the starting solution) or only one of them, produced similar values of Kd. This suggests the absence of competition between the sorbed cations, and consequently a low degree of saturation of the available sites. A fractionation of the lanthanides spectrum is also observed at high pH and high ionic strength whatever the temperature.The conclusion of this study is that the temperature dependence on sorption reflects, as the fractionation of REE or the pH and ionic strength effects, the chemical process which controls the overall reaction. In the case of an exchange dominated reaction (low pH and low ionic strength), the temperature effect is negligible. In the case of surface complexation (high pH and high ionic strength), the observed increase of Kd with temperature reflects either an increase of the sorption equilibrium constant with temperature or an endothermic property for reactions describing the montmorillonite surface chemistry.  相似文献   

9.
Humic substances (HS) were isolated from Penwhirn Reservoir (PR) and Esthwaite Water (EW) and their removal from solution by centrifugation was studied as a function of pH, humic concentration and molecular weight, and CaCl2 concentration. Large amounts (up to 50%) of PR HS could be removed but only small amounts (? 3%) of EW HS. At pH ? 5 removal of PR HS by Ca2+ can be explained satisfactorily in terms of decreases in humic solubilities induced by complexation with the cation. However, removal induced by protonation of the PR HS is unusual in that it decreases with increasing humic concentration.The results suggest that PR HS comprise a range of molecules differing in solubility, with the high-molecular-weight (40,000) components being the least soluble. The EW HS consist of molecules of weight-average molecular weight 5000 and resemble similarly sized PR HS in that they remain unaggregated in solution even when highly complexed with Ca2+.  相似文献   

10.
《Applied Geochemistry》2001,16(14):1611-1619
Biodegradation of polycyclic aromatic hydrocarbon (PAH) was investigated in the whole matrix and in the different aggregate size fractions of a sandy soil contaminated by a mixture of 8 PAHs and incubated at water holding capacity. The distribution of PAHs and of phenanthrene-degrading bacteria were determined in the bulk soil and in 4 size aggregate fractions corresponding to sand, coarse silt, fine silt and clay. The microbial communities able to degrade phenanthrene were detected at a similar level in the different aggregate fractions of the soil before contamination. After soil contamination and incubation, a significant growth of bacteria was observed and their distribution within aggregates was modified. Bacterial communities of phenanthrene-degraders were present in a higher density in the aggregates corresponding to sand (2000–50 μm) and clay (<2 μm). Chemical analysis show that remaining PAHs (low and high molecular weight) were much more concentrated in the fine soil fractions (fine silt and clay) and were present at a very low content in the larger aggregate size fractions. The interactions of well defined aggregates with PAHs and bacteria were also studied using phenanthrene as PAH model substrate and individual aggregates corresponding to sand and clay size fractions. Incubation of sand and clay aggregate fractions enriched with phenanthrene in the presence of a bacterial isolate NAH1 led to the simultaneous solubilization and biodegradation of phenanthrene. Differences in amounts of solubilized phenanthrene between sand and clay aggregate size fractions would be related to difference in adsorption capacities of phenanthrene by clay and sand aggregates.  相似文献   

11.
Elevated polycyclic aromatic hydrocarbon (PAH) concentrations were determined in different Chinese coals, with the highest concentrations in bituminous coals. Phenanthrene (Phen) was chosen as the probe compound for PAHs to study the sorption behavior of coal. No native Phen was detected in desorption experiments indicating irreversible sorption–desorption behavior of PAHs in raw coal samples. Sorption mechanism was further studied under varying conditions of pH value and ionic strength. Different ranks of coal showed different sorption behavior under acidic, neutral, and alkaline conditions. Batch experiments were further processed for the selected coals at pH values from 3 to 11 at a constant aqueous concentration. Sorption capacities of all coals decreased with increased pH except for YJ coal. Furthermore, although DOC-associated Phen mass contributed little to the total Phen mass under different pH values, the significant negative correlations between M DOC and log K OC values were observed for all coal samples, indicating a significant role played by DOC in the coal sorption. In addition, sorption experiments under varying ionic strength showed that the ionic strength influence was more obvious in sorption isotherms for higher rank coals with increasing ionic strength, and this effect was most significant when ionic strength increased from 0 to 0.15 M, especially at relatively low aqueous concentrations.  相似文献   

12.
The mobility of toxic metals in soils or sediments is of great concern to scientists and environmentalists since it directly affects the bioavailability of metals and their movement to surface and ground waters. In this study, a multi-surface soil speciation model for Cd (II) and Pb (II) was developed to predict the partition of metals on various soil solid components (e.g. soil organic matter (SOM), oxide mineral, and clay mineral). In previous study, the sorption of metal cations on SOM and oxide minerals has been evaluated by thermodynamically based surface complexation model. However, metal binding to soil clay fractions was normally treated in a simplistic manner: only cation exchange reactions were considered and exchange coefficient was assumed unity. In this study, the binding of metals onto clays was described by a two-site surface sorption model (a basal surface site and an edge site). The model was checked by predicting the adsorption behavior of Cd (II) and Pb (II) onto three selected Chinese soils as a function of pH and ionic strengths. Results showed that the proposed model more accurately predicted the metal adsorption on soils under studied condition, especially in low ionic strength condition, suggesting that adsorption of metals to soil clay fractions need to be considered more carefully when modeling the partition of trace elements in soils. The developed soil speciation model will be useful when evaluating the movement and bioavailability of toxic metals in soil environment.  相似文献   

13.
广西壮族自治区碳酸盐岩分布面积为96 372 km2,约占全区陆地国土面积的407%。由碳酸盐岩风化形成的土壤中Cd、Pb、Hg等重金属元素普遍富集。初步评价发现,农作物籽实对Cd的吸收量与土壤Cd含量无对应关系,农作物Cd超标多出现在土壤Cd含量较低的地区。进一步研究发现,Cd高含量的土壤中普遍含有铝土矿、Fe Mn结核等颗粒。为了探索土壤中Cd存在形态及其影响因素,选择了含铝土矿和铁锰结核的横县土壤和无铝土矿与铁锰结核的象州土壤,系统研究了土壤Cd形态差异及其影响因素。结果表明：(1)象州土壤中Cd主要以活动态形式存在,生物可利用性高,横县土壤中Cd主要以稳定态形式存在,生物可利用性低。(2)pH值为60是象州土壤Cd活动态含量的突变点,pH值在60处含量达到最大值;而在横县,pH降低使活动态Cd比例增加。(3)象州土壤中活动态Cd随有机质增加而增加,表明Cd被有机质弱吸附;而横县土壤有机质含量与Cd形态无明显相关性。(4)由铝土矿导致的土壤高Cd含量,多以残渣态形式存在,不会对动植物造成危害。  相似文献   

14.
Adsorption of Cr(VI) on γ-alumina was investigated as a function of ionic strength (0.001, 0.01 and 0.1 M NaNO3), pH (4-10), Cr(VI) concentration (10−4 or 10−5 M with 5 g/L solid) and pCO2 (0, atmospheric, 2.5%). Cr(VI) sorption is significant at low pH and decreases with increasing pH, with 50% of the Cr(VI) adsorbed between pH ∼6.5 and 8. Adsorption varies little with ionic strength or pCO2 under most of the studied conditions. However, at low pH under high ionic strength and especially at high ionic strength and high pCO2, Cr(VI) sorption on γ-alumina is suppressed. The adsorption edge data were used to parameterize constant capacitance (CCM), diffuse double layer (DLM) and triple layer (TLM) surface complexation models. None of the models entirely captures the full range of observed adsorption dependence on ionic strength and sorbate/sorbent ratio. The best fits to the full dataset are produced by the CCM, mostly because it has ionic-strength dependent stability constants. The more sophisticated TLM, which requires the most fitting parameters, does not produce better fits than the simpler CCM or DLM approaches for the conditions tested in this study.  相似文献   

15.
The adsorption behavior of chromate on two variable charge soils (Oxisol and Ultisol) was investigated through batch experiments at different ionic strengths and pH values. The adsorption of chromate on the variable charge soils was found to be strongly dependent on the pH of the soil solutions. A characteristic pH was observed, which corresponds to the intersection of the chromate adsorption—pH curves at different ionic strengths. The characteristic pH values are 5.50 for Oxisol and 5.04 for Ultisol, close to the point of zero salt effect (PZSE) of these soils. The zeta potentials measured for these soils provide the evidences to support the interpretation of the effect of ionic strength on the adsorption of chromate on these variable charge soils. The adsorption behavior of chromate was interpreted by a schematic representation of chromate distribution at increasing ionic strength. The chromate desorption–pH curves were also found to intersect at pH of 5.15 and 4.89 for the Oxisol and Ultisol, respectively. It is considered that chromate adsorption by the variable charge soils was mainly determined by the electrostatic potential on the adsorption plane, which was controlled by the ionic strength of the soil solutions.  相似文献   

16.
黄玉冰  赵甜甜  向武  赵云鹏  刘洋 《地球科学》2021,46(5):1862-1870
为了研究泥炭沼泽源铁有机配合物的络合稳定性,利用pH电位滴定法和荧光淬灭滴定法测定了大九湖泥炭沼泽中不同分子量段的DOM和Fe2+、Fe3+的络合稳定常数.pH电位滴定法结果（4.0~6.1）和荧光淬灭滴定法（1.5~4.1）差异较大,这与高pH条件下OH被脱质子化及Fe2+的氧化有关.相对而言,pH滴定法更适用于探究不同分子量段DOM与铁的络合稳定性,荧光淬灭法不改变样品酸碱条件,更适于研究不同价态铁与DOM的络合稳定性.研究结果表明:DOM与Fe3+的络合稳定常数大于Fe2+,低分子量段（< 3 kDa）的DOM与Fe2+、Fe3+的络合稳定常数更大.泥炭沼泽源铁有机配合物具有较好的络合稳定性,分子量相对较小的DOM与铁的络合能力更强.即便Fe2+氧化为Fe3+,仍能与DOM络合并保持较强的稳定性,这有利于陆源溶解性铁向水生态系统的输出.沼泽源铁有机配合物的络合稳定性还会影响铁的生物可利用性.   相似文献   

17.
Numerical codes are applied to calculate chemical reactions following geologic carbon sequestration in deep formations and CO2 leakage in shallow formations. However, using different thermodynamic databases generates variations in the simulation results, which are referred to as the model uncertainty. The PHREEQC and The Geochemist's Workbench codes were used to simulate anorthite dissolution for storage, retention, transfer, and near-surface formation waters in the respective geological units. For each of the formation waters, a simple one-dimensional scenario was simulated using eight different thermodynamic databases. Groundwaters in shallow aquifers commonly exhibit low ionic strengths (<0.5 mol/kgw) and low temperatures, whereas storage formation waters are characterized by high ionic strength (>1.0 mol/kgw) and high temperatures. In storage formations, mineral trapping is the most efficient process for long-term CO2 storage. However, with respect to the geological formations and the time needed for anorthite dissolution, the model uncertainties associated with using different combinations of numerical codes and thermodynamic databases were largest (∼90%) for the storage formation waters at 58 °C and I = 6.5 mol/l. Conversely, in near-surface formation waters, the model uncertainty was less than 1%. Due to CO2 dissolution, the calculated pH of the formation waters decreased to a range between pH 4.0 and 5.5. In this pH range, the dissolution mechanism of anorthite switches from the slow neutral mechanism to the faster acid mechanism, causing dissolution time length variations. The calculated pH variation further increased with rising ionic strength. A detailed examination of the reasons revealed the activity coefficient calculation method of the main aquatic species to have the largest impact on the simulated model results. The calculation method of the CO2 activity coefficient had the second largest impact. Via calibration with the experimental data, a specific thermodynamic database can be chosen to represent these experimental results. However, the calibration of thermodynamic databases is not possible for all potential reactions in more complex geological systems at large ranges of temperature, ionic strength and pressure conditions. The uncertainties associated with using thermodynamic databases quantified in this study for CO2 storage systems will therefore persist independently from previously conducted calibrations of thermodynamic databases with experimental or field data. In view of these model uncertainties, the modeller is encouraged to include a routine in the simulations for quantification of the model uncertainty depending on the specific scenario or to assess the simulation results as a range of values that represent a soft outcome.  相似文献   

18.
To evaluate biogeochemical characteristics, eco-environmental risks and sources of trace elements (TEs: As, Hg, Se, Sb, Te, Sn, Bi and Ge), their total concentrations and chemical speciation in surface sediments collected from the Changjiang Estuary were determined. Total concentrations for As, Hg, Se, Sb, Te, Sn, Bi and Ge were 4.57–30.20, 0.01–0.40, 0.04–0.38, 0.36–1.48, 0.02–0.10, 0.48–6.58, 0.13–0.64 and 0.83–2.43 μg/g, respectively, with higher values at the estuary. This distribution pattern was attributed to the riverine input and high clay and total organic carbon contents. The sequential extraction suggested that TEs mainly occurred in residual fractions. The risk assessment code suggested that As, Hg and Sn were at low risk, whereas Bi, Se, Sb, Te and Ge were at medium risk. The geoaccumulation index (I geo) and principal component analysis indicated that Se and Sn mainly came from the natural input (crustal and biological inputs), whereas As, Sb, Hg, Bi and Te came from both of the crustal and anthropogenic inputs via atmosphere and rivers. In addition, Ge possibly came from the natural (crustal and biological inputs) and anthropogenic inputs.  相似文献   

19.
The dominant phosphorus compound classes were characterized in marine samples using a new, high recovery method for isolating and concentrating bulk dissolved organic matter (DOM) called combined electrodialysis + reverse osmosis (ED/RO). In contrast to earlier studies that use ultrafiltration (UF) to recover only the high molecular weight DOM, ED/RO is capable of isolating both low molecular weight (LMW) and high molecular weight (HMW) DOM. Samples were collected from a broad range of marine environments: along a transect incorporating coastal and offshore waters off the Southeastern United States, in Effingham Inlet, a Pacific fjord located on Vancouver Island, British Columbia and in the Amundsen Sea, Antarctica. Results from phosphorus nuclear magnetic resonance (31P NMR) analysis reveal a similar abundance of P compound classes among samples, phosphate esters (80–85%), phosphonates (5–10%) and polyphosphates (8–13%). These samples contain significantly higher proportions of polyphosphate P and P esters and lower proportions of phosphonates than measured in previous studies using the UF method. The much higher levels of polyphosphate detected in our samples suggests that polyphosphate is present mainly in the LMW dissolved matter fraction. Polyphosphates in dissolved matter may be present as (or derived from) dissolved nucleotides or organismal polyphosphate bodies, or both. Low molecular weight P esters are possibly composed of phosphoamino acids and small carbohydrates, like simple sugar phosphates and/or dissolved nucleotides. Phosphonates in DOM are more prevalent as HMW phosphonate compounds, which suggests that LMW phosphonates are more readily utilized in marine ecosystems. Overall, the investigation of DOM across a size spectrum that includes both the HMW and the LMW fractions reveals a new picture of phosphorus distribution, cycling and bioavailability.  相似文献   

20.
《Applied Geochemistry》1999,14(3):395-407
An ultrafiltration procedure has been developed to study the interaction between organic C and Hg species in natural waters, and a pilot study was conducted in the surface waters of the Florida Everglades. Compared to total Hg, CH3Hg shows different distribution patterns in the suspended particulate, colloidal, and truly dissolved phases. Colloidal forms (0.22 μm, 3 kDa) contain the majority of the total dissolved Hg, while the amount found in the truly dissolved fraction (<3 kDa) is small (about 10%). However, CH3Hg, which shows strong binding capability with low molecular-weight dissolved organic C, is present almost entirely in the lower molecular-weight fraction of the colloids and in the truly dissolved fraction. Quantitative CH3Hg data correlate well with those for dissolved organic C, an indication that the organic matter present in the system plays an important role in the fate and transport of organomercury. Distribution coefficients between water and the different-sized fractions of the dissolved organic C were determined for both total Hg and CH3Hg. Results for total Hg were in general agreement with other reports resulting from studies of molecular size distributions of total Hg in freshwater systems. This is, to the best of our knowledge, the first report of such distribution profiles for CH3Hg between different-sized fractions of dissolved organic C in natural waters.  相似文献   

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