表层土壤中有机污染物的光化学行为

本文首先简要介绍了光化学反应的基本原理。然后 ,重点介绍了研究表层土壤中有机污染物光化学行为的实验方法 ,影响光化学行为的因素及影响机理 ,光化学反应与吸附、迁移等的互相作用。最后阐述了这方面存在的问题 ,并且提出了一些建议     

Ion activity and distribution of heavy metals in acid mine drainage polluted subtropical soils

The oxidative dissolution of mine wastes gives rise to acidic, metal-enriched mine drainage (AMD) and has typically posed an additional risk to the environment. The poly-metallic mine Dabaoshan in South China is an excellent test site to understand the processes affecting the surrounding polluted agricultural fields. Our objectives were firstly to investigate metal ion activity in soil solution, distribution in solid constituents, and spatial distribution in samples, secondly to determine dominant environment factors controlling metal activity in the long-term AMD-polluted subtropical soils. Soil Column Donnan Membrane Technology (SC-DMT) combined with sequential extraction shows that unusually large proportion of the metal ions are present as free ion in the soil solutions. The narrow range of low pH values prevents any pH effects during the binding onto oxides or organic matter. The differences in speciation of the soil solutions may explain the different soil degradation observed between paddy and non-paddy soils.     

The influence of organic matter on sorption and fate of glyphosate in soil - Comparing different soils and humic substances

Soil organic matter (SOM) is generally believed not to influence the sorption of glyphosate in soil. To get a closer look on the dynamics between glyphosate and SOM, we used three approaches: I. Sorption studies with seven purified soil humic fractions showed that these could sorb glyphosate and that the aromatic content, possibly phenolic groups, seems to aid the sorption. II. Sorption studies with six whole soils and with SOM removed showed that several soil parameters including SOM are responsible for the strong sorption of glyphosate in soils. III. After an 80 day fate experiment, ∼40% of the added glyphosate was associated with the humic and fulvic acid fractions in the sandy soils, while this was the case for only ∼10% of the added glyphosate in the clayey soils. Glyphosate sorbed to humic substances in the natural soils seemed to be easier desorbed than glyphosate sorbed to amorphous Fe/Al-oxides.     

Sorption behavior of bensulfuron-methyl on andisols and ultisols volcanic ash-derived soils: Contribution of humic fractions and mineral-organic complexes

Bensulfuron-methyl sorption was studied in Andisol and Ultisol soils in view of their characteristic physical and chemical properties, presenting acidic pH and variable charge. Humic and fulvic acids (HA and FA) and humin (HUM) contributions were established. Sorption was studied by using two synthetic sorbents, an aluminum-silicate with iron oxide coverage and the same sorbent coated with humic acid. Freundlich model described Bensulfuron-methyl behavior in all sorbents (R² 0.969-0.998). K_f for soils (8.3-20.7 μg^1−1/n mL^1/n g⁻¹) were higher than those reported in the literature. Organic matter, halloysite or kaolinite, and specific surface area contributed to the global process. The highest K_f for HA, FA and HUM were 539.5, 82.9, and 98.7 μg^1−1/n mL^1/n g⁻¹. Model sorbents described the participation of variable charge materials with high adsorption capacity. The constant capacitance model was used to assess effects of Bensulfuron-methyl adsorption on the distribution of SOH, SOH₂⁺ and SO⁻ sites of sorbents.     

除草剂在土壤中的吸附行为研究

除草剂在土壤上的吸附和解吸行为是支配该除草剂在环境中的生物有效性和持久性的重要因素之一 ,同时对于预测除草剂在土壤和潜层水中的运动也是有重要作用。本文从吸附机理、实验技术、动力学、影响因素、常数的计算方法等方面阐述了除草剂在土壤中的吸附行为及其环境学意义。     

有机物性质对混凝-微滤-纳滤去除水中重金属的影响

为了探明有机物性质对混凝-微滤-纳滤去除水中重金属的影响,将腐殖酸和乙酸分别作为背景有机物,系统考察了组合工艺对镉(Cd)、铜(Cu)、镍(Ni)和锌(Zn)的去除效能及其膜通量变化过程,并通过物料衡算对4种重金属的去除行为进行了比较分析。结果表明,当原水中不含有机物时,Cu的截留率最高,达到97%以上,纳滤膜是去除其他3种重金属的主要步骤。随着原水中腐殖酸含量的增大,混凝-微滤阶段对重金属的截留能力显著增强,膜通量衰减速度加快。相反地,乙酸的存在对于组合工艺处理效能具有明显的负面效应。此时,重金属既不能被铝盐絮体有效吸附,也不能通过静电作用截留在NF膜表面。4种重金属在滤液和浓水中的回收率Rrec都超过了80%,膜通量的变化与处理无机重金属溶液时相近。     

阿特拉津在土壤中的环境行为研究进展

概述了阿特拉津在土壤中的迁移、降解及其对植物的影响等环境行为,阐述了土壤组成、土壤pH值以及温度、湿度等因素对各种环境行为过程的影响,并结合目前国内外的研究现状,提出了阿特拉津环境行为新的研究方向。     

Sorption-desorption behavior of metsulfuron-methyl and sulfosulfuron in soils

Sorption of metsulfuron-methyl and sulfosulfuron were studied in five Indian soils using batch sorption method. Freundlich adsorption equation described the sorption of herbicides with K_f (adsorption coefficient) values ranging between 0.21 and 1.88 (metsulfuron-methyl) and 0.37 and 1.17 (sulfosulfuron). Adsorption isotherms were L-type suggesting that the herbicides sorption decreased with increase in the initial concentration of the herbicide in the solution. The K_f for metsulfuron-methyl showed good positive correlation with silt content (significant at p = 0.01) and strong negative correlation with the soil pH (significant at p = 0.05) while sorption of sulfosulfuron did not correlate with any of the soil parameter. Desorption of herbicides was concentration dependent and, in general, sulfosulfuron showed higher desorption than the metsulfuron-methyl. The study indicates that these herbicides are poorly sorbed in the Indian soil types and there may be a possibility of their leaching to lower soil profiles.     

土壤有机质对铊在土壤中吸附-解吸行为的影响

研究了土壤有机质对Tl＋在红壤和黄土2种土壤中的吸附-解吸行为的影响。结果表明,去除土壤有机质后红壤和黄土对Tl＋的吸附量均明显下降,下降幅度最高分别达到24.7%和28.2%,黄土的下降幅度大于红壤;黄土对Tl＋吸附率最高下降幅度约为20%,也高于红壤的15%。土壤有机质对Tl＋吸附的贡献率平均值分别是黄土39.2%、红壤32.8%。2种土壤对Tl＋的解吸量在去除有机质之后都明显增大,在初始Tl＋浓度较高的情况下,增大幅度明显;并且Tl＋的初始浓度越高,土壤在去有机质前后的解吸率相差就越大,在Tl＋最大处理浓度为20 mg/L时,红壤和黄土的解吸率增加分别达到60.8%和65.5%。     

Effect of humic matter on metal adsorption onto clay materials: Testing the linear additive model

Migration of contaminants with low affinity for the aqueous phase is essentially governed by interaction with mobile carriers such as humic colloids. Their impact is, however, not sufficiently described by interaction constants alone since the humic carriers themselves are subject to a solid–liquid distribution that depends on geochemical parameters.In our study, co-adsorption of the REE terbium (as an analogue of trivalent actinides) and humic acid onto three clay materials (illite, montmorillonite, Opalinus clay) was investigated as a function of pH. ¹⁶⁰Tb(III) and ¹³¹I-labelled humic acid were employed as radiotracers, allowing experiments at very low concentrations to mimic probable conditions in the far-field of a nuclear waste repository. Humate complexation of Tb was examined by anion and cation exchange techniques, also considering competitive effects of metals leached from the clay materials.The results revealed that desorption of metals from clay barriers, occurring in consequence of acidification processes, is generally counteracted in the presence of humic matter. For all clay materials under study, adsorption of Tb was found to be enhanced in neutral and acidic systems with humic acid, which is explained by additional adsorption of humic-bound Tb.A commonly used composite approach (linear additive model) was tested for suitability in reconstructing the solid–liquid distribution of Tb in ternary systems (Tb/humic acid/clay) on the basis of data determined for binary subsystems. The model can qualitatively explain the influence of humic acid as a function of pH, but it failed to reproduce our experimental data quantitatively. It appears that the elementary processes (metal adsorption, metal–humate complexation, humic acid adsorption) cannot be considered to be independent of each other. Possible reasons are discussed.     

Sequential sorption of lead and cadmium in three tropical soils

It is important to examine mechanisms of Pb and Cd sorption in soils to understand their bioavailability. The ability of three tropical soils to retain Pb, Cd, and Ca was evaluated. The objectives of this study were to (1) determine the extent to which soil sorption sites are metal specific, (2) investigate the nature of reactions between metals and soil surfaces, and (3) identify how metals compete for sorption sites when they are introduced to soils sequentially or concurrently. Lead was shown to be much less exchangeable than Cd and inhibited Cd sorption. Cadmium had little effect on Pb sorption, though both Ca and Cd inhibited the adsorption of Pb at exchange sites. Lead appears to more readily undergo inner-sphere surface complexation with soil surface functional groups than either Cd or Ca. Thus, regardless of when Pb is introduced to a soil, it should be less labile than Cd.     

Effect of fly ash on sorption behavior of metribuzin in agricultural soils

This investigation was undertaken to determine the effect of two different fly ashes [Kota and Inderprastha (IP)] amendment on the sorption behavior of metribuzin in three Indian soil types. The IP fly ash was very effective in increasing the metribuzin sorption in the soils. The sorption with IP amendment was increased by 15–92%, whereas with the Kota fly ash an increase in sorption by 13–38% was noted. The adsorption isotherms fitted very well to the Freundlich adsorption equation and, in general, slope (1/n) values less then unity were observed. Although both the fly ashes significantly decreased metribuzin desorption, the IP fly ash was comparatively more effective in retaining metribuzin in the soils. Metribuzin sorption in the IP fly ash-amended soils showed strong correlation with the fly ash content and compared to K_f/K_d values, K_FA values (sorption normalized to fly ash content) showed less variation. Metribuzin sorption-desorption did not correlate to the organic carbon content of the soil-fly ash mixture. The study demonstrates that all coal fly ashes may not be effective in enhancing the sorption of metribuzin in soils to the same extent. However, among the fly ashes used in this study, the IP fly ash was observed to be significantly effective in enhancing the sorption of metribuzin in soils. This may play an important role in reducing the run off and leaching losses of the herbicide by retaining it in the soil.     

Selenium fractions in organic matter from Se-rich soils and weathered stone coal in selenosis areas of China

A high degree of association between Selenium (Se) and organic matter has been demonstrated in natural environments, but Se fractions and speciation in organic matter is unclear. In this study, a method for quantifying organic matter associated with Se (OM-Se) was developed to investigate Se fractions in organic matter in Se-rich soils and weathered stone coal from Enshi, China, where Se poisoning of humans and livestock has been documented. Initially, Se was extracted using water and a phosphate buffer. Subsequently, OM-Se was extracted using NaOH, and then speciated into Se associated with fulvic acids (FA-Se) and humic acids (HA-Se). Both FA-Se and HA-Se were further speciated into the weakly bound and strongly bound fractions using a customized hydride generation reactor. The results show that FA-Se (1.91-479 mg kg⁻¹) is the predominant form of Se in all Se-rich soils and the weathered stone coal samples, accounting for more than 62% of OM-Se (3.07-484 mg kg⁻¹). Weakly bound FA-Se (1.33-450 mg kg⁻¹) was prevalent in the total FA-Se, while weakly bound HA-Se (0.62-26.2 mg kg⁻¹) was variable in the total HA-Se (1.15-32.5 mg kg⁻¹). These data indicate that OM-Se could play a significant source and sink role in the biogeochemical cycling of Se in the supergene environment. Weakly bound FA-Se seems to act as a potential source for bioavailable Se, whereas strongly bound HA-Se is a possible OM-Se sink which is not readily transformed into bioavailable Se.     

Phosphorus effect on Zn adsorption-desorption kinetics in acid soils

The adsorption-desorption kinetics of Zn in the absence and presence of P was studied by using the stirred flow chamber technique. The results thus obtained were compared with those previously obtained for Cu. As with copper, the simultaneous addition of P and Zn in a 1:1 mole ratio to soil was found to significantly increased Zn adsorption relative to the absence of P. Unlike Cu, however, Zn was only adsorbed at fast adsorption sites in the absence of P. In any case, the increased adsorption of Zn in the presence of P was largely due to slow adsorption sites, where Zn²⁺ ion acted as a bridging element between P and organic matter. Following adsorption in both the presence and absence of P, Zn was desorbed to a much higher extent than was Cu. However, the proportion of Zn desorbed after adsorption in the presence of P was significantly lower than in the absence of P. This indicates that Zn binds more strongly to adsorbing surfaces in the presence of P than in its absence.     

Sorption-desorption behavior of polybrominated diphenyl ethers in soils

Polybrominated diphenyl ethers (PBDEs) are flame retardants that are commonly found in commercial and household products. These compounds are considered persistent organic pollutants. In this study, we used 4,4′-dibromodiphenyl ether (BDE-15) as a model compound to elucidate the sorption and desorption behavior of PBDEs in soils. The organic carbon-normalized sorption coefficient (K_OC) of BDE-15 was more than three times higher for humin than for bulk soils. However, pronounced desorption hysteresis was obtained mainly for bulk soils. For humin, increasing concentration of sorbed BDE-15 resulted in decreased desorption. Our data illustrate that BDE-15 and probably other PBDEs exhibit high sorption affinity to soils. Moreover, sorption is irreversible and thus PBDEs can potentially accumulate in the topsoil layer. We also suggest that although humin is probably a major sorbent for PBDEs in soils, other humic materials are also responsible for their sequestration.     

Characterization of binding site heterogeneity for copper within dissolved organic matter fractions using two-dimensional correlation fluorescence spectroscopy

The heterogeneity of copper binding characteristics for dissolved organic matter (DOM) fractions was investigated based on the fluorescence quenching of the synchronous fluorescence spectra upon the addition of copper and two-dimensional correlation spectroscopy (2D-COS). Hydrophobic acid (HoA) and hydrophilic (Hi) fractions of two different DOM (algal and leaf litter DOM) were used for this study. For both DOM, fluorescence quenching occurred at a wider range of wavelengths for the HoA fractions compared to the Hi fractions. The combined information of the synchronous and asynchronous maps derived from 2D-COS provided a clear picture of the heterogeneous distribution of the copper binding sites within each DOM fraction, which was not readily recognized by a simple comparison of the changes in the synchronous fluorescence spectra upon the addition of copper. For the algal DOM, higher stability constants were exhibited for the HoA versus the Hi fractions. The logarithms of the stability constants ranged from 4.8 to 6.1 and from 4.5 to 5.0 for the HoA and the Hi fractions of the algal DOM, respectively, depending on the associated wavelength and the fitted models. In contrast, no distinctive difference in the binding characteristics was found between the two fractions of the leaf litter DOM. This suggests that influences of the structural and chemical properties of DOM on copper binding may differ for DOM from different sources. The relative difference of the calculated stability constants within the DOM fractions were consistent with the sequential orders interpreted from the asynchronous 2D-COS. It is expected that 2D-COS will be widely applied to other DOM studies requiring detailed information on the heterogeneous nature and subsequent effects under a range of environmental conditions.     

Influence of organic amendments on copper distribution among particle-size and density fractions in Champagne vineyard soils

The intensive use for over 100 years of copper sulfate (Bordeaux mixture) to fight against mildew in vineyard soils has led to an important, widespread accumulation of Cu (100 to 1500 mg Cu kg-1 soil). In Champagne vineyards, organic amendments are used currently to increase soil fertility and to limit soil erosion. Organic amendments may have a direct effect on the retention of Cu in the soil. To assess the influence of the organic management on the fate of Cu in calcareous Champagne vineyard soils, we studied Cu distribution (1) in the soil profile and (2) among primary soil particles, in vineyard parcels with different amendments. Amendments were oak-bark, vine-shoots and urban compost. The results were compared with the amount and the distribution of Cu in an unamended calcareous soil. Physical soil fractionations were carried out to separate soil primary particles according to their size and density. Cu has a heterogeneous distribution among soil particle fractions. Two fractions were mainly responsible for Cu retention in soils: the organic debris larger than 50 microns or coarse particulate organic matter (POM) issued from the organic amendments, and the clay-sized fraction < 2 microns. The POM contained up to 2000 mg Cu kg-1 fraction and the clay fraction contained up to 500 mg Cu kg-1 fraction. The clay-sized fraction was responsible for almost 40% of the total amount of Cu in the four parcels. POM was predominantly responsible for the differences in Cu contents between the unamended and the three amended parcels. Our results attested that methods of soil particle-size fractionation can be successfully used to assess the distribution of metal elements in soils.     

Effects of lipids on the sorption of hydrophobic organic compounds on geosorbents: a case study using phenanthrene

The impact of the lipid fraction of natural geosorbents on the sorption of a polycyclic aromatic hydrocarbon was assessed using several experiments. In the first set of experiments phenanthrene was sorbed on a coastal sediment as well as on its humin and humic acid fractions before and after lipid extraction. Before lipid extraction, sorption shows dominantly partitioning characteristics. However, the extraction of lipids from sediment and humin drastically increases, by up to one order of magnitude, their sorption affinity for phenanthrene at low sorbate concentrations, resulting in increased isotherm nonlinearity. This effect is less pronounced for humic acids. One mechanism proposed for the increasing sorption is that lipids, despite their very low relative abundance in the sediments, can compete with phenanthrene for specific high affinity sorption sites (e.g., matrix pores and adsorption sites). This competition is not surprising considering the similar hydrophobic nature of lipids and phenanthrene. Lipids, or any non-polar molecules, could also act like plasticizers by swelling rigid domains and disrupting high affinity sites. In both cases, the removal of lipids (and extraction solvents) makes those sites available for phenanthrene. These provide alternative explanations to the previously proposed “solvent conditioning effect” believed to occur when geosorbents are treated with non-polar solvents modifying the matrix structure, an effect yet to be proven at molecular scale. To further investigate the impact of lipids on sorption, other independent experiments were performed. In a second experiment, re-addition of lipids to the extracted sediment restored the sorption isotherm linearity observed in the native material supporting the absence of irreversible extraction artifacts. However, high addition of lipids (i.e., after saturation of high affinity sites) seems to also enlarge the low affinity partitioning domain. These results are consistent with dual-mode, hole-filling, sorption models involving diffusion. In the final set of experiments, solid-state ¹⁹F-NMR using F-labeled lipids sorbed onto the sediments confirmed that lipids may be in different domains (mobile or rigid) that interact or not with phenanthrene. The possible effects of lipid removal on sorption have been overlooked and should be considered when geosorbents are pretreated.     

Adsorption-desorption and leaching of pyraclostrobin in Indian soils

Pyraclostrobin is a new broad-spectrum foliar applied and seed protectant fungicide of the strobilurin group. In this paper, adsorption-desorption of pyraclostrobin has been investigated in three different soils viz. Inceptisol (sandy loam, Delhi), Vertisol (sandy clay, Hyderabad) and Ultisol (sandy clay loam, Thrissur). Effect of organic matter and clay content on sorption was also studied in Inceptisol of Delhi. Leaching potential of pyraclostrobin as influenced by rainfall was studied in intact soil columns to confirm the results of adsorption-desorption studies. The adsorption studies were carried out at initial concentrations of 0.05, 0.1, 0.5, 1 and 1.5 μg mL^?1. The distribution coefficient (K_d) values in three test soils ranged from 4.91 to 18.26 indicating moderate to high adsorption. Among the three test soils, adsorption was the highest in Ultisol (K_d 18.26), followed by Vertisol (K_d 9.87) and Inceptisol (K_d 4.91). K_F value was also highest for Ultisol soil (66.21), followed by Vertisol (40.88) and Inceptisol (8.59). S-type adsorption isotherms were observed in all the three test soils. K_d values in organic carbon-removed soil and clay-removed soil were 3.57 and 2.83 respectively, indicating lower adsorption than normal Inceptisol. Desorption studies were carried out at initial concentrations of 0.5, 1 and 1.5 μg mL^?1. Desorption was the greatest in Inceptisol, followed by Vertisol and Ultisol. Amounts of pyraclostrobin desorbed in three desorption cycles for different concentrations were 23.1–25.3%, 9.4–20.7% and 8.1–13.6% in Inceptisol, Vertisol and Ultisol respectively. Desorption was higher in clay fraction-removed and organic carbonremoved soils than normal Inceptisol. Desorption was slower than adsorption in all the test soils, indicating hysteresis effect (with hysteresis coefficient values varying from 0.05 to 0.20). Low values of hysteresis coefficient suggest high hysteresis effect indicating easy and strong adsorption, and slow desorption, of pyraclostrobin in soils. Higher hysteresis coefficient values in organic carbon removed soil (0.25–0.30) and clay fraction removed soil (0.28–0.36) as compared to normal Inceptisol soil suggest relatively weak adsorption and easy desorption of pyraclostrobin. Results of regression analysis suggest that the organic matter and pH of the soil play a major role in adsorption of pyraclostrobin. Leaching studies were carried out in intact soil columns in Inceptisol. The columns were leached with different amounts of water simulating different amounts of rainfall. The results suggest that most of the pyraclostrobin residues will remain present in the top soil layers even under high rainfall conditions and chances of pyraclostrobin moving to lower soil depth are almost negligible.