Sorption of Pesticides on Kaolinite and Montmorillonite as a Function of Hydrophilicity

Pesticides and other organic species are adsorbed by soil via different mechanisms, with bond strengths that depend on the properties of both the soil and the pesticide. Since the clay fraction in soil is a preferential sorbent for organic matter, reference kaolinite and montmorillonite are useful models for studying the mechanism and the strength of sorption. This paper presents the results of batch experiments to investigate the interactions of kaolinite KGa-1 and montmorillonite SWy-1 with the following pesticides and organic species resulting from the natural degradation of pesticides in the environment: atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine), simazine (1-chloro-3,5-bisethylamino-2,4,6-triazine), diuron [1,1-dimethyl-3-(3,4-dichlorophenyl)urea], aniline, 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol. Each of these chemicals has different hydrophilicity. Systems containing 2.0 g of clay were put in contact with 100.0 mL of solutions of the pesticides at known concentration ranging from 1.0 to 5.0 mg/L, and the amount of solute adsorbed was evaluated through RP-HPLC analysis of the pesticide still present in the aqueous suspension. To test for electrostatic interactions between the clay surface and the pesticides, potentiometric titration was used to determine the permanent surface charge of clays. Experiments were performed at different pH values. The results indicate that, for the chemicals studied, neutral molecules are preferentially retained relative to ionized ones, and that montmorillonite is a more effective sorbent than kaolinite.     

Photocatalytic degradation of chlorophenols using Ru(bpy) 3 2+ /S2O 8 2−

Advanced oxidation processes, such as photocatalysed oxidation, provide an important route for degradation of wastes. In this study, the lowest excited state (³MLCT) of Ru(bpy)₃²⁺ is used to break down chlorophenol pollutant molecules to harmless products. This has the advantage of using visible light and a short-lived catalytically active species. Photolysis of deaerated aqueous solutions of a variety of mono- and poly-substituted chlorophenols has been followed in the presence of Ru(bpy)₃²⁺/S₂O₈²⁻ with near visible light (λ > 350 nm) by UV/visible absorption spectroscopy, luminescence, potentiometry, NMR and HPLC techniques. Upon irradiation, a decrease is observed in the chlorophenol concentration, accompanied by the formation of Cl⁻, H⁺ and SO₄²⁻ ions as the main inorganic products. Benzoquinone, phenol, dihydroxybenzenes and chlorinated compounds were the dominant organic products. As the ruthenium(II) complex is regenerated in the reaction, the scheme corresponds to an overall catalytic process. The kinetics of the rapid chlorophenol photodechlorination has been studied, and are described quite well by pseudo-first order behaviour. Further studies on this were made by following Cl⁻ release with respect to the initial Ru(bpy)₃²⁺ and S₂O₈²⁻ concentrations. A comparison is presented of the photodechlorination reactivity of the mono and polychlorophenols studied at acidic and alkaline pH.     

固相微萃取-气相色谱法测定饮用水及其水源水中的氯酚

利用固相微萃取(SPME)-气相色谱法(GC)联用技术测定饮用水及其水源水中的氯酚．优化萃取温度、萃取平衡时间、酸度、离子强度等实验条件．所建方法简便、精确，自来水和太湖水中均检测到氯酚。     

新型树脂对氯酚类物质的吸附研究

合成了乙酰氯修饰树脂NDA-O,与Purolite公司的MN-200相比,合成的树脂比表面积较小,但酸性官能团较多.用两种树脂吸附2-氯酚、4-氯酚和2,4-二氯酚发现,吸附结果可以用Langmuir和Freundlich等温吸附方程很好地模拟,合成的NDA-O对3种氯酚类物质的吸附能力优于MN-200.两种树脂对氯酚类物质的吸附量随着温度的升高而减少,表明吸附是放热过程,同时对氯酚类物质的吸附焓变随着吸附量的增大而减小.对同一种树脂来说,吸附量随着氯代程度的增加而增加,取代氯数相同的时候,吸附量与吸附质的K..成正相关.进一步研究了pH对吸附的影响,在pH大于9时,3种氯酚类物质的吸附量均急剧减少.     

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.     

Enhancement of chlorophenol sorption on soil by geophagous earthworms (Metaphire guillelmi)

Earthworms are the dominant soil biomass of many terrestrial ecosystems and markedly influence the physico-chemical and biological properties of soil; however, little is known about the effects of earthworm activities on the environmental behavior of micropollutants in soil. We studied the sorption and desorption of 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol on geophagous earthworm (anecic Metaphire guillelmi) casts of various aging times and on the parent soil. The casts were characteristic of lower pH and higher content of fine particles (silt and clay) than the parent soil. The sorption of the chlorophenols on the soil and casts were well fitted to linear isotherms, with sorption capacity in the order of pentachlorophenol > 2,4-dichlorophenol > 2,4,6-trichlorophenol. The sorption on the cast with different aging time was quite similar and was higher than on the parent soil. The sorption on the soil did not change between pH 7.07 of the soil and pH 6.76 of the casts. The desorption hysteresis of the chlorophenols on the soil and casts was compound specific and 2,4,6-trichlorophenol showed the highest hysteresis. The higher sorption capacity of the casts was not owing to the lowered pH of the casts, but mainly to the higher fine particles in the casts and the possible changes of nature of the soil organic matter through the earthworm gut passage. Our results indicate that geophagous earthworms may change sorption behavior and thus the bioavailability and transport of chlorophenols in soil. Earthworm effects should be considered when evaluating the environmental behavior and risk of organic pollutants in the ecosystems where earthworms are abundant.     

Chlorophenols and other related derivatives of environmental concern: properties, distribution and microbial degradation processes

Chlorophenols are chlorinated aromatic compound structures and are commonly found in pesticide preparations as well as industrial wastes. They are recalcitrant to biodegradation and consequently persistent in the environment. A variety of chlorophenols derivatives compounds are highly toxic, mutagenic and carcinogenic for living organisms. Biological transformation by microorganisms is one of the key remediation options that can be exploited to solve environmental pollution problems caused by these notorious compounds. The key enzymes in the microbial degradation of chlorophenols are the oxygenases and dioxygenases. These enzymes can be engineered for enhanced degradation of highly chlorinated aromatic compounds through directed evolution methods. This review underscores the mechanisms of chlorophenols biodegradation with the view to understanding how bioremediation processes can be optimized for cleaning up chloroaromatic contaminated environments.     

光化学法降解水中氯代苯酚的研究进展

氯代苯酚（一氯、二氯、三氯、四氯和五氯苯酚）是一类重要的有机污染物。文章综合评述了它们在水中光化学降解的国内外研究进展，并比较各种高级氧化技术（ＵＶ、ＵＶ／Ｈ２Ｏ２、ＵＶ／Ｏ３、ＵＶ／Ｈ２Ｏ２／Ｆｅ（Ⅱ／Ⅲ）、ＵＶ／ＴｉＯ２）降解这些有机物的效率与影响因素，分析了它们的降解产物和分布及其反应机理。     

衍生化吹扫捕集-气相色谱-质谱法测定饮用水中的6种氯酚

建立了饮用水中6种氯酚的检测方法。调节水样pH后,经乙酸酐衍生化、吹扫捕集后经气相色谱-质谱测定,外标法定量。在0.004～0.120mg/L范围内,方法的线性关系良好,相关系数为0.9972～0.9999,加标回收率为94.2%～112%,相对标准偏差为1.88%～5.27%。该方法简便、灵敏度高,完全可以满足饮用水中6种氯酚的痕量检测要求。     

Evaluation of UV/TiO(2) and UV/ZnO photocatalytic systems coupled to a biological process for the treatment of bleaching pulp mill effluent

This paper presents an exploratory study of pulp mill bleaching effluent treatment by a biological-photocatalytic coupled system. A fungus, Trametes pubescens, immobilized on polyurethane foam was used to inoculate the biological pre-treatment system. The pretreated effluent was then exposed to a photocatalytic treatment in which two catalysts (TiO₂ and ZnO) and two supports (aluminum foil and Luffa cylindrica) were tested. Catalyst characterization was carried out by means of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Information about crystalline structure, chemical composition, morphology, homogeneity and distribution on the support surface area was obtained. The overall biological-photocatalytic coupled system achieved degradation of 96% of initial total organic carbon (TOC), 97% of 2-chlorophenol (2-CP), 90% of 2,4-dichlorophenol (2,4-CP) and 99% of 2,4,6-trichlorophenol (2,4,6-TCP). This approach of synergistic coupling of T. pubescens and a semiconductor photocatalyst appears to be a viable alternative for the treatment of these non-biodegradable effluents.