Persistent free radicals in humin under redox conditions and their impact in transforming polycyclic aromatic hydrocarbons

• Regulation of redox conditions promotes the generation of free radicals on HM. • HM-PFRs can be fractionated into active and inactive types depending on stability. • The newly produced PFRs readily release electrons to oxygen and generate ROS. • PFR-induced ROS mediate the transformation of organic contaminants adsorbed on HM. The role of humic substance-associated persistent free radicals (PFRs) in the fate of organic contaminants under various redox conditions remains unknown. This study examined the characterization of original metal-free peat humin (HM), and HM treated with varying concentrations of H₂O₂ and L-ascorbic acid (VC) (assigned as H₂O₂-HM and VC-HM). The concentration of PFRs in HM increased with the addition of VC/H₂O₂ at concentrations less than 0.08 M. The evolution of PFRs in HM under different environmental conditions (e.g., oxic/anoxic and humidity) was investigated. Two types of PFRs were detected in HM: a relatively stable radical existed in the original sample, and the other type, which was generated by redox treatments, was relatively unstable. The spin densities of VC/H₂O₂-HM readily returned to the original value under relatively high humidity and oxic conditions. During this process, the HM-associated “unstable” free radicals released an electron to O₂, inducing the formation of reactive oxygen species (ROS, i.e., ^•OH and ^•O₂⁻). The generated ROS promoted the degradation of polycyclic aromatic hydrocarbons based on the radical quenching measurements. The transformation rates followed the order naphthalene>phenanthrene>anthracene>benzo[a]pyrene. Our results provide valuable insight into the HM-induced transformation of organic contaminants under natural conditions.     

三氯乙醛对土壤-植物系统的污染研究

本研究进行了大量室内外试验和污染实例考察。首先研究了三氯乙醛在土壤环境中的消失和转化规律。发现三氯乙醛在土壤中经微生物作用能转化为三氯乙酸,后者在土壤中有1—3个月持留期,在土壤中三氯乙醛消失后(一般在几天内消失),三氯乙酸成为主要毒害物质。其次研究了三氯乙醛在植物体内的主要代谢产物及其对植物生长的影响。采用衍生物色谱法和气相色谱—质谱联用分析证明三氯乙酸是主要代谢产物。三氯乙酸能富集在植物体内并使之产生枯萎或生长畸形等症状。找出了三氯乙醛和三氯乙酸在植株体内的转化规律,解释了二者单独作用于植物时某些症状相似的原因。此外,还获得了有关三氯乙醛对小麦等作物的致害浓度资料和毒害症状的图谱照片。本工作首次阐明了三氯乙醛对土壤—植物体系的污染规律,为鉴别污染事故和防治提供了科学依据。     

城市生活垃圾堆肥及垃圾专用肥对柑桔增产效应

城市生活垃圾堆肥及垃圾堆肥配制的专用肥对柑桔的肥效实验结果表明，垃圾堆肥作为基肥使用比常规施肥能使柑桔增产１２．４％－１４．５％，比空白对照增产７４．７％，施用垃圾专用肥的柑桔产量比常规施肥增产４．２％－５０．３％，比空白对照增产５８．４％－１２９．０％。施垃圾肥柑桔的营养成份（如维Ｃ，还原糖等）和常规施肥没有明显差异，也未发现重金属对桔子的污染。     

Identification of sources,characteristics and photochemical transformations of dissolved organic matter with EEM-PARAFAC in the Wei River of China

• The source of DOM in surface water and sediment is inconsistent. • The DOC content changes differently in surface water and sediment. • The content of DOC in the surface water is lower than that in the sediment. • The DOM in the surface water had higher photodegradation potentials than sediment. Dissolved organic matter (DOM) in rivers is a critical regulator of the cycling and toxicity of pollutants and the behavior of DOM is a key indicator for the health of the environment. We investigated the sources and characteristics of DOM in surface water and sediment samples of the Wei River, China. Dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm (UV₂₅₄) increased in the surface water and were decreased in the sediment downstream, indicating that the source of DOM in the water differed from the sediment. Parallel factor (PARAFAC) analysis of the excitation-emission matrices (EEM) revealed the presence of terrestrial humus-like, microbial humus-like and tryptophan-like proteins in the surface water, whereas the sediment contained UVA humic-like, UVC humic-like and fulvic-like in the sediment. The DOM in the surface water and sediment were mainly derived from microbial metabolic activity and the surrounding soil. Surface water DOM displayed greater photodegradation potential than sediment DOM. PARAFAC analysis indicated that the terrestrial humic-like substance in the water and the fulvic-like component in the sediment decomposed more rapidly. These data describe the characteristics of DOM in the Wei River and are crucial to understanding the fluctuations in environmental patterns.     

Accumulation,root-shoot translocation and phytotoxicity of substituted polycyclic aromatic hydrocarbons in wheat

Environmental Chemistry Letters - While pollution of the environment by polycyclic aromatic hydrocarbons has been rather well studied, the fate of substituted polycyclic aromatic hydrocarbons in...     

Light-induced variation in environmentally persistent free radicals and the generation of reactive radical species in humic substances

• Light irradiation increased the concentration of free radicals on HS. • The increased spin densities on HS readily returned back to the original value. • The “unstable” free radicals induced the formation of reactive radical species. • Reactive radicals’ concentration correlated strongly with EPFRs’ concentration. Environmentally persistent free radicals (EPFRs) in humic substances play an essential role in soil geochemical processes. Light is known to induce EPFRs formation for dissolved organic matter in aquatic environments; however, the impacts of light irradiation on the variation of EPFRs in soil humic substances remain unclear. In this study, humic acid, fulvic acid, and humin were extracted from peat soil and then in situ irradiated using simulated sunlight. Electron paramagnetic resonance spectroscopy results showed that with the increasing irradiation time, the spin densities and g-factors of humic substances rapidly increased during the initial 20 min and then gradually reached a plateau. After irradiation for 2h, the maximum spin density levels were up to 1.63 × 10¹⁷, 2.06 × 10¹⁷, and 1.77 × 10¹⁷ spins/g for the humic acid, fulvic acid, and humin, respectively. And the superoxide radicals increased to 1.05 × 10¹⁴–1.46 × 10¹⁴ spins/g while the alkyl radicals increased to 0.47 × 10¹⁴–1.76 × 10¹⁴ spins/g. The light-induced EPFRs were relatively unstable and readily returned back to their original state under dark and oxic conditions. Significant positive correlations were observed between the concentrations of EPFRs and reactive radical species (R² = 0.65–0.98, p<0.05), which suggested that the newly produced EPFRs contributed to the formation of reactive radical species. Our findings indicate that under the irradiation humic substances are likely to be more toxic and reactive in soil due to the formation of EPFRs.     

Factors controlling the formation of persistent free radicals in hydrochar during hydrothermal conversion of rice straw

Environmental Chemistry Letters - In the environment, persistent free radicals (PFR) have adverse effects on human health. PFR are generated by thermal conversion of biomass, such as hydrothermal...     

葡枝根霉(Rhizopus stolonifer)YF6脂肪酶基因的克隆及其序列分析

筛选并鉴定了1株高产脂肪酶菌株葡枝根霉YF6,并采用简并PCR等分子技术从中克隆到1个新的脂肪酶基因lipRs及其对应的全长cDNA,序列分析表明,该基因编码区全长1173bp,不含内含子序列,编码1段由26个氨基酸残基组成的信号肽和1个由365个氨基酸残基组成的成熟蛋白,该成熟蛋白计算分子量(Mr)为39268.27,等电点为pH7.66,有5个可能的N-糖基化位点,含有脂肪酶特征序列GHSLGGA,与来自米根霉(Rhizopus oryzae)的脂肪酶(AAF32408)同源性最高,一致性为83%,相似性为89%.该基因序列已提交GenBank,登录号为DQ139862.     

Effect of groundwater geochemistry on pentachlorophenol remediation by smectite-templated nanosized Pd0/Fe0

Zero-valent iron holds great promise in treating groundwater, and its reactivity and efficacy depend on many surrounding factors. In the present work, the effects of solution chemistry such as pH, humic acid (HA), and inorganic ions on pentachlorophenol (PCP) dechlorination by smectite-templated Pd(0)/Fe(0) were systematically studied. Smectite-templated Pd(0)/Fe(0) was prepared by saturating the negatively charged sites of smectite clay with Fe(III) and a small amount of Pd(II), followed by borohydride reduction to convert Fe(III) and Pd(II) into zero-valent metal clusters. Batch experiments were conducted to investigate the effects of water chemistry on PCP remediation. The PCP dechlorination rate critically depends on the reaction pH over the range 6.0~10.0; the rate constant (k (obs)) increases with decreasing the reaction pH value. Also, the PCP remediation is inhibited by HA, which can be attributed to the electron competition of HA with H(+). In addition, the reduction of PCP can be accelerated by various anions, following the order: Cl(-) > HCO (3) (-) > SO (4) (2-) ~no anion. In the case of cations, Ca(2+) and Mg(2+) (10 mM) decrease the dechlorination rate to 0.7959 and 0.7798 from 1.315 h(-1), respectively. After introducing HA into the reaction systems with cations or/and anions, the dechlorination rates are similar to that containing HA alone. This study reveals that low pH and the presence of some anions such as Cl(-) facilitate the PCP dechlorination and induce the rapid consumption of nanosized zero-valent iron simultaneously. However, the dechlorination rate is no longer correlated to the inhibitory or accelerating effects by cations and anions in the presence of 10 mg/L HA.     

重金属离子存在下黏土矿物表面蒽的光化学降解性能

探讨了蒽在Cu、Pb、Zn、Cd、Ni等重金属离子饱和的黏土矿物表面的光降解行为,研究了重金属离子种类,黏土矿物种类、p H、自由基捕获剂和氧气对黏土表面蒽降解速率的影响.研究表明,不同种类金属离子饱和的蒙脱石表面蒽的降解速率Cu2+Pb2+Zn2+Cd3+Ni2+Na+,其中Cu-蒙脱石表面蒽的光降解速率达78.8%;黏土矿物CEC值越高,可交换的铜离子含量越大,对蒽的光降解速率的促进作用越明显;Cu-蒙脱石表面蒽的光降解速率随p H值增大而逐渐减小,p H≥8.71时,蒽的降解率为0,其变化规律与Cu2+随p H值的存在形态的变化趋势相吻合.此外,蒽在Cu-蒙脱石表面的光降解速率随加入的对苯醌增多而减小,对苯醌含量达2.0 mg·g-1时蒽的降解率为0,无氧条件下蒽的降解率为0,推测该反应体系中有氧化活性自由基(O-2·)的产生,可能为光催化氧化降解起始因素之一.