PAHs pass through the cell wall and partition into organelles of arbuscular mycorrhizal roots of ryegrass

The subcellular process and distribution of polycyclic aromatic hydrocarbons (PAHs) in arbuscular mycorrhizal plants remains to be elucidated. This work used a greenhouse experiment to show that, accompanied by the apoplastic and symplastic water movement through the root, acenaphthene (ACE) as a representative PAH passed through the cell-wall boundary, dissolved in the cell solution, and partition organelles in arbuscular mycorrhizal roots of ryegrass (Lolium multiflorum Lam.). The observed concentrations of ACE in organelles were 0.6 to 4.4 times higher than in the cell walls. The cell wall and organelles were the dominant storage domains for ACE in the root, and the distribution of ACE in cells of mycorrhizal ryegrass roots was, in descending order, cell organelles (40.8-70.8%) > cell wall (19.7-3.8%) cell solution (9.6-20.5%).     

Chloropicrin emissions after shank injection: two-dimensional analytical and numerical model simulations of different source methods and field measurements

Understanding the control mechanisms of fumigant movement in soil is a fundamental step for developing management strategies to reduce atmospheric emissions. Most soil fumigants including chloropicrin (CP) are applied by shank injection, and the application process often leaves vertical soil fractures that would potentially cause preferential fumigant movement and increased emissions. This potential transport pathway was evaluated by comparing cumulative emissions and soil air concentrations of CP from direct field measurements with those predicted using analytical and numerical models after assuming either point or rectangle sources for the injected CP. Results clearly showed that shank-injected CP, when treated as vertical rectangle sources, produced cumulative emission losses similar to the field measurements. Treating the shanked CP as point sources caused approximately 50% underprediction than the field measurements. The study also demonstrated that fumigant cumulative emissions can be predicted, with reasonable accuracy, using either analytical or numerical simulations.     

Metal contamination in sediments of the western Bohai Bay and adjacent estuaries, China

Twelve sediment cores were collected in July 2007 in open waters of western Bohai Bay, the Port of Tianjin, and the adjacent estuaries of the Haihe and Yongding Rivers. While overall concentrations of trace metals at incremental depths in these cores met the Marine Sediment Quality (GB18668-2002) criteria of China, the magnitude of both metal enrichment factors (EF) and geoaccumulation indices (I(geo)) suggested that pollution with Ag, Cd, Cr, Cu and Zn was occurring in the estuaries and Port. Risk analysis also suggested that Ag and Ni concentrations were sufficiently elevated as to cause adverse biological effects in the study area. Although metal concentrations in western Bohai Bay were of less concern, a positive relationship between EF values and excess (210)Pb activity for several metals suggested that their concentrations were increasing over time.     

测定地表水中溶解氧的微型化学实验研究

利用微型滴定法测定地表水中溶解氧的含量,并对微型实验和常量实验的平行测定结果进行了比较。微型滴定的测定结果准确可靠,微型实验具有现象明显、节省试剂、分析速度快等特点,能降低实验成本,提高学生的创新能力,完全符合绿色化学的理念,值得推广。     

论促进企业环境守法的制度建构

企业是市场经济中重要的市场主体,其环境守法除了要求环境法律、法规、政策的完善,也有赖于环境执法工作的稳妥开展对企业守法的推动。通过制度和利润两方面分析企业环境守法困境,期望通过环境执法模式的改革,借鉴美国环境执法模式的经验,借助执法理念的变化实现企业自觉的环境守法。     

Rapid degradation of carbon tetrachloride by commercial micro-scale zinc powder assisted by citric acid

We developed an effective method for degradation of carbon tetrachloride (CT) in contaminated water. Zinc metal as a reducing agent for CT in aqueous solutions has been previously studied in some detail, but the rapid corrosion of zinc surface usually reduces its efficiency in removing CT. We assumed that citric acid could enhance the degradation of CT by zinc powder due to the elimination of a passivation layer of Zn(II) (hydr)oxides on the surface of zinc powder through chelating of organic ligands with Zn(II) produced from the reaction and keeping the exposure of active sites to targets. Here the influence of citric acid on the decomposing of CT by commercial micro-scale zinc powder was investigated in a pH range of 3.5–7.5 at 25°C in batch experiments. Reaction mixtures were analysed by gas chromatography/headspace analysis, and Cl⁻ concentration was determined by turbidimetry. The results demonstrate that the degradation of CT by zinc metal alone is very weak, but the addition of citric acid can assist zinc powder to decompose CT more completely and rapidly at all pHs. Degradation of CT took place mainly in the first 10 min of reaction, coupled with 75–95% of CT removal. Maximum dechlorination percentage (82.4%) of CT was obtained at pH 5.5. In that case, chloroform and dichloromethane, as main intermediates, were found at low levels during the whole reaction, suggesting that CT may be sequentially and multiply degraded so quickly that methane is yielded before the intermediates can be desorbed and released to aqueous solution. When compared with the current methods of nano-scale zinc and bimetallic systems, the application of commercial micro-scale zinc particles assisted by organic ligands is of environmental significance since it allows decontamination of aqueous chlorinated organic compounds at low cost and with high efficiency.     

天津水产业磺胺类耐药细菌及其分布

水产养殖中抗生素的滥用可能会诱导水产品和周围环境中的耐药菌.针对天津市北辰区、西青区、东丽区和津南区的6个水产养殖场的底泥和水样,采用抗性平板筛选耐药细菌,通过对磺胺甲恶唑的耐药率分析,发现底泥中的耐药率要大大高于水中的耐药率,并且与国外的某些研究相比,底泥的细菌耐药率呈现较高的趋势.另外,利用16S-rDNA鉴定出8...     

Temporal-spatial variability and fractal characteristics of soil nitrogen and phosphorus in Xinji District, Hebei Province, China

Traditional statistics, geostatistics, fractal dimensions, and geographic information systems (GIS) were employed to study the temporal?Cspatial variability of soil total nitrogen (TN) and total phosphorus (TP) levels in Xinji District, Hebei Province area of the North China Plain from 1980 to 2007. The results indicate that nutrient levels follow normal or lognormal distributions. The TN content was 0.59 ±0.155 g kg^???1 in 2007, an increase of 0.44 g kg^???1 compared with that of 1980. In 2007, the TP content was 1.21 ±0.227 g kg^???1, an increase of 0.01 g kg^???1 from 1980. The geostatistical analysis showed that the distribution of these soil nutrients in the study area exhibits a trend and anisotropy. The range and [C ₀/(C ₀?+?C)] of TN and TP in 1980 were all less than in 2007. The ordinary kriging interpolation method was used to analyze the nutrient contents differences between 1980 and 2007. The results indicate that soil TN levels have increased over the 27-year period, and the area where the TN level had increased by at least 0.4 g kg^???1 was about 61.7% of the district. The area where the TP content increased covered about 58.4% of the district. The variance analysis indicated that land-use type had a clear influence on the distribution and change in TN and TP content. Using the 3-D box-counting dimension method combined with GIS, the fractal dimension of soil nutrient spatial distribution over the two periods showed that in 27 years, the fractal dimension of TN increased from 1.95 to 2.02, and the fractal dimension of TP increased from 1.89 to 2.01, indicating that the complexity of the spatial distribution of all nutrient contents had increased. This study can provide a basis for accurate fertilizing and to enhance the conversion of soil characteristics under different spatial scales.     

Assessment of heavy metals in sediments from a typical catchment of the Yangtze River, China

An intensive investigation was conducted to study the accumulation, speciation, and distribution of various heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in sediments from the Yangtze River catchment of Wuhan, China. The potential ecological risks posed by these heavy metals also were estimated. The median concentrations of most heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) were higher than the background values of soils in Wuhan and were beyond the threshold effect level (TEL), implying heavy metal contamination of the sediments. Carbonate-bound Cd and exchangeable Cd, both of which had high bioavailability, were 40.2% and 30.5% of the total for Cd, respectively, demonstrating that Cd poses a high ecological risk in the sediments. The coefficients of the relationship among Pb, Hg, and Cu were greater than 0.797 using correlation analysis, indicating the highly positive correlation among these three elements. Besides, total organic carbon content played an important role in determining the behaviors of heavy metals in sediments. Principal component analysis was used to study the distribution and potential origin of heavy metals. The result suggested three principal components controlling their variability in sediments, which accounted for 36.72% (factor 1: Hg, Cu, and Pb), 28.69% (factor 2: Cr, Zn, and Ni), and 19.45% (factor 3: As and Cd) of the total variance. Overall, 75% of the studied sediment samples afforded relatively low potential ecological risk despite the fact that generally higher concentrations of heavy metals relative to TEL were detected in the sediments.