Evaluation of sorption-desorption processes for metalaxyl in natural and artificial soils

The main process controlling soil-pesticide interaction is the sorption-desorption as influenced by active soil surfaces. The sorption phenomena can influence translocation, volatility, persistence and bioactivity of a pesticide in soil. The present investigation was conducted on natural and artificial soils in order to enumerate the effect of soil components such as montmorillonite and ferrihydrite on the sorption behaviour of the fungicide metalaxyl and if sorption-desorption of the chiral pesticide affects the enantiomeric ratio. The sorption-desorption characteristics of metalaxyl were investigated by batch equilibration technique in a natural soil, two artificial soils, and in pure montmorillonite and ferrihydrite. After extraction, pesticide residues were analyzed by conventional and chiral chromatography using tandem mass spectrometry. A K_dSorp (2.3–6.5) suggests low level sorption of metalaxyl with an appreciable risk of run-off and leaching. Thus, metalaxyl poses a threat to surface and ground water contamination. Furthermore, desorption tests revealed a hysteretic effect (H ≤ 0.8) in natural and artificial soils. Significant amount of metalaxyl was found tightly bound to the adsorbents without desorbing readily after desorption cycle. Desorption of 22–56% of the total amount of the retained metalaxyl was determined. This study reveals that an artificial soil derived from different soil constituents can be used to assess their influence on sorption/desorption processes. The present investigation showed that both montmorillonite and ferrihydrite play a significant role in the sorption of metalaxyl. The sorption doesn't influence the enantiomeric ratio of racemic metalaxyl.     

Solid phase microextraction applied to the analysis of organophosphorus insecticides in fruits

Trace amounts of organophosphorus pesticides (OPs) were determined in various fruits by headspace solid phase microextraction (HS-SPME) and gas chromatography–nitrogen phosphorous detection (GC-NPD). Sampling from the headspace enhanced method selectivity, whereas at the same time improved fiber life time and method sensitivity. Diazinon, parathion, methyl parathion, malathion and fenithrothion were determined in various fruits: more than 150 samples of 21 types of fruits were studied. SPME-GC-NPD provided a useful and very efficient analytical tool: method linearity ranged from 1.2 to 700 ng/ml. Limits of detection (LODs) and quantitation (LOQs) ranged from 0.03 to 3 ng/ml and 0.12 to 10 ng/ml respectively, values well below the residue limits set by the EU. Less than 2% of the samples were found positive containing amounts higher than the EU limits. The effect of fruit peeling and washing was also investigated.     

Biodegradation of polycyclic aromatic hydrocarbons in the natural waters of the Yellow River: effects of high sediment content on biodegradation

The contamination of polycyclic aromatic hydrocarbons (PAHs) has become one of the major problems in the Yellow River of China. As the Yellow River is the most turbid large river in the world, it remains unknown to which extent the high suspended sediment content in the river may affect the fate and effect of PAHs. Here we report the effect of sediment on biodegradation of chrysene, benzo(a)pyrene and benzo(g,h,i)perylene with phenanthrene as a co-metabolism substrate in natural waters from the Yellow River. Biodegradation kinetics of the PAHs in the river water with various levels of sediment contents were studied in the laboratory by fitting with a biodegradation kinetics model for organic compounds not supporting growth. The results indicated that the biodegradation rates of PAHs increased with the sediment content in the water. When the sediment contents were 0, 4 and 10 g/l, the biodegradation rate constants of chrysene with the initial concentration of 3.80 microg/l were 0.053, 0.084 and 0.111 d(-1), respectively. Further studies suggested the enhanced biodegradation rate in the presence of sediment was caused by the following mechanisms: (1) the population of PAH-degrading bacteria in the water system was found to increase with the sediment content; the bacteria population on sediment phase was far greater than that on water phase during the cultivation process; (2) the sorption of PAHs on the sediment phase was well described by the dual adsorption-partition model. Although the sorption capacity of PAH per unit weight of sediment decreased with the increase of the sediment content, the amount of sorbed PAH increased with the sediment content; and, (3) the desorption of PAHs from the solid phase led to a higher concentration near the water-sediment interface. Since the bacteria were also attached to the interface, this resulted in an increased contact chance between the bacteria and PAHs.     

Simulation of solute transport across low-permeability barrier walls

Low-permeability, non-reactive barrier walls are often used to contain contaminants in an aquifer. Rates of solute transport through such barriers are typically many orders of magnitude slower than rates through the aquifer. Nevertheless, the success of remedial actions may be sensitive to these low rates of transport. Two numerical simulation methods for representing low-permeability barriers in a finite-difference groundwater-flow and transport model were tested. In the first method, the hydraulic properties of the barrier were represented directly on grid cells and in the second method, the intercell hydraulic-conductance values were adjusted to approximate the reduction in horizontal flow, allowing use of a coarser and computationally efficient grid. The alternative methods were tested and evaluated on the basis of hypothetical test problems and a field case involving tetrachloroethylene (PCE) contamination at a Superfund site in New Hampshire. For all cases, advective transport across the barrier was negligible, but preexisting numerical approaches to calculate dispersion yielded dispersive fluxes that were greater than expected. A transport model (MODFLOW-GWT) was modified to (1) allow different dispersive and diffusive properties to be assigned to the barrier than the adjacent aquifer and (2) more accurately calculate dispersion from concentration gradients and solute fluxes near barriers. The new approach yields reasonable and accurate concentrations for the test cases.     

Use of dolomite phosphate rock (DPR) fertilizers to reduce phosphorus leaching from sandy soil

There is increasing concern over P leaching from sandy soils applied with water-soluble P fertilizers. Laboratory column leaching experiments were conducted to evaluate P leaching from a typical acidic sandy soil in Florida amended with DPR fertilizers developed from dolomite phosphate rock (DPR) and N-Viro soil. Ten leaching events were carried out at an interval of 7 days, with a total leaching volume of 1,183 mm equivalent to the mean annual rainfall of this region during the period of 2001-2003. Leachates were collected and analyzed for total P and inorganic P. Phosphorus in the leachate was dominantly reactive, accounting for 67.7-99.9% of total P leached. Phosphorus leaching loss mainly occurred in the first three leaching events, accounting for 62.0-98.8% of the total P leached over the whole period. The percentage of P leached (in the total P added) from the soil amended with water-soluble P fertilizer was higher than those receiving the DPR fertilizers. The former was up to 96.6%, whereas the latter ranged from 0.3% to 3.8%. These results indicate that the use of N-Viro-based DPR fertilizers can reduce P leaching from sandy soils.     

Lead and zinc accumulation and tolerance in populations of six wetland plants

Wetland plants such as Typha latifolia and Phragmites australis have been indicated to show a lack of evolution of metal tolerance in metal-contaminated populations. The aim of the present study is to verify whether other common wetland plants such as Alternanthera philoxeroides and Beckmannia syzigachne, also possess the same characteristics. Lead and zinc tolerances in populations of six species collected from contaminated and clean sites were examined by hydroponics. In general, the contaminated populations did not show higher metal tolerance and accumulation than the controls. Similar growth responses and tolerance indices in the same metal treatment solution between contaminated and control populations suggest that metal tolerance in wetland plants are generally not further evolved by contaminated environment. The reasons may be related to the special root anatomy in wetland plants, the alleviated metal toxicity by the reduced rooting conditions and the relatively high innate metal tolerance in some species.     

县域土地利用细碎度综合度量与空间分异研究——以江苏省东海县为例

土地细碎化是与土地规模经营理念相背离的一种土地形态,细碎化的土地经营模式会造成土地利用效率下降、粮食减产以及景观美观度降低等一系列问题。目前,土地细碎化程度的衡量多通过细碎度表征,但尚无统一标准,且主要针对农用地。以江苏东海县为例,首先结合景观指数与主成分分析,分别计算耕地、基础设施用地、居民点用地以及生态用地的细碎度,再通过系统聚类,分析不同地类细碎度组合的地域分异特征。结果显示：不同用地类型的细碎度是自然、社会经济的综合影响结果,耕地细碎度与居民点细碎度有着较显著的正相关关系,与生态用地细碎度有着较显著的负相关关系,基础设施用地细碎度和居民点细碎度存在一定的正相关关系,与生态用地细碎度存在一定的负相关关系,土地细碎度基于不同自然、社会经济条件,其分区也有着特定的区位特征。探讨不同用地类型细碎度间的关联性及空间分异特征可以为土地利用、经济发展以及景观改善等提供科学的引导     

Indoor particle dynamics in a school office: determination of particle concentrations,deposition rates and penetration factors under naturally ventilated conditions

Recently, the problem of indoor particulate matter pollution has received much attention. An increasing number of epidemiological studies show that the concentration of atmospheric particulate matter has a significant effect on human health, even at very low concentrations. Most of these investigations have relied upon outdoor particle concentrations as surrogates of human exposures. However, considering that the concentration distribution of the indoor particulate matter is largely dependent on the extent to which these particles penetrate the building and on the degree of suspension in the indoor air, human exposures to particles of outdoor origin may not be equal to outdoor particle concentration levels. Therefore, it is critical to understand the relationship between the particle concentrations found outdoors and those found in indoor micro-environments. In this study, experiments were conducted using a naturally ventilated office located in Qingdao, China. The indoor and outdoor particle concentrations were measured at the same time using an optical counter with four size ranges. The particle size distribution ranged from 0.3 to 2.5 μm, and the experimental period was from April to September, 2016. Based on the experimental data, the dynamic and mass balance model based on time was used to estimate the penetration rate and deposition rate at air exchange rates of 0.03–0.25 h^?1. The values of the penetration rate and deposition velocity of indoor particles were determined to range from 0.45 to 0.82 h^?1 and 1.71 to 2.82 m/h, respectively. In addition, the particulate pollution exposure in the indoor environment was analyzed to estimate the exposure hazard from indoor particulate matter pollution, which is important for human exposure to particles and associated health effects. The conclusions from this study can serve to provide a better understanding the dynamics and behaviors of airborne particle entering into buildings. And they will also highlight effective methods to reduce exposure to particles in office buildings.     

Research progress on CRISPR/Cas9-mediated genome editing technique in plants北大核心CSCD

Many physical, chemical, and biotic stresses always threaten plants during their growth and development. Using the genome editing technique is a good strategy to improve plant characteristics. CRISPR/Cas (clustered regulatory interspaced short palindromic repeats / CRISPR-associated protein), the adaptive and heritable immune system of prokaryotes, is a genome editing technique newly developed during recent years. At present, the type II CRISPR / Cas9 system is most widely used. Many plants, such as Arabidopsis thaliana, tobacco, soybean, tomato, potato, rice, wheat, maize, sorghum, petunia, banana, sweet orange, apple, poplar, and Marchantia polymorpha, have been edited successfully for stress tolerance, delay of fruit ripening, herbicide resistance, and disease resistance, etc. This system is achieved by the formation of nuclease Cas9 and crRNA: tracrRNA (CRISPR-derived RNA:trans-activating RNA) complex. Further studies about the effect of the promoters of Cas9 and gRNA and the number of gRNA targets on gene editing efficiency have been discussed. © 2018 Science Press. All rights reserved.     

Seasonal dynamics of labile soil nitrogen from four plantations at the western edge of the Sichuan Basin北大核心CSCD

The objective of this study was to investigate the soil nitrogen components of four native artificial plantations at the western edge of the Sichuan Basin. Soil samples from two layers (0-20 cm and 20-40 cm) were collected from 4 plantations (Cryptomeria fortunei, Michelia wilsonii, Phoebe zhennan, and Quercus acutissima) during March, June, September, and December 2015 at the western edge of Sichuan Basin, to perform a comparative analysis on seasonal dynamics. Soil ammonium, nitrate, microbial biomass nitrogen, and environmental factors were synchronously monitored. The results showed that soil inorganic nitrogen was mainly the result of nitrate. The components of labile soil nitrogen showed significant seasonal dynamics. Soil ammonium during the growing season (June and September) was higher than that during the non-growing season (March and December), but soil nitrate, microbial biomass nitrogen, and inorganic nitrogen showed the opposite pattern. Labile nitrogen components in the 0-20 cm layer were generally higher than those in the 20-40 cm layer. Labile soil nitrogen was significantly affected by forest type, which was dependent on season and soil layer. In general, there were significant correlations between the soil nitrogen pools and labile soil nitrogen and the environmental factors, including soil temperature, water content, and monthly rainfall. In conclusion, the variation of labile soil nitrogen was influenced more by season than forest type or soil layer. Compared to the biological effects of tree species, the environmental factors had a stronger effect on labile soil nitrogen. © 2018 Science Press. All rights reserved.