Formulation of a soil-pesticide transport model based on a compartmental approach

A semianalytical soil-pesticide transport model is formulated based on a compartmental approach to determine spatial and temporal variations of pesticide residues across a soil profile. The compartmental model is implemented by drawing an analogy between a series of continuous-flow stirred tank reactors and a soil horizon that consists of multiple perfectly mixed compartments. The analogy is strengthened by exploiting a relation between the compartment series and the conventional convective-dispersive equation (CDE) for vertical transport in the soil. Consequently, the number of compartments in the model formulation is not free, but dictated as a function of transport parameters. The model formulation allows consideration of arbitrary boundary value specifications and also, for some cases, spatially varying initial concentration profiles. Sorption kinetics is represented via a two-site model that involves a linear sorption isotherm and a first-order irreversible sorption or a radial diffusive penetrating model. For these three cases, analysis of the compartmental model allows the resultant concentration profiles to be expressed in terms of the Poisson distribution. When a nonlinear kinetic sorption model is used to simulate the sorption processes, an analytical solution is not found and a numerical approach is required.     

Detection of free microcystins in the liver and muscle of freshwater fish by liquid chromatography-tandem mass spectrometry

MC analysis of biological tissue is considered to be very difficult due to the lack of validated methods. This is the primary limiting factor for monitoring potential risks in both the flesh of aquatic organisms and the aquatic ecosystem. In this study, an effective method to determine free MCs (MC-LR and MC-RR) in the muscle and liver tissues of freshwater cultured fish was developed using solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC/MS-MS). The extraction solvent, time of extraction, eluent and purification of the extract were optimized. Various SPE cartridges were also investigated. In this optimized analytical procedure, an 85% methanol/water solution (v/v) was selected as the extraction solvent, after which the extracts were purified by removing fats and proteins; a HLB cartridge was chosen for MCs enrichment; and 90% methanol containing 0.02% formic acid/water solution (v/v) was used as the eluent. Under the optimized pretreatment conditions and instrument parameters, good recoveries of MC-LR and MC-RR were obtained at three concentrations (0.5, 1.0 and 2.0 µg g^?1 dry weight (DW)), with values ranging from 92.5 to 98.3% and 92.1 to 98.6%, respectively. The method detection limit (MDL) for muscle samples was 0.5 µg kg^?1 and 0.4 µg kg^?1 (DW) for MC-LR and MC-RR, respectively. The MDL for the liver samples was 0.8 µg kg^?1 (DW) for both MC-LR and MC-RR. The developed procedure was successfully applied to analyze MCs in the muscle and liver of fish samples collected from a Chinese freshwater aquaculture pond during bloom seasons. The MC-LR concentrations ranged from below the MDL to 4.17 µg kg^?1 and the MC-RR concentrations ranged from below the MDL to 2.64 µg kg^?1.     

大气微生物粒子与飘尘粒子的关系

用ＡＮＤＥＲＳＥＮ生物粒子采样器和光散射气溶胶粒子计数器，在北京西单对大气细菌、真菌和飘尘粒子的浓度、粒度分布及它们之间的关系进行了观测和研究。结果表明，大气细菌的粒度是负偏态分布，大气真菌是对数正态分布，飘尘是正偏态分布。大气细菌浓度与飘尘浓度的比值冬季大，为１１９５３８；夏季小，为２４２１７；年平均比值为６７５１７，＞２．０μｍ的菌尘比值为１５２５３８７，２．０μｍ～８．２μｍ的菌尘比值为３３１８，＞８．２μｍ的菌尘比值为３９４。大气真菌浓度与飘尘浓度的比值冬季大，为２１２７７０；夏季小，为６５５８５；年平均比值为１３５３４４，＜２．０μｍ的菌尘比值为９５２６９８，２．０μｍ～８．２μｍ的菌尘比值为５３４３，＞８．２μｍ的菌尘比值为２６３２。     

桑植红色旅游资源与民族文化整合研究

桑植县是一个民族文化旅游资源独特、红色旅游资源突出和自然景观优美的县域．通过分析桑植县的旅游资源现状，从而构建了桑植县红色旅游资源与民族文化整合的模式，并提出了相应的市场整合策略．参7．     

Responses of reproduction and important value of dominant plant species in different plant functional type in Kobresia meadow to temperature increase

Responses of reproduction and IV (important value) of dominant plant species in different PFT to warming were studied at a Kobresia meadow in the Tibetan Autonomous State of Qinghai Province, China (37°29′–37°45′ N, 101°12′–101°33′ E, 3900 m asl) using the temperature gradient method formalized by the ITEX. Responses of Elymus nutans and Poa pratensis (Gramineous PFT) to increasing temperature were similar. The numbers of tillers, buds and IV increased in the chambers treated with higher temperature compared to the control without treatments (CK). Responses of Kobresia humilis and Carex alrofusca (Cyperaceae PFT) to increasing temperature were different, that is, the numbers of tillers and IV reached the maximum in different temperature among species, the numbers of buds decreased with the temperature increasing. The number of buds and IV of Lagotis brachystachya (Forbs PFT) decreased with the warming, but the number of stolons was initially large, and then decreased with increasing temperature. The number of buds of Ranunculus brotherusii (Forbs PFT) increased with the temperature increasing in the first year, but decreased in the second year; and IV decreased with the temperature warming. Under conditions of continued warming in the future, PFT structure will be significantly changed, Cyperaceae PFT dominant plant species original position will be replaced by Gramineae PFT dominant plant species. Cyperaceae plants will become the dominant species, and some species belonging to Forbs PFT will be eliminated from the community.     

Performance investigation of electrochemical assisted HClO/Fe2+ process for the treatment of landfill leachate

Environmental Science and Pollution Research - The feasibility of removal of chemical oxygen demand (COD) and ammonia nitrogen (NH4+–N) from landfill leachate by an electrochemical assisted...     

Prenatal exposure to air pollution and the risk of eczema in childhood: a systematic review and meta-analysis

Environmental Science and Pollution Research - An increasing number of studies investigated the association between air pollution during pregnancy and the risk of eczema in offspring. However, no...     

Effect of applying persulfate on the accumulation of arsenic in rice plants grown in arsenic-contaminated paddy soil

Environmental Science and Pollution Research - Arsenic is known to be a notorious human carcinogen and rice consumption is becoming the primary human exposure route for As, especially in many Asian...     

鞋类保暖性能研究

本文采用鞋类保暖性能的测试方法,测定不同帮面材料、不同鞋底材料对鞋类保暖性能的影响,对于不同的测试对象探索相同环境下的测试结果,从而为企业生产提供一定的科学指导。