Spatial and temporal variations of organochlorine pesticides (OCPs) in water and sediments from Honghu Lake, China

Honghu Lake in Jianghan Plain, central China is an important habitat for many migratory birds and an important site for freshwater fishery, and Honghu Lake region is also a main area for rice and cotton production in China. To understand the status and changes of organochlorine pesticide (OCP) contamination, and to assess the OCPs' risks for the ecosystem in Honghu Lake, thirty surface water samples, fifteen surface sediments, and a sediment core were collected in January and July, 2005. OCPs, such as DDTs, HCHs and chlordanes, were determined by GC-ECD in all samples. Concentrations of OCPs in surface water collected during the wet season (July 2005) were relatively higher than those collected during the dry season (January 2005), indicating that the increasing land runoff during the summer might bring the chemical residues from soils to Honghu Lake. The relatively low alpha-HCH/gamma-HCH ratio and the relatively high o,p'-DDT/p,p'-DDT ratio indicated the application of lindane on regional agricultural lands in late spring and summer (April-August), which increased the increasing contribution of dicofol to DDT in Honghu Lake, respectively. The levels of Sigma HCHs and Sigma DDTs in the surface sediments were relatively lower than those from the Yangtze River Delta, but comparable to those from other lakes and rivers in China. The composition of HCHs and DDTs in the surface sediments showed that there was fresh input of lindane (gamma-HCH), and DDT residues in Honghu Lake were aged and probably mainly originated from weathered agricultural soils of surrounding Jianghan Plain. Wash out of HCHs and DDTs from soil was the possible process which caused the increasing concentrations of these chemicals in recent years. (C) 2013 Elsevier B.V. All rights reserved.Honghu Lake in Jianghan Plain, central China is an important habitat for many migratory birds and an important site for freshwater fishery, and Honghu Lake region is also a main area for rice and cotton production in China. To understand the status and changes of organochlorine pesticide (OCP) contamination, and to assess the OCPs' risks for the ecosystem in Honghu Lake, thirty surface water samples, fifteen surface sediments, and a sediment core were collected in January and July, 2005. OCPs, such as DDTs, HCHs and chlordanes, were determined by GC-ECD in all samples. Concentrations of OCPs in surface water collected during the wet season (July 2005) were relatively higher than those collected during the dry season (January 2005), indicating that the increasing land runoff during the summer might bring the chemical residues from soils to Honghu Lake. The relatively low alpha-HCH/gamma-HCH ratio and the relatively high o,p'-DDT/p,p'-DDT ratio indicated the application of lindane on regional agricultural lands in late spring and summer (April-August), which increased the increasing contribution of dicofol to DDT in Honghu Lake, respectively. The levels of Sigma HCHs and Sigma DDTs in the surface sediments were relatively lower than those from the Yangtze River Delta, but comparable to those from other lakes and rivers in China. The composition of HCHs and DDTs in the surface sediments showed that there was fresh input of lindane (gamma-HCH), and DDT residues in Honghu Lake were aged and probably mainly originated from weathered agricultural soils of surrounding Jianghan Plain. Wash out of HCHs and DDTs from soil was the possible process which caused the increasing concentrations of these chemicals in recent years. (C) 2013 Elsevier B.V. All rights reserved

Extrinsic self-healing asphalt materials: A mini review

Self-healing is a biological phenomenon in which living organism responds to the suffered damage in a complex way. Inspired by the self-healing phenomenon in nature, various biomimetic healing methods rooted in intrinsic or extrinsic healing mechanisms have been explored. Research on novel self-healing asphalt materials with intelligent response is at the cutting-edge of materials science and offers a potential strategy for building long-life and low-carbon asphalt concrete infrastructure. This paper describes the progress of research on extrinsic self-healing asphalt materials and makes a clear distinction between intrinsic and extrinsic self-healing. The asphalt self-healing mechanism is interpreted by capillary flow theory, phase field theory, molecular diffusion theory and surface energy theory form various perspective. The extrinsic self-healing strategies including thermal induced healing and rejuvenator induced healing are proposed to enhance the healing level of cracked asphalt materials. A brief review of the methods including fracture-healing test and fatigue-healing test for assessing the efficacy of different extrinsic healing methods is presented. The thermal induced healing method bring high crack repair efficiency for asphalt concrete and the rejuvenator induced healing strategy not only improve the healing ratio of cracked asphalt concrete but also regenerate the ageing asphalt in situ. Important lessons for prospective research on the creation of novel self-healing asphalt materials are highlighted.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen

Comparisons between centrifuge and numerical modeling results for slope toppling failure

This paper presents series studies on the toppling mechanism by centrifuge tests and numerical simulations. Two different discrete element methods, i.e., the continuum-based discrete element method (CDEM) and the discontinuous deformation analysis (DDA), are adopted. The modeling results show that both the methods can accurately capture the failure modes of the centrifuge tests, including three distinct zones and two failure surfaces. Comparisons are made between the physical test and numerical simulation results. The critical inclination angle of the tilting table where the slope models are fixed on can be moderately predicted by the two methods, with different degrees of precision. The error between the test results and the simulated results is within 1% for the slope models without rock-bridges by both CDEM and DDA. However, it is amplified for the staggered-joint models that simulate the rock-bridges. With DDA, the average error is about 5%, and the maximum error is up to 17%. While with CDEM, the errors for the aligned-joint models are ranged from 1% to 6%, and it is from 10% to 29% for the staggered- joint models. The two numerical methods show the capability in simulating toppling failure of blocky rock mass with and without rock-bridges. The model with rock-bridges which provides a certain bending resistance is more stable than the one without any rock-bridge. In addition, the two failure surfaces were observed, which is different from the common understanding that only one failure surface appears