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1.
Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish 总被引:1,自引:0,他引:1
Robert J. Letcher Jan Ove Bustnes Christian Sonne Mathilakath M. Vijayan 《The Science of the total environment》2010,408(15):2995-10202
Persistent organic pollutants (POPs) encompass an array of anthropogenic organic and elemental substances and their degradation and metabolic byproducts that have been found in the tissues of exposed animals, especially POPs categorized as organohalogen contaminants (OHCs). OHCs have been of concern in the circumpolar arctic for decades. For example, as a consequence of bioaccumulation and in some cases biomagnification of legacy (e.g., chlorinated PCBs, DDTs and CHLs) and emerging (e.g., brominated flame retardants (BFRs) and in particular polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) including perfluorooctane sulfonate (PFOS) and perfluorooctanic acid (PFOA) found in Arctic biota and humans. Of high concern are the potential biological effects of these contaminants in exposed Arctic wildlife and fish. As concluded in the last review in 2004 for the Arctic Monitoring and Assessment Program (AMAP) on the effects of POPs in Arctic wildlife, prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects in relation to OHC exposure, and attempts to assess known tissue/body compartment concentration data in the context of possible threshold levels of effects to evaluate the risks. This review concentrates mainly on post-2002, new OHC effects data in Arctic wildlife and fish, and is largely based on recently available effects data for populations of several top trophic level species, including seabirds (e.g., glaucous gull (Larus hyperboreus)), polar bears (Ursus maritimus), polar (Arctic) fox (Vulpes lagopus), and Arctic charr (Salvelinus alpinus), as well as semi-captive studies on sled dogs (Canis familiaris). Regardless, there remains a dearth of data on true contaminant exposure, cause-effect relationships with respect to these contaminant exposures in Arctic wildlife and fish. Indications of exposure effects are largely based on correlations between biomarker endpoints (e.g., biochemical processes related to the immune and endocrine system, pathological changes in tissues and reproduction and development) and tissue residue levels of OHCs (e.g., PCBs, DDTs, CHLs, PBDEs and in a few cases perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs)). Some exceptions include semi-field studies on comparative contaminant effects of control and exposed cohorts of captive Greenland sled dogs, and performance studies mimicking environmentally relevant PCB concentrations in Arctic charr. Recent tissue concentrations in several arctic marine mammal species and populations exceed a general threshold level of concern of 1 part-per-million (ppm), but a clear evidence of a POP/OHC-related stress in these populations remains to be confirmed. There remains minimal evidence that OHCs are having widespread effects on the health of Arctic organisms, with the possible exception of East Greenland and Svalbard polar bears and Svalbard glaucous gulls. However, the true (if any real) effects of POPs in Arctic wildlife have to be put into the context of other environmental, ecological and physiological stressors (both anthropogenic and natural) that render an overall complex picture. For instance, seasonal changes in food intake and corresponding cycles of fattening and emaciation seen in Arctic animals can modify contaminant tissue distribution and toxicokinetics (contaminant deposition, metabolism and depuration). Also, other factors, including impact of climate change (seasonal ice and temperature changes, and connection to food web changes, nutrition, etc. in exposed biota), disease, species invasion and the connection to disease resistance will impact toxicant exposure. Overall, further research and better understanding of POP/OHC impact on animal performance in Arctic biota are recommended. Regardless, it could be argued that Arctic wildlife and fish at the highest potential risk of POP/OHC exposure and mediated effects are East Greenland, Svalbard and (West and South) Hudson Bay polar bears, Alaskan and Northern Norway killer whales, several species of gulls and other seabirds from the Svalbard area, Northern Norway, East Greenland, the Kara Sea and/or the Canadian central high Arctic, East Greenland ringed seal and a few populations of Arctic charr and Greenland shark. 相似文献
2.
Preparation of sharp-melting hard palm midfraction and its use as hard butter in chocolate 总被引:1,自引:0,他引:1
Satsuki Hashimoto Toru Nezu Hiroshi Arakawa Tomonori Ito Shoji Maruzeni 《Journal of the American Oil Chemists' Society》2001,78(5):455-460
Preparation of hard palm midfractions (PMF) and its use as a cocoa butter equivalent ingredient were studied. Hard PMF is
obtained by multistep fractionation of palm oil involving dry fractionation (DF) and/or solvent fractionation (SF), usually
using hexane or acetone. From our experience, in acetone, a polar solvent, symmetrical 1,3-disaturated triacylglycerols tend
to selectively crystallize more than nonsymmetrical 1,2- or 2,3-disaturated triacylglycerols, making it suitable for obtaining
the solid midfraction. Unfortunately, triacylglycerols are very soluble in hexane, and temperatures at least 15 degrees lower
than those required for acetone must be used for equivalent crystal yields. On the other hand, DF is a less expensive and
safer process. Thus, multistep fractionation combining DF and SF using acetone was developed to achieve sufficient removal
of high-melting components, and further enrichment of 1,3-dipalmitoyl-2-oleoylglycerol and the hard PMF was obtained by triple-step
fractionation of palm olein or double-step fractionation of soft PMF. Compared to conventional hard PMF, this hard PMF had
a steeper melting curve and better snapping and sharp-melting qualities when used in chocolate. Heat resistance of the hard
PMF chocolate was similar to the conventional hard PMF chocolate, and its bloom resistance could be improved by adding polyglycerol
fatty acid esters. 相似文献
3.
4.
YANG Ming-chuan 《数字社区&智能家居》2008,(6)
随着Internet的普及,电子邮件已经逐渐取代传统邮件日益广泛地影响着我们的生活与工作,而邮局协议是保证我们通过客户端软件成功获取电子邮件的协议。本文结合目前市场功能最强大的协议分析软件Sniffer Pro对邮局协议进行直观的分析与研究。 相似文献
5.
基于Java语言的电子邮件系统的实现 总被引:8,自引:0,他引:8
在简单介绍了Java语言和JavaMail API的基础上,讨论了创建一个基于Java语言的电子邮件系统的基本方法。 相似文献
6.
肖禾 《湖南工业大学学报》2003,17(3)
销售点广告,已成为现代艺术设计教学新开设的重要专业课程之一,尚处探索之中。探讨了销售点广告的概念、作用、特点、类型、设计观念等,使我们在销售点广告的设计时思想更加明确。 相似文献
7.
针对计算机基础课中关于上网部分的实验教学中出现学生沉迷Internet网而使教学无法顺利进行的问题,提出相应的实验教学改进措施,使学生在教学规定的学时内更好地掌握上网方面的操作技能和知识。 相似文献
8.
9.
LIU Ben-yong 《电子科技学刊:英文版》2004,2(4):29-36
In recently proposed partial oblique projection (POP) learning, a function space is decomposed into two complementary subspaces, so that functions belonging to one of which can be optimally estimated. This paper shows that when the decomposition is specially performed so that the above subspace becomes the largest, a special learning called SPOP learning is obtained and correspondingly an incremental learning is implemented, result of which equals exactly to that of batch learning including novel data. The effectiveness of the method is illustrated by experimental results. 相似文献
10.
Crystallization kinetics of the three main components of cocoa butter, the triacylglycerols POP, POS, and SOS (where P, O,
and S stand for palmitic, oleic, and stearic acids, respectively) were studied by combined differential scanning calorimetry
and polarized light microscopy. The morphologies, nucleation kinetics, growth kinetics, and phases of the grains formed were
identified with this system. The experimental data, as well as two different models to simulate crystallization and to predict
behavior of the pure triacylglycerols, are presented. The first model is based on a macroscopical approach to solidification
by using time-temperature-transformation (TTT) diagrams and the additivity principle. It allows prediction of the proportion
of the different phases formed for any given thermal path imposed on the sample once the TTT diagram is known for the product.
It is illustrated for SOS at constant cooling rates and is compared with experimental results. The second model directly simulates
growth of the spherulites in the sample by using nucleation and growth rates that are determined experimentally. It provides
a view of the structure as it would be observed with a microscope and shows evolution of the heat released in the sample.
Isothermal solidification of POP at 15°C is displayed. The experiment and the model are in good agreement. 相似文献