Dioxins and dioxin-like compounds (DLCs), including polychlorinated dibenzo-dioxins, polychlorinated dibenzofurans, and polychlorinated biphenyls, are structurally and toxicologically related halogenated dicyclic aromatic hydrocarbons. Dioxins and DLCs are released into the environment from several industrial sources such as chemical manufacturing, combustion, and metal processing; from individual activities including the burning of household waste; and from natural processes such as forest fires. Dioxins and DLCs are widely distributed throughout the environment and typically occur as chemical mixtures. They do not readily degrade; therefore, levels persist in the environment, build up in the food chain, and accumulate in the tissues of animals. Human exposure to these compounds occurs primarily through the ingestion of contaminated foods (Lorber et al., 2009), although exposures to other environmental media and by other routes and pathways do occur. The health effects from exposures to dioxins and DLCs have been documented extensively in epidemiologic and toxicological studies. 2,3,7,8-Tetrachlor odibenzo-p-dioxin (TCDD) is one of the most toxic members of this class of compounds and has a robust toxicological database. Characterization of TCDD toxicity is critical to the risk assessment of mixtures of dioxins and DLCs because it has been selected repeatedly as the 'index chemical' for the dioxin toxicity equivalence factors (TEF) approach.

关键词：电子信息；信息系统；EPA；综合风险信息系统；IRIS；分析

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关键词：化肥；进口关税；配额总量

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The purpose of this toxicological review is to provide scientific support and rationale for the hazard and dose-response assessment in IRIS pertaining to chronic exposure to tetrahydrofuran. It is not intended to be a comprehensive treatise on the chemical or toxicological nature of tetrahydrofuran. The intent of Section 6, Major Conclusions in the Characterization of Hazard and Dose Response, is to present the major conclusions reached in the derivation of the reference dose, reference concentration and cancer assessment, where applicable, and to characterize the overall confidence in the quantitative and qualitative aspects of hazard and dose response by addressing the quality of data and related uncertainties. The discussion is intended to convey the limitations of the assessment and to aid and guide the risk assessor in the ensuing steps of the risk assessment process.

关键词：电子信息；信息系统；四氢呋喃；评论

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报告从战略性分析、环境信息、竞争对手情报、资讯信息快报、市场行情与数据分析等几个方面进行了分析评论。

关键词：石油化工；战略性分析；环境信息；竞争对手情报；资讯信息快报；市场行情

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关键词：尿素；市场价格

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关键词：BPC；钾肥价格；需求规模

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关键词：尿素；关税

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关键词：氯乙酸；成本支撑；市场供应

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关键词：甲醇；价格；原料

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关键词：醋酸行业；出路；发展趋势

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