《环境污染和监测》魔法香蕉nanb

2、Metal(loid) Contaminants

　　1.What are four major differences between metal and organic contaminants?（金属和有机污染物）
　　①Metals occur naturally in the environment, while specific organic pollutants are mostly artificial.
　　②Organisms have evolved to regulate and detoxify trace metals, but this is not always true for organic pollutants.
　　③Metals are non-biodegradable and transform between chemical forms, while organic compounds degrade into a myriad of daughter products.
　　④Metals have broad-spectrum toxic effects on organisms, whereas most organic contaminants have specific toxic mechanisms.
　　Metal concentrations are complex and depend on various factors, while organic compound concentrations can be predicted from a few characteristics

　　2.What are the two main inorganic species of arsenic（砷） present in the environment? How does each species exert toxicity?（有毒），不写来源
　　（1）Species:
　　①Biogenic (Natural)
　　Most abundant mineral is arsenopyrite (FeAsS)毒砂；·
　　As is also closely associated with many other sulfide and oxide minerals硫化物和氧化物矿物（e.g. FeS2 and Fe2O3）；·
　　Soil concentration represents parent rock material and the associated weathered minerals（母岩和风化岩）；·
　　Volcanoes
　　②Anthropogenic (Manmade)
　　·Mining, smelting精炼 and processing加工 of ores矿石；
　　·Fossil fuel combustion；
　　·Pesticide and herbicide （农药和除草剂）use (agriculture)；
　　·Copper chrome arsenate (CCA) timber preservative（木材防腐剂）
　　（2）Toxicity
　　·Toxicity is species dependant：
　　Chemical similarity of arsenate to phosphate(Disrupt metabolic pathways ) ;
　　Arsenite binds strongly to thiols (-SH) and thus inhibits protein structure and function
　　Carcinogenicity: Inhibition of DNA repair修复; Interference with DNA methylation甲基化; Both processes could lead to tumour promotion（肿瘤扩散）
　　Chronic exposure: Skin cancer; Lung, bladder, liver and kidney cancer; Cardiovascular disease; Peripheral vascular disease

　　3.Describe the sources, speciation, mobility and toxicity of selenium in the environment.(硒在环境中的来源、形态、迁移性和毒性)。
　　（1）sources
　　Natural comes from:
　　Marine sedimentary rocks (organic carbon rich); Soils associated with organic-carbon rich parent rock;母岩
　　Natural atmospheric releases of selenium result from环境中自然释放: volatilization of selenium硒的挥发 by plants and bacteria,volcanic activity.
　　Manmade comes from:
　　Irrigation of Se-rich soils in semi-arid climates半干旱条件下灌溉富硒土壤: (Evaporation > rainfall) Concentration of salts and contaminants (like Se)
　　Mining and combustion of oil and coal 石油和煤炭(often enriched in Se)
　　（2）speciation物种形成

　　（3）mobility

　　（4）toxicity
　　? Selenate硒酸盐 – Se(VI) < Selenite硒酸盐 – Se(IV)
　　? Se is an essential micronutrient微量元素 in animals，but Cofactor in reduction of glutathione (antioxidant enzyme)减少谷胱甘肽(抗氧化酶)的辅助因子
　　? Small difference between deficiency缺乏 and toxicity (smallest of all trace elements)
　　? Se can substitute for替代 sulfur硫 in proteins

　　4.Describe the toxicity of Hg species and explain which Hg species is the most toxic and why?
　　①Elemental - Hg(0)元素
　　Hg(gas)is toxic because breathing allows Hg to quickly enter the bloodstream where it can cross the blood-brain barrier.
　　Hg(liquid) is relatively not as highly toxic as the vapor since most can be excreted)排出 but it is extremely volatile readily generating vapor.易挥发
　　②Inorganic - Hg(II)无机汞
　　Hg2+ attacks the central nervous system (CNS),中枢神经系统 but main target organs are the kidney and liver.
　　Hg2+ was used to treat the fur used in felt hats – “Mad Hatter”
　　③Organic - CH3Hg无机汞，最毒
　　·CH3Hg is a potent neurotoxin 强效神经毒素causing serious damage to the CNS. ·Manifested by difficulties with coordination, eyesight, hearing, tactile senses, increased lethargy and irritability.协调能力，视力，听力，触觉，嗜睡和易怒。

　　5. Lead (Pb) is neither as toxic nor as bioavailable as other heavy metals, yet the health threats of Pb are much more significant than for other heavy metals. Explain why.铅毒性不大但为什么危害大
　　①Enzyme Inhibition: 酶抑制
　　While Lead is a non-essential element with no known biological function lead mimics other essential metals (i.e. Ca, Fe, Zn) which are all co-factors in enzymatic reactions. 酶促反应的辅因子.Lead binds tightly to these enzymes and therefore doesn’t allow (inhibits) these enzymes to do what they are supposed to do resulting in indirect toxicity.间接
　　②Organ Accumulation: 器官积累
　　Ingested and inhaled（吸入和摄入） Pb is mainly present in blood. At high levels it will accumulate in soft tissues软组织 including the organs, the brain and eventually bone.
　　? Pb2+ replaces取代 Ca2+ in solid bone as their size and charge densities are similar
　　? In bone marrow骨髓, where red blood corpuscle formation occurs, Pb is a problem
　　? Pb interferes in at least five stages in the formation of the haem complex in haemaglobin, were inhibition of haem synthesis resulting in anemia.抑制血红素合成导致贫血。
　　? Renal and gastrointestinal disease ? 肾和胃肠道疾病
　　Cardiovascular disease心血管病
　　③Neurological Damage:神经学
　　? Reduced cognitive abilities认知能力减弱
　　? Linked to schizophrenia精神分裂 “Mad as a hatter”
　　Organic forms of lead are extremely dangerous because they can be absorbed through intact skin.完整皮肤
　　Lead is a widely used and dispersed trace metal that is a ubiquitous contaminant and pollutant. Compared to other trace metals, it is not as toxic or bioavailable. However, the general population is exposed to lead from various sources at higher levels than any other element, causing adverse health effects. This exposure has resulted in lead being one of the largest environmental medical problems, affecting more people with no known safe level of exposure