文献阅读问题答案

1、文献阅读问题Introduction1. How do heavy metals entry the soils?Answer: Entry of soil-borne metal(loid)s into the food chain depends on the amount and source of metal(loid)s input, the properties of the soil, the rate and magnitude of uptakeby plants, and the extent of absorption by animals.2. Can you give a definition to heavy metal and give us the examples?Answer: The term heavy metal refers to any metallic chemical element that has a relatively high density and is toxic, highly toxic or poisonous at

2、 low concentrations. Examples of heavy metals include mercury(Hg), cadmium(Cd),arsenic(As), chromium(Cr), thallium(Ti), and lead(Pb) . Historically, heavy metal(loid)s toxicity to human health received attention primarily as a result of series of widespread poisoning. 3. Why human kind pays attention to heavy metal(loid)s toxicity?Answer: Historically, heavy metal(loid)s toxicity to human health received attention primarily as a result of series of widespread poisoning. 4. Can you describe chara

3、cteristics of heavy metal(loid)s in soil? Answer: Unlike organic contaminants, metal(loid)s do not undergo microbial or chemical degradation, and the total concentration of these metal(loid)s persist for a long time after their introduction in soils . 5. Can you tell us the difference between phytoextraction and phytostabilization?Answer: Phytoextraction process is used to remove metal(loid)s in soil; phytostabilization is used to immobilize metal(loid)s in soil.Sources of heavy metal(loid)s1. W

4、here does heavy metal in the soil come from?Answer: Heavy metal(loid)s reach the soil environment through both pedogenic and anthropogenic processes. Dynamics of heavy metal(loid)s in soils1. Do metal(loid)s subject to volatilization losses?Answer: Although most metal(loid)s are not subject to volatilization losses, some metal(loid)s such as As, Hg, and Se tend to form gaseous compounds . 2. Please tell the difference between specific adsorption and non-specific adsorption.Answer: In general ter

5、ms, non-specific adsorption is a process in which the charge on the ions balances the charge on the soil particles through electrostatic attraction, whereas specific adsorption involves chemical bond formation between the ions in the solution and those in the soil surface.3. Please tell us the relationship between bioavailability of heavy metal and soilphysicochemical property?Answer: Bioavailability of heavy metal are effected by a number of factors including temperature, steric factors and con

6、centration. All these interactions are controlled by solution pH and ionic strength, the nature of the metal(loid) species, dominant cation, and inorganic and organic ligands present in the soil solution 4. When does the precipitation appear to be the predominant process?Answer: Precipitation appears to be the predominant process in high pH soils and in the presence of anions such as SO42, CO32, OH, and HPO42, and when the concentration of the heavy metal(loid) ion ishigh . 5. What is co-precipi

7、tation? Can you give an example.Answer: Co-precipitation of metal(loid)s especially in the presence of iron oxyhydroxides has also been reported and often such interactions lead to significant changes in the surface chemical properties of the substrate. Lu et al. confirmed that co-precipitation of Pb(II) with ferric oxyhydroxides occurred at pH 4 and is more efficient than adsorption in removing Pb(II) from aqueous solutions at similar sorbate/sorbent ratios and pH. . 6. Does the toxicity of As

8、in soil decrease or increase when it presents in compoundof alkylarsine?Answer: It will be decrease.Approaches and indicators of bioavailability1. What is the bioavailability of heavy metal?Answer: The generic definition of bioavailability is the potential for living organisms to take up chemicals from food (i.e., oral) or from the abiotic environment (i.e., external) to the extent that the chemicals may become involved in the metabolism of the organism. 2. How to indicate the bioavailability of

9、 heavy metal?Answer: Bioavailability of metal(loid)s in soils can be examined using chemical extraction and bioassay tests that determine a fraction of the metal(loid)s is bioaccessible. Chemical extraction tests include single extraction and sequential fractionation. Bioassay involves plants, animals, and microorganisms .3. What is PBET(physiologically based extraction test)?Answer: These innovative tests predict the bioavailability of metal(loid)s in soil and sediments when ingested by animals and humans. Soil amendments for remediation1. What is the mobilization of soil contaminants?Answer: The basic principle involved in the mobilization technique is to release the metal(loid)s in to soil solution, which is subsequently removed using higher plants. I2. Can you explain the mechanism of chelating agents?For example: application of thiosulphate to soi

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