Determination And Analysis Of Heavy Metal In Soils And Plants In Vicinity Of A Lead-zinc Smeltery

Heavy metal, such as Au, Ag, Cu and Fe, which is generally denoted as metal with a specific gravity of5or more, could gradually accumulate in human body and cause chronic poisoning, normally with some typical symptoms like headache, dizziness, insanity, arthralgia, calculi, cancer etc. They can largely affect digestive system and urinary system. All above make it the major research object. As the rapid development of human society and industrialization especially happened in developing countries, increasingly amount of heavy metal is discharging into natural environment. As the most precious natural resource that supports human beings, earth is experiencing heavy metal pollution as a result of chemical abuse and sewage pollution. The accumulation of heavy metal in soil will not only affect the physi-chemical characteristics of soil but also it will go through the path of soil-plant-human to affect human health. What makes the situation worse is the transfer of heavy metal between soil and plant is a long term, hidden and irreversible process, once the heavy metals enter in human or other animals, they are hard to elimination. With the extended area and increasing amount, heavy metal pollution has become one of the most severe environmental problems for human beings.The work was proposed based on the development trend of heavy metal pollution. To in-depth analyze the appearance and transfer mechanism of heavy metal pollution, an area which in vicinity of a lead-zinc smeltery was selected as research region; by soil and plant sampling in the area, total content and fractional content of heavy metals in soils and plants were determined, which provides important data base and reference for the heavy metal pollution control and human body-exposure prevention.1) Microwave-assist digestion for total heavy metals (Cd, Cu, Pb and Zn) concentrations of the certified reference material (soil GBW07445) determination was optimized according to the literature and material. The interactions between variables such as holding time and temperature were investigated with central composite designs (CCDs). All the determination was completed by FAAS. In the total content determination, the relative errors were9.38%,5.38%,2.83%1.95%for Cd, Cu, Pb and Zn, respectively. All the experiments illustrated that the proposed methods were suitable for heavy metal analysis in soil. The optimal condition for microwave-assisted digestion (MAD) was to digest0.2g CRM with the presence of4ml HNO3,2mlH2O2and1ml HF in26min.2) Micro wave-assist extraction for the certified reference material (soil GBW07445) speciation extraction was optimized according to the literature and material. The interactions between variables such as holding time and temperature were investigated with central composite designs (CCDs). The relative errors of Cd, Cu, Pb and Zn in each extraction procedure were in the range of5.88%-16.7%,0%-12.5%,1.24%-12.5%and1.18%-11.0%, respectively. The optimal condition for microwave-assisted extraction (MAE) is:F1:65℃extraction for50s; F2:70℃for90s; F3:100℃for260s, F4:80℃for30s and F5:same as the condition of microwave-assisted digestion of total heavy metal concentrations.3) The total and each fraction concentrations of heavy metals in soils as well as their corresponding plants which received transferred heavy metals were analyzed. It could be found that the order of total content was Zn>Pb>Cu>Cd in contaminated soils, which is much above the recommended level. The distribution of each fraction for heavy metals was different from each other. The majority for Pb、Zn、Cu、Cd is F3and F2, F5and F2, F4and F3, F1and F2, respectively. F1and F2are easily bioavailable, making the heavy metal pollution in plants took on the relative trend.4) It indicated that the accumulation ability of plants was in an order of Cd, Zn> Cu> Pb. The BCF of Cd, Zn, Cu and Pb ranged from3%-43%,2.7%-35%,1.4%-12%and0.4%-5.1%, respectively, for the different tissues of plant. The Cu, Zn, Cd, Pb content in different vegetables ranged from9.82to39.3mg·kg-1,1321to3153mg·kg-1,4.47to18.9mg·kg-1,28to102mg·kg-1, respectively, higher than the results in other reports.5) There were also differencies of heavy metal accumulation ability for tissues of different plants found in this study. For Potato, Garlic and Bok choy, the trend of heavy metal accumulation ability of their stem and leaf were in the same order, which is Cd>Zn>Cu>Pb; and for the stem and leaf of Calamus, Radish and Alfalfa, the same trend for their stem and leaf was also found, which is Zn>Cd>Cu>Pb. But the differences were found in the stem and leaf of Chenopdium album L and Fennel, for Chenopdium album L it was Zn>Cu>Cd>Pb for stem and Zn>Cd>Cu>Pb for leaf; for fennel it was Cd>Zn>Cu>Pb for stem and Zn>Cd>Cu>Pb for leaf.6) By determination of heavy metal concentration in soil and plants, study was carried out on the accumulation ability of plants towards the heavy metal in soil. Generally the accumulation ability of different tissues of plant follows an order:leaf> stem. For Pb, the most and the least accumulation ability were found in fennel leaf and potato stem, respectively. For Cu, the most and least accumulation ability were found in potato leaf and garlic stem, respectively. For Cd, the most and least accumulation ability were found in potato leaf and garlic stem, respectively. And for Zn, the most and least accumulation ability were found in Chenopdium album L leaf and garlic stem, respectively. Besides, the heavy metal concentration in the steam and leaf as well as edible parts of vegetables, such as garlic stem, bok choy and fennel, were analyzed.It showed that all the plants which had been investigated have certain accumulation ability of heavy metal, the heavy metal could thus be introduced into food chain, thereby endanger human being’s health.