Evaluation Of Heavy Metal Pollution And Its Phytoremediation Effect In Farmland

In order to understand the heavy metal content and pollution degree of farmland soil,the field soil around the factory area of Jiyuan lead plant,Zhumadian Xiping County electroplating plant and Kaifeng leather factory(0～20cm)was studied.The heavy metal Pb,Cr,Zn content was tested by single factor pollution index method and principal component analysis was used.The source of heavy metals around the factory area.In view of the increasing heavy metal pollution in farmland,plant Impatiens,corn,ryegrass,rape,peanut,soybean,wheat and tall fescue were repaired.The growth characteristics,physiological and biochemical indexes of plants with different levels of EDTA under the stress of heavy metal Pb,Cr and Zn were deeply analyzed.The transport coefficient and enrichment factor provide a scientific basis for solving the problem of heavy metal pollution remediation.The results show that:(1)there are 3 kinds of heavy metals around the factory area exceeding standard or pollution,among which Pb and Cr pollution are more serious,and the 3 kinds of heavy metals have obvious differences,which are Pb>Cr>Zn,Cr>Zn>Pb and Cr>Zn>Pb in turn.The content of heavy metal Cr in farmland soil around Kaifeng leather factory was greater than the standard limit,and the level of different points reached moderate pollution.The content of Pb in farmland soil around Jiyuan lead plant and the content of Cr in farmland soil around Zhumadian Xiping County electroplating plant were all beyond the national soil standard value and the soil background value of Henan province.Source apportionment shows that the sources of heavy metals Pb and Cr in farmland soils around the plant may be affected by pollutant emission and road traffic.(2)after applying chelating agents in the tested soil,the growth of each plant changed significantly.The results are as follows:on the fifth day of applying EDTA,all parts of plants are affected to varying degrees,and the leaves of plants appear yellowing and chlorosis.The plant height ratio of plant to CK decreased by 31.9%,59%,29.3%,31%,23.6%,47.6%,57.1%,21.4%,31.8%and 31.9%,and the biomass,dry weight and root length of the tested plants decreased,and the concentration of EDTA(7.5mmol·Kg-1)was too high to inhibit the growth of plants.(3)compared with CK,under the treatment of compound heavy metal stress,when 2.5mmol·kg-1 EDTA was applied,the total changes of chlorophyll content in different plants were not obvious.When the concentration of EDTA reached 5.0mmol·kg-1,the chlorophyll content of various plants decreased and the chlorophyll content of some plants was higher than CK,and the concentration was 7.5mmol·Kg-1 EDTA.The chlorophyll content of plants decreased significantly,and plants were poisoned.Some plants even died.Compared with CK,when 5.0mmol·kg-1EDTA was applied,the activity of SOD increased significantly under the stress of low and medium concentration combined with heavy metals,and the activity of SOD increased slightly under the high concentration of heavy metal stress.At this time,the resistance of plants was the strongest and the most resistant to heavy metal toxicity.Compared with CK,when 5mmol·kg-1 EDTA was applied,the activity of POD decreased gradually under the stress of low,medium and high concentration compound heavy metals,and the activity of POD decreased to the lowest under high concentration of heavy metal stress,which was lower than CK,and the damage degree of plant body decreased,and the normal metabolism of plants could be maintained.Compared with the CK,the level(5mmol·kg-1,7.5mmol·Kg-1)was applied to EDTA,and under the low concentration of heavy metal stress,the content of MDA content changed little or slightly,the plant body was not damaged or slightly damaged.and the content of MDA in all the plant leaves increased significantly under the high concentration of heavy metal stress.Compared with CK,when 5mmol·kg-1 EDTA was applied,the content of soluble protein content in the leaves of the tested plants rose to the highest,and the resistance of the plant was the strongest,which helped to maintain the normal metabolism of the cells.(4)compared with CK,with the increase of EDTA concentration,the contents of Pb,Cr and Zn in aboveground and underground parts of all plants increased significantly.When the concentration of EDTA reached 2.5mmol·kg-1.there was no significant difference in the content of Pb.Zn and Cr in different plants.When the concentration of EDTA was increased to 5mmol·kg-1,the contents of Pb.Cr and Zn in various plants were obviously improved,the restoration effect was excellent,the content increased by 1.02 to 1.99 times,and the content increased by 0.93 to 2.75 times.When the concentration of EDTA increased to 7.5mmol·kg-1,the content of Cr in various plant sites decreased compared with 5mmol·kg-1 at the level of 5mmol·kg-1,but it was significantly higher than that of CK.which indicated that the plant root system had an inhibitory effect on the absorption of heavy metals when the concentration was too high.(5)with the increase of EDTA concentration,the transport and enrichment coefficients of various plants increased to varying degrees.When the concentration of EDTA was increased to 5mmol·kg-1,the enrichment coefficient and transport coefficient of all kinds of plants reached the maximum,which increased 0.42 to 4.02 times more than that of CK.The enrichment coefficient and transport capacity of Zn and Cr also showed a different multiplier,and the concentration increased to the maximum value.When the concentration of EDTA was increased to 7.5mmol·Kg-1 The enrichment coefficient and translocation coefficient decreased,but still far greater than CK.