Screening And Identification Of Resistant Strains And Remediation Of Lead Pollution In Wheat Field Soil

In recent years,with the increasing use of lead products and industrial “three wastes” emissions,the state of the soil lead pollution is getting worse and worse.Heavy metal pollution is irreversible,when bioaccumulation exceeds a certain limit,it will cause harm to humans.Traditional remediation methods of heavy metals pollution are mainly physical and chemical methods such as reverse osmosis,ion exchange and chemical precipitation.But they would secondary pollution,high costs,energy consumption,operational difficulties and other problems.Fortunately microbial remediation has less pollution,less investment,simpler operation,which brought it to the attention of people.Thus,in order to provide a theroitical basis and method for the remediation of Pb contaminated soil,two highly lead-resistant strains were screened and indentified from long-term heavy mental polluted soil.Firstly,microorganisms play a significant role in bioremediation of heavy metal contaminated soil and wastewater.In this study,two lead-resistant strains denoted by BY-10 and FB-6 were isolated from contaminated soil around a lead refinery.And then biosorption characteristics of Pb²⁺ of the strains were discussed,as well as the optimal growth conditions and identification of the strains.The results showed that,strains BY-10 and FB-6 belonged to Bacillus cereus and Penicillium commune respectively,and the highest concentrations of Pb²⁺ tolerated by them reached 1700 mg/L and 2500 mg/L respectively.Concretely the optimal temperature of Bacillus cereus was 35? and that of Penicillium commune was 30?;to both of them,the optimal growth pH was 7 and the liquid medium volume was 80 mL¹00 m L?in 250 mL bottle?.With the initial concentration of Pb²⁺ increasing from 0 mg/L to 600 mg/L,the growth of two strains became slower and slower gradually.And at a certain concentration of Pb²⁺,the adsorption rate of Pb²⁺ by strains all increased firstly and then decreased gradually along with the growth time of strains.The dynamic change of biological adsorption quantity of Pb²⁺ by strains was similar to the adsorption rate of Pb²⁺.But in a certain growth time of the strains,there was a descending trend in the adsorption rate of Pb²⁺ and an ascending trend in the biological adsorption quantity with the concentration of Pb²⁺ increasing.Secondly,the growth of wheat seedling was studied by water-culture experiment.Lead resistance strains Bacillus cereus and Penicillium commune were added to lead solution at different level.The resultsshowed that the growth of wheat seedlings was inhibited by Pb²⁺.The higher the concentration was,the more severely inhibited it was.At the same concentration of lead,the lead content in wheat seedling roots were higher than in seedlings;with the concentration of Pb²⁺ increasing,the lead content in seedlings and roots of wheat seedlings increased.A descending trend was also be seen in root activity and the content of Chlorophyll?Chl?and an ascending trend was noticed in the activities of Superoxide Dismutase?SOD?,Peroxidase?POD?and the content of Malondialdehyde?MDA?of the wheat seedings with the increasing of Pb²⁺ concentration.Affter adding Bacillus cereus,the reduction of lead accumulation in seedlings and roots of wheat seedling were 26.23%³4.05% and 13.35%¹7.55% respectively;while after adding Penicillium commune,the reduction of lead accumulation in seedlings and roots of wheat seedling were15.29%²4.09% and 8.77%¹0.85% respectively.We also saw an increase in the root activity and the content of Chl.The activity of SOD,POD and the content of MDA had decreased.Finally,to study the repairing effect of the lead-resistant strains in lead contaminated soil pot experiments were launched.The test was divided into three pot experiments.To begin with,in order to determine the optimal ratio of the lead-resistant strains,the growth and lead enrichment of wheat in the contaminated soil with different ratio of lead-resistant strains were tested.Next,under the best ratio determined by the last experiment,the weights of mixed agents added were set as 1 g/kg,2 g/kg,3 g/kg and4 g/kg respectively,the growth and lead enrichment of wheat with different weights of mixed agent were researched,in order to determine the optimum weight of the mixed agents.Then the restorative effects of lead resistant strains under the best ratio and dosage were studied in the end.The main results are as follows:1.When the ratio of Bacillus cereus and Penicillium commune was 1:1,wheat seedlings grew better than other treatments,which was the best ratio.2.When the dosage of mixed agents were 1 g/kg,2 g/kg,3 g/kg,4 g/kg,respectively,the growth of wheat were better than the control treatment.The content of Pb²⁺ in wheat leaves and roots was reduced by9.47%²3.5% and 7.36%²6.95%,respectively;available Pb content in soil was reduced by 8.8%²2.86%.When dosage was 2 g/kg,the wheat grew best,which was the best dosage of the mixed agents.3.The higher lead concentration was,the more obvious inhibition of wheat was.The lead content of each part in wheat and available lead content in soil also increased accordingly.After adding the mixedagents,the growth of wheat had been improved,the lead content of the different parts of wheat decreased.Soil pH increased,reducing the bioavailability of lead,as well as the available lead content in soil.