Effects Of Selenium On Soil Microorganisms And Its Environmental Criteria

Selenium is an essential trace element for organism.The lack of selenium will lead to many diseases,while excessive selenium will also cause human and ecological toxicity.In China,the development of selenium rich agriculture industry is vigorously promoted in many areas.Whether the development of selenium rich agriculture will lead to the change of selenium content in the environment matrix,whether the environmental selenium will cause a threat to terrestrial organisms,aquatic organisms,and how to define the environmental criteria are subjects remaining to be researched.In present study,the distribution of soil selenium content in Boshan District,Zibo City,Shandong Province,a typical selenium rich agricultural development area in China,was investigated,the effect of selenium fertilizer application on soil selenium content was discussed;the relationship between the number of soil microorganisms and selenium content or other physical and chemical properties in the field soil was analyzed,the effect of exogenous selenium on the number of soil microorganisms under laboratory conditions was explored,and the national soil quality criteria for the protection of terrestrial organisms and water quality criteria for the protection of aquatic organisms were derived.It provides scientific basis for the sustainable development of selenium rich agriculture and data support for the establishment of environmental selenium standard in China.The conclusions are as follows:（1）The soil selenium content ranges from 0.101 to 4.56 mg/kg in Boshan,with a geometric average value of 0.369 mg/kg.The highest concentration was located near the Boshan Park in the northwest area,where used to be a coal mine.The lowest point was located in the southeast area.Soil application of selenium fertilizer can significantly increase the content of selenium in the soil in the short term,and the selenium will exist for a long period.（2）Under field conditions,the total number of bacteria,Gram-positive bacteria and Gram-negative bacteria in soil were positively correlated with selenium content（p<0.05）;the total number of bacteria,Gram-positive bacteria and Gram-negative bacteria in soil were positively correlated with TN in soil（p<0.01）;the total number of bacteria and Gram-positive bacteria in soil were positively correlated with TN in soil The number of Gram-negative bacteria was positively correlated with TOC（p<0.01）.（3）Under laboratory conditions,low dose of sodium selenite（0.2-10mg/kg）can promote the growth of the number of soil microorganisms,while high dose of sodium selenite（10-70 mg/kg）can inhibit the growth of the number of soil microorganisms in 2 days.The effect of sodium selenite on the number of soil microorganisms was shown as inhibition at all levels after 21days.（4）Under laboratory conditions,the lowest observable effect concentration（LOEC）was 0.2 mg/kg for sodium selenite（0.0913 mg/kg selenium）to reduce the number of soil microorganisms significantly.（5）Based on 25% effect concentration(EC₂₅),20%effect concentration(EC₂₀)and LOEC,the national soil quality criteria derived by use of species sensitivity distribution（SSD）methods to gain hazardous concentration for 5%of species（HC₅）,which would protected 95%terrestrial organisms or soil ecosystem process from unacceptable influence,was 51.3μg/kg.（6）Based on maximum ineffective concentration（NOEC）and LOEC,the first-level national fresh water quality criteria derived by use of species sensitivity distribution（SSD）methods was 0.580μg/L.While,based on half lethal concentration(LC₅₀),half effect concentration(EC₅₀)and the half inhibitory concentration(IC₅₀),the second-level national fresh water quality criteria was 0.520 mg/L.