Establishment Of An Evaluation System To Evaluate The Passivation Remediation Effect Of Cadmium Pollution In Typical Acid Paddy Soils

After the remediation project for heavy metal contaminated farmland,whether the soil and the heavy metal content of the crops meet the repair requirements,it is necessary to evaluate the repair effect of heavy metal contaminated farmland with scientific and effective methods,In this way,whether the confirmed soil fertility,the heavy metal content of the edible part of the crop and the soil can meet the standard,and can reduce the threat of heavy metal pollution on human health and ecosystem.Therefore,the assessment of the remediation effect of heavy metal contaminated soil is an essential and important part of farmland soil remediation project.The purpose of the remediation effect assessment of contaminated soil is to objectively examine the remediation effect and evaluate the changes brought by the remediation project to soil properties and crops.At the same time,it can supervise the remediation project and provide the basis for the reuse of contaminated soil after treatment.In this study,the whole system of soil-crop-repair materials as the object before and after in-situ repair of cadmium pollution.From the literature data,field test data and related standards,theoretical design,literature analysis,Delphi and analytic hierarchy process were used to screen the index and design.questionnaire,after expert consultation,establish an evaluation index system for the cadmium pollution remediation effect of southern acid paddy soil.The established remediation effect evaluation index system includes a target layer index,four criteria layer indicators,and 14 specific evaluation indicators.The expert system and the analytic hierarchy process are used to determine the weight of the indicator system.The four criteria were: soil fertility index(0.12),heavy metal pollution index(0.34),rice growth safety index(0.43),and remediation agent index(0.11).Soil fertility indexes include seven evaluation indexes: alkali-hydrolysis N(0.009),effective P(0.012),rapidly available K(0.006),organic matter(0.021),pH(0.034),cation exchange capacity(0.018),and secondary pollution(0.018).Heavy metal pollution index includes two evaluation indexes: total cadmium content in soil(0.121),effective cadmium abatement %(0.219);Rice growth safety index includes three evaluation indexes: cadmium content in brown rice(0.253),cadmium content reduction in brown rice %(0.111),and rice yield(0.067).The index of restoration agent includes two evaluation indexes: cost performance of restoration(0.051)and cadmium content of restoration agent(0.059).Three methods are used to determine the indicator standard: the first is to make use of existing standards,The first is to make use of existing standards,such as the whole cadmium,brown rice cadmium content index standards;The second is based on the results of relevant research.,such as effective cadmium abatement,brown rice cadmium abatement index standards;The third is to refer to the local average level or conventional requirements,such as rice yield,repair material cadmium content index standards.In the process of standard setting,the indicators are dimensionlessly processed,and the corresponding scores are given according to the size or level of the indicators.Considering the complexity and hierarchy of the remediation effect evaluation system,and the changes and scores of the four indexes in the criterion layer before and after remediation,the multi-objective weighting method was adopted as the evaluation method in this study.After the establishment of the restoration effect evaluation system,The case study of the passivation effect of cadmium contaminated paddy fields in hechi city of guangxi province and xiangtan city of hunan province was conducted with two different application amounts of restoration materials(restoration material A and restoration material B).Assessment results indicate that in the two places to control the cadmium demonstration area to repair,both get the best results of the 200 kg / acre repair material A and 100 kg / acre repair material B.