基于风险管理的镉砷污染稻田修复治理案例分析

Case Study on Remediation and Treatment of Paddy Fields Contaminated by Cadmium and Arsenic Based on Risk Management

基于稻米镉砷污染风险,构建了农田重金属污染风险分级体系,并依据土壤污染特征建立了石灰、土壤调理剂、镉砷同步钝化剂为主体的修复技术体系,在祁阳市肖家镇和白水镇504 hm^(2)典型重金属污染稻田进行修复治理示范。结果表明:4个基于稻米镉砷污染风险分级的分区治理模式在6个项目村修复效果明显。经过2 a的实施,石灰+镉钝化剂、石灰+镉砷同步钝化剂的技术模式皆显著提升了土壤pH值,降低了土壤有效态镉含量和稻米镉含量,显著提升了稻米镉达标率,土壤pH值增加了0.76~1.31,土壤有效态镉含量下降了18.18%~21.43%,稻米镉含量下降了31.03%~90.32%,稻米镉达标率增加了47.57~84.70个百分点;石灰+镉砷同步钝化剂的技术模式实施2 a后,对土壤有效态砷含量无显著变化,但稻米砷含量降低了22.22%~36.36%,稻米砷达标率达到了100%。结果还表明,针对大面积稻米镉砷超标区域,以优先降镉、协同控砷的策略可逐步实现污染农田安全利用,但应根据稻米镉砷超标风险程度和土壤镉砷污染特征进行技术优化。

In this study,the risk classification system of heavy metal pollution in farmland was established based on the risk of cadmium and arsenic pollution in rice,and the remediation technology system with the lime,soil conditioner,and cadmium and arsenic synchronous passivator as the main body was established according to the characteristics of soil pollution.The remediation and treatment demonstration was carried out in 504 hm^(2) typical paddyfields contaminated by heavy metal in Xiaojia Town and Baishui Town of Qiyang(county-level city).The results showed that four regional management modes based on the risk rating of cadmium and arsenic pollution in rice had obvious remediation effects in six project villages.After two years of implementation,the technical modes of lime+cadmium passivator and lime+cadmium and arsenic synchronous passivators both significantly increased soil pH,and reduced the available cadmium content in soil and the cadmium content in rice,significantly increasing the cadmium compliance rate of rice.Specially,soil pH increased by 0.76-1.31 units,the available cadmium content in soil decreased by 18.18%-21.43%,the cadmium content in rice decreased by 31.03%-90.32%,and the cadmium compliance rate of rice increased by 47.57-84.70 percentage points.Moreover,two years after the implementation of the technical mode of lime+cadmium and arsenic synchronous passivators,there was no significant change in the available arsenic content in soil,but the arsenic content in rice decreased by 22.22%-36.36%,and the arsenic compliance rate of rice reached 100%.The results of this study also showed that in large areas where cadmium and arsenic contents in rice exceed national standards,the strategy of prioritizing cadmium reduction in coordination with arsenic control could gradually realize the safe use of polluted farmland,but the technical optimization should be carried out according to the risk degree of cadmium and arsenic contents in rice and the characteristics of cadmium and arsenic pollution in soil.