持续污染下洛克沙胂在土柱中的迁移转化及其风险评估

Migration and transformation of roxarsone in the soil column and its risk assessment under continuous pollution

由于禽畜粪便未做防渗的露天堆积,导致饲料添加剂洛克沙胂(ROX)进入环境从而诱发无机砷污染。本研究通过157 d的一维土柱模拟探究了ROX长期持续污染的前提下,垂向包气带上砷化合物形态和含量的时空变化,并通过高通量测序技术揭示了不同深度的微生物群落结构响应。结果显示,在157 d的ROX持续污染模拟过程中,ROX降解速率很高,显著高于迁移速率,ROX的降解与吸附均发生在土壤浅层(0~10 cm)。ROX降解产物主要为As(Ⅴ)和As(Ⅲ),其中As(Ⅴ)含量明显高于As(Ⅲ)含量,砷化合物均主要聚集在0~40 cm深度,土壤中砷化合物含量显著高于土壤溶液中的含量,土壤对砷化合物的固定能力很强,砷化合物的迁移速度十分缓慢,157 d最大迁移深度为40 cm。由此可见,土壤一旦被砷污染,其长期危害难以消除。表层土壤中微生物群落结构与其他深度显著不同,结合RDA与PERMANOVA分析证明深度和ROX含量是控制不同深度土壤中微生物群落多样性的主要影响因素。通过健康风险评估得知,表层土壤中ROX持续污染会诱发较大的砷致癌风险。因此,建议全面执行我国禁止使用ROX的规定,在仍然允许使用ROX的国家和地区,要加强对禽畜废弃物的规范处理,避免长期在未防渗的地面上露天堆积。

Poultry waste is typically disposed in the open without seepage prevention,leading to the feed additive roxarsone(ROX)entering the environment and causing inorganic arsenic(As)pollution.In this study,157-day one-dimensional soil column simulation was conducted to explore the spatial and temporal variations of As compound morphology and concentration in the vertical vadose zone under continuous ROX contamination.The microbial response at different depths was analyzed using high-throughput sequencing technology.The results showed that during the 157-day simulation of continuous ROX contamination,the degradation rate of ROX was very high,being significantly higher than the migration rate.The degradation and adsorption of ROX occurred in the shallow soil layer(0-10 cm).ROX degradation products were mainly As(Ⅴ)and As(Ⅲ),and the concentration of As(Ⅴ)was significantly higher than that of As(Ⅲ),and As compounds were mainly clustered at a depth of 0-40 cm.The concentration of As compounds in soil was significantly higher than that in soil solution.Soil had a strong ability to fix As compounds,and the migration rate of As compounds was very slow.The maximum migration depth was 40 cm in 157 days,which showed that once the soil was contaminated by As,the long-term harm caused by its compounds was difficult to eliminate.The microbial community structure of surface soil differed significantly from that at other depths.Combined with RDA and PERMANOVA analysis,it was shown that depth and ROX concentration were the main factors controlling the microbial community diversity at different soil depths.The health risk assessment revealed that persistent ROX contamination in topsoil would lead to a major carcinogenic risk due to As.Therefore,it is recommended to fully implement regulations prohibiting the use of ROX.In countries and regions where the use of ROX is still allowed,it is necessary to strengthen the standardized treatment of livestock waste and avoid long-term accumulation in the open.