南方酸性红壤区不同种植方式土壤重金属的生物有效性

Bioavailability of Soil Heavy Metals under Different Planting Types in Acid Red Soil Zone of Southern China

测定了南方酸性红壤区5种农业种植方式(旱地、水田、果园、茶园和竹林)土壤重金属及其不同形态含量,借助潜在生态风险指数(RI)法、风险评估指数(RAC)法和次生相与原生相分布比值(RSP)法对土壤重金属的生态风险进行评估。结果表明,土壤中镉(Cd)、汞(Hg)、砷(As)、铅(Pb)、铬(Cr)和镍(Ni)的含量分别为0.080~0.290、0.078~0.150、1.54~6.90、39.13~91.30、20.35~73.98、15.03~40.81 mg/kg。Cd、Pb、Hg含量在旱地土壤中最高,As含量在茶园土壤中最高,Cr、Ni含量在竹林土壤中最高。除旱地土壤Pb外,其他重金属含量均未超出农用地土壤污染风险管控标准(GB 15618—2018)筛选值。Cd、Pb、Ni含量均超出福建省元素背景值,超标倍数排序为Cd?Ni?Pb?Hg?Cr?As,Cd超标最严重。土壤中Cd以离子交换态为优势态,表现为水田(50.56%)?旱地(44.14%)?果园(38.64%)?竹林(37.62%)?茶园(36.25%)。RI值表现为旱地(270.70)>果园(201.98)>竹林(194.09)>水田(171.92)>茶园(107.05)。RI平均值为189.15,处于中等生态风险危害级别,Cd是主要生态风险贡献因子。RAC评价结果表明,土壤中Cd处于高(果园、茶园和竹林)—极高(旱地和水田)风险水平,Pb处于低—中风险水平,Hg、As、Cr、Ni为低风险水平。RSP评价结果显示,旱地、水田和竹林土壤中的Cd及果园土壤中的As为重度污染,茶园和果园土壤中的Cd及竹林土壤中的Hg为中度污染,旱地和水田土壤中的As为轻度污染。Cd是研究区最易迁移转化的生态风险因子,需采取必要的防控措施。

The contents of heavy metals and different speciation in soils of five agricultural planting modes(dryland,paddy field,orchard,tea garden,bamboo forest)were determined in acid red soil zone of southern China. The ecological risk of soil heavy metals was evaluated using potential ecological risk index(RI),risk assessment code(RAC)and the ratio of secondary phase to primary phase(RSP).The results showed that the concentrations of Cd,Hg,As,Pb,Cr and Ni in the soil of the study area were 0. 080—0. 290, 0. 078—0. 150, 1. 54—6. 90, 39. 13—91. 30, 20. 35—73. 98, 15. 03—40. 81 mg/kg,respectively. The contents of Cd,Pb and Hg in dryland soil were the highest,the content of As in tea garden soil was the highest,and the contents of Cr and Ni in bamboo forest soil were the highest. The contents of different heavy metals,except for Pb in dryland soil,were lower than the screening value of risk control standard of soil contamination in agricultural land(GB 15618—2018).The contents of Cd,Pb and Ni exceeded the soil background values of Fujian Province,exceeding multiple decreased in the order of Cd?Ni?Pb?Hg?Cr?As,and the accumulation of Cd was the most severe. The predominant speciation of Cd was the ion exchangeable fraction,showing paddy field(50. 56%)? dryland(44. 14%)? orchard(38. 64%)? bamboo(37. 62%)? tea garden(36. 25%). RI value from high to low was dryland(270. 70)>orchard(201. 98)>bamboo forest(194. 09)>paddy field(171. 92)>tea garden(107. 05). The average value of RI was 189. 15,which belonged to medium ecological hazard on the whole,and Cd was the major ecological risk contributing factor. The results of RAC estimation showed that Cd belonged to high(orchard,tea garden and bamboo forest)to very high(dry land and paddy field)risk level,Pb belonged to low to medium risk level,and Hg,As,Cr and Ni belonged to low risk level. The results of RSP evaluation showed that Cd in dryland,paddy field and bamboo forest,and As in orchard were at heavy pollution level,Cd in tea garden and orchard,and Hg in bamboo forest were at moderate pollution level,and As in dryland and paddy field was at slight pollution level. Cd is the most easily translocated ecological risk factor in the study area,so necessary prevention and control measures should be taken.