贵州丹寨县土壤-水稻中硒和重金属的积累及迁移特征

Translocation and Accumulation of Selenium and Heavy Metals in Paddy Soil-Rice Plant System in Danzhai County, Guizhou Province

通过测定贵州丹寨县主要水稻种植区30件水稻土及对应的水稻中硒和重金属的含量,分析硒和重金属Cd、Hg、As、Pb在根系土及对应水稻中的分布特征,研究了土壤有机质和pH对硒和重金属在土壤-水稻系统中迁移的影响。结果表明:该地区水稻根系土中硒含量变化范围为0.27~0.98 mg/kg,平均值为0.65 mg/kg, 70%的样品达到富硒土壤标准,但是仅23.3%水稻籽实样品达富Se大米标准。土壤重金属污染风险较大,特别是Hg和Cd,其中80%的样品Hg超《土壤环境质量农用地土壤污染风险管控标准(试行)》(GB 15618—2018)中污染风险筛选值,但水稻籽实中尚无重金属超标现象。水稻根系对硒的富集能力相对最强,其次为茎、叶和籽实。重金属也主要积累在根系中。水稻籽实Se含量与土壤Se总量的相关性不显著,与土壤pH和有机质含量呈显著负相关。水稻籽实中Cd与土壤Se和pH呈显著的负相关关系。土壤中As和Hg向水稻的迁移则主要受总量的控制。水稻各部位Se的吸收能力与土壤重金属存在极显著负相关性,据此可采取措施如降低土壤中的重金属尤其是Cd和Hg的含量及减少有机肥的施用来提高Se在籽实中的积累。

A total of 30 paired rice samples and relative soils were collected to understand the concentration and distribution of selenium and heavy metals in rice and rice soils in Danzhai county, Guizhou province. The factors governing the migration of selenium and heavy metals in rice-soil system were also analyzed. The results showed that the total selenium content in soils ranged from 0.27 mg/kg to 0.98 mg/kg, with 70% were selenium-rich soils. But only 23.3% of the rice grain selenium content was higher than the national cereal food selenium-rich standard.It was also found that there was a serious heavy metal pollution risk in the soil, especially Hg and Cd, but not in the rice grain. The content of Hg in more than 80% of the soil samples exceeded the soil standard value. The concentration characteristic of selenium in different parts of rice was: root>stem>leaf>grain. Heavy metals also mainly existed in the roots, and the average absorption coefficient of As in roots was even reached to 122.09%. There was a significant negative correlation between selenium in rice grain and pH and organic matter in soil, but not with the total selenium content in soil. pH was the dominated factor controlling the migration capacity of Cd from soil to the rice. Acid soils may facilitate the migration of Cd. The migration of As and Hg was under the control of soil parent. It was also found that there was a significant negative correlation between the absorptivity of selenium in different parts of rice and heavy metals in soils. Thus, it would be proposed to take some steps such as reducing the contents of heavy metals and organic fertilizer in soil so as to improve the accumulation of selenium in rice.