腐植酸对土壤砷化学形态及生物可给性的影响

利用in vitro方法研究了腐植酸(HAs)的两种活性组分——富里酸(FA)和胡敏酸(HA)及其不同比例(HA/FA)对土壤As在胃与小肠阶段生物可给性的影响,分析了As的生物可给性与HAs影响下As形态转化的关系。结果表明:在添加量≤1%C时FA和HA均可提高交换态As的分配比例,FA能显著促进土壤As由铝型As和铁型As向残渣态As转化,且随用量的增加转化作用增强,而HA的这种作用强度较弱,在HA添加量为5%C时甚至表现出相反的作用;FA和含3%C的HA处理显著增加了土壤As胃阶段生物可给性,FA和HA均显著增加了土壤As肠阶段生物可给性;HAs添加总量为1%C时,不同HA/FA的HAs均增加了土壤As的生物可给性,HA/FA为5/5时胃肠生物可给性最大,HA/FA为7/3时肠阶段生物可给性最小;HAs对土壤As生物可给性的影响与其影响As形态分布密切相关,在胃阶段对土壤生物可给性As具有显著影响的形态是交换态As和钙型As,单位交换态As对生物可给性As的贡献比钙型As大,在肠阶段对生物可给性As影响显著的是钙型As。

Chemical speciation and bioaccessibility of arsenate in soil as influenced by humic acids

The speciation and bioaccessibility of heavy metals in soil are influenced by humic acids(HAs), which exist widely in the envi-ronment. An in vitro experiment was carried out to elucidate the effects of the two active components of HAs(fulvic acid, FA; and humic acid, HA)and the HA/FA ratio on the speciation and bioaccessibility of arsenate(As)in soils. The relationship between the bioaccessibility and transformation of As in soils, as influenced by HAs, was analyzed. The results showed that HAs could increase the allocation proportion of Ex-As in soil at an application dosage of≤1%(as carbon, C, basis). FA could observably promote the transformation of soil As from Al-As and Fe-As forms to Res-As species, and the effects were enhanced with an increase in the FA dosage. However, HA showed a weaker or even reversed role in affecting such a transformation process at the highest usage of 5%C. FA and HA at 3%C usage could increase the bioaccessibility of soil As in the gastric phase. The bioaccessibility of soil As in the small intestinal phase was always enhanced by HA and FA regardless of their usage levels. HAs with different HA/FA ratios always enhanced the bioaccessibility of soil As in both gastric and small intestinal phases at a constant usage of 1%C;the degree of the effect was related to the HA/FA ratio, with a maximum bioaccessibility of soil As in the gastric phase and a minimum bioaccessibility of soil As in the small intestinal phase at HA/FA ratios of 5/5 and 7/3, respec-tively. The bioaccessibility of soil As was strongly linked to As speciation in soil as influenced by HAs. Ex-As and Ca-As forms were found to have significantly positive contributions to the bioaccessible As in the gastric phase, with Ex-As being greater than Ca-As per unit, and only Ca-As showed a significant positive contribution to the bioaccessibility of soil As in the small intestinal phase.