土壤中可离子化农药存在形式对其生物有效性的影响机制及表征

The bioavailability of pesticides in soil is the key in assessing the pesticide ecological risk. It is generally accepted that organisms can take up pesticide that are present in the pore water, and the pore water concentration has been used to estimate the bioavailability. However, for the pesticides which possess either an acidic or a basic functional group, they can be exist in neutral or ionic form in soil depending on soil pH. The influence of different speciation states not only on the adsorption by soil, but also the bioactivity of the pesticide presented in pore water at adsorption equilibrium. The influence of both the adsorption and bioactivity on bioavailability in soil is not clear. Our previous studies indicate when the weak acid herbicide nicosulfuron and weak base fungicide carbendazim exists as different species, the pore water can not estimate the bioavailability. In the present study, the nicosulfron and carbendazim will be studied as the mode ionizable pesticide, the influence of speciation states on adsorption by soil and dissolved organic matter, uptake by organism and the bioavailability in soil will be studied to understand the mechanism by which the bioavailability was affected by speciation states. In addition, the influence of the excreta from animal and plant on the soil pH and pore water concentration also be studied to understand the mechanism. Finally, the biomimetic method matrix solid-phase microextraction, triolein-embedded cellulose acetate membranes and hollow fiber based liquid phase microextraction will be used to estimate the bioavailability of ionizable pesticide in soil.

土壤中农药的生物有效性是其生态风险评估的关键。通常认为土壤孔隙水中农药是对土壤中生物体有效的部分,能表征农药的生物有效性。然而，可离子化农药的存在形式不但影响吸附，吸附平衡时孔隙水中的部分也具有不同的生物活性，两者共同作用对生物有效性的影响仍然是不清楚的。前期研究表明，当土壤中弱酸性除草剂烟嘧磺隆和弱碱性杀菌剂多菌灵的存在形式不同时，孔隙水浓度不能很好的评价其生物有效性。本研究将继续以烟嘧磺隆和多菌灵为研究对象，研究土壤和可溶性有机质对其不同存在形式吸附的影响，不同存在形式对农药生物毒性和生物富集的影响，动植物分泌物对土壤pH及孔隙水浓度的影响，土壤pH对可离子化农药生物有效性的影响，综合阐明土壤中可离子化农药不同存在形式对生物有效性的影响机制，并探索用固相微萃取、三油酸甘油酯-醋酸纤维素复合膜和中空纤维支载液膜微萃取等仿生技术来表征土壤中可离子化农药的生物有效性。

随着人工合成化合物的增加，可离子化有机污染物所占比例越来越高，由于不同pH条件下可离子化有机污染物可能以分子和离子形式存在，其生物有效性比中性分子更加复杂。本项目首先明确了弱酸性有机污染物磺胺嘧啶和弱碱性化合物氯喹对大型溞毒性为中性分子显著高于离子形式后，应用中空纤维液相微萃取模拟大型溞对磺胺嘧啶的吸收，用接受相浓度评价磺胺嘧啶对大型溞的急性毒性，发现与直接测定浓度相比，中空纤维液相微萃取测定浓度计算的抑制率和实际测定的抑制率之间的差异显著降低，显著提高水环境中可电离化合物对大型溞毒性的评价，研究结果对将来可电离化合物生物毒性评价奠定了基础，有望在将来可电离化合物风险评估中推广应用。为了明确吸附和pH在生物有效性中的作用，我们在土壤中添加生物碳和调节土壤pH后测定土壤中甲磺草胺和2,4-D对水稻的药害，发现添加生物碳后，这些除草剂对水稻的药害均不同程度降低，增加pH后，除草剂药害有所增加，分析药害与吸附的关系，发现吸附是影响药害的主要因素，用中空纤维液相微萃取浓度较总浓度能更好的评价土壤中除草剂对水稻的药害，但和原位孔隙水浓度相比较，没有显著提高，具体机理还需进一步研究。在本项目已发表论文3篇，其中SCI论文2篇，累计影响因子8.0，申请发明专利1项，获湖南省技术发明二等奖1项。

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