土壤酶对As(Ⅲ)与As(V)毒性转化的响应机制及主要控制因素研究

Arsenic (As) pollution in some areas in China has resulted in severe environmental consequence posing great potential risk to human, livestock and food safety. There are two forms of ionic arsenic, As(III) and As(V), in soil with the former being more toxic to organism than the latter. Transition between the two forms of As occurs frequently. It is very important to understand the changes in As toxicity during transition between As(III) and As(V) with response from soil enzyme for accurately charactering environmental impact from different forms of As. Common types of soil in Chinese soil taxonomy and the correspond As spike soil will be selected for this study with addition of pure enzyme, fix enzyme and soil enzyme under laboratory and aging study. Using advanced enzyme analytical tools, content of two forms of As and characteristics of soil enzyme (activity, kinetics and thermodynamics) will be routinely monitored under varied pH and moisture content. The monitored results can be used correlate response of soil enzyme with toxicity of As in different valence state and select soil enzyme which is more sensitive to toxic response from either form of As . The selected soil enzyme sensitive to As toxicity can be used to establish does - response relationship curve between As concentration in soil and soil enzyme so that threshold value of As toxicity in soil can be obtained. Under Burr III and other related modelling methods, the critical factors affect As toxicity which is harmful to soil enzyme activity in major types of soil in China can be quantified. Therefore, change in As toxicity during transition between As(III) and As(IV) affecting soil enzyme activity under varied pH and moisture content can be better understood. The result obtained from this project will provide valuable information for the research scientist on rapid and accurate in situ monitory, assessment and remediation of extent of As pollution to the environment. Furthermore, data generated from this work may also add some new fundamental knowledge to soil enzyme theory.

三价和五价是土壤中砷（As）两种主要形态，前者生物毒性远大于后者，且二者频繁转化。研究As(Ⅲ)与As(V)转化中As总体毒性变化与土壤酶的响应机制并揭示影响的主要控制因素，对准确表征不同价态砷的环境效应具有重要意义。本项目拟以不同体系的纯酶、固定化酶和土壤酶（我国典型类型及砷污染的土壤）为材料，采用室内模拟和砷老化试验，借助酶动力学和热力学手段，通过定期检测不同pH和水分等条件下As(Ⅲ)和As(Ⅴ)含量及酶活性特征参数的变化，揭示砷的土壤酶响应机制，筛选对As(Ⅲ)、As(Ⅴ)毒性敏感的酶类；建立砷与土壤酶间的剂量~效应曲线，获得不同污染程度的生态剂量；通过Burr Ⅲ模型等数学方法，构建影响砷对土壤酶毒性的主要土壤控制因素；探明不同pH、水分条件对不同价态砷转化及土壤酶砷毒性的影响。结果为土壤砷污染的原位、分段、快速监测和污染的科学评定、调控修复及土壤酶学理论完善等提供科学依据。

研究As(Ⅲ)、As(V)与土壤酶的响应机制并揭示影响的主要控制因素，对准确表征不同价态砷的环境效应及砷生态风险评估具有重要意义。本项目以不同体系的纯酶、固定化酶和土壤酶（我国典型类型及砷污染的土壤）为材料，采用室内模拟和砷老化试验,以及对矿区长期砷污染土壤的检测，借助酶动力学和热力学等手段，研究了砷对土壤酶毒性效应及作用机理，获得了以下研究成果：（1）急性污染下对砷敏感土壤酶，包括磷酸酶、FDA水解酶、脱氢酶、芳基硫酸酯酶等，其中磷酸酶仅对As(V)敏感；（2）急性As(V) 污染对酸性和碱性磷酸酶的抑制机制不同，前者为非竞争抑制为主的混合抑制，而后者则主要以竞争性抑制为主。热力学研究表明砷对碱性磷酸酶抑制属于焓控过程。（3）土壤水分通过影响砷有效性、砷形态转化等过程对土壤酶产生不同效应。干燥和淹水均能改变土壤酶活性和微生物活性，从而影响土壤酶对砷污染的响应规律。pH主要通过改变As与酶结合能力而影响砷的毒性效应。pH增加，As(V)与土壤碱性磷酸酶结合能力增强，导致其对土壤磷酸酶抑制越强。（4）酸、中性土壤对As(V)的吸附能力强于碱性土。土壤对As(V)的吸附能力主要受到无定型铁、粘粒含量的影响。As(V)老化显著增加了土壤团聚体中的速效磷含量，对土壤各粒级团聚体中碱性磷酸酶抑制程度不同。（5）矿区土壤酶对长期砷污染的响应与急性砷污染不同。微生物在适应长期砷污染过程中通过合成高亲和力同工酶及不同酶量来维持土壤酶的功能多样性和稳定性。（6）建立了土壤酶指标与砷浓度的剂量-效应模型，发现酶动力学指标（Vmax/Km）是评价土壤急性和长期污染的最佳敏感指标；通过模型计算得到急性砷污染和田间长期砷污染临界浓度阈值分别为7.4和35 mg kg-1。研究结果为土壤砷污染的科学评定、调控修复及土壤酶学理论完善等提供科学依据。