This study is designed to pinpoint the effect of salinity (NaCl and Na2SO4, add at salinity levels of 0%~5%, respectively) on methylation of exogenous Hg (II) in wastewater-irrigated areas of Tianjin City. Solutions containing stable isotope tracers of 199 Hg 2+were spiked into the soils at the concentrations of 80% of the total soil mercury. The formation of CH3 199 Hg+(MeHg) was measured in time series experiments using gas chromatographic separation and isotope-specific detection by inductively coupled plasma mass spectrometry. The results manifested that, generally, changes in concentrations of CH3 199 Hg+in soil with incubation time were similar in direction and pathways, and three regions (retarded-sharp-stable) could be distinguished. Logistic equation can well fitted kinetic experimental data of concentrations of CH3 199 Hg+formed during the incubation time. According to Logistic model, the maximum amount of formed MeHg of control soil (without salinity addition) was 0.698μg/kg, while the maximum methylation rate of exogenous Hg was 0.217μg/(kg·d). In NaCl spiked soils, methylation rate of exogenous Hg increased first and then decreased with the increasing salinity level of NaCl. It found that the maximal amount of formed MeHg and the methylation rate of exogenous Hg were significantly higher in 0.2%~0.6% NaCl spiked soils by comparison with control soil. The highest amounts of them were in 0.4% NaCl soil, which accounted for 3.589μg/kg and 0.415μg/(kg·d), respectively. The maximal amount of formed MeHg over incubation time and the methylation rate of exogenous Hg in 1%~2% NaCl spiked soils were close to them in control soil. It also found that high salinity level of NaCl (5%) inhibited the methylation of exogenous Hg. In Na2SO4 spiked soils, salinity (0.2%) constrained the availability of mercury for methylation. The results of these studies demonstrated higher MeHg production potentials in comparatively lower salinity environments, which may enhance Hg bioavailability in the soil and cause a hazard to human body through the food chain.%将汞同位素示踪剂199Hg2+(土壤背景含量的80%)加入不同盐分和盐度处理的盐渍化土壤中,利用多重标记稳定同位素示踪技术,研究盐分累积对外源汞在土壤中甲基化的影响.盐分种类为 NaCl 和 Na2SO4,设置的盐度梯度为7个,添加质量分数为0%~5%.结果表明,外源199Hg2+加入土壤后,在培养期间,土壤中CH3199Hg+生成量变化趋势总体呈S型曲线,表现出迟缓-最大速率-稳定3个阶段,用Logistic方程可以理想拟合盐处理下外源汞添加入土壤后生成甲基汞的动力学过程.在未添加盐分处理的对照土壤中,甲基汞最大生成量为0.698 μg/kg,最大甲基化速率为0.217 μg/(kg·d).NaCl处理下,随着盐度的增长,外源Hg进入土壤后汞甲基化程度总体呈现先增长后降低的趋势.0.2%~0.6%盐度下,甲基化程度显著提高,0.4%盐度下最高,最大生成量和最大甲基化速率分别达到3.589 μg/kg和0.415 μg/(kg·d).盐度在1%~2%时汞甲基化程度与对照比较接近,高盐度(5%)对汞甲基化有明显的抑制作用.Na2SO4处理下,当盐度水平超过0.2%时,会显著抑制外源汞加入土壤后甲基汞的生成.
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