State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
School of Geographic Sciences, East China Normal University, Shanghai 200241, China.
Sci Total Environ. 2021 Jul 15;778:146325. doi: 10.1016/j.scitotenv.2021.146325. Epub 2021 Mar 10.
Sulfur could be introduced into paddy soils via dry or wet deposition, irrigation, and fertilization, which subsequently impacts the production of methylmercury (MeHg), a bioaccumulative neurotoxicant. However, effects of sulfur input on MeHg production are variable, possibly due to the multiple effects of sulfur on Hg mobility and/or microbial Hg methylators, leading to uncertainties in predicting MeHg risk. To address that, we explored the effects of different types and amounts of sulfur as well as concentrations of ambient sulfate on Hg methylation in paddy soils, and elucidated the mechanisms by quantifying changes in (1) Hg mobility and (2) microbial Hg methylators (e.g., sulfate-reducing bacteria, SRB). Our results indicated that MeHg levels increased by 40-86% and 30-96% in soils under various types (i.e., 200 mg kg elemental sulfur, ammonium sulfate, sulfur-coated urea and potassium sulfate (KSO)) and different amounts (i.e., 100, 200 and 400 mg kg KSO) of sulfur input. The enhanced MeHg production could be explained by increased Hg mobility but not changes in microbial Hg methylators. Besides, sulfate input increased MeHg levels (89-240%) in soils with low ambient sulfate levels (<100 mg kg) but had no effect on high-sulfate soils (>380 mg kg). These could be explained by the diverse responses of Hg mobility and microbial Hg methylators to sulfate input at different ambient sulfate levels. Our study opens the "black box" of Hg methylation under sulfur input, which would help reduce uncertainties in predicting MeHg risk in soils.
硫可以通过干湿沉降、灌溉和施肥等方式进入稻田土壤，从而影响甲基汞（MeHg）的生成，而甲基汞是一种生物累积性神经毒素。然而，硫输入对 MeHg 生成的影响具有变异性，这可能是由于硫对 Hg 迁移性和/或微生物 Hg 甲基化作用的多种影响，导致预测 MeHg 风险的不确定性增加。为了解决这一问题，我们研究了不同类型和用量的硫以及环境硫酸盐浓度对稻田土壤中 Hg 甲基化的影响，并通过量化（1）Hg 迁移性和（2）微生物 Hg 甲基化作用（如硫酸盐还原菌，SRB）的变化来阐明机制。研究结果表明，在不同类型（即 200 mg kg 元素硫、硫酸铵、硫磺包衣尿素和硫酸钾（KSO））和不同用量（即 100、200 和 400 mg kg KSO）的硫输入下，土壤中 MeHg 水平分别增加了 40-86%和 30-96%。增强的 MeHg 生成可以用 Hg 迁移性的增加来解释，但不能用微生物 Hg 甲基化作用的变化来解释。此外，在环境硫酸盐水平较低（<100 mg kg）的土壤中，硫酸盐输入增加了 MeHg 水平（89-240%），但对高硫酸盐土壤（>380 mg kg）没有影响。这可以用 Hg 迁移性和微生物 Hg 甲基化作用对不同环境硫酸盐水平下硫酸盐输入的不同响应来解释。我们的研究揭示了硫输入下 Hg 甲基化的“黑箱”，有助于减少预测土壤中 MeHg 风险的不确定性。
