Abstract

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 predictingMeHg risk. To address that, we explored the effects of different types and amounts of sulfur aswell as concentrations of ambient sulfate on Hgmethylation 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(-1) elemental sulfur, ammonium sulfate, sulfur-coated urea and potassium sulfate (K2SO4)) and different amounts (i.e., 100, 200 and 400 mg kg(-1) K2SO4) of sulfur input. The enhanced MeHg production could be explained by increased Hgmobility but not changes in microbial Hg methylators. Besides, sulfate input increased MeHg levels (89-240%) in soils with low ambient sulfate levels (<100mg kg(-1)) but had no effect on high-sulfate soils (>380mg kg(-1)). 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. (C) 2021 Elsevier B.V. All rights reserved.

Keywords

Methylmercury; microbial methylators; mobility; sulfate; fertilization

Published in

Science of the Total Environment
2021, volume: 778, article number: 146325
Publisher: ELSEVIER

Authors' information