Suppression of mercury methylation in soil and methylmercury accumulation in rice by dissolved organic matter derived from sulfur-rich rape straw

• Published in: Environmental pollution (1987) 2024-04, Vol.346, p.123657-123657, Article 123657
• Main Authors: Zheng, Zhoujuan, Hu, Jie, He, Tianrong, Liu, Chengbin, Zhou, Xian, Yin, Deliang
• Format: Article
• Language: English
• Subjects: bioaccumulation factor; Brassica rapa; Dissolved Organic Matter; glutathione; humification; Mercury; Mercury - analysis; Methylation; Methylmercury Compounds; molecular weight; Oryza; paddies; pollution; Rape straw; Rice; Soil; Soil Pollutants - analysis; straw; Sulfates; sulfur; transportation
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2024.123657

Straw amendment significantly enhances mercury (Hg) methylation and subsequent methylmercury (MeHg) bioaccumulation in Hg-contaminated paddy fields by releasing dissolved organic matter (DOM). This study comprehensively investigates the regulatory mechanisms of DOM and its different molecular weights derived from sulfur-rich rape straw (RaDOM) and composted rape straw (CRaDOM) applied in the rice-filling stage on soil MeHg production and subsequent bioaccumulation in rice grains. The results indicated that the amendment of RaDOM and CRaDOM significantly reduced soil MeHg content by 42.40–62.42%. This reduction can be attributed to several factors, including the suppression of Hg-methylating bacteria in soil, the supply of sulfate from RaDOM and CRaDOM, and the increase in the humification, molecular weight, and humic-like fractions of soil DOM. Additionally, adding RaDOM increased the MeHg bioaccumulation factor in roots by 27.55% while inhibiting MeHg transportation by 12.24% and ultimately reducing MeHg content in grains by 21.24% compared to the control group. Similarly, CRaDOM enhanced MeHg accumulation by 25.19%, suppressed MeHg transportation by 39.65%, and reduced MeHg levels in the grains by 27.94%. The assimilation of sulfate derived from RaDOM and CRaDOM into glutathione may be responsible for the increased retention of MeHg in the roots. Over the three days, there was a significant decrease in soil MeHg content as the molecular weight of RaDOM increased; conversely, altering the molecular weight of CRaDOM demonstrated an inverse trend. However, this pattern was not observed after 12 days. Applying sulfur-rich rape DOM can help mitigate MeHg accumulation in paddy fields by regulating the quality of soil DOM, sulfur cycling, and Hg-methylating bacteria. [Display omitted] •Rape straw-derived DOMs elevate soil DOM humification, molecular weight and humic-like fraction.•Sulfur-rich rape straw-derived DOMs elevate glutathione levels in rice root.•Rape straw-derived DOMs reduce Hg-methylating bacteria and MeHg production in soil.•Rape straw-derived DOMs have the potential to reduce MeHg bioaccumulation in rice grains.