NDMA formation during ozonation of metformin: Roles of ozone and hydroxyl radicals

Xiaobin Liao; Linlu Shen; Zhibin Jiang; Menglan Gao; Yu Qiu; Huan Qi; Chao Chen

doi:10.1016/j.scitotenv.2021.149010

NDMA formation during ozonation of metformin: Roles of ozone and hydroxyl radicals

Sci Total Environ. 2021 Nov 20:796:149010. doi: 10.1016/j.scitotenv.2021.149010. Epub 2021 Jul 13.

Authors

Xiaobin Liao¹, Linlu Shen², Zhibin Jiang³, Menglan Gao³, Yu Qiu⁴, Huan Qi⁵, Chao Chen⁶

Affiliations

¹ Institute of Municipal and Environmental Engineering, College of Civil Engineering, Huaqiao University, Fujian 361021, China. Electronic address: liaoxb@hqu.edu.cn.
² Institute of Municipal and Environmental Engineering, College of Civil Engineering, Huaqiao University, Fujian 361021, China; State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 195000, China.
³ Institute of Municipal and Environmental Engineering, College of Civil Engineering, Huaqiao University, Fujian 361021, China.
⁴ State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
⁵ College of Textiles and Apparel, Quanzhou Normal University, Fujian 362002, China.
⁶ State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China. Electronic address: chen_water@tsinghua.edu.cn.

PMID: 34280626
DOI: 10.1016/j.scitotenv.2021.149010

Abstract

Metformin, a high-consumed pharmaceutical for diabetes, has been reported to generate carcinogenic nitroso-dimethylamine (NDMA) during treatment of its containing wastewater. However, whether it would produce NDMA during ozonation or not is unclear, let alone discriminate roles of ozone (O₃) and hydroxyl radicals (OH). In this paper, effects of ozonation on NDMA formation from metformin were investigated, roles of O₃ and OH were also distinguished by adding tert-butyl alcohol (tBA) as OH scavenger. Moreover, various influencing factors and reaction mechanisms were demonstrated. The results indicated that NDMA could be directly formed from metformin during ozonation, the addition of OH scavenger significantly enhanced its formation (0-46.2 ng/L vs 0-139.1 ng/L). The formation of NDMA by O₃ and OH was more affected by bromide and HCO₃^- than those with only O₃; while the impacts of pH and sulphate on the latter were more notable. No matter without/with tBA in the solution, the formed NDMA during ozonation of metformin increased with raising pH (from 5 to 9) and achieved the maximum 69.6 ng/L and 235.9 ng/L at pH 9, respectively; small amount of bromide (0.1 μM) promoted NDMA production, high levels of bromide (10 μM) inhibited its formation; the existence of HCO₃^- enhanced the amounts of NDMA from 44.5 to 73.5 ng/L (raised by 65.2%) by O₃ and OH and from 102.9 to 130 ng/L with only O₃ (raised by 26.3%); with the addition of sulphate, NDMA concentration raised by 43.8% by O₃ and OH, while the value was high up to 134.6% with only O₃. Based on the result of UPLC-Q-TOF and density functional theory, the oxidation intermediates were identified and possible transformation pathways of metformin during ozonation were proposed. The findings in this paper would provide reference when treating metformin-containing water in future.

Keywords: Hydroxyl radical scavengers; Metformin; NDMA; Ozonation.

MeSH terms

Dimethylnitrosamine
Hydroxyl Radical
Metformin*
Oxidation-Reduction
Ozone*
Water Pollutants, Chemical* / analysis
Water Purification*

Substances

Water Pollutants, Chemical
Hydroxyl Radical
Ozone
Metformin
Dimethylnitrosamine