[A-HW20] Hydrology & Water Environment

[AHW20-13] Measurement of reactive oxygen species (ROS) and fluorescent organic matter in selected rivers in Hiroshima Prefecture, Japan.

*Taiwo Tolulope Ayeni¹, Takashi Umeda¹, Yoko Iwamoto¹, Kazuhiko Takeda¹, Hiroshi M. G. Sakugawa¹, Khan M. G. Mostofa² (1.Hiroshima University Japan, 2.Tianjin University, China)

Keywords:hydroxyl radical, nitric oxide radical, singlet oxygen, dissolved organic matter, PARAFAC, river water

The incidence of solar irradiation on natural water surfaces could excite their inorganic or organic components to produce some transitory species otherwise called reactive oxygen species (ROS) such as hydroxyl radical (•OH), nitric oxide radical (NO•) and singlet oxygen (¹O₂). These species could facilitate the photochemical degradation of natural organic matter or pollutants and also partake in some biological or redox reactions. Recent comprehensive study on Japanese rivers reveals that nitrite was the major source of •OH and NO• while ¹O₂ was predominantly sourced from Chromophoric dissolved organic matter (CDOM). In the present study, the photogeneration of these three ROS and investigation of their dissolved organic components were carried out across 23 stations in four rivers (Niko, Seno, Kurose, and Nuta) located in the Hiroshima Prefecture of Japan during the winter of 2020. Analysis involving dissolved organic carbon (DOC), absorption properties, and ions were carried out using TOC-V_CSH analyzer, UV-Visible spectrophotometer, and Ion chromatography, respectively. Parallel factor analysis (PARAFAC) modelling was employed in identifying the DOM components of the rivers. The photogeneration rates of the ROS were determined by means of established HPLC methods. The DOC values across the rivers ranged from the low of 34.7 µM C in the Nuta river to the high of 259 µM C in the Kurose river. The absorption coefficient at 300 nm (a₃₀₀), which is a measure of CDOM abundance and the concentration of inorganic nitrite also followed the same pattern as that of the DOC and were within the ranges of (1.61 to 9.06) m^–1 and (0.07 and 17.9) µM, respectively. The ROS values ranged from (12.4 – 392) × 10 ^–12 M s ^–1 for •OH, (4.17 – 1050) × 10 ^–12 M s ^–1 for NO• and (4.66 – 32.4) × 10 ^–9 M s ^–1 for ¹O₂ and were also minimum in the Nuta river and maximum in the Kurose river. Humic-like and tryptophan-like components were the predominant organic matter across the rivers, however fluorescent whitening agent was observed in some stations of the rivers.