Photochemical fate of nonionic polyacrylamide induced by hydroxyl radicals in the natural water: Mineralization mechanism exploration and half-life time evaluation

• Published in: The Science of the total environment Vol. 947; p. 174485
• Main Authors: Jia, Daqing, Therias, Sandrine, Voelker, François, Kieffer, Johann, Favero, Cédrick, Mailhot, Gilles
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-10-2024; Elsevier
• Subjects: Chemical Sciences; Environmental fate; Half-life time; Hydroxyl radical; Polyacrylamide; UV irradiation; Environmental fate; UV irradiation; Polyacrylamide; Hydroxyl radical; Half-life time
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.174485

Water-soluble polyacrylamide (PAM) compounds have been used extensively in various sectors. The abundance of PAM in the environment raises concerns about its environmental impact. However, the mineralization of PAM in water under natural light irradiation remains insufficiently explored. This study utilizes nonionic PAM (nPAM) as a representative model to investigate both the mechanism and efficiency of nPAM degradation in water when exposed to ultraviolet (UV) light with hydrogen peroxide (H2O2) as the hydroxyl radical source. In the dark or with only UVA irradiation, negligible mineralization of nPAM occurred. In contrast, the presence of hydroxyl radicals (produced by the UVA/H2O2 system) produced 50 % nPAM mineralization over 7 days under our experimental conditions. The corresponding molecular weight (MW) of the nPAM was swiftly reduced from 1.58 ×106 Da to 1.59 ×103 Da in 3 days. Moreover, five carboxylic acids and nitrate ions were identified as the photodegradation intermediates of nPAM. The efficiencies of nPAM photodegradation by the UVA/H2O2 system in different natural waters and environmental conditions were assessed. The rate constant for the reaction between the hydroxyl radical and nPAM was 2.17 ×109 M-unit−1 s−1. The half-lives of nPAM in the sea and continental surface waters were determined to be several years and dozens of days, respectively. The application of UVB obviously accelerated the mineralization of nPAM in ultrapure water (71 % degradation in 7 days). Moreover, mineralization of concentrated nPAM (200 mg/L) in sea water was more efficient when both UVA- and UVB-activated H2O2 were used. Additionally, toxic acrylamide was not generated during nPAM photodegradation. Moreover, the photodegradation intermediates from nPAM were found to be neither acutely nor chronically toxic to aquatic organisms. This comprehensive study sheds light on the photochemical fate of nPAM in natural waters and provides essential insight for practical treatment of PAM in water systems.
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•Degradation and mineralization of nPAM with UVA/H2O2 was evaluated.•Nitrate and five carboxylic acids were identified as nPAM photodegradation products.•The half-lives of nPAM in various natural waters were evaluated.•nPAM photodegradation efficiencies with UVA or UVB/H2O2 were probed in sea water.•Acrylamide formation was not observed during nPAM photodegradation.