β-cyclocitral and β-ionone are broadly detected as taste and odor compounds during algal bloom events. These compounds are derived from degradation of carotenoids, and can be precursors of disinfection byproducts. β-cyclocitral has fruity odor and its odor threshold is 19,000 ng/L and β-ionone has violets odor with 7 ng/L of odor threshold. These compounds were detected around tens to hundreds of ng/L in waterbody. In this study, we investigated the degradation kinetics and byproducts of β-cyclocitral and β-ionone using UV photolysis and UV/chlorination reactions. UV photolysis and UV-chlorination experiments were conducted with a batch type quartz vial reactor. The initial concentration of odorants was 50 μg/L, and free chlorine concentration was 1 mg/L as Cl<sub>2</sub>. For UV experiment, low pressure UV-A lamp (320 nm) was used and its intensity was 1 mW/cm<sup>2</sup>. During the reactions, the concentrations of β-cyclocitral and β-ionone were measured by headspace SPME-GC/MS method, and the degradation byproducts was identified by purge and trap–GC/MS with the same GC-MS condition used for β-cyclocitral and β-ionone analysis except for scan mode (m/z 40 ~ 250). The degradation kinetics of two odorants under both UV and UV-chlorination showed that UV-chlorination was more effective (90% for β-cyclocitral, and 100% of β-ionone in an hour for UV-chlorination). Since β-ionone has one more double bond, thus is fragile to radical attack, resulting in faster degradation than β-cyclocitral. The degradation byproducts of β-ionone during UV-chlorination reaction were identified using GC-MS. The result showed that β-ionone changes its form to α-ionone and γ-ionone under UV irradiation. In addition, β-cyclocitral, 4,4,7-trimethyl-2,3-dihydro-1H-naphthalene (ionene), 1-cyclohexene-1-carboxaldehyde, decanal, and 4a,6,7-trimethyl-3,4,4a,5,8,8a-hexahydro-1(2H)-naphthalenone were identified as the byproducts of β-ionone during UV-chlorination reaction, indicating that two carbon-carbon double bond of β-ionone is a reactive site forming these byproducts.

Degradation mechanisms of algal odorants of β-cyclocitral and β-ionone during UV photolysis and UV/chlorination reactions

253rd National Meeting (2017)

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