Determination of Hydroxyl Radical in Seto Inland Sea and its Potential to Degrade Irgarol

Abstract

Photo-production rates and overall scavenging rate constants of the highly reactive hydroxyl radicals (•OH) were measured by irradiation of surface seawater samples collected from the Seto Inland Sea, Japan. Photo-production rates of •OH ranged from 7.2 × 10-12 M s-1 to 424 × 1012 M s-1 and scavenging rate constants were 1.3 – 4.1×106 s -1 . The steady state concentrations of •OH in seawater, which were calculated from the photo-production rates and scavenging rate constants were in the range 2.6 –189 × 10-18 M. Estimation from the scavenging rate constant showed that the lifetime of •OH in seawater ranged from 0.29 ×10-6 s to 0.55 ×10-6 s. Nitrates and hydrogen peroxide contributions to OH radical formation rates were negligible in the samples studied. However, direct photolysis of NO2 - accounted for up to 73% of the observed •OH formation rates. The rate constant for the reaction •OH with irgarol was found to be (9.7 ± 0.52) × 109 M - 1 s -1. Based on the steady state concentration of •OH, the calculated half-lives for Irgarol due to the reaction with hydroxyl radicals in the Seto Inland Sea were in the range 4.3-318 days