Determination of Hydroxyl Radical Photoproduction Rates in Natural Waters

Abstract

The photochemical formation rates of hydroxyl radicals (OH radicals) in river water and seawater were determined by a simple, rapid and sensitive benzene probe method, in which phenol formed by the reaction between benzene and photochemically-generated OH radicals was analyzed by on-line preconcentration HPLC. The OH radical formation rates from well-known OH radical sources, such as nitrate, nitrite and hydrogen peroxide, were in good agreement with those reported previously. River water samples containing high concentrations of nitrate and nitrite were found to show high OH radical formation rates. Ten to 80% of the OH radical formation in river water and seawater was due to the photolysis of nitrate and nitrite, but OH radical formation from hydrogen peroxide was negligible. The OH radical formation from unknown sources other than nitrate, nitrite and hydrogen peroxide was strongly correlated to the amount of fluorescent matter.

Effect of dissolved organic compounds on the photodegradation of the herbicide MCPA in aqueous solution

“…Phenol could be a model for the antioxidants present in the pool of surface-water dissolved organic matter, and its presence would decrease Φ MCPA by up to 40% (Figure 3). A concentration of 0.30 mM phenol would correspond to a dissolved organic carbon (DOC) content of over 20 mg C L −1 , while the DOC values of surface waters are often lower (Takeda et al, 2004). However, Chiron et al (2007) have observed a ratio of the MCPA photodegradation rate (R MCPA ) in river compared to ultra-pure water of about 0.5, while the corresponding ratio of the photon fluxes absorbed by MCPA in the two systems was 0.7.…”

Pesticide behavior in modified water-sediment systems

“…29,30,56) Through the photolysis of benzene derivatives as probe molecules, it was found in the ·OH production that the relative contribution of NO 2 − and NO 3 − highly depended on the river water quality 35) and that CDOM dominantly participated via H 2 O 2 -independent mechanism. 35,57) Some ionic species of metal hydroxides, such as [Fe(OH)] 2+ , participated in the photo-induced Fenton reaction producing ·OH. 13) Ferrous/ferric ions in montmorillonite could produce ·OH under illumination, showing the importance of clay minerals for indirect photolysis, 58) but its contribution may be lessened by the light scattering effect.…”

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

“…F b in Seto Inland Sea seawater samples was reported to be 0.68 [8]. For the purpose of calculating R OH in (1), the values for Y p and F b were used accordingly.…”

“…These include H 2 O 2 [3,4], hydrated electrons [5], superoxide ion [6] organo peroxyl radicals [7], hydroxyl radicals [1, 2,8] and nitric oxide radicals [9][10][11] These species are reactive and play important roles in chemical and biological processes in aquatic environments, such as photochemical degradation of natural organic matter and organic pollutants, redox reactions and biological reactions [12][13][14]. Among the reactive species that can be photochemically generated in natural waters, hydroxyl radicals play an important role because of the elevated reaction rate constants towards a very wide variety of organic and inorganic compounds [15].…”

“…However, the reactions of •OH with Cl -, Br -, HCO 3 -and DOM have been identified as the possible pathways for •OH loss in natural waters [1]. Due to the high reactivity and short lifetime, the steady state concentrations of •OH in natural waters are generally very low and thus it is difficult to monitor directly [8]. Based on this, the photochemical formation rates of •OH are determined by indirect methods using probe compounds to scavenge the •OH produced.…”