Journal of Oceanography, Vol. 61 (No. 3), pp. 561-568, 2005
Takemitsu Arakaki1*, Hiroyuki Fujimura1, Asha Mansour Hamdun1, Kouichirou Okada1, Hiroaki Kondo1, Tamotsu Oomori1, Akira Tanahara2 and Hatsuo Taira1
1Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Senbaru, Nishihara-cho, Okinawa 903-0213, Japan
2Instrument Research Center, University of the Ryukyus, Senbaru, Nishihara-cho, Okinawa 903-0213, Japan
(Received 12 September 2003; in revised form 8 April 2004; accepted 15 April 2004)
Abstract: The northern part of Okinawa Island suffers from red soil pollutionrunoff of red soil into coastal seawaterwhich damages coastal ecosystems and scenery. To elucidate the impacts of red soil pollution on the oxidizing power of seawater, hydrogen peroxide (HOOH) and iron species including Fe(II) and total iron (Fe(tot), defined as the sum of Fe(II) and Fe(III)) were measured simultaneously in seawater from Taira Bay (red-soil-polluted sea) and Sesoko Island (unpolluted sea), off the northern part of Okinawa Island, Japan. We performed simultaneous measurements of HOOH and Fe(II) because the reaction between HOOH and Fe(II) forms hydroxyl radical (OH), the most potent environmental oxidant. Gas-phase HOOH concentrations were also measured to better understand the sources of HOOH in seawater. Both HOOH and Fe(II) in seawater showed a clear diurnal variation, i.e. higher in the daytime and lower at night, while Fe(tot) concentrations were relatively constant throughout the sampling period. Fe(II) and Fe(tot) concentrations were approximately 58% and 19% higher in red-soil-polluted seawater than in unpolluted seawater. Gas-phase HOOH and seawater HOOH concentrations were comparable at both sampling sites, ranging from 1.4 to 5.4 ppbv in air and 30 to 160 nM in seawater. Since Fe(II) concentrations were higher in red-soil-polluted seawater while concentrations of HOOH were similar, OH would form faster in red-soil-polluted seawater than in unpolluted seawater. Since the major scavenger of OH, Br-, is expected to have similar concentrations at both sites, red-soil-polluted seawater is expected to have higher steady-state OH concentrations.