Dissolved organic iodine in marine waters: role in the estuarine geochemistry of iodine

Non-volatile dissolved organic iodine (DOI) can be a major, or even the dom inant, species of dissolved I in coastal, inshore and estuarine waters. It can be converted to IO3- in the presence of an oxidizing agent and to I- by reacting it with a reducing agent. Depending on the exact experimental con ditions, the yields of these reactions may not be quantitative. In previous analytical schemes for the determination of IO3-, I- and DOI in marine wat ers, if oxidation or reduction steps are involved and the concentrations of one or more species are estimated by difference, the presence of DOI can l ead to an overestimation of the concentrations of the inorganic species det ermined by difference and an underestimation of the concentration of DOI. I n two cruises covering the James River to the southern Chesapeake Bay and f rom the southern Chesapeake Bay to the Atlantic, above a salinity (S) of 2, the contribution of DOI to total I increased with decreasing salinity and reached a maximum of 80%. DOI, I- and IO3- were successively the dominant f orm of dissolved I at 0.1 < S < 15 in the James River estuary, 15 < S < 30 in the Southern Chesapeake Bay and S > 30 in the Atlantic Ocean at the Bay mouth, respectively. Total I behaved conservatively (i.e., no evidence of c onsumption or production) during estuarine mixing during both cruises. In t he southern Chesapeake Bay, total inorganic I was also approximately conser vative. The primary process affecting the speciation of dissolved I was the conversion of IO3- to I-. In the James River estuary, there were indicatio ns of the conversion of both IO3- and I- to DOI. The concentrations of tota l I, IO3-, I- and DOI in James River water were 0.121, undetectable, 0.068 and 0.053 muM, respectively. These concentrations of total I and I- are sig nificantly higher while that of IO3- is noticeably lower than those used pr esently for estimating global riverine input of these I species to the ocea ns. The riverine flux of DOI to the oceans is presently unknown.