Determination of phenolic concentrations in dissolved organic matter pre-concentrate using solid phase extraction from natural water

The concentrations of phenolic moieties in dissolved organic matter pre-concentrated by solid phase extraction (SPE-DOM) from river water and seawater were determined using the Folin–Ciocalteu phenol reagent. Samples were taken from four rivers in the Hiroshima Prefecture of western Japan, and the Seto-Inland Sea. Phenolic concentrations in river samples increased with increasing dissolved organic carbon (DOC) concentrations. In river water, the phenolic concentrations per unit of carbon in SPE-DOM were in the range of 0.48–1.91 mol kg−1-C. In seawater samples, relationships between phenolic and DOC concentrations were not clear, and the phenolic concentrations per unit of carbon were in the range of 0.07–0.76 mol kg−1-C. In Osaka Bay, which is a typical enclosed urban coastal area with a large river, phenolic concentrations in the surface seawater collected near the river mouth were higher than those at offshore points. A river water–seawater end-member conservative mixing model indicated that phenolic moieties of DOM in Osaka Bay are characterized by a “net loss” during mixing in the bay. To understand their characteristic behaviors, the photochemical and biological effects on the variation of phenolic concentrations in DOM were investigated.