Abstract
The abiotic removal (i. e., flocculation and photolysis) of alkylphenols (i. e., nonylphenol (NP) and octylphenol (OP)) from the estuarine environment was studied by investigating the environmental distributions of these compounds in the Tamagawa river, Japan and the photoinduced decrease in their concentration in water and on the tidal flat. The concentrations of NP and OP in the dissolved from (<0.7μm) as well as in the ‘total’ (dissolved and particulate form) form decreased by 50% in the upper part of the inter tidal zone (salinity : 0-7‰). The ‘mixing experiment’ in which river water (salinity : 0‰) was mixed with seawater (salinity : 31.3‰) at various rates revealed an almost linear inverse relationship between total-NP and -OP concentrations and water salinity. These results suggest that alkylphenols are removed from the water column through a process other than flocculation. Irradiated for 8 hours using a solar simulator, the concentration of NP and OP dissolved in 1 mg·l-1 humic acid solution decreased significantly (-50%), whereas those in distilled water behaved more conservatively, this suggests that the photolytic decomposition of NP and OP can occur in natural waters. Although small, but significant amounts of alkylphenols were removed from a river sediment after a 6-hour exposure to sunlight, the anoxic production of NP and OP from their precursors in the sediment was revealed to be a far more important process than the photolytic decomposition.
