Persistence and distribution of 4-nonylphenol following repeated application to littoral enclosures

The persistence and distribution of Lt-nonylphenol (NP) were monitored for 440 d, following application to 18 littoral enclosures (4 x 7-8 m), situate d in a 2-ha mesotrophic pond near Duluth, Minnesota. Application was accomp lished by subsurface, gravity-fed injection over a 20-d period, with a 2-d frequency, to achieve nominal aqueous concentrations of 0, 3, 30, 100, and 300 mu g/L. Mean maximum concentrations in the water over the 20-d applicat ion period ranged from 75.7 to 81.0% of nominal for the three highest treat ment levels and was 181% of nominal at the lowest treatment level. Water wa s the major compartment, on a mass balance basis, for NP until 2 to 4 d aft er the application period, with a mean time to 50% dissipation (DT50) of 0. 74 d and a mean time to 95% dissipation (DT95) of 13.8 d. 4-Nonylphenol par titioned to enclosure wall material, macrophytes, and sediment within 2 d o f initial application. Macrophytes accumulated maximum NP concentrations of 11.5 and 139 mg/kg 1 to 2 d after the application period at the 30- and 30 0-mu g/L treatment levels, respectively. Mean DT50 and DT95 estimates of NP persistence in/on the macrophytes were 10.3 and 189 d, respectively. Sedim ent from the 30- and 300-mu g/L treatments accumulated maximum dry weight N P concentrations of 2.74 and 27.4 mg/kg, respectively within 20 to 48 d of the first application. The mean sediment porewater NP concentration was 18. 6 mu g/L for the period 2 to 34 d after application 1 at the 300-mu g/L tre atment. The sediment was the primary sink for NP 440 d after the initial ap plication with a concentration of 1.97 mg/kg at the 300-mu g/L treatment. M ean sediment DT50 and DT95 values were 66.0 and 401 d, respectively, indica ting a long-term persistence of NP. Ecocores collected 1 d after the final NP application did not show significant decreases in sediment NP concentrat ion during a 55-d incubation period, corroborating the NP persistence obser ved in the littoral enclosures.