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

The persistence and distribution of 4‐nonylphenol (NP) were monitored for 440 d, following application to 18 littoral enclosures (4 × 7–8 m), situated in a 2‐ha mesotrophic pond near Duluth, Minnesota. Application was accomplished 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 μg/L. Mean maximum concentrations in the water over the 20‐d application period ranged from 75.7 to 81.0% of nominal for the three highest treatment levels and was 181% of nominal at the lowest treatment level. Water was the major compartment, on a mass balance basis, for NP until 2 to 4 d after 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 partitioned to enclosure wall material, macrophytes, and sediment within 2 d of 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 300‐μg/L treatment levels, respectively. Mean DT50 and DT95 estimates of NP persistence in/on the macrophytes were 10.3 and 189 d, respectively. Sediment from the 30‐ and 300‐μg/L treatments accumulated maximum dry weight NP 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 μg/L for the period 2 to 34 d after application 1 at the 300‐μg/L treatment. The sediment was the primary sink for NP 440 d after the initial application with a concentration of 1.97 mg/kg at the 300‐μg/L treatment. Mean sediment DT50 and DT95 values were 66.0 and 401 d, respectively, indicating a long‐term persistence of NP. Ecocores collected 1 d after the final NP application did not show significant decreases in sediment NP concentration during a 55‐d incubation period, corroborating the NP persistence observed in the littoral enclosures.