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Abstract-The effects of 4-nonylphenol (NP) on freshwater zooplankton were evaluated in 18 littoral enclosure mesocosms in northeastern Minnesota. The 18 enclosures were allocated to three blocks of six units with each block including two untreated control enclosures and one enclosure for each of four NP treatments (3, 30, 100, and 300 g/L). Treated enclosures received 11 applications of NP over a 20-d period between July 8 and 28, 1993. Maximum NP concentrations measured in the water column 2 h after each application averaged (ϮSD) 5 Ϯ 4, 23 Ϯ 11, 76 Ϯ 21, and 243 Ϯ 41 g/L over the 11 applications. Nonylphenol dissipated rapidly from the water column but was more persistent in sediments and in/on macrophytes. All cladoceran and copepod taxa were significantly reduced in abundance at 243 Ϯ 41 g/L; some sensitive taxa were also affected at 76 Ϯ 21 and 23 Ϯ 11 g/L. While many rotifer taxa were unaffected at any of the test concentrations, several were affected at Ն76 Ϯ 21 g/L. Ostracods were only affected at 243 Ϯ 41 g/L. No zooplankton taxon was affected at 5 Ϯ 4 g/L. The period of maximum impact usually occurred within 1 to 7 d of the last NP application, and recovery to control abundance levels generally occurred within 7 to 28 d of the last NP application. Two sensitive taxa, Acroperus and Calanoida, did not recover at Ն76 Ϯ 21 g/L by the end of the study. The maximum acceptable toxicant concentration for protection of all zooplankton taxa was estimated at ϳ10 g/L, although overall community diversity was unaffected at 23 Ϯ 11. The water was the most probable route of NP exposure, but the greater persistence of NP residues in/on macropyhtes may have contributed to the lack of recovery of some macrophyte-associated taxa.

Abstract-The persistence and distribution of 4-nonylphenol (NP) were monitored for 440 d, following application to 18 littoral enclosures (4 ϫ 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 g/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)

No abstract

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.