Effects of Repeated Exposure to 4-Nonylphenol on the Zooplankton Community in Littoral Enclosures

Abstract

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.

Effects of nonylphenol on zooplankton in aquatic microcosms

“…One study reported significantly lower offspring survival of D. magna at a concentration of 39 g/L [14], which is similar to concentrations in this study at which abundances of Cladocerans were affected. The sensitivity of rotifer taxa differed between our study and that of O'Halloran et al [17]. Polyarthra abundances were not affected in the latter, whereas it was the second-mostsensitive taxon after Synchaeta spp.…”

“…Only one field study has so far investigated the effects of NP on complex zooplankton assemblages. A NP stock solution was added directly and repeatedly to the water of littoral enclosures, resulting in large variations of NP concentrations [17]. In our study, we added NP via controlled release to achieve a slow increase and more constant concentrations over a period of time.…”

Effects of 4‐nonylphenol on phytoplankton and periphyton in aquatic microcosms

“…Effects were apparent during the six-week treatment period as well as the six-week postapplication period, when NP concentrations were below detection limits. The recovery period found by O'Halloran [3] for zooplankton was one to four weeks. However, continuous exposure to NP, as simulated in this study, which occurs at sites receiving industrial and municipal effluents, might prevent recovery over a much longer time.…”

“…We found no effects of NP on species richness, diversity, and assemblage composition of periphyton. O'Halloran [3] suggested that periphyton growth might have been indirectly affected by a reduction in grazer numbers. We found that A. minutissimum, which is common in the presence of grazers, was dominating the assemblages in the controls and at higher NP concentrations during the treatment period but was less abundant at intermediate concentrations.…”

Nonylphenol, an Integrated Vision of a Pollutant

“…For example, after 20 days of exposure to NP at concentrations from 76 to 243 µg L-1, recovery generally appeared after 1-4 weeks; however, beyond 20 days of exposure, recovery may not take place [89]. In addition, there is evidence of transgenerational effects of NP on oysters, where offspring from oysters previously grown in the presence of NP for 8 days at the larval stage, showed lower survival rates and poorer embryonic and larval development compared to those oysters that were never exposed [53].…”