Effects of 4-nonylphenol on benthic macroinvertebrates and insect emergence in littoral enclosures

The effect of 4‐nonylphenol (NP) on benthic, freshwater macroinvertebrates in littoral enclosures was evaluated over a 2‐year period. Enclosures received 11 NP applications, 48 h apart, with nominal rates of 3, 30, 100, and 300 μg/L. Mean measured peak concentrations in integrated water column samples over the 20‐d application period were 5 ± 4, 23 ± 11, 76 ± 21, and 243 ± 41 μg/L NP. Concentrations of NP in the water column decreased rapidly after the last application. Maximum NP concentrations measured in sediments, pore water, and macrophytes of a 300‐μg/L enclosure were 27.4 mg/kg, 29.9 μg/L, and 89.6 mg/kg, respectively. The most abundant macroinvertebrate groups, Chironomidae, Oligochaeta, and Mollusca, decreased in abundance after application. Effects on Mollusca were the most severe. Their numbers were significantly reduced at the highest treatment (243 ± 41 μg/L NP) throughout most of the study. Oligochaetes (Naididae, Tubificidae) and chironomids (Tanytarsini, Chironomini) were also significantly reduced at the highest treatment, but populations recovered within 6 weeks. Snails and naidid oligochaetes were slightly affected at the second highest treatment (76 ± 21 μg/L NP). Insect emergence was reduced during and immediately postapplication, but the effects were likely caused or compounded by a surfactant sheen on the surface of the water that interfered with emergence and/or oviposition. The observed effects on the benthic community were most likely due to exposure from the water, although more persistent macrophyte‐associated residues may have contributed to effects on Gastropoda, Naididae, and Tanytarsini. Macrophyte‐associated NP residues may pose a small risk to benthic organisms, but it is probably minor compared to water exposures. The no‐observed and lowest‐observed‐effect concentration for the benthic community was 23 ± 11 and 76 ± 21 mg/L NP, respectively.