John Wiley & Sons, Ltd.

Sublethal effects of multi‐walled carbon nanotube exposure in the invertebrate Daphnia magna

Carbon nanotubes were previously demonstrated to accumulate on the carapace and in the gut of daphnids in aquatic exposures. The purpose of the present study is to assess the effects of multi‐walled carbon nanotube (MWNT) exposure on the sublethal Daphnia magna endpoints swimming behavior, algal feeding, growth, and reproduction and to determine the relative magnitude of difference between lethal and sublethal toxicity thresholds in 48‐h and 14‐d exposures. A stable dispersion of MWNTs was prepared using 100 mg/L natural organic matter (NOM), and all treatments were compared statistically to a NOM control. The swimming behavior endpoints of mean velocity and total distance moved were determined using digital tracking software. For the acute (48‐h) exposure, a LC50 of 29.3 (23.6 ‐ 36.3) mg/L and an EC50 of 6.7 mg/L in the swimming velocity endpoint were determined. While swimming response was non‐monotonic below 2 mg/L, consistent reductions in velocity were observed at 6.9 mg/L and above. Median effect concentrations were lower in the chronic (14‐d) bioassay. The 14‐d LC50 was 4.3 mg/L (3.3 ‐ 5.6 mg/L), and the reproduction EC50 was 5.0 mg/L. LOECs for survival and reproduction were 5.4 and 1.7 mg/L, respectively. Significantly less (23.1% less) algal cells were consumed in the 3.9 mg/L treatment relative to the control. No significant effects to swimming behavior were observed for the 14‐d bioassay. Less traditional sublethal endpoints such as swimming behavior and feeding rate may be especially important to assess for MWNTs and other materials expected to be more physically than chemically toxic through mechanisms such as gut clogging. This article is protected by copyright. All rights reserved

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