title: Sublethal effects of multiwalled carbon nanotube exposure in the invertebrate Daphnia magna.
abstract: 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 was to assess the effects of multiwalled carbon nanotube (MWCNT) 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 MWCNTs 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 50% lethal concentration (LC50) of 29.3 (23.6-36.3) mg/L and a 50% effective concentration (EC50) of 6.7 mg/L in the swimming velocity endpoint were determined. When swimming response was nonmonotonic 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. Lowest-observed-effect concentrations for survival and reproduction were 5.4 mg/L and 1.7 mg/L, respectively. Significantly fewer (23.1%) algal cells were consumed in the 3.9-mg/L treatment relative to the control. No significant effects on 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 MWCNTs and other materials expected to be more physically than chemically toxic through mechanisms such as gut clogging.
authors.affiliation: US Army Engineer Research and Development Center, Environmental Laboratory, Vicksburg, Mississippi.
authors.forename: Jacob K
authors.initials: JK
authors.lastname: Stanley
authors.affiliation: US Army Engineer Research and Development Center, Environmental Laboratory, Vicksburg, Mississippi.
authors.forename: Jennifer G
authors.initials: JG
authors.lastname: Laird
authors.affiliation: US Army Engineer Research and Development Center, Environmental Laboratory, Vicksburg, Mississippi.
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Kennedy
authors.affiliation: US Army Engineer Research and Development Center, Environmental Laboratory, Vicksburg, Mississippi.
authors.forename: Jeffery A
authors.initials: JA
authors.lastname: Steevens
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003621:Daphnia / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005247:Feeding Behavior / Q000187:drug effects; D007928:Lethal Dose 50; D037742:Nanotubes, Carbon / Q000633:toxicity*; D019055:No-Observed-Adverse-Effect Level; D012098:Reproduction / Q000187:drug effects; D013550:Swimming; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D037742:Nanotubes, Carbon; D014874:Water Pollutants, Chemical
keywords: Aquatic invertebrate; Aquatic toxicology; Behavioral toxicology; Multiwalled carbon nanotube; Nanoecotoxicology; Natural organic matter