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The use of carbon-based nanomaterials (CNMs) such as multiwalled carbon nanotubes (MWCNTs), graphene, and graphene oxide (GO) is increasing across many applications because of their unique and versatile properties. These CNMs may enter the aquatic environment through many pathways, creating the potential for organism exposure. The present study addresses the bioaccumulation and toxicity seen in Daphnia magna exposed to CNMs dispersed in sodium dodecyl benzene sulfonate (SDBS). In study I, D. magna were exposed to varying outer diameters of MWCNTs for 24 h in moderately hard or hard freshwater. Bioaccumulation of MWCNT was found in all treatments, with the highest concentrations (0.53 ± 0.27 μg/g) in D. magna exposed in hard freshwater (p < 0.005). The median lethal concentration (LC50) was determined for D. magna exposed to CNMs in moderately hard and hard freshwater. In study II, D. magna were exposed to CNMs for 72 h in moderately hard freshwater to assess swimming velocity and generation of reactive oxygen species (ROS) detected by dichlorofluorescein fluorescence. An overall decrease was seen in D. magna swimming velocity after exposure to CNMs. The generation of ROS was significantly higher (1.54 ± 0.38 dichlorofluorescein mM/mg dry wt) in D. magna exposed to MWCNTs of smaller outer diameters than in controls after 72 h (p < 0.05). These results suggest that further investigation of CNM toxicity and behavior in the aquatic environment is needed. Environ Toxicol Chem 2017;36:2199-2204. © 2017 SETAC.

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Single-wall carbon nanotubes (SWNTs) are projected to increase in usage across many industries. Two studies were conducted using Zea L. (corn) seeds exposed to SWNT spiked soil for 40 d. In Study 1, corn was exposed to various SWNT concentrations (0, 10, and 100 mg/kg) with different functionalities (non-functionalized, OH-functionalized, or surfactant stabilized). A microwave induced heating method was used to determine SWNTs accumulated mostly in roots (0-24 μg/g), with minimal accumulation in stems and leaves (2-10 μg/g) with a limit of detection at 0.1 μg/g. Uptake was not functional group dependent. In Study 2, corn was exposed to 10 mg/kg SWNTs (non-functionalized or COOH-functionalized) under optimally grown or water deficit conditions. Plant physiological stress was determined by the measurement of photosynthetic rate throughout Study 2. No significant differences were seen between control and SWNT treatments. Considering the amount of SWNTs accumulated in corn roots, further studies are needed to address the potential for SWNTs to enter root crop species (i.e., carrots), which could present a significant pathway for human dietary exposure.

Fatty acid methyl ester (FAME) profiling for characterizing microbial community composition typically is conducted via phospholipid fatty acid (PLFA) or ester‐linked fatty acid methyl ester (EL‐FAME) methods. As soil health assessments aim to be utilized across the nation and globe, the robust measurement and interpretation of microbial communities across a range of soils and environments will be necessary. This study compared PLFA and EL‐FAME methods for detecting and interpreting profiles of microbial community composition in croplands across a wide geographic area using a total of 172 soil samples from 14 states representing a wide range of soil properties. Overall, PLFA and EL‐FAME provided comparable biomarkers in terms of microbial community composition. The Spearman's Rank correlation test showed positive correlations (r = 0.37–0.71) between PLFA and EL‐FAME methods for absolute abundance of total FAME and individual microbial groups including fungi (saprophytic fungi [SF], arbuscular mycorrhizal fungi [AMF], and general fungi [F]) and all bacterial groups (Gram positive [GMP], Gram negative [GMN], and Actinobacteria). In both methods, a common set of fatty acids were influential in differentiating samples. The main differences in biomarker abundances between the two methods were that fungal and Actinobacteria biomarkers (e.g., 16:1ω5c [AMF], 18:1ω9c [F], 18:3ω6c [F], and 10Me16:0 [Actinobacteria]) were more abundant or critical in EL‐FAME profiling (large variation among soil samples and sensitive to soil properties), but bacterial biomarkers such as i15:0 (GMP), 16:1ω7c (GMN), 18:1ω7c (GMN), and cy19:0ω7c (GMN) were more dominant and responsive to soil properties in PLFA profiling. The practical advantages of EL‐FAME are lower cost and simpler methodology. Although both methods produced similar microbial profile abundances for important microbial markers, PLFA was more sensitive to the wide range of soil chemical properties in this sample set including pH, clay content, soil organic matter, and active carbon.

The increase in use of nanomaterials such as multiwalled carbon nanotubes (MWCNTs) presents a need to study their interactions with the environment. Trophic transfer was measured between Daphnia magna and Pimephales promelas (fathead minnow, FHM) exposed to MWCNTs with different outer diameter (OD) sizes (MWCNT1 = 8-15 nm OD and MWCNT2 = 20-30 nm OD) in the presence and absence of copper. Pristine FHM were fed D. magna, previously exposed for 3 d to MWCNT1 or MWCNT2 (0.1 mg/L) and copper (0.01 mg/L), for 7 d. D. magna bioaccumulated less MWCNT1 (0.02 μg/g) than MWCNT2 (0.06 μg/g), whereas FHM accumulated more MWCNT1 (0.81 μg/g) than MWCNT2 (0.04 μg/g). In the presence of copper, MWCNT bioaccumulation showed an opposite trend. Mostly MWCNT1 (0.03 μg/g) bioaccumulated in D. magna, however less MWCNT1 (0.21 μg/g) than MWCNT2 (0.32 μg/g) bioaccumulated in FHM. Bioaccumulation factors were higher for MWCNT1s than MWCNT2. However, an opposite trend was observed when copper was added. Plasma metallothionein-2 was measured among treatments; however concentrations were not statistically different from the control. This study demonstrates that trophic transfer of MWCNTs is possible in the aquatic environment and further exploration with mixtures can strengthen the understanding of MWCNT environmental behavior.