Effects of fullerenes and functionalized fullerenes on Daphnia magna: Behavioral responses and interactions of functionalized fullerene with hydrophobic organic contaminants



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Nanotechnology is a growing industry that utilizes nano-sized materials. In recent years, manufactured nanoparticles have been introduced into many consumer products as a result of unique properties related to their size. Due to the wide range of potential uses, it is likely that carbon nanomaterials will be found in the aquatic environment. However, the environmental risks of nanotechnology in aquatic systems are relatively unknown. This research evaluates potential effects of fullerenes (C60) and functionalized fullerenes ((1,2-methanofullerene C60)-61-carboxylic acid) (fC60) on the aquatic invertebrate Daphnia magna. One proposed use of carbon nanomaterials, especially functionalized nanomaterials, is in agricultural production as smart delivery systems and nanosensors. Due to this proposed use, the potential exists for fullerene and agricultural chemicals to co-occur as contaminants in the aquatic environment. The potential interaction effects of fC60 and the hydrophobic pesticides bifenthrin, a pyrethroid insecticide, and tribufos, an organophosphate cotton defoliant, were investigated. Observed endpoints included D. magna 48-h survival, 70-d reproduction (bifenthrin), 21-d reproduction (tribufos), and 5 and 10-d growth. Both mixtures and pesticides alone reduced D. magna survival and reproduction (p < 0.05). Forty-eight h LC50values were 0.86 (0.70 – 1.06) for bifenthrin only and 0.22 (0.18 – 0.25) for bifenthrin–fC60 mixtures. IC50 values for reduced number of days surviving and reduced reproduction were 0.55 (0.36 – 0.80) and 0.49 (0.28 – 0.72) μg/L for bifenthrin only and 0.39 (0.16 – 0.53) and 0.77 (0.31 – 0.94) μg/L for bifenthrin–fC60 mixtures. For tribufos experiments, forty-eight h LC50values were 6.63 (5.50 – 8.01) for tribufos only and 9.17 (8.03 – 10.49) for tribufos–fC60 mixtures. IC50 values for reduced number of days surviving and reduced reproduction were 9.89 (8.15 – 10.70) and 5.79 (4.48 – 7.60) μg/L for tribufos only and 8.17 (5.97 – 9.30) and 6.59 (5.29 – 8.12) for tribufos mixtures with fC60. No growth effects were observed. These results suggest that although fC60 had an effect on bifenthrin acute toxicity, they had little effect on pesticide chronic toxicity. In addition to potential interaction effects, changes in D. magna behavior in response to fullerene exposure have been reported. Behavioral endpoints are important because changes in behavior can influence Daphnia spp. predator avoidance behaviors, alter predator-prey interactions, increase predation of Daphnia spp., and potentially affect Daphnia populations. This is important to consider because Daphnia spp. serve as an important food source for fish. To evaluate potential changes in D. magna behavior, several responses were measured and included: phototactic behavior, swimming velocity, vertical variance, net angle, sinuosity, average angle, curvature coefficient, modal angle upward, and modal angle downward, were evaluated. C60 affected phototactic behavior over time with organisms being found lower in the exposure chamber when in the absence of food and higher in the exposure chamber when in the presence of food (p < 0.05). Additionally, exposed D. magna were higher in the exposure chamber when in the presence of predator kairomones than control organisms (p < 0.05). Additionally, a 38.8% reduction in swimming velocity was observed in organisms exposed to 545.4 μg/L C60 (p < 0.05). No other components of D. magna swimming behavior were affected and functionalized fullerenes did not affect any of the observed endpoints. This research adds to the knowledge of fullerene effects on aquatic invertebrates and is important in evaluating the risks of nanotechnology to aquatic ecosystems.

This thesis won 1st Place in the Texas Tech University Outstanding Thesis and Dissertation Award, Mathematics, Physical Sciences & Engineering, 2010.

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