AN EVALUATION OF THE TOXICITY OF ZINC OXIDE AND TITANIUM DIOXIDE NANOPARTICLES TO Caenorhabditis elegans

Nanoparticles, which are used in a large variety of commercial and industrial applications, have high surface reactivity, increasing production volume and unregulated release into the environment which might pose a health risk to environmental and human health. This project evaluated the potential for toxicity of zinc oxide and titanium dioxide nanoparticles (present in sunscreens, fungicides, etc.) to the nematode Caenorhabditis elegans under controlled laboratory conditions. C. elegans were dosed with zinc oxide at concentrations ranging from 200 mg/L to 6.25 mg/L, and titanium dioxide nanoparticles at concentrations of 150 mg/L to 18 mg/L along with a control (C. elegans grown in reconstituted hard water). After a 3-day dosing regimen, the endpoints growth inhibition and lethality were observed. Titanium dioxide nanoparticles caused growth inhibition at concentrations as low as 18 mg/L but were not lethal even at the highest concentration tested (150 mg/L). Zinc oxide nanoparticles were lethal at concentrations 75 mg/L and above but caused growth inhibition from 50 mg/L to 6.25 mg/L. Cytoviva imaging showed that zinc oxide nanoparticles were present inside the body of the worm. Titanium dioxide nanoparticles caused growth inhibition at 18.5 mg/L but are unlikely to be toxic in the environment where they would be present at significantly lower concentrations. Zinc oxide nanoparticles caused death at 75 mg/L and above, and inhibited growth below that concentration. Thus, at environmentally relevant concentrations (6 mg/L and below), zinc oxide nanoparticles have the potential for growth inhibition which warrants further testing to elucidate mechanism of toxicity. The results of this study could also be used to design new studies to determine if factors such as pH, temperature and sunlight affect the toxicity of nanoparticles.