||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.