Responses of Caenorhabditis elegans to nanomaterials

Overview: 

We have made several important nanotoxicological findings, and have also contributed new methods for NP testing.

Key Findings:

-       AgNPs are the most toxic of the NPs tested to date (tested: seven varieties of AgNP, cerium oxide, TiO2, ZnO, single-walled carbon nanotubes, C60).

-       AgNPs are both assimilated and passed on to the next generation by C. elegans.

-       Toxicity is highly dependent on medium; higher ionic strength, natural organic matter, and sulfidation of the NPs are all protective. TiO2 and ZnO exhibit phototoxicity in C. elegans.

-       Toxicity of AgNPs correlates with dissolution, which appears to depend on coating and somewhat on size (Yang et al., in press).

-       The mechanism of toxicity of AgNPs is size-dependent, with a lesser role for oxidative stress in the case of the smaller particles, based on genetic as well as pharmacological rescue (not shown) data (Yang et al., in press).

-       The observed toxicity of mesocosm water (death of mesocosm macrophytes, etc.) was recapitulated by (in-lab) toxicity of sampled water to C. elegans (Bone et al., in prep.).

-       However, while AgNPs are almost never more toxic than an equivalent mass of dissolved Ag in the laboratory (Yang et al., in press), AgNPs were more toxic than dissolved Ag in mesocosm water (Bone et al., in prep.). 

Methodological Improvements:

-       We developed (Meyer et al., 2010) a robust method for feeding with UV-inactivated bacteria that removes the potential confounder of NP toxicity to the food source.

-       Utilization of the COPAS biosorter for higher-throughput and higher-confidence growth data (growth is our most common first measurement of sublethal toxicity) (Meyer et al., 2010).

-       We adapted our QPCR for DNA damage assay to Japanese medaka to facilitate collaborative work with the Hinton laboratory.

-       We characterized a strain of C. elegans that carries a mutation in the nth-1 DNA repair in the hope of using it to test for genotoxicity of NPs (Hunter et al., in prep.).