Aquatic nanotoxicity testing: Insights at the biochemical, cellular, and whole animal levels

Abstract

Aquatic organisms are susceptible to waterborne nanoparticles and there is only limited understanding of the mechanisms by which these emerging contaminants affect biological processes. The unique properties of nanomaterials necessitate evaluation of standard toxicity testing techniques to provide a solid foundation for thorough and accurate biological effects testing. I discovered that many biochemical assays used to test toxicity are affected by nanoparticles, thus hindering our ability to properly evaluate nanotoxicity. A meta-analysis showed that ca. 95% of papers from 2010 assessing nanotoxicity did not account for nanoparticle interference, with only minimal improvement in 2012. I then performed a series of biological tests with various nanomaterials. I evaluated the effects of functionalized silicon nanoparticles in cell and zebrafish exposures and determined that they are a less-toxic alternative to cadmium selenide quantum dots. Then, I tested medically relevant hydroxyapatite nanomaterials, and established that nanoparticle shape affects uptake and toxicity in vivo and in vitro. Using whole animal experiments I determined that nanoparticles could delay or prevent zebrafish hatch, likely due to the inhibition of hatching proteases. Replicating more realistic aquatic environments, I examined whether humic acid, an important component of natural waters, would alter nanoparticle toxicity. The presence of humic acid changed the physicochemical characteristic of nanoparticles, and some biological effects were abrogated, indicating that laboratory toxicity tests might not be representative of effects in the natural environment. Finally, I focused on the physiological and systemic effects of nanoparticles. I determined that silver nanoparticles affects sodium uptake in juvenile trout, and inhibits ionoregulatory transporter activity. I propose that many of the nanoparticle effects seen in biochemical assays, cellular experiments, and whole animal exposures are often related to nanoparticle interactions with proteins, enzymes, dyes, and other biologically-relevant molecules. Importantly, I found that some biological effects could be attributed to nanoparticle-specific properties, as opposed to the bulk or dissolved components. Determining the potential toxic effects caused by nanoparticle exposure and understanding the mechanism by which nanoparticles cause effects will help properly regulate these materials and allow for their safe development and production.