Impacts of titanium dioxide nanoparticles and ocean acidification on early-life stage estuarine fish

Titanium dioxide nanoparticles (nano-TiO₂) are emerging contaminants which are used in a wide variety of industries. Over the past several decades, reductions in water pH have rendered increased acidity a stressor that can potentially modify the uptake rate, bioavailability, and toxicity of nano-TiO₂ in the aquatic environment. Thus, we conducted a series of experiments using early-life stage sheepshead minnow (Cyprinodon variegatus) to explore the impact of nano-TiO₂ on swimming performance, tissue accumulation ability, and the impact of co-exposure to low pH and nano-TiO₂ on oxidative stress levels, a topic largely unexplored. Our data showed significant reductions in the swimming performance of sheepshead minnows following exposure to nano-TiO₂, with similar patterns of reduced average velocity, maximum velocity, and distance swum. Further, we found that with increased exposure to nano-TiO₂ in the aquatic environment, there was an increase in the Ti tissue content of sheepshead minnows. Additionally, when sheepshead minnows were co-exposed to low pH and nano-TiO₂ during our pilot study, low pH appeared to be the primary driver of oxidative stress. To our knowledge, this is the first study that has explored the potential impact of co-exposure to low pH and nano-TiO₂ in an estuarine fish species. Since there are currently only a limited number of studies (n = 6) exploring the impact of exposure to low pH and nano-TiO₂ present in the literature, we highlight the need for further exploration.