Silver nanoparticle toxicity is related to coating materials and disruption of sodium concentration regulation

Silver nanoparticles (AgNPs) have been increasingly commercialized and their release into the environment is imminent. Toxicity of AgNP has been studied with a wide spectrum of organisms, yet the mechanism of toxicity remains largely unknown. This study systematically compared toxicity of 10 AgNPs of different particle diameters and coatings to Japanese medaka (Oryzias latipes) larvae to understand how characteristics of AgNP relate to toxicity. Dissolution of AgNPs was largely dependent on particle size, but their aggregation behavior and toxicity were more dependent on coating materials. 96 h lethal concentration 50% (LC50) values correlated with AgNP aggregate size rather than size of individual nanoparticles. Of the AgNPs studied, the dissolved Ag concentration in the test suspensions did not account for all of the observed toxicity, indicating the role of NP-specific characteristics in resultant toxicity. Exposure to AgNP led to decrease of sodium concentration in the tissue and increased expression of Na(+)/K(+ )ATPase. Gene expression patterns also suggested that toxicity was related to disruption of sodium regulation and not to oxidative stress.