Morphologic alterations across three levels of biological organization following oral exposure to silver-polymer nanocomposites in Japanese medaka (Oryzias latipes)

Abstract

Polymer nanocomposites have diverse industrial and commercial uses. While many toxicity studies have assessed the individual materials (e.g., polymer, nanomaterial) comprising nanocomposites, few have examined the potential toxicity of the nanocomposite as a whole. Furthermore, products undergo machining during their manufacture and/or degradation as they age thereby resulting in potentially altered mixture exposures and differential effects compared to the parent nanocomposite. We assessed potential toxic effects of repeated oral exposure to silver nanoparticle (AgNP) embedded nanocomposites and compared them to individual component materials using a transparent strain of the fish model Japanese medaka (Oryzias latipes). This strain allowed for the comparison of morphologic alterations at three levels of biological organization: whole animal; organ/tissue by examination of histologic sections; and, subcellular using transmission electron microscopy (TEM). Adult fish were exposed to AgNPs, silver nitrate, abraded PETG microplastics, or abraded nanocomposites via 7 oral gavages over the course of 2 weeks. In vivo observations showed alterations in the liver and gallbladder of fish exposed to pristine AgNPs and nanocomposites. When histologic sections of these same individuals were examined by light microscopy, hepatic and biliary alterations were observed. Similarly, alterations of the head kidney were also observed in fish exposed to silver and its composites, with both tubules and glomeruli affected. In both of these organs, many of the changes occurred adjacent to large blood vessels, suggesting material translocated from the bloodstream to adjacent tissues. TEM of the liver supported histological findings, with increased glycogen as well as hepatocellular swelling and abundant lipid vesicles in exposure groups. Very few morphological changes at any level of biological organization were observed in fish exposed to the plastic matrix alone. This transparent fish model proved advantageous in evaluating risks and potential human health concerns associated with the ingestion of silver nanocomposites.