Effects of graphene oxide nanomaterial exposures on the marine bivalve, Crassostrea virginica.

Since its discovery in 2004, graphene has been used in a wide variety of fields including biomedicine, electronics, filtration materials, and surface coatings. The rapidly expanding consumer market for graphene family nanomaterials (GFNs), such as graphene oxide (GO), raises concern regarding their environmental toxicity. The aim of this study was to evaluate the effects of GO exposures in a marine filter-feeding bivalve (Crassostrea virginica) using sublethal biomarker approaches that can contribute to the development of an adverse outcome pathway (AOP). A 14-day study was conducted to identify tissue-specific molecular markers of GO toxicity using a static renewal design. Elevated lipid peroxidation and changes in glutathione-s-transferase (GST) activities were observed in gills and digestive gland tissues of the GO-exposed oysters. These cellular changes were noted for 2.5 and 5 mg/L GO exposures in seawater. Based on our results, reactive oxygen species (ROS)-induced oxidative damage is identified as a key event in the proposed AOP. Additionally, detoxification enzymes, such as GST, are thought to be involved in stress signaling leading to adverse effects on cellular health. This study is a part of our two-tier approach towards the identification of short- and long-term effects of GO exposures. This work, together with our previous 72 h exposure, represents the application of biomarker-based investigations in the process of AOP development for graphene family nanomaterials.

A 72-h exposure study with eastern oysters (Crassostrea virginica) and the nanomaterial graphene oxide.

Graphene is a 2-dimensional nanomaterial with unique mechanical, thermal, electrical, and optical properties. With increasing applications of graphene-family nanomaterials (GFNs) in electronics, biomedicine, and surface coatings, concern for their impacts on aquatic ecosystems is rising. Current information on the toxicity of GFNs, including graphene oxide, is scarce. Filter-feeding bivalves, such as eastern oysters, are good models for nanomaterial exposure studies. We present results from a 72-h static renewal oyster study using 1 and 10 mg/L graphene oxide, which, to our knowledge, is the first report on in vivo effects of graphene oxide exposures in marine bivalves. Water samples were analyzed for graphene oxide concentration and size assessments. Gill and digestive gland tissues were evaluated for lipid peroxidation and glutathione-S-transferase (GST) activity. In addition, gill sections were fixed for histopathological analyses. Elevated lipid peroxidation was noted in oysters exposed to 10 mg/L graphene oxide. No significant changes in GST activity were observed, but reduced total protein levels were found in digestive gland tissues of exposed oysters at both concentrations. Loss of mucous cells, hemocytic infiltration, and vacuolation were observed in gills of exposed oysters. The results indicate that short-term graphene oxide exposures can induce oxidative stress and epithelial inflammation and adversely affect overall oyster health. Further investigations regarding the fate and sublethal effects of graphene oxide are critical to understanding the risks associated with a rapidly growing graphene consumer market. Environ Toxicol Chem 2019;38:820-830. Published 2019 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.