Ecotoxicity of graphene oxides on human and murine cell lines, bacteria, and microalgae: Insights and perspectives for environmental applications

Abstract

The toxicity and environmental applications of graphene oxide (GO) are largely unknown. The procedures involved in GO synthesis can impact biological responses and toxicity. In this study, the experimental methods involved in the synthesis of lyophilized sonicated graphene oxide (LSGO) followed by 1 h (1 h-LSGO) and 5 h sonication (5 h-LSGO), and the physicochemical characterization of both GOs is compared. A battery of toxicity tests performed with both GOs, using adenocarcinoma and fibroblast cells as representatives of the animal eukaryotic cell model, the bacteria Escherichia coli and Staphylococcus aureus as representatives of the prokaryotic model, and the microalga Chlorella vulgaris as representative of microalgae eukaryotic model, in a wide range (0.1–100 mg L−1) was developed, to find out possible differences between both LSGOs cytotoxicity on different biological models. In addition, physicochemical analysis of C. vulgaris exposed to both LSGOs, by scanning electronic microscopy and spectrofluorimetric analysis were performed. There was no cytotoxic effect (viability < 70%) on human alveolar adenocarcinoma A549 cells, nor to murine fibroblast L929 cells exposed to 1 h-LSGO and 5 h-LSGO. Similarly, no antibacterial activity against E. coli and S. aureus (0.1–100 mg L−1 of LSGO) was observed. Conversely, C. vulgaris responded with greater sensitivity than bacteria and animal cells, more relevant in 5 h-LSGO than in 1 h-LSGO, mainly in the higher GO concentration tested (100 mg L−1). These remarkable results could be attributed to the greater concentration of covalent bonds in 5 h-LSGO (~ 48% sp2, ~ 10% sp3) than in 1 h-LSGO (~ 8% sp2, ~ 39% sp3), and their interaction with the unsaturated fatty acids of the phospholipids of the microalgae´s membranes lipid bilayer. These relevant results report that 1 h-LSGO is nontoxic and can be used in biotechnological applications. On the other hand, GO and C. vulgaris are used as biofertilizers, so it is proposed to explore the potential biostimulant of the 1 h-LSGO-C. vulgaris consortium, among other environmental applications consistent with the sustainable agriculture approach.