Ecotoxicological Properties of Pure and Phosphorus-Containing Graphene Oxide Bidimensional Sheets in Daphnia magna

In this work, the synthesis and structural, thermal, vibrational, morphological, and electronic characterization of 2D-like pure graphene oxide (GO) and phosphorus-containing graphene oxide (GOP) sheets were investigated. The average thicknesses of GO and GOP were 0.8 μm and 3.1 μm, respectively. The electron energy-loss spectroscopy spectra were used to analyze the differences in the C-K and O-K energy edge bands between GO and GOP. In addition, colloidal stability was studied using dynamic light scattering and zeta potential physicochemical techniques, determining that as the concentration increases, the hydrodynamic diameter and electrostatic stability of GO and GOP increase. The colloidal stability was quite important to ensure the interaction between the suspended solid phase and the biomarker. The 2D-like materials were used to determine their ecotoxicological properties, such as the medium lethal concentration, a crucial parameter for understanding ecotoxicity. Acute ecotoxicity experiments (24 h) were conducted in triplicate to obtain robust statistics, with corresponding mean lethal concentration (LC50) of 11.4 mg L−1 and 9.8 mg L−1 for GO and GOP, respectively. The morphological parameters of GO and GOP were compared with a negative control. However, only the case of GO was analyzed, since the Daphnia magna (D. magna) set exposed to GOP died before completing the time required for morphological analysis. The results indicate that the GOP sample is more toxic than the GO, both during and after exposure. Furthermore, the morphological parameters with the greatest statistically significant changes (p<0.05) were associated with the heart and body, while the eye and tail showed less significant changes.