Role of Conductivity in the Ecotoxicological Effects of Lyophilized Graphene Oxides on <i>Lactuca sativa</i> and <i>Allium cepa</i>

The ecotoxicity of graphene oxide (GO) remains insufficiently characterized, particularly regarding how synthesis parameters influence its environmental behavior. In this study, we investigated the physicochemical properties and biological effects of GO synthesized by a modified Hummer’s method and exposed to two oxidative interaction times with hydrogen peroxide (H2O2) for 1 h (1h-LSGO) and 5 h (5h-LSGO) under identical sonication conditions. GO was characterized by UV–vis spectroscopy, FTIR-ATR, zeta potential, electrical conductivity, and atomic force microscopy (AFM). Ecotoxicological responses of 1h-LSGO and 5h-LSGO were evaluated in Lactuca sativa and Allium cepa, focusing on germination, root elongation, antioxidant activity, chromosomal aberrations, and mitotic index, mainly due to the effects of GO conductivity. Treatment with a shorter oxidative interaction (1h-LSGO) produced GO with higher oxygen content (21.2%), partial restoration of sp2 domains (7.6%), conductivity (0.0249 mS·cm–1), and a more negative zeta potential (−40.1 mV). Meanwhile, the longest interaction (5h-LSGO) favored partial restoration of sp2 domains (48.1%), showing ∼20-fold higher conductivity (0.485 mS·cm–1) and zeta potential (−32.2 mV). Both materials caused only slight effects on seed germination, but their sublethal responses differed between species: 1h-LSGO significantly inhibited L. sativa root elongation (30%) and modulated antioxidant activity, while 5h-LSGO reduced A. cepa root growth (60%), decreased the mitotic index, and increased chromosomal aberrations at 100 mg L–1 (p < 0.05). In summary, the oxidative interaction time of H2O2 was revealed as a critical parameter that controls the surface chemistry of GO, its electronic structure, its conductivity, and its ecotoxic potential, with higher conductivity in 5h-LSGO correlating with stronger genotoxicity in A. cepa (e.g., reduced mitotic index and increased chromosomal aberrations at 100 mg L–1, p < 0.05).