Graphene-Based Nanomaterials in Soil: Ecotoxicity Assessment Using Enchytraeus crypticus Reduced Full Life Cycle

Abstract

Graphene-based nanomaterials (GBNs) possess unique physicochemical properties, allowing a wide range of applications in physical, chemical, and biomedical fields. Although GBNs are broadly used, information about their adverse effects on ecosystem health, especially in the terrestrial environment, is limited. Therefore, this study aims to assess the toxicity of two commonly used derivatives of GBNs, graphene oxide (GO) and reduced graphene oxide (rGO), in the soil invertebrate Enchytraeus crypticus using a reduced full life cycle test. At higher exposure concentrations, GO induced high mortality and severe impairment in the reproduction rate, while rGO showed little adverse effect up to 1000 mg/kg. Collectively, our body of results suggests that the degree of oxidation of GO correlates with their toxic effects on E. crypticus, which argues against generalization on GBNs ecotoxicity. Identifying the key factors affecting the toxicity of GBNs, including ecotoxicity, is urgent for the design of safe GBNs for commercial purposes.

Graphene and Reproduction: A Love-Hate Relationship

“…Similar experiments were performed with the soil invertebrate Enchytraeus crypticus (E. crypticus) to evaluate the effects of commercial GO and rGO at concentrations of 250 and 1000 mg/Kg of dry soil. By evaluating the life cycle of the soil, the Authors confirmed reduced hatching, survival and reproduction rates after the treatment with the highest concentrations and in a dose-dependent way [ 60 ] for the sole GO samples and correlated this effect to the oxidation degree of graphene. GO and oxMWCNT were also supplied with the diet of the generalist insect Spodoptera frugiperda (S. frugiperda) by Martins et al at different doses (10, 100, 1000 µg/g of food).…”

“…The majority of GO is synthesized by using the Hummer’s method [ 46 , 47 , 56 , 57 , 58 ] even though sometimes this information is omitted (overall in the case of commercial samples). However, the use of this synthetic methodology does not ensure a precise characterization of the final product that may differ in terms of exfoliation degree (single, SLGO, or few layered sheets, FLGO) [ 48 ], oxygen content (either in terms of C/O w / w , that may vary from 0.25 [ 59 ] to 0.39 [ 48 ] or as final oxygen weight with respect to the total weight, i.e., 20% [ 41 ] or >36% [ 60 ]), dimensions of the sheets (i.e., from 297 nm mean size [ 61 ] to 3–5 µm [ 41 , 47 ]), surface charge (i.e., from ζ -potential −14.13 ± 11.1 mV [ 60 ] to −56.7 ± 1.5 mV [ 46 ]). In a few studies GO sheets are named nano-GO (nanoGO or NGO) [ 62 , 63 ] or are distinguished in small GO (S-GO) and large GO (L-GO) [ 64 ] sheets when the protocol of preparation involves a further step of cutting into small pieces by sonication [ 64 ] or harsh oxidation conditions.…”

Time-Dependent Effect of Graphene on the Microbial Activity of the Soil Under Single and Repeated Exposures

“…By 2023, the worldwide market volume of graphene composites will reach 1521 tons (Mendona et al 2019). During the course of production and application, graphene will inevitably be discharged into the environment.…”