The environmental biodegradability profile of graphene related materials (GRMs) is important to know in order to predict whether these materials will accumulate in soil or will be transformed by primary decomposers. In this study, few-layer graphene (FLG) was exposed to living and devitalized axenic cultures of two white-rot basidiomycetes (Bjerkandera adusta and Phanerochaete chrysosporium) and one soil saprotrophic ascomycete (Morchella esculenta) with or without lignin, for a period of four months. Over this time, the increase of fungal biomass and presence of H2O2 and oxidizing enzymes [laccase/peroxidase and lignin peroxidase (LiP)] in growth media was assessed by gravimetric and spectrophotometric measurements, respectively. Raman spectroscopy and transmission electron microscopy (TEM) were used to compare the structure of FLG before and after incubation. All of the test fungi decreased pH in growth media and released H2O2 and laccase/peroxidase, but only basidiomycetes released LiP. Independent of growth media composition all fungi were found to be capable to oxidize FLG to a graphene oxide-like material, including M. esculenta, which released only laccase/peroxidase, i.e. the most common enzymes among primary decomposers. These findings suggest that FLG involuntarily released into terrestrial environments would likely be oxidized by soil microflora.

Applications involving graphene-related materials (GRMs) are becoming very common, raising concerns for their environmental impact. GRMs induce various effects on plants, but those on the sexual reproduction are still largely unknown. Here, the effects of graphene oxide (GO) and GO purified from production residues (PGO) were tested in vivo on the stigma of Cucurbita pepo L. ssp. pepo ”Greyzini” (summer squash). Stigmas were exposed to GO or PGO for three hours and were then analyzed by environmental scanning electron microscopy to verify possible alterations to their surface. Stigmas were then hand-pollinated to verify the effects of the two GOs on pollen adhesion and germination on the stigma, and, subsequently, on the development of fruits and seeds. Severe damages to the stigma were not detected; nevertheless, both pollen adhesion and germination on the stigma decreased. Moreover, fruits developed defectively with signs of necrosis in the case of GO, whereas fruits did not ripen in the case of PGO and ovules did not develop seeds after both GOs treatments. These results highlight different mechanisms of interaction of the two materials with the pollen-stigma system, suggesting a possible negative impact of GO on the sexual reproduction of other seed plants.

Products containing graphene-related materials (GRMs) are becoming quite common, raising concerns for environmental safety. GRMs have varying effects on plants, but their impact on the sexual reproduction process is largely unknown. In this study, the effects of few-layer graphene (FLG) and a similarly layered phyllosilicate, muscovite mica (MICA), were tested in vivo on the reproductive structures, i.e., pollen and stigma, of Cucurbita pepo L. ssp. pepo ‘greyzini’ (summer squash, zucchini). Pollen was exposed to FLG or MICA, after careful physical-chemical characterization, at concentrations of 0.5 and 2 mg of nanomaterial (NM) per g of pollen for up to six hours. Following this, pollen viability was tested. Stigmas were exposed to FLG or MICA for three hours and then analyzed by environmental scanning electron microscopy to verify possible alterations to their surface. Stigmas were then hand-pollinated to verify the effects of the two NMs on pollen adhesion and in vivo pollen germination. FLG and MICA altered neither pollen viability nor the stigmatic surface. However, both NMs equivalently decreased pollen adhesion and in vivo germination compared with untreated stigmas. These effects deserve further attention as they could impact on production of fruits and seeds. Importantly, it was shown that FLG is as safe as a naturally occurring nanomaterial.