Effects Of Humic Acid On Toxicity Of Graphene-Family Materials To Alage

Graphene-family materials?GFMs?have been widely used in various fields because of their excellent physicochemical properties,which greatly increase the risks of their emissions into environment.However,the potential risks of GFMs to organisms are still unknown.Humic acid?HA?,as the main component of natural organic matters?NOMs?,contains many hydrophilic groups that impart excellent ability to adjust the environment behaviors and toxicities of nanomaterials.However,limit is known about the effect of HA on the bio-toxicity of GFMs,especially the interaction mechanisms between GFMs and HA.This study investigated the toxicity of four GFMs,i.e.graphene?G?,graphene oxide?GO?,carboxyl-modified graphene?G-COOH?and amine-modified graphene?G-NH₂?,with or without HA,using Scenedesmus obliquus?S.obliquus?as model organism.The toxicity level and difference of GFMs,as well as the influence of HA on their toxicities,were demonstrated with the following endpoints?i.e.cell growth and chlorophyll-a?Chl-a?synthesis,cell viability,membrane integrity and mitochondrial membrane potential?MMP??.The toxicity mechanisms were reflected with the characterization of interface alterations of GFMs with algae,the intracellular oxidative stress and extracellular hydroxyl radical??OH?induced by GFMs in suspension.The results showed that the four GFMs induced significantly inhibition on cell growth and Chl-a synthesis,with the median effect concentration(EC₅₀)of G,GO,G-COOH and G-NH₂ were 8.2,20.6 and 32.2 and 84.0 mg/L,suggesting that G exhibited the highest toxicity to S.obliquus,while G-NH₂ exhibited the lowest toxicity to S.obliquus.Also,the GFMs also induced the loss of cell viability,membrane integrity as well as the MMP.Meanwhile,HA mitigated the toxicity of GFMs in the order of G-NH₂>G-COOH>GO>G for the most of endpoints.Furthermore,the surface envelopment,physical damage,intracellular oxidative stress and extracellular?OH were the main mechanisms of GFMs to S.obliquus.While three possible mechanisms of the HA alleviation on GFMs toxicity were speculated as:?1?reduce the contact of GFMs with algae cells through regulating the structures and surface negative charges of GFMs;?2?mitigate the physical penetration and damage through decreasing the deposition of GFMs on cells by interacting with HA;?3?react as an antioxidant with intracellular reactive oxygen species?ROS?and extracellular?OH.This work provides useful information for the environmental toxicity of GFMs and the possible antidotal mechanisms in the presence of HA,which could aid to avoiding the overestimation of potential risk of GFMs in natural aquatic environment.