Single And Combined Toxicity Of Polystyrene Nanoplastics (PSNPs) And Cadmium To Wheat(Triticum Aestivum L.)

Microplastics and nanoplastics have become emerging pollutants of global concern.Recently,a growing number of studies have found that the micro-/nanoplastic pollution of the soil environment is more serious than that of the marine environment.It is worth noting that most of the ecotoxicity studies of micro-/nanoplastics are currently focused on marine aquatic organisms and freshwater algae,but their ecological impact on terrestrial higher plants is limited.Although the effect of residual plastic film on the growth performance of wheat has been reported,the underlying mechanism of nanoplastics-induced effect on wheat growth is still unclearThe present study conducted the systematic research to reveal the impact of polystyrene nanoplastics(PSNPs)on seed germination and seedling growth of wheat(Triticum aestivum L.)at ambient concentrations(0.01–10 mg/L).The results showed that PSNPs had no discernible effect on seed germination rate,whereas significantly increased root elongation by 88.6%–122.6% when compared with the control.Similarly,remarkable increases in plant biomass,chlorophyll content,photosynthesis rate,leaf carbon and nitrogen contents were also observed after exposure to PSNPs.However,PSNPs could reduce the shoot to root biomass ratio(S:R ratio)and the contents of the four micronutrients(Fe,Mn,Cu and Zn)in wheat seedlings.Furthermore,the imagings of a 3D laser confocal scanning microscopy(LCSM)and scanning electron microscopy(SEM)indicated that PSNPs were taken up by roots and subsequently down-top transported to shoots via xylem.Moreover,metabolomics analysis revealed that all PSNPs treatments altered the leaf metabolic profiles mainly by regulating energy metabolisms and amino acid metabolisms.These findings are expected to provide new insights into the effects of PSNPs on crop plants.Previous studies have shown that microplastics can act as carriers of toxic chemicals and thus increase their health and environmental risks,but the interaction of nanoplastics with heavy metals and their co-toxicity to plants is still rarely reported.As no single and combined toxicity of PSNPs and Cd to wheat has been reported to date,this paper therefore assessed the toxicity of cadmium(0,20 ?M)to hydroponically grown wheat in the presence of PSNPs(0,10 mg/L).Results showed that the presence of PSNPs could partially reduce Cd contents in leaves and alleviate Cd toxicity to wheat,which might be due to the weakened adsorption capacity of PSNPs affected by ionic strength.In addition,PSNPs could not activate the activities of catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD),which suggested that antioxidant defense systems might not be the main mechanism to reduce the oxidative damage induced by Cd in wheat.Electron paramagnetic resonance(EPR)analysis showed that PSNPs could accelerate the formation of long-lived radicals in leaves after exposure to Cd.Notably,our metabolomic profiling further indicated that the simultaneously elevated carbohydrate and amino acid metabolisms induced by PSNPs could partly alleviate Cd toxicity to wheat.Nevertheless,the present study provides important implications for the toxicological interaction and future risk assessment of co-contamination of nanoplastics and heavy metals in the environment.