Effects Of Microplastics On The Remediation Of Cadmium-Contaminated Water By Nano-Zero-Valent Iron Combined With Ryegrass

Microplastics,as emerging pollutants,have become a global problem and concern due to their potential harmful biological effects and hard to be degraded in nature.In addition to the toxicity of microplastics themselves,chemical additives contained in microplastics or substances adsorbed by microplastics in the environment are also toxic.It has been reported that microplastics may coexist with heavy metals in water,which may have an impact on heavy metal removal from water,while the effect of microplastics on the efficiency of plants and environmental materials to remove heavy metals is unclear.In this experiment,the effect of polystyrene microplastics(PSMPs)on removal efficiency of cadmium(Cd)by nano-zero-valent iron(nZVI),carboxymethylcellulosemodified nano-zero-valent iron(C-nZVI)and sulfided nano-zero-valent iron(S-nZVI)combined ryegrass(Lolium perenne L.),Cd content in ryegrass,ryegrass root slices,ryegrass physiological properties and traits(dry weight,chlorophyll content,malondialdehyde(MDA)content,superoxide dismutase(SOD)and catalase(CAT)activities)were measured and analyzed.Experiment results found that the presence of PSMPs would promote ryegrass to take in more Cd,inhibit the growth and photosynthesis of ryegrass,and destroy its antioxidant defense system.The antioxidant chain composed of SOD and CAT enzymes can well resist the oxidative damage caused by PSMPs,and maintaining a high level of CAT activity may be one of the main antioxidant responses in response to PSMPs-induced plant oxidation.PSMPs were observed to enter plant roots in ryegrass supplemented with nZVI or C-nZVI,and more Cd was found in plants of these two groups.Therefore,four possible mechanisms were proposed to explain why plants that observed the internalization of PSMPs contained more Cd.In conclusion,this work revealed the impact of coexisting microplastics in water on the co-remediation efficiency of nZVI combined with ryegrass,and provided new insights into the entry of polystyrene microplastics into plant roots.