Penetration of micro/nanoplastics into biological barriers in organisms and associated health effects
Plastics are widely applied in industry,agriculture,medicine and daily life products due to their excellent physicochemical properties.However,the vast production and disposal of plastics have resulted in large amounts of plastics debris entering into terrestrial,atmospheric,freshwater,and marine environments.These plastic debris can be gradually fragmented into microplastics(1 μm-5 mm)or nanoplastics(1 nm-1 μm)through physical abrasion,photodegradation,chemical degradation,and biodegradation.The environmental pollution of micro/nanoplastics has become a major environmental issue of global concern because of the widespread detection of micro/nanoplastics in various environmental media and organisms.The small-sized micro/nanoplastics are often hard to be degraded and easy to migrate.When present in food,water,air,and daily necessities,micro/nanoplastics can enter the human body through the digestive tract,respiratory tract,and skin contact.This is supported by the fact that micro/nanoplastics have been detected in human feces,blood and placenta.The accumulation of micro/nanoplastics may induce toxic effects on tissues and organs,and further endanger human health.Although many literatures have reported the adverse effects of micro/nanoplastics on living organisms,the internal processes and modes of toxic action,particularly the penetration of micro/nanoplastics into important biological barriers,the accumulation,transfer and distribution of micro/nanoplastics inside the receptors,have not been systematically reviewed and analyzed.This study focuses on the research topic of toxic effects and health risks of micro/nanoplastics.The related studies of micro/nanoplastics in human body,model animals and typical human cells are systematically teased out.The main exposure routes of micro/nanoplastics and their potential penetration into gastrointestinal barrier,lung barrier and skin barrier are critically reviewed.The capacity of micro/nanoplastics penetrating into the biological barriers is mainly determined by their physicochemical properties,especially particle size and surface charge.The behavioral process and controlling factors of the transfer and accumulation of micro/nano plastics in various organs including liver,brain,testis,fetal through blood circulation are analyzed.Micro/nanoplastics can be adsorbed on the surface of erythrocyte or be internalized by erythrocyte by means of van der Waals forces,electrostatic attraction,hydrogen bonding and hydrophobic effect,thereby reducing the possibility of micro/nanoplastics being removed by the liver and spleen during blood circulation,extending their residence time in the blood and increasing the risk of their transfer to other secondary organs.The toxic effects of micro/nanoplastics on different tissues and organs and the underlying mechanisms at the molecular level are further identified.Oxidative damage and metabolic disturbance are found to be the common mechanisms responsible for the toxicity of different types of micro/nanoplastics.Given that micro/nanoplastics can persist in the environment for a long time,the damage can possibly transfer from parents to offspring.Through revisiting the relevant studies,we highlight that the transgenerational and multigenerational toxicity cannot be ignored.The possible release of various additives from micro/nanoplastics is suspected to be an important source of risk.Therefore,the joint interactions and effects of micro/nanoplastics and plastic additives are also evaluated.The bottlenecks and technical challenges in the research area of the health risk assessment of micro/nanoplastics are discussed.We propose that future research efforts should be devoted to the development of precise approaches for qualifying and quantifying micro/nanoplastics,the exploration of carrier effects of micro/nanoplastics,and the initiation of epidemiological investigation of micro/nanoplastics pollution.This is expected to lay a foundation for further guiding research on the human health effects of micro/nanoplastics.
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