Health Hazards Caused by Fragmented Plastics
Humans are consuming a huge amount of micro- and nanoplastics through ingestion and inhalation. These fragmented plastics are capable of accumulating and exerting chemical toxicity and induce or enhance immune response. Chemical toxicity usually occurs due to localized leaching of additives or adsorbed pollutants. Chronic exposure to such fragmented plastics and chemicals is of greater concern.
Toxicological Pathways of Fragmented Plastics
Microplastics are capable of generating toxicological effects upon consumption by the oral or inhalational route. Solubility, size, shape and surface charge collectively influence the cytotoxic effect of particles to tissues in vivo . If microplastics are retained in the biological system, they may lead to genotoxicity, apoptosis, oxidative stress and even necrosis of cells. Upon prolonged exposure, these conditions may even worsen to cause carcinogenesis, fibrosis and damage to tissues. Oxidative stress and inflammation have been reported upon inhalation of micro- and nanoplastics . Micro- and nanoplastics, upon weathering, form free radicals by dissociation of the C-H bonds [66,67]. These free radicals pose more danger to human health than the microplastics.
Inflammatory and Immune Response by Fragmented Plastics
Extensive research is available concerning inflammation due to microparticles formed owing to abrasion of prosthetic implants made up of plastics. Individuals with plastic endoprostheses have been reported to contain microparticles of varying shapes in the joint cavity and joint capsules . Particles of less than 1 pm accumulate in the mobile macrophages by means of lymphatic transport . These particulate matters provoke immune activation of macrophages and production of cytokines . All these results suggest that the chemical composition of micro- and nanoplastics determines the type of immunological response upon exposure.
Effect on the Airway and Gastrointestinal Tract
Macrophages along with antigens and toxins, in conjugation with microparticles, enhance T-cell proliferation . Corona formed on microplastics not only influences particle uptake but also induces toxicity [72,73]. Zeta potential, surface charge, size and shape also tend to influence toxicity. In a study on rats, smaller particles have been found to induce greater influx to neutrophils and cause inflammation of lungs . There are limited data available on inflammatory responses in the gastrointestinal tract.