Impact of Microplastics and Nanoplastics on Human Health

Abstract

Plastics have enormous impacts to every aspect of daily life including technology, medicine and treatments, and domestic appliances. Most of the used plastics are thrown away by consumers after a single use, which has become a huge environmental problem as they will end up in landfill, oceans and other waterways. These plastics are discarded in vast numbers each day, and the breaking down of the plastics from micro- to nano-sizes has led to worries about how toxic these plastics are to the environment and humans. While, there are several earlier studies reported the effects of micro- and nano-plastics have on the environment, there is scant research into their impact on the human body at subcellular or molecular levels. In particular, the potential of how nano-plastics move through the gut, lungs and skin epithelia in causing systemic exposure has not been examined thoroughly. This review explores thoroughly on how nanoplastics are created, how they behave/breakdown within the environment, levels of toxicity and pollution of these nanoplastics, and the possible health impacts on humans, as well as suggestions for additional research. This paper aims to inspire future studies into core elements of micro- and nano-plastics, the biological reactions caused by their specific and unusual qualities.

Keywords: environmental impacts; health impacts; nanomaterials; nanoplastics; nanotoxicity; plastics; pollution; toxicology.

Figure 1

Sources and fate of micro- and nanoplastics in the environment. Micro- and nanoplastics are generated from primary and secondary sources through consumers and industries. Macroplastic products that disintegrate into micron-sized can break down into nanoplastics via biodegradation or non-biodegradation process. Both micro- and nanoplastics can occur in both aquatic and terrestrial environment, and eventually enter the food chain and water supplies, leading to the uptake and bioaccumulation of these plastic particles in the human body.

Figure 2

Routes of plastic particles entry into human body. There are three key routes for micro- and nanoplastics entry into the human body: Inhalation, ingestion and skin contact. Nanoplastics may interact with proteins, lipids, carbohydrates, nucleic acids, ions, and water in human body, leading to the formation of coronated nanoplastic particles for absorption. The plastic particles can enter human body through ingestion of contaminated food and water supplies, or inhalation of the airborne plastic particles that originate from synthetic textiles and polluted outdoor air. While, the skin membrane is too fine for these plastic particles to pass through, nanoplastics may penetrate through wound and weakened skin barrier, directly or indirectly.

Figure 3

Routes of cellular uptake of plastic particles. Phagocytosis, macropinocytosis, clathrin- and caveolae-mediated endocytosis are the common endocytotic pathways that have been identified for cellular uptake of plastic particles. Micro- and nanoplastics can be absorbed by cells through different routes, of which endocytotic nanoparticle uptake is the primary route where adhesive interaction of nanoparticles (or inactive permeation of the cell membrane) with channel- or transport-protein occurs.

Figure 4

Overview of the toxic effects of chemicals leaching from plastics. Plastics are made up of different chemical compositions, in which some are hazardous that can leach to the surroundings upon degradation. Plastics typically contain additives that can improve their properties, such as durability and elasticity. The leaching of these additives from plastics to the surrounding environment, not only causing harmful impacts to the aquatic environment, but also human health. For instance, bisphenol A (BPA), an industrial chemical that is widely used to make polycarbonate (PC) plastics and epoxy resin as lining layer of food and beverage containers. Studies reported that the leaching of BPA from food containers into the food and drinks can cause a series of diseases, including obesity and cardiovascular diseases. BPA also acts as a hormonal disruptor, imitating or blocking the production, action, and function of hormones in the human body. BPA also known to affect brain development in the womb, causing damage to the developing fetus. Polyvinyl chloride (PVC) polymers and plastisol generally contain phthalate esters as plasticizers, in order to increase their durability and flexibility. Human exposure to phthalate esters has been shown to associate with abnormal sexual development and changes in the levels of sex hormones. Additionally, studies have demonstrated that some phthalate esters such as butyl benzyl phthalate (BBP) and di-2-ethylhexyl phthalate (DEHP) can increase tumor incidence in human, representing potential carcinogens.