Sources of Human Consumption of Fragmented Plastics
There are various sources through which humans are consuming micro- and nanoplastics. They can be broadly classified into marine and non-marine source.
Marine Source of Consumption
Biomagnification and bioaccumulation are the major phenomena through which micro and nanoplastics reach higher levels of the food chain . However, consumption of fishes and shellfishes are not the only source of fragmented plastics. It is quite difficult to conclude the actual amount of microplastics being consumed from fishes because of the limited data available. Most of the studies are limited to analysis of stomach or gut content . Microplastics have also been reported in canned fish. Apart from that, sea salt is another source of microplastic. One kilogram of sea salt is expected to contain over 600 microplastics, but this number increases depending upon the consumption of salt.
Non-Marine Source of Consumption
Globally, the intake of microplastics is far more from non-marine sources than the sea. Land animals also eat a lot of microplastics from different sources. Scientists have also confirmed the presence of microplastics in chickens, honey and beer, nevertheless the biggest source of microplastics consumption is bottled water. A study between singleuse and reused water bottles showed that reused water bottles contain 5-14-fold more microplastics than single-use water bottles. There is evidence of microparticles being present in huge amounts in indoor dust .
Inhalation Exposure to Fragmented Plastics
Debris and municipal effluents usually contain fragmented plastics. They are retained in sludge and reach agricultural lands in the form of fertilizer. The dried sludge-based fertilizers are transported through wind . In a recent study, it was reported that microplastics are also present in the atmospheric dust . Out of the total fallout studied, 30% were plastics and fibers. Densely populated areas were found to contain more microplastics than less-populated areas. Thus, humans living in urban areas are at higher risk of inhalational exposure to microplastics . In another study, it was confirmed that synthetic rubber or tires contain microplastics. Abrasion of such materials has been reported to contain particulate matter. Exposure concentration and size of the fragmented plastics determines the potential risk. Once the micro- and nanoplastics or fibers enter into the respiratory tract, they are likely to be trapped in the lung lining fluid. However, in individuals with impaired mechanism of defense, these fibers may reach the lungs.