The role of airborne particles and environmental considerations in the transmission of SARS-CoV-2

Abstract

Corona Virus Disease 2019 (COVID-19) caused by the novel coronavirus, results in an acute respiratory condition coronavirus 2 (SARS-CoV-2) and is highly infectious. The recent spread of this virus has caused a global pandemic. Currently, the transmission routes of SARS-CoV-2 are being established, especially the role of environmental transmission. Here we review the environmental transmission routes and persistence of SARS-CoV-2. Recent studies have established that the transmission of this virus may occur, amongst others, in the air, water, soil, cold-chain, biota, and surface contact. It has also been found that the survival potential of the SARS-CoV-2 virus is dependent on different environmental conditions and pollution. Potentially important pathways include aerosol and fecal matter. Particulate matter may also be a carrier for SARS-CoV-2. Since microscopic particles can be easily absorbed by humans, more attention must be focused on the dissemination of these particles. These considerations are required to evolve a theoretical platform for epidemic control and to minimize the global threat from future epidemics.

Keywords: Aerosol; Airborne particles; COVID-19; Environmental media; SARS-CoV-2.

Graphical abstract

Fig. 1

Morphological characteristics of SARS-CoV-2 as viewed by transmission electron microscopy. The spherical viral particles may range from 60 to 140 nm in diameter (CDC, 2020).

Fig. 2

Molecular architecture of SARS-CoV-2 which contains structural proteins (CDC, 2020).

Fig. 3

A schematic diagram to show the different environmental transmission routes of SARS-CoV-2 in animals and humans. Routes 1 and 2: Bats may either directly or indirectly act as a vector to pass on the SARS-CoV-2 viral infection to humans; Route 3: Infections are caused directly or indirectly by aerosols and droplets exhaled by the humans; Route 4: Falling aerosols or droplets may resuspend through the soil causing transmission; Route 5: The entry of excreta into sewage may cause water spread; Route 6: The excreta enters the sewage and the virus-containing air around the sewage may cause transmission; Route 7: Water containing the virus entering the soil can cause infection; Route 8: Animals (e.g., cockroaches) that can transmit pathogens to humans may cause the spread of SARS-CoV-2; Route 9: Animals can spread SARS-CoV-2 through contact with contaminated surfaces and secretions from sick people; Route 10: People can become infected by touching contaminated objects with their hands; Route 11: It may cause long-distance cold chain transmission through low temperature treatment of food, freezing storage and the cold-chain for transporting.

Fig. 4

Morphology and composition of different types of particles. (a–e) Scanning electron microscope [SEM] image. (f) Transmission electron microscope [TEM] image.

Fig. 5

The size range of different types of particles. The graph denotes the size ranges between ambient aerosol (e.g., Ca aluminium silicate Grossular) with irregular morphology; scanning electron microscope [SEM] image), PM₁₀ (e.g., coal fly ash particles; SEM), PM_2.5 (e.g., an aggregate of carbon black particles, SEM image), nanoparticles (ultrafine particles) (e.g., aggregate, transmission electron microscope [TEM] image), respiratory aerosol (e.g. soot particles, SEM), respiratory droplets (SEM), virus SARS-CoV-2 (TEM). The SARS-CoV-2 viral particles with aerodynamic diameters of 0.06–0.14 μm fall within the “highly respirable” size range.

Fig. 6

Aerosol propagation in sewage pipes (modified after Gormley et al., 2017).