key: cord-282964-dmc8mlxu
authors: Wathore, Roshan; Gupta, Ankit; Bherwani, Hemant; Labhasetwar, Nitin
title: Understanding air and water borne transmission and survival of coronavirus: Insights and way forward for SARS-CoV-2
date: 2020-08-04
journal: Sci Total Environ
DOI: 10.1016/j.scitotenv.2020.141486
sha: 
doc_id: 282964
cord_uid: dmc8mlxu

Abstract The ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in unprecedented disease burden, healthcare costs, and economic impacts worldwide. Despite several measures, SARS-CoV-2 has been extremely impactful due to its extraordinary infection potential mainly through coronavirus-borne saliva respiratory and droplet nuclei of an infected person and its considerable stability on surfaces. Although the disease has affected over 180 countries, its extent and control are significantly different across the globe, making it a strong case for exploration of its behavior and dependence across various environmental pathways and its interactions with the virus. This has spurred efforts to characterize the coronavirus and understand the factors impacting its transmission and survival such as aerosols, air quality, meteorology, chemical compositions and characteristics of particles and surfaces, which are directly or indirectly associated with coronaviruses infection spread. Nonetheless, many peer-reviewed articles have studied these aspects but mostly in isolation; a complete array of coronavirus survival and transmission from an infected individual through air- and water-borne channels and its subsequent intractions with environmental factors, surfaces, particulates and chemicals is not comprehensively explored. Particulate matter (PM) is omnipresent with variable concentrations, structures and composition, while most of the surfaces are also covered by PM of different characteristics. Learning from the earlier coronavirus studies, including SARS and MERS, an attempt has been made to understand the survival of SARS-CoV-2 outside of the host body and discuss the probable air and water-borne transmission routes and its interactions with the outside environment. The present work 1) Helps appreciate the role of PM, its chemical constituents and surface characteristics and 2) Further identifies gaps in this field and suggests possible domains to work upon for better understanding of transmission and survival of this novel coronavirus.

J o u r n a l P r e -p r o o f inanimate surfaces, and other chemicals. Chemical composition of these factors is also looked into, which can significantly impact SARS-CoV-2 survival and transmission. Finally, this study outlines probable air and water borne routes and suggest a way forward highlighting the need for investigating the effect of particulate matter characteristics on survival and transmission of SARS-CoV-2 due to the prominent presence of PM in ambient, spaces, and on the surfaces.

Hospitals and quarantine centres (institutional and residential) are high-risk environment for nosocomial transmission; data which included information on whether the patient was a healthcare worker in the United States, reported that 19% were healthcare workers (N = 49,370) (CDCMMWR, 2020) compared to 20% for MERS and around 21% for SARS (Mackay and Arden, 2015; . These numbers suggest that extra disinfection and preventive measures, as well as precautions, need to be taken in the healthcare facilities to minimize the cross infection, as the staff spends most of their time in close vicinity of the infected patients.

Outside of the hospital, community transmission can happen through close contact with infected family members or in crowded public spaces (Jiaye Liu et al., 2020) . Community transmission from an asymptomatic carrier is also a possibility (Al-Tawfiq, 2020; Bai et al., 2020; Gandhi et al., 2020; Kaur et al., 2020; . Once inhaled , SARS-CoV-2 targets a cell-surface receptor called angiotensin-converting enzyme 2 (ACE2), which is highly expressed in the respiratory tract, lungs, intestine, kidney, and heart; this pathogenesis mechanism is described in detail elsewhere (Docea et al., J o u r n a l P r e -p r o o f (van Doremalen et al., 2020) . SARS-CoV-2 can survive on inanimate surfaces such as printing papers and tissue papers for up to 3 hours, treated-wood for up to 2 days; can last longer on smoother surfaces such as glass and banknotes for up to 4 days, and stainless steel and plastic for up to 7 days.

Interestingly the virus was detected even after seven days on the outer layer of a surgical mask (Chin et al., 2020) . The survival of SARS-CoV-2 on surfaces is summarized in Figure 1 . Therefore, fomite transmission would depend on the surface characteristics, which can affect virus survival and can help determine extent of spread of the disease. However, it is not justifiable to consider that these surfaces will always be free from dust and particles, which can have significant impacts on virus survival in addition to inherent surface properties as often studied. These interactions have been explored in Section 5.

The third mode of probable transmission of coronaviruses is via faeces. A controlled study on aerosolization of faecal waste contaminated with avian influenza virus shows that faecal transmission could be a serious risk for both humans and animals (Sedlmaier et al., 2009) . In an earlier study, SARS-CoV is reported to be stable in faeces at room temperature for a minimum of 1-2 days and can survive for up to 4 days in stool from diarrheal patients (Lai et al., 2005) . SARS-CoV-2 is also detected in faeces raising the possibility of faecal-oral transmission Yeo et al., 2020) ; especially during flushing which can aerosolize faecal matter, resulting in airborne transmission (Section 2.1) (McDermott et al., 2020) . Such probability of transmission is high in hospital and quarantine centers settings where toilets are shared.

Flushed water entering into sewerage systems also becomes another carrier medium for this virus. A previous study determined that coronaviruses can survive up to 2-3 days in sewage water and up to 10 days in tap water at 23 °C; factors for survival include temperature, organic matter levels and presence J o u r n a l P r e -p r o o f of antagonistic bacteria and oxidants such as chlorine (Gundy et al., 2009) . These aspects of aerosolization through flushing and entry into sewage calls for detailed analysis and focused research in this area. Such type of probable routes of transmissions should be thoroughly researched for virus transmission and survival in these mediums as these possibilities may aggravate the problem to community transmissions (Heller et al., 2020) . Some of the early researches in this area has suggested presence of RNA of SARS-CoV-2 in sewage water , however, the persistence of the virus in water and sewage is yet to be determined (La Rosa et al., 2020) . 

The research studies have highlighted that the air-borne transmission of coronavirus is one of the most potential ways of its infection (Morawska and Cao, 2020; Setti et al., 2020) . The studies have also suggested that intractions of virus laden droplet nuclei can possibly infect an individual in direct contact, however the droplet nuclei (diameter < 5 µm) can become air-borne and travel greater distances compared to respiratory droplets (diameter > 5-10 μm), thereby increasing the zone of spread. Ultrafine particles present in ambient air have residence times in the order of days or weeks enabling transport up to thousands of kilometers in the atmosphere, while coarser particles, which are heavier tend to deposit quicker and typically travel less than 10 km from their place of generation. ( Although the PM can play a role in harboring microorganisms including coronavirus, the interaction of varied composition of the PM with coronavirus remains unaddressed i.e. transmission and survival of virus on PM with different constituents/compositions, including black carbon and heavy metal particulates etc. On the other hand, exposure to PM levels exceeding the guidelines (for yearly average PM 2.5 and PM 10 exposure is 20 µg/m 3 and 40 µg/m 3 respectively) and will adversely affect the immune system (WHO, 2018) thus further aggravating not only infection potential of virus but also severity of health impacts. There is substantial evidence of both short-term and chronic exposure to high levels of fine-ultrafine PM and other anthropogenic pollutants being associated with detrimental health effects including exacerbating pre-existing respiratory diseases, by deposited deep inside the lungs, especially pulmonary alveoli (Chen et al., 2016) , through a combination of inertial impaction, gravitational sedimentation, and diffusion mechanisms (Darquenne, 2014) . Inhaled PM 2.5 can get deposited in different compartments in the respiratory tract and interact with epithelial cells and resident immune cells, inducing local or systematic inflammatory responses (Wei and Tang, 2018) . Thus, if the particulates are virus laden, the exposure may worsen the health condition of an individual, by not only infecting a person with COVID-19 but could also impact the individual immune system, thereby increasing the viral infectivity, morbidity and mortality, especially in children and adults (Pope III, 2007; Li et al., 2016; Pope et al., 2018; Kirrane et al., 2019; Tsatsakis et al., 2020) .

Apart from air-borne intractions of the virus and PM, these intractions could also frequently happen on the different environmental surfaces, where the coarse PM and virus-laden respiratory nuclei can settle and contaminate surfaces. Along with the PM, atmospheric bioaerosols including viruses, fungi, Journal Pre-proof J o u r n a l P r e -p r o o f bacteria, and algae, whose combination with PM, could be associated with improved virus survivability, possibly promoting the ability of the virus to grow and multiply (Turaga et al., 2012) . Increased abundance of microbes have been reported during high PM pollution and smog events as compared to clear and sunny days (Cao et al., 2014; Wei et al., 2016) . Now, when such infected surfaces are touched, can act as a path to introduce the virus to an individual by mouth, nose, or eyes. These surfaces can also re-suspend in the virus-laden particulates during high wind turbulence, simultaneously enabling airborne infections.

It is also critically essential to investigate and to understand the impact of PM compositional charateristics and morphology on virus survival, which will prominently determine its spread from air and surfaces, as many compounds associated with PM can be toxic to the virus survivability. As a first step, highlighting the need, the presence of heavy metal particulate matter and its interaction with the virus is discussed in subsequent Section 4.1. It can be inferred that different PM compositions can have different survivability of the virus and thus, the role of PM aiding the air-borne and surface transmission can't be generalized and present an important subject for further study.

There has been a substantial number of recent studies characterizing SARS-COV-2 and its association with criteria pollutants and environmental parameters. Table 1 summarizes outcomes of selected recent studies, which looked into associations of some of these factors with COVID-19 transmission and fatality. From Table 1 , it could be inferred that higher temperature, UV radiation and wind speeds are associated with lower risk of COVID-19 transmission, although other political/administrative, demographic, environmental and scientific factors will have confounding effects (Bherwani et al., 2020a (Bherwani et al., , 2020c Goumenou et al., 2020) . The effect of humidity on the virus transmission, is not clearly understood and would require more scientific evidence to establish the cause and effect relationships. It is also reported that the effect of environmental factors, will be greatly undermined, the social (physical) distancing is not properly followed (Bherwani et al., 2020b; Gupta et al., 2020) .

Studies looking into both short-and long-term exposure to criteria pollutants found confirmed associations of pollution levels with COVID-19 spread or fatalities, with higher levels resulting in increased fatalities. This could be mainly due to the health impacts of such pollutants, which would make the people more vulnerable to COVID-19 infection and may not be actually considering the stability of the virus on polluted surfaces, especially with respect to PM composition. Interestingly, short-term exposure to a higher concentrations of SO 2 is associated with decreased risk of COVID-19 infection (Y. , thereby further strengthening and testifying the present hypothesis that atmospheric chemistry and PM characteristics can significantly affect virus survival as this can play a vital role in the spread of disease through both most potential modes of transmissions, i.e. airborne and fomite.

Studies on virus survival and interaction with different surfaces and chemicals have also been reported in an effort to better understand SARS-CoV-2 survival characteristics.

Metal ions play an important role in the survival of viruses. Mg, Zn, and Cu are some of the metal ions that can bind to virus proteins and can be part of RNA and DNA processes (Tunde et al., 2020) .

Derivatives of Bismuth have shown to efficiently inhibit the growth of SARS-CoV . Zinc 

Antiviral properties of essential oils and their components have been well documented and studies have demonstrated substantial inhibition of different strains of the influenza virus, dengue virus, and others (Nerio et al., 2010; Raut and Karuppayil, 2014) . More recently, a study showed that organosulfur Hence, PM plays a multifaceted role of providing surfaces for pathogen transmission and interaction, enabling fomite transmission by deposition, as well as chronic weakening of the immune and respiratory system, making the virus more potent in regions with higher PM levels. Its omnipresence in the atmosphere and on surfaces (due to deposition), makes it an important subject for further study to understand the impact of PM composition on virus survival, which will prominently determine its spread from surfaces rather than the only type of surfaces as studied so far.

Further, the chemical composition and mass concentrations of PM is highly variable and dependent on Journal Pre-proof J o u r n a l P r e -p r o o f local geography, meteorology, seasonal patterns and sources of emissions such as traffic, re-suspended dust, industrial, residential, biomass burning, natural and other sources (Karagulian et al., 2015) . SARS-CoV-2 (diameter 60-140 nm) can attach itself to PM components such as dust or marine organic aggregates and eventually deposit (Sanità di Toppi et al., 2020) . Some of the constituents of PM which may interact with these viruses are compiled in Table 2 . This lack of above information prevents complete understanding on the stability of coronavirus on PM and PM-contaminated common surfaces. These particles are almost omnipresent and can significantly influence the interaction of viruses with different surfaces studied so far, as often these surfaces are not completely clean in real world conditions. This certainly presents a very complex matrix to be explored, however considering its presence in spaces and atmosphere, such investigations will be of great 

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