Letter to the Editor regarding Mathavarajah et al. (2020) Pandemic danger to the deep: The risk of marine mammals contracting SARS-CoV-2 from wastewater.

Dear Profs. Barceló and Gan,

We read with great interest the work by Mathavarajah et al. (2020) “Pandemic danger to the deep: The risk of marine mammals contracting SARS-CoV-2 from wastewater,” (doi: https://doi.org/10.1016/j.scitotenv.2020.143346). We appreciate the novelty of the work and the focus on marine mammal protection from SARS-CoV-2 transmission via wastewater, but we would like to take the opportunity to highlight new relevant research and contextualize some of the discussion in the article.

To this date, infectious SARS-CoV-2 has not been detected in untreated or treated wastewater or aquatic environments. Despite this, it is becoming increasingly common for researchers to overemphasize the risk resulting from exposure to wastewater. This overestimation of risk is frequently based on two sources of data: the detection of SARS-CoV-2 RNA in various wastewater matrices, and the detection of viable virus in feces.

Given the presence SARS-CoV-2 RNA and its extensive use for wastewater surveillance efforts, concentrations of SARS-CoV-2 RNA in sewage are widely available in the literature (Sherchan et al., 2020; Jones et al., 2020). Data on infective virus survival in wastewater, however, is very limited and not interchangeable or correlated with RNA concentrations. The recent work by Bivins et al. (2020) is currently the only study to date that assessed survival of infective SARS-CoV-2 in spiked wastewater samples in parallel with SARS-CoV-2 RNA. Bivins et al. (2020) reported a 90% reduction in viable SARS-CoV-2 concentrations in 1.5 days in wastewater at room temperature and demonstrated that SARS-CoV-2 RNA was significantly more persistent than infectious virus. This work was not available at the time of publication of Mathavarajah et al. (2020). We agree with the authors that more research on survival of infectious SARS-CoV-2 in wastewater is needed to better interpret risk in various environments.

Mathavarajah et al. question whether primary treatment and lagoons are effective at managing SARS-CoV-2 transmission risk through wastewater. Recent evidence has confirmed the affinity of this virus to associate with solids in wastewater, which are partially removed in primary treatment (Balboa et al., 2020; D'Aoust et al., 2020; Randazzo et al., 2020) confirming previous findings by various authors (Ye et al., 2016; Gundy et al., 2009). Previous work also highlights that the 2015 World Health Organization guidance of holding latrine waste for more than 7 days was deemed protective against enveloped viruses (e.g., Ebola virus) in non-centralized treatment systems (Casanova and Weaver, 2015). This retention time in combination with extreme weather conditions and dilution effects, would be expected to negatively impact virus infectivity. Furthermore, the WHO addressed the water sanitation and hygiene risks of SARS-CoV-2 and COVID-19 to humans and concluded that such risks are negligible due to lack of documented presence of infectious virus in wastewater and the effectiveness of current management systems against this and other viruses in wastewater and water treatment systems (WHO, 2020).

Jefferson et al. (2020) provided a detailed review of the nine publications reporting presence of infective SARS-CoV-2 in feces. We agree that the potential for transmission of SARS-CoV-2 via the fecal-oral route exists, but we would like to highlight that current data suggests that this risk is low and mainly relevant in areas where sanitation and hygiene are compromised and exposure to fresh feces is expected (Jones et al., 2020). This is supported by the recent work by Yuan et al. (2020), which epidemiologically linked fresh sewage and faulty plumbing in an outbreak, similar to what happened with the SARS-CoV-1 Amoy Gardens outbreak. Yuan et al. recommended regular inspection and maintenance of plumbing systems to limit transmission of SARS-CoV-2 in densely populated areas; a recommendation that aligns with other authors (Gormley et al., 2020). Interestingly, Yuan et al. (2020) also reported that they were unable to provide direct evidence of sewage transmission because cell culture assays of clinical and environmental samples were negative. This corresponds with recent studies that have shown that the colonic environment is inhospitable for new SARS-CoV-2 virions released into the intestinal lumen (Zang et al., 2020; Wölfel et al., 2020). This evidence implies that concentrations of viable SARS-CoV-2, and thus exposure, are both highly variable and typically low.

In addition, Mathavarajah et al. reference various surrogate studies that used tap or freshwater matrices and use these to extrapolate potential SARS-CoV-2 survival in marine environments. They cite the SARS-CoV-2 viability estimate of 25 days modeled by Shutler et al. (2020) which used a ratio of infective adenoviruses to DNA concentrations in sewage to estimate SARS-CoV-2 viability; this is a highly conservative estimate using a non-enveloped virus that likely significantly overestimates viral persistence and risk. Finally, Mathavarajah et al. are vague about reported results in different parts of the manuscript. For example, they cite La Rosa et al. (2020) stating that “…, in Italy, SARS-CoV-2 was recently detected in untreated wastewater, and as such, its survival in water and wastewater represents a significant form of transmission to consider.” In fact, this study looked for SARS-Cov-2 RNA only and made no effort to detect or quantify infectious virus by initially heat inactivating their collected samples. Meanwhile, Rimoldi et al. (2020) reported no infective SARS-CoV-2 in wastewaters and rivers in Italy. At times when so many knowledge gaps exist, clarity and specificity of methods and findings is helpful.

We appreciate the importance of mitigating risks from emerging contaminants in wastewater to protect public and environmental health. We also agree that given the demonstrated susceptibility of marine mammals to SARS-CoV-2 infection restricting access between marine mammals and humans can prevent the most significant form of COVID-19 transmission. However, based on scientific evidence to date, wastewater does not appear to be a significant transmission route for SARS-CoV-2. Diverting critical and limited resources from arctic communities by focusing on wastewater treatment upgrades in the midst of this pandemic will not aid the battle against COVID-19. It is unlikely to protect marine mammals. Unfortunately, the tendency to overstate the risk resulting from exposure to wastewater based on presence of viral RNA has resulted in much confusion amongst the public, decision makers and utilities.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.