1. Introduction
Antarctica has long been considered a geographically isolated continent [
1]. Consequently, the introduction of any organism has the potential to disrupt the existing biota [
2,
3,
4]. Even microorganisms responsible for causing infections in humans face substantial barriers in reaching the continent [
5]. This is primarily attributed to the stringent regulations imposed by the signatory governments of the Antarctic Treaty, which strictly control access to Antarctica. Moreover, during the winter months, human presence is notably limited, with around 90% of activities being concentrated in the spring and summer seasons. One of the advantages of maintaining controlled access to Antarctica is the preservation of a complete absence of SARS-CoV-2, causative agent of COVID-19, on the continent for approximately nine months. However, in December, the first case of COVID-19 was detected at the Chilean O’Higgins station. One of the primary concerns regarding the spread of COVID-19 in Antarctica was the limited availability of medical equipment at the research stations and the inability to transfer potentially critically ill patients to more advanced healthcare facilities. Fortunately, there were no reports of severely ill patients, and no one had to be transported to the South American continent. Nonetheless, a significant concern revolved around the potential transmission of the virus to wildlife [
6,
7].
The spread of the pandemic in Antarctica was closely linked to the start of summer campaigns at different research stations. As of December 16th, 2020, Chilean health authorities had reported 60 confirmed cases. One of the initial steps taken to mitigate the rise in cases was to administer diagnostic tests to all personnel, both at the scientific stations and before their arrival on the Antarctic continent. Nonetheless, even with infected individuals under control, it remained essential to determine whether the virus was being released into the environment. To achieve this, wastewater monitoring was implemented in some of the Chilean scientific stations. The detection of SARS-CoV-2, in this type of sample has been extensively documented in the scientific literature [
8,
9,
10,
11]. Currently, measuring and quantifying the SARS-CoV-2 in wastewater has been established as an effective surveillance measure [
12,
13]. Once the virus enters wastewater due to its release in the feces and secretions of infected individuals, its persistence in water is limited, as it undergoes accelerated degradation processes, especially in the marine environment [
14,
15,
16]. This characteristic minimizes the risk of infecting potential hosts in the marine ecosystem, which could serve as animal reservoirs for the virus.
Despite the limited amount of research describing the presence of SARS-CoV-2 in marine animals, its detection has been documented in species such as Pacific oysters and other bivalves [
17,
18]. These filter feeders reveal the virus’s ability to reach coastal and estuarine environments. A primary concern lies in the compounds released by wastewater treatment plants (WWTP) that utilize biological treatment systems. Several studies detail different methods through which the virus can be released, including its complete form (comprising the envelope, nucleocapsid, and genetic material), only the nucleocapsid in combination with the genetic material, or solely the genetic material [
19,
20]. In Antarctica, most scientific stations, whether permanent or seasonal, are equipped with biological treatment systems in their wastewater facilities [
21]. Consequently, there is a potential impact on wildlife due to the release of materials contaminated with SARS-CoV-2 in this region.
To assess the potential presence of SARS-CoV-2 traces in the WWTP of scientific stations where cases of SARS-CoV-2 infection have been identified, samples were collected from both the effluent and the influent. Furthermore, an investigation was conducted to ascertain the presence of the virus in the feces of animals inhabiting nearby areas, aiming to determine its existence in the surrounding wildlife.
4. Discussion
The first Covid-19 outbreak in Antarctica was reported in December 2020, with 60 positive cases confirmed by PCR test. These cases were detected at scientific stations in the South Shetland Islands and the Antarctic Peninsula, raising concerns about the potential contact between infected humans and wildlife, as well as the release of fecal material into the marine environment. Hughes and Convey, (2020) [
7] expressed their concern regarding the potential for zoonotic transmission of SARS-CoV-2 from humans to Antarctic wildlife, which could lead to rapid spread within colonies and even mass mortality events among animals, or the creation of a new reservoir with zoonotic potential [
36,
37].
Our data indicates the presence of SARS-CoV-2 in the WWTPs of the scientific Antarctic stations, each with variations in their technology. While the WWTP at Escudero and O’Higgins stations utilize both mechanical and biological processes, the Frei WWTP employs a red worm in the treatment process, which feed on bacteria in both the activated sludge and trickling filter systems. Ultimately, UV light is employed for purification at all three stations as part of the final treatment phase. Several authors have previously reported the potential release of the virus into the environment. Randazzo et al. (2020) [
27] demonstrated that WWTPs with only secondary treatment can release SARS-CoV-2 RNA in their effluents, mirroring the findings of our study in the WWTPs sampled [
38] suggest, at least part of SARS-CoV-2 virions or their RNA present in sewage effluents may flow into watercourses and eventually be released into coastal areas.
Interestingly, the initial detection of SARS-CoV-2 at King George Island aligns with the first outbreak reported in December 2020. The substantial number of genomic copies identified at the Escudero WWTP was substantiated by the isolation of a single symptomatic suspect case, following the protocol established for suspected cases in Antarctica. However, the continued presence of SARS-CoV-2 in the WWTP could be attributed to asymptomatic cases that went undetected during quarantine due to certain shortcomings in the protocol. This is even though all personnel were tested before their arrival in Antarctica. SARS-CoV-2 is a recent emergence, and we require more data to comprehend its behavior in the environment. An analysis of surrogate coronaviruses’ survivability in water and sewage was conducted by Casanova et al., (2009) [
39], revealing their persistence and infectiousness at both low (4 °C) and moderate (25 °C) temperatures [
40]. Additionally, some studies have reported that certain coronaviruses can endure extreme cold, surviving for years at temperatures as low as -60°C while retaining their infectious properties [
41]. These lower temperatures might contribute to the viral particles’ persistence in polar environments.
Other factors, such as organic matter or solid fraction in water, could enhance survival of the viral population. Organic matter particles, for instance, can physically shield the virus, as documented by Paul et al. (2021) [
40]. The detection of SARS-CoV-2 RNA in the influent wastewater at the Antarctic station suggests that WWTPs, influenced by factors like temperature and organic matter, might intensify the potential interaction of the virus with wildlife. This necessitates the quantification of the infective dose, determination of the number of viable virus particles in feces, and the collection of additional data regarding its viability in water systems [
42].
However, it’s essential to note that the presence of SARS-CoV-2 RNA in the aquatic environment does not necessarily confirm the presence of infectious virus. Estimating the number of viable virus copies requires knowing the proportion of infectious virus in wastewater [
43]. Consequently, further research is necessary for WWTPs in Antarctica. Based on the current literature and scientific evidence to date, it is crucial enhance the efficiency of greywater treatment plant systems, potentially incorporating new technologies [
44]. One consideration could be the addition of a final disinfection step, like ozonation of wastewater, to further reduce the risk posed by viral pathogens, such as SARS-CoV-2, before discharge into the sea. Also, it is equally important to ensure the timely replacement and optimal maintenance of UV lamps if they are used in the final treatment process [
40].
Coronaviruses have been identified from a variety of wild birds and mammals [
45,
46]. Among wild birds, gammacoronavirus is the predominant type of CoV, followed by deltacoronavirus [
47]. Notably, a potential species of deltacoronavirus has been observed in healthy Antarctic penguins [
48,
49]. Although this virus does not induce illness, its presence in these penguins underscores the extensive geographical coronaviruses of this type.
The initial evidence of SARS-CoV-2 presence emerged in clam populations of the
Ruditapes sp. genus due to untreated water discharges in Galicia, Spain [
38]. A related species, the bivalve filter-feeder known as the Antarctic clam (
Laternula elliptica), has the potential to accumulate viral RNA in areas near WWTPs discharges. Aquatic mammals such as cetaceans, including the Antarctic minke whale (
Balaenoptera bonaerensis) and killer whale (
Orcinus orca), as well as the Antarctic fur seals and Wedell seals, which retain many key receptor binding domains for SARS-CoV-2, are subjects for assessing the virus persistence [
50]. Further investigations are required to evaluate the susceptibility of Antarctic mammals to coronaviruses, including SARS-CoV-2 [
6]. However, our study did not detect SARS-CoV-2-RNA-positive free-ranging animals, suggesting that there was no widespread circulation among the few species examined during the study period.
Invasive species such as insects on King George Island generate a significant concern, and this concern should be heightened in the current pandemic context. Most of the insects arriving in Antarctica are as sociated with treatment plants, increasing the likelihood of interaction with contaminated feces. It is essential to continue monitoring insects like
Trichocera maculipennis found in the treatment plants of King George Island, which could potentially serve as vectors for virus transmission to the environment through routes other than aquatic [
51]. Although the ACE2 receptor in insects differs significantly from that of mammals, making efficient binding with SARS-CoV-2 unlikely it has been reported that arthropods were involved in the mechanical transmission of the turkey coronavirus, parapoxvirus, and SARS-CoV-2 [
52,
53]. Experimental studies have demonstrated that houseflies may be a vector for SARS-CoV-2 genomic RNA transmission to the surrounding environment up to 24 h post-exposure [
54]. Finally, it is advisable to implement a monitoring program to assess the potential presence of SARS-CoV-2 in WWTP using PCR techniques or biosensor-based technologies, which have been extensively employed for virus detection. This monitoring should also include an evaluation of the impact of human activities on the Antarctic ecosystem.
Author Contributions
Conceptualization: J.O.P., M.G.A.; Methodology: J.O.P., M.G.A., E.C.N., A.A.; Validation: J.O.P., M.G.A.; Formal Analysis: J.O.P., M.G.A., G.B., V.M., L.K.; Investigation: J.O.P., M.G.A., A.A., V.N., L.K. Resources: J.O.P., M.G.A., E.C.N., G.B.; Data Curation: J.O.P., M.G.A., E.C.N., G.B., V.N.; Writing – Original Draft Preparation: J.O.P., M.G.A.; Writing – Review & Editing: J.O.P., M.G.A., C.G.M., E.C.N., G.B., V.N., L.K., A.A.; Visualization: J.O.P., M.G.A., G.B.; Supervision: J.O.P., M.G.A.; Project Administration: J.O.P., M.G.A,; Funding Acquisition: J.O.P., M.G.A., E.C.N., G.B.