On February 11, 2020, the World Health Organization identified the causative agent as the coronavirus and named it coronavirus disease (COVID-19). Reference Hoehl, Rabenau, Berger, Kortenbusch, Cinatl and Bojkova1,2 As of May 31, 2023, more than 767 364 million people have been infected with the disease and nearly 7 million deaths have been recorded. In addition to endangering the lives of millions of people worldwide and a variety of social and economic consequences, its direct and indirect effects on the environment have also been discussed. 3
Negative effects related to human activities in the environment include global warming, urban sprawl, and accelerated species extinction. The view that humans play a major role in threatening species and ecosystems suggests that global human quarantine to reduce COVID-19 health hazards may reduce human impact and result in positive environmental responses. Indeed, initial reports indicate that the restrictions have led to an immediate reduction in air, land, and water travel, with similar reductions in industry, commercial exploitation of natural resources and production, and lower levels of PM10, NO2, CO2, SO2, and noise pollution.
However, a more comprehensive examination of the links between human activities, species, and ecosystems acknowledges the role of humans as conservationists, who participate in environmental protection research, biodiversity monitoring, habitat restoration, and wildlife-related executive activities. Indeed, COVID-19 global human quarantines have disrupted conservation, research, and policy processes to improve the global environment and biodiversity. The quarantine has also created economic insecurity in rural areas, which may pose a threat to biodiversity as humans seek to earn a living through illegal hunting and fishing. Reducing ecotourism in and around national parks and other protected areas has reduced funding for hunting restrictions and invasive species management programs. In general, there is a combination of positive and negative effects of lockdown following an epidemic on nature, which has the potential to lead to chain reactions that in turn affect wildlife and nature conservation. However, the effect of an issue such as lockdown requires more than several years of evaluation, and with the availability of data and the emergence of persistent epidemic effects, the response is being mapped around the world. Reference Bates, Primack and Biggar4,Reference Bates, Primack, Moraga and Duarte5
As mentioned, COVID-19 is one of the emerging infectious diseases that, along with the increase in human population, has increasingly disrupted natural ecosystems. 6 The outbreak of COVID-19 has caused concern around the world and changed the way people live. This change in human lifestyle has brought advantages and disadvantages to the environment, which necessitates research on these effects focusing on the presence and evolution of the COVID-19 pandemic in water, soil, and other environmental factors, as well as providing solutions to improve the environment. Despite the positive effects of coronavirus on the environment such as improving air quality, cleaning beaches, and reducing noise pollution, there are primary and secondary negative aspects such as excessive water consumption, reduced waste recycling, and increased organic and inorganic waste that lead to air, water, and land pollution. Policy-makers’ responses to the epidemic have also had profound effects on the environment. These effects include a combination of aggravating and improving factors of environmental pollution. Reference Sunyer, Dadvand and Foraster7 Since the positive and negative effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on the environment are not clear, this research aims to review the published articles examining the effects of the COVID-19 pandemic on environmental health.
Material and Methods
A systematic review was conducted to investigate the association between the COVID-19 pandemic with air quality, water resources, and the environment. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standard guidelines were used to follow up the review process and report findings. Reference Moher, Shamseer and Clarke8
Search Strategy and Selection Criteria
This review focused on studies about environmental pollution and or environmental impact that were published in English language journals up to the end of February 2022. The databases of Web of Science, PubMed, and Scopus were searched for medical subject headings (MeSH) and relevant key words, including “Environment,” “environmental pollution,” “Environmental Impact,” “COVID-19,” “COVID-19 virus,” “coronavirus disease 2019,” “SARS-CoV-2,” “pandemic,” and “outbreak.” They were used in isolation or combination through the Boolean method.
Inclusion and exclusion criteria
All English-language articles published in the world on air quality, water, environment, or a combination of these indicators and COVID-19 that were of high quality entered the study.
Exclusion criteria included articles of low quality, and studies conducted on other infectious diseases were excluded from the study. Those articles published in non-English language were also excluded. Additionally, meta-analysis, case reports, or series of cases were excluded, as well.
Quality assessment
The quality of the articles was assessed using the Strobe checklist (Strengthening the Reporting of Observational Studies in Epidemiology). This checklist has 6 scales, including: title, abstract, introduction, methods, results, and discussion. Some of these scales have subscales, resulting in a total of 32 subscales. Therefore, the maximum score that can be captured from the assessment using the checklist is 32, considering the score of 16 as the cutoff point. Reference Salari, Mohammadi and Vaisi-Raygani9 In this study, an acceptable score of 16 was considered. Scores 16–24 were medium, and scores greater than 24 (high quality) were considered.
Screening and Data Extraction
The search results were imported into the Mendeley software and duplicate titles were deleted. Selected studies were entered into abstract reading and were checked against the inclusion criteria, of which the most relevant studies were selected for independent full-text reading by 2 researchers (SD, JB) and a third person as the expert-epidemiologist checked the result. Reasons for the rejection of studies were mentioned and in case of disagreement between the researchers, the perspective of a third researcher was sought. A checklist was used to extract data from the selected studies in terms of the sample size, study location, study year, type of study, COVID-19 pandemic, environmental pollution, and/or environmental impact.
Selection of articles
By searching databases, 264 studies were extracted. Initially, the articles were entered into Mendeley software and after an initial review, 27 articles were removed from the study due to duplication. Then, by reviewing the titles and abstracts of articles, 5 articles were excluded due to not corresponding with inclusion criteria and 169 articles were removed due to irrelevance, and after reviewing the full text of articles, 5 articles were excluded due to lack of the required information. Finally, 58 articles met the inclusion criteria and entered the process of systematic review (Figure 1).
Figure 1. In total, 58 articles met the inclusion criteria and entered the process of systematic review.
Findings and Discussion
Of the total 58 studies presented, 26% of the articles worldwide reported their results, and about 28% of these studies were dedicated to India. About 69% of the articles were published in 2020, according to the time of publication (Figure 2).
Figure 2. Number of articles published by year.
Among the findings of this study, out of a total of 58 articles, 47 studies referred to the impact of positive aspects of the COVID-19 pandemic on water, air, and environmental quality, and the remaining 11 articles simultaneously examined the positive and negative effects of this disease (Table 1).
Table 1. General characteristics of the studied articles that were eligible for the review
AAI, absorbing aerosol index; CO, carbon monoxide; and GHG, greenhouse gas.
In total, 62% of the studies examined only air quality variables such as NO2, NO, CO, CO2, PM10, and PM2.5 Reference Wang and Su10,Reference Chakraborty and Maity12,Reference Abdullah, Mansor and Napi20,Reference Muhammad, Long and Salman22,Reference Srivastava, Kumar and Bauddh35,Reference Gupta, Tomar and Kumar40 ; 15.5% Reference Selvam, Jesuraja and Venkatramanan34,Reference Karunanidhi, Aravinthasamy and Deepali41,Reference Chakraborty, Roy and Bera43,Reference Najah, Teo and Chow50 examined water quality variables; 10.5% Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Barcelo15,Reference Kafeel, Ansari, Khan and Owens17,Reference Mukherjee, Babu and Ghosh33,Reference Mousazadeh, Paital and Naghdali44 probed both climate quality indicators; and 12% Reference Saadat, Rawtani and Hussain13,Reference Cheval, Adamescu and Georgiadis14,Reference Lal, Kumar and Kumar16,Reference Shakil, Munim, Tasnia and Sarowar18,Reference Bar42 assessed the overall effects of COVID-19 pandemic on the environment. Due to the emergence of this disease, there are still many unknown aspects, but the main research in this field can be divided into 3 parts: the impact of the pandemic on air quality, water quality, and other environmental resources. These articles have studied positive or negative, or both (+ and-), aspects of the pandemic.
Effect of the COVID-19 Pandemic on Air Quality
The results of studies in this regard indicate a significant reduction in air pollutants and improved air quality in the short lockdowns and national quarantines of the COVID-19 pandemic. Reference Wang and Su10,Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Saadat, Rawtani and Hussain13,Reference Lal, Kumar and Kumar16–Reference Shakil, Munim, Tasnia and Sarowar18,Reference Chakraborty, Roy and Bera43 Air pollutants, such as emissions of NO2 and carbon dioxide (CO2), were significantly reduced due to industrial shutdowns and reduced worldwide transportation. Reference Lokhandwala and Gautam28 Also, the amount of greenhouse gases has decreased significantly in the short term. Reference Wang and Su10,Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11 In the study of Muhammad et al., air pollution was reduced by 30% and the level of mobility was reduced by about 90%. Reference Muhammad, Long and Salman22 Collivignarelli reported a significant decrease in NO2 concentration due to reduced traffic in different cities: in London from 71.1-80.8%, in Milan from 8.6-42.4%, and in Paris from 65.7-79.8%, respectively. Reference Collivignarelli, De Rose and Abbà23 In their study of Southeast Asia, Kanniah reported that levels of PM10: 26-31%, PM2.5: 22-32%, NO2: 63-64%, SO2: 9-20%, and CO: 25-31% have decreased. Reference Kanniah, Kamarul Zaman, Kaskaoutis and Latif24 By analyzing air quality before and after 21 days of lockdown in India, Srivastava showed that these restrictions had major effects on reducing the levels of NO2, SO2, CO, and PM2.5. Reference Srivastava, Kumar and Bauddh35 During the COVID-19 pandemic, global demand for coal fuel in March and April 2020 decreased by 8% compared to the same time in 2019. In terms of emissions, the lockdown has reduced nitrogen oxide emissions by 20 to 30% in China, Italy, France, and Spain and by 77.3% in Sao Paulo, Brazil. Emissions of nitrogen oxides in India decreased between 20 and 77% and in different cities this reduction varied between 16 and 67%. Some studies have reported a reduction in particulate matter from 5–15% in Western Europe to 200% in New Delhi, which in turn has increased air quality in an unprecedented way in recent times. In some areas, such as New York, CO2 emissions have been reduced by 5–10%. Reference Menut, Bessagnet and Siour46 The air quality index in Baghdad improved by 13% compared to before the quarantine period and NO2 emissions decreased by 35–40% compared to before. Reference Hashim, Al-Naseri, Al-Maliki and Al-Ansari31
Despite what has been said, studies have shown that the reduction in pollutants is short-lived and the level of PM2.5 has not changed. Reference Bekbulat, Apte and Millet25 The findings do not support a reduction in greenhouse gases in the long run, because, after the cancelation of the national holiday, the start of economic activities, increased energy consumption, and subsequent increase in traffic, greenhouse gas emissions have increased again. Reference Wang and Su10 A study by Bekbulat in the United States found that PM 2.5 was reported to be 1–30% higher than expected during home quarantine and that shortfalls in O3, NO2, and CO levels were short-lived after lockdown and PM2.5 did not change. Reference Bekbulat, Apte and Millet25 According to the results of studies by Lal, Wang, Barchelo, and Zambrano, air pollution improves in the short term after closures and its long-term effects need further investigation. Reference Wang and Su10,Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Barcelo15,Reference Lal, Kumar and Kumar16
Effect of the COVID-19 Pandemic on Water Quality
Findings from some studies have shown that the lockdown and COVID-19-induced quarantine have improved the water quality of some rivers, canals, and seas, and the pandemic has had beneficial effects on surface water quality in some areas. In total, 34% of the articles mentioned an increase in water quality indicators, its transparency, and an increase in the amount of dissolved oxygen in water. Reference Saadat, Rawtani and Hussain13,Reference Kafeel, Ansari, Khan and Owens17,Reference Shakil, Munim, Tasnia and Sarowar18,Reference Rupani, Nilashi and Abumalloh27,Reference Selvam, Jesuraja and Venkatramanan34,Reference Karunanidhi, Aravinthasamy and Deepali41,Reference Chakraborty, Roy and Bera43
In Selvam’s study, a mirrored reduction in industrial waste was reported in industrial waste following the COVID-19 pandemic, and coliforms were reduced following the lockdown, COVID-19-induced quarantine, and closure of industrial activities, including fisheries. In addition, analytical factors showed better water quality. A significant decrease was observed in AS: 51.3%, Se: 42%, Fe: 60%, Pb: 50%, and NO3: 56%. Total coliform and fecal coliform were estimated to be 52% and 48%, respectively. Reference Selvam, Jesuraja and Venkatramanan34 In another study by Chakraborty in India, the heavy physical and chemical elements were beyond the standard in the pre-lockdown period. Cations and anions, including Mg, Ca, K, Na, NO3, SO4, Cl, and F, were observed in the lockdown period. Examination of water quality in the pre-lockdown period and COVID-19-induced quarantine showed that 100% of the water was highly polluted, and during the outbreak of COVID-19 disease and restrictions, about 90.90% of the samples were upgraded to good quality and 9.10% of the samples were moderately infected. Reference Chakraborty, Roy and Bera43 In some studies, a decrease in water turbidity and suspended particles was also reported during the pandemic. Reference Yunus, Masago and Hijioka49,Reference Patel, Mondal and Ghosh51 In Karunanidhi’s study in India, fluoride concentration decreased by 17%, and water pollution by nitrates decreased by 32.4%. Reference Karunanidhi, Aravinthasamy and Deepali41 Another study reported an improvement in surface water quality at Vembanad Lake, India, showing that suspended particulate matter (SPM) concentrations decreased by an average of 15.9% compared to last year. Reference Yunus, Masago and Hijioka49
In contrast, in some studies, the content of Cr, Ca, Zn, and Cd was similar to before and fluoride did not show any change. E. coli and fecal streptococci did not change significantly in the waters of industrial coastal cities. Reference Selvam, Jesuraja and Venkatramanan34 In a post-peak study in China, the re-reduction of water quality parameters and intensity of fluorescent components were recorded. Reference Shen, Liu and Lv53 In the study conducted by Patel, the amount of changes in water quality was reported to be variable, and the need for more attention to increase domestic wastewater production during the disease and its impact on receiving water sources such as rivers was highlighted. Reference Patel, Mondal and Ghosh51 In Bar’s study, it was reported that during the lockdown and COVID-19-induced quarantine, the use of a variety of means of transport on the river, such as motor boats and steamboats, was restricted. Some people in East Asia are economically dependent on river fishing. During this period, economic activities in rivers, including fisheries, stopped significantly. Reference Mukherjee, Babu and Ghosh33 Overall, water quality worldwide has improved, Reference Saadat, Rawtani and Hussain13,Reference Cheval, Adamescu and Georgiadis14 water pollution has been reduced, and surface and groundwater quality has been improved following the COVID-19 pandemic. Reference Saadat, Rawtani and Hussain13,Reference Cheval, Adamescu and Georgiadis14,Reference Shakil, Munim, Tasnia and Sarowar18,Reference Rupani, Nilashi and Abumalloh27,Reference Mukherjee, Babu and Ghosh33,Reference Karunanidhi, Aravinthasamy and Deepali41
The Effect of the COVID-19 Pandemic on the Environment
The effects of this disease on the environment cannot yet be fully described. However, it seems that with the outbreak of the COVID-19 pandemic and the closures that have occurred in different parts of the world, especially in industrialized countries, the amount of air, water, and coastal pollution has decreased. Reference Wang and Su10–Reference Cheval, Adamescu and Georgiadis14 The results of some studies indicate that noise pollution has decreased with the onset of the lockdown and COVID-19-induced quarantine. Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Shakil, Munim, Tasnia and Sarowar18,Reference Bar42 In Bar’s study, noise pollution was reported to be significantly below 60 db. Reference Bar42 The quality of coastlines has improved, but household and medical waste has increased, and this increase in non-recyclable waste and medical waste leads to environmental and water pollution. For example, masks are used for a short time and usually daily. Reference Zambrano-Monserrate, Ruano and Sanchez-Alcalde11,Reference Saadat, Rawtani and Hussain13 Their contamination is palpable after the outbreak of COVID-19. These contaminants have entered the living environment of animals on land and at sea, which will have consequences such as death and disease for them. Reference Saadat, Rawtani and Hussain13 On the other hand, the resumption of activities and efforts to compensate for the lockdown and COVID-19-induced quarantine have different effects, which highlight the need for more research to identify these effects in the long run. Reference Cheval, Adamescu and Georgiadis14
This study aimed to investigate the effect of the COVID-19 pandemic on air quality, water resources quality, and the environment. The findings of most studies in this regard have compared previous measures with the post-lockdown and COVID-19-induced quarantine period. In this regard, quarantines and restricting communications have been effective in reducing toxic gases such as nitrogen dioxide, aerosols, atmospheric ozone, and particulate matter and improving air quality.
In a systematic review by Silva et al. Reference Silva and Branco68 (2022), it was reported that air quality improved during quarantine compared to before the quarantine. According to the findings of this research, reductions between 9% and 60%, 21.4% and 61.6%, were reported for PM2.5, PM10, respectively. Studies have reported a reduction in pollutant concentrations during quarantine compared to the same period in previous years and even more robustly with historical data of more than 5 years. Reference Silva and Branco68 Based on the results of a systematic review by Bakola et al. (2022), several air pollutants, including NO2, NO, PM2.5, PM10, CO, carbon dioxide (CO2), benzene, black carbon, and air quality index (AQI)) related to the quarantine of COVID-19, showed a significant and strong decrease. Reference Bakola, Hernandez Carballo, Jelastopulu and Stuckler69
According to the results of a systematic review study by Faridi et al., Reference Faridi, Yousefian and Janjani70 in 2021, quarantine measures related to the COVID-19 epidemic significantly reduced the concentration of PM2.5, NO2, PM10, SO2, and CO globally. Apart from measuring pollutants at ground stations, studies using satellite data have confirmed the results obtained with ground-level measurements and found that AQI improved during the quarantine period. A higher decrease was observed mainly for industrial areas. Reference Gebeyehu, East, Wark and Islam71
Several mechanisms have been reported to significantly reduce pollutant levels: reducing people’s driving and public transportation, Reference Bakola, Hernandez Carballo, Jelastopulu and Stuckler69,Reference Gebeyehu, East, Wark and Islam71 reducing or stopping the activity of industries and factories, Reference Bakola, Hernandez Carballo, Jelastopulu and Stuckler69 and reducing energy consumption Reference Silva and Branco68 ; A remarkable point is that, in the case of some pollutants such as ozone, different results have been reported. Based on the results of the systematic review by Faridi et al. Reference Faridi, Yousefian and Janjani70 (2021), Silva et al. Reference Silva and Branco68 (2022), and Bakula et al. Reference Bakola, Hernandez Carballo, Jelastopulu and Stuckler69 (2022), O3 concentration has increased compared to the conditions before COVID-19. Various reasons for the increase in O3 have been reported: decrease in NO and increase in solar radiation, Reference Silva and Branco68 decrease in the titration of O3 by NOX due to a significant decrease in local emission sources of NOX, possible increase in solar activity level due to decrease in PM2.5, and increase in the number of Hydroperoxyl radicals (HO2) as a mediator to increase ozone production. Reference Gebeyehu, East, Wark and Islam71
However, the findings do not indicate a long-term reduction in these gases because industrial activity has increased significantly after the restrictions were reduced. The results of some studies also indicate that the reduction of air pollutants during the pandemic is temporary, and after the end of the imposed restrictions and the removal of quarantine regulations, we will see an increase in air pollutants again. In the systematic review study by Silva et al. (2022), the increase in pollutants in the post-quarantine period was also reported. Reference Silva and Branco68
On the other hand, a significant increase in household and medical waste has led to further environmental pollution. China Center for Energy and Clean Air Research reports that SARS-CoV-2 emission control methods, such as quarantines and travel bans, have reduced carbon emissions by 25%. Reference Zhang, Zhang, Lin, Feng, Fu and Wang72 The LIU’s study, published in May 2020, also found that global carbon emissions fell by 17% since quarantine in early April, which could reduce annual carbon emissions by up to 7%, the largest drop since World War II. Second, researchers attribute these reductions mainly to reduced use of transportation and industrial activities. Reference Liu, Ciais, Deng, Lei, Davis and Feng73
Following the application of traffic restrictions, the air pollution index decreased significantly and vehicle emissions such as sulfur dioxide and nitrogen dioxide were reduced, so the EU Air Pollution Monitoring Service reported the production of particulate matter by 20 to 30% and the reduction of sulfur dioxide and nitrogen dioxide emissions. Reference Kafeel, Ansari, Khan and Owens17
According to the results of the systematic review by Silva et al. Reference Silva and Branco68 (2022), the amount of nitrogen dioxide has decreased 30-66% during the COVID-19 pandemic, and in the systematic review by Faridi et al. Reference Faridi, Yousefian and Janjani70 (2021), this reduction was 18-96%.
Overall, the outbreak of the COVID-19 pandemic appears to have reduced air, water, and coastal pollution in the short term. This finding, in line with some other studies that have made it possible to compare atmospheric composition with and without the lockdown and COVID-19-induced quarantine, showed that the effect of lockdown was particularly important for several atmospheric components through the widespread reduction of traffic and industrial activity, which has been accompanied by a large decrease in NO2 concentration, a decrease in particulate matter (PM) and air pollutants. Reference Wang and Su10,Reference Lal, Kumar and Kumar16,Reference Abdullah, Mansor and Napi20,Reference Dantas, Siciliano and França21,Reference Rupani, Nilashi and Abumalloh27,Reference Rodríguez-Urrego and Rodríguez-Urrego36
According to satellite imagery, one of the positive effects of COVID-19 has been clearer waters after 1 month of the national COVID-19 pandemic-induced lockdowns and quarantines. Reference Khan, Shah and Shah19,Reference Chakraborty, Roy and Bera43,Reference Yunus, Masago and Hijioka49,Reference Patel, Mondal and Ghosh51
Based on the results of the systematic review by Jiang et al. Reference Jiang, Xu, Ye, Pahlow, Hu and Qu74 (2022), the improvement of the quality of coastal waters and the reduction of underwater pollution have been reported. It is noteworthy that COVID-19 has caused an increase in some environmental pollutants for several reasons. Due to the frequent washing of hands and the use of chemical detergents and the release of the resulting effluents, an increase in environmental pollution is expected. According to the results of a systematic review by Chirani et al. Reference Chirani, Kowsari, Teymourian and Ramakrishna75 (2021), during the COVID-19 epidemic, frequent and increasing use of handwashing products leads to environmental pollution. Furthermore, the increase in the use of personal protective equipment (PPE) such as masks and gloves has also caused an increase in the production of waste and the release of these wastes into the environment and increased environmental pollution, especially with microplastic particles. Reference Ammendolia, Saturno and Brooks76–Reference Rakib, De-la-Torre and Pizarro-Ortega86 According to the results of a systematic review by Jiang et al. Reference Jiang, Xu, Ye, Pahlow, Hu and Qu74 (2022), the increase in medical waste related to COVID-19, such as PPE, leads to severe pollution that threatens the marine ecosystem and wildlife.
Travel bans and reduced boat traffic have led to sedimentation and reduced water turbidity, which have made the water clearer. The canals of Venice are illustrative; in the pre-pandemic period, the TSM concentration averaged 3 g/m, but during the COVID-19 pandemic it dropped to 1.4 g/m, that is, a 50% reduction in concentration was observed. Reference Braga, Scarpa and Brando52 The unprecedented increase in the use of the mask and its release into the water and the environment has been one of the negative consequences of the COVID-19 pandemic. Other issues include the increasing use of detergents and their role in the state of wastewater.
Conclusion
With the outbreak of the COVID-19 pandemic and the closures that have occurred in various parts of the world, especially in industrialized countries, the amount of air, water, and coastal pollution has been reduced in the short term. Due to the emergence of the disease, the study period has been limited in some studies. For better conclusions about the effect of the COVID-19 pandemic on environmental health, we will need to examine the quality of water, air, and the environment in the long run. On the other hand, few studies have examined the effects of pandemics on the environment, and most of them have focused on air quality, which paves the way for research into the effects of pandemics on the environment. The effects of quarantine on the quality of the environment have been different.
Acknowledgments
Hereby, the Research Committee of University of Social Welfare and Rehabilitation Sciences, Tehran, Iran is sincerely appreciated.
Authors’ contributions
All authors contributed significantly to this paper. MF and HR KH contributed to the study design. MS and SH A created the search strategy. ZH and SAM and YM and ZMN completed the data extraction and analysis and critically appraised studies. JSH and NP drafted the manuscript. all authors contributed to its revision.
