Investigation of the Effects of Heavy Metal Pollution on Surface Waters Before and During the COVID-19 Lockdown Periods in Bursa, Turkey

16 17 The first COVID-19 case in Turkey was reported on March 10, 2020, by the Ministry of Health of the Republic 18 of Turkey. Due to the increasing number of cases, a curfew was declared on weekends as of 11-12 April 2020. 19 Although curfews were only implemented on public holidays and weekends, there were reductions in industrial, 20 traffic, and human activities. The restrictions and curfews implemented to prevent the spread of the COVID-19 21 pandemic are a unique opportunity to understand the effects of anthropogenic sources on water quality. In this 22 study, it was aimed to determine the temporal variations of the concentration of seven heavy metals (HMs) (Fe, 23 Mn, Cu, Al, Cr, Ni, and Zn) in surface waters before and during the COVID-19 lockdown period, and their 24 carcinogenic and non-carcinogenic risks that may occur through digestion and dermal absorption. Surface water 25 samples were taken from 14 different sampling points within the borders of Bursa (Turkey). HM concentrations 26 except Ni increased at rates ranging from 7.92% to 83.33% during the COVID-19 lockdown period compared to 27 before the COVID-19 lockdown period. The heavy metal pollution index and heavy metal evaluation index 28 increased during the COVID-19 lockdown period compared to before the COVID-19 lockdown period. Also, 29 according to the results regarding the carcinogenic risk that may occur via digestion and dermal absorption, 30 serious risks were determined for adults and children in both periods. Generally, similar correlation coefficients 31 were obtained in both sampling periods, and it was concluded that HMs were affected by similar sources.


Introduction
Towards the end of 2019, the first signs of the coronavirus pandemic  were reported in Wuhan, China, and it started to spread rapidly all over the world.Tens of millions of people worldwide have been infected with this virus, and millions have died (Kumar et al. 2020;Sher 2020).According to the World Health Organization (WHO), from the first date of the virus to this time (September 10, 2020), a total of 223,002,538 cases of COVID-19 have been seen worldwide, and 4,602,882 people have died (WHO, 2021).The first COVID-19 case in Turkey occurred on March 10, 2020, and the first death due to COVID-19 occurred on March 15, 2020 (Şimşek 2020;Sari and Esen 2021).Due to the increasing number of cases at later dates, a curfew was declared in 31 provinces in mid-April, 2020.The curfew was only enforced on weekends and public holidays.
However, there was a reduction in traffic, industrial, and human activities (Sari and Esen 2021).
Heavy metals (HMs) refer to metal elements with densities higher than 4.5 g/m 3 .Naturally, 54 of the 60 metal elements have a density of more than 4.5 g/m 3 (Zhang et al. 2020).Among these 54 HMs, Iron (Fe), Magnesium (Mn), Copper (Cu), Aluminum (Al), Chromium (Cr), Nickel (Ni), and Zinc (Zn) are the most abundant HMs in aquatic environments (Joseph et al. 2019;Kiran Marella et al. 2020;Zhu et al. 2021).Some factors, such as increased industrial activities, rapid urbanization, and excessive use of natural resources, cause environmental pollution (Khazaal et al. 2019).Due to all these factors, HMs are released into the aquatic environment (Lu et al. 2019).Although HMs in the environment have natural sources (forest fires, volcanoes, evaporation from the soil, degradation of minerals, etc.), they also originate from industrial processes, especially in many developing countries (He et al. 2013;Tomno et al. 2020).Industrial wastes, metal mining, and geochemical structure constitute the primary sources of HM pollution in surface waters (Altindaǧ and Yiǧit 2005;Lu et al. 2019).
Other sources of HMs in surface waters are erosion, rock weathering, atmospheric deposition, and hydrodynamic processes (Goher et al. 2019).
HMs cause serious environmental problems, especially in aquatic environments such as rivers, streams, and lakes, due to toxicity, ecological risk, persistence, and bioaccumulation (Zhang et al., 2018;Zhao et al., 2018).
HMs found in aquatic environments can accumulate in aquatic life, cannot be biodegraded, enter the food chains, and seriously affect human health (Ezemonye et al. 2019).These effects include cancer, damage to the nervous system, slowing of the growth of organs, and deterioration of the defense system (Hasanpour and Hatami 2020).
Humans are exposed to HMs through three main routes: mouth and nose inhalation, direct ingestion, and dermal absorption (El-Kady and Abdel-Wahhab 2018;Zhao et al. 2020).Prolonged exposure to HMs causes cardiovascular disease, chronic poisoning, and growth and developmental disorders.
Surface waters are polluted continuously by various natural and anthropogenic sources in Turkey and all other countries.Bursa, in terms of population and economy, is one of the largest cities in Turkey.For this reason, human, agricultural and industrial activities in big cities such as Bursa rapidly pollute the surface waters (Karacaoğlu and Dalkıran 2017).The main purposes of this study were to: i) determine the changes of HM concentrations during the COVID-19 lockdown period compared to before the COVID-19 lockdown period, ii) reveal the quality of surface waters in both periods by using various indices, and iii) calculate the carcinogenic and non-carcinogenic risk in adults and children via digestion and dermal absorption.

Sampling points
The sampling points are located within the borders of Bursa province in western Turkey (Figure 1).According to the 2020 population data, Bursa is the fourth largest city in Turkey, with a population of 3,101,833.In addition, Bursa has 17 organized industrial zones with textile, automotive, food, furniture, and machinery industries.34% of automotive production and 22% of textile production in Turkey take place in Bursa.Agricultural activities in Bursa are also at a significant level.In Turkey, 64% of tomato paste production, 61% of frozen food production, 47% of canned food production, and 26% of fruit juice production take place in Bursa.
Bursa generally has a temperate climate, but this also varies according to the region.For example, while it has a mild and warm climate in the north, it has a harsh climate in the south.Bursa's annual average temperature is 14.5 °C, and the annual average precipitation is 700 mm.Nilüfer Stream is one of the most important rivers of both Bursa and the Marmara Region with a total length of 203 km.Nilüfer Stream rises on the southern slopes of Uludag Mountain and generally flows through a very narrow valley towards the northwest.Although its average slope does not exceed 2%, its annual total flow value is 743.77hm 3 /year and its average flow rate is 23.58 m 3 /sec.In addition, the majority of the sampling regions are located in regions where industrial and agricultural activities are intense.

Sample collection and analysis
Surface water samples (n = 14) were collected using the techniques recommended by APHA (2012) from the sampling points in Bursa before the COVID-19 lockdown (January 2020) and during the COVID-19 lockdown (June 2020) periods.The date before the COVID-19 lockdown period represents the winter season and the date during the COVID-19 lockdown period represents the summer season.Surface water samples were collected approximately 10 cm below the surface and collected in 2 L pre-cleaned polyethylene bottles.The surface water samples brought to the laboratory were analyzed using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) according to EPA Method 6010D.The pH parameter was measured in the field based on the SM 4500-H + B electrometric method.
The surface water samples were first pre-digested with a microwave device (CEM MARS-5).Then, the sample with a volume of 40 mL was placed in the cell.6 mL of HNO3 (65% analytical grade) and 4 mL of HCl (37% analytical grade) were added to the surface water samples placed in the cell.Then, the cells were closed, and a temperature of 160 o C and a pressure of 180 psi were applied for approximately 20 min.At the end of this period, the surface water samples were allowed to cool for 10 min (Üstün 2009).After approximately 30 minutes, the surface water samples were cooled to room temperature and transferred to a 100 mL bottle.Finally, distilled water with a final volume of 100 mL was added to the digested surface water samples, and ICP-AES was used in the analysis.In this study, 7 HMs were targeted: Iron (Fe), Magnesium (Mn), Copper (Cu), Aluminum (Al), Chromium (Cr), Nickel (Ni), and Zinc (Zn).

The heavy metal pollution index
The heavy metal pollution index (HMPI) is one of the most frequently used methods to evaluate HM pollution in surface and ground waters (Giri and Singh 2014;Tiwari et al. 2015).This method is powerful in assessing the effects of pollution on overall water quality by assigning weights (Wi) or ratings for individual HMs (Bhuiyan et al. 2010;Giri and Singh 2014;Rezaei et al. 2019;Varol et al. 2021).The HMPI value is computed as (Eqn.1): where Wi and Qi are the weight of the unit and sub-index for the ith HMs, respectively, While n represents the number of HMs (n=7) (Fe, Mn, Cu, Al, Cr, Ni, and Zn).Qi is calculated by Eqn. 2. 1 100 where Mi is the ith HMs concentration (mg/L), Ii and Si are the ideal and standard values for the ith HMs (mg/L).
Ii, and Si values are given in Table S1 (Supplementary material).In general, the critical HMPI value is 100.If the HMPI value is higher than 100, water is not suitable for consumption (Abou Zakhem and Hafez 2015;Milivojević et al. 2016;Karaouzas et al. 2021).

The heavy metal evaluation index
The heavy metal evaluation index (HMEI) is used to evaluate the general quality of water according to HM pollution (Mokarram et al. 2020).HMEI is calculated by Eqn. 3.
where Mi is the ith HMs concentration (mg/L) and MACi is the maximum permissible concentration of the ith HMs (Table S1) (Egbueri and Unigwe 2020;Mokarram et al. 2020).In general, HMEI is divided into three categories.If the HMEI value is less than 10, it means that there is low-level pollution.If the HMEI value is between 10 and 20, it means that there is moderate-level pollution, and if the HMEI value is higher than 20, it means that there is a high level of pollution (Mokarram et al. 2020).

Classification of surface water
The classification of water resources is made with the Caboi diagram by using the pH level and metal concentrations of the surface water (Khan et al. 2021).This method was described by Ficklin et al. (1992) and later developed by Caboi et al. (1999).For each sampling point, heavy metal loads (sum of Fe, Mn, Cu, Al, Cr, Ni, and Zn per mg/L) are calculated by Eqn. 4 (Sharmin et al. 2020).
1 Heavy Metal Load (mg/L) where i represents the concentrations of individual HMs (mg/L) at each sampling point.

Human health risk assessment
Humans are exposed to HM in surface waters via direct ingestion or dermal absorption (Xiao et al. 2019;Proshad et al. 2020).The health risk assessment of individual HMs is classified as carcinogenic and noncarcinogenic (Mohammadi et al. 2019).Average daily doses (ADD) by ingestion and dermal absorption are calculated using Equations 5 and 6, respectively (Saha et al. 2017;Mohammadi et al. 2019;Nyambura et al. 2020;Proshad et al. 2020).
where ADDingestion and ADDdermal are the average daily doses via ingestion and dermal absorption (mg/(kg×day)), respectively.Ci is the ith HMs concentration (mg/L) in surface water, IR is the ingestion rate (2 L/day for adults and 0.64 L/day for children) (Xiao et al. 2019), EF and ED are the exposure frequency (350 days/year) (USEPA, 2004), and exposure duration (70 years for adults and 6 years for children), respectively.BW is the body weight (65 kg for adults and 20 kg for children), AT is the average exposure (25,500 days for adults and children for carcinogenic risk, and 10,950 days for adults and 2,190 days for children for non-carcinogenic risk) (Xiao et al. 2019), SA is the skin surface area (1.80 m 2 for adults and 0.66 m 2 for children) (Prasad et al. 2020), Kp is the permeability constant (0.001 cm/h for Fe, Mn, Cu, Al, Cr; 0.0004 cm/h for Ni; 0.0006 cm/h for Zn) (Imran et al. 2019;Xiao et al. 2019; Ustaoğlu and Aydın 2020), ET is the exposure time (0.58 h/day) (Prasad et al. 2020), and CF is the conversion factor (10) (Saha et al. 2017;Imran et al. 2019;Mohammadi et al. 2019;Nyambura et al. 2020).The risk of cancer that may occur as a result of ingestion and dermal absorption of HMs in the surface water is determined by the incremental lifetime cancer risk (ILCR) model from Equations 7 and 8, respectively (Saha et al. 2017;Mohammadi et al. 2019;Nyambura et al. 2020;Proshad et al. 2020).where ADD is the average daily dose via ingestion and dermal absorption (mg/(kg×day)), and RfD is the toxicity reference dose for ingestion and dermal absorption (mg/(kg×day)) (Saha et al. 2017;Imran et al. 2019).The RfD values for ingestion are 1.0 for Al, 0.3 for Fe and Zn, 0.02 for Mn and Ni, 0.04 for Cu, and 0.003 for Cr.
If the HI value is higher than 1, it indicates that the surface waters are at an unacceptable level and that there is a potential non-carcinogenic health risk.Similarly, if the HI value is lower than 1, it means that there is a noncarcinogenic health risk (Githaiga et al., 2021;Lee et al., 2006).

HM concentrations in surface water before and during COVID-19 lockdown periods
In this study, the differences in water quality at 14 different points were measured from surface water within the borders of Bursa in two different periods (before and during the COVID-19 lockdown periods).The minimum, maximum, and mean concentration values in 14 different sampling points before and during the COVID-19 lockdown periods are summarized in Table 1.In general, it was determined that there were increases during closure compared to before the COVID-19 lockdown period in all HMs except Ni.Also, Bursa is one of the most developed cities in Turkey both in terms of population and industry.For this reason, most industrial facilities continued their activities during the COVID-19 lockdown period.
The mean pH values of the surface water samples at the sampling points were 8.151 before the COVID-19 lockdown period and 7.963 during the COVID-19 lockdown period.Although there was a slight variation in mean pH values between the two sampling periods, no significant difference was observed (p>0.05).In addition, it was thought that the main reason for the decrease in the pH level during the COVID-19 lockdown period was because fewer industrial wastes containing high alkaline solutions were released into the surface water (Chakraborty et al. 2021).The results obtained at the pH level were similar to those of most studies in the literature (Bahukhandi et al. 2020;Patel et al. 2020;Selvam et al. 2020).
The concentration of Fe in surface water ranged from 0.032 to 4.672 mg/L (0.821±1.142 mg/L, mean±std dev.) (2014) (Iraq).Also, during the COVID-19 lockdown period, an increase of 7.917% was observed in Fe concentrations compared to before the COVID-19 lockdown period (Table 1).However, domestic sewage is among the most important sources of Fe in surface waters (Patel et al. 2018) 2018) (India).During the COVID-19 lockdown period, an increase of 13.077% was observed in Zn concentrations compared to before the COVID-19 lockdown period.Zn concentrations also increased due to the increase in domestic waste during the COVID-19 lockdown period (Hussain et al., 2017;Noulas et al., 2018;Singh and Kumar, 2017).
Most of the sampling points are located on the Nilüfer Stream (S4-S14), and the Nilüfer Stream is among the most important streams of Bursa.Agricultural activities cover approximately 54% of the basin, while 34% is covered by forests, 5% by meadows, and 7% by settlement areas (Karaer and Küçükballi 2006).Industrial and agricultural wastes and wastewater are continuously discharged into the Nilüfer Stream, and only 70% of these wastewaters are treated (Summak et al., 2010).For this reason, especially agricultural activities are among the most significant polluting sources of the stream in Bursa.Since the COVID-19 lockdown period coincided with summer, agricultural activities increased during this time.As a result, the concentration values during the COVID-19 lockdown period were mainly higher than before the COVID-19 lockdown period.

Heavy metal pollution index and metal evaluation index
HMPI and HMEI parameters were calculated to evaluate the pollution degrees of surface water.The results obtained before and during the COVID-19 lockdown periods are shown in Figure 2.
HMPI values in all sampling points ranged from 56.11 to 439.99 (Mean: 128.21) before the COVID-19 lockdown period and from 60.99 to 189.17 (Mean: 128.71) during the COVID-19 lockdown period.Also, while 28.57% of the HMPI values were above the critical level of 100 before the COVID-19 lockdown period, 64.29% of the HMPI values were above this level during the COVID-19 lockdown period.The highest increase in HMPI values was calculated at sampling points S10 (203.49%) and S6 (194.71%) for the two sampling periods.
Similarly, the highest decrease in HMPI values was calculated at sampling points S1 (-75.79%) and S12 (-65.82%) for the two sampling periods.It is thought that the main reason for the increase in HMPI values at S10 and S6 sampling points was the intense agricultural and industrial activities at these sampling points.Especially during the COVID-19 lockdown period, most industrial facilities continued their activities; consequently, serious increases were determined in HMPI values.
HMEI values in all sampling points ranged from 1.16 to 61.92 (Mean: 14.85) before the COVID-19 lockdown period and from 1.74 to 27.04 (Mean: 15.43) during the COVID-19 lockdown period.The highest increase in HMEI values was calculated at sampling points S5 (623.17%) and S4 (323.05%) for the two sampling periods.
S5 and S4 sampling points represent regions away from industry with only agricultural activities.From this, it has been determined that agricultural activities seriously affect HM concentrations, especially in Bursa.
According to the HMPI and HMEI results, it has been demonstrated that agricultural activities negatively affect water quality.

Classification of surface water
The Caboi diagram was used to classify surface waters in this study.The results obtained before and during the COVID-19 lockdown periods are shown in Figure 3.
The pH of surface water samples in the sampling points varied from 7.250 to 8.999 before the COVID-19 lockdown period and from 6.700 to 8.420 during the COVID-19 lockdown period.For this reason, the surface waters at the sampling points were classified as "Near Neutral" for both sampling periods.In addition, 64.31% of the water samples before the COVID-19 lockdown period and 85.74% of the water samples during the COVID-19 lockdown were classified in the "High Metal" category.Mobility and bioavailability of HMs such as Mn, Cu, and Zn increase in acidic surface waters, which causes an increase in HM concentrations (Maity et al.

2020
).However, most surface waters in the sampling points were classified as near-neutral/high-metal in both sampling periods.Also, most of the waters at the sampling points in this study have a similar classification to most studies in the literature (Bhuiyan et al. 2010;Prasanna et al. 2012;Chung et al. 2016;Plaza et al. 2018).
Generally, surface waters close to agricultural and industrial activities are included in this classification (Chung et al. 2016).Also, high metal load in the near-neutral pH range indicates that anthropogenic sources are effective (Singh et al. 2018).Thus, it was concluded that anthropogenic sources were effective due to the high HM content in surface waters in both periods.

Carcinogenic and non-carcinogenic health risk assessment
HM contamination in surface waters harms human health via ingestion and dermal absorption (Aravinthasamy et al. 2021).In this study, the carcinogenic risk results for children and adults via ingestion and dermal absorption were determined by the incremental lifetime cancer risk (ILCR) model (Saha et al. 2017;Mohammadi et al. 2019;Nyambura et al. 2020;Proshad et al. 2020).The non-carcinogenic risk results for children and adults via ingestion and dermal absorption were determined by the hazard index (HI).The results of the ILCR model and HI values obtained are given in Figure 4 and Figure 5, respectively.
For this reason, high Al concentration levels (~1.0 mg/L) were obtained in both sampling periods due to the high organic matter content.
The total HI values for adults ranged from 8.0×10 -1 to 1.8×10 +1 and 8.1×10 -1 to 8.7×10 0 before and during the COVID-19 lockdown periods, respectively.Similarly, the total HI values for children ranged from 3.6×10 -1 to 7.9×10 0 and 3.6×10 -1 to 3.6 ×10 0 before and during the COVID-19 lockdown periods, respectively (Table S10-13).Cr has the highest total HI values in adults and children.The HI values obtained in before and during the COVID-19 lockdown periods in this study were found to be higher than most studies in the literature (Mohammadi et al. 2019;Xiao et al. 2019;Njuguna et al. 2020;Githaiga et al. 2021;Varol et al. 2021).Cr generally has various sources such as raw material in home furnishing production, coating tools, mixing antifouling paint compounds, and agricultural activities (Giri and Singh 2014;Harmesa and Cordova 2021).
Even if the widespread use of Cr in industrial activities is reduced, it negatively affects human health due to increased agricultural activities.

Relationship among HMs during the sampling period
The correlation analysis among the concentrations of HMs in the two sampling periods is demonstrated in Figure 6.
A negative correlation was observed between pH and all HMs, especially during the COVID-19 lockdown period.Before the COVID-19 lockdown period, a very low correlation was observed between pH and all HMs except Ni and Zn.Many HMs are unstable and cause precipitation, especially at high pH (Xiao et al. 2022).In addition, with the decrease in pH, the mobility and bioavailability of many HMs increase.This situation causes a negative correlation between pH and HM concentrations (Maity et al. 2020).Mn has significant and positive correlations with Fe, Al, and Cr in both sampling periods.Mn and Fe both have similar natural sources.For this reason, it is possible to obtain positive and significant correlation results between Mn and Fe in both sampling periods (Huang et al. 2009).In addition, the positive correlation between Fe and Mn indicates that they are affected by similar lithogenic sources (Islam et al. 2020).While a weak correlation was observed between Cr and Fe (R=0.14, p>0.05) before the COVID-19 lockdown period, a positive correlation (R=0.47 p<0.005) was observed during the COVID-19 lockdown period.Also, mean Fe and Cr concentrations were 0.821 mg/L and 0.019 mg/L before the COVID-19 lockdown period and 0.886 mg/L and 0.022 mg/L during the COVID-19 lockdown period, respectively.Due to the presence of natural and anthropogenic sources of Fe in surface waters, no significant changes were observed in the concentration values before and during the COVID-19 lockdown periods.In addition, iron-steel and metal industries, which are the sources of Fe, continued their production during the COVID-19 lockdown period, despite the restriction of their activities (Khatri et al., 2017).Due to the increase in agricultural activities during the COVID-19 lockdown period, there was a 15.789% increase in Cr concentrations.From this, it has been determined that agricultural activities significantly affect Cr concentrations in surface waters (Cheng et al. 2014;Giri and Singh 2014).The high correlation among HMs means that the same sources are effective (Atangana and Oberholster 2021).Mainly, higher correlation coefficients were obtained among HMs during the COVID-19 lockdown period than before the COVID-19 lockdown period.This situation is generally thought to be due to the fact that agricultural activities were more effective due to the restrictions on industrial activities during the COVID-19 lockdown period.

Conclusions
There were significant increases in HM concentrations except for Ni and Cu during the COVID-19 lockdown period (June 2020) compared to before the COVID-19 lockdown period (January 2020).This situation was explained by the increase in agricultural activities, especially in the summer months.In addition, the fact that most industries continued their activities during the COVID-19 lockdown caused an increase in HM concentrations.Due to the increase in concentrations, the heavy metal pollution index (HMPI) and heavy metal evaluation index (HMEI) were elevated during the COVID-19 lockdown period compared to before the COVID-19 lockdown period.In addition, the carcinogenic and non-carcinogenic health risks of HMs increased for both adults and children compared to before the COVID-19 period.Finally, according to the Pearson correlation method, HMs before and during the COVID-19 lockdown periods were affected by similar sources but with different severity.The findings obtained in this study showed that the discharge of wastes generated as a result of agricultural activities into surface waters without treatment seriously deteriorates the water quality.
. Increases in Fe concentrations may have occurred due to the increase in domestic sewage during the COVID-19 lockdown period, especially in urban cities such as Bursa.In addition, the wastewater of industrial facilities during the COVID-19 lockdown period may also have contributed to HM concentrations in surface waters.Similar to Fe concentrations, Mn concentrations also increased during the COVID-19 lockdown period.Generally, Mn and Fe have similar sources, and with the increase of Fe concentrations in waters, Mn concentrations also increase.The presence of high concentrations of Mn in surface waters means that there are intense industrial and human activities in these areas(Karunanidhi et al. 2021).The study conducted byTokatlı and Varol (2021)  stated that the increased Mn concentrations during the COVID-19 lockdown period might have been caused by the industrial facilities that were forced to work during this period.The concentration of Cu in surface water ranged from 0.005 to 0.019 mg/L (0.006±0.004 mg/L.) and from 0.005 to 0.082 mg/L (0.011±0.018 mg/L) before and during the COVID-19 lockdown periods, respectively.The Cu concentrations obtained in before and during the COVID-19 lockdown periods in this study were similar to those recorded byKar et al. (2008) (West Benga), Varol and Şen (2012) (Turkey), Goher et al. (2014) (Egypt), and Tiwari et al. (2015) (India); lower than those recorded by Islam et al. (2015) (Bangladesh), Alonso et al. (2004) (Spain), and Wang et al. (2011) (India).During the COVID-19 lockdown period, an 83.333% increase in Cu concentrations was observed compared to before the COVID-19 lockdown period.It is thought that the increase in Cu concentrations was caused by fertilizers used in agricultural lands and municipal landfill leachate(Selvam et al. 2020).In addition, agricultural activities increase in the summer months(Qu et al. 2015).In this study, the surface water samples representing the COVID-19 lockdown period were taken in June.For this reason, it was thought that the increase in fertilizer use due to the increase in agricultural activities (agricultural activities allowed during the COVID-19 lockdown period), especially during the COVID-19 lockdown period, increased the Cu concentrations.The concentration of Al in surface water ranged from 0.034 to 5.412 mg/L (0.993±1.415 mg/L) before the COVID-19 lockdown period and from 0.052 to 2.385 mg/L (0.995±0.756 mg/L) during the COVID-19 lockdown period.The Al concentrations obtained in before and during the COVID-19 lockdown periods in this study were higher than those recorded byAhmed et al. (2019) (Malaysia), Githaiga et al. (2021) (Kenya), and Guibaud and Gauthier (2003) (France); lower than those recorded by Muisa et al. (2011) (Zimbabwe), and Yayintas et al. (2007) (Turkey).During the COVID-19 lockdown period, an increase of 0.201% was observed in Al concentrations compared to before the COVID-19 lockdown period.Sources of Al in surface waters includegeological weathering, industrial metalworking, and landfill leachate.In addition to these sources are the accumulation of airborne aerosols, accidental oil spills, agricultural sources, and sewage effluents(Muisa et al. 2011).This increase in Al concentrations was thought to be due to the continuation of industrial activities and more agricultural activities, especially in summer.The concentration of Cr in surface water ranged from 0.005 to 0.116 mg/L (0.019±0.028 mg/L) before the COVID-19 lockdown period and from 0.005 to 0.121 mg/L (0.022±0.035 mg/L) during the COVID-19 lockdown period.The Cr concentrations obtained in before and during the COVID-19 lockdown periods in this study were similar to those recorded bySelvam et al. (2020) andSahoo and Swain (2020 (India), and Sharmin et al. (2020) (Bangladesh), higher than those recorded by Njuguna et al. (2020) (Kenya), Hussain et al. (2017) (India), and Xiao et al. (2019) (China).During the COVID-19 lockdown period, an increase of 15.789% was observed in Cr concentrations compared to before the COVID-19 lockdown period.Cr has agricultural and industrial sources(Giri and Singh, 2014;Harmesa and Cordova, 2021).It is known that agricultural activities increase, especially in the summer months(Qu et al. 2015).Even though industrial activities were reduced during the COVID-19 lockdown period, it was thought that Cr concentrations increased due to increased agricultural activities.The concentration of Ni in surface water ranged from 0.005 to 0.194 mg/L (0.028±0.045 mg/L) before the COVID-19 lockdown period and from 0.005 to 0.123 mg/L (0.021±0.032 mg/L) during the COVID-19 lockdown period.The Ni concentrations obtained in before and during the COVID-19 lockdown periods in this study were similar to those recorded by Maity et al. (2020) and Giri and Singh (2014) (India), Üstün (2009) (Turkey), Wu et al. (2009) (China), and Proshad et al. (2020) (Bangladesh), while higher than those recorded by Mohammadi et al. (2019) and Rezaei et al. (2019) (Iran), and Ustaoğlu and Aydın (2020) (Turkey).During the COVID-19 lockdown period, a decrease of -25.000% was observed in Ni concentrations compared to before the COVID-19 lockdown period.From this, it is thought that most industries that did not work or reduced their capacity during the COVID-19 lockdown period may be plants producing metal plating and batteries.The concentration of Zn in surface water ranged from 0.005 to 1.308 mg/L (0.130±0.301 mg/L) before the COVID-19 lockdown period and from 0.005 to 1.207 mg/L (0.147±0.296 mg/L) during the COVID-19 lockdown period.The Zn concentrations obtained in before and during the COVID-19 lockdown periods in this study were higher than those recorded by Xiao et al. (2019) (China), Hameed et al. (2014) (Iraq), Prasanna et al. (2012) (Malaysia), and Sharmin et al. (2020) (Bangladesh); similar to those recorded by Maity et al. (2020) and Singh et al. ( Figures (Saha et al. 2017;Xiao et al. 2019;Nyambura et al. 2020values range from 1×10 −6 to 1×10 −4 , it means acceptable carcinogenic risk.If the ILCR values are lower than 1×10 −6 , it means non-carcinogenic risk, and if the ILCR values are higher than 1×10 −4 , it means high carcinogenic risk(Wang et     al. 2019).The potential non-carcinogenic risks are determined by the hazard quotient (HQ).The HQ values are calculated by Eqn.9(Saha et al. 2017;Xiao et al. 2019;Nyambura et al. 2020).