key: cord-0920693-5y4m1qrs
authors: Kumari, Minashree; Kumar, Arun
title: Can pharmaceutical drugs used to treat Covid-19 infection leads to human health risk? A hypothetical study to identify potential risk
date: 2021-03-09
journal: Sci Total Environ
DOI: 10.1016/j.scitotenv.2021.146303
sha: debcc60089af8e11025bdbcd8feb2fa35dbf5245
doc_id: 920693
cord_uid: 5y4m1qrs

This is the first study to assess human health risks due to the exposure of ‘repurposed’ pharmaceutical drugs used to treat Covid-19 infection. The study used a six-step approach to determine health risk estimates. For this, consumption of pharmaceuticals under normal circumstances and in Covid-19 infection was compiled to calculate the predicted environmental concentrations (PECs) in river water and in fishes. Risk estimates of pharmaceutical drugs were evaluated for adults as they are most affected by Covid-19 pandemic. Acceptable daily intakes (ADIs) are estimated using the no-observed-adverse-effect-level (NOAEL) or no observable effect level (NOEL) values in rats. The estimated ADI values are then used to calculate predicted no-effect concentrations (PNECs) for three different exposure routes (i) through the accidental ingestion of contaminated surface water during recreational activities only, (ii) through fish consumption only, and (iii) through combined accidental ingestion of contaminated surface water during recreational activities and fish consumption. Higher risk values (hazard quotient, HQ: 337.68, maximum; 11.83, minimum) were obtained for the combined ingestion of contaminated water during recreational activities and fish consumption exposure under the assumptions used in this study indicating possible effects to human health. Amongst the pharmaceutical drugs, ritonavir emerged as main drug, and is expected to pose adverse effects on r human health through fish consumption. Mixture toxicity analysis showed major risk effects of exposure of pharmaceutical drugs (interaction-based hazard index, HIint: from 295.42 (for lopinavir + ritonavir) to 1.20 for chloroquine + rapamycin) demonstrating possible risks due to the co-existence of pharmaceutical in water. The presence of background contaminants in contaminated water does not show any influence on the observed risk estimates as indicated by low HQadd values (<1). Regular monitoring of pharmaceutical drugs in aquatic environment needs to be carried out to reduce the adverse effects of pharmaceutical drugs on human health.

specifically designed for removing these specified drugs, as a result, large quantity of untreated effluent is being discharged into the surrounding water bodies such as rivers, lakes, and streams (Xu, et al., 2007; Choi et al., 2008) . Incessant discharge of untreated pharmaceutical drugs will increase the pharmaceutical load of the receiving water bodies (Wollenberger et al., 2000; Wang et al., 2014; Yan et al., 2016) and plants (Migliore et al., 2003; Pan et al., 2016) and may lead to possible bioaccumulation and their subsequent bio-magnification in the underlying aquatic organisms specially fishes (Edwards et al., 2009) . The accumulation of pharmaceutical drugs in the aquatic environment can pose risk to the underlying organisms possibly through food chain transfer, even at low concentrations (Wellington et al., 2013; Sharma et al., 2016) . Possible human health risk exposure can occur if the contaminated water is accidentally ingested by human beings during recreational activities or through consumption of fish grown in contaminated waters, or both (Kumari and Kumar, 2020a; Parsai and Kumar, 2020) . This study addresses health risk exposure effects of repurposed pharmaceutical drugs to humans. No such studies are available in published literature to the author's best knowledge till date. The prime objective of this study was to assess the health risk effects by the exposure of repurposed drugs used for treating Covid-19 infected patients. The study applied the recommended risk assessment framework for estimating human health risk exposure effects of repurposed drugs. Human health risks is estimated for three different exposure pathways (i) accidental ingestion of contaminated 6 The pharmaceutical drugs were selected based on their effectiveness in treating SARS-CoV-2 infection as reported by clinical trial studies (WHO, 2020c) . The proposed structure can be used in determining health risks exposure of other-related drugs as well. The outcome of the study can benefit risk evaluators in estimating risk due to exposure of repurposed drugs, and also furnish details to controllers in identifying the need for treating the water bodies prior to its use, and also restricting fish extraction from contaminated water.

The diagrammatic representation of the proposed methodology to determine the human health risks of repurposed drugs used to fight Covid-19 infection is given in Figure1. This study evaluated risk exposures for three different pathways which will be discussed later on. The study applied a six-step approach comprising of hazard identification, dose-response assessment, exposure assessment, risk estimation, risk characterization and management to estimate human health risks (Sohaili et al., 2017; Parsai and Kumar, 2020) . Briefly, this framework ( Fig.1) assumes that pharmaceutical drugs taken via the oral route are excreted through feces and urine either metabolized or un-metabolized as parental drugs. The untreated pharmaceutical wastewater effluents are usually discharged into the near-by surface water from which these drugs can enter into aquatic organisms through food chain. Surface water is the major source of water used by human beings for recreational activities, but uncontrolled and untreated discharge of pharmaceutical wastewater effluent makes the water contaminated. Under any circumstances, if these contaminated water is accidentally ingested, they might show adverse health effects and possible risk Gibs et al., 2013; Yao et al., 2017) . Pharmaceutical drugs present in the surface water can also get accumulated in fish muscles and tissues which on consumption by human Excreted via urine /feces, goes into wastewater treatment plants and discharged into surface water such as lakes, rivers, etc.

Hazard Identification ( Step

Pharmaceutical drugs J o u r n a l P r e -p r o o f 9

Hazard identification is the first step in the risk assessment process. This step involves identifying the toxicity of contaminants selected for risk exposure.

This study selected five different pharmaceutical drugs named as lopinavir (LOP), ritonavir (RIT), chloroquine (CHQ), ribavirin (RIB), and Sirolimus or rapamycin (RAP) on the basis of their efficacy in conducted clinical trials to treat Covid-19 infection (Gordon et al., 2020; WHO 2020c) . LOP-RIT has been projected as a possible treatment for COVID-19 based on preclinical and empirical studies (Horby et al., 2020) . LOP is a HIV-1 protease inhibitor, which is combined with ritonavir to increase its plasma half-life. LOP is also an inhibitor of SARS-CoV main protease, which is crucial for replication and was found to be exceedingly conserved in SARS-CoV-2 (Nukoolkarn et al., 2008; Liu and Wang, 2020) . RIB, an antiviral agent, is generally used in combination with lopinavir-ritonavir and helps in minimizing the risk of dreadful clinical aftermaths besides reducing viral load amongst patients infected with SARS (Chu et al., 2004; Rabi et al., 2020) . CHQ, an antimalarial drug, and could be effective tool against SARS-CoV-1 and SARS-CoV-2 (Colson et al., 2020; Yao et al., 2020) . Sirolimus, also known as RAP, is an immunosuppressant and its immuno-therapeutic potential (mTOR inhibitor) has been found to be effective against COVID-19 infection (Omarjee et al., 2020) which is currently under phase 2 trial in USA (NCT04341675) (NIH, 2020) . J o u r n a l P r e -p r o o f (Abafe et al., 2018; Wood et al., 2015) . Predicted environmental concentrations (PECs) is a practical approach (Franquet-Griell et al., 2015) to identify the concentration level of pharmaceutical drugs in water environment. This approach has been successfully used to predict the concentration of antibiotics (Kumari and Kumar, 2020a) , and other related drugs (Burns et al., 2018; Guo et al., 2016) in drinking water, wastewater and surface waters. In this study, PEC values of selected pharmaceutical drugs were estimated for two different set-ups. The methodological approach is represented in Figure 2 . (1)

Where, Dose* inhab (mg/person/day) is the consumed amount of each pharmaceutical drug administered per person per day in USA; F pen is market penetration and represents the fraction of J o u r n a l P r e -p r o o f the total population that consumes the pharmaceutical on any given day. A default value of 0.01 was applied for PEC river_NDD whereas, for PEC river_Covid-19 , the value is taken as 0.47 (Elflein et al., 2020) ; F Exec is the fraction of parent drug excreted unaltered via human metabolism. Both urine and feces are considered. Excretion profile of the drugs were extracted from the published literature, and the drug bank database. For those pharmaceutical drugs whose data was not available, a default value of 0.5 was applied, assuming that a drug will not be completely 2003) . W represents the number of person in a defined zone (in this case USA population was considered), and lastly, DF is the dilution factor from WWTP effluents to surface waters.

Discrepancies in this data can differ the results by more than 100-fold (Elflein, 2020 Concentrations of pharmaceutical drugs in fishes were calculated using previously estimated concentration values of drugs in river (PEC river ), bio-concentration factors (BCF) for fish, and bio-magnification factors (BMF), as given in Eq.

(2). Since, the BCF values of selected pharmaceutical drugs are not available in published literature, the values were calculated using the octanol-water partition coefficient (K ow ) values of drugs and and lipid content fraction in fishes, using Eq. (3).

(2)

Where, BCF is the bio-concentration factors (LKg -1 ); BMF is the bio-magnification factor of pharmaceutical drugs, the value is assumed to be 1 in this study (unit less); f W is water content fraction of the organism; f lip is lipid content fraction of the organism; pH int is internal pH, and pH ext is external pH; D lip-water is lipid-water partition coefficient, and was calculated as log D lipwater = 0.904 × log K ow + 0.515 (Fick et al., 2010) .

This study estimated risks of pharmaceutical drugs to adults as they are reported to be the most sensitive sub-population category affected by SARS CoV-2 infection (Grant et al., 2020) and are prone to higher risks as suggested by Centers for Disease Control and Prevention, USA.

Exposure assessment study was carried out for two different set-ups considering three different J o u r n a l P r e -p r o o f exposure routes as mentioned in Fig. 1 . Exposure route-1 indicates risks due to the accidental ingestion of contaminated surface water during recreational activities, exposure route-2 for consumption of fishes grown in pharmaceutical-contaminated water, and in route-3, exposure was estimated for the combined accidental ingestion of contaminated water during recreational activities and through fish consumption.

The acceptable daily intake (ADI) is one of the crucial parameter in determining risk estimates. ADI signifies the highest intake level of a substance that does not give rise to minimal or no risk observable adverse effects (Dennis and Wilson, 2003) . When clinical studies in humans are inappropriate or could not be found, the ADI is estimated from reliably conducted toxicity studies in laboratory animals by using the no observed adverse effect level (NOAEL) or the no observable effect level (NOEL) associated with the most sensitive endpoint in the most sensitive species (Hurt et al., 2010) . To account for differences between animals and humans (interspecies variability) and for intra-individual variability between humans, the NOAEL is divided by a safety (uncertainty) factor to establish an ADI. In this study, ADI values of 'repurposed' pharmaceutical drugs was estimated using NOAEL or NOEL values in rats, the conversion from rats to human was carried out using a safety factor of 100 as given in Eq. (4). A default safety factor of 100 takes into account both the differences in species and differences in toxicokinetics and toxicodynamics properties (Dankovic et al., 2015) . It is generally based on the assumption that humans are 10 times more sensitive to a substance than experimental animals and that there is a 10-fold range in sensitivity within the human population (Gilsenan, 2011) .

(4)

A PNEC signifies the concentration in surface water at or below which no adverse human health effects are expected to occur (Schwab, 2005) . In this study, PNEC values were calculated for three different exposure routes (i) accidental ingestion of pharmaceutically contaminated surface water during recreational activities (PNEC RA ); (ii) consumption of fishes grown in pharmaceutically contaminated surface water (PNEC fish ); and (iii) combined exposure due to the accidental ingestion of contaminated surface water during recreational activities and through fish consumption (PNEC river+fish ) using Eqs. (5-7).

(5)

Where, ADI is the acceptable daily intake (mg kg-day -1 ); BW is the body weight (Kg); AT is the average lifetime (Days); IR DW is the surface water ingestion rate (L day -1 ); EF is the exposure frequency (days Year -1 ); ED is the exposure duration (Year). ED values were taken as per the scenario considered: for normal drug dose, ED value of 70 Yrs. was applied to estimate PNECs for the three different categories mentioned above. However, for Covid-19 case, ED value was considered to be 1 year assuming that the Covid-19 cases would decline in near future once the J o u r n a l P r e -p r o o f 17 vaccine is developed; BCF is the bio-concentration factor in fish (L Kg -1 ). CR Fish is the fish consumption rate (Kg day -1 ). Table S1 in the supplementary information provides the values of input parameters used for PNEC estimation.

The study estimated risk exposure effects for the hypothetical exposures of individual pharmaceutical drugs by means of hazard quotient, HQ. Hazard quotient value was calculated as a ratio of PEC/PNEC Eq. (8). In Eq. (8), PECs values are taken from the exposure assessment section and PNECs from the dose-response assessment section. If the calculated HQ are larger than 1 then concern exists to human health for the exposure route studied and vice versa (Kumari and Gupta, 2018) . The total HQ of 'repurposed' pharmaceutical drugs was calculated by adding up the individual HQ values of surface water (river) and the individual HQ values of river_Covid-19 (Eq. 9).

(8)

It is expected that under realistic scenario i.e. in surface waters, pharmaceutical drugs usually exist in mixture combinations and not as individual drugs. Therefore, it is essential to determine the risks exposure effects of co-existing pharmaceutical drugs on human health for the different J o u r n a l P r e -p r o o f exposure routes mentioned above. Risk estimation of pharmaceutical drugs in binary mixtures is represented as HI int , and was calculated using the modified USEPA weight of evidence approach, as given in Eq. (10-12) (Kumari and Kumar, 2020a; US EPA, 2000) .

(10)

Where, HQi and HQ j is the hazard quotient of i th compound and j th compound; f ij is the toxicity hazard of j th compound (j≠1 

Comprehensive hazard risk assessment study was performed to determine the risk exposure effects of background contaminants on pharmaceutical drugs. It is believed that several type of background contaminants like nanoparticles, antibiotics, etc., might be present in aquatic J o u r n a l P r e -p r o o f environment (Gros et al., 2010; Osorio et al., 2016) . This study considered antibiotics as background contaminants for calculating the overall health risk exposure to humans.

Fluoroquinolones are the most frequently detected antibiotics in the environmental media (Sukul and Spiteller, 2007) of which ciprofloxacin (CIP) and norfloxacin (NOR) are primarily detected in higher concentrations (Mahmood et al., 2019; Ma et al., 2015; Yao et al., 2017) . Drug-drug interaction data of binary mixture drugs are hardly available in scientific literature, hence, we have used the concentration or dose-addition approach to determine the total risk, referred to as HI total . HI total was calculated by summing up the individual HQ values of background contaminants and individual pharmaceutical drugs as given in Eq. (13). HI values of antibiotics CIP and NOR is taken from our previous published work ( Kumari and Kumar 2020a, b) , and HI values of individual pharmaceutical drugs is taken from risk estimation exposure of co-occurring pharmaceutical drugs section 2.4.2.

(13)

Sensitivity index analysis was performed to identify the most influential parameters governing risk estimates (Kumari and Gupta, 2018) 

PEC values of pharmaceutical drugs in surface water was estimated for three different cases i.e.

PEC river_NDD , PEC river_Covid-19 , and PEC fish. (Pradat et al., 2014) , and there is a chance that the untreated wastewater effluent is discharged into the nearby rivers or lakes resulting in high levels.

In order to predict the concentration of pharmaceutical drugs (PECs) in fishes, BCF values were first estimated. The calculated BCF values of the pharmaceutical drugs ranged from 1.32 L Kg -1 (for RIT) to 0.58 L Kg -1 (for RIB). Four of the five pharmaceutical drugs have BCF values of more than 1.0 L/kg either because the drug is ionic with a log K ow of less than 5 (2 of 5). Only one pharmaceutical drug has BCF value smaller than 1.0L/kg because the drug is nonionic but has a log K ow of less than 1.0 (Table 1) . A bioconcentration factor greater than 1 is indicative of a hydrophobic or lipophilic chemical. It is an indicator of how probable a chemical is to bioaccumulate (Landis et al., 2011) .

PEC values in fishes ranged from 2245 µg Kg -1 (for RIB) to 26 µg Kg -1 (for RAP).

Concentration of RIB appeared to be maximum in fishes as indicated by high PEC values (Table   2 ). Since there is a possibility that pharmaceutical drugs might get accumulated in the fish tissues, hence, the bio-accumulative potential of drugs was also considered for predicting the concentration in fish tissues. Bio-accumulation factor (BAF, L Kg -1 ) was calculated as a ratio of pharmaceutical drug concentration in fish tissues to that in water. The results revealed that RIT showed the highest bio-accumulative potential followed by LOP, while RIB has the lowest BAF values. As observed in this study, BAF values of pharmaceutical drugs RIT, LOP, RAP and CHQ was more than 1, representing that the bio-accumulative potential. BAF values > 1 show that the accumulation of pharmaceutical drugs in the fish tissues is greater than that of the medium, for instance, soil or water in which the drug is present (US EPA, 2009). Earlier studies have also reported that concentration of pharmaceuticals drugs in fishes is considerably higher in plasma than in ambient water (Fent et al., 2006) . 

ADI values of pharmaceutical drugs were calculated using NOAEL or NOEL values in rats. The conversion of NOAEL/NOEL values from rats to human was done using a safety factor as mentioned in the exposure assessment section. The estimated ADI values of pharmaceutical drugs was 0.1 mg kg -1 day -1 for LOP, RIT: 0.05 mg kg -1 day -1 CHQ: 16.6 mg kg -1 day -1 , RIB: 15 mg kg -1 day -1 , and RAP: 0.01 mg kg -1 day -1 . It can be seen that CHQ has the highest ADI value whereas RIT has the lowest ADI values.

PNEC values of pharmaceutical drugs in adults were estimated for two different scenarios (1) for normal drug dose, and (2) for 'repurposed' drugs dose used to treat Covid-19 infection for three different exposure route as mentioned above in the exposure assessment section. contaminated water during recreational activities ranged from 1.05 × 10 8 µg L -1 (for RIB) to 7 × 10 3 µg L -1 (for RAP). For fish consumption exposure, PNEC fish values ranged from 2.76 × 10 2 µg L -1 (RIB) to 9.04 × 10 -2 µg L -1 (for RAP). For the combined exposure to ingestion of contaminated water during recreational activities and fish consumption exposure, PNEC fish+RA ranged from 2.36 × 10 2 µg L -1 (for RIB) to 8.34 × 10 -2 µg L -1 (for RAP). Overall, it was witnessed that ribavirin has the maximum PNEC values for all the three exposure routes whereas rapamycin has the lowest. Thus, it is possible that ribavirin might show adverse effects to human health for the three exposure routes studied.

In set-up 2 (drug dose, Covid-19 infection), the estimated PNEC values for all the three different exposure routes studied is quite similar to those observed for set-up 1. The sequence of exposure followed (maximum to minimum): fish consumption exposure only > combined ingestion of water and through fish consumption exposure > ingestion of water only (Table 3) .

Similar PNEC values obtained for the two set-ups could be attributed to variation in the values of input parameters considered, for instance, exposure duration value was taken as 70 years for normal drug dose whereas, ED of 1 year was assumed for Covid-19 infection. The similarity is also due to average lifetime, AT values taken for both these set-ups. Schwab et al., 2005) . The results revealed that consumption of fishes is unlikely to be the major route of exposure to humans for pharmaceutical drugs considered. Amongst the pharmaceutical drugs, RIB has the highest reported PNEC values for three different routes analyzed thus, its presence in either contaminated water or in fishes is unexpected to cause any health effects on humans. Lowest PNEC value indicates drug-of-concern for a given exposure pathway. The lower the PNEC values, higher is the concern. The lowest PNEC values are shown in bold text and has been italicized in the Table provided below. The outcomes of this assessment show that the occurrence of low levels of pharmaceuticals drugs in surface waters pose no appreciable risk to human health during the accidental ingestion of contaminated water for both the set-ups considered. Earlier studies have also reported no adverse effect to human health from exposure to trace quantities of pharmaceuticals in drinking water or surface water (Schulman et al., 2002; Webb et al., 2003; Bercu et al., 2008) . The combined route to contaminated water during recreational activities and consuming fishes grown in contaminated water pose maximum risks to human health under the conditions and assumptions used in this work. This is mainly because at the moment no specific treatment methods are available which can remove these pharmaceuticals from wastewater effluents (Osborne et al., 2020) . The untreated effluents are discharged into the surrounding water-bodies and via food chain transfer the drugs can enter into aquatic organisms and gets accumulated in their muscles and tissues. The high HQ levels of pharmaceuticals observed in this study under the assumptions used can be indicative of the bioaccumulative potential of the drugs in fish tissues which on consumption by humans leads to potential health risks (Table 4 ).

Journal Pre-proof 28 

As we know that under the current Covid-19 pandemic, number of cases are increasing day by day which has increased the consumption of drugs creating an additional burden to the existing pollution load in water. It is important to estimate health risks considering both the set-ups to get a realistic HQ values which will help in better assessing the associated human health risks. For this purpose, total HQ values of individual pharmaceutical drugs was calculated by summing up the observed HQ values in set-up 1 and set-up 2. The calculated HQ total of pharmaceutical drugs is given in Table 5 .

For the accidental ingestion of contaminated water during recreational activities, HQ total of individual pharmaceutical drugs were less than 1 and falls within the acceptable risk level (HQ total < 1). This indicates that the accidental ingestion of contaminated surface water does not pose any risks to human health. For fish consumption exposure, HQ total values of pharmaceutical drugs ranged from 313.90 (for RIT) to 10.89 (for CHQ) and are very high, exceeding the acceptable risk levels. RIT, RAP, and LOP emerged as the top three pharmaceutical drugs.

Higher values of these pharmaceuticals can be due to high PECs/PNECs ratio. For the combined exposure to inadvertent ingestion of contaminated water during recreational activities, calculated HQ total values of all pharmaceutical drugs were higher than 1 (HQ total > 1) and exceeded the acceptable risk levels (Table 5) . Amongst the three exposure routes, no health risk exists to humans for exposure to ingestion of contaminated water. Higher risk effects of exposure come through the combined ingestions of contaminated water and fish consumption than through consuming fishes grown in contaminated water under the conditions assumed this work. The results obtained in this study gives a vital information as none of the studies reported on Covid-19 has considered and investigated the risk assessment aspect of 'repurposed' pharmaceutical J o u r n a l P r e -p r o o f drugs involved for any of the exposure routes studied. Though in some occasions the risk estimates were observed to be less than 1 and display no health effects, however, continuous monitoring of these pharmaceutical drugs in water and fishes is required. 

HI interaction values were calculated to determine the effects of co-existence of pharmaceutical drugs (Kumari and Kumar, 2020a) . It was observed that combined exposure of pharmaceutical drugs through the accidental ingestion of contaminated water during recreational activities gives

higher HQ values than the other two exposure routes therefore, the risk exposure effects of coexistence of pharmaceutical drugs was investigated considering this particular route only. The results revealed that the HI int values for mixture combinations ranged from 295.42 (for LOP + J o u r n a l P r e -p r o o f RIT) to 1.20 (for CHQ + RAP). HI int values more than 1 indicates possible health risks and significant concerns due to the co-occurrence of pharmaceutical drugs in water under the assumptions applied in this study. Higher HI int values can be attributed to obtained high HQ values of single pharmaceutical drugs. Previous studies have also reported even higher HI int values for nanoparticle exposure (Parsai and Kumar, 2020) . The findings of this study can provide an important information about health risk issues due to the co-exposure of pharmaceutical drugs in water. Co-occurrence of pharmaceutical drugs in water shows detrimental effects to human health and needs to be monitored. observed that HQ add for all the possible binary mixture combinations was found to be less than 1 (Table 7) . This indicated that no significant health risk effects exist to humans due to the presence of these background contaminants in water environment. Though insignificant risk was witnessed using dose-addition approach, still more specific studies using the USEPA weight-ofevidence approach need to be performed to attain precision in risk estimates. NOR + RIT 1.24 × 10 -9 3.65 × 10 -3 3.65 × 10 -3 NOR + RAP 1.24 × 10 -9 3.12 × 10 -3 3.11 × 10 -3 NOR + LOP 1.24 × 10 -9 2.65 × 10 -3 2.66 × 10 -3 HQ 1 * indicates background contaminants; HQ 2 # indicates pharmaceutical drugs considered in this study

Sensitivity index analysis was carried out to identify the effect of variables on risk estimates for the three different exposure routes. The results of sensitivity index analysis for the three exposure routes is depicted using spider chart diagram as given in Fig 3. For route-1 (the accidental ingestions of contaminated water during recreational activities), IR showed highest sensitivity and appeared as the major parameter affecting risk estimates which was closely followed by body weight, BW (Fig. 3a) . For fish consumption exposure (route 2), BCF has the highest sensitivity index values and showed major effects on calculated HQ values (Fig. 3b) followed by BW, EF, ED, and CR. Similarly, for route-3 (combined ingestion of contaminated water during recreational activities and fish consumption exposure), BCF has the maximum sensitivity index values which was followed by water intake rate (Fig. 3c) An understanding of uncertainty in risk assessment studies is important in conveying the likelihood of an adverse event or the magnitude of its consequences (Kumari and Kumar, 2020a; Kumari and Gupta, 2018) . Reductions in uncertainty do not change the risks, but they increase the mathematical precision of evaluation. It is necessary to address the uncertainty associated with risk assessment studies (Parsai and Kumar, 2020; Kumari et al., 2015) . Uncertainty may also arise due to variation in input parameters used to estimate PECs and PNECs for risk estimation. Some of these are discussed below.

 Uncertainty may arise due to scarcity of environmental occurrence data of drugs considered.

Because of beneficial health effects and economic importance of these pharmaceutical drug, the best available evidence should be used to fully evaluate any additional actions that may be required to reduce environmental burden as a result of perceived human health risks. A thorough monitoring and analysis of these drugs is required to achieve more clarity on the data obtained.

 DF is another parameter which creates uncertainty in data analysis. For consumer products, an average DF value of 10 is recommended for sewage from municipal wastewater treatment (Lindim et al., 2016; Veith et al., 1979; Mackay, 1982) . In this study BCF values are determined using pKa and logK ow of the contaminants, and lipid fraction of the organism but the available regression equations do not consider the lipid content involved which may lead to some kind of uncertainty in BCF values.

 ADI is another parameter which needs to be studied carefully. Due to lack of information on ADI values of the pharmaceutical drugs, this study used the NOAEL or NOEL values in rats to determine the ADI values, and transition to humans was made using a safety factor which might add uncertainty in risk estimates. Specific human based studies in vivo is required and must be carried out to avoid inaccuracy in risk estimates. J o u r n a l P r e -p r o o f

1) RIB has the highest consumption rate which is indicated by their high concentrations (PEC values = 3840 µg L -1 ) in surface water and in fishes (2245 µg Kg -1 ) Therefore, regular monitoring of must be carried out in water and in fishes to protect the human health from their adverse health effects.

2) High risk values (HQ > 1) were obtained for the combined exposure to the accidental ingestion of contaminated water during recreational activities and fish consumption than the other two exposure routes, indicating significant concerns to human health. Amongst the pharmaceutical drugs studied, RIT is expected to pose adverse health effects followed by RAP and LOP. Our findings indicate that RIT emerged as the priority contaminant which needs to be regularly monitored in wastewater effluents discharged to nearby rivers and lakes to reduce risks.

3) Mixture toxicity risk exposure analysis revealed also showed high HI interaction values (HI int > 1) for all the studied combinations. Total risk assessment revealed that the presence of background contaminants in the water environment does not pose any significant risk to humans. Proper drug-drug interaction data (synergistic/antagonistic effects) must be taken into account for future risk assessment studies.

4) Sensitivity analysis index showed that BCF (SI = 181.80) and intake rate (0.35) are the two most sensitive variable affecting risk estimates, the contribution of other variables was found to be insignificant.

J o u r n a l P r e -p r o o f Regular and seasonal monitoring of receiving surface/ground water bodies and drinking water supplies for the presence of drugs is required to reduce spatial and temporal variability in drugs concentration. Continuous monitoring of priority contaminants in surface water must be carried out to protect aquatic organisms and human beings from their prolonged exposure and subsequent adverse health effects. The results presented in this study indicate only point estimates which might have added uncertainty in risk estimates (Kumari and Kumar, 2020a; Kumar and Xagoraraki, 2010) . Therefore, to reduce uncertainty and variability in risk assessment, Monte Carlo based simulation study must be carried out in future risk studies. There is an urgent need for establishment of PNECs based on experimental data, and the consequences involved in not regulating releases of pharmaceutical drugs into the environment could further escalate a problem that might reach very serious proportion under the current Covid-19

pandemic. Research investigations must be carried out to determine ADI values based on appropriate toxicological studies to determine risk estimates, and to reduce variability in evaluating HQ values for characterizing the risk (Kumar and Xagoraraki, 2010) . Due to limited information available on drug-drug interaction data of the pharmaceutical drugs, we have used dose addition approach to calculate total risk exposure of additional background contaminants in water environment. There is a need to use weight of evidence approach to conduct human health risk evaluation of these drugs in either binary or tertiary mixture using drug-drug interaction data and magnitude of interaction. Many risk assessment approaches, particularly those focused on human health protection, are based on the assumption of binary pair toxicity predicting the mixture effects of an overall mixture. In an environmental context where there are so many potential combinations might often be present as unidentified components and it is difficult to address all of binary mixtures at a time. To address this problem, certain approaches or rank J o u r n a l P r e -p r o o f

The authors would like to thank Department of Civil Engineering, Indian Institute of Technology (Delhi, India) for supporting this study. The work carried is a part of the corresponding author (Dr. Minashree Kumari) research from her Post-Doctoral work

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Human health risk assessment of pharmaceuticals in water: an uncertainty analysis for meprobamate, carbamazepine, and phenytoin

Introduction to Environmental Toxicology: Molecular Structures to Ecological Landscapes

Evaluation of human pharmaceutical emissions and concentrations in Swedish river basins

Efficacy of chloroquine versus lopinavir/ritonavir in mild/general COVID-19 infection: a prospective, open-label, multicenter, randomized controlled clinical study

Potential inhibitors against 2019-nCoV coronavirus M protease from clinically approved medicines

Occurrence ad regional distributions of 20 antibiotics in water bodies during groundwater recharge

Detection of Antibiotics in Drinking Water Treatment Plants in Baghdad City

Correlation of bioconcentration factors

Phytotoxicity to and uptake of enrofloxacin in crop plants

Molecular dynamic simulations analysis of ritonavir and lopinavir as SARS-CoV 3CL(pro) inhibitors

Targeting T-cell senescence and cytokine storm with rapamycin to prevent severe progression in COVID-19

Lopinavir-ritonavir in the treatment of COVID-19: a dynamic systematic benefit-risk assessment

Concentration and risk of pharmaceuticals in freshwater systems are related to the population density and the livestock units in Iberian Rivers

Phytotoxicity of veterinary antibiotics to seed germination and root elongation of crops

Tradeoff between risks through ingestion of nanoparticle contaminated water or fish: Human health perspective

Ribavirin at the Era of Novel Direct Antiviral Agents for the Treatment of Hepatitis C Virus Infection: Relevance of Pharmacological Monitoring

SARS-CoV-2 and Coronavirus Disease 2019: What We Know So Far

A human health risk assessment of pharmaceuticals in the aquatic environment

Human pharmaceuticals in US surface waters: a human health risk assessment

A review of the influence of treatment strategies on antibiotic resistant bacteria and antibiotic resistance genes

Drug repurposing approach to fight COVID-19

Dose response and exposure assessment of household hazardous waste

Fluoroquinolone Antibiotics in the Environment

Environmental Protection Agency, Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health. Oyce of Water, Oyce of Science and Technology

Environmental Protection Agency) (2009c) Risk Assessment Guidance for Superfund vol I: human health evaluation manual (Part F, Supplemental Guidance for Inhalation Risk Assessment). Office of Superfund Remediation and Technology Innovation

Environmental Protection Agency) (2009d) Risk Assessment Guidance for Superfund volume 1: human health evaluation manual (Part F, Supplemental Guidance for Dermal Risk Assessment). Office of Superfund Remediation and Technology Innovation

Supplementary Guidance for Conducting Health Risk Assessment of Chemical Mixtures

UESPA, KABAM Version 1.0 (K ow (based) Aquatic BioAccumulation Model)

Environmental Fate and Effects Division, Office of Pesticide Programs

Remdesivir and chloroquine effectively inhibit the recently emerged novel coronavirus (2019-nCoV) in vitro

Toxicity evaluation of β-diketone antibiotics on the development of embryo-larval zebrafish

The role of the natural environment in the emergence of antibiotic resistance in Gram negative bacteria

Indirect human exposure to pharmaceuticals via drinking water

Director-General's opening remarks at the media briefing on COVID19

Solidarity" clinical trial for COVID-19 treatments. Latest update on treatment arms

Landscape analysis of therapeutics

DrugBank 5.0: a major update to the DrugBank database

Acute and chronic toxicity of veterinary antibiotics to Daphnia magna

The occurrence of anti-retroviral compounds used for HIV treatment in South African surface water

Occurrence and elimination of antibiotics at four sewage treatment plants in the Pearl River Delta (PRD), South China

In vitro antiviral activity and projection of optimized dosing design of hydroxychloroquine for the treatment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)

Occurrence and Risk Assessment of Antibiotics in Surface Water and Ground Water from Different Depths of Aquifers: A Case Study at Jianghan Plain, Central China

Long-term effects of antibiotics, norfloxacin, and sulfamethoxazole, in a partial life-cycle study with zebrafish (Danio rerio): effects on growth, development, and reproduction

Measuring and estimating the bioconcentration factor of chemicals in fish