Temporal Variation in Leachate Composition of A Newly Constructed Landll Site in Lahore in Context To Human and Environmental Risks

The present study was aimed to explore the seasonal and temporal variation in the extent and sources of physiochemical and trace elements in the Lakhodair solid waste Landll site in Lahore, Pakistan. For the seasonal and temporal study of leachates, systematic composite samples were collected monthly (for one year) and analyzed for physiochemical and trace elements. The concentration of TDS, TSS, COD, NH 3 -N, BOD 5 , sulfate, suldes, phenolic compounds, oil and grease were higher than the National Environmental Quality standard (NEQs). The trace elements, namely Mn (1.7 mg/L), and Cd (0.05 mg/L), while in a few samples Fe (14 mg/L), Ni (1.6 mg/L), and Zn (6.7 mg/L) were higher than the NEQs. In Lakhodair leachates, TDS, COD, NH3-N, BOD 5 , suldes, and Cl have a high concentration coecient (i.e., CC 3 to > 6), which may cause considerable to high contamination, while remaining parameters may cause low to moderate contamination (CC 1 to ≤ 3). The lower BOD 5 /COD ratio (< 0.1) in the Spring and Autumn seasons, represents the active methanogenesis and anaerobic activities in the Lakhodair landll site. The anaerobic and methanogenesis enhance the redox reaction as a result CO 2 is emitted and alternatively increases pH, TDS, COD, Cl, BOD 5 , NH 3 -N, suldes, phenolic compounds in leachates. However, the lower concentration of some trace elements may be because of an anaerobic process that may immobilize the trace elements. It is presumed that the trace elements in the Lakhodair landll may be in a metastable state, which is not easy to leach out. It’s hereby recommended that Leachate produced in the Lakhodair landll site need to handle carefully so as to limit the environmental and health implication.


Introduction
Solid waste management and minimization is a global issue being faced by the world especially the developing countries, where the national budget for solid waste management is negligible. Alternatively, global awareness about the impacts of solid waste associated with human health, water, soil, and air are increasing rapidly. Earlier, solid waste management was not a big issue and societies manage their wastes effectively, however increasing population and urbanization rendering solid waste management much more complex (Singh et al. 2014). Due to the nancial crisis, both developing and under-developing countries are not focusing to carry out waste management under controlled parameters (Fernando 2019). The major sources of solid waste are domestic wastes (i.e., food waste, housekeeping), agricultural waste (i.e., fertilizers waste, crops residue, farm wastes), commercial wastes (i.e., markets, hospitals, hotels, schools, and o ces), Industrial wastes (metals scraps, oils, chemicals, trash), and mining wastes (i.e., rock gangue, soil-gravels, toxic elements) ( In Pakistan, the solid wastes generation rate is 0.283 to 0.65 kg/capita/d with an annual growth rate of 2.4 % ( Azam et al. 2020). By an instant increase in solid waste, the morbidity rate is increasing with an increasing mortality rate in Pakistan due to improper solid waste management and associated diseases (Nisar et al. 2008). Further, the unplanned disposal and deposition of solid wastes affect the food crops, air, and water quality of Lahore, where the mortality rate is ~ 25,000/ year through waterborne disease (Muhammad &Zhonghua 2014). The local government dealing and handling the SWM, however, the lack of proper nancial resources, infrastructure, planning, and unavailability of effective machinery fails to the handling of solid wastes, properly (Batool &Ch 2009). The improper collection and transportation boost the solid waste accumulation in urban territories i.e., streets, streams, roadside, corners, and rivers, which pose serious threats to local inhabitants, groundwater, and to the mesoscale environment (Ferronato &Torretta 2019). The negative impacts of solid wastes in an urban environment is increasing continuously, which need to quantify and comprehend the extent of problems, ndings, and appropriate solution.
In developing countries, the rate of solid wastes generation is higher than the developing countries. The solid waste generation in the United States is 2.08 kg/capita/d, Europe 1.5 kg/capita/d, OECD countries recovery technology applied in effective incineration, which was higher than those reported by World Bank i.e., 7100 kJ/kg (Melikoglu 2013, World Bank 1999. However, in Lahore (Pakistan), about 14,490 kJ/kg energy is probed by using the bomb calorimeter (Azam et al. 2020). Similarly, the nal wastes having no longer value can be disposed of safely in a speci c land lling site, which limits the environmental consequences and improves the urban aesthecity (Mian et al. 2017).
Additionally, Land ll leachate released major contamination, especially toxic trace elements, which affect the groundwater through in ltration and surface water through run-off. These leachates can transfer the microbial, chemical, and physical contaminants to water bodies and the environment, which pose serious threats to humans' health and nearby land use (Hui et al. 2006). The open dumping of solid wastes can increase ecotoxicity by the presence of organic compounds, trace elements, ammonia-nitrogen (NH 3 -N), and chlorinated inorganic compounds (Bhalla 2013). The major in uencing factors of leachates are the composition of waste, decomposition phase, climate, oxygen, land ll hydrology, and microbial activity (Umar et al. 2010

Experimental work
The pH, EC, and TDS in the leachate sample were measured through a digital meter (Lovibond Con-200).
Oil and grease were measured through a separating funnel using n-Hexane, COD was measure through the Open Re ux method, BOD 5  Where C n represents the target values in leachates, R f represents the reference value. For comparison and evaluation, the contamination degrees (i.e., CC) can read as CC < 1 low contamination, CC 1-3 moderate contamination, 3-6 considerable contamination, and CC > 6 indicate high contamination (Table S2).

Results
Leachate samples collected (monthly) from the Lakhodair land ll site were analyzed for various physiochemical parameters and toxic trace elements, which were further arranged monthly and seasonally (Table 1 and Table 2). Most of the parameters, namely TDS, TSS, BOD 5 , COD, NH 3 -N, sulfate, sul des, chloride, oil and grease, and some toxic trace elements were higher than the standard permissible level (Table 1)   Similarly, the analyzed samples showed some compliance with respective standards, and the signi cant deviations were equally noticed. The physiochemical characteristic of leachate indicates alkaline nature with a pH of 8.27 to 9.18 and NH 3 -N 288 to 1250 mg/L, which was higher than the standard permissible level (40 mg L − 1 ) ( Table 1). The pH of old land ll leachate is more stable and high than the young one, which indicates the decomposition of humus (organic compounds) and oily wastes (Tanikawa et al. 2018). The TDS was ranged from 6736-25640 mg/L and TSS was 60-920 mg/L, which was higher than those report by Bhalla (2013) i.e., TDS 6863 mg/L. The COD concentration in Lakhodair leachate was 4553-12620 mg/L, which was higher than the NEQs level i.e., 400 mg/L. The source of higher COD is due to the lack of aeration, presence of organic matter, higher temperature, and bacterial community (Noer triyani et al. 2018). The Lakhodair land ll is considered to be an old land ll site because of stable leachate pH i.e., 8.3-9.2 (throughout the year) and its age is > 10 years. The pH of mature leachate is mostly stable with slight variation in seasons, however, the pH of the leachate is increasing with decreasing/ decomposition of oil and fatty materials (Khalil et al. 2020, Renou et al. 2008). The concentration of sulfate was 16-10400 mg/L and sul des was 0.3-21 mg/L, which was both comparably higher than the NEQs i.e., 1000, and 01 mg/L, respectively ( Table 1). The highest concentration of sulfate was measured in November i.e., 10400 mg/L, while sul de in February i.e., 21 mg/L (Table 2).
Similarly, the chloride concentration was 350-8097 mg/L, while NH 3 -N was 288-1250 mg/L, which higher than the standard permissible level i.e., Cl 1000 mg/L and NH 3 -N 40 mg/L, respectively (Table 1,  (Table 1). Additionally, BOD 5 in spring was 1400, summer 1588, autumn 829, and winter 1696 in mg/L (Fig. 2). The high concentration in winter was due to the higher availability of oxygen which is inversely proportion to temperature.
The concentration of oil and grease in land ll leachates was ranged from 03 to 40 mg/L with an average of 22 mg/L, which was exotically higher than the NEQs level i.e., 10 mg/L (Fig. 1). The oil and grease in the spring season were 26, summer 25, autumn 21, and winter 14 in mg/L (Fig. 1). The major source of oil and grease is the use of oily compounds in foods. After using oily resources (meat, oil and ghee, baked goods, cheese, butter, and automobile oil), the major portion is being wasted/ disposed of in land ll sites. Further, these oily wastes can pass naturally through various processes and nally add to the local plumbing systems that may affect human health and the surrounding environment (Husain et al. 2014).
Phenolic compounds in Land ll Leachate were 0.138-0.8 mg/L with an average of 0.3 mg/L, which was equivalent to the NEQs level ( Table 1). The highest concentration of phenolic compounds was observed in autumn (0.38 mg/L) and winter seasons (0.5 mg/L), while the lowest values were in the summer (0.27 mg/L) and spring (0.17 mg/L) (Fig. 1, Table S3). The highest concentration of phenolic compound was 0.800 mg/L in December, while the lowest was 0.138 mg/L in April (Fig. 2). The source of phenolic compounds in leachates is the degradation of organic matter especially fruits and owering plants, which pose harmful threats to groundwater (Anku et al. 2017). Similarly, the concentration of ionic detergent was 0.009 to 15.5 mg/L with an average of 3 mg/L, which was lower than the NEQs level i.e., 20 mg/L (Table 1). However, the concentration in the spring seasons was 6.3, summer 2.7, autumn 0.016, and winter 2.1 in mg/L (Fig. 2, Table S3). The concentration of uoride was 0.2 to 4.2 with an average of 1.9 mg/L, which was lowered than the acceptable level i.e., 10 mg/L ( Table 1). The active source of uoride is minerals and associated materials, including glass, construction materials, medical wastes, soil plants,  (Table 1 and Fig. 3). The concentration of total toxic metal was 0.25-13 with an average of 2.26 mg/L, which was higher than the accepted level i.e., 2 mg/L ( Table 1). The source of trace elements in leachates is electronic waste, glass materials, hazardous waste, metals, textile, and plastic waste (Masood et al. 2014). The decomposition/ degradation of inorganic and organic material may also dissolve the trace elements from solid wastes and added to leachates, which pose signi cant impacts on the surrounding environment, groundwater, and as well as infrastructure, and construction materials (Abdus-Salam 2009). The high concentration of total toxic elements was due to the dissolution of the toxic metal, which is strongly correlated with high pH and electrical conductivity (Banar et al. 2006).
Leachate from Lakhodair land ll has a high concentration of some elements than corresponding standards/ NEQs i.e., Zinc, Boron, Manganese, Nickel, and Cyanide (Table 2 and Fig. 3). A surge in the zinc values was observed in the spring season and the lowest was measured in the winter season. The highest concentration was measured in April 2017 i.e., 6.680 mg/L, and the lowest concentration was 0.190 mg/L in November 2017 ( Table 2). The maximum trend of boron was observed in winter (i.e., 15.2 mg/L in November) and the minimum trend was observed in the summer (i.e., zero). The highest concentration of Mn was 11.80 mg/L in October 2017 and the lowest was 0.030 mg/L in December 2017 ( Table 1). The highest peak of nickel was in the autumn season i.e., October 1.560 mg/L, while the lowest was in winter i.e., 0.000 mg/L. Cyanide was high in the summer season i.e., 0.968 mg/L in July, while the lowest in the spring season i.e., 0.007 mg/L in March 2017 ( Table 2).

Discussions
Lahore is one of the major city of Pakistan continuously facing solid wastes generation problems for the last 20 years. These wastes are generated from various sources including household waste, industrial waste, commercial wastes, and hospital wastes, which have been collected and disposed of improperly.
Approximately, 0.5 to 0.7 kg/capita/day along with an average of ~ 5301 tons/day (entire Lahore city) has been generated in Lahore (Banar et al. 2006, Khan et al. 2019. It was reported that the pilot cause of solid wastes generation in bulk production and product consumption without applying proper/ or adopted nal disposal, safely. Additionally, the disposal of wastes in a land ll for a long time will alternatively generate harmful leachates, which pose negative impacts on humans and the surrounding environment (Mikhailov et al. 2017).
The present study's physiochemical parameters and few toxic elements were comparably higher than the NEQs (Pak-EPA 2000) and international reputed studies (Borjac et al. 2019, Kanmani &Gandhimathi 2013, Kjeldsen et al. 2002, Shrestha et al. 2020). The pH concentration in Lakhodair leachates was 8.86 in autumn followed by winter i.e., 8.863, which was strongly correlated with TDS and oil & grease production. The high TDS may cause considerable to high contamination (Fig. 4a), while oil and grease may cause moderate to considerable contamination (Fig. 4f). The source of TDS and oil & grease are biological degradations of organic matter, animal wastes, chicken wastes, and dissolution of elements in land ll solid wastes (Palma eming et al. 2000).
The concentrations of COD were higher in autumn i.e., 8878 mg/L, which was higher than the NEQs level i.e., 400 mg/L (Fig. 3a). The COD is strongly correlated with oil & grease and BOD 5 . The high COD and BOD represent the presence of organic matter and animal wastes, and inversely, there will be less availability of non-biodegradable compounds (Zainol et al. 2012). Further, the average concentration of both COD (7192.3 mg/L) and BOD 5 (1441.8) mg/L) were comparably higher than the NEQs level (Table   1). This high COD caused high contamination throughout the year (CC > 6), which represents the presence and degradation of complex organic compounds and oily wastes (Kulikowska &Klimiuk 2008). The concentration of NH 3 -N was 1250 mg/L in February, while the lowest concentration was in September i.e., 288 mg/L (Fig. 2i), which was consistent with the results of those reported by Aziz et al. (2004). In Lakhodair, the NH 3 -N may cause high contamination (CC > 6) (Fig. 4e), which considerably may affect the soil, water, and the surrounding environment (He et al. 2011). The presence and production of NH 3 -N in the leachates is a major issue, especially in the optimization of solid wastes leachates. The major source of NH 3 -N is agriculture wastes, animal's wastes, and food wastes, which commonly produced free nitrogen radicle, nitrogen oxides. The NH 3 -N is may further induced soil acidity, leaves damaging and affect soil habitat, while it can also produce NOx (nitrogen oxides) pollution through nitri cation and denitri cation (He et al. 2011, Wang &Zeng 2018. Similarly, the Lakhodair land ll has a high concentration of sul des, sulfate, and chlorides, while a somewhat lower concentration of uorides and ionic detergents when compared with NEQs (Table 2, Fig.   2 and Fig. 3). Sul des in Lakhodair leachate are producing through the decomposition of complex organic compounds/ or either through the addition of an anionic surfactant or detergent soap, which contaminated the soil/ or releases in the form of H 2 S gas (Selberg et al. 2007). The contamination coe cient of sul des was exhibited in moderate to high contamination (i.e., CC 1 to > 6) (Fig. 4h), while chloride was included in considerable to high contamination i.e., CC 3 to > 6 (Fig. 4d). Similarly, the sulfate value was lower in Feb, March, June, July, May, and Oct., while the sul de concentration was high in the aforementioned months (Fig. 5). However, the sulfate was grouped negatively (-0.24) in the F2 of factor analysis (FA), while sul des were positively in the F2 i.e., 0.12 (Table 3, Fig. 5). The study revealed that the sulfate in Lakhodair leachate was reduced to sul de by the availability of an anaerobic environment and reducing bacteria, which was also reported by Chatterjee et al. (2017), Lee et al. (2014). The reduction of sulfate, Cr, and B was an important feature of FA analysis, which was proved through the cluster analysis (Fig. 6).  was negatively loaded with TDS, TSS, COD, BOD 5 , Cl, CN, phenolic compound, Mn, Ni, and Ag (Fig. 5), which revealed the redox reaction mainly controlled by methanogenesis and anaerobic reaction (Lyu et al. 2018). To prove the methanogenesis and anaerobic reaction in Lakhodair land ll, the BOD 5 /COD taking under consideration, which was lower than 0.1 in the months of March-November, while higher winter i.e., December, January, and February (Table S1). The Cu were positively appeared in F2 (Fig. 5), which was comparatively undergoes/ followed the same redox reaction either increase or decrease in the reactants (Fig. 6). The elements in 2nd cluster of Fig. 6 were mainly controlled by ammonium redox (at an anaerobic condition) followed by nitri cation and denitri cation, which surely convert the NH 4 -N to NH 3 Table S3) revealed a strong correlation with pH and temperature. The high temperature at Lakhodair areas may induce the production of ionized NH 3 , which are extremely toxic to the surrounding environment and living organisms (Purwono et al. 2017). The high toxicity and concentration NH 3 -N was exhibited in high contamination level (i.e., CC > 6) (Fig. 4e). Similarly, the high pH/ alkalinity provides a favorable environment for bacterial growth where CO 2 will be emitted to the atmosphere and the leachates will be converted to alkaline. At the same time, denitri cation will be started to form NH 3 (Daigger 2011, Purwono et al. 2017).
The F4 is loaded with pH, phenolic compounds, CN, Pb, and As, which is mostly generated through the degradation of petrochemical, liquor, agricultural wastes, fruits, vegetable decomposition, and hydrocarbons (Martinez-Avila et al. 2014, Shirahigue &Ceccato-Antonini 2020). The phenolic compound is mostly controlled by normal pH and low temperature. The highest phenolic compounds were found in the winter season i.e., 0.53 mg/L (Fig. 2h). During bacterial degradation, especially the fermentation process, the organic matter (fruits, vegetables) is converted to phenolic compounds, CN, and antioxidants with the presence of Pb as a catalyst (Shin et al. 2015). However, the low As availability in Lakhodair leachate was also part of biological degradation and redox reaction with a speci c pH, which was consistent with the result of those reported by Blakey (1984). The present study proved that F4 of factor analysis is mainly controlled by the biogenic process and followed the same reaction/ group, which was also proved through cluster analysis (Fig. 6).
Additionally, the Lakhodair land ll leachate has toxic trace elements in a lower range than NEQs. The lower concentration of trace elements maybe because of solid waste restraining capability/ or lack of environmental conditions for the dissolution of trace elements (Prechthai et al. 2008). The lower concentration of trace elements in the Lakhodair land ll site because of the anaerobic process, which immobilizes the trace elements and retains the solid wastes in a land ll site. He et al. (2006) reported that the anaerobic activity restrains the production of free cations and immobilizes the trace elements. The present study presumed that elements in oxidizable/ reducible form trickling under speci c conditions.
The presence of trace elements in the Lakhodair land ll may be in a metastable state, which is not easily to leach out.

Conclusions
The high concentration of physiochemical and few trace elements in the Lakhodair land ll was evolved through anaerobic degradation of dumping wastes. The lower BOD 5 /COD (< 0.1) was observed in March, April, September, October, and November indicated methanogenesis and anaerobic redox reaction in leachates. Further, the anaerobic activities enhance the production of TDS, BOD 5 , COD, Cl, NH 3 -N, phenolic compounds, and sul des. The high contents of NH 3 -N in the Spring season was 785 mg/L and Summer 531 mg/L revealed the dependent correlation with temperature and pH. The high temperature at Lakhodair with stable pH may induce the production of ionized NH 3 -N through denitri cation and nitri cation. The anaerobic activity immobilizes the trace elements, resulting in the lower elemental contents available in Lakhodair leachates. The lower concentration of trace elements in Lakhodair leachates revealed the metastability of trace elements, which reduced their dissolution and percolation capability. The contamination factor revealed that TDS, NH3-N, COD, Cl, BOD 5 , and sul des may cause considerable to high contamination (CC 3 to > 6), while remaining chemical species may cause low to moderate contamination (CC 1 to ≤ 3). The lower concentrations of toxic compounds do not always confer the leachate to be less hazardous while an enormous volume of leachates entering into the environment. The study concluded that the leachates in Lakhodair produce toxic elements/ compounds, which pose serious threats to humans and the surrounding environment. The study recommended installing a cost-effective and environmentally friendly system to reduce the pollutants in leachates to a satisfactory level before their nal disposal.