The study focused on evaluating the seasonal distribution, source apportionment, and probabilistic risk assessment of polycyclic aromatic hydrocarbons (PAHs) in groundwater. Groundwater samples were obtained from Owo, southwestern Nigeria and subjected to liquid–liquid extraction and quantified using gas chromatography–mass spectrometry. Total PAH concentrations varied from about 180 to 23,600 ng/L during the dry season. The wet season, on the other hand, exhibited a wider range, from about 1,550 to 150,000 ng/L. Seasonal variations were also found in PAH types and concentrations, with relatively higher concentrations recorded during the wet season. Diagnostic ratios and positive matrix factorization indicated that coal/biomass combustion and traffic-related vehicular emissions were the prevalent sources of PAHs in groundwater. Health risk assessment indicated potential carcinogenic risks (incremental lifetime cancer risk (ILCR) > 1E − 04), while ecological assessment suggested medium (RQNC < 800 and RQMPC ≥ 1) and high ecological risks (RQNC ≥ 800 and RQMPC ≥ 1). The study reflected the need for effective mitigation strategies.

  • The study examined the risk assessment of PAHs in groundwater.

  • PAH concentrations were relatively higher in the wet season.

  • Coal/biomass combustion and vehicular emissions were the sources of PAHs.

  • Carcinogenic risks and medium to high ecological risks were associated with the water quality.

Polycyclic aromatic hydrocarbons (PAHs) are organic molecules composed of several carbon rings. They emanate from natural and anthropogenic processes including incomplete combustion of organic matter (Adekunle et al. 2017). They are found all over the environment and have been the focus of much investigation due to the harm they might do to human health and/or the natural world (Balcıoğlu 2016). Most PAHs are discharged into the environment as a result of human activities including fossil fuel combustion, industrial operations, and waste disposal (Li et al. 2015; Varjani et al. 2018). Because they are persistent, many accumulate in living beings and have been linked to cancer, and their prevalence in different aspects of the environment, including groundwater, is worrisome (Ali et al. 2021).

Groundwater is a vital drinking water resource for millions of people worldwide (Mishra 2023). It can represent a major hazard to both the environment and public health if it becomes polluted with PAHs (Hojjati-Najafabadi et al. 2022). It is critical to understand how PAHs are dispersed in groundwater, where they come from, and what hazards they represent, to control pollution properly and safeguard human health, as well as develop strategies for cleaning up contaminated groundwater and preventing further pollution.

The prevalence of PAHs in groundwater is influenced by several variables, including climate, geology, and land use (Burri et al. 2019). Seasonal variations can also have a substantial influence. Changes in rainfall, temperature, and the pace of groundwater recharge, for example, can all affect contaminant movement (Saravanan et al. 2021). PAHs can be washed out of contaminated soil and transferred to groundwater during wet seasons when there is more rainfall. Raised water levels may also result in increased subsurface water flow, potentially distributing PAHs to new regions (Jiang et al. 2022). During dry seasons, however, when groundwater levels are lower and water moves more slowly, PAHs may linger in the ground for extended periods, resulting in increased concentrations. Temperature fluctuations can also influence PAH levels in groundwater by changing the activity of soil bacteria (Alegbeleye et al. 2017). PAHs may be broken down by microbes, reducing their concentrations in groundwater (Padhan et al. 2021). When temperatures rise, microbial activity increases, resulting in quicker PAH degradation, suggesting that PAH concentrations in groundwater may decline more quickly in warmer seasons due to greater microbial breakdown (Logeshwaran et al. 2018; Adetunji & Anani 2021).

In order to minimize pollution and clean it up, it is critical to identify the sources of PAH contamination. PAHs can be found in both man-made and natural environments, and anthropogenic sources include automobile exhaust, industrial pollution, and inappropriate garbage disposal. These PAHs are released into the atmosphere, from where they can settle on the ground and eventually enter groundwater (Kozak et al. 2017; Li et al. 2021). However, in many situations, PAH pollution of groundwater results primarily from human activity (Ren et al. 2021). Profiles can be constructed to assist in pinpointing pollution sources by analyzing the precise types and concentrations of PAHs found.

Many PAHs are known or suspected causes of cancer, and being exposed to excessive quantities of them by drinking water or skin contact can be harmful. PAHs can also accumulate in aquatic creatures, altering ecosystems, and potentially entering the food chain (Okechukwu et al. 2021; Oyekunle et al. 2023; Vijayanand et al. 2023). PAH mobility in the environment is influenced by factors such as geology, how easily they adhere to soil particles, and how rapidly they degrade. Understanding how PAHs migrate makes it possible to forecast whether they will end up in sensitive places such as wells or bodies of surface water (Adeola & Forbes 2021a, 2021b).

Therefore, effective water resource management depends on PAH source identification and risk evaluation (Li et al. 2017). Many recent studies have been carried out on PAH seasonal distribution, source identification, and risk assessment in water resources (Apata et al. 2022; Aralu et al. 2023; Areguamen et al. 2023; Ogunbisi et al. 2023; Ololade et al. 2023). However, this study is the first known attempt at evaluating groundwater, the predominant water resource in the study area.

Sample collection and preparation

Water samples were collected from randomly selected wells around dumpsites in Owo, southwestern Nigeria, during the dry and wet seasons in 2021. Prior to analysis, the samples were pretreated with 20 mL chloroform and refrigerated, to inhibit microbial action.

Reagents

All reagents were of analytical grade and were obtained in Nigeria. They included chloroform, acetone, and methanol (BDH Poole House, England), dichloromethane and nitric acid (Sigma-Aldrich), anhydrous sodium sulfate (BDH Poole House, England), and silica gel 60-200 PF254 (MERK, Germany).

PAH extraction

Sample aliquots of 100 mL were measured into a 500 mL separatory funnel to determine their PAH content. The samples were extracted in triplicate with 200 mL of dichloromethane, before being mixed in an amber-colored vial, which was kept at 4 °C in preparation for further clean-up. This method provides for precise determination of PAH levels in water samples.

Clean-up

Clean-up was based on chromatography and involved mixing stationary (silica gel) and mobile phases (1:2:2 acetone–dichloromethane–ethanol). A small quantity of glass wool was used as a plug to prevent the loss of the stationary phase before the addition of silica gel. Anhydrous sodium sulphate was added on top of the silica gel. The solvent mixture was introduced first into the packed column to prevent contaminant interference.

Clean-up is essential to remove or reduce impurities that might be present in the eluate. The eluate was left to dry completely, then reconstituted with 1 mL of dichloromethane and stored in amber-colored vials prior to GC-MS determination.

Recovery

The recovery experiments were carried out by introducing 20 ng/L of the available PAHs – i.e., chrysene, phenanthrene, anthracene, and fluorene – into a known volume of the groundwater sample while the same quantity was left unspiked. The two samples were then subjected to the same liquid–liquid extraction process adopted for PAH extraction and clean-up as described above. The proportional recovery was calculated using the following equation:
formula
(1)
where C is the concentration in the spiked sample and D is the concentration in the un-spiked sample.

The recovery analysis result is presented in Table 1. The proportional recoveries ranged between 89 and 108%, well within the 70–110% recovery range stipulated, for instance, by the European Union (2006).

Table 1

PAH recovery analysis

PAHsAmount in spiked sample (ng/L)Amount in unspiked sample (ng/L)%R
Chrysene 92.8 75 89 
Phenanthrene 91.4 72.6 94 
Anthracene 82.6 63.6 95 
Fluorene 70.3 48.7 108 
PAHsAmount in spiked sample (ng/L)Amount in unspiked sample (ng/L)%R
Chrysene 92.8 75 89 
Phenanthrene 91.4 72.6 94 
Anthracene 82.6 63.6 95 
Fluorene 70.3 48.7 108 

Gas chromatography

The PAHs were determined by a gas chromatograph (Agilent Model 7890B) coupled with a Pegasus 4D mass spectrometer (GC-MS). An Agilent DB-7890 capillary GC column, 30 m × 0.25 mm id × 0.25 μm film thickness, was used at 340 °C. The operating conditions were: splitless (1 μL) injection, injector temperature 250 °C, helium carrier gas (99.99% purity) flowing at 0.9 mL min−1 with column head pressure 7.4 psi. The oven temperature was kept at 70 °C for 2 min, and then programed to rise to 130 °C at 25 °C min−1, and on to 220 °C at 2 °C min−1, and finally to 280 °C at 10 °C min−1. The final temperature was maintained for 4.6 min.

The MS settings were electron impact ionization mode with 70 eV electron energy, scan mass range 100–400 at 0.62 s/cycle, ion source temperature 230 °C, MS quad temperature 150 °C, EM voltage 1450, and solvent delay 4 min. The MS system was routinely operated in selective ion monitoring (SIM) mode with electron ionization. The PAH compounds were identified on the basis of a comparison of peak retention times with those of standard PAHs, after which an internal standard method was used for PAH quantification (Oyekunle et al. 2022).

Data analysis

Data were processed using Microsoft Excel and Origin software and source identification was estimated using EPA-PMF (version 5) (Ambade et al. 2023). Health risk was assessed using the method developed by USEPA to calculate the incremental lifetime cancer risk (ILCR) associated with groundwater ingestion – Equation (2) as well as the toxic equivalent quantity (TEQ) – Equation (3):
formula
(2)
formula
(3)
where C is the concentration of PAH, TEF is the toxic equivalent factor, DR is the daily water intake (L/day), CSF is the carcinogenic slope coefficient of BaP (10 (kg day)/mg), EF is the number of days of exposure per year (set to 365 days), ED is the exposure duration (years), BW is the body weight (kg), and AT is the averaging time for life (day) (Ambade et al. 2021).
The ecological risk was assessed using the risk quotient, which was subdivided into two categories – maximum permissible concentrations (MPCs) and negligible concentrations (NCs). They were estimated using the following equations
formula
(4)
formula
(5)
formula
(6)

where CPAHs is the PAH concentration in water (ng/L), CQV is the corresponding PAH risk standard value (ng/L), CQV(MPCs) is the PAH MPC value, CQV(NCs) is the PAH NC value (ng/L), and RQ the PAH ecological risk quotient.

Seasonal PAH distribution in groundwater

The descriptive seasonal distribution statistics of the PAHs in the groundwater in the dry and wet seasons are presented in Table 2. During the dry season, total PAH concentrations ranged from 182 to 2.36 × 104 ng/L. However, total PAH concentrations during the wet season ranged from 1.55 × 103 to 1.49 × 105 ng/L.

Table 2

Descriptive statistics of PAHs in groundwater (ng/L) during dry and wet season

TypeNapAcyAceFluPheAntFlaPyrBaAChrBbFBkFBaPDbaBPyInP 
Dry season 
Min 1.15 19.1 29.3 125 ND 7.84 ND ND ND ND ND ND ND ND ND ND 182 
Max 2.51 × 103 3.79 × 103 3.45 × 103 3.36 × 103 2.31 × 103 258 2.63 × 103 195 88.4 412 1.79 × 103 529 1.81 × 103 316 30.8 165 2.36 × 104 
Wet season 
Min 138 526 301 355 158 12.4 ND ND ND 2.45 10.1 39.8 ND 2.62 ND 3.99 1.55 × 103 
Max 3.43 × 103 1.42 × 104 2.82 × 104 7.74 × 103 8.30 × 103 2.36 × 103 1.42 × 103 482 3.02 × 103 6.24 × 103 2.12 × 104 1.49 × 104 3.69 × 104 273 640 626 1.49 × 105 
TypeNapAcyAceFluPheAntFlaPyrBaAChrBbFBkFBaPDbaBPyInP 
Dry season 
Min 1.15 19.1 29.3 125 ND 7.84 ND ND ND ND ND ND ND ND ND ND 182 
Max 2.51 × 103 3.79 × 103 3.45 × 103 3.36 × 103 2.31 × 103 258 2.63 × 103 195 88.4 412 1.79 × 103 529 1.81 × 103 316 30.8 165 2.36 × 104 
Wet season 
Min 138 526 301 355 158 12.4 ND ND ND 2.45 10.1 39.8 ND 2.62 ND 3.99 1.55 × 103 
Max 3.43 × 103 1.42 × 104 2.82 × 104 7.74 × 103 8.30 × 103 2.36 × 103 1.42 × 103 482 3.02 × 103 6.24 × 103 2.12 × 104 1.49 × 104 3.69 × 104 273 640 626 1.49 × 105 

Nap, naphthalene; Acy, acenaphthylene; Ace, acenaphthene; Flu, fluorene; Phe, phenanthrene; Ant, anthracene; Fla, fluoranthene; Pyr, pyrene; BaA, benz [a] anthracene; Chr, chrysene; BbF, benzo[b]fluoranthene; BkF, benzo[k]fluoranthene; BaP, benzo[a]pyrene; Dba, dibenzo[a,h]anthracene; BPy, benzo[g,h,i]perylene; InP, indeno[1,3,3-cd]pyrene; Min, minimum; Max, maximum; ND, not detected.

The PAHs exhibited different compositional profiles in the dry and wet seasons. While acenaphthylene had the highest concentration (3.79×103 ng/L) in the dry season, benzo[a]pyrene had the highest (3.69 × 104 ng/L) in the wet season. Apart from fluoranthene, the concentrations of the other PAHs in the groundwater were relatively higher in the wet than in the dry season. One-way analysis of variance (Table 3) indicated that the concentrations of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, benzo[g,h,i]perylene, and indeno[1,3,3-cd]pyrene were significantly higher (p < 0.05) in the wet season than the dry one. The increased wet season PAH concentrations could be due to the promotion of soil permeability by rainfall when PAHs in soils are dissolved and subsequently migrate into groundwater (Yang et al. 2012; Sun et al. 2019). In essence, the difficulty associated with the migration of these PAHs during the dry season might explain why their concentrations are relatively lower then (Perrette et al. 2013), as the relative increase in soil moisture during the wet season ensures the carriage of PAHs into groundwater by colloids and dissolved organic matter (Schwarz et al. 2011).

Table 3

One-way analysis of variance – ANOVA – showing the significant PAH concentration differences in groundwater during the dry and wet seasons

Sum of squaresdfMean squareFSig.
Nap Between groups 16.935 16.935 25.801 0.000 
Within groups 11.815 18 0.656   
Total 28.750 19    
Acy Between groups 109.319 109.319 12.959 0.002 
Within groups 151.848 18 8.436   
Total 261.167 19    
Ace Between groups 821.085 821.085 16.417 0.001 
Within groups 900.237 18 50.013   
Total 1,721.322 19    
Flu Between groups 55.395 55.395 14.945 0.001 
Within groups 66.717 18 3.707   
Total 122.112 19    
Phe Between groups 34.428 34.428 12.979 0.002 
Within groups 47.748 18 2.653   
Total 82.176 19    
Ant Between groups 1.685 1.685 5.575 0.030 
Within groups 5.440 18 0.302   
Total 7.124 19    
Fla Between groups 0.037 0.037 0.086 0.772 
Within groups 7.796 18 0.433   
Total 7.834 19    
Pyr Between groups 0.013 0.013 0.983 0.335 
Within groups 0.237 18 0.013   
Total 0.250 19    
BaA Between groups 0.514 0.514 1.146 0.299 
Within groups 8.077 18 0.449   
Total 8.591 19    
Chr Between groups 2.760 2.760 1.467 0.242 
Within groups 33.874 18 1.882   
Total 36.634 19    
BbF Between groups 26.033 26.033 1.202 0.287 
Within groups 389.758 18 21.653   
Total 415.791 19    
BkF Between groups 20.698 20.698 1.933 0.181 
Within groups 192.727 18 10.707   
Total 213.425 19    
BaP Between groups 66.264 66.264 0.975 0.337 
Within groups 1,223.341 18 67.963   
Total 1,289.605 19    
Dba Between groups 0.005 0.005 0.602 0.448 
Within groups 0.147 18 0.008   
Total 0.152 19    
BPy Between groups 0.106 0.106 4.843 0.041 
Within groups 0.396 18 0.022   
Total 0.502 19    
InP Between groups 0.268 0.268 10.305 0.005 
Within groups 0.469 18 0.026   
Total 0.737 19    
Sum of squaresdfMean squareFSig.
Nap Between groups 16.935 16.935 25.801 0.000 
Within groups 11.815 18 0.656   
Total 28.750 19    
Acy Between groups 109.319 109.319 12.959 0.002 
Within groups 151.848 18 8.436   
Total 261.167 19    
Ace Between groups 821.085 821.085 16.417 0.001 
Within groups 900.237 18 50.013   
Total 1,721.322 19    
Flu Between groups 55.395 55.395 14.945 0.001 
Within groups 66.717 18 3.707   
Total 122.112 19    
Phe Between groups 34.428 34.428 12.979 0.002 
Within groups 47.748 18 2.653   
Total 82.176 19    
Ant Between groups 1.685 1.685 5.575 0.030 
Within groups 5.440 18 0.302   
Total 7.124 19    
Fla Between groups 0.037 0.037 0.086 0.772 
Within groups 7.796 18 0.433   
Total 7.834 19    
Pyr Between groups 0.013 0.013 0.983 0.335 
Within groups 0.237 18 0.013   
Total 0.250 19    
BaA Between groups 0.514 0.514 1.146 0.299 
Within groups 8.077 18 0.449   
Total 8.591 19    
Chr Between groups 2.760 2.760 1.467 0.242 
Within groups 33.874 18 1.882   
Total 36.634 19    
BbF Between groups 26.033 26.033 1.202 0.287 
Within groups 389.758 18 21.653   
Total 415.791 19    
BkF Between groups 20.698 20.698 1.933 0.181 
Within groups 192.727 18 10.707   
Total 213.425 19    
BaP Between groups 66.264 66.264 0.975 0.337 
Within groups 1,223.341 18 67.963   
Total 1,289.605 19    
Dba Between groups 0.005 0.005 0.602 0.448 
Within groups 0.147 18 0.008   
Total 0.152 19    
BPy Between groups 0.106 0.106 4.843 0.041 
Within groups 0.396 18 0.022   
Total 0.502 19    
InP Between groups 0.268 0.268 10.305 0.005 
Within groups 0.469 18 0.026   
Total 0.737 19    

Unsurprisingly, in both dry and wet seasons, lower molecular weight PAHs were predominant. This has a direct link with PAH physical and chemical properties, as these relatively light molecules have low hydrophobicity and high-water solubility, while the heavier PAHs are relatively more resistant to degradation (Montuori et al. 2016; Li et al. 2017; He et al. 2020). The PAH concentrations found in this study are relatively higher than those reported elsewhere (López-Macias et al. 2019; Ibigbami et al. 2022).

PAH source identification

The PAH source apportionment in groundwater was estimated using diagnostic ratios and positive matrix factorization. The diagnostic ratio is a qualitative determination through a comparison of the concentration ratios of PAH isomers in a particular sample with those ascribed to specific pollution sources (Jiang et al. 2022). The PAH diagnostic ratios used in this study comprise Ant/(Ant + Phe), Fla/(Fla + Pyr), BaA/(BaA + Chr), and InP/(InP + BPy) – Figure 1. Ant/(Ant + Phe) ratios < 0.1 and > 0.1 indicate petroleum and combustion sources, respectively. Fla/(Fla + Pyr) ratios of > 0.5, 0.4 to 0.5, and < 0.4 correspond to coal/biomass combustion, petroleum combustion, and petroleum sources, respectively. BaA/(BaA + Chr) ratios of > 0.35, 0.2 to 0.35, and < 0.2 suggest coal/biomass combustion, mixed, and petroleum sources, respectively, while InP/(InP + BPy) ratios of >0.5, 0.2 to 0.5, and <0.2 indicate coal/biomass combustion, petroleum combustion, and petroleum sources, respectively (Deng et al. 2013; Cai et al. 2017). The estimated groundwater-PAH diagnostic ratios in this study indicate that the PAHs originate predominantly from coal/biomass combustion and petroleum.
Figure 1

PAH diagnostic ratios in groundwater.

Figure 1

PAH diagnostic ratios in groundwater.

Close modal
PMF was also used to assess possible PAH sources in groundwater. Three factors were identified – Figure 2. Factor 1 accounted for about 31% of data variance, with significant loadings from naphthalene, fluorene, fluoranthene, and pyrene, and was widely characterized by low molecular weight PAHs probably emanating from oil spills (Friesen et al. 2007).
Figure 2

Factor profiles and PAH contributions in groundwater using PMF.

Figure 2

Factor profiles and PAH contributions in groundwater using PMF.

Close modal

Factor 2 accounted for 40% of data variance, with high factor loadings from benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, and benzo[g,h,i]perylene. It comprises PAHs with 4–6 aromatic rings, which are predominantly fossil fuel combustion products (Tian et al. 2019) and can be ascribed to traffic-related vehicular emissions.

Factor 3 had the lowest data variance contribution – 29% – and arose from predominant loadings from acenaphthylene, anthracene, benzo[b]fluoranthene, dibenzo[a,h]anthracene, and indeno[1,3,3-cd]pyrene, high molecular weight PAHs implicated as tracers of incomplete PAH combustion from internal combustion engines and biomass (Li et al. 2017). Based on the foregoing, it is clear that the combustion of coal/biomass and petroleum are the chief PAH sources in the groundwater.

Risk assessment of PAHs in groundwater

The possible health risks associated with PAH ingestion through drinking groundwater were assessed. The estimated ILCR and risk index (RI) for adults and children are presented in Table 4. In both dry and wet seasons, the carcinogenic PAH ILCRs were relatively higher for children than adults, except for chrysene. Regardless of season, benzo[a]pyrene contributed the greatest risk of cancer and chrysene the least. ILCR values ≤ 1 × 10−6 have been classified as acceptable, while those ≥ 1 × 10−4 have been described as indicating high risk (Huang et al. 2016). Most ILCRs exceeded the USEPA's acceptable level (1 × 10−4), indicating that drinking groundwater carries potential carcinogenic risk (Qiao et al. 2021).

Table 4

ILCR and RI of carcinogenic PAHs in groundwater

PAHsDry season
Wet season
Carcinogenic PAHsTEQILCR
TEQILCR
AdultsChildrenAdultsChildren
BaA 1.24 0.24 0.01 33.31 6.66 13.30 
Chr 0.04 0.09 2.96 × 10−4 0.79 1.58 0.07 
BbF 27.47 5.49 9.05 255.65 51.13 783.43 
BkF 9.03 1.80 0.97 212.48 42.49 541.20 
BaP 185.74 37.14 413.53 3,826.19 765.23 175,476.40 
Dba 60.15 12.03 43.37 91.56 18.31 100.50 
InP 3.06 0.61 0.11 26.23 5.24 8.24 
RI  57.44 467.07  890.67 176,923.20 
PAHsDry season
Wet season
Carcinogenic PAHsTEQILCR
TEQILCR
AdultsChildrenAdultsChildren
BaA 1.24 0.24 0.01 33.31 6.66 13.30 
Chr 0.04 0.09 2.96 × 10−4 0.79 1.58 0.07 
BbF 27.47 5.49 9.05 255.65 51.13 783.43 
BkF 9.03 1.80 0.97 212.48 42.49 541.20 
BaP 185.74 37.14 413.53 3,826.19 765.23 175,476.40 
Dba 60.15 12.03 43.37 91.56 18.31 100.50 
InP 3.06 0.61 0.11 26.23 5.24 8.24 
RI  57.44 467.07  890.67 176,923.20 

TEQ, toxic equivalent quantity.

The PAH ecological risk was evaluated using the NCs and MPCs, which are presented in Figures 3 and 4, respectively. NCs indicate that PAH concentrations below this level are likely to have negligible negative impact, while MPCs indicate that negative impacts on the ecosystem are likely to be severe if PAH concentrations exceed them (Chen et al. 2019). Consonant with trends in this study, RQNC and RQMPC values were relatively higher in the wet than the dry season. Apart from chrysene – RQNC 0.72 – during the wet season, all other PAHs had RQNC values exceeding 1, indicating that the ecological risk posed by them is not negligible. The PAH RQMPC values are below 1 in some cases. The PAH cumulative RQNC and RQMPC suggested that total PAHs posed a medium ecological risk in the dry season, but, in the wet season, it indicated that they posed a high ecological risk (Chen et al. 2019).
Figure 3

Ecological risk assessment of PAH NCs in groundwater.

Figure 3

Ecological risk assessment of PAH NCs in groundwater.

Close modal
Figure 4

Ecological risk assessment of PAH MPCs in groundwater.

Figure 4

Ecological risk assessment of PAH MPCs in groundwater.

Close modal

The study's aim was to investigate the seasonal distribution and likely sources of 16 PAHs in groundwater. There were considerable changes in PAH concentrations between the dry and rainy seasons. The major influence of seasonal fluctuations on PAH concentrations was produced by rainfall, with higher PAH concentrations found during the wet season due to increased soil permeability, which allows PAHs to migrate into groundwater.

The study also showed that the PAH mix differed between the dry and rainy seasons. Because of their relatively low hydrophobicity and higher water solubility, lower molecular weight PAHs were more abundant than those with higher molecular weights in both seasons.

Diagnostic ratios and PMF were used to identify PAH origins in groundwater. The diagnostic ratios indicated that coal/biomass combustion and petroleum were the primary PAH sources. PMF identified three sources: low molecular weight PAHs from oil spills, higher molecular weight PAHs from car emissions, and another source associated with incomplete combustion from internal combustion engines and biomass. This emphasizes the need to consider both temporal fluctuations and probable sources when assessing PAH contamination in groundwater.

Risk assessment indicated the potential for cancer risks from drinking groundwater, as well as potential medium and high ecological risks. The findings have human health and environmental consequences, emphasizing the need for focused initiatives to minimize the effects of PAH pollution, particularly during rainy seasons.

The authors sincerely acknowledge the management of their respective institutions for providing an enabling environment for the research.

All authors have approved the final version of the manuscript for publication.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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