Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Water, Sediments, and Fish of Ijegun-Egba River, Lagos State, Nigeria: Implications for Environmental and Public Health

1. Introduction

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds composed of two or more fused aromatic rings, released from both natural and anthropogenic sources. Natural sources include forest fires and volcanic eruptions, while anthropogenic sources encompass the combustion of fossil fuels, wood burning, and vehicle emissions (Boström et al., 2002; Abdel-Shafy & Mansour, 2016). Due to their hydrophobic nature, PAHs strongly adsorb onto surface soils and sediments, particularly binding to organic matter. This adsorption prolongs their environmental persistence, making PAHs priority pollutants of global concern (Zhang & Sun, 2013). Their chemical stability, persistence, and toxicity contribute to their genotoxic, mutagenic, and carcinogenic effects on humans and wildlife (Onyemaechi et al., 2018; Rabani et al., 2020).

PAHs are ubiquitously distributed across environmental matrices, including soils, air, water, and even food products, reflecting their pervasive nature (Onyemaechi et al., 2018). Low molecular weight PAHs (e.g., naphthalene, phenanthrene, anthracene, and fluorene) are generally less carcinogenic and more volatile, reducing their environmental persistence, although they can still bioaccumulate in aquatic organisms, posing ecological risks (Rabani et al., 2020; Ambade et al., 2021). High molecular weight PAHs, in contrast, are more stable, lipophilic, and potentially carcinogenic, representing a more significant threat to ecosystem and human health.

Freshwater resources are critical for human consumption, agriculture, and industrial use. In Lagos, Nigeria, despite abundant surrounding water bodies, only a small fraction (~10%) of the population has access to treated water; the majority rely on wells, boreholes, or street-vended water (Internet Geography, 2016). Daily water demand significantly exceeds supply, with untreated sources frequently contaminated by industrial, domestic, and agricultural effluents, leading to elevated incidences of waterborne diseases such as dysentery and cholera (Abdus-Salam et al., 2010). The lack of efficient sewerage systems exacerbates water contamination as untreated sewage infiltrates surface and groundwater, eventually reaching drinking water sources.

The Ijegun-Egba area in Lagos represents a critical environmental hotspot due to intensive industrial and commercial activities, including the country’s largest oil depot. Petroleum storage and transportation activities release crude oil, refined petroleum products, and associated heavy metals into surrounding ecosystems, contributing to water pollution (OISD, 2012; Owamah, 2013; Uzoekwe & Oghosanine, 2011). Crude oil and petroleum products contain complex mixtures of PAHs, heavy metals, and additives, many of which exhibit high toxicity and persistence in the environment (Rasmussen, 1976; Abdus-Salam et al., 2010). Industrial effluents and accidental spills exacerbate environmental contamination, threatening both aquatic life and human health. Globally, PAHs have attracted significant research attention due to their persistence, toxicity, and bioaccumulative potential. Sixteen PAHs are listed as priority pollutants by the U.S. Environmental Protection Agency (EPA), emphasizing their regulatory and environmental significance (Hussain et al., 2015; Yang et al., 2014). While many studies have focused on PAH occurrence in environmental matrices and associated human and ecological risk assessments, data on their presence in drinking water remain limited (Yuan & Wang, 2008; Zhang & Sun, 2013). Direct measurement of PAHs in drinking water is crucial for accurate estimation of chronic daily intake and subsequent health risk assessment (Badawy & Emababy, 2010; Brindha & Elango, 2013; Caylak, 2012).

The persistence and toxicity of PAHs in surface water, sediments, and aquatic organisms pose a serious ecological and public health threat. These compounds, introduced via atmospheric deposition, industrial discharge, and river runoff, are slowly biodegradable and capable of bioaccumulation in aquatic organisms, thereby entering the human food chain (Ambade et al., 2021; Umeh et al., 2023). The widespread presence of PAHs underscores the need for systematic monitoring and management strategies to mitigate ecological and human health risks.

2. Methods

2.1. Study Area

Lagos State, located in southwestern Nigeria, is the most populous city in Nigeria and the largest urban center in Africa, with an estimated population of 14.86 million in the city proper and approximately 21.3 million in the metropolitan area (Wikipedia, 2021). Lagos is a major financial and economic hub, hosting one of Africa’s busiest seaports and a diverse industrial base. Ijegun, situated in Ojo Local Government Area (coordinates: 6°31'2" N, 3°15'24" E; Longitude: 3.2612, Latitude: 6.4460), is a coastal Awori community within the Badagry Creek region. Ibasa Ijegun-Egba, part of the community, is an industrial and commercial hub, bordered by Irede, Ikaare, Ibeshe, Ilashe, Imore, Amuwo Kuje, and Ado lands. The study area encompasses the Jetty-Ijegun river, surrounding tank farms, and adjacent environments (Akinyanmi, 2020).

2.2. Population of the Study

Ibasa Ijegun-Egba hosts approximately four million residents across towns and villages including Ibasa, Ijegun-Egba, Opetedo, Oguntedo, Satellite Town, Igbojegun, and Igbonla. The area serves as both an industrial and administrative center, with numerous manufacturing industries and petroleum product depots.

2.3. Sample Collection

Water Samples: River water samples were collected twice, at four-week intervals, from two distinct points along the river. Samples were collected in pre-rinsed polyethylene bottles and stored in ice-packed coolers to preserve integrity before laboratory analysis.

Fish Samples: Fresh fish specimens were obtained with assistance from local fishermen. Fish were captured using standard fishing techniques, immediately stored on ice, and transported to the laboratory within one hour for analysis. Sampling was repeated during the second collection.

Sediment Samples: Sediments were collected in pre-rinsed plastic containers by local assistants familiar with the river. Samples were stored in temperature-controlled containers during transport to the laboratory.

2.4. Research Instruments

The study employed a combination of experimental and survey-based approaches:

Experimental Analysis: Four water samples were collected twice for physicochemical and PAH analysis.

Questionnaire and Interviews: Structured questionnaires were administered to residents, fishermen, factory workers, and pharmacists/chemists. Section A captured demographic data, while Section B focused on perceptions of water and environmental contamination from tank farm activities.

2.5. Gas Chromatography Analysis

PAH concentrations in water, sediments, and fish tissues were determined using an Agilent 7890 series Gas Chromatograph equipped with a flame ionization detector (GC-FID). Separation was achieved on an HP-5 fused silica capillary column (30 m × 0.25 mm, film thickness 0.25 μm). Helium served as the carrier gas. The oven temperature program was: 60°C for 5 min, ramped at 6°C/min to 120°C (hold 2 min), then increased at 20°C/min to 250°C (hold 5 min). Injection was performed in splitless mode at 250°C, with an oven equilibrium time of 0.25 min, column pressure of 28 psi, and peak flow rate of 104.5 mL/min. Total run time was 45.75 min. Data acquisition and analysis were performed using ChemStation software, and compound identification was based on retention times.

3. Results and Discussion

3.1. Physicochemical Parameters of Water Samples

The physicochemical analysis of river water samples from Ijegun-Egba indicates significant deviations from both World Health Organization (WHO) and Nigerian regulatory standards (NSDWQ/NESREA). Both samples were visually clear, though Sample B contained minor suspended particles; odour was unobjectionable in all cases, and water temperature ranged between 25.1–26.2°C, within typical tropical freshwater ranges (Onyemaechi et al., 2018).

Electrical conductivity (EC) values were exceptionally high (7,245 μS/cm), nearly three times above the WHO limit of 2,500 μS/cm and seven times above NESREA standards (1,000 μS/cm), reflecting substantial dissolved ionic content likely from industrial effluents and petroleum depot activities. Similarly, total dissolved solids (TDS) were elevated (5,217 mg/L), well above typical freshwater limits (500 mg/L), indicating high mineralization and possible contamination by anthropogenic inputs (Rabani et al., 2020). The pH was slightly alkaline (7.15), within WHO and NESREA recommended limits (6.5–8.5), suggesting that the water maintains moderate buffering capacity.

Salinity levels were extremely elevated (5,200 mg/L), far exceeding the WHO guideline of 250 mg/L and NESREA limit of ≤350 mg/L, highlighting the influence of brackish water intrusion and industrial discharge (Ambade et al., 2021). Dissolved oxygen (DO) was moderately low (6.52 mg/L), below the WHO recommended ≥9 mg/L for healthy freshwater ecosystems, which may negatively affect aquatic life. Biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) were highly elevated (80.84 and 188 mg/L, respectively) compared to recommended limits (≤5 and ≤30 mg/L), suggesting substantial organic pollution, likely from sewage and oil-related effluents.

Overall, the elevated EC, TDS, salinity, BOD, and COD values indicate that the river is heavily impacted by anthropogenic activities, including petroleum depot operations and local industrial discharge. These findings are consistent with studies in other Nigerian urban rivers, where industrialization and oil-related activities significantly increased conductivity, TDS, and organic load (Uzoekwe & Oghosanine, 2011; Owamah, 2013). Low DO coupled with high BOD and COD further corroborates the ecological stress imposed on the river system, raising concerns for aquatic life and human use.

Table 1. Mean values of Physicochemical Parameters of Water Samples.

S/N	PARAMETER	SAMPLE A	SAMPLE B	MEAN	WHO/IEPA	NSDWQ/NESREA
1	Appearance	Clear Colourless liquid	Colourless liquid with particles		NS	NS
2	Odour	Unobjectionable	Unobjectionable	-	Unobjectionable	Unobjectionable
3	Temperature	25.09	26.15	25.62	25	NS
4	Conductivity	7,290	7,200.00	7245	2,500	1,000
5	pH	7.1	7.2	7.15	6.5 - 8.5	6.5 - 8.5
6	TDS	5,250	5,184.00	5217	-	500
7	Alkalinity	80.85	95.55	88.2	200	NS
8	Acidity	2.97	4.95	3.96	NS	NS
9	Salinity	5,230	5,170	5200	250	≤350
10	DO	7.58	5.46	6.52	≥9.00	≥4.0
11	BOD5	84.28	77.4	80.84	≤5.0	≤6.0
12	COD	196	180	188		≤30.0

N.A – Not Available. NS – Not Specified.

Table 1. Mean values of Physicochemical Parameters of Water Samples.

S/N	PARAMETER	SAMPLE A	SAMPLE B	MEAN	WHO/IEPA	NSDWQ/NESREA
1	Appearance	Clear Colourless liquid	Colourless liquid with particles		NS	NS
2	Odour	Unobjectionable	Unobjectionable	-	Unobjectionable	Unobjectionable
3	Temperature	25.09	26.15	25.62	25	NS
4	Conductivity	7,290	7,200.00	7245	2,500	1,000
5	pH	7.1	7.2	7.15	6.5 - 8.5	6.5 - 8.5
6	TDS	5,250	5,184.00	5217	-	500
7	Alkalinity	80.85	95.55	88.2	200	NS
8	Acidity	2.97	4.95	3.96	NS	NS
9	Salinity	5,230	5,170	5200	250	≤350
10	DO	7.58	5.46	6.52	≥9.00	≥4.0
11	BOD5	84.28	77.4	80.84	≤5.0	≤6.0
12	COD	196	180	188		≤30.0

N.A – Not Available. NS – Not Specified.

3.2. Polycyclic Aromatic Hydrocarbons (PAHs) Determination

The analysis of polycyclic aromatic hydrocarbons (PAHs) in the Ijegun-Egba river system revealed significant differences in concentrations across environmental matrices (river water, sediments, and fish tissues). The total PAH levels were highest in fish gills (0.0167 mg/L), followed closely by sediments (0.0155 mg/L), fish muscle (0.0106 mg/L), and river water (0.0093 mg/L). This pattern indicates that PAHs preferentially accumulate in biota and sediments rather than remaining dissolved in water, consistent with the hydrophobic nature and strong sediment adsorption of PAHs (Boström et al., 2002; Ambade et al., 2021).

Low molecular weight (LMW) PAHs, including fluoranthene (~30%), pyrene (~15%), naphthalene, anthracene, phenanthrene, acenaphthylene, acenaphthene, and fluorene, dominated the profile. LMW PAHs, despite lower carcinogenicity than high molecular weight (HMW) PAHs, are more soluble and bioavailable, facilitating uptake by aquatic organisms (Rabani et al., 2020). Among HMW PAHs, fluoranthene, pyrene, and benzo[a]pyrene were detected in appreciable amounts, indicating potential genotoxicity and carcinogenic risk to aquatic biota and humans consuming contaminated fish (Umeh et al., 2023).

The highest concentrations in fish gills suggest that PAHs enter the organism primarily via water filtration and sediment contact, with subsequent partial transfer to muscle tissue through trophic distribution. Sediments act as both a sink and secondary source, accumulating hydrophobic PAHs from water and serving as a pathway for bioaccumulation (Onyemaechi et al., 2018). These findings align with other studies on PAH distribution in urban Nigerian rivers, where sediments and fish tissues frequently exhibit higher concentrations than water due to adsorption and bioaccumulation processes (Uzoekwe & Oghosanine, 2011; Owamah, 2013).

Overall, the data indicate persistent contamination of the river ecosystem by PAHs, likely attributable to oil depot operations, industrial discharge, and urban runoff. The accumulation in fish tissues raises public health concerns, underscoring the need for continuous monitoring and mitigation measures.

Table 2. Mean values of the 16 PAHs detected.

S/N	Compound	River water (mg/l)	Fish Gills (mg/l)	Fish Muscle (mg/l)	Sediments (mg/l)
1	Naphthalene (Naph)	0.00291512	0.000384728	0.000271193	0.00138457
2	Acenaphthylene (Acy)	0.00202145	0.0003732	0.000366609	0.000956861
3	Acenaphthene (Ace)	0.00078612	0.000495588	0.000371915	0.000343326
4	Flourene (Flu)	0.00029735	0.000573013	0.000440371	0.000450491
5	Phenanthrene (Phen)	0.00037171	0.00133192	0.000927776	0.000786692
6	Anthracene (Ant)	0.00039247	0.000719257	0.000757619	0.00185822
7	Flouranthene (Flt)	0.00205802	0.009535635	0.00554824	0.00722376
8	Pyrene (Pyr)	0.00012027	0.00273929	0.001496625	0.00197561
9	Benzo (a) anthracene (BaA)	2.903E-05	7.84065E-05	8.06002E-05	7.64502E-05
10	Chrysene (Chry)	9.4475E-06	2.61865E-05	1.78571E-05	0.000017835
11	Benzo (b) fluoranthene (BbF)	2.6807E-05	4.79482E-05	2.51031E-05	4.94663E-05
12	Benzo (k) fluoranthene (BkF)	2.0706E-05	4.15914E-05	2.78281E-05	3.27721E-05
	Benzo (a) pyrene (BaP)	0.00023987	0.000274976	0.000188249	0.000342264
	Indeno (1,2,3-cd) pyrene (IP)	4.2822E-06	8.58464E-06	6.01259E-06	6.02099E-06
	Dibenzo (a,h) anthracene (DbA)	1.3129E-05	8.92329E-05	1.31352E-05	1.35576E-05
	Benzo (ghi) perylene (BgP)	6.4607E-06	2.20634E-05	1.13514E-05	1.72802E-05

Table 2. Mean values of the 16 PAHs detected.

S/N	Compound	River water (mg/l)	Fish Gills (mg/l)	Fish Muscle (mg/l)	Sediments (mg/l)
1	Naphthalene (Naph)	0.00291512	0.000384728	0.000271193	0.00138457
2	Acenaphthylene (Acy)	0.00202145	0.0003732	0.000366609	0.000956861
3	Acenaphthene (Ace)	0.00078612	0.000495588	0.000371915	0.000343326
4	Flourene (Flu)	0.00029735	0.000573013	0.000440371	0.000450491
5	Phenanthrene (Phen)	0.00037171	0.00133192	0.000927776	0.000786692
6	Anthracene (Ant)	0.00039247	0.000719257	0.000757619	0.00185822
7	Flouranthene (Flt)	0.00205802	0.009535635	0.00554824	0.00722376
8	Pyrene (Pyr)	0.00012027	0.00273929	0.001496625	0.00197561
9	Benzo (a) anthracene (BaA)	2.903E-05	7.84065E-05	8.06002E-05	7.64502E-05
10	Chrysene (Chry)	9.4475E-06	2.61865E-05	1.78571E-05	0.000017835
11	Benzo (b) fluoranthene (BbF)	2.6807E-05	4.79482E-05	2.51031E-05	4.94663E-05
12	Benzo (k) fluoranthene (BkF)	2.0706E-05	4.15914E-05	2.78281E-05	3.27721E-05
	Benzo (a) pyrene (BaP)	0.00023987	0.000274976	0.000188249	0.000342264
	Indeno (1,2,3-cd) pyrene (IP)	4.2822E-06	8.58464E-06	6.01259E-06	6.02099E-06
	Dibenzo (a,h) anthracene (DbA)	1.3129E-05	8.92329E-05	1.31352E-05	1.35576E-05
	Benzo (ghi) perylene (BgP)	6.4607E-06	2.20634E-05	1.13514E-05	1.72802E-05

4. Conclusions and Recommendations

The Ijegun-Egba community, located in Oriade Local Government Area, Lagos State, is significantly impacted by the operations of Nigeria’s largest petroleum tank farms. Analysis of river water, sediments, and fish tissues revealed the pervasive presence of polycyclic aromatic hydrocarbons (PAHs), with higher concentrations observed in fish gills and sediments than in water. Low molecular weight (LMW) PAHs, including fluoranthene, pyrene, naphthalene, anthracene, phenanthrene, acenaphthylene, acenaphthene, and fluorene, dominated the profile, while high molecular weight (HMW) PAHs were present at lower concentrations. These findings indicate that PAHs preferentially accumulate in sediments and biota due to their hydrophobic nature and strong sediment adsorption, consistent with previous studies in urban and industrialized river systems (Onyemaechi et al., 2018; Umeh et al., 2023; Ambade et al., 2021).

Physicochemical parameters of the river including conductivity, total dissolved solids (TDS), salinity, biochemical oxygen demand (BOD), and chemical oxygen demand (COD)—exceeded WHO and NESREA standards, highlighting severe organic and ionic pollution. Elevated PAHs in fish tissues suggest bioaccumulation, posing potential risks to human health through consumption. Feedback from residents linked common health issues, such as typhoid, dysentery, skin irritation, and respiratory disorders, to environmental contamination. In addition, the Jetty-Ferry transport system and petroleum tanker traffic contribute to ongoing PAH inputs into the river ecosystem, reinforcing the link between industrial activity and contamination.

To mitigate these environmental and public health impacts, the study recommends the following actions, directly aligned with the observed contamination patterns:

• Healthcare Interventions: Establish and maintain functional primary healthcare facilities within the community and organize periodic medical outreaches to address pollution-related health issues.
• Safe Water Supply: Expand Lagos State water supply infrastructure to provide safe and affordable water, reducing reliance on contaminated river water and shallow groundwater sources.
• Environmental Management: Lagos Waste Management Agency (LAWMA) should implement regular cleaning of drains and stagnant waters to reduce mosquito breeding and associated malaria risk.
• Regulatory Oversight: The Environmental Protection Agency (EPA) should intensify monitoring of petroleum depots, enforce environmental guidelines, identify pollutant sources, and raise public awareness about environmental hazards.
• Traffic and Transport Control: Relocate truck stations and garages outside the community to minimize heavy traffic and reduce air pollution from vehicle emissions.
• Water Treatment Measures: Residents should adopt cost-effective water treatment methods, such as activated carbon filtration or reverse osmosis, to reduce PAH exposure through drinking water (Borneff et al., 1962; Reichert et al., 1971).

However, the study underscores the persistent contamination of the Ijegun-Egba river ecosystem and the urgent need for a multi-faceted approach combining regulatory enforcement, infrastructure development, community education, and environmental remediation to safeguard both ecological and human health. Future research should examine seasonal variations in PAH concentrations, long-term bioaccumulation in aquatic organisms, and the efficacy of mitigation strategies.