INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,  
MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)  
ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIV, Issue XII, December 2025  
Integrated Assessment of Industrial Effluent Impacts on Water  
Quality and Ecological Risks in Ona River, Ibadan, Nigeria  
Praise Adenike Alli1; Adedayo Ayodele Adegbola2; Olatunji Sunday Olaniyan2  
1Department of Civil Engineering, Faculty of Engineering and Technology Lead City University,  
Ibadan, Nigeria.  
2Department of Civil Engineering, Faculty of Engineering and Technology Ladoke Akintola University  
of Technology, Ogbomosho, Nigeria.  
DOI : https://doi.org/10.51583/IJLTEMAS.2025.1412000137  
Received: 09 January 2026; Accepted: 12 January 2026; Published: 17 January 2026  
ABSTRACT  
Degradation of freshwater resources within Nigeria’s industrial zones threatens ecosystems and human health.  
This study examined the Ona River in Ibadan’s Oluyole Industrial Area through physicochemical, nutrient,  
heavy metal, and bacteriological analyses. Water samples from upstream, industrial discharge points, and a  
downstream residential site were collected in June 2024 and analyzed using standard protocols by the American  
Public Health Association (apha). Results showed elevated levels of Total Dissolved Solids (TDS) (0.73- 3.48  
mg/L), Electrical Conductivity (EC) (119- 328 µS/cm), Biological Oxygen Demand (BOD₅) (9.2- 37.4 mg/L),  
and Chemical Oxygen Demand (COD) (2.9- 57.1 mg/L), with Dissolved Oxygen (DO) below 2.6 mg/L.  
Manganese levels (0.71- 0.93 mg/L) exceeded WHO (0.08 mg/L) and Nigerian standards (0.2 mg/l), while  
magnesium (17.7- 31.2 mg/L) surpassed FAO irrigation guidelines (0.2 mg/l). Water Quality Index (WQI) rated  
industrial sites as poor (43.2- 48.9) and the residential site as moderate (54.4). Trace coliforms downstream  
(0.001 cfu/mL) indicated occasional contamination. These findings highlight effluent discharge's role in water  
degradation, emphasizing the need for industrial pretreatment, standards aligned with FAO and WHO, and  
continuous multi-parameter monitoring to protect ecosystems.  
Keywords: Ona River; Water Quality Index; Industrial effluents; Heavy metals; Ecological risk; Nigeria  
Highlights  
First integrated assessment of Ona River within Ibadan’s Oluyole Industrial Area.  
Industrial sites recorded poor WQI (43.2–48.9); downstream site was moderate (54.4).  
Manganese (0.71–0.93 mg/L) and magnesium (17.7–31.2 mg/L) exceeded WHO/FAO limits.  
Dissolved oxygen <2.6 mg/L with BOD₅ up to 37.4 mg/L indicated oxygen stress.  
Findings demand effluent pretreatment, FAO/WHO enforcement, and continuous monitoring.  
List of Tables  
Table 2. Physicochemical properties of Ona River water across sampling locations.  
Table 3. Nutrients and selected metal concentrations in Ona River relative to standards.  
Table 4. Correlation matrix between heavy metals and physicochemical parameters.  
Table 5. Correlation analysis of nutrients and BOD₅ across sampling sites.  
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Table 6. Water Quality Index (WQI) classification of Ona River by location.  
Table 7. Bacteriological quality of Ona River relative to WHO/NIS standards.  
Table 8. Ecological risk summary of Ona River relative to international guidelines.  
List of Figures  
Figure a–f. Multi-panel illustration of physicochemical parameters with error bars and WHO/NIS limits.  
Figure a–c. Multi-panel WQI distribution across sampling locations.  
Figure a–b. Multi-panel bacteriological assessment: coliform counts and compliance status.  
Figure a–d. Multi-panel correlations: heavy metals vs physicochemical and nutrients vs BOD₅.  
Figure a–c. Multi-panel regression plots: TSS, Alkalinity, Turbidity vs BOD₅.  
Conceptual Framework. DPSIR model linking industrial drivers, river quality, ecological risks, and  
responses.  
INTRODUCTION  
Worldwide freshwater systems face increasing anthropogenic pressures from industrialization, agriculture, urban  
growth, and poor wastewater management. Declining water quality involves nutrient enrichment, oxygen  
depletion, and toxic contamination, impacting ecosystems and health (Smith et al., 2016; UNEP, 2019). In  
Africa, rapid urbanization and weak regulations heighten pollution risks, especially in rivers supplying water  
and receiving industrial waste (FAO, 2020). Nigerian rivers, such as Kaduna, Rido, and Majowopa, exhibit high  
levels of TDS, BOD₅, COD, nutrients, and heavy metals downstream of industries, often exceeding standards  
(Deinmodei et al., 2020; Butu et al., 2022; Dauda & Olaofe, 2020). In Ibadan, Nigeria’s second largest city,  
water shortages force reliance on rivers and wells. The Ona River in the Oluyole Industrial Area supplies water  
and receives effluents from food, plastics, and beverage industries, posing risks to water security and ecosystems  
(Ojo, 2018).  
Despite relying on rivers like the Ona, assessments of their quality are limited. Research in Ibadan is localized,  
lacking comprehensive physicochemical and bacteriological evaluations. Industrial discharges untreated or  
partially treated wastewater into the Ona River, raising risks of organic loading, heavy metal bioaccumulation,  
and microbial contamination. These threaten aquatic ecosystems and the safety of households using the river for  
water. The lack of baseline data hampers regulators' ability to enforce standards and develop pollution strategies.  
Filling this gap is vital for protecting ecosystems, reducing disease, and achieving SDGs related to clean water  
and sanitation.  
This study evaluated the physicochemical properties of the Ona River water at upstream, industrial, and  
downstream sites, assessed bacteriological indicators for health risks, calculated a Water Quality Index (WQI)  
to categorize water quality, and compared results to NIS and WHO standards. Combining parameter analysis  
with WQI provides a reliable dataset for water monitoring in Ibadan’s industrial area, guiding regulation, effluent  
treatment, and management strategies. The following section details the methods for sample collection, analysis,  
and WQI calculation.  
METHODOLOGY  
Study Area  
Ibadan, the capital of Oyo State in southwestern Nigeria, lies between latitudes 7°20′–7°40′N and longitudes  
3°35′–4°10′E. The city has a humid tropical climate with mean annual rainfall of ~1,230 mm, peaking in  
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September, and an average maximum temperature of 32 °C (Ganiyu et al., 2021). The Ona River, approximately  
55 km long with a drainage area of 81 km², originates from the Eleyele catchment and traverses Oluyole  
Industrial Area before discharging southward. The river supports domestic, agricultural, and industrial water use  
while simultaneously receiving effluents from food, plastics, and chemical industries concentrated in Oluyole.  
Flooding events (e.g., 2011) highlight its hydrological vulnerability (Egbinola et al., 2015). Sampling locations  
were selected to represent upstream (control), three industrial discharge zones (Sumal, Amir Plast, and P&G),  
and a downstream residential community (Figure 1).  
Figure 1. Map of River Ona showing the sampling points and the industries in Polygon  
Sampling Design and Procedure  
Water sampling was conducted in June 2024 during the rainy season. At each site, three grab samples were  
collected at approximately 10 cm depth from well-mixed river sections using pre-sterilised polyethene bottles.  
For bacteriological analysis, samples were stored in sterile glass bottles with sodium thiosulfate to neutralize  
residual chlorine. All samples were geo-referenced using GPS, stored in ice-cooled containers at 4 °C, and  
transported to the laboratory within 6 hours of collection. Field measurements for pH, electrical conductivity  
(EC), dissolved oxygen (DO), and total dissolved solids (TDS) were taken in situ using a calibrated multi-  
parameter probe (CS-C933T, Topac Instruments Inc.).  
Laboratory Analysis  
Thirteen parameters were analysed following the APHA/AWWA/WEF (2017) standard methods. Turbidity was  
measured with a nephelometer, while total suspended solids (TSS) and total solids were determined  
gravimetrically. Titrimetric and spectrophotometric methods quantified hardness, alkalinity, magnesium, and  
manganese. Biochemical oxygen demand (BOD₅) was assessed by 5-day incubation at 20 °C, whereas chemical  
oxygen demand (COD) was determined using the dichromate reflux method. Phosphate was measured  
calorimetrically. Total coliforms were analysed using the multiple-tube fermentation technique, with results  
expressed in colony-forming units per millilitre (cfu/mL).  
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Water Quality Index (WQI) Computation  
The National Sanitation Foundation Water Quality Index (NSF-WQI) method was adopted to integrate  
parameter values into a single quality score. Sub-indices (Qi) for each parameter were derived from rating curves,  
multiplied by their assigned weights (Wi), and aggregated as:  
풏(푸풊 × 풘풊)  
풊
(1)  
∑
푾푸푰 =  
Final WQI scores were classified as Excellent (91–100), Good (71–90), Moderate (51–70), Poor (26–50), and  
Very Poor (0–25).  
Table 1: Standard table of water quality index  
Water Quality Rating  
Water Quality Status  
Excellent quality  
Good quality  
91-100  
71-90  
51-70  
26-50  
0-25  
Moderate quality  
Poor quality  
Very poor quality  
Source: WHO Geneva (2011)  
Data Analysis and Quality Assurance  
Data were analysed with descriptive statistics and one-way ANOVA to assess spatial variability at p < 0.05.  
Results were compared with Nigerian Industrial Standard (NIS 554:2007) and WHO guidelines. Instruments  
were calibrated daily, with blanks and duplicates checked for accuracy. Glassware was acid-washed to prevent  
contamination.  
Methodological Framework  
Figure 2.2 shows how spatial sampling, lab procedures, Water Quality Index (WQI), and statistical analysis form  
a framework to assess industrial effluents' impact on the Ona River. These methods help attribute variations in  
physicochemical and bacteriological parameters to industrial pressures. The next section presents results by  
parameter, WQI, and bacteria, discussing these findings in relation to literature and regulations to assess effects  
on ecosystem health and public safety.  
Figure 2: Methodology Workflow Schematic Diagram  
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RESULT AND DISCUSSION  
Physicochemical Properties  
The physicochemical traits of the Ona River at industrial and residential sites are shown in Table 2 and Figure  
3a–f. Significant spatial differences in EC, TDS, DO, BOD₅, and COD were noted, with p < 0.05 for all except  
pH and temperature.  
Water samples' pH ranged from 6.22 to 7.55, with site means of 6.98 ± 0.67 at Sumal and 7.48 ± 0.08 at Amir  
Plast. The residential site recorded 7.15. All values fall within WHO and NIS standards (6.5–8.5), indicating  
general compliance. The acidity at Sumal suggests effluent enrichment, neutralized downstream, consistent with  
Andem et al. (2015), who observed pH buffering in polluted Ona River sections. Water temperature was steady  
at 26 °C, reflecting seasonal conditions. While pH and temperature pose low immediate risks, transient acidity  
could mobilize heavy metals and raise bioavailability in waters.  
Electrical conductivity averaged 194.7 ± 115.5 µS/cm at Sumal, versus 127.3 ± 13.6 µS/cm at Amir Plast and  
121 µS/cm at the residential site. TDS peaked at P&G (2.14 ± 1.49 mg/L), with residential samples at 1.41 mg/L.  
EC values were below the WHO and NIS limit of 1000 µS/cm, but TDS at industrial discharge points exceeded  
500 mg/L when scaled correctly. Butu et al. (2022) reported increased dissolved solids in River Rido, Kaduna,  
downstream of industrial areas, due to detergent and ionic effluent. Elevated TDS reduces palatability, causes  
scaling, and raises treatment costs, posing operational and health concerns.  
The most critical issue was oxygen dynamics, with DO below the recommended 4–5 mg/L, ranging from 1.91  
mg/L at Amir Plast to 2.57 mg/L at P&G. BOD₅ values were very high, peaking at 37.4 mg/L at Sumal, and  
COD reached 22.8 mg/l, both exceeding WHO and NIS limits of <10 mg/L for BOD₅ and <3 mg/L for COD.  
Similar trends were noted in River Majowopa, Ogun State, as effluent discharges raised BOD₅ and COD beyond  
limits, causing oxygen depletion. The low DO in Ona River indicates hypoxic stress, harming aquatic life and  
reducing self-purification.  
Table 2 and Figure 3a–f show that while pH and temperature stay within safe limits, ionic enrichment and oxygen  
depletion threaten water quality. Exceedances in BOD₅, COD, and DO highlight heavy organic load from  
industrial effluents, consistent with other Nigerian rivers affected by food and plastics industries (Deinmodei et  
al., 2020; Butu et al., 2022). These findings stress the need for effluent pretreatment and strict regulation to  
protect ecosystems and reduce health risks for downstream communities.  
Table 2 Physicochemical properties of water samples from Ona River across industrial and residential locations  
compared with WHO/NIS guideline values.  
Parameter  
WHO  
NIS  
Sumal  
Amir  
Plast  
(n=3)  
P&G  
(n=3)  
Residential p-  
(n=1) value  
Guideline Guideline (n=3)  
pH  
6.5–8.5  
Ambient  
1000  
6.5–8.5  
Ambient  
1000  
6.98 ± 0.67  
26.0 ± 0.0  
7.48  
0.08  
± 7.27 ± 0.03 7.15 ± 0.00  
0.064  
(ns)  
Temperature  
(°C)  
26.0 ± 0.0 26.0 ± 0.0  
26.0 ± 0.0  
ns  
Electrical  
Conductivity  
(µS/cm)  
194.7  
115.5  
± 127.3  
± 163.0  
58.0  
± 121.0 ± 0.0  
0.003  
**  
13.6  
Total Dissolved 500  
Solids (mg/L)  
500  
0.71 ± 0.30  
0.91  
0.30  
± 2.14 ± 1.49 1.41 ± 0.00  
0.001  
***  
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Dissolved  
Oxygen (mg/L)  
4.0–5.0  
–
2.21 ± 0.43  
1.91  
1.24  
± 2.57 ± 0.40 2.51 ± 0.00  
<0.001  
***  
Biochemical  
Oxygen Demand  
(mg/L)  
<10.0  
–
37.4 ± 42.6  
11.5 ± 2.7 13.6 ± 2.9  
9.95 ± 0.00  
5.99 ± 0.00  
<0.001  
***  
Chemical  
Oxygen Demand  
(mg/L)  
<3.0  
–
22.8 ± 29.8  
8.92 ± 1.1 9.03 ± 0.7  
<0.001  
***  
Note: p < 0.05 (), p < 0.01 (), p < 0.001 (), ns = not significant.  
Figure 3. Multi-panel illustration of physicochemical parameters of Ona River across industrial and  
residential sites: a) Electrical conductivity (EC), b) Dissolved oxygen (DO), c) Biochemical oxygen demand  
(BOD₅), d) Chemical oxygen demand (COD), e) Manganese (Mn), and f) Magnesium (Mg). Bars represent mean  
± standard deviation (SD).  
Significant spatial variation was confirmed by one-way ANOVA (p < 0.05), with industrial discharge sites  
(Sumal, Amir Plast, and P&G) consistently exceeding permissible limits for DO, BOD₅, COD, Mn, and Mg,  
while EC remained below guideline values. These results highlight the impact of effluent discharges on river  
water quality, with implications for ecosystem integrity and public health. Overall, the physicochemical  
assessment demonstrates severe effluent-driven degradation of Ona River water quality. Parameters most  
affected include DO, BOD₅, COD, TDS, Mn, and Mg, all exceeding WHO/NIS limits with significant spatial  
differences. Sumal emerged as the hotspot for organic pollution, while P&G showed the highest heavy metal  
enrichment. These findings highlight urgent needs for effluent pretreatment, catchment-based management, and  
stricter regulatory enforcement.  
Nutrients and Specific Metals  
The nutrients and certain metals recorded at various locations along the Ona River are summarized in Table 3  
and illustrated in Figures 3a–f. Statistically significant differences were observed in total suspended solids (TSS),  
alkalinity, magnesium (Mg), and manganese (Mn). Conversely, turbidity and hardness did not exhibit significant  
variation among the sampling sites.  
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TSS levels were highest at the residential site (1.58 mg/L), slightly above the WHO threshold of 1.0 mg/l, while  
industrial sites ranged from 0.28 to 0.94 mg/L. Turbidity was minimal everywhere (0.02–0.11 NTU), well below  
WHO limits. The high TSS at the residential site likely results from domestic runoff and waste, not industrial  
discharges. Green et al. (2023) found similar sediment buildup in Iwofe River, highlighting settlement impacts.  
Surpassing WHO TSS limits indicates reduced water clarity, increased sedimentation, and possible microbial  
transport in low-flow areas.  
Alkalinity ranged from 25.0 mg/L at the residential site to 48.7 ± 15.5 mg/L at P&G, all within WHO guidelines  
of <120 mg/L. Hardness was consistently low (<36 mg/L), classifying the river water as soft, below the desirable  
100–150 mg/L. Oladele et al. (2015) also reported low hardness in effluent-impacted rivers of Ibadan. Soft water  
reduces scaling but increases pipe corrosion and lacks beneficial minerals, affecting its long-term domestic use.  
The most critical risks stem from metal contamination. Manganese levels were significantly higher at industrial  
sites, from 0.71 ± 0.18 mg/L at Amir Plast to 0.93 ± 0.57 mg/L at P&G, compared to 0.014 mg/L at the residential  
site. These exceed WHO (0.08 mg/L) and NIS (0.2 mg/L) limits, indicating industrial chemical inputs and  
increased solubility under localized acidity. Magnesium levels also surpassed the NIS limit, with means of 17.7  
± 10.4 mg/L at Sumal, 31.2 ± 27.1 mg/L at Amir Plast, and 22.7 ± 23.5 mg/L at P&G. Similar Mn and Mg  
enrichment has been linked to industrial effluents in southern Nigeria, where metals persisted beyond discharge  
zones (Amadi et al., 2016). Chronic Mn exposure links to neurological damage (Bjørklund et al., 2017), while  
high Mg may cause operational issues and ecological stress.  
Phosphate was not detected, indicating limited agricultural inputs during early wet season sampling. Chloride  
was present at all sites but below WHO and NIS guidelines of 250 mg/L. The absence of phosphate contrasts  
with heavily farmed catchments (Adefemi & Awokunmi, 2010), highlighting the dominance of industrial over  
agricultural inputs in this area.  
Table 3 and Figure 3a–f show minor nutrient impairments, with only TSS exceeding limits. Metals like Mn and  
Mg are consistently above WHO and NIS standards. These findings align with Nigerian river studies (Deinmodei  
et al., 2020; Butu et al., 2022), highlighting metals as primary pollutants. They emphasise the need for effluent  
pretreatment, strict discharge enforcement, and monitoring to prevent ecological harm and protect health.  
Table 3: Nutrients and specific metal concentrations in water samples from Ona River across industrial and  
residential locations  
Parameter  
WHO  
NIS  
FAO  
Sumal  
Amir  
Plast  
(n=3)  
P&G  
(n=3)  
Residential p-  
(n=1) value  
Guideline Guideline Guideline (n=3)  
Total  
Suspended  
Solids (mg/L)  
1.0  
–
–
0.54 ± 0.94 ± 0.28 ± 1.58 ± 0.00  
0.56 0.30 0.03  
0.048  
*
Turbidity  
(NTU)  
4.0  
–
–
0.11 ± 0.03 ± 0.02 ± 0.04 ± 0.00  
0.18 0.03 0.01  
0.29  
(ns)  
Alkalinity  
(mg/L)  
<120  
100–150  
5.0  
–
–
35.7 ± 32.3 ± 48.7 ± 25.0 ± 0.00  
17.2 8.7 15.5  
0.041  
*
Hardness  
(mg/L)  
150  
–
–
18.0 ± 15.0 ± 36.0 ± 10.0 ± 0.00  
0.061  
(ns)  
8.5  
3.6  
15.3  
Phosphate  
(mg/L)  
5.0  
ND  
ND  
ND  
ND  
–
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Chloride  
(mg/L)  
250  
–
250  
0.2  
0.2  
–
–
–
Present Present Present  
(+) (+) (+)  
Present (+)  
–
Magnesium  
(mg/L)  
17.7 ± 31.2 ± 22.7 ± 12.0 ± 0.00  
10.4 27.1 23.5  
0.001  
***  
Manganese  
(mg/L)  
0.08  
0.90 ± 0.71 ± 0.93 ± 0.014  
0.21 0.18 0.57 0.00  
± 0.002  
**  
Note: p < 0.05 (), p < 0.01 (), p < 0.001 (), ns = not significant; ND = not detected.  
Figure 4. Multi-panel illustration of nutrients and major ions in Ona River:  
Total suspended solids (TSS), b) Turbidity, c) Alkalinity, d) Hardness, e) Phosphate, and f) Chloride. Bars  
represent mean ± standard deviation (SD) for quantitative parameters, with WHO/NIS guideline thresholds  
shown as dashed red lines.  
ANOVA indicated significant site differences for TSS (p < 0.05) and alkalinity (p < 0.05), while turbidity  
remained consistently below the WHO limit of 4 NTU. Hardness values confirmed soft water status across all  
sites. Chloride and phosphate exhibited spatial presence/absence patterns, reflecting episodic effluent  
contributions. Elevated TSS at the residential site highlights contributions from domestic runoff and poor waste  
management.  
Correlation Analysis of Heavy Metals and Physicochemical Parameters  
Table 4 and Figure 4, panel (a-d), show the correlation between heavy metals (Mn, Mg) and physicochemical  
parameters. Manganese has a strong positive correlation with electrical conductivity (r = 0.728, p = 0.272) and  
COD (r = 0.568, p = 0.432). Magnesium correlates positively with pH (r = 0.810, p = 0.190) and negatively with  
DO (r = –0.689, p = 0.311). Although not statistically significant due to small sample size (n = 4 sites), the  
associations align with effluent–water interactions in industrial catchments.  
Higher ionic concentrations and organic matter loading increase Mn levels due to Mn's solubility in low-oxygen  
conditions. Similar findings occur in River Kaduna, where industrial effluents raise EC and Mn, increasing  
oxygen demand and stress (Deinmodei et al., 2020). Also, Butu et al. (2022) linked dissolved solids with trace  
metal enrichment in River Rido.  
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The WHO and NIS limits (Mn = 0.08 and 0.2 mg/L; Mg = 0.2 mg/L) were consistently exceeded at industrial  
sites, indicating anthropogenic pressure rather than natural background. These exceedances pose risks: Mn  
toxicity links to neurological disorders (Bjørklund et al., 2017), and Mg enrichment causes scaling and  
operational issues.  
Panel (a-d) shows a positive Mn–EC/COD link and a negative Mg–DO relationship, highlighting how effluent  
chemistry affects oxygen levels and metal solubility. Table 4 and Figure 4a-d support that industrial effluents at  
Ona River degrade water quality and mobilize metals, risking long-term impacts on ecosystems and health.  
Table 4. Correlation matrix of heavy metals and physicochemical parameters in Ona River.  
(p-values in parentheses)  
Metal  
pH  
DO  
EC  
COD  
BOD  
TDS  
Mn  
0.052 (0.948)  
–0.266 (0.734)  
0.728  
0.568 (0.432)  
0.503 (0.497)  
–0.007 (0.993)  
(0.272)  
Mg  
0.810 (0.190)  
–0.689 (0.311)  
–0.114  
–0.098 (0.902)  
–0.207  
–0.103 (0.897)  
(0.886)  
(0.793)  
Note: p < 0.05 (), p < 0.01 (), p < 0.001 (), ns = not significant.  
Figure 5a-d. Heatmap visualizes the direction and strength of these correlations, highlighting positive Mn–  
EC/COD relationships and negative Mg–DO association.  
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Correlation Analysis of Nutrients and BOD  
The relationship between nutrient indicators and BOD₅ is summarized in Table 5 and illustrated in Figures 5a–  
c. Turbidity showed a very strong positive correlation with BOD₅ (r = 0.950, p = 0.050), while TSS had a  
moderate negative relationship (r = –0.453, p = 0.547), and alkalinity weakly and positively correlated with  
BOD₅ (r = 0.133, p = 0.867). Phosphate and chloride were excluded due to constant values across sites.  
The strong turbidity–BOD₅ link indicates fine particulates from effluent discharges increase oxygen demand,  
aligning with Dauda and Olaofe (2020), who identified turbidity as a main cause of high BOD₅ in Ogun State  
streams. The weak, non-significant TSS–BOD₅ correlation suggests bulk solids may not directly affect oxygen  
depletion, unlike finer suspended particles.  
BOD₅ levels at industrial sites far exceeded the WHO limit of <10 mg/L, despite turbidity staying below the 4  
NTU guideline. This suggests that low-turbidity effluents can still impose high oxygen demand due to organic-  
rich particulates and dissolved constituents, not sediment loads.  
Figures 5a–c show regression slopes: a steep positive trend for turbidity vs BOD₅, a flat association for alkalinity  
vs BOD₅, and a negative slope for TSS vs BOD₅. These results, along with Table 5, indicate that particulate and  
colloidal fractions in industrial discharges mainly cause oxygen stress in Ona River.  
Table 5. Correlation of nutrients with BOD₅ in Ona River. (p-values in parentheses)  
Nutrient  
TSS  
r-value (BOD₅)  
p-value  
0.547 (ns)  
0.867 (ns)  
0.050 (*)  
–
–0.453  
0.133  
0.950  
–
Alkalinity  
Turbidity  
Phosphate  
Chloride  
–
–
Note: p < 0.05 (), p < 0.01 (), p < 0.001 (), ns = not significant.  
Figure 6a-c. Nutrients vs BOD₅: a) TSS vs BOD₅; b) Alkalinity vs BOD₅; c) Turbidity vs BOD₅  
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Water Quality Index of Physicochemical Parameters in Ona River  
The Ona River's Water Quality Index (WQI) data show industrial discharge sites- Sumal (43.2), Amir Plast  
(47.3), and P&G (48.9)- are consistently Poor. The downstream residential site has a WQI of 54.4, categorised  
as moderate. This suggests the industrial corridor mainly impacts river quality, with limited downstream  
recovery due to dilution and self-purification.  
Poor-quality ratings at industrial sites result from high BOD₅, COD, low DO, and ionic enrichment, heavily  
influencing index scores. Similar findings occurred in River Kaduna (Deinmodei et al., 2020) with WQI 35–49  
near effluents, and in River Rido (Butu et al., 2022). Ona River findings reflect broader industrial impacts on  
Nigerian urban rivers.  
Although the site had moderate quality, its WQI of 54.4 is below the “good” threshold of 71–90. According to  
WHO (2011) and NIS (SON, 2007), this means the water isn't fit for direct consumption and only marginally  
suitable for agriculture. The slight improvement over industrial zones shows dilution and re-aeration downstream  
but doesn't offset ongoing oxygen stress and metal pollution.  
Table 6 shows Ona River classification at sampling points, while Figures a–c compare WQI categories. Results  
indicate the water is highly compromised, affecting domestic, agricultural, and ecological uses. This highlights  
the urgent need for industrial wastewater pretreatment, stricter effluent standards, and ongoing monitoring to  
protect ecosystems and public safety.  
Table 6. Water Quality Index (WQI) classification of Ona River across sampling locations.  
Location  
Sumal  
WQI Value  
43.2  
Classification  
Poor  
Status  
Unsuitable without treatment  
Unsuitable without treatment  
Unsuitable without treatment  
Marginally suitable (requires treatment)  
Amir Plast  
P&G  
47.3  
Poor  
48.9  
Poor  
Residential  
54.4  
Moderate  
Note: WQI ratings follow NSF-WQI and WHO classification ranges (Excellent: 91–100; Good: 71–90;  
Moderate: 51–70; Poor: 26–50; Very Poor: 0–25).  
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Figure 7(a–c): Distribution of WQI classifications across River Ona: a) Bar chart of WQI values at each  
location, with WHO/NIS thresholds shown as dashed lines; b) Line graph showing the spatial trend of WQI  
across sites (industrial → residential); c) Distribution of WQI classifications, highlighting that most sites fall  
within the poor category.  
Bacteriological Properties of the Ona River  
The Ona River's bacteriological assessment showed very low coliform counts (~0.001 cfu/mL) across all sites,  
not significantly different among locations, indicating minimal microbial contamination compared to other  
Nigerian rivers impacted by effluents, where levels often exceed WHO thresholds due to pollution sources like  
open defecation and waste pits. The river's flow and dilution likely suppress microbial survival downstream.  
Results fall within WHO/NIS safe drinking standards (<1 cfu/mL), suggesting microbiological safety at  
sampling time, though trace levels imply potential episodic contamination risks during peak runoff.  
Summarized data confirm compliance and highlight that, while physicochemical pollution dominates, microbial  
risks persist for communities depending on untreated water, warranting ongoing monitoring.  
Table 7. Bacteriological quality of the Ona River across sampling sites.  
Location  
Sumal  
Total Coliform (cfu/mL)  
WHO/NIS Guideline  
Compliance  
Within limit  
Within limit  
Within limit  
Within limit  
0.001  
0.001  
0.001  
0.001  
<1.0  
<1.0  
<1.0  
<1.0  
Amir Plast  
P&G  
Residential  
Note: WHO and NIS standards require zero detectable E. coli in 100 mL; <1 cfu/mL is acceptable for general  
coliforms.  
Ecological Risks and Monitoring Implications  
Ecological risks in the Ona River mainly stem from heavy metals and oxygen depletion. Manganese (0.71–0.93  
mg/L) exceeded US EPA TEL (0.08 mg/L) and NIS (0.2 mg/L), while magnesium (17.7–31.2 mg/L) surpassed  
FAO irrigation limits (0.2 mg/L), indicating bioaccumulation and reduced agricultural suitability, similar to  
polluted reservoirs (Arslan et al., 2025). Nutrient risks were moderate; TSS at 1.58 mg/L slightly exceeded  
WHO’s 1.0 mg/L guideline, possibly affecting aquatic productivity. Bacteriological contamination was low,  
though occasional traces downstream pose episodic risks. Continuous monitoring of metals, oxygen, and  
microbes, using biological indicators as recommended by UNEP (2019), is vital for enforcing standards and  
safeguarding ecological and human health, as shown in Table 8.  
Table 8. Ecological risk summary of Ona River water quality relative to standards.  
Parameter  
Range/Mean  
Guideline  
Standard  
Exceedance  
Ecological/Health Implication  
Manganese  
(Mn)  
0.71–0.93  
mg/L  
WHO: 0.08; NIS: Yes  
0.2 mg/L  
Bioaccumulation, benthic toxicity,  
neurological risks  
Magnesium  
(Mg)  
17.7–31.2  
mg/L  
FAO: 0.2 mg/L  
Yes  
Irrigation unsuitability, scaling,  
crop impacts  
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TSS  
0.28–1.58  
mg/L  
WHO: 1.0 mg/L  
Slight  
(downstream)  
Reduced clarity, productivity loss,  
habitat stress  
DO  
1.9–2.6 mg/L  
WHO/NIS:  
mg/L  
4–5 Yes  
Oxygen depletion, biodiversity  
decline  
BOD₅  
Coliforms  
9.95–37.4  
mg/L  
WHO: <10 mg/L  
Yes  
Organic overload, ecological stress  
0.001 cfu/mL  
WHO/NIS:  
cfu/mL  
<1.0 No  
Generally safe; trace episodic risk  
downstream  
Synthesis of Findings  
This study offers the initial comprehensive evaluation of risks in the Ona River, Ibadan, Nigeria. Findings  
indicate substantial degradation at industrial discharge locations, characterised by elevated levels of TDS, EC,  
COD, BOD₅, manganese, and magnesium surpassing regulatory standards. Dissolved oxygen measurements fell  
below 2.6 mg/L, signifying oxygen deficiency. Nutrient concentrations and suspended solids exhibited moderate  
increases; bacteriological quality remained predominantly acceptable, although residual coliform presence  
downstream presents episodic hazards. The Water Quality Index classified industrial areas as poor (scores 43-  
49) and the residential area as moderate (score 54), underscoring deterioration attributable to effluent discharge  
with limited downstream recovery. Ecological assessments revealed manganese and magnesium concentrations  
exceeding permissible thresholds, thereby endangering benthic organisms, crops, and human health. These  
results underscore the necessity for continuous multi-parameter environmental monitoring as advocated by  
UNEP (2019). In conclusion, the Ona River is impacted by industrial activities, oxygen depletion, and heavy  
metal contamination, with minimal microbial pollution, rendering it unsuitable for domestic or irrigation  
purposes without appropriate treatment. This evidence underpins the need for regulatory oversight, wastewater  
treatment implementation, and ecosystem surveillance to safeguard water resources in Nigeria.  
Figure 8. Conceptual Framework: DPSIR Model of Ona River Water  
CONCLUSION AND RECOMMENDATIONS  
This study assessed the Ona River, revealing significant impairment from industrial effluents. Elevated Mn and  
Mg exceeded standards set by USEPA, WHO, and FAO. Dissolved oxygen stayed below 2.6 mg/L. High BOD₅  
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and COD confirmed oxygen stress. Water Quality Index classified industrial zones as poor (43–49) and the  
residential site as moderate (54). Trace coliform bacteria downstream indicated episodic contamination. The Ona  
River is unsuitable for drinking or irrigation without treatment.  
Recommendations:  
Industrial effluent pretreatment to reduce metals and organics.  
Regulatory enforcement aligned with WHO/FAO standards, led by NESREA.  
Continuous monitoring, integrating physicochemical, microbial, and biological indicators.  
Community participation in surveillance for accountability.  
Ecosystem restoration, including riparian buffers, to enhance resilience.  
Closing Remarks  
This study highlights the urgent need for integrated water quality management in Nigeria’s industrial catchments.  
By combining physicochemical, nutrient, bacteriological, and ecological risk assessments, it provides baseline  
evidence for regulatory enforcement, industrial pretreatment, and sustainable monitoring frameworks. The Ona  
River findings reflect broader patterns across West Africa and emphasize the necessity of proactive interventions  
to safeguard water resources, public health, and ecosystem integrity.  
ACKNOWLEDGEMENT  
The authors gratefully acknowledge the support of the Department of Civil Engineering, Ladoke Akintola  
University of Technology (LAUTECH), Ogbomoso, Nigeria, for providing laboratory facilities and technical  
assistance. We also thank the local community of Oluyole Industrial Area, Ibadan, for granting access to  
sampling locations.  
FUNDING  
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit  
sectors.  
Authors’ Contributions  
Praise Adenike Alli: Conceptualization, Data Collection, Laboratory Analysis, Drafting of Manuscript.  
Adebayo Ayodele Adegbola: Methodology Design, Data Analysis, Critical Review.  
Olatunji Sunday Olaniyan: Supervision, Manuscript Editing, Policy Implication Framing.  
All authors reviewed and approved the final version of the manuscript.  
Conflicts of Interest  
The authors declare no conflicts of interest.  
Data Availability  
The datasets generated and analyzed during this study are available from the corresponding author upon  
reasonable request.  
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