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Article

Urbanization and Environmental Sustainability: Planning Diagnosis of Symbiosis Between Osogbo City and UNESCO World Heritage Site in Osun State, Nigeria

by
Oyewale Oyeleye
1,2 and
Liora Bigon
1,*
1
School of Architecture, Ariel University, Ariel 40700, Israel
2
Department of Tourism Studies, Osun State University, Osogbo 230101, Nigeria
*
Author to whom correspondence should be addressed.
Land 2025, 14(4), 707; https://doi.org/10.3390/land14040707
Submission received: 16 February 2025 / Revised: 18 March 2025 / Accepted: 24 March 2025 / Published: 26 March 2025
(This article belongs to the Special Issue Local and Regional Planning for Sustainable Development)
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Abstract

:
Recently, the only UNESCO river in Nigeria has become polluted, with its color turning dark brown. Osun River serves not only domestic purposes in the city of Osogbo, but also spiritual purposes during the annual Osun Osogbo Festival (OOF). This study examines the physicochemical properties and presence of heavy metals in Osun River, and the air quality at the heritage site before, during, and after the festival. Water samples from Osun River at the UNESCO site were collected before, during, and after the 2024 festival. The water was analyzed at the Department of Environmental Health Sciences of Osun State University, Nigeria, to determine the quantity of heavy metals present in the river. Additionally, an air quality detector was used to assess the quantity of pollutants (CO2, CO, PM2.5, PM10, TVOC, and HCHO) in the air before, during, and after the festival. In Osun River, the quantities of arsenic and copper were within the permissible levels set by the World Health Organization (WHO) for drinking water, while those of lead, chromium, and cadmium were far above the safety standards set by the WHO. The pollution rate of the river was in the order of festival day > before the festival > after the festival. The air quality on the festival day was hazardous to human health, as particulate matter (PM2.5 and PM10) and carbon dioxide were found to be far above the permissible levels set by the WHO. The implications of the findings of this study are discussed, and measures to ensure the future sustainability of this important UNESCO site in the city of Osogbo are recommended.

1. Introduction

In the last decade, urbanization has been a subject of discussion among scholars worldwide. The recent global trend of urbanization with its ecological and environmental impacts cannot be separated from the United Nations post-2015 “New Urban Agenda”, which primarily aims to ensure the sustainable development of human settlements, particularly cities. In the literature, the continuous debate on what urbanization connotes spans three perspectives, i.e., the population, the economy, and spatiality. Urbanization is seen as an increase in the population of a particular urban area due to a natural increase and migration patterns, either rural–urban or urban–urban migration patterns [1,2,3,4]. Urbanization is defined as a phase of growth in the economic status, infrastructure concentration, and industrialization process, which serve as centripetal forces in the development of a particular urban area [5,6,7,8,9]. Urbanization is also described as the level of urban physical development expanding from the city core to the hinterlands, leading to urban sprawl due to uncontrollable land use and land cover changes [10,11,12].
From the aforementioned perspectives, one could infer that urbanization is largely driven by human migration patterns in the direction of infrastructure and economic opportunities, which, in turn, place extensive pressure on land resources and urban ecosystems. Human mobility patterns as a characterization of urbanization have been linked to urban pollution, and this has been confirmed, for instance, by the sharp drop in urban pollution globally during the COVID-19 lockdown in 2020 [13,14]. Urbanization has been extensively attributed to an ecological imbalance and environmental degradation in cities, notably in developing countries [15,16]. A strong connection between urbanization and environmental pollution, as determined by economic complexity, has been established in the environmental Kuznets curve (EKC) [9,17,18]. The EKC is theorized based on the hypothesis that environmental pollution is directly and inversely related to economic growth at the onset of the relationship and later on, respectively. The trend of the relationship is influenced by the priority placed on economic growth at the expense of the environment at the beginning, while the economic prosperity attained later on is deployed to remediate the polluted environment. This is in tandem with the view of Urban Alert [19] in the case of Osogbo city, where governments at all levels place focus on economic prosperity from the gold mining activities ongoing in the catchment areas of the city, with less concern for environmental protection. This situation has not only become a serious threat to the environmental sustainability of the UNESCO site in the city but also threatens the lives of tourists and local communities, as the historic Osun River in the city is polluted with heavy metals hazardous to human health. Anifowose et al. [20] opined that indiscriminate waste disposal and mining activities have polluted Osun River with chromium, arsenic, and nickel, which have carcinogenic effects on humans, and that their quantities surpass the international standards for drinking water. Similarly, Odesanya and Oyediran [21] concluded that the mortality and morbidity rates surge in Osogbo, shortly after the annual OOF. However, a strong tie has been established between the low economic conditions of Osogbo residents and an increase in environmental pollutants in the city [22].
The human exploration and consumption of environmental resources to support the needs of the growing population during the urbanization and industrialization processes are not without environmental consequences. Environmental sustainability agendas in both the literature and practice aim to ensure that the human environment is safe for living, working, and recreation at any point in human life, from generation to generation. The most life-threatening factor in environmental sustainability discourse is pollution [23]. This is also in line with the conclusion of the United Nations General Assembly [24] that the health implications of environmental pollution are the key determinants of a sustainable environment. For example, a leading causative factor of kidney problems in humans is over exposure to heavy metals (chromium, cadmium, lead, and arsenic, inter alia) and fluoride through water and soil pollution [25,26,27,28].
From the North to the Global South, pollution has been a challenging environmental factor due to the intricacies of urban complexity and diversity [29]. China and India (as well as the US) are reported to top the number of deaths recorded in the world from air pollution caused by urban transportation [30]. In 2013, child fatality was triggered by water pollution in the Bagega community, Nigeria, resulting in the deaths of about 400 children [19]. In addition, Dhaka, the capital city of Bangladesh, with a population of about 16 million, was declared as one of the most polluted cities in the world, with millions of residents exposed to the risk of cancer through chromium-polluted rivers in the city, which serve domestic and irrigation purposes [31]. The findings of a study conducted in San Luis Potosi, Mexico, by Cárdenas-González et al. [28] documented a strong correlation between kidney problems in children and soil and water pollution with high quantities of metallic substances, namely, chromium and arsenic. Additionally, in 2016, Delhi, India, was noted by the WHO to be the second most polluted city in the world, with persistent cases of air-borne diseases [32]. Globally, about 4 million people have died as a result of over exposure to air pollution, particularly PM2.5 (particulate matter of 2.5 μm), with the highest number of deaths recorded in China and India [29,33,34].
Environmental pollution, a global challenge impeding environmental sustainability, continues to be treated with various methodologies and strategies which differ by nations in order to control or reduce its effects on the urban ecosystem. A study by Solarin and Bello [35] on the methodology of energy innovation (renewable energy) adopted by the USA between 1974 and 2016 found that it was successful in reducing the discharge of greenhouse gases into the atmosphere. In addition, the most urbanized cities in the world are in China [36], and studies conducted in China between 1995 and 2020 by Lv et al. [37] and Fiscal et al. [3] confirmed that the adoption of the smart city strategy through the use of ICT and green transportation (no/low-carbon transportation) made a major contribution to environmental sustainability in the country. Additionally, two prominent methods adopted in South Australian cities to ensure water protection from pollution and environmental sustainability are integrated urban water management (IUWM) and total water cycle system [38].
Furthermore, in Pakistan, efforts to decimate environmental pollution from small and medium enterprises (SMEs) and enhance environmental sustainability have led to two approaches, i.e., environmental management accounting (EMA) and environmental proactivity (EP), which have been found to be successful [39]. Urban greenery and/or green infrastructure is a recurring strategy gaining global recognition as a means to reduce air pollution, urban heat, and other environmental challenges in order to promote urban ecosystem wellbeing. Similarly, different environmental laws and policies subsist in different countries to ensure environmental protection. Urban planning is a crucial aspect of city environmental management with strategies for environmental sustainability incorporated into the master plan (urban design) and urban planning policies guiding the development of a city. Urbanization in the absence of effective and modern urban planning policies is not without environmental consequences. In fact, it constitutes a major factor as to why environmental degradation is more prominent in cities within developing and under-developed nations. A study by Piracha and Chaudhary [14] stressed the importance of urban planning in promoting environmental sustainability, as urban wellness can be achieved through paradigm shifts from traditional planning to modern strategies such as transit-oriented development (TOD), smart growth (SG), and new urbanism (NU).
Although Osogbo is one of the fastest urbanizing cities in Southern Nigeria, its physical expansion is occurring without a physical development plan, with an annual urban growth rate of 3.15% [40,41]. The population of the city was 250,951 in 1991 [42], and it increased to about 800,000 in 2025 [43]. The city is very important for Nigeria’s tourism industry, as it hosts the only UNESCO World Heritage Site (WHS) in southern Nigeria, that is, Osogbo Sacred Grove (OSG). The grove covers 75 hectares of land, and it is the most visited tourist destination in Nigeria [44]. The WHS has a sacred river (Osun River), which tourists and Osun River goddess’ devotees drink from and is used for other domestic and irrigation purposes in the city. A cultural festival supported by UNESCO, the OOF, is celebrated annually in August at the WHS, with the average number of attendees from different countries being about 100,000 [45]. Studies have confirmed that urbanization and mining activities in the catchment areas of the city have polluted the important Osun River at the WHS with heavy metals [19,46]. However, no study has been conducted during the annual festival to examine the actual exposure of the thousands of tourists and participants to the environmental pollution of the WHS.
Thus, the aims of this study are to assess the water quality of Osun River by determining its physicochemical properties (dissolved oxygen (DO), biochemical oxygen demand (BOD), and pH) and the presence of heavy metals (arsenic, cadmium, chromium, lead, copper, and mercury) and to analyze the air quality at the WHS by measuring the levels of formaldehyde (HCHO), total volatile organic compounds (TVOCs), particulate matter (PM2.5 and PM10), carbon oxides (CO and CO2), and other air quality parameters (temperature, humidity, and the air quality index), sampled a week before, during, and a week after the grand finale of the OOF—on 2, 9, and 16 August 2024. In this study, we also examine whether there is a significant difference in the physicochemical properties and presence of heavy metals in Osun River before, during, and after the OOF. The specific objectives of our research include the following: (1) measuring the pollution level of Osun River and comparing it with WHO standards; (2) analyzing the short-term impact of the OOF on air quality; and (3) making data-based pollution mitigation recommendations. The findings and conclusions of this study will be useful in policy formulation to protect the ecosystem of this important WHS, as well as to safeguard the health of the thousands of participants in the annual festival and the Osogbo residents who rely on Osun River for domestic and irrigation purposes.

2. Materials and Methods

2.1. Study Area

Osogbo is a city that was declared the capital of Osun State on 21 August 1991, which won its independence from the old Oyo State. The city is located in southwestern Nigeria, with an estimated population of 795,808 [43]. Osogbo is on latitudes 7°40′ N and 7°59′ N and longitudes 4°22′ E and 4°39′ E. The city is mainly comprised of the two local government areas of Osogbo and Olorunda (Figure 1). Its metropolitan area extends to about five other adjoining local government areas. Osogbo is a prominent and renowned city in Nigeria, as it contains the only surviving sacred grove in the country, OSG. The grove was inscribed as a UNESCO WHS in 2005. The heritage site is a sacred forest containing the spiritual Osun River, which, according to Yoruba mythological and cosmological beliefs, has been ruled by the Osun River goddess since the creation of the city about 700 years ago right inside the grove. The grove occupies about 75 hectares of land in its core zone (primary forest) and has about 47 hectares of land in its buffer zone. The grove is described by the Nigerian archaeologist Akinwumi Ogundiran [47] as a typology where bio-environmental, cultural, and spiritual values form a unique landscape, which must be carefully sustained beyond the present generation. The heritage site is the leading tourist destination site in Nigeria and the center of the city’s lived heritage in terms of civilization and urbanization.

2.2. Data Sources and Processing

This study employed the use of mixed methods for data collection. The quantitative data used for this study consisted of water and air samples collected in OSG. Sampling was conducted on three occasions, namely, 2, 9, and 16 August in 2024, between 9:30 a.m. and 2:00 p.m., which covered the peak period of visits to the WHS. The sampling period aligned with the scheduled date for the 2024 OOF, which began on 1 August; the grand finale of the festival was held on 9 August. The three sampling dates represent before, during, and after the grand finale of the OOF, which was attended by 91,000 persons [45].
Three water samples were collected per visit: at the central point of the river (Osun shrine spot) and at the north-west and north-east points of the river. These points represent the three sides of the river where visitors, tourists, and Osun devotees usually fetch water. Altogether, nine water samples were collected for this study. The water was collected into well-labeled (point, date, and time of collection) white plastic bottles of 1 L for analysis of heavy metals (lead, arsenic, chromium, cadmium, mercury, and copper) and physicochemical assessment (dissolved oxygen, biochemical oxygen demand, and pH). This is in accordance with the standard practice in analyzing water quality, as provided by the American Public Health Association [48]. The pH values of all the water samples were determined using a standardized digital pH meter with a glass electrode (Rex Model PHS-25 m) at the water collection point. Additionally, the DO of all the water samples was measured using a standardized digital dissolved oxygen meter (DO9100) at the collection point. The samples were kept in sterilized black polythene bags and transported to the Laboratory of the Department of Environmental Health Science, Osun State University, Osogbo, Nigeria, for analysis. The selection of the laboratory was based on the proximity to the study area; additionally, the laboratory is well equipped for the necessary analyses relevant to this study.
Furthermore, to determine the environmental air quality of the WHS, a handheld 6-in-1 Air Quality Detector was used to assess the quantity of pollutants (carbon dioxide (CO2), carbon monoxide (CO), fine particulate matter of 2.5 μm (PM2.5), fine particulate matter of 10 μm (PM10), TVOCs, and HCHO) in the air on the same dates that the water samples were taken (as detailed above). For good calibration, the device was mounted on a platform 3 m above ground level and left stationary for at least 1 h at each sampling location with the readings of CO and CO2 activated at 0 ppm and 400 ppm, respectively. Meanwhile, the readings of TVOCs and HCHO were activated on the device at 0.00 mg/m3 in a controlled environment, before measurements were taken. This is in line with the standard practice for air quality assessment [49]. At each visit, the air was sampled at three different locations about 30 m apart, which covered the riverside, the mid-point to the entrance, and the entrance to the WHS. Similarly, a digital hygrometer (UNI-T) was used to determine the temperature and humidity at all three locations where the quality detector was employed. In order to ensure data accuracy of temperature readings, ice-water calibration method was used, as the device was placed near the surface of a cold glass-container to reset its reading to 0 °C. Additionally, to ensure data reliability of humidity measurements, at the laboratory, the UNI-T hygrometer was placed beside a calibrated reference hygrometer in a controlled environment, with the observation of same reading of 75% relative humidity. The device was kept inside a sealed bag and transported to the study area. For sensor stabilization, the device was left for about 15 min after being switched on at the study area, before it was used to take humidity readings at OSG. All the devices were battery-powered, and they were fully charged before deployment to the study area.
To determine the air quality index (AQI) of the WHS, the formula in Equation (1) was adopted from a previous study conducted by Olufemi et al. [50]:
I p = I h − I l B P h − B P l   C p − B P l + I l
where Ip stands for the pollutant index value of CO, CO2, PM2.5, PM10, TVOCs, and HCHO; Cp refers to the pollutant (P) concentration; and BPh and BPl denote the concentration limits that are ≥ and ≤Cp, respectively, with reference to the air quality index values of low (Il) and high (Ih) [50]. The air quality indices of all the pollutants (CO, CO2, PM2.5, PM10, TVOCs, and HCHO) were determined with respect to Equation (1) above [50,51].
For qualitative data, an ethnography survey was carried out; interviews were conducted between 2 August 2024 and 9 November 2024, with the gatekeepers relevant to this study including the Director of the National Commission for Museums and Monuments (NCMM) (R1) in charge of the WHS and all six Directors (R2–7) of Osogbo’s urban planning agencies (federal: Ministry of Housing and Urban Development; state: Ministry of Lands and Physical Planning, Capital Territory Development Authority, and Property Development Corporation; and local: Osogbo Town Planning and Land Services, and Olorunda Town Planning and Land Services). The interviews included two themes: the nexus of the WHS and the urbanization of the city (R1); and the roles of urban planning agencies in ensuring the environmental sustainability of the city and the challenges confronting them (R2–7).

2.3. Laboratory Assessment of Heavy Metals (As, Cu, Pb, Cr, Cd, and Hg) in the Sampled Water

A small quantity of each water sample (100 mL) was digested in concentrated HNO3 at 80 °C in a fume cupboard. Concentrated HNO3 at a high temperature (≥60 °C) is a potent oxidizing agent capable of liberating metals from materials in the form of soluble nitrate salt. The total As, Cu, Pb, Cr, and Cd concentrations in parts per million (ppm) of the water samples were determined using atomic absorption spectrometry, while mercury (Hg) was not detected.

2.4. Statistical Data Analysis with R-Studio

R-studio software (R version 4.4.2) developed by R Core Team [52] for statistical analysis was employed to analyze the data in this study. The laboratory results of the three samples of water taken at each visit were used to generate the means ± standard deviations ± standard errors of the physicochemical variables (DO, BOD, and pH) and heavy metals (As, Cu, Pb, Cr, and Cd). R-studio was used to run a one-way analysis of variance (ANOVA) to determine the significance of the differences in the means of the physiochemical parameters and heavy metals pollutants of Osun River (at an alpha level of 0.01) across three groups (before, during, and after festival day). A post-hoc test was conducted to determine the actual significant differences among the three groups.

3. Results

3.1. Physicochemical and Heavy Metal Assessments of Water Sampled from Osun River

As shown in Table 1, the physicochemical characteristics of Osun River, which determine the quality of the aquatic ecosystem, showed variations in terms of the DO and BOD in the following order: BFD (before the festival day) > FD (the festival day) > AFD (after the festival day). The DO levels BFD and during FD were higher than the minimum standard set by the National Environmental Standards and Regulation Enforcement Agency (NESREA) and the World Health Organization (WHO), which is between 4.0 and 6.0 mg/L; however, the DO level AFD (3.03 mg/L) was lower than the set standards. Osun River showed a relatively high level of DO; the higher the DO, the better the quality of the water and the life within the aquatic ecosystem. Additionally, the BOD levels obtained during FD (4.3 mg/L) and AFD (0.27 mg/L) were within the permissible levels set by the NESREA and WHO at ≤5.0 mg/L, while the BOD level BFD (5.9 mg/L) was higher than the standard. The high BOD level of Osun River BFD has a strong correlation with harmful effects on aquatic organisms and human health, as the higher the BOD level above the permissible level, the lower the water quality and, consequently, the higher the water pollution.
pH measures the level of water acidity or basicity, and it ranges from 0 to 14, with 7 being the neutral point and the best; this level provides the highest level of water quality for human consumption and aquatic life. The pH levels of Osun River BFD, during FD and AFD were 6.56 mg/L, 6.8 mg/L, and 6.57 mg/L, respectively, and within the range of the permissible standard of 6.5–8.5 mg/L set by the NESREA and WHO (Table 1). However, the observed values were below the neutral point of 7.0 mg/L, which indicates that the river was more acidic; nevertheless, they still indicate that it was healthy for human consumption and aquatic life. Thus, generally, it can be deduced that the physicochemical characteristics (dissolved oxygen, biochemical oxygen demand, and pH) of Osun River support healthy living in the aquatic ecosystem and are within the permissible levels of safe water quality for human consumption, as tourists, visitors, and residents of Osogbo rely on the river at the WHS and its tributaries for their domestic and irrigation purposes.
The presence of heavy metals in surface or sub-surface water indicates pollution, which has varying health implications for humans. However, the severity of such pollution is determined by the quantity of the pollutants present in the water in relation to the permissible level set by the WHO and/or other national or international standards dealing with human health and environmental standards, such as regulatory bodies in the country under discourse.
Arsenic (As) was one of the heavy metals examined in the water sampled from Osun River at the WHS in Osogbo, Nigeria. The source of arsenic has been attributed to increasing anthropogenic activities in the urbanization process and mining operations. As shown in Table 1, Osun River contained arsenic, with the mean values being in the order of FD > BFD > AFD at 0.01 mg/L, 0.009 mg/L, and 0.008 mg/L, respectively. Osun River was found to contain the highest mean level of arsenic (0.01 mg/L and a low standard deviation of 0.0001 mg/L) on the festival day, meeting the exact permissible level set by the WHO and NESREA. This may be connected to Osun River goddess’ devotees or adherents pouring different substances into the river during the OOF.
The presence of lead (Pb) in water consumed by humans can quickly damage the brain due to the high levels of neurotoxins in the heavy metal. It is evident in Table 1 that the Osun River at the WHS was seriously polluted with Pb, as the mean values at the three visits (BFD: 0.19 mg/L; FD: 0.29 mg/L; and AFD: 0.22 mg/L) were higher than both the national and international standards of the permissible levels of Pb in water (0.01 mg/L) set by the NESREA and WHO. The continuous usage of water from the river for domestic and irrigation purposes without treatment is unsafe for human health. The standard deviations obtained for the mean values of Pb at the three visits (BFD: ± 0.06; FD: ± 0.10; and AFD: ± 0.09) still showed that the metal substance was deposited in the river at a quantity that can cause health challenges such as cardiovascular problems in humans. Pb metal has no health benefits for humans, and its presence in the environment is hazardous to humans and aquatic life, as it is described as a highly toxic metal. The quantity of Pb in Osun River being far above the permissible levels set by the NESREA and WHO puts the city residents and tourists to the WHS, who drink and use the water for irrigation purposes, at risk of memory loss, renal dysfunction, and vascular endothelia diseases, among other life-threatening diseases [53,54].
Table 1. Physicochemical and heavy metal tests on the water sampled from Osun River.
Table 1. Physicochemical and heavy metal tests on the water sampled from Osun River.
ParametersMeans ± Standard Deviations ± Standard Errors (mg/L)Permissible [55]Permissible [56]
BFDFDAFD
DO10.4 ± 0.76 ± 0.43886.8 ± 0.10 ± 0.05773.03 ± 0.6 ± 0.34644.0 mg/L4.0–6.0 mg/L
BOD5.9 ± 0.8 ± 0.46194.3 ± 0.10 ± 0.05770.27 ± 0.8 ± 0.4619≤5.0 mg/L≤5.0 mg/L
pH6.56 ± 0.06 ± 0.03466.8 ± 0.10 ± 0.05776.57 ± 0.06 ± 0.03466.5–8.5 mg/L6.5–8.5 mg/L
Arsenic0.009 ± 0.0002 ± 0.00010.01 ± 0.0001 ± 0.000060.008 ± 0.0001 ± 0.000060.01 mg/L0.01 mg/L
Lead0.19 ± 0.06 ± 0.03460.29 ± 0.10 ± 0.05770.22 ± 0.09 ± 0.05200.01 mg/L0.01 mg/L
Chromium0.25 ± 0.02 ± 0.01150.33 ± 0.09 ± 0.05200.30 ± 0.07 ± 0.04040.05 mg/L0.01 mg/L
Cadmium0.013 ± 0.01 ± 0.00580.015 ± 0.15 ± 0.08660.11 ± 0.02 ± 0.01150.003 mg/L0.003 mg/L
Copper0.031 ± 0.03 ± 0.01730.039 ± 0.10 ± 0.05770.35 ± 0.12 ± 0.06931.0 mg/L2.0 mg/L
The maximum acceptable or permissible concentrations of chromium (Cr) in water safe for drinking by humans have been proposed as 0.05 mg/L [48] and 0.01 mg/L [49]. As shown in Table 1, all the mean values of chromium in Osun River (BFD: 0.25 mg/L; FD: 0.33 mg/L; and AFD: 0.30 mg/L) were above the permissible levels set by both the NESREA and WHO. The order of chromium pollutants in the river was FD > AFD > BFD. Thus, the level of exposure to chromium reached the peak during the festival day, and this requires urgent attention, as over exposure to chromium in water can cause liver damage.
Furthermore, the mean values of cadmium found in the water sampled from Osun River were 0.013 mg/L, 0.015 mg/L, and 0.11 mg/L BFD, during FD and AFD, respectively, which were higher than the permissible level set by the WHO and NESREA at 0.003 mg/L. This shows that this important heritage river of local/global relevance is polluted with chromium metal, and the severity of this pollution reached its peak after the festival day. The exposure of the WHS host community and tourists to chromium pollutants from Osun River poses serious implications for their health; in particular, it can result in pathophysiological conditions in children and cause bone dysfunctions and diarrhea in adults.
However, the mean values of the copper pollutant found in Osun River were below the permissible levels of 1.0 mg/L set by the NESREA and 2.0 mg/L set by the WHO. The mean value of 0.031 mg/L was obtained before the festival day, 0.039 mg/L was observed on the festival day, and 0.35 mg/L (the highest) was obtained after the festival day. Thus, during the time of this study, the quantity of copper in Osun River was not excessive, and was safe for human consumption without any health threats. Furthermore, the order of the presence of heavy metals in Osun River followed the same pattern BFD and during FD, with Cr > Pb > Cu > Cd > As, while that AFD was Cu > Cr > Pb > Cd > As (Table 1).
As illustrated in Figure 2, concentration change in heavy metal pollutants found in Osun River shows that the river pollution trend can be summarized as FD > AFD > BFD. Thus, activities during FD may have short term impact by increasing the pollution level of heavy metals in the river, particularly, chromium and lead, which are categorized as toxic heavy metals [20]. The concentration of heavy metal pollutants in Osun River AFD surpassed that of BFD (see Figure 2). This may also be an indication of residual effects of the high pollution level of the river during FD.
Culturally, the number of persons exposed to the water from the Osun River is usually expected to reach the peak on the festival day, as several attendees are usually seen carrying various containers with water from the river (Figure 3). The health implications of drinking water from this important river may be severe, as the river was evidently polluted with heavy metals and was even brown in color at the time of this study.

3.2. Assessment of Air Quality in Osogbo Sacred Grove

In assessing the air quality in Osogbo Sacred Grove (OSG), before the festival day (BFD), on the festival day (FD), and after the festival day (AFD), the parameters under examination were the total volatile organic compounds (TVOCs), formaldehyde (HCHO), particulate matter 2.5 μm in diameter and 10 μm in diameter (PM2.5 and PM10), carbon monoxide (CO), carbon dioxide (CO2), temperature, and humidity. As shown in Table 2, the level of TVOCs in the ambient air of OSG at the three visits—BFD, during FD, and AFD—with mean values of 0.014 mg/m3, 0.012 mg/m3, and 0.01 mg/m3, respectively, were very low and below the permissible level set by the WHO (0.3 mg/m3–0.5 mg/m3); the NESREA regulations only contained the permissible level of indoor air. The pattern of TVOC occurrence in the air showed a reduction from BFD to AFD (AFD < FD < BFD).
Similarly, the level of air pollutants (formaldehyde) in OSG was lower than the permissible level of 0.02 mg/m3 provided by both the NESREA and WHO. Regarding HCHO, BFD was observed to have the highest mean value at 0.01 mg/m3, followed by FD with 0.005 mg/m3, and AFD was observed to have the lowest mean value at 0.004 mg/m3. However, particles of 2.5 microns (PM2.5) and 10 microns (PM10) in the air in OSG BFD (24 µg/m3 and 31 µg/m3) were within the permissible levels provided by the NESREA at 40 µg/m3 and 150 µg/m3, respectively. Similarly, the obtained mean values of particulate matter of 2.5 and 10 microns (PM2.5 and PM10) AFD were 30 µg/m3 and 39 µg/m3, respectively, which were healthy and lower than the minimum permissible levels of 40 µg/m3 for PM2.5 and 150 µg/m3 for PM10 provided by the NESREA. However, the mean values of both PM2.5 and PM10 during FD were 182 µg/m3 and 238 µg/m3, respectively, which are unhealthy for humans after prolonged exposure and above the limits set by the NESREA. Meanwhile, the mean values of particulate matter (PM2.5) BFD, during FD, and AFD were 31 µg/m3, 182 µg/m3 (extremely high), and 30 µg/m3, respectively, which were above the permissible limit of 45 µg/m3 set by the WHO. However, only the PM10 obtained during FD (238 µg/m3) was found to be above the permissible level of 45 µg/m3 set by the WHO. It can be deduced from Table 1 that the level of air pollution with PM2.5 and PM10 on the festival day was unhealthy, and long exposure could cause severe respiratory disorders in humans.
The mean values of carbon monoxide (CO) in the air in OSG were 1 ppm (parts per million) for both BFD and AFD, and 2 ppm during FD, which were low compared to the permissible levels of 8.7 ppm set by the NESREA and between 9 and 10 ppm set by the WHO. Thus, the level of poisonous CO as an air pollutant in OSG was very low and not harmful to human health. However, the mean value of carbon dioxide (CO2) present in the air on the festival day (1309 ppm) was at the extreme and far higher than the permissible level of 250–400 ppm set by the NESREA and WHO. This may be connected to the 91,000 attendees of the grand finale of the OOF on 9 August 2024 [45]. Additionally, the mean CO2 values observed BFD and AFD were slightly higher than the permissible range of 250–400 ppm but still healthy for humans. The mean temperature values BFD, during FD, and AFD were between 28 °C and 33 °C, which were higher than the average temperature range deemed suitable for healthy human living by the NESREA at 20 °C to 25.5 °C and by the WHO at 20 °C to 24 °C. A temperature below 20 °C indicates coldness and that above 25.5 °C is hot. Thus, the temperature of OSG was the hottest (33 °C) during FD, as compared to BFD and AFD at 28 °C (Table 2). There is an inverse relationship between temperature and humidity; the mean value of humidity during FD (66%) was the lowest compared to the humidity value of 78% for both BFD and AFD. However, the humidity level at the three visits was higher than the permissible range set by the WHO at 30–50%; meanwhile, the humidity level during FD was within the NESREA standard of 40–70%, and that for BFD and AFD was 78%, above the NESREA standard. A high humidity causes dryness of the body and general body discomfort.
An overall assessment of the air quality of OSG, considering all the parameters examined in this study (TVOCs, HCHO, PM2.5, PM10, CO, and CO2) vis-à-vis the air quality index guidelines of the WHO, is presented in Figure 4. The air quality index of OSG was very satisfactory, with values of 33 and 42 BFD and AFD, respectively. However, the air quality of OSG was poor on the festival day (FD), with an index value of 232. Thus, the air quality during the 2024 Osun Osogbo Festival was poor, indicating high level of air pollution, which can lead to various health challenges in humans and be harmful for the overall ecosystem of this important World Heritage Site (WHS).

3.3. ANOVA Results on the Pollution Level of Osun River

A one-way analysis of variance was conducted to examine the significance of the variations in the water pollution level of Osun River BFD, on FD, and AFD, using physicochemical parameters (DO, BOD, and pH) and heavy metals (As, Pb, Cr, Cd, and Cu). The results presented in Table 3 show that there were no significant differences in the pH level, Pb, Cr, or Cd in Osun River BFD, on FD, and AFD, with p-values > 0.01. However, significant differences were observed for the variations in DO, BOD, As, and Cu in Osun River BFD, on FD, and AFD, with p-values < 0.01. On FD, in contrast to BFD and AFD, several substances serving as sacred materials and liquid substances are usually poured into Osun River. The ANOVA results (see Table 3) indicate that these traditional practices on FD did not significantly elevate the pollution of the river with toxic heavy metals, such as Pb, Cr, and Cd, or its pH level in relation to BFD and AFD. Thus, exposure to Pb, Cr, and Cd by the tourists and community members in Osogbo who rely on the river for domestic use does not differ BFD, on FD, or AFD. Furthermore, for the parameters (DO, BOD, AS, and Cu) with significant differences across groups (BFD, FD, and AFD), a post hoc comparison analysis was carried out to determine the exact parameter means that were significant across the groups (see Table 4).
The mean DO in Osun River on FD was not significantly different from that BFD and AFD, with p adjusted using Bonferroni correction >0.01 (see Table 4). The mean DO in the river BFD was significantly higher than that AFD (p < 0.01). Similarly, only the mean BOD in the river BFD was significantly higher than that AFD at a 99% confidence level (p < 0.01). Other comparisons across the groups showed no significant differences in the mean BOD, with p > 0.01. The level of patronage to the WHS by tourists and Osun devotees usually reduces after the festival, and this may account for the increase in the BOD available for aquatic life, through the by-product of green space at the WHS.
The mean value of arsenic (As) in Osun River on FD was significantly higher than that AFD (p < 0.01). The high arsenic content in the river on FD may have a strong connection to the substances in the different brands of drinks that tourists and Osun devotees pour into the river during the festival, as Maduabuchi et al. [57] averred that most of the beverages and drinks in Nigeria contain high levels of arsenic. The arsenic contents in the river across other groups did not vary significantly, with p > 0.01 (see Table 4). Comparisons of the Cu means across the three groups showed no significant variations at a 99% confidence level. Thus, the copper content in Osun River was not significantly influenced during the festival compared to that BFD and AFD. Furthermore, there was no significant difference in the copper content BFD and AFD.

3.4. Nexus of Urban Planning, Urbanization of Osogbo, and the Environmental Sustainability of OSG

The urbanization of Osogbo in the last few decades in the absence of a physical development plan has resulted in the urban space of the city being largely built up [40]. In recent years, anthropogenic activities in the city and the ongoing industrialization in the catchment areas of Osogbo have played significant roles in distorting the ecological system of an important World Heritage Site in the city, OSG. The sacred river in OSG turned brown in 2019 [19], and there is encroachment on the buffer zone of the heritage site. The directors and managers of planning agencies in the city (federal, state, and local governments) stated the following:
Development control by government planning agencies is making great efforts in ensuring physical developments within the capital area of Osogbo metropolis follow necessary planning standard, while there is no master plan for the city, which is a pressing physical planning problem for the city. Osogbo is fast urbanizing and its impacts on Osogbo Sacred Grove are both positive (social, economy) and negative (environment). Developments are pushed to the hinterlands of the city due to scarce space in the city; developments are encroaching on the buffer zone of Osogbo Sacred Grove and Osun River is being polluted due to mining activities and other urbanization factors. Planning agencies seek cooperation from all relevant government agencies in ensuring protection of OSG.
[see link to Supplementary Materials below: R2, R3, R4–R7]
Another major setback preventing the enforcement of planning regulations in Osogbo, as well as inhibiting the environmental sustainability drive of the heritage city, is the lack of operational urban and regional planning laws in the state. A localized planning bill relevant to the urban planning challenges of the city, and the entire state, was recently passed into law but is yet to be implemented by Osun State Government. The planning agencies also face a shortage of staff, and their main duty, which revolves around development control, is impeded by high levels of insecurity [see link to Supplementary Materials below: R2–R5].
A senior staff member of the National Commission for Museums and Monuments (NCMM) made the following remark:
Osun Osogbo Festival is very important to the development and urbanization of the city. Osogbo is a town that started with an agreement between the first settlers and Osun River goddess within OSG many centuries ago. The river goddess requested that a virgin lady from royal family must carry appeasement materials, once a year to the river in OSG, and the city will continue to grow and develop. It is this that metamorphosed into Osun Osogbo Festival which has become a global cultural festival. Since about 16th century, there was never a year that OOF did not hold. In 2020, during a total lockdown of COVID-19, the festival was held, and it was attended by 21,500 persons.
[see link to Supplementary Materials below: R1] (see also Figure 5 and Figure 6)

3.5. Future Research Directions

The level of pollution of Osun River, one of the most cosmo-historic rivers in Nigeria and a UNESCO site, calls for more intense and collaborative studies in order to ensure the eco-social sustainability of the cultural heritage site and to protect the health of tourists and Osogbo residents who depend on the river for domestic and irrigation purposes. This research is limited to the water pollution of Osun River and the ambient air at the heritage site. However, it is strongly recommended that future studies examine the actual sources of heavy metals discharge into Osun River using a relevant Geographic Information System (GIS) spatial analysis and that tests are carried out on water samples from the river at different points across the city in order to determine the severity of its pollution beyond the heritage site. Such studies should be able to propose technical solutions for the water pollution remediation of the Osun River and suggest measures to forestall the future discharge of pollutants into the river.

4. Discussion and Conclusions

4.1. Implications of Physicochemical Properties and Heavy Metal Pollutants in Osun River

The importance of clean water to human livelihood and wellbeing is eminent beyond this research. As city populations increase, threats to natural resources and urban ecosystems also increase. Although, the health implications of surface water pollution in developing countries are already a global concern [53,58], the pollution of Osun River has only received academic attention in recent years [20,46,59,60]. However, the physicochemical characteristics of the river, which include dissolved oxygen, biochemical oxygen demand, and pH, are within the range that can support aquatic life and within the permissible standards for potable water set by the WHO and NESREA. This is in line with a study by Akindele et al. [46], who concluded that the DO in Osun River during both the dry and wet seasons fell within the permissible range of 4.0 to 6.0 mg/L set by the WHO. Similarly, in this study, the BOD in Osun River (FD and AFD) was ≤5.0 mg/L, which is in line with the WHO and NESREA’s standards; however, the BOD observed BFD was slightly above the standards. On average, the BOD is sufficient for the survival of microbes responsible for the decomposition of matter in the river.
The chemical property of the river (BFD, FD, and AFD) was found to be more acidic but still within the permissible range of 6.5–8.5 mg/L set by WHO and NESREA. The influence of anthropogenic activities through waste discharge into surface water has been linked to the acidic nature of Osun River [20]. However, Anifowose et al. [20] also confirmed that the pH of Osun River is safe for human consumption, as it aligns with the international standard. Conversely, another study found that the pH of a river at a UNESCO site in Argentina, Quebrada De Humahuaca, was basic, with a mean value of 9.62 during spring, and waste dumping was blamed for the pollution of this important river [61]. Additionally, a study by Okafor et al. [62] showed a connection between the acidic nature of a river in Onitsha, Nigeria, with a pH value of 6.9, to industrial effluents discharged into major streams in the city. Thus, the physicochemical characteristics of surface water, which also determine the water quality, are largely influenced by anthropogenic activities. The mean values of the physicochemical parameters (DO, BOD, and pH) BFD were significantly (p < 0.01) higher than those AFD.
The presence of heavy metals is hazardous to human health, and over exposure to such metals can result in mortality [25]. Among the heavy metals (As, Pb, Cr, Cd, Cu, and Hg) tested in the water sampled from Osun River in OSG, only mercury (Hg) was not detected. Similarly, Hg was not detected in previous studies conducted on the pollution of the river [20,46,59]. This does not necessarily mean that Hg is totally absent from the river, as its quantity could be insignificant. The pollution of the heritage river with heavy metals is a serious concern, as the water serves not only local communities in Osogbo but also the global community. Recent studies have confirmed that Osun River is polluted with heavy metals [20,46]. Except for arsenic and copper, the proportions of lead, chromium, and cadmium pollutants found in Osun River (BFD, FD, and AFD) in this study were far higher than the permissible levels set by the WHO and NESREA. Studies by Olajire and Imeokparia [59] and Akindele et al. [46] also corroborate the findings of this study. Lead contamination of water can lead to death, especially if children are over exposed to such polluted water. According to Urban Alert [19], a river in Begaga, Zamfara State, Nigeria, was polluted with lead beyond the permissible level, and about 400 children died in the city in 2013. Similarly, a strong link has been established between lead-polluted water and intellectual disabilities in children [63]. Among the water pollutants, chromium and cadmium have been categorized as two of the top five heavy metals with high degrees of toxicity [20]; chromium can lead to skin cancer [31], while cadmium can cause kidney failure [46].
The community members in the city who rely on Osun River for domestic and irrigation purposes are vulnerable to the aforementioned health challenges. Similarly, tourists who drink from the river, particularly during the annual festival, where tens of thousands are in attendance, may also be at risk of health issues such as renal dysfunction and, cardiovascular and mental health issues, which have been associated with heavy metal pollution in water [46]. The pollution sources of Osun River were attributed to the indiscriminate discharge of industrial and urban wastes into the surface water in the city [59]. However, post-2020 studies on the contamination of Osun River with heavy metals put the blame on the increasing mining activities in the catchment areas of the city [19,20,46]. Meanwhile, the level of arsenic found in Osun River on FD was significantly higher than that found AFD (p > 0.01). This increase in arsenic may be connected to the ritual activities performed on the river, as sacred solid and liquid substances, which may contain arsenic substances, especially drinks and beverages, are poured into the river [57]. During this study, the level of arsenic in the river was found to be far below the WHO standard for drinking water; thus, tourists and the host community were not vulnerable to arsenicosis [64]. Furthermore, an ANOVA carried out in this study showed that the quantities of other heavy metals (Cd, Cr, Pb, and Cu) in the river were not significantly influenced by the festival.
In order to ensure that the UNESCO heritage river is sustainable and safe for human use and aquatic life, the approaches of the sustainable water management systems employed in South Australia, namely, the integrated urban water management (IUWM) and total water cycle system [38] can be adopted as part of the rolling plan action of the Osun State Ministry of Water Resources, to ensure wastes are not discharged into the river, but to a controlled sewage plant. Similarly, the WHS in Osogbo is significant to the livelihood and economy of the city in terms of tourism, trade, hospitality, history, cultural diffusion, spirituality, and recreational activities. Environmental preservation and protection laws have been found to be successful in the remediation and protection of several heritage rivers, namely, the River Tweed in Scotland [65], River Elbe in Hamburg, Germany [66], and the Three Parallel Rivers of Yunnan Protected Areas, a UNESCO WHS in China [64]. In the case of Osun River, as a matter of urgency, this study recommends the establishment of Osun River Protection and Preservation Agency, funded and controlled by the Nigerian government (at the federal, state, and local levels), UNESCO, and Osogbo Progressive Forum (Indigenous people of the city), with special focus on the implementation of highly effective and necessary legal instruments to forestall further pollution of the historic river, the technical remediation of the river, the continuous monitoring and preservation of the heritage site. Additionally, gold mining has been largely blamed as the cause of heavy metal pollutants in the Osun River. Thus, the Departments of Water and Environmental Sanitation (DWES) in the two main local governments (Atakunmosa East and West), that share boundaries with Osogbo where gold mining activities are carried out, need to be well-equipped, staffed, and financed in order to effectively carry out a water pollution abatement plan through the following action plans: (1) profiling all the legal and illegal gold miners in the local areas; (2) carrying out environmental auditing of the miners; (3) collaboration with NESREA and Federal Ministry of Solid Minerals Development, for the enforcement of necessary penalties on the offenders, and possibly, withdrawal or suspension of licenses of miners discharging mining wastes into water bodies; and (4) identifying means of ensuring effective remediation of polluted water bodies from the mining activities. Also, DWES across local governments in the State need to introduce environmental marshals, whose responsibilities are to control indiscriminate disposal of refuse by the members of the public, through periodic environmental monitoring patrol, with the enforcement of laws and strict penalties to the violators.

4.2. Implications of Air Quality Conditions in Osogbo Sacred Grove

OSG, a primary forest and the only surviving sacred grove in southern Nigeria, covering about 75 hectares of green land [44], has a healthy ambient air quality, and the levels of pollutants are far below the permissible levels set by the WHO. The importance of urban greenery has been demonstrated through associations with human wellbeing and balance in urban ecosystems [44,67]. However, a major festival, the Osun Osogbo Festival (OOF), is celebrated in OSG for about two weeks every August, and there is a high possibility that the air quality at the heritage site is distorted during the festival. Little academic attention has been paid to the air quality in OSG during the OOF and its health implications; however, the claim of this study is in tandem with that of Odesanya and Oyediran [21], who concluded that during the festival in 2015, local fireworks and other human activities polluted the ambient air in OSG, with the levels of PM2.5 and PM10 increasing far above the permissible levels set by the WHO.
In this study, the parameters used to examine the air quality (TVOCs, HCHO, PM2.5, PM10, CO, and CO2) in OSG, before and after the festival fell within the permissible range set by the NESREA and WHO. The mean values of all the parameters, aside from those of TVOCs and HCHO, showed that OSG was seriously polluted during the 2024 OOF. Particulate matter, particularly PM2.5, is very poisonous and can lead to various pulmonary diseases and death [50]. In OSG during the OOF, the pollution of air with PM2.5, PM10, CO, and CO2 can be attributed to the local fireworks and gun shots usually released into the air by local security outfits; the dust particles in the air due to there being a large population in an untarred environment; the driving of vehicles by dignitaries to the festival venue; and the exhalation of air by the large population, respectively. Odesanya and Oyediran [21] noted that mortality and morbidity rates soar during the OOF due to the high levels of air pollution. As the heritage site continues to attract more tourists and visitors during the annual festival, the use of local fireworks as part of the celebrations should be discouraged; parking spaces should be created away from the festival zone, and roads leading to the heritage site should be reconstructed; these changes would reduce the effect of air pollution during the OOF and create a healthy environment for the participants of the festival.

4.3. Urban Planning and Environmental Sustainability of Osogbo

Environmental sustainability remains the most important goal of urban planning [14]. The environmental challenges facing several cities in developing countries are linked to poor urban planning [10]. Osogbo, a fast-growing city with a popular UNESCO heritage site, will continue to face various dimensions of environmental challenges, including pollution, as the six planning agencies in the city have confirmed that there is no physical development plan for the city. Urban planning can only be sustainably achieved when there is a working document guiding the activities and policies of professionals in the built environment. Thus, this study recommends the engagement of adequate professionals, particularly at the local government level, so as to strengthen the enforcement and implementation of planning standards in line with a physical development plan to control urban sprawl in the city. Similarly, planning agencies need to carry out periodic follow-ups to ensure that developers follow the approved environmental impact assessment reports of their industrial and commercial developments, to protect the environment from indiscriminate waste discharge. Additionally, this study strongly recommends that the planning agencies in the city harmonize their operations and work together. Collaboration with other government agencies by carrying out environmental impact assessments of all industries in the city is a necessity, as it allows for the identification of diverse bodies in the metropolitan catchment areas that are responsible for the pollution of OSG, at UNESCO site. These activities should be accompanied by appropriate sanctions and counter-measures to forestall such an occurrence.

Supplementary Materials

The following supporting information can be downloaded at: https://drive.google.com/drive/folders/1Lzw_QRQ0TIBbuXLz_5Cb2vbFWGrU_hCz?usp=drive_link (accessed on 12 February 2025).

Author Contributions

Conceptualization, O.O. and L.B.; methodology, O.O.; software, O.O.; validation, L.B.; formal analysis, O.O. and L.B.; investigation, O.O. and L.B.; resources, L.B.; data curation, L.B.; writing—original draft preparation, O.O. and L.B.; writing—review and editing, L.B.; visualization, O.O.; supervision, L.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions of this study are presented in the article. However, any inquiry can be extended to the corresponding author.

Acknowledgments

The authors appreciate the support of Ariel University, Israel, for providing electronic materials. The authors also thank the Department of Environmental Health Sciences of Osun State University for carrying out laboratory analyses for this study. Lastly, the authors would like to thank the National Commission for Museums and Monuments, Osogbo, for their cooperation and access to records.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

COVID-19Coronavirus disease
PMparticulate matter
IUWMintegrated urban water management
ICTinformation and communication technology
EMAenvironmental management accounting
EPenvironmental proactivity
TODtransit-oriented development
SGsmart growth
NWnew urbanism
WHSWorld Heritage Site
OSGOsogbo Sacred Grove
UNESCOUnited Nations Educational, Scientific and Cultural Organization
DOdissolved oxygen
BODbiochemical oxygen demand
TVOCtotal volatile organic compound
HCHOformaldehyde
OOFOsun Osogbo Festival
COcarbon monoxide
CO2carbon dioxide
AQIair quality index
NCMMNational Commission for Museums and Monuments
ANOVAanalysis of variance
Asarsenic
Cucopper
Pblead
Crchromium
Cdcadmium
Hgmercury
BFDbefore the festival day
FDfestival day
AFDafter the festival day
NESREANational Environmental Standards and Regulation Enforcement Agency
WHOWorld Health Organization
DWESDepartment of Water and Environmental Sanitation

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Figure 1. Osogbo within Nigeria (the yellow portion is the WHS). Source: authors’ map, 2024.
Figure 1. Osogbo within Nigeria (the yellow portion is the WHS). Source: authors’ map, 2024.
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Figure 2. Concentration trend plot of heavy metal pollutants in Osun River before the festival, during the festival, and after the festival of 2024.
Figure 2. Concentration trend plot of heavy metal pollutants in Osun River before the festival, during the festival, and after the festival of 2024.
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Figure 3. A moment from the 2024 OOF at the entrance of Osogbo Sacred Grove. Source: authors’ photo, summer 2024.
Figure 3. A moment from the 2024 OOF at the entrance of Osogbo Sacred Grove. Source: authors’ photo, summer 2024.
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Figure 4. Overall air quality assessment of Osogbo Sacred Grove before, during, and after the 2024 Osun Osogbo Festival.
Figure 4. Overall air quality assessment of Osogbo Sacred Grove before, during, and after the 2024 Osun Osogbo Festival.
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Figure 5. Appeasement materials being carried to Osun River in OSG during the 2024 OOF. Source: authors’ photo, summer 2024.
Figure 5. Appeasement materials being carried to Osun River in OSG during the 2024 OOF. Source: authors’ photo, summer 2024.
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Figure 6. A decade trendline in attendance of the OOF. Source: authors’ compilation, 2024.
Figure 6. A decade trendline in attendance of the OOF. Source: authors’ compilation, 2024.
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Table 2. Air quality assessment of OSG.
Table 2. Air quality assessment of OSG.
ParametersAssessment Results at the Three VisitsPermissible [55]Permissible [56]
BFDFDAFD
TVOCs (mg/m3)0.0140.0120.01-0.3–0.5
HCHO (mg/m3)0.010.0050.0040.020.02
PM2.5 (µg/m3)24182304015
PM10 (µg/m3)312383915045
CO (ppm)1218.79–10
CO2 (ppm)4101309402250–400250–400
Temp (°C)28332820–25.5 °C20–24 °C
Humidity (%)78667840–70%30–50%
Table 3. ANOVA test on pollution level (BF, FD, and AFD) of Osun River.
Table 3. ANOVA test on pollution level (BF, FD, and AFD) of Osun River.
ParametersFPDecisionSignificant
DO128.9940.0000117p < 0.01Yes
BOD58.7180.0001p < 0.01Yes
pH9.64530.0134p > 0.01No
Arsenic (As)1500.0000075p < 0.01Yes
Lead (Pb)1.09220.3940p > 0.01No
Chromium (Cr)1.09710.3926p > 0.01No
Cadmium (Cd)1.20250.3679p > 0.01No
Copper (Cu)11.77150.0080p < 0.01Yes
Table 4. Multiple comparisons of pollution level of Osun River using post hoc test.
Table 4. Multiple comparisons of pollution level of Osun River using post hoc test.
ParametersMeanTestt-Valuesdfp Valuesp AdjustedSignificant
DOBFD: 10.4BFD vs. FD8.13432.06920.13360.0401No
FD: 6.8BFD vs. AFD13.18323.79560.00030.0008Yes (BFD > AFD)
AFD: 3.03FD vs. AFD10.73492.11100.00710.0212No
BODBFD: 5.9BFD vs. FD3.43742.06250.07200.2160No
FD: 4.3BFD vs. AFD8.61914.00000.00100.0029Yes (BFD > AFD)
AFD: 0.27FD vs AFD8.65782.06250.01190.0357No
AsBFD: 0.009BFD vs. FD−7.74602.94120.00470.0144No
FD: 0.01BFD vs. AFD7.74602.94120.00470.0144No
AFD: 0.008FD vs. AFD24.49504.00000.00160.0001Yes (FD > AFD)
CuBFD: 0.031BFD vs. FD−0.13272.35710.90491.0000No
FD: 0.039BFD vs. AFD−4.46692.24900.03740.1122No
AFD: 0.35FD vs. AFD−3.44853.87400.02740.0824No
Note: BFD: before the festival day; FD: the festival day; AFD: after the festival day; df: degree of freedom; alpha (α) level at 0.01; p adjusted using Bonferroni correction.
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Oyeleye, O.; Bigon, L. Urbanization and Environmental Sustainability: Planning Diagnosis of Symbiosis Between Osogbo City and UNESCO World Heritage Site in Osun State, Nigeria. Land 2025, 14, 707. https://doi.org/10.3390/land14040707

AMA Style

Oyeleye O, Bigon L. Urbanization and Environmental Sustainability: Planning Diagnosis of Symbiosis Between Osogbo City and UNESCO World Heritage Site in Osun State, Nigeria. Land. 2025; 14(4):707. https://doi.org/10.3390/land14040707

Chicago/Turabian Style

Oyeleye, Oyewale, and Liora Bigon. 2025. "Urbanization and Environmental Sustainability: Planning Diagnosis of Symbiosis Between Osogbo City and UNESCO World Heritage Site in Osun State, Nigeria" Land 14, no. 4: 707. https://doi.org/10.3390/land14040707

APA Style

Oyeleye, O., & Bigon, L. (2025). Urbanization and Environmental Sustainability: Planning Diagnosis of Symbiosis Between Osogbo City and UNESCO World Heritage Site in Osun State, Nigeria. Land, 14(4), 707. https://doi.org/10.3390/land14040707

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