Anthropogenic Impacts on Physicochemical and Heavy Metal Concentrations of Ogbor Hill River Water, Southern Nigeria

Abstract

The present study assessed the effects of human pressure on the surface water quality of the Ogbor Hill River, southern Nigeria. This river is among one of the important rivers in Southeast Nigeria for domestic, agricultural and industrial purposes. To assess the water quality, samples of water were collected monthly for eight months, and were preserved and transferred to the laboratory for further analysis. Electrical conductivity, pH, total dissolved solids, salinity, turbidity and temperature were determined in situ. Other parameters were determined in the laboratory using standard laboratory methods. The results revealed that the mean pH was acidic across the months with no significance difference (p > 0.05). Additionally, the mean total dissolved solids showed a significant difference (p < 0.05), with a higher value of 582.10 ± 83.41 in April and a lower value of 243.67 ± 40.62 in May. The highest mean conductivity of 1392.33 ± 156.18 was observed in April, and the lowest mean of 289.33 ± 97.37 in May. Dissolved oxygen indicated there was a significant difference among the study months (p < 0.05), with the highest mean concentration of 4.80 ± 0.37 in June and the least of 3.30 ± 0.20 in April. Biochemical oxygen demand, chloride and temperature all showed a significant difference (p < 0.05) across the sampling months. The mean concentration of Zn showed no significant difference among the study months. The mean concentration of Fe recorded showed the highest value of 2.68 ± 0.16 in April and the lowest mean of 1.96 ± 0.13 in July. Pb showed a higher concentration of 0.44 ± 0.33 in March and a lower mean of 0.033 ± 0.008 in July. A higher mean Cd of 0.052 ± 0.004 was observed in March and a lower mean of 0.023 ± 0.002 in December. Generally, the water parameters were elevated beyond the threshold for surface water, which was an indication that the river water was badly impacted due to human pressure and needed to be kept safe for human use. The present study revealed that most of the water quality parameters such as TDS, DO, BOD, pH, turbidity, and concentrations of the heavy metals Pb and Cd were higher in selected months, and further water management should be carried out while anthropogenic activities should be reduced around the river ecosystem.

1. Introduction

Rivers represent a significant source of water used for human consumption, irrigation, aquaculture, hydroelectric power generation and other industrial purposes [1]. Conversely, river water remains one of the most threatened natural resources globally, due to anthropogenic impacts emanating from industrialisation and urbanisation, and unregulated use of agrochemicals such as inorganic fertilizers, herbicides and pesticides, which empty into the river ecosystem as runoffs, thereby causing impairment and distortion in the water quality [2]. For efficient and effective management of river resources, requisite information on the water quality of the river is needed, and this includes knowledge of physical, chemical and biological properties [3], and this is to ensure the river water is maintained below certain threshold levels, which will guarantee a healthy aquatic system for humans, plants and benthic organisms. However, understanding of the anthropogenic impacts on river water plays a pivotal role in sustainable management and remediation strategies of the river ecosystem [4,5].

All over the world, studies on anthropogenic disturbances are considered one of the top most areas that need attention by different researchers because of their link with climate change, rise in sea levels, water pollution and other negative environmental impacts [6]. Previous studies on influences of anthropogenic activities on river water have reported increased water pollution all round the world, despite the global demand for freshwater being projected to rise by 2050 to one-third, and industrial, agricultural and domestic discharges are considered key sources of waste causing environmental degradation, particularly in the aquatic ecosystem [7,8]. Moreover, there are reports of seventy thousand unidentified chemicals in circulation in the global market outside the three hundred thousand chemicals known and registered for use. Many of them contain toxic compounds, and hydrophilic, volatile and non-biodegradable elements like heavy metals, which enter into the aquatic environment as liquid discharges, solid wastes and gaseous emissions, causing unprecedented harm to humans and their environment [8,9,10].

The challenges of elevated heavy metals in an aquatic environment have also been reported to affect various ecological properties of river water across the globe [11,12]. Heavy metals are known as pollutants due to their eminent toxicity, bioaccumulation, tenacity and non-biodegradable nature when they are found in aquatic environments [13]. The rate of heavy metal enrichment in surface water has drastically increased in recent times due to increases in anthropogenic activities. Theses metals can enter the aquatic environment via untreated wastewater, effluent discharges from mechanic work, boat making, metallurgy, pesticidal and fungicidal sprays, debris of corroded materials and petroleum exploration. When these potentially toxic elements gain entrance into the aquatic ecosystem, they undergo both physical and chemical changes and, in some cases, enter the food chain through bioaccumulation and biomagnification in some aquatic species [14]. The availability of heavy metals within surface water like rivers can be detrimental to human health when they are eventually absorbed and accumulated in fish tissues, and later consumed by humans [15]. According to Gad et al. [16], heavy metals in their elevated state are poisonous even though some of them are essential for life in living organisms.

Apart from heavy metals, such as Cd, Cu, Cr, Fe, Mn, Ni and Pb, which are regarded as major indicators of water quality, physicochemical parameters like DO, BOD, TDS, EC and pH are also considered essential markers for determining the suitability of river water for both aquatic life and domestic use [16,17]. Thus, the elevation of these physical and chemical parameters beyond the threshold of quantification impacts the water quality negatively and leads to serious health hazards for drinking water used within the local area, with regional implications [18,19,20]. The physicochemical properties of an aquatic system also influence the diversity and abundance of living organisms, and any negative impacts on these parameters will have inimical effects [21,22]. Consequently, the degradation in physicochemical parameters impacts the water quality negatively, leading to water-borne diseases such as diarrhoea, dysentery and jaundice, particularly in developing countries like Nigeria where a good number of people in rural communities depend on the river water for their livelihood.

In Nigeria and some other parts of the world, it is notable that people live close to the river because of the well-being and health benefits they derive [2,23], and one such river is the Ogbor Hill River in southern Nigeria. The Ogbor Hill River is a freshwater river of significant importance that provides drinking water for many communities around the watercourse and harbours flora and fauna biodiversity to maintain ecological balance and support livelihoods. Meanwhile, different researchers have reported the water quality of the Ogbor river to be moderately good [24,25,26]. With the recent proliferation of industrial activities, and commercial and infrastructural development around the Ogbor Hill River, there is need to evaluate the impacts of anthropogenic disturbance in the river water quality of Ogbor using indicators and markers like physicochemical and heavy metal parameters.

Therefore, a study on the anthropogenic impacts on physicochemical and heavy metal concentrations of the Ogbor Hill River was necessitated due to a paucity of recent data to this effect. The study aimed to assess the impacts of human pressure on the suitability of the Ogbor Hill River water for domestic and agricultural use by comparing the physicochemical and heavy metal parameters with the standard limit imposed for drinking water by the World Health Organization (WHO). Data obtained from the study will provide background information to the government and water management authority to plan water treatment and remediation strategies of the river ecosystem.

2. Materials and Methods

2.1. Study Area

The present study was carried out in the Ogbor River in the commercial city of Aba, Southeast Nigeria (Figure 1). The area lies between longitudes 7°15 to 7°40 east and latitude 5°05 to 5°30 north. The city of Aba has a population of over 1,277,300 people and covers an area of 72 km². The Ogbor Hill River is located within the city of Aba, a beehive of many small and multinational industries, playing host to the popular Ariaria international market and other marketing activities. The area is prominently known for its abattoir businesses, sand mining, mechanic workshops, electrical and battery recharges, shoe making, oil milling, paper production and other manufacturing activities. With this array of anthropogenic activities going on within the city of Aba, the area has experienced indiscriminate waste generation that empties as runoff into the Ogbor Hill River and, as a result, the river has become an aquatic ecosystem of great research interest because of its usefulness to city dwellers. Sampling hotpots were carefully selected within the Ogbor Hill River to have a good representation of spatial variability of quality indicators of water quality monitoring, and this was based on different activities around the hotpots.

The Ogbor Hill River is a tributary of the Imo River located in the city of Aba, Abia State, Nigeria. The river flows from the Ngwa rural territories of Aba down to Opobo, and empties alongside its creeks into the Atlantic Ocean through Ikot Abasi (Figure 1). The area is situated within the humid tropical climate, with an average yearly precipitation of 2285 mm, with March to November being the wet season, and the dry season from November through to early March, with characteristic higher temperatures and windy weather. The study location is part of the Niger Delta Basin underlain by the Benin formation from the Miocene to the recent age, and the formation is made up of friable fine-to-coarse-grain sand with minor intercalations of clay and gravel [24].

2.2. Sample Collection

Water samples for the assessment of physicochemical characteristics were collected in a 1-litre plastic bottle and kept in an ice chest until analysis within 24 h. A 75 mL amber bottle was used to provide a suitable place for future determination of dissolved oxygen (DO), and the samples collected were fixed onsite using Winkler 1 and 2. Five drops of conc. H₂SO₄ acid was added to the sample to dissolve the precipitate formed, while another 75 mL amber bottle was used to collect water samples for the determination of biochemical oxygen demand (BOD). For determination of heavy metal levels, a 120 mL glass bottle was used to collect water samples, 5 drops of conc. HNO₃ was then added to the samples for preservation before the analysis. Sample collection was done for 8 months (December 2019 to July 2020), being four months of dry and four months of rainy seasons.

2.3. Sample Analysis

Water samples were analysed in situ for electrical conductivity (EC) and total dissolved solids (TDS) using a handheld Hanna portable conductivity meter using the conductometry analytical method. Water temperature was analysed with a mercury-in-glass thermometer using the temperature probe analytical method, pH was analysed with an electric digital pH meter (Jenway ltd model 350 pH meter) using the pH probe analytical method, and water turbidity was analysed with a turbidity meter (Turner designs Aqua fluor 8000-001) using the turbidimetry method [27]. All other in situ measurements were done using the previous methods provided by Okey-Wokeh et al. [28]. Heavy metal parameters (Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn) were analysed with the use of a Perkin Elmer 300 Spectrophotometer (AA), and the instrument was calibrated according to the manufacturer’s standard using standards and blanks. However, the analytical calibration curve was set up according to the calibration solution standard (Merck, Germany) at the appropriate wavelength and concentration for each metal. The analysis of heavy metals and physicochemical parameters such as DO, total hardness (TH), BOD, chloride and HCO₃⁻ were measured in the laboratory using conventional analytical techniques outlined by APHA [29].

2.4. Quality Control and Quality Assurance

Quality control and assurance were applied throughout the experimental process. First, the equipment used for sampling was washed with water and laboratory-graded detergent and, thereafter, rinsed with methanol and allowed to dry. The equipment used on-site was calibrated according to the manufacturer’s standard, and system verification was carried out to ensure the calibration range was not less than three linear concentration points. Repeated analyses of the samples were performed against spectrochemical grade BDH reference metal solutions that were globally recognised in order to ensure accurate instrument reading and accuracy of the analytical technique. The samples were examined for the content of heavy metals (Cd, Cr, Ni, Mn, Ni, Zn, Fe and Pb) using a Perkin Elmer Spectrophotometer (AA) 300.

2.5. Statistical Analysis

Data of physicochemical and heavy metal levels obtained in this study were statistically analysed using a one-way analysis of variance (ANOVA) to determine any significant difference at the 95% interval across the sampling months.

3. Results and Discussion

The results of physical and chemical parameters obtained from the Ogbor River water samples for eight months, as shown in

Table 1. Summary of mean physicochemical properties of surface water parameters of Ogbor River.

Months/Parameters	December	January	February	March	April	May	June	July
pH (mg/L)	6.20 ± 0.50 a	6.10 ± 0.20 a	6.23 ± 0.42 a	6.37 ± 0.58 a	6.06 ± 0.23 a	6.42 ± 0.65 a	6.73 ± 0.55 a	6.13 ± 0.31 a
Temp (°C)	28.10 ± 0.30 c	29.00 ± 0.27 d	29.37 ± 0.31 de	29.60 ± 0.20 e	29.80 ± 0.27 e	25.97 ± 0.38 b	24.65 ± 0.47 a	24.73 ± 0.35 a
EC (µS/cm)	970.03 ± 53.32 b	1256.38 ± 293.08 c	1281.0 ± 189.45 c	1357.0 ± 181.06 c	1392.33 ± 156.18 c	289.35 ± 97.37 a	306.67 ± 98.33 a	398.0 ± 72.0 a
Salinity (mg/L)	13.43 ± 4.40 b	16.51 ± 5.15 bc	17.06 ± 1.32 bc	20.49 ± 1.26 c	20.39 ± 2.82 c	5.60 ± 1.48 a	4.53 ± 0.62 a	4.51 ± 0.77 a
Turbidity (NTU)	23.56 ± 3.66 c	25.14 ± 2.37 c	14.60 ± 3.61 ab	16.00 ± 0.75 b	10.68 ± 1.79 a	18.33 ± 1.53 b	26.39 ± 2.15 c	26.7 ± 2.95 c
TDS (mg/L)	369.09 ± 39.79 bc	409.93 ± 30.02 c	524.53 ± 87.30 d	564.53 ± 73.89 d	582.10 ± 83.41 d	243.67 ± 40.62 a	263.0 ± 33.71 a	273.67 ± 26.08 ab
DO (mg/L)	4.03 ± 0.21 bc	3.93 ± 0.47 bc	3.73 ± 0.45 ab	4.07 ± 0.15 bc	3.30 ± 0.20 a	4.47 ± 0.33 cd	4.80 ± 0.37 d	4.42 ± 0.39 cd
BOD (mg/L)	3.28 ± 0.15 ab	6.59 ± 5.53 b	2.76 ± 0.54 ab	3.02 ± 0.17 ab	2.86 ± 0.09 ab	4.00 ± 0.81 ab	3.25 ± 0.67 ab	2.63 ± 0.12 a
HCO3− (mg/L)	4.90 ± 0.26 b	6.03 ± 1.09 b	5.41 ± 1.19 b	9.36 ± 0.95 d	7.40 ± 0.67 c	1.72 ± 0.56 a	1.45 ± 0.29 a	2.27 ± 0.18 a
Cl− (mg/L)	7.42 ± 2.44 b	9.12 ± 2.84 bc	9.41 ± 0.73 bc	11.30 ± 0.70 c	11.25 ± 1.55 c	3.09 ± 0.82 a	2.49 ± 0.34 a	2.41 ± 0.46 a
Hardness (mg/L)	37.97 ± 9.63 b	46.72 ± 9.27 b	44.12 ± 6.07 b	44.60 ± 1.81 b	25.56 ± 2.69 a	18.22 ± 3.84 a	20.10 ± 4.35 a	26.46 ± 3.29 a

Note(s): In each row, means with a common letter are not significantly different (p > 0.05).

, revealed there was a higher mean value of pH observed in June (6.73 ± 0.55), while the least mean value (6.06 ± 0.23) was observed in April, this being the onset of the rainy season in southern Nigeria. The concentration of water pH showed no significant difference (p ˃ 0.05) across the sampling months. The pH of the water is one of the fundamental water parameters used to check both the acidity and alkalinity of water in order to determine the usability for human consumption and irrigation [17]. The result of water pH, as seen in this study, revealed a higher mean value in June, while the least mean value was obtained in April, this being the onset of the rainy season in the southern parts of Nigeria. The values of pH obtained across the months were slightly acidic, and fell below the WHO [30] recommended limit for surface water quality, except for the value recorded in the month of June. The lower values of water pH observed in this study is indicative of water quality that is badly impacted by anthropogenic wastes such as industrial effluents, sewage discharge and abattoir waste [26]. The result of water pH observed in the Ogbor River system is aptly comparable with the values previously reported by Anyanwu et al. [31] in the Ikwu River, South-east Nigeria. Natural water with a pH value below 6.5 affects the growth and survival of water-dependent organisms like fish [32], while a pH value greater than 6.5 influences the ability of some aquatic species to preserve their salt equilibrium, which can also bring about decline in reproductive performance until the pH value is restored to normal [2,33].

The mean value of water temperature showed there were lower values of temperature in core months of the rainy season compared with the dry season. Higher mean temperatures were observed in February (29.37 ± 0.31), March (29.60 ± 0.20) and April (29.80 ± 0.27), with no significant difference (p ˃ 0.05) between them, but they were significantly different from the values recorded in May (25.97 ± 0.38), June (24.65 ± 0.47) and July (24.73 ± 0.35). The values of water temperature were significantly higher in the months of December to March, being the dry season, and in April, being the onset of the rainy season, but the values were lower in the months of May through to July, this being the rainy season. The higher mean values of water temperature observed in the dry season are common characteristics in most tropical aquatic ecosystems [34]. Generally, the water temperature documented in the Ogbor River was within the recommended value for surface water. Similar results were previously observed in some aquatic ecosystems in the Niger Delta [17,35]. Water temperature is considered as one of the strongest physicochemical properties due to its influence on oxygen solubility, microbial activities and other chemical reactions that go on in water [36].

The mean values of salinity showed that the values recorded in December through to April were higher, with visible statistical variation (p < 0.05) between them. The mean salinity recorded in March (20.49 ± 1.26) had the highest mean concentration, while the value observed in July (4.51 ± 0.77) was the least. Salinity is referred to as the amount of saltiness of a water body, which is a dynamic indicator of the nature of the exchangeable system expressed as the total concentration of electrical charge ions [37]. The mean values of water salinity showed that values obtained in the months of December through to April were higher, with March as the highest, while the mean values observed in May through to July, this being the rainy season, were lower, with the value observed in July recording the least. Onojake et al. [38] reported similar observations of higher salinity in the dry season at the New Calabar River, attributed to the increase in evaporation because of high sun intensity in the tropics. The lower mean values of salinity observed in the months of May through to July could be due to the dilution effect of water inflow into the river system during the rainy season [39]. The overall result of salinity across the eight months revealed that the values obtained from the river water fell below the 1000 mg/L recommended by the WHO [30] for freshwater. This indicates that the Ogbor River is a freshwater ecosystem. Higher values of salinity in a freshwater system have been noted to bring about elevated water temperatures and incidentally increased bioavailability of heavy metals [40]. The increase in salinity content of a freshwater system is an indication of an anthropogenic pressure such as sewage discharge, which will affect growth and deplete freshwater biota [41].

The concentration of electrical conductivity (EC), presented in Table 1, showed there was a higher mean value of EC observed in April (1392.33 ± 156), March (1357.07 ± 181.06) and February (1281.0 ± 189.45), with no observable significant difference (p > 0.05). The mean EC concentrations observed in December (970.03 ± 53.32), May (289.35 ± 97.37), June (306.67 ± 98.33) and July (398.0 ± 72.0) revealed there was a significant difference (p < 0.05. Electrical conductivity (EC) is a measure of the ability for water to conduct electric current and is an excellent indicator of salinity. The EC mean values were higher during the dry season (December–March) except for April, this being the onset of the rainy season. All the values of EC obtained in the dry season (Dec–March) were above the WHO [30] recommended standard limit, except for the value observed in the month of January, while the values recorded in the rainy season (April–July) fell below the standard, except for the month of April. The higher values of EC observed in this study could be attributed to high contents of dissolved ions in the water body caused by anthropogenic impacts such as discharges of industrial effluents, sewage and other waste materials. The highest mean concentrations of turbidity were observed in the months of July (26.70 ± 2.95) and June (26.39 ± 2.15), while the mean values recorded in April (10.68 ± 1.79) and February (14.60 ± 3.61) were the least observed across the sampling period.

The turbidity values measured in all the months were beyond the allowed limit for surface water, indicating the consequences of anthropogenic pressure on water quality. The turbidity values observed in this study might be related to major activities such as sand mining, erosion and industrial effluent discharges into the water body. The turbidity results of this study agree with those of Onojake et al. [38] in the New Calabar River and Amah-Jerry et al. [8] in the Aba River. The implication of higher values of water turbidity is that it will affect light penetrations in water and the photosynthesis rate, thereby making food availability difficult for the aquatic organisms [42].

The mean value of TDS followed a similar pattern to that of EC, and the values recorded in April (564.53 ± 73.89) and February (524.53 ± 87.30) showed higher concentrations than in other months. The mean value obtained in April was above the value recommended as standard for surface water. The higher TDS values observed in the dry season could be attributed to the concentration factor and reduction of water volume due to evaporation. The presence of TDS in an elevated value in the Ogbor River will affect the taste of water, influence osmoregulation of the freshwater organisms and reduce oxygen solubility in the water body [43,44].

The monthly mean value of DO revealed that the concentration recorded in June (4.80 ± 0.37) was significantly different from other months, except May (4.47 ± 0.33) and July (4.42 ± 0.34), these typically being in the rainy season. The monthly mean values of dissolved oxygen (DO) showed that there were higher values obtained in the months of May through to July, with the value recorded in June as the highest. The least DO value observed in the study was in April, this being the onset of the rainy season. This observation was consistent with the finding of George and Abowei [40] in the upper New Calabar River. The result indicates that higher DO values were observed in the rainy season (May–July), and this was attributed to low water temperature that allowed solubility of gases [45,46]. Generally, DO values observed in the Ogbor surface water system fell below the WHO recommended standard for surface water [30]. Similar observations of low DO levels have been reported in the past in some aquatic ecosystem in the Niger Delta, due to impacts of human pressures such as abattoir discharges, industrial effluents, sewage disposal and oil exploration [26,40,45]. Water DO is one of the basic physicochemical parameters that depicts water quality, and it is commonly used to evaluate the degree of river freshness to determine organic pollution. Its depletion will adversely affect the metabolism of the biological community and aquatic life [47,48].

The mean concentration of BOD showed the value observed in January (6.59 ± 5.53) was highest; while the concentration recorded in July (2.63 ± 0.13) had the least observed value. Biochemical oxygen demand (BOD) values in this study showed that the value obtained in January had highest mean, which was above the WHO [30] accepted limit for surface water, while the mean value recorded in July was observed to be the least in all the months. The values of BOD fluctuated in both the rainy and dry seasons based on the pattern of the anthropogenic impacts that brings about loads of organic matter into the water body [49]. All the values of BOD observed across the months were within the 5 mg/l recommended standard for drinking water, except for the month of January where the value exceeded the acceptable limit. However, Afolabi et al. [43] posited that any water with a BOD value within 2–3 mg/L was termed contaminated and was unwholesome for human consumption. The mean chloride values recorded in March and April were substantially higher than the lower concentrations of Cl⁻ found in June and July. All the readings recorded from December to July were below the WHO [30] limit of 250 mg/L for fresh water. The low Cl⁻ values found in this study were previously observed in the Aba River [26]. This result supports the argument that Cl⁻ concentrations in natural water are typically low (Smitha and Shivashanker, 2013). Chloride in natural water indicates the presence of organic waste, particularly that of animal origin [44], and this was abundant around the Ogbor watercourse due to the presence of an abattoir in the area.

The results of TH showed that the values obtained in the dry season (Dec–March) were higher than the values obtained in the rainy season (April–July), with January recording the highest mean value while the lowest mean was observed in May. Low values of water hardness recorded in the rainy season could be attributed to the dilution effect of water runoff, and this conforms to the report of Dapam et al. [49] in River Jibam, Plateau State, Nigeria. The concentration of total hardness (TH) observed in this study was generally low and fell far below the acceptable WHO standard [30]. Water hardness has been reported by Mitharwal et al. [50] as a useful parameter to check the suitability of water for both domestic and industrial purposes.

The results of HCO₃⁻ concentration showed that the highest mean (9.36 ± 0.09) was observed in March and the lowest value of 1.45 ± 0.29 was recorded in June. The mean value of bicarbonate (HCO₃⁻) showed that the highest value occurred in March, while the lowest value was observed in June. As in the situations of EC and TDS, the trends in HCO₃⁻ might be the consequence of seasonal impacts [48]. HCO₃⁻ readings, in both the dry and rainy seasons, were below the 100 mg/L acceptable limit established by the WHO [30]. The low HCO₃⁻ values recorded in this study were similar to those reported by [51] in the Kwa River, which was indicative of the river being a soft water.

The mean summary of eight months of results for heavy metal concentrations, presented in

Table 2. Summary of mean heavy metals ion concentration in surface water of Ogbor River.

Heavy Metals	December	January	February	March	April	May	June	July
Fe2+ (mg/L)	2.250 ± 0.399 ab	2.433 ± 0.351 b	2.607 ± 0.313 b	2.573 ± 0.061 b	2.683 ± 0.162 b	2.250 ± 0.202 ab	2.503 ± 0.015 b	1.960 ± 0.131 a
Pb2+ (mg/L)	0.052 ± 0.011 a	0.049 ± 0.034 a	0.329 ± 0.298 ab	0.436 ± 0.326 b	0.051 ± 0.011 a	0.049 ± 0.015 a	0.051 ± 0.021 a	0.033 ± 0.008 a
Cr2+ (mg/L)	0.048 ± 0.011 ab	0.059 ± 0.008 b	0.042 ± 0.005 ab	0.060 ± 0.021 b	0.045 ± 0.005 ab	0.036 ± 0.005 a	0.043 ± 0.036 ab	0.032 ± 0.005 a
Cu2+ (mg/L)	0.528 ± 0.349 ab	0.621 ± 0.488 b	0.800 ± 0.159 b	0.023 ± 0.152 a	0.528 ± 0.350 ab	0.498 ± 0.273 ab	0.472 ± 0.142 ab	0.061 ± 0.020 a
Cd2+ (mg/L)	0.023 ± 0.002 a	0.031 ± 0.009 b	0.036 ± 0.016 b	0.052 ± 0.005 c	0.039 ± 0.009 bc	0.038 ± 0.006 bc	0.027 ± 0.004 b	0.025 ± 0.003 b
Zn2+ (mg/L)	1.076 ± 0.939 a	0.359 ± 0.571 a	0.931 ± 0.209 a	0.689 ± 1.152 a	1.086 ± 0.959 a	0.413 ± 0.319 a	0.647 ± 0.149 a	0.111 ± 0.013 a
Ni2+ (mg/L)	0.042 ± 0.011 c	0.023 ± 0.013 b	0.001 ± 0.00 a	0.001 ± 0.00 a	0.003 ± 0.001 a	0.001 ± 0.00 a	0.002 ± 0.001 a	0.007 ± 0.004 a
Mn2+ (mg/L)	0.221 ± 0.25 b	0.078 ± 0.014 ab	0.060 ± 0.008 ab	0.065 ± 0.007 ab	0.064 ± 0.004 ab	0.056 ± 0.006 ab	0.043 ± 0.006 ab	0.018 ± 0.002 a

Note(s): In each row, means with a common letter are not significantly different (p > 0.05).

, was differentiated from the international (WHO) permissible limit for human drinking water levels. The highest Fe²⁺ concentration (2.683 ± 0.162 mg/L) was observed in April, which showed no significant difference (p > 0.05) from the data generated in other months, except for July (1.960 ± 0.131 mg/L), which recorded the lowest value. The results of Fe²⁺ analysis in the Ogbor River system showed there were higher values of Fe²⁺ through all months. The Fe²⁺ values observed in all months were above the 0.3 mg/L stipulated as safe for water by the World Health Organization (WHO). Significant reports from several researchers have confirmed a geological abundance of Fe, which may be the cause of the abundance of Fe²⁺ in surface water due to runoffs [52,53]. The noticeable increase in Fe²⁺ concentrations in this study was attributed to diverse anthropogenic activities that generate Fe-bearing wastes that empty into the river. The consumption of water with an Fe²⁺ content above the threshold is capable of causing health problems such as cirrhosis of the liver, and heart and nervous system related diseases, as well as liver cancer and infertility in some cases [54].

The Pb²⁺ value observed in March (0.436 ± 0.326 mg/L) was the highest mean while the mean value documented in July (0.033 ± 0.008 mg/L) was the lowest. The Pb²⁺ concentration observed in March showed a significant difference (p < 0.05) from the mean values recorded in other sampling months, except for the value observed in February. All the values of Pb obtained in this study exceeded the 0.01 mg/L recommended for surface water [30]. The higher values of Pb²⁺ generally observed in this study could be due to dense mechanical activities, industrial effluent discharges and other consequential human impacts prominent around the Ogbor hill area of Aba [55]. Elevated concentrations of Pb²⁺ due to increased human impacts on surface water have been similarly reported by [38,56] in the past. The higher values of Pb²⁺ observed in this study are capable of causing high blood pressure and anaemia in humans when water contaminated with Pb is consumed, and can result in formation of coagulated mucus over the gills of fish, which leads to death in ponds [57].

Similarly, the value of Cr²⁺ was higher in March (0.060 ± 0.02 mg/L) and January (0.059 ± 0.008 mg/L), while the lowest mean concentrations were recorded in July (0.032 ± 0.005 mg/L) and May (0.036 ± 0.005 mg/L). The values of Cr²⁺ recorded across the months were below the 0.05 mg/l stipulated standard for surface water, except in January and March, which exceeded the WHO [30] limit. The higher values of Cr²⁺ in these months could be due to the increased anthropogenic and natural sources. Similar observations were previously reported by Onojake et al. [38], but varied with the findings reported by Okey-Wokeh and Wokeh, [15] in the Mini-Ezi stream. However, when Cr²⁺ is found in a higher concentration it can be toxic, causing eczematous dermatitis, and paranasal sinus and lung [58]. Even the moderate Cr²⁺ values observed in months that fall within the rainy season in southern Nigeria call for close monitoring of the river water to avoid unimaginable and untold risk that could result from elevated Cr²⁺ values in water.

The mean Cu²⁺ observed in February (0.800 ± 0.59 mg/L) recorded the highest concentration and the lowest value (0.023 ± 0.152 mg/L) was observed in March. The concentration of Cu²⁺ observed in this study fell below the 2 mg/L admissible limit stipulated by the WHO [30]. The result of Cu²⁺ obtained in the present study was similar to the findings of Bhuyan et al. [59], in the Old Brahmaputra River, Bangladesh. The low concentration of Cu²⁺ observed in this study was attributed to little input of anthropogenic sources on the release of materials with high Cu content into the Ogbor water body. Cu is an essential element required in minute concentration of 0.9 mg for an adult, and any form of elevation beyond the threshold for proper biological function results in consequential effects such as hepatic and renal damage [60].

The higher mean concentration of Cd²⁺ recorded in March (0.052 ± 0.005) showed a significant difference from the value observed in other months, except for April (0.039 ± 0.009 mg/L) and May (0.038 ± 0.006 mg/L). According to the result observed, the Cd²⁺ mean in this study revealed that the highest Cd²⁺ concentration was found in March. The higher mean value observed in March could be attributed to the evaporation effect caused by increased sunlight. The Cd²⁺ value observed in this study was significantly higher than the 0.003 mg/L permissible limit recommended for surface water, which indicates that the river is highly polluted with toxic metals like Cd²⁺. The Cd²⁺ value recorded in this study is in consonance with the values previously reported in some aquatic systems badly impacted by anthropogenic activities [61,62]. The high amount of Cd²⁺ found in the Ogbor River may have been caused by domestic garbage and emissions from nearby well-known industries [63]. Cadmium is a non-essential metal that can induce proteinuria, tubular lesions, renal cancer and liver cancer when it accumulates in human organs [63].

The concentration of Zn²⁺ showed no significant difference (p > 0.05) across the sampling months. The mean values of Zn²⁺ recorded in the months December to July showed that the value obtained in December was the highest mean. From the overall results of Zn²⁺, the mean values observed in all the months were below the 3 mg/L acceptable limit of the WHO for surface water [30]. Low Zn²⁺ concentrations in some aquatic environments within the Niger Delta have previously been reported by Nwankwoala and Ekpewerechi [11] in the Waterside River Ogbor Hill. This finding agrees with the assertion of Seiyaboh and Izah [64] that most essential metals, like Zn, are always within the recommended standard in surface water except in few cases. The mean Ni²⁺ recorded in December (0.042 ± 0.011 mg/L) was significantly higher than the value obtained in other sampling months. According to the seasonal fluctuation in the concentrations of Ni, the values recorded in all the months were under the limit, with the exception of the result observed in December, which was marginally above the 0.02 mg/L acceptable limit for surface water [30]. The results of this study’s analysis are comparable to the Ni values reported for the Bonny/New Calabar River [38].

The mean concentration of Mn²⁺ recorded in December (0.221 ± 0.25 mg/L) was the highest, and showed no significant difference (p > 0.05) from other mean values recorded in other months, except for July (0.018 ± 0.002), which had the lowest value. Higher values of Mn²⁺ were generally observed in the dry season rather than the rainy season, which recorded values that were within the 0.05 mg/L recommended for drinking water, except for April and May, which were slightly higher. Mn is essential particularly in early life development because it functions as a co-factor in several enzymes, and it is needed for proper biological functioning [65]. Increases in the level of Mn beyond the body usability can lead to toxicity, which results in neurological and neuromuscular impairment [66].

4. Conclusions

This study evaluated the anthropogenic impacts of physicochemical and heavy metal parameters on the Ogbor Hill River water quality systematically, and, based on the results, it was concluded that the water quality of the Ogbor River is generally contaminated and unfit for drinking and aquaculture use. This is supported by the mean concentrations of some key physicochemical and heavy metal parameters (DO, TDS, pH, BOD, EC, turbidity, Cd, Fe and Pb) investigated that fell short of standards imposed for surface/drinking water by the Environmental Regulatory Agencies. Thus, the river water in its current state poses health risks for humans and aquatic life. Therefore, the findings of this study present vital information for the government, water managers and other critical stakeholders on the need to carry out water treatment and develop remediation strategies for the Ogbor Hill River as a way to safeguard the health of communities that depend on this water body for drinking and as means of livelihood. Meanwhile, data on the biological parameters of this river are needed, and we recommend further study on this river.