Abstract

INTRODUCTION

Water is one of the most abundant and important compounds in the ecosystem. All the organisms that are living on earth need water for survival and growth. The pollution of water causes diseases which result to the death of million people. Safe drinking water is one of the natural resources and a basic need for the survival and development of all humans (1, 2). Often, the source and potability of water supply are reflected on the health conditions of communities as bacteriological contamination of water is the primary cause of disease outbreaks in many communities particularly in many developing countries (3). Water can be grouped into surface water (such as oceans, rivers, lakes, reservoirs, lagoons, streams), ground water (which is regarded as a purer source of water than any type of surface water) and then rain water (which is as a result of the clouds condensing and precipitating).

Surface water usually contains components that must be eliminated before it could be considered potable while groundwater is expected to be contaminant-free. Numerous places, worldwide receive their water sources from surface waters, such as rain, creeks, rivers, lakes, etc and therefore, it is essential to ensure that these surface sources of water are contaminants free. Rivers provide a variety of services for human populations, including water for drinking and irrigation, recreational opportunities, and habitat for economically important fisheries (4). The increasing problem of river ecosystem pollution has necessitated the monitoring of water quality. Rivers are a major source of water for different purposes for highly populated residential areas. A river’s flow is affected by surface run-off, direct precipitation; interflow, and water table discharge. The physicochemical and biological components of the various flows influence the quality of the river and other surface waters. The quality of the river water is also influenced by the atmospheric inputs, climatic conditions, lithology of the basin, and anthropogenic inputs (5, 6).

Rivers play a major role in the accumulation and carrying off of municipal and industrial wastewater and runoff from agricultural land. The assimilation of waste constitutes of constant polluting non-point sources while runoff of municipal and industrial wastewater is a seasonal phenomenon (7). The rapid development in agriculture, mining, urbanization, and industrialization activities has led to an increase in surface water (including rivers and streams) contamination, depositing hazardous wastes and wastewater in the water bodies. It was reported that in South Africa, over 15% of rural dwellers depend on polluted river waters for their domestic needs; 70% of people in Sudan get their water supply from surface waters, which in most cases are polluted by agricultural chemicals and industrial effluents (4). About 47 million Nigerians depend on either polluted surface waters or wells for their domestic activities (8).

Farmers are the predominant people residing close to rivers and they use poultry droppings as well as chemical fertilizers to enrich their farmlands; these constitute pollutants which drain into the river through run-offs. All the domestic and industrial wastes as well as sewage from surrounding areas are washed into rivers during runoff (9). Also, the topography of the city slopes into the river and drainage channels are emptied into the river. This situation may eventually lead to pollution of the river which might have dire consequences on the ecosystem. There are temporal and spatial variations in the biological and physicochemical properties of rivers but these depends on the nature and amount of effluents received at different points in time (10).

There is paucity of information on the physicochemical and bacteriological qualities of the rivers in these studied rivers except a study on the microbial and physicochemical qualities of river Owena water reported by Ayo and Arotupin (11). The aim of this study was to determine the physicochemical and bacteriological qualities of ten major rivers in Ondo State, Nigeria.

MATERIALS AND METHODS

RESULTS

Bacteriological analysis.

The bacterial loads of the rivers investigated in this study are given in Table 2. The total viable bacterial count (TVBC) in the rivers ranged from 1.5 × 10⁵ to 6.3 ×10⁵ CFUmL⁻¹ as found in Laje river and NCI river respectively, while the total coliform count (TCC) ranged from 1.3 × 10³ to 4.8 × 10³ CFUmL⁻¹ as in Laje river and Omolore river respectively. A total of 283 bacterial isolates were obtained from the different river water samples and these were characterized into eight bacterial species. These bacterial species were S. aureus, Pseudomonas aeruginosa, Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae, Salmonella enterica, Citrobacter freundii and Shigella flexneri. The percentage occurrence of bacteria isolated from the various river waters is shown in Fig. 1. E. coli had the highest percentage occurrence of 23.68% in the river waters, followed by P. aeruginosa (21.2%), S. aureus (19.08%), K. pneumoniae (14.84%), C. freundii (8.48%); E. aerogenes (6.36%), Salmonella enterica (4.24%) and Shigella flexneri (2.12%).

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Fig. 1.

Percentage occurrence of bacterial species isolated from river waters in Ondo State, Nigeria

Table 2.

The microbial loads of selected rivers in Ondo State, Nigeria

Water Sample	River location	Total viable bacterial count (TVBC) × 105 (CFU/mL)	Total coliform count (TCC) × 103 (CFU/mL)
S1	Itanla River	4.7	2.3
S2	Owena River	4.3	3.8
S3	Ofosu River	4.4	1.5
S4	NCI River	6.3	1.7
S5	Ile-Oluji River	5.2	2.1
S6	Igbado River	3.1	1.2
S7	Omolore River	1.9	4.8
S8	Ajue River	5.4	4.2
S9	Oka River	2.1	4.1
S10	Laje River	1.5	1.3

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Values represent the mean of the three replicate samples.

The data obtained from the physicochemical parameters and bacteriological analyses of the river waters were compared with WHO standards for drinking water (Table 3). Although there variations in values of the physicochemical parameters recorded but there were no significant differences between the pH, colour, temperature, electrical conductivity, alkalinity, nitrate content, turbidity, aluminium, dissolved oxygen, organic matters and the WHO permissible standards for drinking water. In the contrary, there were statistical differences between ammonium, total viable bacteria count, total coliform count and the WHO permissible standards (Table 3).

Table 3.

Statistical differences between the WHO standard values and the parametric values of river water samples

	One-sample t test
	T	df	Sig. (2-tailed)	Mean Difference	95% Confidence Difference Lower	Interval of the Upper
pH	−2.167	9	.058b	−.120	−.25	.01
Temperature (°C)	.557	9	.591b	.100	−.31	.51
Turbidity (NTU)	2.150	9	.060b	2.390	−.12	4.90
Colour (TCU)	−.211	9	.838b	−.350	−4.11	3.41
Electrical conductivity (mg/L)	−2.190	9	.056b	−123.640	−251.33	4.05
Ammonium (mg/L)	−17.336	9	.000a	−8.2700	−9.349	−7.191
Aluminium (mg/L)	1.209	9	.258b	.1990	−.173	.571
Organic matters (mg/L)	.956	9	.364b	.2790	−.381	.939
Alkalinity (mg CaCO3 L−1)	−.423	9	.681b	−15.8818	−99.510	67.747
Nitrates (mg/L)	1.155	9	.278b	4.100	−3.93	12.13
Dissolved oxygen (mg/L)	−.075	9	.942b	−.030	−.93	.87
Total viable bacterial count (CFU/100 mL)		9	.000a	353181.818	222032.50	484331.13
Total coliform count (CFU/mL)		9	.000a	2454.545	1421.90	3487.19

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The p values with superscript

^a indicate significant differences from the WHO standards for drinking water while p values with superscript

^b show no significant difference.

DISCUSSION

Information about physicochemical and bacteriological qualities of the major rivers in Ondo State, Nigeria was scanty prior to this study. Ayo and Arotupin (11) earlier studied one of the rivers and reported a total of ten bacterial species from Owena river. They reported a pH of water ranging from 6.72 to 7.52 ± 0.01, dissolved oxygen from 5.95 to 7.63 ± 0.01 mg/l, while biological oxygen demand ranged from 3.20 to 11.47 ± 0.01 mg/L. The physicochemical properties of the river waters sampled during the study period were summarized in Table 1. The pH of the water ranged from 6.6 to 7.1. All the river waters were within the acceptable range for domestic water as indicated by WHO Guidelines for Drinking Water Quality (14). This result deviates from the report of Gintamo et al. (15) who reported the pH range of water from 5.5 to 8.0 in the dry season and a range of 6.4 to 7.9 in the wet season. A pH value greater than 7.0 is vital for the growth and reproduction for the majority of mesophilic pathogenic bacteria involved in the biodegradation of organic matter dissolved in water. Total alkalinity ranged from 186.5 to 440 mg CaCO₃ L⁻¹. The values of the total alkalinity in the rivers investigated fell within the acceptable limit for domestic water (Table 1). This depicts that the river waters sampled had stable pH. Total alkalinity is an estimate of the ability of water to resist change in pH when an acid is introduced (7). The alkalinity of water is known to be primarily dependent on CO₃, HCO₃ and OH ions, it is therefore substantial that such ions were less in the investigated rivers. The alkalinity of these river waters was consistent with the report of Gambo et al. (16) which was also in the range of WHO recommended standards. However, Joshi et al. (17) who investigated river ganga, India reported values that deviated from the findings of this study.

The dissolved oxygen (DO) of the sampled water ranged from 3.8 to 7.5 mg/L. This concentration was higher than the minimum concentration of 3.0 mg/L required for the protection of aquatic lives. The concentrations of DO measured in the river waters investigated fell within the range for excellent quality potable water for domestic supply and recreational purposes. Water meant for domestic and recreational purposes should not contain DO concentration less than 3.0 mg L⁻¹ (14). The dissolved oxygen levels in waters above the 5.0 mg L⁻¹ concentrations suggest their potentials of supporting fish life and aerobic organisms.

Turbidity levels revealed a range of 4.3 to 15.2 NTU. In most of the river waters investigated, turbidity levels were above the acceptable maximum limit for drinking water (Table 1). Water with high turbidity is normally considered to have a high load of microorganisms, and elevated turbidity levels may make the water difficult to get disinfected. The river waters have high turbidity values and this could be attributed to soil erosion and runoff, which are usually high during the high rainfall months. Heavy rainfall results into flooding, thus washing silt, nutrients, and household wastes into the water bodies, thereby, fluctuating the turbidity levels of the water bodies (7).

The values for water colour ranged from 4 to 20 NTU. Most of the water sources investigated had water colour above the acceptable limit for drinking water (Table 1). The variation in water colour of the water bodies investigated could be linked with the variation in the amount of dissolved and colloidal humic substances. The high level of water colour in the sources is significant as it increases the cost of water treatment. Electrical conductivities (ECs) of the sampled river waters ranged from 123.5 to 580.2 mgL⁻¹. The conductivity values of the most of the river waters investigated fell within the WHO acceptable range for domestic water. This could be associated with the high rainfall during the study period. Amin et al. (18) reported that conductivity was high during low rainfall months while low conductivity values were obtained during the high rainfall months.

The TVBC in the rivers investigated in this study ranged from 1.5 × 10⁵ to 6.3 × 10⁵ CFUmL⁻¹ while the TCC ranged from 1.3 × 10³ to 4.8 × 10³ CFUmL⁻¹. The notion of coliforms as bacterial indicators of microbial quality of water is primarily based on the fact that coliforms are found in excessive numbers in the faeces of human and other warm-blooded animals. Thus, their presence in river waters suggests contamination with matter of faecal origin (19). The bacteria isolated were S. aureus, P. aeruginosa, E. aerogenes, E. coli, K. pneumoniae, S. enterica, C. freundii and S. flexneri. E. coli had the highest percentage occurrence of 23.68% in the river waters, followed by P. aeruginosa (21.2%), S. aureus (19.08%), K. pneumoniae (14.84%), Citrobacter freundii (8.48%); E. aerogenes (6.36%), Salmonella enterica (4.24%) and S. flexneri (2.12%) (Fig. 1).

All ten river waters analyzed contained markers of faecal pollution such as total coliforms, and thermotolerant coliforms (E. coli, K. pneumoniae, C. freundii and E. aerogenes) (Table 2) and the presence of these organisms were indicative of the fact that the river waters were unfit for human consumption and should undergo thorough treatment before drinking. This is consistent with the reports of Agwu and Avoaja (20) in Aba, Abia State; Nduka et al. (21) in Warri, Delta State; and Cabral et al. (22). Similar microorganisms were also earlier reported by Egberongbe et al. (23) in their study of stream water for domestic use in Ijebu North Local Government, Ogun State, Nigeria.

The organisms encountered in this study are of public health importance. E. coli is conventionally inhabitant of the intestines of most man and animals. It causes bacterial intestinal and extra-intestinal infections including septicaemia, diarrhoea, urinary tract infections, and neonatal meningitis in man and livestock (24). It is often linked with multiple antimicrobial resistances (25), and among bacteria isolated from animal foods, such as pigs, cattle, and poultry (26).

P. aeruginosa inhabits water, soil, plants, and animals. It easily causes infections in immune-compromised but hardly establish infections in healthy individuals (27, 28). It has been labelled among the topten hospital ‘superbugs’ as a result of its widespread antimicrobial-resistant strains leading to life-threatening health conditions (29, 30). C. freundii occurs mostly in water, food, soil and sewage. The organism is also associated with non-potable water that normally undergo poor chlorination process (31).

Infections caused by E. aerogenes include bacteremia, endocarditis, septic arthritis, skin and soft-tissue infections, lower respiratory tract infections, urinary tract infections (UTIs), osteomyelitis, CNS infections, intra-abdominal infections, and ophthalmic infections (32). S. aureus is a normal flora of humans. It causes a wide range of infections such as endocarditis and septicaemia (33). Food poisoning by the staphylococcal toxin is characterised by diarrhoea, nausea, abdominal cramping, and vomiting within 24 h of ingestion (34). K. pneumoniae could be found in surface waters, soil, plants, and intestines of man and animals. It is an opportunistic pathogen as it causes infections such as pneumonia, UTIs, and bloodstream infections, in immunocompromised individuals. K. pneumoniae infections are a threat to public health because of its potential acquisition of multidrug-resistant genes (35). S. enterica is transmitted through faecal-oral route (36). Shigella causes an infection known as shigellosis. Most infected individuals develop fever, diarrhoea, and stomach cramps, but often recover without chemotherapeutic interventions (37).

CONCLUSION

This study revealed that the river waters investigated are mostly unfit for domestic purposes and were contaminated with potential pathogenic microbial species. Some physicochemical properties and bacterial loads in the waters deviated significantly from the recommended WHO guidelines for domestic waters. The implications are that there is lack of safe and sanitary water supply in certain populations in Nigeria, hence the reason the country, just like many Sub-Saharan African population suffer markedly from water-borne infections. It is, therefore, recommended that the water from these sources be treated to suit domestic purposes.

REFERENCES