ABSTRACT
Poor quality water is known to contain pathogenic microorganisms primarily belonging to the family Enterobacteriaceae and chemical contaminants with toxic characteristics have been identified as human health threat responsible for waterborne diseases. This study evaluated the prevalence of enteric bacteria and risk assessments of heavy metals in Ossiomo River, Orhionmwon Local Government Area, Edo State, Nigeria.
A total of 36 water samples were collected for a period of twelve months at monthly interval from upstream, midstream and downstream locations of Ossiomo River and transported to the laboratory for analysis. The physicochemical parameters, which included pH, temperature, total dissolved solids (TDS), electrical conductivity (EC), magnesium, calcium, sodium, phosphate, bicarbonate, nitrite and the heavy metals (iron, cadmium, chromium, zinc and lead) were analysed using standard analytical procedures. Human exposure risk assessment was estimated according to the United States Environmental and Protection Agency Risk Assessment Guidance. Water Quality Index (WQI) was estimated by weighted arithmetic methods. The enumeration and isolation of total heterotrophic bacteria, Yersinia spp. and total coliform were carried out using standard bacteriological techniques. The hemolytic properties were conducted using standard methods and antibiotic susceptibility tests was investigated using antibiotic disc diffusion methods.
The results of the physicochemical parameters revealed that, pH ranged from 5.4 ± 0.0 – 5.7 ± 0.1, chromium 0.0 ± 0.0 – 0.3 ± 0.0 mg/L and lead 0.1 ± 0.0 – 0.8 ± 0.0 mg/L. Among the physicochemical and heavy metals studied, the pH, lead, cadmium and chromium were above the permissible limit set by WHO and FEPA. The average carcinogenic risks (CRing) of the studied metals were 11.25 × 10-6 mg/kg/day for children and 10.06 × 10-6 mg/kg/day for the adults. The water quality index results ranged from 275.74 mg/L (Upstream) - 394.01 mg/L (Midstream). The total heterotrophic bacterial counts ranged from 1.1 ± 0.0 × 103 cfu/mL (Upstream) - 17.8 ± 4.9 × 103 cfu/mL (Midstream). The total Yersinia spp. counts ranged from 0.0 × 103 cfu/mL (Upstream) – 1.2 × 103 cfu/mL (Midstream) while the mean total coliform counts ranged from 14 MPN/100 mL (Upstream) - 201 MPN/100 mL (Midstream). The results of Yersinia and enteric bacteria population were above the WHO permissible limit. The molecular characterisation revealed the presence of Yersinia ruckeri 100 % (MK548507.1), Shigella flexneri 91.57 % (MK918539.1), and Providencia alcalifaciencs 88.57 % (HQ407250.1). The percentage frequency of the bacterial isolates showed Escherichia coli had the highest percentage frequency of occurrence (13.8 %), while the least was revealed for Yersinia ruckeri (2.3 %). This study showed that Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae produced Beta (β) hemolysin. Yersinia ruckeri, Serratia marcescens, Shigella sonnie, Klebsiella variicola, Pseudomonas otitidis, Ralstonia mannitolilytica, Proteus cibarius, Proteus mirabilis, Providencia rettgeri, Providencia stuartii, Salmonella enterica and Shigella flexneri produced Alpha (α) hemolysin. The results of the antibiotic sensitivity test revealed that the enterobacteriaceae were sensitive to levofloxacin, ciprofloxacin, leftazidine, gentamycin, cefuroxime, ceftrioxine and ofloxacin. The study revealed that Ossiomo river contain different concentrations of organic pollutants constituting public health risk, hence the water must be treated prior to consumption.
