Quantitative Risk Assessments of Bacteria and Heavy Metals in Ossiomo River, Orhionmwon Local Government Area, Edo State, Nigeria

Abstract

Water contaminated with heavy metals causes human health risk after prolonged exposure. This study aimed to evaluate the quantitative risk of heavy metals and bacterial diversity of Ossiomo River, Orhionmwon Local Government Area, Edo State, Nigeria. Water samples were collected in triplicates from July 2019 to December 2019, for physiochemical and bacteriological analysis. Heavy metals were determined using Atomic Absorption Spectrophotometer (AAS).The concentrations of metals calculated were chromium (0.003 mg/l), lead (0.009 mg/l and cadmium (0.005 mg/l) using the USEPA risk assessment guidance. Heterotrophic and coliform bacteria were isolated and enumerated using pour plate and most probable number techniques respectively. Antibiogram test was carried out using Kirby-Bauer antibiotic disc diffusion method. Non-carcinogenic risk (CR) of Pb for adult ranged from 2.91 × 10-5 – 3.72 × 10-5 mg/kg/day, Cd 1.30 × 10-6 – 9.72 × 10-8 mg/kg/day and Cr 1.6 × 10-6 – 9.88 × 10-6 mg/kg/day while Pb for children ranged from 1.42 × 10-5 – 5.65 × 10-5 mg/kg/day, Cd 1.23 ×1 0-1 – 9.84 × 10-8 mg/kg/day and Cr 1.5×10-6 – 3.76×10-6 mg/kg/day and the average cancer risk were 11.47 × 10-6 mg/kg/day for children and 11.30 × 10-6 for the adults mg/kg/day. Total heterotrophic bacterial counts ranged between 2.4 ± 1.1 and 17.8 ± 4.9 × 103 cfu/ml and mean coliform counts ranged from 23 to 201 MPN/100 ml. Four bacterial isolates were found and identified as Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica and Klebsiella pnuemoniae. Escherichia coli 37.0 % was found to be the most frequent bacterial isolate while Pseudomonas aeruginosa 12.0 % was least. Ciprofloxacin 100 %, ceftriaxone 100 %, azithromycin 90 %, gentamycin 100 %, pefloxacin 95 %, oflaxacin 75 %, cefuroxime 70 % and ceftazidine 60 % were effective drugs against enterobacteriaceae infections whereas, augmentin 0 % and nitrofurantoin 0 % were ineffective. There is the need to improve awareness, monitoring and surveillance of coastal water bodies to curb outbreak of water borne diseases among the dependent communities