Assessment of health risk association with groundwater from Collins Chabane and Makhado Municipality of Vhembe District

Abstract

Water is essential to life, but many people lack access to clean and safe drinking water, and many die of preventable waterborne diseases. The study conducted assessed groundwater vulnerability to Physico-chemical and microbial contamination across the Collins Chabane and Makhado Municipality. A three-set of samples (for metals, non-metals and microbial analysis) were randomly collected from twenty (20) primary schools, fifteen (15) private boreholes, and three (3) communal boreholes of Vhembe district, Limpopo province, South Africa. The physicochemical water quality parameters (pH, EC, and TDS) were measured using the YSI Professional Plus meter . At the same time, turbidity and salinity were measured using an Orbeco-Hellige portable turbidimeter and Extech multimeter, respectively. The physicochemical parameters measure in the field comply with the recommended standard set by South African Nation Standard SANS (2015) apart from the pH value detected in one sample collected in the wet season. Nitrate concentration (2.03–1532 mg/L) was obtained in high values in the most sample in the wet season. Some boreholes can have a noticeable taste due to chloride concentration (14.12–690 mg/L). The following metals Cd, Pb, Hg, As, Al, Mn, Fe, Co, Ni, Cu, Cr and Zn, Ca, K, Mg, and Na were analysed using an Inductively coupled plasma Mass spectrometer. The analytical results for major cations i.e., Ca, Mg, K and Na range between 14.20 – 349 mg/L, 11.40 – 309 mg/L, 0.49–12.80 mg/L, and 13.60 – 97.80 mg/L, respectively. The high concentration of Ca and Mg recorded in some of the sites exceeded the recommended limit set by DWAF (1996) and WHO (2015). The analytical results of heavy metal indicated that Ni (16.35 – 308.53 μg/L), Cr (27.46 – 72.84 μg/L), and Al (0.14 – 0.76 mg/L) were above the standard limits of SANS 241 (2015) in some of the sites. The membrane filtration method was employed to determine faecal indicator organisms. The results obtained for E. coli ranged between 0.0 – 76 cfu/100 ml in the dry season, while numerous values were detected for total coliform in both dry and wet season. All borehole failed to comply with SANS 241 and WHO standard limit in terms of total coliform while, 42.11% of borehole failed to comply with SANS 241 in terms of E. coli. Groundwater geochemistry was evaluated through Gibb’s diagram and Piper plot. The most dominant water type across all groundwater sample was Mg-HCO3 (40.79%, n=76) and Mg-Cl water type (38.16%, n=76) throughout the study period. Twenty one parameters (pH, EC, Cl-, NO3- , F-, SO4-2, HCO3-, Ca, Mg, K Na, Total Hardness as CaCO3, Cr, Mn, Co, Ni, Cu, Zn, Hg, Pb and Fe) were taken into consideration for the computation of water quality index (WQI). The WQI values of the selected school, household, and communal samples (50-103 and 25-101, 26-485 and 21-442, and 35-57 and 50-56, respectively) fell between the excellent to poor, excellent to unsuitable and excellent to good water based on the physico-chemical parameters used during dry and wet season, respectively. Some household samples had poor (21.43%), and unsuitable water (10.71%) during the assessment period. Nitrate was the principal element with enormously high concentrations that violated the WHO and SANS 241 permissible limit for drinking purpose which caused high levels of WQI. The source of contamination could be anthropogenic activities. Human health risk associated with the water quality parameters assessed was calculated using noncarcinogenic effects using hazard quotient toxicity potential (HQing), cumulative hazard index (HI) and daily human exposure dose (Ding) of drinking water through ingestion pathway. The computed non-carcinogenic effects (HQing) and HI for children and adult were ≥1 throughout the assessment. The main contributors to non-carcinogenic health risks in this investigation were Cr, Hg, and As. The carcinogenic risk assessment evaluated from selected heavy metals (Cr, Cd, Hg, Pb and As) exceeded the suggested potential risk limits apart from As and Hg for Adult in Dry season. Cr and Pb were above the carcinogenic indices of 1E-04 and 1E-06 throughout the season. Hence, these parameters can pose potential risk to both age group. Therefore, preventive measure should be implemented to prevent long term cumulative exposure risk. Quantitative microbial risk assessment (QMRA) was carried out to determine the risks of infection and illness due to consumption of groundwater. The estimation of QMRA indices values suggest that school boreholes had higher risk of infection than household and communal sites. Highest risk of infection has been detected during the month of November (wet season) in 2019. Only 30% school boreholes had an extremely high annual risk (90.52-100% probability) of E. coli infections to children. High probability values (90.5-100% probability) for annual risk of infection in all age group has been observed in 35.90% school samples throughout the assessment. Only 10.26% of school samples had annual risk of illness probability value of 35% in all age group. The annual risk of E. coli infections and illness was high in household site with 100% and 35% for all age group respectively. Meanwhile, 80.94 and 28.33% were the highest maximum values assessed for infection and illness in communal site. The estimation of QMRA indices suggest groundwater from the investigated study being a hazard. The methods of analysis in this study, suggested possible contamination of groundwater by anthropogenic activities such as small-scale agricultural activities, faecal contamination (pit latrines and septic storage), domestic waste on land, waste from concentrated livestock and natural processes such as microbial interference, weathering and dissolution. Preventive and mitigation measures to minimise such risks are indispensable.