Assessment of the radiological risks and heavy metal pollution on the water quality of the Vaal River, South Africa

Abstract

Anthropogenic activities close to water bodies contribute to poor water quality, degrading the natural conditions of plants and animals and elevating health risks concerning humans. The Vaal River supplies potable water to the Gauteng, North West, Free State, Northern Cape, and Mpumalanga provinces of South Africa. Consequently, the water quality of the Vaal River needs to be monitored and assessed for radioactivity and heavy metal risks. The aim of this study was to investigate the concentration levels of NORM radionuclides and heavy metals and their effect on the water quality of the Vaal River. As a result, 27 water samples were collected and analysed for U, Th & K as well as toxic heavy metal concentrations that may potentially cause risks to the public around the study area, using the inductively coupled plasma mass spectroscopy (ICP-MS) technique. The risks of pollutant exposure of humans to heavy metals in water were evaluated using chronic daily intake (CDI), hazard quotient (HQ), and hazard index (HI), heavy metal pollution index (MPI) and heavy metal evaluation index (HEI). Ion chromatography (IC) was also used to examine water types from the cations and anions therein. The cations measured are calcium (Ca2+), sodium (Na+), magnesium (Mg2+), and potassium (K+). Anions measured were sulphate, phosphate, nitrite and reflected on a Piper diagram.

Results show that: i. The activity concentrations of K, U and Th (Bq/l) were used to assess the radiological health indices by calculating the radium equivalent activity (Raeq), dose rate (D), annual effective dose (AEDE), external hazard (Hex) and internal hazard (Hin). The calculated average radiation hazard index for Raeq was (33.803 Bq/l), D (18.158 nGy/hr), AEDE 0.0222 (nGy/hr), Hex (0.091) and Hin (0,096) in this study. These hazard parameters were lower than the world average permissible limit. A a result, the water from the Vaal River does not pose radiological risks to members of the public. ii. The HEI values for all heavy metals, like Li and Fe were less than 40, indicating low pollution level, while for Mn, HEI = 80.35. From the MPI & HEI values of Li, Fe & Mn, we conclude that Mn & Fe, are the major pollutant of the water in the Vaal River. This could be due to human activities such as discharges from nearby industries and mines. According to the findings of the study, the Vaal River is not suitable for use (drinking or recreational) due to pollution by these two heavy metals emanating from nearby industries. iii. Ion chromatography (IC) was used also to examine the cations and anions of the study. The cations: calcium (Ca2+), sodium (Na+), magnesium (Mg2+), and potassium (K+), had an average concentration of 34.4, 58.9, 13.8, and 6.3 mg/l, respectively. The anions:sulphate (SO42-), phosphate (PO43-), and nitrite (NO2), had an average concentration of 87.5, 0.7, and 0.1 mg/l, respectively. The piper results indicated that the Vaal River is of a Ca-Mg-SO2 water type, with no dominating phase. Based on the findings of the study, we concluded that there is no radiological risk from the Vaal River waters in the study area. However, the heavy metal concentrations in this study prove that the Vaal River is not safe for public use due to increased levels of Mn and Fe at 1.34 mg/l and 4.02 mg/l respectively across the river flow. As a result, additional river monitoring is required to maintain public safety. This study recommends a conceptual management plan to assist relevant stakeholders in the maintenance of the water quality for the Vaal River