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Identification and Determination of Potentially Toxic Elements in Water and Sediments from Blood and Mokolo Rivers In

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Identification and Determination of Potentially Toxic Elements in Water and Sediments from Blood and Mokolo Rivers In IDENTIFICATION AND DETERMINATION OF POTENTIALLY TOXIC ELEMENTS IN WATER AND SEDIMENTS FROM BLOOD AND MOKOLO RIVERS IN LIMPOPO PROVINCE, SOUTH AFRICA By DITHOBOLONG LOVIA MATABANE DISSERTATION Submitted in partial fulfilment of the requirements for the degree of MASTER OF SCIENCE In CHEMISTRY In the FACULTY OF SCIENCE AND AGRICULTURE (School of Physical and Mineral Sciences) At the UNIVERSITY OF LIMPOPO SUPERVISOR: DR. A.A. AMBUSHE CO-SUPERVISORS: PROF. T.W. GODETO PROF. R.M. MAMPA JUNE 2018 DECLARATION BY CANDIDATE I hereby declare that the full dissertation submitted for the degree of Master of Science in Chemistry at the University of Limpopo titled “Identification and determination of potentially toxic elements in water and sediments from Blood and Mokolo Rivers in Limpopo province, South Africa”, is my own original work and has not previously been submitted to any other institution of higher education. I further declare that all sources cited are indicated and acknowledged by means of a comprehensive list of references. …………………………………………. ……………………………… DITHOBOLONG LOVIA MATABANE Date Copyright© University of Limpopo 2018 i DEDICATION In memory of my late close ones, Rakgadi ‘’Ntswaki” Ramadimetja Rebecca Matabane, Malome Kotole Meshack Mamaro, and Rakgolo Disego William Mamaro, Robalang ka kgotso. This study is dedicated to my mother Margaret Machoey Matabane who always supported me through thick and thin and my son Dimpho for being my source of inspiration at all times. ii ACKNOWLEDGEMENTS All glory and honour to the Almighty God for granting me the gift of life and strength throughout my studies. My sincere gratitude to my supervisor Dr. Abayneh Ataro Ambushe for his constant support and guidance towards the completion of this study. He has been of great assistance despite his many other academic and professional commitments. Thank you for allowing me to absorb all the information I have from you. Much appreciation to my Co-supervisor Prof. Taddese Wondimu Godeto for his guidance and instrumental contribution towards my analysis work at the Department of Chemistry, University of Johannesburg, Auckland Park Campus. My heartfelt appreciation to my Co-supervisor Prof. Richard Mampa for the assistance towards the submission of the dissertation. Many thanks to Dr M Mujuru for his companionship during the wonderful sampling trips and guidance during sample collections. My gratitude to Mr. Masibane Patrick Kgaphola for drawing the Mokolo and Blood Rivers sampling site maps. This work is based on research supported in part by the National Research Foundation (NRF) of South Africa under the Thuthuka Programme Grant Number 108672 and the Water Research Commission (WRC) of South Africa Project Number K5/2515//1. I also acknowledge Sasol Inzalo Foundation and NRF for bursary, and University of Johannesburg for allowing me to use their ICP-MS for sample analysis. My sincere gratitude to Zama Ngubane and Mokibelwana Ledwaba from Limpopo Agro-Food Technology Station for analysis by ICP-AES. I am grateful to my lab mates for the help during the academic years and the wonderful sampling trips and experiences: Tumelo Monty Mogashane, Meldred Matjena, Conny Putsane Mokgohloa and Miyelani Chauke. iii To my MSc fellows, Kabelo Edmond Ramohlola and Bafana Njabulo Mbokane from the University of Limpopo; Nombuzo Mabuza, Bienvenu Gael Fouda Mbanga and Harold Shiri from the University of Johannesburg, together we ran the race and together we made it despite the enormous work pressures we were all facing. To my friends Mamolato Magdeline Takalo and Mogorosi Titus Selemale, your presence kept me going in order to complete the write up of this dissertation. “Ba ga Matabane more favorably my mother (Margaret Machoey) and siblings ke tla dula ke leboga thekgo le lerato leo le mphilego le ge kele kgole le gae”. iv ABSTRACT The increase in industrialisation such as mining and smelting activities is among the main sources of heavy metal pollution in the environment. These potentially toxic elements may be adsorbed directly by sediments of water course and may affect the inhabiting flora and fauna. Potentially toxic elements are not permanently fixed by the sediments since changes in environmental conditions can mobilise these elements from sediments to water. Thus, analysis of sediments could indicate the degree of environmental contamination by potentially toxic elements and therefore are suitable for pollution studies. The aim of this study was to assess and quantify the levels of selected potentially toxic elements (Mn, Zn, Ni, Cu, Cr, Pb, V, Cd, As, Se and Fe) in sediments and water samples collected from Blood and Mokolo Rivers in Limpopo Province, South Africa. Water and sediments samples were collected from 10 sampling sites from each river. Water samples were filtered and acidified with HNO3 prior to analysis for preservation of elements. Potentially toxic elements in water samples were analysed by ICP-MS and the results validated by analysing standard reference material of water (SRM 1634f). Concentration levels of potentially toxic elements in samples from the water of Mokolo and Blood Rivers during low and high flow seasons were determined with ICP-MS. The levels in the water of Mokolo and Blood Rivers followed the order of Mn > Se > Zn > Cr > Pb > V > Cu > As > Ni > Cd > Fe in Mokolo River and Mn > Se > Zn > Cr > V > Ni > Cu > As > Pb > Cd > Fe during high flow season, Mn > Se > Zn > Cr > Cu > V > As > Pb > Ni > Cd > Fe and Mn > Zn > Se > Cr > V > Ni > Cu > As > Pb > Cd >Fe during low flow season, respectively. As expected, the concentrations of selected elements determined during the low flow season exceeded the high flow season for both rivers, which confirms acceptability of the analytical method performance. The analysis of variance (ANOVA) showed significant differences (P<0.05) in the concentrations of the elements seasonally. The concentrations of the toxic metals in the water samples of Mokolo and Blood Rivers were below the maximum permissible levels (MPLs) set by different organisations such as World Health Organisation (WHO) and Department of Water and Sanitation (DWS). v Comparison of concentrations of elements in sediments determined during high flow and low flow seasons was done to establish the variation on the levels of the elements between seasons. Levels of potentially toxic elements in sediments of Mokolo and Blood Rivers followed the order Fe > Cr > Mn > V > Zn > As > Ni > Cu > Pb > Cd > Se and Fe > Mn > Cr > Ni> V > Zn> Cu > Pb > As > Cd> Se during high flow season as well as Fe > Mn > Cr > V > Zn > Ni > Pb > Cu > As > Cd > Se and Fe > Mn > Cr > Zn > V > Ni > Cu > Pb > As > Cd > Se during low flow season, respectively. The ANOVA results showed significant differences in the concentrations of the elements between two seasons and that concentrations of the elements determined in sediments during low flow season were significantly higher than the high flow season levels. Compared with sediments quality guidelines (SQGs), the concentrations of Fe, Mn, Ni and Cr in the sediments of Mokolo and Blood Rivers were above the SQGs, which could pose the risk to sediments dwelling organisms. The Community Bureau of Reference (BCR) sequential extraction method was applied to extract selected potentially toxic elements (Cd, Cr, Cu, Fe, Ni, Pb and Zn) in sediments samples. Microwave-assisted sequential extraction procedure was developed and employed for extraction of the selected potentially toxic elements in sediments samples. This method enables safe and fast extraction of potentially toxic elements in sediments using smaller volume of reagents. The methods employed were validated with the BCR-701 certified reference material of sediments. The Efficiency and reliability of the microwave-assisted sequential extraction method was shown by calculating the percent recoveries. The percent recoveries were within acceptable range for method validation. Following the sequential extraction analysis, the risk assessment study was done to determine the effect of the potentially toxic elements in the sediments to the water quality. The calculated individual contamination factor (ICF), global contamination factor (GCF) and risk assessment code (RAC) values of Cd, Cu, Ni and Pb indicated that the elements were mobile and may be bioavailable in the aquatic environment. vi The assessment of eco-toxicological risk indicated that the elements in sediments samples collected from Blood River are at high toxicity risk level and thus, could pose threat to sediments dwelling organisms and humans through consumption of crops irrigated with the river water. vii LIST OF TABLES Table 3.1: Description of Mokolo River sampling sites ............................................. 36 Table 3.2: Description of Blood River sampling sites ............................................... 40 Table 3.3: Instrumental conditions for microwave-assisted acid digestion ............... 46 Table 3.4: Instrumental conditions for the BCR sequential extraction procedure ..... 48 Table 3.5: Instrumental conditions for microwave-assisted sequential extraction procedure ................................................................................................................. 49 Table 3.6: Instrumental conditions of ICP-MS .......................................................... 50 Table 3.7: Instrumental conditions of ICP-AES ........................................................ 51 Table 3.8: Instrumental conditions of F-AAS ...........................................................
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