Assessment of coastal aquifer contamination using geochemical and health risk assessment in Maputaland formations, South Africa
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Date
2021
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Publisher
University of Zululand
Abstract
The Maputaland coastal plain of KwaZulu-Natal is among the popular tourist areas in South Africa. Groundwater is the foremostsource for drinking and irrigation abstracted from the unconsolidated aquifers where the infiltration rate is very high. This could possibly increase the risk of aquifer contamination.The main objectives of this study is to evaluate the hydrogeochemical processes, identify the intended sources of groundwater contamination, and understanding the extent of trace metal contamination and health risk assessment. In this study, 53 and 42 groundwater samples were collected from bore wells during 2018 and 2019 and were analysed for major ions, minor ions, nutrients and trace metals. Na-Cl water type was dominant in groundwater followed by Ca-HCO3. Cross plots revealed that ion exchange, reverseion exchange, silicate weathering, seawater mixing, and anthropogenic inputs from agricultural activities govern the groundwater chemistry. GIS methods were adopted to produce spatial distribution maps of major ions through which locations of groundwater contamination and the intensity of hydrogeochemical processes were identified. The water quality index (WQI) varied from 18.9 to 157.1 with an average value of 45.55. Majority of the samples are classified as good, 22 % as poor, 2 % as very poor and 7% under unsuitable category, which are spatially distributed towards the southern and western parts of the study area. Mean concentration of trace metals were in the order: Zn>Li>Al>Fe>Mn>Cu>Pb>As>Co>Cd in 2018 , Fe>Zn>Mn>Sr>B>Pb>Cu>Co>Cr>Cd>Ag>Al>Ni in 2019. Most of the trace metals were found to be within the WHO standards for drinking water except for Cd, Zn, Pb, Mn, Al and Fe. Health risk assessment of trace elements via ingestion and dermal absorption pathways was carried out. Hazard quotient through dermal absorption (HQdermal) and hazard index (HI) for Co and Mn were above 1 in adults, children and infants. HQ derma land HI for Cd was greater than 1 in children and infants. HQ derma land HI for As and Pb were greater than 1 in infants. This implies that these metals pose serious adverse risk on local people and infants are more vulnerable to health risk than children and adults. The heavy metal pollution index shows that the groundwater samples vary from low to high pollution class and 21% of the samples exceed the critical limit of 100 implying that they are highly polluted with respect to heavy metals and are unfit for human consumption. The heavy metal evaluation index and degree of contamination reveal that all the groundwater samples have low pollution with regards to heavy metals and are suitable for human consumption. Moreover, the results of ecological risk assessment reveal that the studied heavy metals pose low ecological risk. Based on the pollution index of groundwater, majority of the samples fall in the insignificant pollution zone. The synthetic pollution index reveal that 2%, 74% and 24% of the samples are suitable, slightly and moderately polluted respectively with heavy metals. Similarly, the overall index of pollution reveal that majority of the samples are excellent and suitable for drinking purpose. Multivariate statistical analysis were adopted to evaluate sources of heavy metals in groundwater. Correlation matrix and principal component analysis reveal that weathering of aquifer matrix and anthropogenic activities are accountable for the release of heavy metals into groundwater. Furthermore, R-mode and Q-mode cluster analysis revealed two clusters. All the clusters from R-mode and Q-mode cluster analysis are linked to mixed sources including weathering and anthropogenic activities. This study provides the baseline data on hydro geochemistry that can be utilised further in future studies. It is recommended that contaminated groundwater in this region be treated before utilisation in order to maintain the sustainability of public health and recommends for further extended studies.
Description
A thesis submitted to the Faculty of Science and Agriculture in fulfilment of the requirements for the Degree of Master of Science in the department of Hydrology at the University of Zululand, South Africa, 2021.
Keywords
Coastal aquifer contamination, Geochemical and health risk assessment, Maputaland formations