Quantifying toxic contaminants in four major dump sites of Thabo Mofutsanyane district, Eastern Free State

Abstract

The large number of cases of groundwater pollution at landfills and the substantial resources spent on remediation suggests that landfill leachate is a significant source of pollutants, especially when considering different kinds o f contaminants in landfill leachates. The longterm effect of the geological barrier beneath municipal-waste landfills is a critical issue for soil and groundwater protection. Soil to plant transfer of trace metals is the major pathway of human exposure to metal contaminations. Therefore, the present study was conducted to determine trace meta l levels such as arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), cobalt (Co) and zinc (Zn) in soil and plant samples collected from four major dumpsites in Thabo Mofutsanyane District, Eastern Free State in South Africa. Samples (soil and plants) were collected from Harrismith, Qwaqwa and Bethlehem from two different landfills. Soil samples were collected at a depth of 0-15 cm from each part and pooled to form a composite sample. Plant samples were pulled from the soil together with their roots using an ager. Four acid digest techniques (HCl, HN03, HCl04 and HF) were used and inductively coupled plasma optical emission spectrometry (ICP-OES) determined the concentrations of heavy meta ls. During the four seasons (spring, summer, autumn and winter), the concentration of Zn was higher in summer with value o f 3076.56± 12.02 compared to winter 1733.5 1 ±39.33. The concentration of Pb was within the threshold except in Qwaqwa and Bethlehem site A with values of 3 15.79±30.26 and 230.82±35.24. Cd concentration fluctuates during the seasons but the highest value of 6. 15±0.06 was recorded during winter. The level of Mn in all dumpsites was very unstable and above the standard permissible limit. The common plants identified in the dumpsites are Cosmos species, Eragrostis plana, Elusine indica, and were all found to contain high level of heavy metals. Principal Correlation Analysis (PCA) analysis showed that Qwaqwa and Harrismith had the highest load of heavy metals and the dendrogram confirmed the similarity in metal distributions in the dumpsites. This study highlights environmental implications of heavy and trace metals in all dumpsites studied. There was no significant difference in the concentration of metals within and outside the dumpsites which confirms metals can be distributed above I0 m range. All the trace metals analysed in this study had higher concentrations above the permitted limits set by USEPA and WHO. This study revealed the levels and impacts of heavy metal concentrations on the dumpsites, as well as the risks they may pose to near or far surroundings and its attendant health implications.