Heavy metals pollution status of the Katima Mulilo Urban open land wastewater disposal centre and the immediate vicinity

Abstract

Abstract The main objective of this study was to assess the current pollution status of environmentally concerned heavy metals in the surface soil within the vicinity of the Katima Mulilo urban open land wastewater disposal centre. Multiple top soil samples (at 0–10 cm depth) were collected at four different points fortnightly over five sampling days from June to July 2018. The samples collected at each point were pooled together, homogenized and 12 sub-samples (<2 mm soil fraction) were obtained for laboratory digestion according to EPA method 3050B. Then, the digestates were analyzed for the heavy metals’ concentrations using ICP-OES (Perkin Elmer Optima 7000 DV). The results revealed consistent pattern with Fe recording the highest mean concentration (mg/kg) at each sampling point while Cd recorded the lowest mean concentration. Result of analysis of variance of the metals’ mean concentrations differed statistically (p < 0.05). The sites contamination revealed that the Point source > A200m > B400m > Control site, but the potential ecological risk indices revealed environmental low-risk levels (Er <40). Apart from Arsenic which showed moderate contamination at the point source, the geo-accumulation indices of the heavy metals mainly revealed uncontaminated to moderately contaminated levels (0 < Igeo < 1). Generally, the mean concentrations of the heavy metals were lower than the WHO’s maximum permissible limits for the protection of human and ecosystem’s health. However, due to their environmental persistence, non-degradable and bio-accumulative characteristics, heavy metals are potential toxins. Therefore, we recommend periodic monitoring of the metals levels and advising precautionary measures to minimize unintended human exposures to excessive metal contents.