Enrichment and geo-accumulation of heavy metals in superficial sediments, macrophytes and edible leafy vegetables.

Abstract

Wetlands play a vital role in maintaining ecological balance, supporting biodiversity, and providing essential ecosystem services such as flood control, water purification, and carbon sequestration. However, increasing levels of metal contamination threaten these ecosystems and public health. This study investigated the concentration, accumulation, and translocation of trace and heavy metals in wetland sediments, aquatic macrophytes, and edible leafy vegetables, with a focus on assessing phytoremediation potential. Field samples of sediments (n = 2) were collected across three seasons (hot-dry, cool-dry, and hotwet) from urbanised riverside wetlands in Mbombela, South Africa. The m etal pollution indices, such as contamination factor, enrichment factor, geo–accumulation factor and pollution load index were used to determine the pollution of metals in the sediments across different sites among seasons. Results showed that wetland sediments were highly contaminated, particularly with Mn, Co, Cu, Pb, Zn, Al, and Fe most significantly during the cool-dry season. The four aquatic macrophytes (Typha capensis, Cyperus papyrus, Cyperus dives, and Phragmites australis) collected from same location as sediments were divided into roots, stems and leaves. The study used the bioconcentration and translocation factors to determine the accumulation and translocation of metals within macrophyte species. The study indicated that different macrophytes accumulated different metals within the roots and leaves of all species during the cool–dry followed by hot–dry and hot–wet seasons. Among the macrophytes studied, C. dives and T. capensis demonstrated strong phytoremediation potential, indicated by high bioconcentration and translocation factors. Additionally, edible vegetables (cabbage, rape, pumpkin leaves, and spinach) were obtained from local markets in Tonga town for metal analysis and human health risk assessment. Vegetables exhibited elevated metal concentrations, with several exceeding permissible intake limits, posing potential health risks as indicated by bioconcentration factors and target hazard quotients. To validate the phytoremediation of aquatic macrophytes ,Dryopteris pentheri, Penther’s wood fern was grown in water amended with metals which showed the ability to tolerate and accumulate metals, confirming its suitability for phytoremediation applications. The study hypothesise that sediments, macrophytes, edible vegetables and ferns will accumulate and translocate the contaminants. Overall, this study highlights the urgent need for stricter regulation of industrial emissions into wetland systems and the importance of using plant-based remediation strategies to mitigate metal pollution. These findings contribute valuable insights for environmental management and public health protection in peri-urban and rural communities. In conclusion, to minimise the heavy metal contamination in wetlands. The findings of this study generally reveal that the concentrations of the analysed metals exceeded the permissible limits established by the World Health Organisation and the Food and Agricultural Organisation. Furthermore, since this study showed that the four aquatic macrophyte species can accumulate metals, it is recommended to also evaluate other plant species growing around the wetlands, not just aquatic macrophytes. Policymakers from Government Departments should develop clear frameworks to improve regulations for wetland protection against metal pollution and establish safety standards for agricultural practices and environmental protection, especially to safeguard vulnerable peri-urban and rural communities.