Assessment of Heavy Metal Accumulation in Wastewater–Receiving Soil–Exotic and Indigenous Vegetable Systems and Its Potential Health Risks: A Case Study from Blantyre, Malawi

Chimwemwe Chiutula (), Andrew G. Mtewa, Amon Abraham, Richard Lizwe Steven Mvula, Alfred Maluwa, Fasil Ejigu Eregno and John Njalam’mano
Additional contact information
Chimwemwe Chiutula: Department of Energy Resources, Ndata School of Climate and Earth Sciences, Malawi University of Science and Technology, Limbe, Blantyre P.O. Box 5196, Malawi
Andrew G. Mtewa: Department of Applied Studies, Chemistry Section, Malawi Institute of Technology, Malawi University of Science and Technology, Limbe, Blantyre P.O. Box 5196, Malawi
Amon Abraham: Department of Energy Resources, Ndata School of Climate and Earth Sciences, Malawi University of Science and Technology, Limbe, Blantyre P.O. Box 5196, Malawi
Richard Lizwe Steven Mvula: Department of Earth Sciences, Ndata School of Climate and Earth Sciences, Malawi University of Science and Technology, Limbe, Blantyre P.O. Box 5196, Malawi
Alfred Maluwa: Directorate of Research and Outreach, Malawi University of Science and Technology, Limbe, Blantyre P.O. Box 2109, Malawi
Fasil Ejigu Eregno: Department of Building, Energy and Material Technology, Faculty of Engineering Science and Technology, UiT, The Arctic University of Norway, Postboks 385, 8514 Narvik, Norway
John Njalam’mano: Department of Water Resources Management, Ndata School of Climate and Earth Sciences, Malawi University of Science and Technology, Limbe, Blantyre P.O. Box 5196, Malawi

IJERPH, 2025, vol. 22, issue 11, 1-19

Abstract: Urban and peri-urban farmers in Malawi increasingly use treated and untreated wastewater for vegetable production, but little is known about the extent of heavy metal accumulation in both exotic and indigenous vegetables, particularly with respect to differences between edible tissues (leaves vs. stems). This study addresses this gap by measuring the concentrations of cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), and copper (Cu) in wastewater, soils, and six vegetables including three exotic and three indigenous irrigated with effluent from the Soche Wastewater Treatment Plant in Blantyre. Metal concentrations were determined using Atomic Absorption Spectrophotometry. Wastewater contained Zn (0.01 ± 0.001 mg/L) and Cu (0.02 ± 0.018 mg/L), both below World Health Organization (WHO) and Malawi Bureau of Standards (MBS) limits (Zn: 0.2 mg/L; Cu: 2 mg/L), while Cd, Cr, and Pb were below detection limit. In soils, Zn reached 56.4 ± 0.5 mg/kg, exceeding the WHO limit of 36 mg/kg; other metals remained within WHO permissible values. Vegetables showed species- and tissue-specific variation in metal accumulation: Cr reached 4.65 mg/kg in Cucurbita moschata stems, Cd up to 0.31 mg/kg in Amaranthus retro-flexus leaves, and Pb up to 4.09 mg/kg in Brassica rapa stems—all above FAO/WHO permissible limits (2.3, 0.2, and 0.3 mg/kg, respectively). Duncan’s post hoc analysis confirmed significant differences ( p < 0.05) across matrices and plant parts, with leaves generally accumulating more Zn and Cu than stems. Principal component analysis (PCA) revealed that Zn, Cu, Cr, and Pb in the wastewater-soil-vegetable system largely share a common source, likely wastewater effluent and historical soil contamination, while Cd showed a more sporadic distribution, highlighting differential accumulation pathways. Health risk assessments revealed high Health Risk Index (HRI) values, with Brassica rapa stems (HRI = 92.3) and Brassica rapa subsp. chinensis leaves (HRI = 82.2) exceeding the safe threshold (HRI > 1), indicating potential chronic risks. This study reveals potential health risks associated with wastewater irrigation due to heavy metal accumulation in edible vegetables, and therefore recommends further research on metal speciation, seasonal variation, and bioaccumulation at different crop growth stages.

Keywords: consumption; daily intake; health risks; heavy metals; vegetables; wastewater (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2025
References: Add references at CitEc
Citations:

Downloads: (external link)
https://www.mdpi.com/1660-4601/22/11/1614/pdf (application/pdf)
https://www.mdpi.com/1660-4601/22/11/1614/ (text/html)

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:gam:jijerp:v:22:y:2025:i:11:p:1614-:d:1777721

Access Statistics for this article

IJERPH is currently edited by Ms. Jenna Liu

More articles in IJERPH from MDPI
Bibliographic data for series maintained by MDPI Indexing Manager ().