Owusu Adoma et al. 2024 — Heavy metals in lettuce and spring onion at anthropogenic sites in Kumasi, Ghana
This study measured Cu, Cr, Fe, Ni, and Zn concentrations in lettuce and spring onion collected from six anthropogenic activity sites (traffic, market, sewage farm, school grounds) in the Kumasi Metropolis, Ghana. Nickel contamination was particularly severe at the Buokrom Second Grade School site (BSGS), with mean Ni concentrations of 137.15 mg/kg in lettuce and 173.55 mg/kg in spring onion, far exceeding WHO/FAO maximum permissible limits. Sites near sewage treatment and heavy traffic corridors showed the highest multi-metal contamination, demonstrating that urban farming on anthropogenic land presents substantial food safety hazards for consumers.
Key numbers
Analytical method: AAS (ICP-MS or graphite furnace, details in source); dry weight basis. Values in mg/kg dry weight unless noted.
- Ni in lettuce: mean 137.15 mg/kg at BSGS (highest site); substantially exceeds WHO/FAO limit.
- Ni in spring onion: mean 173.55 mg/kg at BSGS (highest site); substantially exceeds WHO/FAO limit.
- Cr in lettuce: elevated across multiple sites; exact means by site tabulated in source.
- Zn and Fe: within or near permissible limits at most sites; highest concentrations at sewage farm site.
- Cu: variable across sites; some exceedances of permissible limits at high-traffic sites.
- Bioaccumulation factors were calculated for all metals; spring onion showed higher bioaccumulation efficiency than lettuce for most metals.
Methods (brief)
Vegetable samples digested with acid mixture; metals quantified by AAS. Total metals only; no Cr speciation (total Cr, not Cr-VI). Dry weight basis. Quality control with certified reference material.
Implications
Certification: Documents high Ni, Cr, and Cu in leafy vegetables from urban farming sites in Ghana, relevant to ingredient sourcing guidance for brands using Ghanaian leafy vegetable ingredients.
Courses: Illustrates urban food safety risks from proximity to traffic, sewage, and other anthropogenic contamination sources in developing-country urban agriculture.
App: Lettuce and spring onion from urban farming sites in West African cities warrant elevated Ni, Cr, and Pb flags when geographic provenance is urban/peri-urban.