Does consumption of leafy vegetables grown in peri-urban agriculture pose a risk to human health?

Concentrations of potentially toxic elements were measured in soils and five contrasting tropical leafy vegetables grown in a replicated field trial at five contaminated urban agriculture sites in Kampala City, Uganda. Soil contamination at each site could be tentatively ascribed to known waste disposal practices. There was considerable variation in metal uptake between vegetable types. Washing leafy vegetables reduced chromium and lead concentrations but exogenous contamination of leaves also depended on vegetable type, with Gynandropsis gynandra L. showing a marked tendency to accumulate Pb and Cr. For the worst case scenario of children consuming unwashed vegetables, some metal ‘hazard quotient’ (HQ) limits (1.0) were violated at four of the five sites studied. For the 25 ‘site-vegetable’ combinations assessed, the HQ for Pb exceeded 1.0 in 36% of cases. A vegetable-specific site screening tool based on soil extraction with 0.01 M CaCl2 and extrapolation to provide HQ values was assessed.

► Solubility of toxic metals in soils used for urban agriculture is highly variable.
► Washing leafy vegetables prior to cooking reduces consumption of Cr, Pb, As and Ni.
► Lead (Pb) presents the greatest hazard in produce from agriculture in Kampala City.
► Agriculture in East African cities can be practiced safely with the right choices.
► Soil screening to predict hazard to consumers may be useful in site surveys.