Assessment of concentrations of heavy metals in three leafy vegetables irrigated with wastewater in Hadnet district, Mekelle, Ethiopia

Abstract

ABSTRACT Mekelle is one of the Ethiopian cities suitable for urban and peri-urban agriculture for cultivating leafy vegetables using wastewater. The consumption of unprocessed and processed leafy vegetables is also very high in the city. Wastewater samples collected from four experimental sites (ESs) in Hadnet district of the city had higher concentrations in 4 (i.e., Cd, Cr, Cu, and Mn) of the 10 heavy metals tested than the permissible limit established by pertinent standards. Spring water samples collected from another site called Kallamino, designated as a comparison site, also had higher concentrations in 4 (i.e., Al, As, Cd, and Cu) of the 10 heavy metals tested. However, the leafy vegetables grown in the least contaminated ES had higher concentrations in 6-7 of the 10 heavy metals tested. The lettuce and spinach samples had elevated concentrations of As and Al, respectively. The wastewater used to irrigate vegetable farms in Hadnet district is not safe enough. More importantly, the soils of the farms might have accumulated far more heavy metals. The cultivated lettuce, spinach, and cauliflower are highly contaminated. Thus, the use of wastewater for irrigating urban and peri-urban farms needs to be regulated.