Cadmium Concentration in Vegetables Grown on Urban Soils Irrigated with Untreated Municipal Sewage

Abstract

Cadmium (Cd) is considered as a potential toxin that is principally dispersed in natural and agricultural environments through anthropogenic sources. Untreated municipal sewage, often a potential source of Cd, is generally used to irrigate urban agricultural soils in many developing countries. A study was carried out to determine Cd concentration in untreated municipal sewage and sewage-irrigated soils and vegetables. The metal ion concentration in municipal sewage was found 3-fold (0.03 mg L−1) its permissible concentration in irrigation water (≤0.01 mg L−1). Ammonium bicarbonate–diethylene triamine pentaacetic acid NH4HCO3–DTPA) extractable Cd concentration in top 0.15 m soil ranged between 0.25 and 0.34 mg kg−1. Soil Cd concentration was significantly correlated with soil clay content, pH, electrical conductivity, and cation exchange capacity. Cadmium availability index (CDI) decreased with an increase in soil depth. The metal ion was found in leaf (0.17–0.24 mg kg−1 fresh weight) and fruit (0.07–0.18 mg kg−1 fresh weight) portions of all the sampled vegetables: bitter gourd (Momordica charantia L.), cauliflower (Brassica oleracea L.), eggplant (Solanum melongena L.), fenugreek (Trigonella foenumgraecum L.), okra [Abelmoschus esculentus (L.) Moench], onion (Allium cepa L.), pumpkin (Cucurbita pepo L.), and spinach (Spinacia oleracea L.). Leafy tissue accumulated Cd about twice that of the fruit portion. Our results suggest that prolonged ingestion of sewage-irrigated leafy vegetables can develop such Cd levels in human body that may cause a number of illnesses.