Cadmium‐enriched Sewage Sludge Application to Acid and Calcareous Soils: Relation Between Treatment, Cadmium in Saturation Extracts, and Cadmium Uptake

Abstract

AbstractThe objective of this study was to determine the effect of soil pH on the availability of saturation‐extract Cd. Four acid and four calcareous soils were treated with a uniform amount of sewage sludge enriched with different amounts of CdSO4 to yield soil Cd concentrations ranging from 0.1 to 160 µg Cd/g of sludge‐amended soils. These treated soils were placed in plastic containers and cropped for approximately 7 weeks with sweet corn (Zea mays L.), tomato (Lycopersicon esculentum Mill.), and Swiss chard (Beta vulgaris var. ‘cicla’). Shoot weights were obtained as a measure of yields. The concentration of Cd in the shoot (Cd uptake) was taken as a measure of Cd availability.Saturation extracts from each treated soil (7 Cd rates × 3 replicates × 8 soils) collected at harvest time were analyzed for pH, ECe, principal soluble anions, and cations with Cu, Cd, Ni, and Zn. The chemical analyses of the saturation extracts were used as input data to calculate the concentration of free ionic Cd (Cd2+), the activity of Cd2+ (aCd2+), and the concentration of Cd complexes. These Cd parameters, along with the measured concentration of all Cd forms present in saturation extracts (CdT), were compared to Cd concentrations in each of the test plants (µg Cd/g shoot). Results of these comparisons showed: (i) CdT was more available in acid than calcareous soils; (ii) Cd uptake by the test plants correlated equally well with the concentration of CdT, Cd2+, or aCd2+; and (iii) uptake of Cd was plant‐species dependent. Chard and tomato accumulated 2 to 3 times more Cd than corn when grown on the acid soils.