Micropollutants in Sewage Sludge: Elemental Composition and Heavy Metals Uptake by Phaseolus vulgaris and Vicia faba Seedlings

Abstract

Sludge is a major economic and environmental concern, and it can be reused for agricultural purposes. The germination success of seed and early growth regulation of plants treated with sludge requires more attention. The study evaluated the influence of municipal sewage sludge (0 and 5%) containing Cd, Co, Cu, Ni, Pb, and Zn, obtained from several sites and sampling dates, on germination and growth of bean (Phaseolus vulgaris L.) and Faba bean (Vicia faba L.) incubated at 25°C in the dark. Water uptake, reserve mobilization, and mineral nutrition in germinating P. vulgaris and V. faba seedlings were analyzed. Among studied heavy metals, zinc concentration was highest in sewage sludge (450 ± 5 mg kg−1 DW), while cadmium concentration was lowest (0.54 ± 0.1 mg kg−1 DW). The contents of Co, Cu, Ni, and Pb in the sewage sludge were about 5 ± 0.5, 104 ± 4, 17 ± 0.4, and 35 ± 0.5 mg kg−1 DW, respectively. Heavy metal concentrations were relatively similar independent of sewage sludge site (S1; S2; S3). Concentration of Zn is 85 ± 2 and 124 ± 2 μg g−1 dry weight in P. vulgaris and V. faba controls, respectively, to about 127 ± 2 and 148 ± 2 μg g−1 in both plants treated with sewage sludge. Metal amounts in this sewage sludge application rate (5%) are not toxic for germination process and growth of two tested leguminous plants. In this context, we shall try to use the 5% sewage sludge for seed germination. It appears that treatment of seed with the 5% sewage sludge was beneficial to germination and early plant development.