Abstract

The effects of cadmium and lead and their interaction on germination behavior and early seedling growth stage of the medicinal plant (Nigella sativa L.) were investigated. Seeds were grown in Petri dishes (9 cm diameter) in a complete randomized design with three replicates for each treatment. The heavy metals were Cd (100 and 300 mg/L), Pb (600 and 1500 mg/L) and all possible combinations. Results showed that final germination percentage and root length were greatly reduced at all heavy metals treatment. Reduction was markedly higher at higher concentrations. Root growth (length and fresh weight) was relatively higher than shoot growth at control. Dry weight showed another reduction with the increase in heavy metals concentrations. Cadmium was more toxic than lead where no growth measurements were recorded for seedlings treated with the high concentration of Cd whether applied alone or combined with Pb. The synergistic effect of Cd and Pb was stronger than their effects as single metals. The synergistic and antagonistic interactions of both heavy metals were discussed.