Nutrients and heavy metals accumulation by the giant milkweed Calotropis procera (Aiton) WT Aiton in urbanized areas, Egypt

The present study was conducted to evaluate the accumulation potential of Calotropis procera for nutrients and heavy metals and its impact on the forage quality of such medicinal plant. Three plant individuals of C. procera as well as three composite soil samples, collected from four urban habitats (residential areas, road sides, railways, and fallow lands) were analyzed for nutrients and heavy metals. It was indicated that all soil heavy metals, except Cd and Pb in railways, were in the safe range. The plant leaves from residential areas contributed to the highest concentrations of total N, P, Na, and Mg, in addition to ash content, crude protein, and crude fibers, while those from railway habitat had the highest values of digestible, metabolized, net, and gross energy. On the average, all investigated metals had bioaccumulation factor (BF) more than unity with the highest value recorded for Cd. Moreover, the order of uptake capability of heavy metal was in the order Cd > Fe > Mn > Zn > Cu > Pb. C. procera had a good forage quality, but it could not be used as animal forage in polluted areas, since it can accumulate high concentrations of heavy metals in toxic levels. The high BF of this species to Mn and its significant positive correlation with its soil content renders this species suitable as a good bioindicator and biomonitor for this heavy metal.