Assessment of heavy metal bioaccumulation in sorghum from neutral saline soils in the Po River Delta Plain (Northern Italy)

Po River Delta is situated in the Padania Plain at the confluence with the Adriatic Sea. Since the second half of the nineteenth century, human activities have been focused on the reclamation of wetlands, in order to use them for agricultural purposes. Nowadays these reclaimed soils are mainly used to cultivate cereals and horticultural crops. The mail problem related to this kind of soils is their capability to retain heavy metals. These can be transferred to the cultivations and to the humans, being in some cases very dangerous. It is therefore fundamental to investigate the amount of heavy metals present in reclaimed soils and that which could be transferred to the plants. With this aim, a reclaimed soil that has been used for sorghum cultivation was chosen as test field. Heavy metal concentrations of the soil, the rhizosphere and the seeds, as well as the roots and some aerial parts of the sampled sorghum were measured, respectively. High Cr and Ni concentrations were detected in the soil and rhizosphere samples, related to their natural availability due to the presence of chlorite and serpentine in these soils. On the contrary in the seeds, micronutrients such as Zn and Cu have higher concentrations with respect to Cr and Ni, but all the metals (except Cd) are below the national admitted limits. Metals classified as non-essential for humans (As, Cd, Cr, Ni) are scarcely absorbed by the plant, and their average concentrations decreased according to this pathway: soil > rhizosphere > root > aerial parts > seed. Cd, Zn and As are richer in the rhizosphere with respect to the bulk soil.