Total and DTPA-extractable forms of potentially toxic metals in soils of rice fields, north Nile Delta of Egypt

The soil quality of rice fields in Egypt has been increasingly studied; however little attention has been paid to metal pollution. The current work aimed at investigating the distribution of total and DTPA-extractable Cd, Co, Cu, Pb, Ni and Zn in Kafr El-Sheikh Governorate, one of the greatest rice-producing regions in Egypt. The studied area covers 88709 ha between 31 degrees 01' 30 '' to 31 degrees 25' 05 '' N and 30 degrees 25' 34 '' to 30 degrees 54' 64 '' E. Twenty-five soil profiles were dug and 75 samples were collected at 0-30, 30-60 and 60-100 cm. The total and DTPA-extractable fractions of the studied metals showed decreases with depth. Total Co was within the safe limit, while Cd, Cu, Pb, Ni, and Zn showed potential risks in the three layers. The DTPA-extractable forms of Cd, Co, Pb, and Ni were within the safe limits, while Cu and Zn surpassed these limits. The single pollution index and enrichment factor followed the sequence: Cd > Pb > Cu > Zn > Ni > Co. The pollution load index indicated high to extreme pollution levels in the topsoil, while moderate levels in the subsurface and deep layers. Metal availability ratios were less than 3% and closely related to pH, organic matter and Fe and Mn. Effective measures should be implemented to alleviate metals accumulation (mainly Cu and Zn) in rice soils to reduce their translocation from soil to edible parts of crops. (C) 2020 Elsevier B.V. All rights reserved.