Indirect impacts of irrigation with low quality water on the environmental safety

Using low quality water for irrigation is probably one of the main reasons for contaminating the arable lands with potentially toxic elements (PTEs), especially within the arid and semiarid regions. On the other hand, most farmers depend therein on natural inefficient drainage systems to get rid of excess water flows. It was thought that the hydraulic continuities exist, totally or partially, among (a) the underground waters of the arable lands that receive low quality water for irrigation, (b) the underground waters of the nearby lands that use fresh Nile water for irrigation and (c) the sources of fresh water themselves.Therefore, the following assumptions were considered because of their potentially high ecological implications: H1: soil leakage of low quality irrigation water might have negative consequences on the quality of fresh water itself that is used for irrigating the nearby arable lands. H2: concentrations of PTEs in irrigation water are probably the main factors controlling their corresponding available and total concentrations in soil. H3: concentrations of PTEs within the edible parts of plants grown on the nearby areas irrigated with fresh water are relatively high and may be considered not suitable for consumption.To investigate the above-mentioned hypotheses, irrigation water (fresh Nile, underground and wastewaters), soil and plant samples were collected from three different governorates i.e. New Salhia (El -Sharqia), ElSaff (Giza) and Meet Kenana (Qualubia). One site from each governorate was selected to represent the arable lands that use fresh Nile water for irrigation while the other sites were irrigated with either the underground water or wastewater solely. Quality of the fresh (Nile) irrigation water used in the studied locations was estimated as class II on the basis of its salinity hazards. The other water samples were estimated to be,according to the same basis, as of potentially high or very high salinity hazards. In case of water sodicity, SAR values did not exceed “13” in nearly most water samples. The BOD and COD values exceeded the acceptable levels (even in the Nile fresh water). Moreover, the measured values in fresh water seemed to be comparable, to some extent, with the corresponding ones estimated for either the underground or wastewaters; accordingly, we accept H1. Concentrations of the PTEs i.e. Pb, Co and Cd in all the collected water samples, generally, did not exceed the maximum permissible levels (MPLs). However, Ni was the only one among the studied PTEs whose concentration exceeded the MPL only in the underground water of New Salhia during the summer season. It is worthy to mention that AB-DTPA extractable PTEs were correlated significantly with PTEs concentrations in irrigation water. Also, AB-DTPA extractable PTEs were correlated significantly with their total contents in soil; hence, we partially accept the second hypothesis i.e. H2 Furthermore; concentrations of PTEs in the edible parts of plants irrigated with fresh Nile water exceeded their permissible levels and therefore, we partially admit H3since using low quality water for irrigation showed potential hazards on the food quality obtained from the nearby arable lands irrigated with fresh water.