Assessment of pollution and metal toxicity in the bed sediment of El-Rayan Lakes, Fayoum, Egypt

Abstract

Sediments are vital components of aquatic ecosystems, which trap and store various essential elements as well as harmful polluting substances. This is why sediment quality assessment is of great importance in measuring the quality, or pollution, of water bodies. In this study, the levels, ecological risk, and toxicity indices of 17 heavy metals (HMs) were evaluated in the sediments of the two lakes: Upper Wadi El-Rayan Lake (UWRL) and Lower Wadi El-Rayan Lake (LWRL). Both are important wetlands in Egypt used as agricultural drainage water reservoirs for Fayoum province. As revealed by the texture of the sediments, the sand represented the major sediment portion of the UWRL, while the mud was dominant in the LWRL. According to ecological risk assessment, the sediments of the two lakes suffer different degrees of metal pollution, mainly Cd, Pb, and Ni. Based on sediment quality guidelines, toxicity indices indicated different potential toxic effects of the studied HMs on benthic-dwelling organisms, but Ni and Ba had the highest potential biological risk. Results also revealed that the area facing the El-Wadi Drain is the most polluted due to its proximity to the water drainage entrance. However, LWRL is generally more polluted than UWRL. This is related to the shrinkage of water volume and lake area; it causes an increase in the concentration of metals in water, and thus an increase in the sedimentation rate of these metals into the bottom.