Biomonitoring of radioactive contamination using benthic invertebrate communities in Manzala Lake, Egypt

Manzala Lake, the largest in Egypt’s Nile Delta, has significant human activity. The Lake’s ecological condition has recently been impacted by a significant increase in agricultural, industrial, and urban wastewater discharge. A valuable tool for monitoring the water quality of Manzala Lake is the sensitivity of invertebrate species to various types of pollution, such as radioactive contamination. Activity concentrations of radionuclides Radium-226 (²²⁶Ra), Thorium-232 (²³²Th), Potassium-40 (⁴⁰K), and Caesium-137 (¹³⁷Cs) were measured in water, sediments and benthic invertebrate samples in 2020. The benthic community’s spatial distribution and the radionuclides’ bioaccumulation were evaluated to determine possible relationships. Thirty taxa of benthic invertebrates were recognised. The data illustrated that the mean activity concentration of radionuclides in water was in the order of ⁴⁰K > ²³²Th > ²²⁶Ra > ¹³⁷Cs, which changed into ⁴⁰K > ²²⁶Ra > ²³²Th > ¹³⁷Cs in the sediment and benthic invertebrates. Gastropoda and Ostracoda are the dominating groups of benthos in the lake and are related to the highest concentrations of radionuclides. The benthos species with shells dominated at the sites with the highest activity concentration of ²²⁶Ra, while soft-bodied organisms dominated in sites with the highest average ¹³⁷Cs activity in these samples.