Short-term anomalous ecotoxicity and ecological risks from phosphorus in the surface sediments in Rosetta and Damietta Estuaries, East Mediterranean Egypt

The Rosetta and Damietta estuaries, located along Egypt’s northern coast, are critical ecosystems that have been significantly impacted by human activities, leading to increased phosphorus input and subsequent ecological risks. This study assesses the distribution and ecological risks of phosphorus fractions in the surface sediments of these estuaries. Surface sediment samples from 22 sites were analyzed for water content, grain size, total organic carbon (TOC), total carbonates (TCO 3 ), and various phosphorus fractions. The results reveal that inorganic phosphorus (IP) dominates the total phosphorus (TP) content, with an average contribution of 91% in the Rosetta estuary and 88% in the Damietta estuary. The study finds significant correlations between phosphorus content and finer sediment fractions, such as silt and clay. Sediment quality guidelines and ecological risk indices indicate that while most sediment samples fall within the “moderately polluted” range, some areas exhibit severe phosphorus enrichment, posing substantial risks to benthic organisms. The ecotoxicological assessment, using risk quotient (RQ) and toxic unit (TU) values, shows that phosphorus presents moderate to high risks, particularly for algae, followed by fish and invertebrates. The study highlights the need for continuous monitoring and management of phosphorus pollution to protect the ecological integrity of these vital estuarine systems.