Fractionation, bioavailability and risk evaluation of phosphorus in lagoons surface sediments, Red Sea, Saudi Arabia

ABSTRACT In this study, eighteen surficial sediments were collected from two shallow lagoons of the Red Sea, King Saudi Arabia (Al-Shaibah and Al-Budhia lagoons), and analyzed for their grain size, CaCO3, and organic matter (O.M.) contents. The concentration of total phosphorus (TP), Organic-P (OP), and Inorganic-P (IP) were determined. In addition, Phosphorus bioavailability was also investigated by a sequential extraction procedure. The results of the current study showed variation in the levels of total phosphorus and the organic and inorganic form (TP, IP, OP). Al-Shaibah lagoon showed higher TP contents (274.78–389.24 and 265.91 ± 29.03 µgg-1) more than Al-Budhia lagoon (227.25–318.55 and 265.91 ± 29.03 µgg-1). The distribution of phosphorus bioavailability concentrations in the studied fractions in Al-Shaibah lagoon sediments was increased in the following order: hot H2O-P (0.10–0.25µgg−1) < NaHCO3-P (1.85–3.11 µgg−1) < exchangeable fraction (NH4Cl-P; 2.64–10.64 µgg−1) < Fe and Al-associated phosphorus (NaOH-P; 29.67–7.32 µgg−1). A similar order was observed in the Al-Budhia lagoon with slight differences in its content. The different fractions of the contribution of phosphorous bioavailability from the Total-P concentration were recorded as: NaOH-P (14.63–18.62%) >> NH4Cl-P (2.11–1.99%) > NaHCO3-P (0.75–1.04%) >H2O-P (0.05–0.09%). The phosphorus concentrations in the HCl-P fraction (calcium-associated phosphate/apatite) represent 32.67–59.60% of the total phosphorus in lagoon sediments.