Distribution, speciation, and assessment of heavy metals in sediments from Wadi Asal, Red Sea, Egypt

Abstract

Globally, the environmental contamination of stream sediments due to geogenic and anthropogenic sources is of growing concern. In this study, the heavy metals (Cd, Co, Cr, Cu, Ni, Pb, and Zn) in 22 superficial sediments in Wadi Asal, Red Sea, Egypt, were explored to assess sediment sources, the mobility of chemical species, and the degree of contamination in sediments. Therefore, the total heavy metal values in the fine fraction (< 63 μm), a five-step sequential extraction on selective samples, risk assessment, and principal component analysis (PCA) were applied. The mobility of heavy metals in Wadi Asal sediments, according to non-residual fraction percent, declines in the following order: Cd (90.9%) > Pb (85.2%) > Co (84.4%) > Cu (80.8%) > Zn (75.9%) > Ni (48.4%) > Cr (39.6%); indicating the high mobility of Cd, Zn, Pb, Cu, and Co. The mean metal contamination factor (CF) order is Cd (10.96) > Ni (3.91) > Cr (2.77) > Zn (2.18) > Pb (2.10) > Co (1.12) > Cu (0.70). The Geo-accumulation Index (Igeo) is decreased in the following order: Cd (2.19) > Ni (0.78) > Cr (0.55) > Zn (0.44) > Pb (0.42) > Co (0.22) > Cu (0.14). The risk assessment code (RAC) revealed very high to high risk for Cd, Co, and Pb. The results pointed out that the metals Cr, Co, Cu, and Ni are from geogenic sources, while Zn, Cd, and Pb are from anthropogenic sources due to Pb–Zn mining activities. Based on the threshold effect level (TEL), Cd, Cr, Ni, and Pb have adverse effects on living organisms. According to these findings, the area along Wadi Asal and the downstream regions on the beach are highly polluted and heavy metal monitoring in sediments and aquatic organisms is recommended.

Environmental zoning based on the distribution of potentially toxic elements, risk contamination indices, and bioindicators in three areas affected by gold mining in Antioquia, Colombia

“…Indices such as PLI, ecosystem risk indices like NIPI, RAC, and GAI, serve as indicators of contamination levels in soils and/or sediments. However, they do not represent the biological systems' response to variations in contaminants concentration (Kowalska et al, 2018;Rodríguez-Seijo et al, 2020;Yari et al, 2021;Mosalem et al, 2024;Salazar et al, 2024). The use of plants and/or other organisms has been employed to complement mathematical indices (Nannoni & Protano, 2016;Rodríguez-Seijo et al, 2020;Salazar et al, 2024).…”

“…For example, the total and bioavailable concentrations of these elements, along with their comparison to background values, have been employed (Marrugo-Negrete et al, 2017;Gallego and Olivero-Verbel 2021). Various pollution indices have been calculated, including geochemical, ecological risk, human health risk, among others indices (Kowalska et al, 2018;Rodríguez-Seijo et al, 2020;Yari et al, 2021;Mosalem et al, 2024;Salazar et al, 2024). Furthermore, bioindicators have emerged as valuable tools, facilitating the evaluation of biological responses to changes in contaminant levels within the environment.…”