Author(s): Beatriz Gonzalez_Perez; Maria Vicenta Esteller-Alberich; Sofia E. Garrido Hoyos; Carlos Diaz Delgado; Martin E. Jara Marini; Christophe Renac; Aurelie Barats

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Keywords: Complex costal system; Potential toxic elements; Sediment; Bioavailability; Ecological risk

Abstract: Due to the location between land and sea, the dynamics of a lagoon are often threatened by human activities. Sediments can be an important sink for potential toxic elements (PTE), they can also act as a secondary source of contamination when environmental conditions change, releasing contaminants in the water. Therefore, the human population could be put at risk due to its persistence, toxicity, non-destructible nature in the environment and its bioaccumulation in the food chain. The Tobari Coastal Lagoon (TCL), located in the Gulf of California, receives water discharges from agricultural areas, shrimp farms, livestock facilities, and raw municipal wastewater. During four seasons, the concentration of 10 PTE (As, Cd, Pb, Ni, Cu, Fe, Mn, Zn, Cr and Hg) was assessed in water before (FW, irrigation water) and after discharged through agricultural drains (DW, agricultural runoff) as well as in sediments. To obtain information on the mobility, distribution, and bioavailability of PTE and pollution status of TCL, a pollutant load of PTE was estimated, and sediments were evaluated using enrichment factor (EF), geoaccumulation index (Igeo), pollution index load (PLI), and potential ecological risk (PER) using Sediment Quality Guidelines (SQGs) and threshold effect level/probable effect level (TEL/PEL). In water, excluding Cd and Hg, the PTE concentration was DW > FW, increasing concentrations between FW and DW could be due to transport from agricultural soils to water drains by runoff. Concentrations in TCL water were the lowest; however, Mn, Zn, Cr and Hg exceed values estimated globally for this environment. The estimated pollutant load for a typical day was (kg/d/ ha): > 1 (Cd, Pb, Hg, Ni); 1 -3 (As, Cu, Cr, Zn) and > 10 (Mn, Fe). In sediments, mean total concentration was Fe > Mn > Zn > Pb > Cr > Cu > Ni > Cd > Hg > As; whereas bioavailable fraction (%) was As > Mn > Hg > Zn > Cd > Ni = Cr > Cu > Fe > Pb, that shows the bioavailability of PTE does not depend on the amount as a total concentration. EF and Igeo > 1 suggests that PTE are derived from anthropogenic activities, such is the case of Cd, Pb, Zn, and Hg for EF; and Hg and Cd for Igeo, with "strong and very strong" contamination levels. PLI (1.51) indicating TCL presents a progressive anthropogenic pollution. Finally, for PER assessment, only Hg concentrations suggest the probability of frequent ecological adverse effects. PTE are related to fertilizers (As, Cd, Pb, Cu, Zn), pesticides (As, Cd, Pb, Cu, Zn) and aquaculture farms (Cd, Cu, Pb, Zn). In addition, an important source of contamination by Cd and Hg is the atmospheric one and by As, Fe and Mn it is geogenic.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221720

Year: 2022