Metal pollution in aquatic ecosystems: a case study on Sontecomapan coastal lagoon (State of Veracruz) considered as a reference of pristine ecosystems

The presence of Cr, Ni, Zn, Cu, Co, Cd and Pb in sediments, submerged vegetation and bivalve mollusks on the Sontecomapan Lagoon, Veracruz during 1991-1992 were evaluated as well as their physicochemical and sedimentological parameters related to the solubility, geoaccumulation and bioavailability. The total and bioavailable concentration of metals in surface sediments was quantified, the highest levels were obtained at locations with large river discharges; Cr, Ni and Zn had the highest total concentrations and Ni presented a high ecological risk which represents more than 90 % mortality incidence for benthic species due to the intrinsic toxicity of this metal accumulated in the lagoon sediments. The low-carbonate sediment contains evidence of terrestrial origin, and there was a good correlation between the silts and clays with the organic carbon which values were within those reported for coastal lagoon ecosystems. The content of essential metals such as Cu and Zn were high in Crassostrea rizophorae oysters while potentially toxic elements such as Ni and Cr had high concentrations in the seagrass Ruppia maritima and mussel Brachidontes exustus. The Cd reported levels higher than the Pb in all evaluated organisms, mainly bivalves