Rare Earth Elements and Yttrium (REE+Y) patterns in recent Anadara brasiliana shells from Playa Norte, Barra de Cazones (Veracruz, Mexico): Evidence of anthropogenic contamination linked to river output?

摘要

We measured and interpreted Rare Earth Element and Yttrium concentrations of ten recent Anadara brasiliana (Lamarck) shells from Playa Norte (Barra de Cazones, Veracruz, Mexico). We aimed to identify the source of these elements, along with addressing some environmental conditions attributable to them. REE + Y patterns show modern seawater signals, particularly positive La/La* and Y/Y* anomalies as well as marked depletions of light REEs and middle REEs in comparison to heavy REEs) (x over line PrSN/YbSN = 0.127, x over line NdSN/YbSN = 0.16 and x over line DySN/YbSN = 0.444, respectively). The cause for La/La* anomalies can also be explained by means of anthropogenic contamination, yet this question remains unresolved. Pronounced negative cerium anomalies were also recognised [(Ce/Ce*) = 0.262], which point to oxidising conditions. Y/Ho ratios (ranging from 35.85 to 64.91; average = 44.68) are in part superchondritic (range 44-74). Values lower than these (35.85-39.83) may account for the closeness to the nearby-flowing Cazones River, which runs through many important cities and populations in Veracruz, such as Poza Rica, Coatzintla and Barra de Cazones. In addition to the referred REE anomalies, we report notable positive Sm/Sm* and Gd/Gd* anomalies. The former may be an evidence of contamination caused by petroleum industry in this region, which is well known for its hydrocarbon production. For its part, the latter may mirror river contamination by means of contrast reagents poured into freshwater and ultimately into the ocean. This study shows the first results of a long-term project, which aims to elucidate the REE + Y dynamics in the Gulf of Mexico coastal system at the state of Veracruz, eastern Mexico.