Distribution of the bioavailable and total content of copper and lead, in river sediments of the Jamapa-Atoyac fluvial system, Mexico.

The Jamapa-Atoyac fluvial system (JAFS) is tropical river system, which flows from the Pico de Orizaba, the highest elevation in Mexico, to end in the city of Veracruz, in the southern Gulf of Mexico. The geology of the watershed is dominated by Tertiary igneous rocks and Cretaceous limestones in the upper basin, and Quaternary alluvial sediments in the lower basin. Seventy percent of the land in the watershed has been deforested, and there are various urban and industrial areas. The JAFS is been widely known as source of trace elements to the coastal zone, and considered as contaminated. So, the aim of this study was to assess the environmental quality of the JAFS, using the total (TC) and the bioavailable (BF) concentrations of Cu and Pb, in surface fluvial sediments samples, in the dry (DS) and rainy (RS) seasons of the 2016. Average concentrations and ranges for the JAFS were Cu 10.2 ± 5.2 μg/g (2.2-41.5 μg/g); Cu 1.1 ± 1.4 μg/g (0.04-10.7 μg/g); Pb 5.0 ± 1.2 μg/g (1.8-10.9 μg/g); and Pb 0.7 ± 0.4 μg/g (0.1-2.0 μg/g). The BF only accounts for the ~ 10% of the total concentration for both elements, and is highly correlated to the mud content. No differences in average concentrations were found between the upper and lower bassins, nor among areas with different lithology. Cu presented higher concentrations during the RS, which suggest an enrichment of fluvial sediments from soil erosion, contrary, to Pb with higher concentrations during the DS. Although, some sampling stations, those located immediately after the Cordoba and Miguel Aleman cities, presented higher than average Cu and Pb concentrations, they did not exceeded the limits established by national environmental regulations, sediment quality guidelines, geoaccumulation index, and potential ecological risk indexes. Hence, the JAFS may be considered as not contaminated by Cu and Pb.