210Pb-derived ages for the reconstruction of terrestrial contaminant history into the Mexican Pacific coast: potential and limitations.

(210)Pb is widely used for dating recent sediments in the aquatic environment; however, our experiences working in shallow coastal environments in the Pacific coast of Mexico have demonstrated that the potential of (210)Pb for reliable historical reconstructions might be limited by the low (210)Pb atmospheric fallout, sediment mixing, abundance of coarse sediments and the lack of (137)Cs signal for (210)Pb corroboration. This work discusses the difficulties in obtaining adequate sedimentary records for geochronological reconstruction in such active and complex settings, including examples of (210)Pb geochronologies based on sediment profiles collected in two contrasting areas coastal areas (mudflats associated to coastal lagoons of Sinaloa State and the continental shelf of the Gulf of Tehuantepec), in which geochemical data was used to support the temporal frame established and the changes in sediment supply recorded in the sediment cores which were related to the development of land-based activities during the last century.