Historical trends of polychlorinated dibenzo-p-dioxins and dibenzofurans in three dated sediment cores from Mexico

This paper describes the first report of dioxins and furans (PCDDs/Fs) in sediment cores from Mexico. Sedimentation rates and vertical fluxes were estimated using 210Pb dating. Two cores correspond to marine sediments and one to an endorheic lake. Concentrations of PCDDs/Fs found in the three sites are typical of non-impacted areas with low concentrations when compared to reference values. However the PCDDs/Fs sediment profiles show an increasing concentration trend in the upper core sections. This behavior is different from that found at many sites around the globe where diminishing concentrations have been reported. A strong predominance of OCDD was observed, and a comparison to typical composition profiles of industrial and other sources did not result in clear origin assignments for these measured compounds. We suggest that local sources may be responsible for the increase in concentration and, because these undetermined sources have not been curtailed, their importance is still growing.

Research highlights► PCDDs/Fs are reported for the first time in three dated core sediments from Mexico. ► It was determined that one characteristic of congener profiles for the three sites is that they are quite similar. ► The most preponderant congener was the OCDD, which may indicate similarity of sources, persistence of this congener or even long term transport and degradation of less chlorinated congeners. ► The increase in concentration for the sum of PCDDs/Fs for all three sites is not in agreement with reported trends at other sites suggesting that local sources may be growing in importance. ► PCDDs/Fs concentrations are typical of un-impacted sites.