Selenium and tellurium fractionation, enrichment, sources and chronological reconstruction in the East China Sea

Surface and core sediments of the East China Sea (ECS) were collected to study spatio-temporal distributions and chemical fractions of Se and Te and to evaluate their enrichment and sources. Higher Se and Te concentrations in surface sediments appeared in the inner shelf and near the Cheju Island. It seemed to be controlled by sources and sediment characteristics. Enrichment factors (EFs) showed that Se and Te were at minor and moderate enrichment, respectively. Sequential extraction suggested that non-residual fractions of Se and Te accounted for high percentages (29.5 ± 16.2% and 50.9 ± 13.2%) in total, combined with risk assessment code (RCA), indicating that Se and Te were at medium and high risks, respectively. All temporal profiles of abundances, EFs and burial fluxes (BFs) of Se and Te displayed higher values before 1900, in 1989 and 2009, and in the period of 1960–1980 with a peak in 1970. These higher values were closely associated with biological and anthropogenic activities.