Reliability assessment of using different heavy metals in remote sedimentary records to reconstruct historical pollution.

Interpreting heavy metal variations in sedimentary records is an important approach to reconstruct historical pollution. However, few studies have investigated the reliability of using different heavy metals in sedimentary records for reconstructing historical pollution. This study retrieved sediment cores from two adjacent remote lakes in North China and investigated their temporal changes in excessive metal fluxes. Combined with a novel index of the ratio of atmospheric emissions of anthropogenic metals to background metal concentrations in lake sediments, the reliability and influencing factors of using eight metals (Cr, Co, Ni, Cu, As, Zn, Cd, and Pb) in sediments to reconstruct historical pollution were studied. (1) Vertical As variations in the sediments were controlled mainly by early diagenesis effects, although anthropogenic pollution might also have had an impact. Consequently, As profiles in lake sediment records are usually difficult to reflect historical pollution. (2) Among the eight metals, Zn, Cd, and Pb in both lakes have been affected considerably by anthropogenic pollution and insignificantly by natural factors. Their excessive flux variations in the two records were highly consistent with the historical trend of economic/industrial development. Relatively, these three metals can reliably reflect historical pollution. (3) Compared with Zn, Cd, and Pb, Cr, Co, Ni, and Cu in the two lakes have been relatively less affected by anthropogenic pollution. During the high anthropogenic metal emission period (post-∼1980), they could roughly reflect historical pollution in the region; however, during the low emission period (before ∼1980), they appeared to exhibit no signs of pollution. This suggests the complexity of using heavy metals in remote sediment records to reconstruct historical pollution. The importance of this study lies in its potential to provide guideline for the use of aquatic sediment records from relatively remote areas in reconstructing the history of metal pollution.