Background construction for tracing metal inputs in estuarine sediments of the Liaodong Bay (NE China): Linear-regression method.

Intertidal sediments are a significant reservoir of trace metals originating from human activities and natural weathering. However, the absence of geochemical background levels and the heterogeneity of sediment components are challenging to quantify the extent of trace metal contamination. For distinguishing the contribution of natural and anthropogenic inputs, dynamic background functions were established by linear regressions of trace metals (i.e., Zn, Cr, Ni, Cu, Cd, and Pb) against normalizer Al in three cores of the Daliao River estuary. Lead-210 geochronology indicated that trace metals have accumulated rapidly in the sediments since 1985 CE. The calculation results of enrichment factors and excess fluxes confirmed that the increased contents of Zn and Cd were contaminated by human activities. Conversely, the increased contents of others (i.e., Cr, Ni, Cu, and Pb) were attributed to variations in geological background levels, driven by the combination of grain size and organic matter. Overall levels of trace metals were at medium-low ecological risks (MSQG-Q: 0.19-0.38), and Ni at high-medium ecological risks (PEL-Q > 0.5) in recent decades. Interestingly, these Ni probably originated from natural weathering rather than anthropogenic inputs because sediment quality guidelines lacked consideration for the differences in regional background levels and grain size. This procedure could provide the fundamental framework for regional investigations of spatial and temporal contamination, applied to other similar intertidal zones of sediment quality management.