Risk assessment of toxic metals in marine sediments from the Arctic Ocean using a modified BCR sequential extraction procedure

Surface sediment samples were collected from the Pacific sector of the Arctic Ocean during the 6(th) Chinese National Arctic Research Expedition (CHINARE), 2014. Concentrations and extractabilities of six toxic metals (Cd, Cr, Cu, Ni, Pb, and Zn) were determined using a modified sequential extraction procedure as described by the European Community Bureau of Reference (BCR). A new analytical hierarchy approach to risk assessment, involving sediment quality guidelines and risk-assessment codes, is described for metals in marine sediments from the Arctic Ocean. Results indicate a mobility order of Pb > Cd > Cu > Zn > Ni > Cr with mean liable fraction (F1+F2+F3) being 83.0%, 81.6%, 62.0%, 47.1%, 42.1%, and 15.6%, respectively. Ni presents the most serious ecological risk in the study area, with most samples (93.9%) indicating medium risk, followed by Cu (54.5%) and Zn (27.3%). For Ni and Zn, there are also samples showing high ecological risk (Ni at site NB02, northern Bering Sea; Zn at R07, northern Chukchi Sea). The ecological risk for Cr indicates low ecological risk (93.9%) and some medium risk (6.1%). All Cd assessments indicate low ecological risk, while most Pb assessments indicate zero (33.3%) to low risk. The new ecological risk assessment method improves on assessments based on metal mobility or concentration alone.