Metals in size-fractionated core sediments of Jiaozhou Bay, China: Records of recent anthropogenic activities and risk assessments

Highlights: • Metal contents showed a decreasing trend with increasing grain sizes. • The metal fractions loaded on 32–63 μm and > 63 μm grain sizes were higher. • The fraction with grain size > 63 μm was more linked to anthropogenic activities. • Cd, Co, Cu and Ni in > 63 μm fractions were at medium risks. - Abstract: Total contents and chemical speciation of Co, Ni, Cu, Ga, Mo, Cd, In, Sn, Sb, V, W, Tl, Bi and U in size-fractionated ( 63 μm) core sediments from Jiaozhou Bay were investigated to reveal their responses to anthropogenic activities. Metal contents showed a decreasing trend with increasing grain sizes. However, the loadings of metal fraction on 63 μm grain sizes were 16%, 47% and 37%, respectively. Anthropogenic fluxes and enrichment factors of metals in > 63 μm fraction were closely linked to anthropogenic activities, with an obvious increase in upper 27 cm (1998–2015) and a slight decrease in 2009 year. Metals (especially for Cd, Co, Cu and Ni) in > 63 μm fraction were more easily released, with the highest percentage of acid soluble form and lowest residual form. Thus, the size fraction of > 63 μm cannot be ignored.