Speciation, Distribution, Ecological and Health Risk Assessment of Cobalt and Nickel in Surface Sediment of a Typical Bay Along the Southeast Coast of China

Surface sediments collected from 36 sites in Xiamen Bay were studied, using the sequential extraction method, ecological and health risk assessment, in order to understand the speciation, distribution, and potential risks of the Cobalt (Co) and Nickel (Ni) in this area. The residual state is the main occurrence form of the study objects, followed by the exchangeable state. The mobility and bioavailability inferred from the chemical speciation was greater for Co than for Ni. The high concentrations were observed in nearshore areas where the human activities were intensive. The two elements were mainly derived from terrestrial weathering and human activities, while their distributions were mainly affected by organic matter. The results of multiple evaluation methods showed that the pollution and ecological risk in this area were at a medium-low level. The non-carcinogenic risks of Co for children and the carcinogenic risks of Ni for adults exceeded the safety threshold.