Speciation and Ecological Risks of Cobalt and Antimony in Black-Necked Crane (Grus nigricollis) Habitat Sediments in China's Caohai Lake

摘要

The potential ecological risks of cobalt (Co) and (Sb) in the sediments of the black-necked crane habitats in Caohai Lake, Guizhou Province were assessed based on total concentration and speciation via Tessier sequential extraction procedure. The results showed that the concentration of Co in the study region is in the range of 4.29-23.79 mg.kg(-1), with an average of 15.41 +/- 3.4 mg.kg(-1), which is lower than the soil background concentration in Guizhou Province. The concentration of Sb is in the range of 1.4-1.69 mg.kg(-1), with an average of 1.51 +/- 0.3 mg.kg(-1), which is 13.7 times higher than the soil background value of Sb in Guizhou Province. The concentrations of Sb in the west and southeast regions were greater than those in the other parts of the habitats. Co mainly existed in residual and Fe-Mn oxides forms, which account for 68.73-89.14% of total Co. However, Sb mainly existed in residual forms, which account for 79.84-93.11% of the total Sb. The carbonate and organic forms of the two elements and the Fe-Mn oxides of Sb decreased along with decreased water depth. The exchangeable fractions of the two elements were lower than 1% and do not exhibit obvious changes with water depth. The potential ecological risk index of Co (E-Co) shows that Co in the five habitats (Liujiaxiang, Zhujiawan, Wangjiayuanzi, Huyelin, and Yangguanshan) was at a moderate risk level. The potential ecological risk index of Sb (E-Sb) shows that Sb in the five habitats was at a considerable risk level. All of the RI indexes were at mild and moderate risk levels, which Sb makes a large contributor. According to an assessment of the ratio of the secondary phase to the primary phase, Co and Sb present little pollution and potential ecological risk in the study regions. It can be seen that the evaluation of the ecological impact by the total amount of heavy metals does not necessarily reflect its hazards objectively, and should be monitored and evaluated in combination with heavy metal forms.