Using Zn Isotopic Signatures for Source Identification in a Contaminated Estuary of Southern China

Zinc isotope ratios in water and suspended particles (SP) were measured in the Pearl River Estuary (PRE), China. Site-to-site delta Zn-66 values in water varied by approximately 1.3 parts per thousand (i.e., -0.66 parts per thousand to 0.65 parts per thousand relative to IRMM-3702 in August 2017). There were larger variations in delta Zn-66 values in water collected from the east shore (i.e., -0.66 parts per thousand to 0.37 parts per thousand) of the PRE close to industrialized areas, in comparison to those from the western shore (i.e., -0.23 parts per thousand to 0.13 parts per thousand), indicating that the PRE was influenced by different Zn sources. The variations in delta Zn-66 values in water from estuarine locations were much larger than those collected from river mouths. Similarly, larger variations in delta Zn-66 values were observed in suspended particles (i.e., -1.45 parts per thousand to 0.63 parts per thousand) relative to the water. Zinc isotopic differences (i.e., Delta Zn-66 parts per thousand) between particles and water were significantly (p < 0.05) and linearly correlated with Zn concentrations in particles between 0.8 and 10 mu m in size at most of the estuary stations, suggesting that Zn partitioning between dissolved and particulate phases influences the observed differences in Zn isotope ratios. A significant (p < 0.0001) linear correlation between the predicted delta Zn-66 values (using variations in water salinities) vs observed delta Zn-66 values indicates that Zn isotope ratios in water in the PRE can be useful for predicting the mixing processes in the water.