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 δ66Zn values in water varied by approximately 1.3‰ (i.e., -0.66‰ to 0.65‰ relative to IRMM-3702 in August 2017). There were larger variations in δ66Zn values in water collected from the east shore (i.e., -0.66‰ to 0.37‰) of the PRE close to industrialized areas, in comparison to those from the western shore (i.e., -0.23‰ to 0.13‰), indicating that the PRE was influenced by different Zn sources. The variations in δ66Zn values in water from estuarine locations were much larger than those collected from river mouths. Similarly, larger variations in δ66Zn values were observed in suspended particles (i.e., -1.45‰ to 0.63‰) relative to the water. Zinc isotopic differences (i.e., Δ66Zn‰) between particles and water were significantly (p < 0.05) and linearly correlated with Zn concentrations in particles between 0.8 and 10 μm 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 δ66Zn values (using variations in water salinities) vs observed δ66Zn values indicates that Zn isotope ratios in water in the PRE can be useful for predicting the mixing processes in the water.