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(66/64)Zn values in water varied by approximately 1.3 per thousand (i.e., -0.66 per thousand to 0.65 per thousand relative to IRMM-3702 in August 2017). There were larger variations in delta(66/64)Zn values in water collected from the east shore (i.e., -0.66 per thousand to 0.37 per thousand) of the PRE close to industrialized areas, compared to those from the western shore (i.e., -0.23 per thousand to 0.13 per thousand), indicating the PRE was influenced by different Zn sources. The variations in delta(66/64)Zn values in water from estuarine locations were much larger than those collected from river mouths. Similarly, larger variations in delta(66/64)Zn values, were observed in suspended particles (i.e., -1.45 per thousand to 0.63 per thousand) relative to the water. Zinc isotopic differences (i.e., (66/64)Zn per thousand) between particle and water were significantly (p<0.05) and linearly correlated with Zn concentrations in particles between 0.8 to 10 microm 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(66/64)Zn values (using variations in water salinities) vs. observed delta(66/64)Zn indicates that Zn isotope ratios in water in the PRE can be useful for predicting the mixing processes in the water.