An investigation of cadmium, zinc and lead isotope signatures and their use as tracers in the environment

• Main Author: Shiel, Alyssa Erin
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/27739

Environmental monitoring and remediation require techniques to identify the source and fate of metals emissions. In this study, Cd and Zn isotopes were evaluated as tools for the identification of metal sources through (1) the assessment of metallurgical processing as a source of Cd and Zn isotopic fractionation and (2) the measurement of isotopic compositions in bivalves from sites receiving variable metal contributions from natural and anthropogenic sources. This study was facilitated by the successful development of a technique to measure Cd and Zn isotopes (MC-ICP-MS) in environmental and anthropogenic samples. Cadmium, Zn and Pb isotopic ratios were measured for samples from an integrated Zn–Pb smelting/refining complex in B.C. (British Columbia, Canada). Significant fractionation of Cd and Zn isotopes during processing is demonstrated by the total isotopic variation in δ¹¹⁴/¹¹⁰Cd (1.04‰) and δ⁶⁶/⁶⁴Zn (0.42‰) among smelter samples. Characterization of Cd and Zn isotopic compositions in emissions as fractionated relative to ores demonstrates the tracing capability of this new tool. Moreover, Pb isotopic signatures may be used to identify sources contributing metals to environmental samples. Combined Cd, Zn and Pb isotope systematics were used to trace the source and distribution of these metals in bivalves from western Canada (B.C.), the USA and France. Variability in δ¹¹⁴/¹¹⁰Cd of bivalves (-1.20 to -0.09‰) is attributed to differences in the relative contributions of Cd from natural and anthropogenic (e.g., smelting) sources between sites. High Cd levels in B.C. oysters are identified as primarily natural, with some additional variability attributed to anthropogenic sources. In contrast, high Cd levels in French bivalves (Gironde estuary and Marennes-Oléron basin) are primarily anthropogenic. Variability in δ⁶⁶/⁶⁴Zn values exhibited by bivalve samples is small (0.28 to 0.46‰), with the exception of oysters from the polluted Gironde estuary (1.03 to 1.15‰). Lead isotopes are used to identify emissions from industrial processes and the consumption of unleaded gasoline and diesel fuel as metal sources to bivalve samples. This study demonstrates the effective use of Cd and Zn isotopes to trace anthropogenic sources in the environment and the benefit of combining these tools with Pb “fingerprinting” techniques.