Stable zinc isotopes as tracers in environmental geochemistry

Abstract

Zinc (Zn) is both an essential micronutrient and a common environmental contaminant. Addressing global Zn deficiency and pollution requires effective tools to track its biogeochemical pathways. Zn stable isotopes have become valuable tracers for identifying Zn sources, cycling processes, and anthropogenic impacts across different environmental systems. This review provides a comprehensive survey of Zn isotope signatures (δ⁶⁶Zn) across natural and anthropogenic sources and systematically evaluates the fractionation mechanisms operative during aqueous complexation, mineral sorption, biological uptake, and anthropogenic activities. It also covers advances in multi-collector inductively coupled plasma mass spectrometry and provides standardized protocols for sample preparation and isotope measurement. Key findings include bimodal δ⁶⁶Zn distributions in anthropogenic sources. Common sources (δ⁶⁶Zn = 0.23 ± 0.27‰) are isotopically lighter than natural sources (δ⁶⁶Zn = 0.46 ± 0.38‰), while smelting residues (δ⁶⁶Zn = 0.76 ± 0.40‰) and coal fly ash (δ⁶⁶Zn = 1.14 ± 0.69‰) are significantly heavier. In supergene environments, mass-dependent processes cause δ⁶⁶Zn variations of about 3‰. Zn isotopes have been applied in source apportionment, soil-plant system Zn translocation, and marine biogeochemical cycling studies. The review concludes that Zn isotopes are robust geochemical tracers for environmental systems, capable of resolving complex source inputs and pathways. To fully realize their potential, future work should focus on improving analytical methods for complex matrices, expanding applications in medical geology, and integrating digital technologies like artificial intelligence.