Tracing Sources and Pathways of Trace Elements in Polar Regions by Isotopic Analysis

This PhD thesis focuses on the development, optimization and validation of robust analytical methods for accurate and precise isotopic analysis of Pb, Sr, Hg and Cd and their subsequent environmental application in extreme environments such as Antarctica and the Arctic. This work has been carried out in the contex of the National Antarctic Research Programme (PNRA). The primary objective is to trace the sources of heavy metals and assess their environmental impact using advanced inductively coupled plasma mass spectrometry (ICP-MS) techniques. The thesis is organized into eleven chapters as follows. The first chapter of this PhD thesis provides a description of the importance of Pb, Sr, Hg, and Cd, with a focus on their environmental applications. This includes a summary of their chemical characteristics, most common sources, toxicity, exposure pathways, health implications, and a general overview of their complex biogeochemical cycles. In addition, the capabilities of high-precision isotopic analysis as a means to study the occurrence of these heavy metals in the Antarctic and Arctic environment and a general overview of the their isotopic signatures reported for several environmental matrices, are provided. Chapter 2 summarizes the basic operating principles of ICP-MS, the technique of choice for isotopic analysis. In this chapter, the setup used during this PhD, comprising a cold-vapor generation (CVG) system for Hg introduction, an Aridus II desolvating system, single- and multi-collector ICP-MS instruments, are briefly described. Finally, the last part of this chapter is devoted to instrumental mass discrimination, a phenomenon strongly affecting MC-ICP-MS measurement results. This section discusses the origin of instrumental mass discrimination, the most widely applied approaches used for mass bias correction within the scientific community, and a more in-depth description of the correction approach selected in this PhD research project for Hg isotopic analysis. Chapter 3 investigates the biogeochemical cycle of lead in Antarctic coastal waters. In this work, the isotopic composition of Pb, together with the concentration, in marine biota, suspended particulate matter (SPM) and sediments collected in 1996-98 and 2021 was used to investigate the temporal trends and identify potential natural/anthropogenic sources of contamination in the coastal marine environment of Terra Nova Bay. Chapter 4 examines the Hg cycle in Antarctic coastal waters by determining its total content andn isotopic composition in the same fish Trematomus bernacchii, bivalve molluscs Adamussium colbecki and sediment samples used in Chapter 3. This work focused on the Hg isotopic variations related to trophic transfer in marine fauna and sex- and organ-specific differences in the fish. The Chapter 5 explores the Cd biogeochemical cycle in the Antarctic environment, emphasizing chromatographic separation, isotope ratio measurements, and method validation. The objective of this study was to establish a method for accurate and precise Cd isotopic analysis at low concentration levels using MC-ICP-MS with a standard sample introduction system (wet plasma conditions) and Faraday cup amplifiers equipped with 1013 Ω resistors. The developed method was subsequently applied to determine Cd isotope ratios in Adamussium colbecki bivalve and Trematomus bernacchii fish samples collected during the 1996-98 and 2021 in Terra Nova Bay, Antarctica. This analysis aimed to provide insights into the natural and anthropogenic sources of Cd and to investigate potential changes in its biogeochemical cycle in this environment over time. Chapter 6 analyzes atmospheric Pb sources in the Arctic by combining isotopic analysis of airborne particulate samples with back-trajectory modeling to identify anthropogenic and natural contributions. In this work, the experimental design approach was used to optimise the operating conditions of the quadrupole-based ICP-MS. Chapter 7 focuses on atmospheric Sr sources reaching the Antarctic plateau. This chapter describes the optimization of analytical methods and their application to Antarctic snow samples to identify Sr sources. This study focused on two primary objectives: (1) to develop and optimize a cost-effective single-quadrupole ICP-MS method for accurate Sr isotopic fingerprinting, enabling source apportionment of mineral dust and particulate matter (PM); and (2) to enhance 87Sr/86Sr records for the East Antarctic Plateau by analyzing 132 snow pit samples collected at Dome C, covering the period 1958–2019, along with surface samples from 2016–2017 and reference soils from Patagonia and Chapter 8 summarizes the key findings of the thesis, linking them to the initial objectives and discussing the environmental implications of the study. Finally, Chapter 9 contains supplementary materials, including tables, figures, and Chapter 10 and 11 contain the references, and the list of the scientific publications.