Anthropogenic and natural sources of lead at Terra Nova Bay (Antarctica) based on elemental and isotopic evidence

Environmental context Lead (Pb) is a toxic element that accumulates in the environment due to natural and anthropogenic processes. Antarctic ecosystems, mainly influenced by long-range transport, are ideal regions to investigate global Pb pollution and its evolution over time. Pb concentrations in Antarctic biota have reduced over time, likely due to reduced use of leaded petrol, but still contains a substantial human-derived fraction. Rationale In the assessment of chemical contamination by heavy metals, it is difficult to distinguish the relative contributions of natural and anthropogenic sources, and to ascertain how they change over time. This study aimed at providing new information on the sources of lead (Pb) in the Antarctic coastal waters of Terra Nova Bay, in past and present times. Methodology The samples were collected at Terra Nova Bay, during 1996–98 and in 2021, and analysed for their Pb mass fraction and isotopic composition. Samples included marine biota (Trematomus bernacchii fish and the Adamussium colbecki mollusc), suspended particulate matter (SPM) and surface sediment. The sediment was further fractionated both physically (fine fraction, <63 µm, and coarse fraction, 63–2000 µm) and chemically (labile and total Pb). Results Pb mass fractions in organisms collected in 1996–98 (0.13–1.00 µg g−1) were higher than those from 2021 (0.02–0.17 µg g−1), with significant differences (P < 0.05) in specific tissues and organs: shell for the mollusc, gonads and spleen for the fish. The labile Pb mass fraction in the fine sediment averaged 3.27 µg g−1, representing <10% of the total Pb. In seawater, the concentration of Pb associated to SPM was at the nanogram per litre level, peaking at 25-m depth. The Pb isotopic composition in biota revealed mixing of natural and anthropogenic inputs, with near-equal contributions. A similar pattern was also evident for Pb associated with SPM and the labile Pb in the fine sediment fraction, whereas labile Pb associated to the coarse fraction and total Pb were mostly composed of natural origin Pb. Discussion The decrease in Pb mass fraction in biota from 1996–98 to 2021 suggests a general reduction of global Pb pollution, likely due to a decline in the use of leaded petrol. Nonetheless, isotopic data indicate that a significant fraction of Pb in Terra Nova Bay is still of anthropogenic origin, although the amount of bioavailable Pb is far from being of concern.