Anthropogenic and natural sources of lead at Terra Nova Bay (Antarctica) from an earlier and recent sampling campaign, based on elemental and isotopic evidence

Rationale. In the assessment of chemical contamination by so-called 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 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 1996-1998 and in 2021, and analyzed for their Pb mass fraction and isotopic composition. Samples included marine biota (the fish T. bernacchii and the mollusc A. colbecki), 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 (p<0.05) differences in specific tissues/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 ng/L level, peaking at 25-m depth. The Pb isotopic composition in biota testified of the mixing of natural and anthropogenic inputs, with near-equal contributions. A similar pattern was also evident for Pb associated to SPM and the labile Pb in the fine sediment fraction, whereas the coarse and refractory fractions were mostly constituted by Pb of natural origin. Discussion. The decrease in Pb mass fraction in biota suggests a general reduction of global Pb pollution, likely due to the decline of leaded gasoline use. However, isotopic data also evidence that a significant fraction of Pb in the environment of Terra Nova Bay is still of anthropogenic origin, although the amount of bioavailable Pb is far from being of concern.