Fingerprints of Anthropogenic Bromine and Chlorine in Sediments From a Highland Lake and Coastal Marshes of Portugal

Abstract

[Abstract] The bromine (Br) and chlorine (Cl) cycles significantly influence tropospheric chemistry, with implications for contaminant levels and climate. Both natural and anthropogenic sources (e.g., leaded gasoline combustion, flame retardants, chlorofluorocarbons—CFCs) contribute to the global budget of atmospheric Br and Cl, but their relative contribution has changed over time. This study aims to explore how the historical anthropogenic emissions of Br and Cl during the twentieth century are preserved in upland lakes and coastal sediments in Portugal and their relationship with the lead (Pb) record. For that, we analyzed two high marsh cores from Caminha (NW Portugal) and Alfeite (SW Portugal) and a lake core from Serra da Estrela (central Portugal). These cores provided a unique opportunity to study human-environment interactions and atmospheric contamination over the last ca. 100 years. X-ray Fluorescence Spectrometry (EDXRF) and X-ray fluorescence (XRF) core scanning were applied. The chronology is based on 210Pb supported by 137Cs. The results revealed significant correlations between Br/Al and Pb/Al (0.57–0.90; ρ < 0.02 to ρ < 0.001) and between Cl/Al and Pb/Al (0.76–0.90; ρ < 0.05 to ρ < 0.001) since the early twentieth century, indicating a common source of contamination. The increases of Br/Al, Cl/Al, and Pb/Al from the beginning of the century display peak values between the 1940s and 2000s. The SW record shows the highest Pb/Al ratios, with a single peak at AD 1982 ± 2, likely derived from the industrialization process, intensified in the 1960s. The sedimentary records of central and NW Portugal exhibit Pb/Al peaks that matched the Br/Al and Cl/Al ratios until AD 1988 ± 4, potentially reflecting the delayed phase-out of leaded gasoline in the European Union, particularly in southern countries. The remaining Br/Al peaks can be attributed to enhanced levels of Br gaseous species resulting from fumigation and flame retardants commonly applied to avoid wildfires in Iberia for the last decades. Recent peaks of Cl/Al (AD 1995 ± 2, AD 1998 ± 3) do not correlate with Pb/Al, possibly indicating the influence of anthropogenic emissions from CFCs, chloride (Cl−), and hydrogen chloride (HCl). In the lake record, this can also come from road de-icing practices. Our findings provide valuable insights for contaminant dispersion modeling studies across timescales.