Unraveling lead sources in a tropical urban Swamp Forest: Insights and challenges

We investigate the contributions of natural (geogenic) and anthropogenic sources of lead (Pb) to the Nee Soon Swamp Forest, a relatively undisturbed catchment in Singapore. Using a Bayesian statistical source tracking approach with Pb isotopes preserved in sediment sections, our findings reveal a predominance of geogenic Pb in contemporary sediments, despite the significant presence of anthropogenic Pb in aerosols from local and distant sources. However, the geogenic Pb isotope signatures of the two main soil types in the catchment overlap with those of anthropogenic sources, introducing considerable uncertainty in using Pb isotopes as tracers within this catchment and potentially across larger areas. This uncertainty raises concerns about past interpretations of Pb contamination in both terrestrial and aquatic environments in Singapore and the broader region. To address these challenges, we emphasize the importance of accurately determining the signatures of all natural sources before using Pb isotopes as tracers in future studies. We also suggest that incorporating additional Pb isotope ratios or other stable isotope ratios (e.g., Ba, Cu, Sr, Zn) could enhance our ability to distinguish between natural and anthropogenic Pb sources. Ultimately, our study highlights the complexity of Pb sources in the environment and underscores the need for more comprehensive approaches to assessing their impacts.

Synopsis

This paper highlights insights and challenges in lead (Pb) source tracing studies conducted in urban catchments. These challenges primarily stem from the inadequate identification of all Pb isotope sources. We address these challenges by employing a Bayesian statistical approach to effectively identify, discriminate, and quantify Pb sources within a wetland ecosystem in Singapore.