Black Crusts as Geochemical Archives: Preliminary Results from Antwerp, Belgium

Interaction between the historical built environment and environmental pollution can result in the accumulation of weathering crust on building material surfaces. A subgroup of weathering crusts are black crusts, which consist of gypsum layers formed by sulfation on calcium-rich substrates. These crusts occur more often and are more pronounced in polluted environments such as urban settings. As a result, they can incorporate particulate matter, polyaromatic hydrocarbons, and heavy metals. Black crusts can act as non-selective passive samplers, accumulating distinct layers of air contaminants depending on historical pollution levels.
Existing studies provide only coarse-resolution reconstruction of pollution, differentiating solely between inner and outer crust layers. Just a few explore the correlation between different periods of exposure to pollution and the variation of the composition of these crusts. This study focuses on the stratigraphic analysis of black crusts to assess their potential as a reliable geochemical archive for the reconstruction of past anthropogenic pollution within urban settings.
Following technological developments in transportation and combustion, the composition of pollutants in the atmosphere has evolved over the centuries, likely reflected within weathering crusts where pollutants accumulate. For the identification of past air pollution signatures, lead can serve as a useful tracer due to its isotopes, their presence is the result of different historical pollution sources. Variations in the ratios of lead isotopes provide a means to attribute and differentiate among these pollution sources. For lead isotope analysis, high-resolution laser ablation mass spectrometry will be used to distinguish between 206Pb, 207Pb, and 208Pb.
This study deepens the understanding of localized pollution levels in urban settings, allowing the implementation of conservation interventions including cleaning and consolidation, strategies to mitigate the impact on human health, local ecosystems, and biodiversity, and to support urban planning.