Industrial and mining impacts on the organic matter of soils in a protected area of the Central Portuguese Coast: A petrographic and geochemical approach

Long-term industrial operations fueled by coal and oil have the potential to significantly impact surrounding ecosystems, particularly in the past when environmental regulations were less stringent. In this study, organic contamination was investigated in soils surrounding a former industrial complex and coal mining area on the Portuguese Atlantic coastline, active from the 19th century through the early 21st century. This area is currently included in the Natural Monument of Cabo Mondego, which highlights concerns regarding its environmental quality. Surface soil samples were investigated through a multi-technique approach using organic petrography, an uncommon yet powerful tool that provides unequivocal evidence of contaminants, and geochemical methods to identify sources of fossil fuel-derived contaminants. Results indicate that most of the samples exceed national reference levels for priority polycyclic aromatic hydrocarbons (PAH), with the highest concentrations found in the samples located up to 500 m from the former industrial facilities. These findings suggest that emissions from the industrial complex are the primary source of organic contamination in the area. Elevated levels of PAH (recognized environmental pollutants and human carcinogens) associated with contaminant combustion-derived organic particles (coke and char) raise environmental concerns. The presence of both local and imported coal particles in soil, along with the disposal of coal residues in the area, highlights contamination linked to historical coal handling and transport. The detection of charcoal particles in soil reflects the influence of regional wildfires that occurred in recent decades. These findings contribute to understanding the environmental vulnerabilities of the Cabo Mondego Natural Monument.