Mercury pollution in terrestrial ecosystems of North Macedonia: insights from an 18-year moss biomonitoring programme

Moss biomonitoring was conducted in 2002, 2005, 2010, 2015 and 2020 to evaluate atmospheric mercury (Hg) deposition across N. Macedonia as part of a comprehensive survey of potentially toxic elements (PTEs). More than 70 samples of the dominant moss species Hypnum cupressiforme and Homalothecium lutescens were collected during the summer field campaigns. Mercury concentrations were determined using cold vapour atomic absorption spectrometry and inductively coupled plasma mass spectrometry (ICP-MS). The results revealed marked temporal fluctuations: median Hg content increased from 56 μg/kg in 2002 to 68 μg/kg in 2005, peaked at 93 μg/kg in 2010, then decreased to 84 μg/kg in 2015, and further to 52 μg/kg in 2020. Over the study period, Hg concentrations ranged from 10 to 595 μg/kg, with the highest variability observed in 2010. Spatial distribution maps and regional comparisons indicate that elevated Hg contents correspond predominantly to anthropogenic sources, particularly in industrialised zones and regions affected by mining and metallurgical activities. The 2020 dataset shows a significantly lower median value (52 μg/kg) compared to previous surveys, indicating a slight improvement in air quality, although local hotspots persist. These results highlight the importance of long-term moss biomonitoring as a cost-effective approach for tracking atmospheric mercury trends and informing national environmental policy.