Bibliometric and systematic evaluation of lichens for biomonitoring in hydrocarbon pollution and mining

Hydrocarbon pollution from oil spills, traffic emissions, and industrial processes continues to be a significant global threat to biodiversity, soil quality, water quality, and human health. Lichens, mutualistic life forms between fungi and photobiont symbionts that lack a protective cuticle, are widely used as biomonitors because they integrate atmospheric inputs and accumulate organic and inorganic contaminants. However, evidence for lichen-based hydrocarbon biomonitoring is methodologically heterogeneous, with limited comparability across studies regarding taxon selection, analytical endpoints, exposure design, and reporting practices. Here, we combine a global bibliometric analysis with a systematic review to map research trends in environments influenced by mining, where co-exposure to metals is frequently reported alongside organic fractions. The literature shows the recurrent use of taxa such as Xanthoria parietina , Pseudevernia furfuracea , Evernia mesomorpha , Cladonia mitis , and Hypogymnia physodes , but there is substantial variability in the measured variables and protocols. Polycyclic aromatic hydrocarbons and total petroleum-related fractions are the primary organic targets across studies, often accompanied by metal tracers (e.g., Hg, As, Pb, Cu) for source attribution and characterization of co-pollutants. We highlight implications for environmental monitoring in resource-limited regions and propose priority elements for standardization to improve reproducibility and cross-study synthesis.