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.