Grimmia pulla as a bioindicator of potentially toxic element contamination in the abandoned Angel Mine, Pinal de Amoles, Mexico

This study investigates the potential of the moss Grimmia pulla as a bioindicator for soil contamination by potentially toxic elements (PTE) from abandoned stibnite mine waste. Moss colonies were exposed to a concentration gradient of substrate contaminated with Zinc (Zn), Arsenic (As), Antimony (Sb), and Lead (Pb) over a three-month period. Metal accumulation, translocation, and the moss's biochemical oxidative stress response, quantified via glutathione (GSH) concentration, were evaluated. G. pulla exhibited a remarkable ability to accumulate four PTE, with concentrations in the phyllidia and rhizoids showing a direct, dose-dependent increase up to the highest treatment (C5). Bioconcentration Factor (BCF) analysis, however, classified the moss as an excluder under high-stress conditions. BCF values for Zn and As dropped precipitously from ≈ 1.0 in control soil to extremely low values (≤0.08) in high-contamination substrates. Translocation Factor (TF) analysis showed an initial retention pattern in the rhizoids at low-to-moderate contamination. At moderate contamination (C2) the TF for all elements Zn, As, Sb, and Pb maintained TF < 1, while at higher concentrations (C3-C5) TF increased to ≈ 1. GSH concentration in the moss was highest at but decreased at the highest concentrations (C3-C5), suggesting a saturation or overwhelming of the primary antioxidant defense system. Evans Blue (EB) staining showed a complex, non-linear dose-response for cell damage, peaking at the initial high-dose (C1) and then decreasing. Results confirm G. pulla's high tolerance and ability to accumulate PTE, validating its potential utility as a biomonitoring species for mining-impacted soils.