In a recent article published in Frontiers in Environmental Science, researchers investigate the potential of using tree rings from the Ficus insipida species as biomonitors for gaseous elemental mercury (GEM) emissions in the Peruvian Amazon, particularly in areas impacted by artisanal and small-scale gold mining (ASGM).
The significance of this study lies in the urgent need to address the ambiguous estimates of mercury emissions globally, largely due to the informal and poorly regulated nature of ASGM activities. By accumulating atmospheric GEM in trees' wood following stomatal uptake, the research aims to leverage dendrochemistry to provide a clearer spatial and temporal picture of mercury emissions from such mining activities.
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Background
Artisanal and small-scale gold mining is recognized as a leading source of anthropogenic mercury emissions worldwide. Despite its widespread existence, accurate data on mercury emissions from this sector are scarce, undermining efforts to develop effective mitigation strategies.
The study contextualizes the role of trees, particularly Ficus insipida, in accumulating atmospheric mercury. This species has been selected due to its abundance in the neotropics and its potential to retain mercury in its tree rings over time.
As previous studies have primarily focused on coniferous species in temperate regions, this research pioneers the use of tropical hardwood for assessing mercury exposure due to mining activities in the Amazon.
The Current Study
The methodology involved collecting tree core samples from Ficus insipida at various sites within the Peruvian Amazon. A total of five sites were selected: three were in proximity to mining activities, while two were remote and unimpacted by ASGM. At each site, cores from four individual trees were extracted.
The collected cores were analyzed for total mercury concentrations using advanced spectrometric techniques to understand the differences between mining-impacted and remote sites.
The study compared these concentrations to corresponding atmospheric GEM measurements to evaluate potential correlations. The analysis focused on historical trends in mercury presence during two distinct periods: the pre-mining era (1941-1999) and the post-mining expansion era (2000-2019).
Results and Discussion
The results revealed significant variations in tree ring mercury concentrations based on their proximity to ASGM activities. Near mining towns, tree rings exhibited an average mercury concentration of 6.0 ng/g, compared to merely 0.9 ng/g observed at remote sites. A strong linear correlation was observed between recent tree ring mercury levels and atmospheric GEM concentrations across all sampling locations (p < 0.0001, r² = 0.64).
Notably, this correlation was even stronger during the dry season, characterized by heightened ASGM activity (p < 0.0001, r² = 0.76). These findings underscore the utility of tree rings as effective biomonitors of atmospheric mercury levels in affected regions.
The temporal analysis demonstrated an increasing trend in mercury concentration in tree rings from the most impacted sites, indicating a consistent rise corresponding to the intensification of ASGM activities over time.
The study also addresses potential limitations regarding the translocation and diffusion of mercury across tree ring boundaries; however, it concludes that the overall average mercury concentrations in bolewood serve as a reliable proxy for assessing spatial variability in mercury emissions on both local and regional scales.
In terms of broader implications, the outcomes of this study contribute meaningful insights into global mercury regulation efforts. The data support the objectives of the UNEP Minamata Convention, which is designed to reduce mercury emissions and associated health risks. By utilizing tree rings in this capacity, the research enhances our understanding of the persistent impacts of mercury pollution from AML practices and offers a substantial foundation for evaluating the effectiveness of ongoing pollution reduction policies.
Conclusion
The study concludes that Ficus insipida is an effective biomonitoring tool for quantifying atmospheric mercury levels in areas influenced by artisanal gold mining in the neotropics.
The research demonstrates that tree rings can successfully characterize the spatial and temporal impacts of GEM emissions from ASGM activities.
The findings advocate for integrating dendrochemistry into broader environmental monitoring frameworks, which could assist policymakers in more accurately determining regional baselines of mercury contamination.
Such information is crucial for crafting appropriate interventions to mitigate the adverse effects of mercury pollution, particularly to protect vulnerable human populations and ecosystems in affected regions.
Overall, this research presents a novel approach to understanding and addressing mercury pollution associated with artisanal mining activities, highlighting the importance of continuous monitoring and the implementation of environmentally friendly regulatory practices.
Source:
Gerson J., Lehnherr I., et al. (2025). Ficus insipida tree rings as biomonitors for gaseous elemental mercury in the artisanal gold mining-impacted Peruvian Amazon. Frontiers in Environmental Science, 13, 1531800. DOI: 10.3389/fenvs.2025.1531800, https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2025.1531800/full