Mercury flowing through ecosystem

Mercury's Journey: Unveiling How Toxins Accumulate in Upland Ecosystems

Nico Varela in Climate & Environment September 2025 • 4 min read.

"Discover the surprising path of methylmercury in northern Minnesota's forests and peatlands, and what it means for wildlife."

Mercury, especially in its methylated form (MeHg), poses a significant threat to both human and wildlife health. Gaseous mercury emissions travel long distances, impacting even remote ecosystems. Once deposited in terrestrial environments, mercury can either accumulate in soils or be re-emitted into the atmosphere. However, some of it transforms into complexes with organic matter and contaminates aquatic and wetland ecosystems.

Wetlands, particularly peatlands, are prime locations for MeHg production due to their wet, oxygen-poor conditions that favor anaerobic microbes responsible for mercury methylation. Higher MeHg concentrations occur where groundwater surfaces, or at the boundary between upland forests and peatlands. This zone becomes a "hot spot" for mercury methylation.

While we know mercury methylation is elevated at the terrestrial-peatland interface, it's unclear how this translates into actual accumulation within living organisms. This article investigates the levels of total mercury and MeHg in peat, invertebrates, and tissues of masked shrews (Sorex cinereus) living in a northern Minnesota forest-peatland ecotone to examine how effectively MeHg is bioaccumulated in an atmospherically-contaminated environment

Unpacking Mercury's Path: From Peat to Predators

Researchers examined the "S7" watershed within the Marcell Experimental Forest in northern Minnesota. The watershed includes an upland forest and a bog peatland, creating a clear upland-peatland ecotone. Samples of surface peat, invertebrates (captured using pitfall traps), and juvenile masked shrews were collected during the summer. Scientists measured both total mercury (Hg) and methylmercury (MeHg) levels in these samples.

The study revealed that peat collected from the upland-peatland interface contained a relatively high proportion of MeHg (3.5% of total Hg). Concentrations of MeHg were also found in various invertebrate taxa, including:

Lumbriculidae (oligochaete worms)
Lycosidae (wolf spiders)
Araneae (mixed spiders)
Carabidae (ground beetles)
Polydesmus spp. (millipedes)
Pholcidae (cellar spiders)

Predatory spiders (Lycosidae and mixed Araneae) exhibited the highest MeHg concentrations, suggesting that MeHg biomagnifies as it moves up the food web. While earthworms had relatively low concentrations of Methylmercury. Muscle tissue from shrews had the highest mercury concentrations, while the brain and liver had lower concentrations. Nearly all mercury in the shrews was in methylated form. Interestingly, mercury concentrations in shrews increased with age, implying a continuous accumulation of mercury in their bodies.

The Bigger Picture: What Does This Mean for Ecosystem Health?

Although the peatland environment was efficient at producing methylmercury, this did not lead to particularly elevated concentrations in invertebrates or shrews. Concentrations were below those considered a toxicological risk to the health of wildlife. The research suggests that in areas without significant mercury pollution sources, the risk of mercury bioaccumulation in terrestrial food webs may be lower than previously thought.

This study underscores the complex interplay between mercury methylation, bioaccumulation, and food web dynamics in upland-peatland ecosystems. While the study site did not exhibit alarming levels of mercury accumulation, it highlights the importance of ongoing monitoring and research to assess the potential risks of mercury contamination in these sensitive environments.

Further research could explore the long-term effects of MeHg exposure on shrew populations, investigate the role of other prey items in MeHg accumulation, and examine how climate change might influence mercury methylation rates and bioaccumulation in peatland ecosystems.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1007/s00128-017-2198-z, Alternate LINK

Title: Accumulation Of Methylmercury In Invertebrates And Masked Shrews (Sorex Cinereus) At An Upland Forest–Peatland Interface In Northern Minnesota, Usa

Subject: Health, Toxicology and Mutagenesis

Journal: Bulletin of Environmental Contamination and Toxicology

Publisher: Springer Science and Business Media LLC

Authors: Ilana Tavshunsky, Susan L. Eggert, Carl P. J. Mitchell

Published: 2017-10-23

Everything You Need To Know

What exactly is methylmercury (MeHg), and why is it so concerning?

Methylmercury, abbreviated as MeHg, is a particularly dangerous form of mercury because it's a potent neurotoxin. It's created through a process called methylation, where inorganic mercury is transformed by microorganisms into this organic form. MeHg can accumulate in living organisms, posing health risks to both wildlife and humans who consume contaminated organisms. It's especially concerning because it can biomagnify, meaning its concentration increases as it moves up the food chain.

Why are peatlands considered prime locations for the production of methylmercury?

Peatlands, because of their unique environmental characteristics, are ideal sites for methylmercury production. Their waterlogged, oxygen-deprived conditions promote the activity of anaerobic microbes, which are responsible for mercury methylation. The area where groundwater surfaces, specifically at the boundary between upland forests and peatlands, creates a hotspot where mercury methylation occurs at an elevated rate.

What key elements within the northern Minnesota forest-peatland ecotone were analyzed to understand methylmercury accumulation?

The research examined the levels of total mercury and methylmercury in peat, various invertebrate taxa (including Lumbriculidae, Lycosidae, Araneae, Carabidae, Polydesmus spp., and Pholcidae), and the tissues of masked shrews (Sorex cinereus). By measuring mercury concentrations in these different components of the ecosystem, the study sought to understand how effectively methylmercury bioaccumulates in an atmospherically-contaminated environment.

Which organisms in the study area exhibited the highest concentrations of methylmercury, and what does this suggest about the food web?

The study found that predatory spiders, specifically Lycosidae (wolf spiders) and Araneae (mixed spiders), had the highest concentrations of methylmercury, indicating that MeHg biomagnifies as it moves up the food web. This means that predators accumulate higher concentrations of MeHg from their prey. Additionally, the muscle tissue of masked shrews contained the highest mercury concentrations, nearly all of which was in the methylated form. Mercury concentrations in shrews increased with age, suggesting a continuous accumulation of mercury in their bodies over time.

What are the broader implications of these findings for ecosystem health, considering the levels of methylmercury found in invertebrates and shrews?

Despite efficient methylmercury production in peatlands, the concentrations found in invertebrates and masked shrews were below levels considered a significant toxicological risk to wildlife health. This suggests that in areas without significant local mercury pollution sources, the risk of mercury bioaccumulation in terrestrial food webs might be lower than previously assumed. This highlights the complex interplay between mercury methylation rates, environmental conditions, and the overall health of the ecosystem, underscoring the importance of considering broader ecological factors when assessing mercury contamination risks.