In a research paper published in the journal Water, Air, & Soil Pollution, lead author Matheus Bortolanza Soares and his team investigate a novel approach to addressing the critical issue of mercury contamination in the Amazon biome. The study explores the environmental potential of nanobiochar and thiol-modified nanobiochar derived from açaí processing residues as a means to immobilize mercury in soils affected by illegal artisanal gold mining. This type of contamination is a significant public health and ecological concern in South America, particularly for river-dwelling populations whose diet heavily depends on fish that may accumulate mercury through the food chain. By converting abundant local waste into a reactive remediation tool, the researchers provide a sustainable strategy that addresses both waste management and toxic pollution in tropical environments.

The investigation reveals that reducing the particle size of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More to a nanometric scale, combined with chemical modification using sulfur-containing thiol groups, significantly improves the material’s ability to stabilize mercury in the soil. The pristine nanobiochar particles, which averaged approximately 27 nanometers in size, already showed an ability to decrease the most mobile forms of mercury. However, the introduction of thiol functional groups through a process called functionalization optimized the surface chemistry of the particles, creating specific sites with a high chemical affinity for mercury ions. This modification resulted in a 13 percent increase in the specific surface area and a 30 percent increase in negative surface charges compared to the untreated nanobiochar, which directly enhanced the material’s overall reactivity.

A primary finding of the study is the marked shift in how mercury is distributed among different soil compartments following the application of the modified particles. The researchers used a sequential extraction process to track mercury across exchangeable, reducible, oxidizable, and residual fractions. Both the standard and modified nanobiochar successfully reduced the exchangeable mercury fraction, which is the form most easily taken up by living organisms. The thiol-modified version proved to be 10 percent more efficient than its pristine counterpart in this regard, ultimately reducing the most available mercury pools by a total of 17 percent. This outcome is significant because it indicates that the mercury is being held in much more stable forms that are resistant to leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More or plant absorption.

The mechanism driving this superior performance in the thiol-modified particles is the formation of strong covalent bonds between the mercury and the sulfur-containing groups on the biochar surface. While oxygen-containing groups like carboxyl and phenolic structures in standard biochar do provide some binding capacity, the mercury-sulfur complexes formed in the modified version are thermodynamically much more stable. The research also highlights how the application of these particles influences the overall soil chemistry, such as increasing the soil solution pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More from 5.4 to as high as 6.8. This rise in pH further aids in the immobilization of mercury by promoting the precipitation of mercury compounds and increasing the binding affinity of other soil minerals.

While the study was conducted under controlled laboratory conditions, the findings suggest that this technology is a scalable and cost-effective option for large-scale environmental recovery efforts in the Amazon. The use of açaí waste as the raw material is particularly beneficial, as it provides a valuable use for a byproduct that is produced in massive quantities in the region—over 200,000 tons annually in Brazil alone—and often causes disposal problems. The authors conclude that while more long-term field trials are necessary to observe how these materials behave under varying weather conditions over many years, the current results offer a clear mechanistic understanding of how nanobiochar can mitigate ecological risks in contaminated tropical soils.

Source: Soares, M. B., Silva, R. A. G., & Alleoni, L. R. F. (2026). Potential use of thiol-modified biochar nanoparticles for Hg immobilization in Amazon biome soil. Water, Air, & Soil Pollution, 237(830).