Microbial Biodegradation of Cyanide in Mining-Affected Sediments from Southern Ecuador

The exponential rise in global demand for precious metals has driven gold extraction activities across more than 70 countries. In Ecuador, artisanal and small-scale gold mining (ASGM) accounts more than 50% national gold production. However, the lack of adequate waste management in ASGM operations results in significant contamination of aquatic ecosystems, primarily due to the use of cyanide (CN⁻) in ore processing. Previous studies in southern Ecuador have reported cyanide concentrations as high as 1 mg/L in rivers impacted by mining activities, with detectable levels persisting up to 3 km downstream from the contamination sources. Given that the maximum permissible limit established by Ecuadorian environmental regulations is 0.01 mg/L, these findings indicate a severe level of contamination in the affected water bodies. In this context, bioremediation emerges as a promising approach to mitigate cyanide pollution using native microbial communities. This study investigated the biodegradation potential of indigenous microorganisms in sediments and mine tailings from two key mining regions in Ecuador. Samples were collected from Yantzaza (Zamora Chinchipe), the site of Ecuador’s largest industrial gold mine, and from rivers Amarillo and Puyango in Portovelo, a historically significant ASGM zone. Microbiological assays were conducted under alkaline conditions to evaluate microbial adaptation and cyanide degradation efficiency at an initial concentration of up to1000 mg/L, as this concentration can be applied for gold processing. The microbial consortia present in both sediments and tailings exhibited high resilience to alkaline pH and cyanide stress. Tailings and sediments from Fruta del Norte (Yantzaza) showed the highest degradation efficiencies, reaching 72% and 69%, respectively. In Portovelo, sediments from the Amarillo River achieved 60% cyanide removal, while Puyango River sediments reached 51%. These results demonstrate the intrinsic potential of native microbial communities to degrade cyanide in situ, providing a foundation for nature-based remediation in mining-impacted environments. Future work will focus on metagenomic profiling to identify the key microbial taxa involved in the degradation process and to support future bioengineering strategies aimed at enhancing bioremediation performance in tropical aquatic systems.