Mobilisation of hazardous elements from arsenic-rich mine drainage ochres by three Aspergillus species

Natural ferric ochres that precipitate in streambeds at abandoned mining sites are natural scavengers of various metals and metalloids. Thus, their chemical and structural modification via microbial activity should be considered in evaluation of the risks emerging from probable spread of contamination at mining sites. Our results highlight the role of various aspergilli strains in this process via production of acidic metabolites that affect mobility and bioavailability of coprecipitated contaminants. The Mo center dot ssbauer analysis revealed subtle structural changes of iron in ochres, while the elemental analysis of non-dissolved residues of ochres that were exposed to filamentous fungi suggest coinciding bioextraction of arsenic and antimony with extensive iron mobilisation. However, the zinc bioextraction by filamentous fungi is less likely dependent on iron leaching from ferric ochres. The strain specific bioextraction efficiency and subsequent bioaccumulation of mobilised metals resulted in distinct tolerance responses among the studied soil fungal strains. However, regardless the burden of bioextracted metal(loid)s on its activity, the Aspergillus niger strain has shown remarkable capability to decrease pH of its environment and, thus, bioextract significant and environmentally relevant amounts of potentially toxic elements from the natural ochres.

Automated summary

The study investigates the microbial activity of natural ferric ochres at abandoned mining sites and its impact on the risk of contamination spread, highlighting the role of various aspergilli strains in affecting mobility and bioavailability of coprecipitated contaminants. Results show the remarkable bioextraction and environmental capability of Aspergillus niger strain in decreasing pH and extracting potentially toxic elements from natural ochres.