Sterols and fatty acid biomarkers as indicators of changes in soil microbial communities in a uranium mine area

Included in the 2nd tier of a site specific risk assessment that is being carried out in an abandoned uranium mine (Cunha Baixa uranium mine, Central Portugal), fatty acids biomarkers and sterols were analyzed to assess the impact of soil contamination with metals and radionuclides in the structure of the microbial community in seven sampling sites located at different distances from the mine. Surface soil samples were collected in those sampling sites in the four different seasons of the year. Principal component analysis (PCA) was performed on fatty acid biomarkers and sterols. Subsequently PCA scores obtained for both components were used to test the effect of sites and seasons, on soil samples collected in the Cunha Baixa uranium mine, through bi-factorial ANOVAs. Through PCA analysis, two distinct groups were set apart along the first two components. One group included sites at a great distance from the mine which were negatively correlated with higher contents of iC15:0 and iC17:0, both indicators of Gram-positive bacteria, as well as with ergosterol, cholestanol and cholesterol. The second group, in turn, was composed of the sampling sites most impacted by ore exploration, in situ leaching of poor ore, and spread of sludge from the effluent treatment pond. These sites were positively correlated with higher levels of iC16:0 (Gram-positive bacteria indicator), cyC17:0 (generally common in gram negative bacteria) and C18:0 and C17:0 biomarkers of non-specific bacteria. The profile of fatty acids obtained in the sampling sites revealed variable predominance of groups of bacteria which are a clear indication of differences in the soil microbial communities that are directly related to the environmental conditions prevailing in the uranium mine area.