Geochemical soil dynamics on a bimodal post-collisional intrusive complex.

The importance of environmental quality for global social and ecological development, including soil degradation, cannot be overstated. Trace elements dispersed in the environment due to anthropogenic or geogenic activities can result in ecotoxicological impacts, negatively influencing environmental quality. The reference values for soil quality concerning trace elements are primarily based on geological, geomorphological, and pedological patterns. However, intrinsic geological factors may diverge some concentration levels from established norms. Therefore, conducting comprehensive surveys of environmental quality reference values becomes imperative, incorporating geological, geomorphological, and pedological patterns. A deeper understanding of the distribution of these elements is also required. Multivariate analysis proves crucial in compartmentalizing the most relevant factors, particularly in regions marked by bimodal magmatism arising from post-collisional distensional processes, such as the Santa Angélica intrusive suite in southeast Brazil. This study collected soil samples from pastures and natural grasslands with minimal anthropogenic intervention at two depths. These samples underwent various chemical and physical analyses. Statistical techniques such as correlation analysis, principal component analysis, hierarchical clustering, and geostatistics were utilized to interpret the data. The analysis revealed a correlation between the clay fraction and trace elements, demonstrating that clustering is an effective methodology for ascertaining landscape distribution patterns of these components. When compared to quality reference values, it was observed that most soil content levels exceeded both global and local standards. This study suggests that the presence of barium (Ba) in the soil might be due to the isomorphic replacement of feldspathic minerals in acidic and intermediate rocks, whereas molybdenum (Mo) seems to be associated with soils in the domain of porphyritic allanite granite. However, additional research is warranted to determine the concentration factor of Mo in this scenario accurately.

Mine tailings in a redox-active environment: Iron geochemistry and potential environmental consequences.

Iron (Fe) oxyhydroxides provide many functions in soils, mainly owing to their large surface area and high surface charge density. The reactivity of Fe oxyhydroxides is function of their mineralogical characteristics (e.g., crystallinity degree and crystal size). Detailed studies of these features are essential for predicting the stability and reactivity of these minerals within soil and sediments. The present study aimed to evaluate geochemical changes in Fe-rich tailings after the world's largest mining disaster in SE Brazil (in 2015) and to predict the potential environmental implications for the estuary. The mineralogical characteristics of the tailings were studied at three different times (2015, 2107, and 2019) to assess how an active redox environment affects Fe oxyhydroxides and to estimate the time frame within which significant changes occur. The study findings indicate a large decrease in the Fe oxyhydroxides crystallinity, which were initially composed (93%) of highly crystalline Fe oxyhydroxides (i.e., goethite and hematite) and 6.7% of poorly crystalline Fe oxyhydroxides (i.e., lepidocrocite and ferrihydrite). Within 4 years the mineralogical features of Fe oxyhydroxides had shifted, and in 2019 poorly crystalline Fe oxyhydroxides represented 47% of the Fe forms. Scanning electron microscope micrographs and the mean crystal size evidenced a decrease in particle size from 109 nm to 49 nm for goethite in the d111 direction. The changes in mean crystal size increased the reactivity of Fe oxyhydroxides, resulting in a greater number of interactions with cationic and anionic species. The decreased crystallinity and increased reactivity led to the compounds being more susceptible to reductive dissolution. Overall, the findings show that the decrease in crystallinity along with higher susceptibility to reductive dissolution of Fe oxyhydroxides can affect the fate of environmentally detrimental elements (e.g., phosphorus and trace metals) thereby increasing the concentration of these pollutants in estuarine soils and waters.