SANS probing of bacteria-silica-Hg interactions as encapsulation mechanism of mercury

High Hg levels, up to 4 ppm, in Amazonian fish indicate significant heavy metal (HM) pollution and stimulate research on bacterial bioremediation of these media. Simultaneous nanoparticles' aggregation and HM-bacterial uptake offer an unmatched test on how both phenomena can limit Hg-species' mobility. Since aggregation is a microstructural phenomenon dependent on time and pH, we propose contrast-matching and time-resolved SANS experiments on the SiO2 nanoparticles (NPs)-HgCl2-HM resistant bacteria system. We hypothesise that silica's aggregation in the presence of HM-resistant bacteria can encapsulate Hg, reducing its levels in the liquid phase. Measurements on 1 and 8 ppm Hg series will comprise ~60% and 100% D2O liquid buffers, pH ~7, pressure and temperature ambient conditions, totaling 4 time-resolved SANS experiments to probe the vector q range from ~0.004 to 0.3 Å^-1 at Larmor beamline. At pH~7, cationic Hg species predominate, raising our expectation to observe aggregates up to 157 nm. A ~60% D2O buffer matches the SLD of SiO2-NPs, which could help observe HgCl2-bacteria interactions. At 100% D2O, bacterial lipids display high squared contrast, providing the best conditions to probe silica–bacteria interactions. This proposal focuses on biosilica initial formation stages and could be important for the bioremediation of Amazonia media where Hg levels largely exceed the Brazilian law's threshold (0.5 Hg ppm).