Résumé - Abstract
Selenium contamination can be generated through a variety of human activities including mining, coal combustion, and smelting of Se-rich ores. Releasing Se into the environment can disrupt reproduction in aquatic species, making it important to remediate Se before it discharges into open water bodies from ground water sources. Various processes control the concentration and mobility of Se in groundwater, such as abiotic and biotic reduction, precipitation, adsorption, and dispersive dilution. The process controlling Se mobility will determine whether Se is merely being retarded before it discharges, or if it is being successfully remediated by intentional or natural means. But how to determine the controlling factors?
Stable isotope ratio measurements can give insight as to the mechanism that is causing Se removal in the subsurface. The Se stable isotope fractionation for many processes have been investigated under laboratory settings, allowing for the unraveling of more complicated systems. However, there has been little work done on natural microbial consortiums, and minimal work done on organic amendments.
We conducted a laboratory experiment in which lucerne hay was used as an organic source for a natural sulfur reducing bacteria (SRB) consortium to reduce Se(IV) and Se(VI) and investigate the resulting isotopic fractionation. A small quantity of zero valent iron (ZVI) was also added to prevent excess S(-II) from poisoning the SRB in the system.
Although Se was quickly removed from solution in the Se(IV) experiment, there was only a slight decrease in the Se concentration by the end of the Se(VI) experiment after an initial increase. Scanning electron microscope (SEM) images suggest organic matter in the Se(VI) experiment was more readily digested than in the Se(IV) experiment. Stable isotope ratio measurements suggest reduction was occurring in the Se(VI) experiment, and may have continued if the experiment was run for longer.
Selenium stable isotope ratio measurements can provide insight into the reactions occurring in more complex systems. This insight can allow for decision making in the construction and maintenance of remediation systems, both for passive and active treatment systems.