Evaluation of the application of Aquatic Humic Substances as a remediation technique for the removal of metals from water bodies

In this work, we studied the potential effects of aquatic humic substances on the water concentrations of major and trace elements in aquatic systems to evaluate their possible use as an alternative to heavy metals’ pollution. Daphnia magna was used as a control for the test organisms. Aquatic humic substances are the first reservoir of carbon in freshwater bodies. To assess their potential as a remediation technique through complex formation, their physicochemical properties must be evaluated as a first step. This study was carried out to characterise the AHS compounds formed with Cu, Mn, Pb and Zn, corroborate their stability under natural conditions, and evaluate their potential for in situ or ex situ removal of heavy metals from aquatic systems. The results indicate that the studied metal humates (Cu, Mn, Pb and Zn) are soluble at an acidic pH (< 4) and insoluble at a neutral or alkaline pH. The decomposition temperature for all compounds (metal humates) exceeds 573.15 K, indicating that they are stable under normal environmental conditions. It was also identified that aquatic humic substances radically decrease the access of heavy metals to organisms, and, modify the concentrations of nutrients in the water which can impact the development of organisms, making direct application unviable. The technique can be applied to wastewater before it is discharged into water bodies. Results indicate that: the coordination compounds (metal humates) formed are stable in environmental conditions and this technique can be applied as a pretreatment or ex situ remediation process.