Adsorption of heavy metals to chia seeds' mucilage

Plant roots actively modify the physical properties of the soil in their area by secreting mucilage. Chia seed mucilage (CSM) is used as a model for plant root exudates primarily because of its similarities in physicochemical properties to natural root mucilage and its easy extraction in substantial, consistent quantities for laboratory experiments to study plant-soil-water relations. CSM can form highly viscous solutions at low concentrations and exhibits excellent properties, including water-holding capacity, surface tension, and emulsion stabilization. Most previous studies focused on chia seed mucilage as a conceptual model to describe the effect of mucilage on soil hydraulic properties, solute movement and gas diffusion in soil. However, the interactions between CSM and heavy metals have not been studied yet. Here, we showed the role of CSM as a bio-adsorbent for the removal of heavy metals and contaminants. Due to its sensitivity, non-destructivity, and simplicity, molecular fluorescence spectroscopy has been used to provide qualitative and quantitative information on the interaction between natural dissolved organic matter and metal ions. CSM was extracted from hydrated chia seeds and characterized using fluorescence Excitation-Emission Matrices combined with the Parallel Factor Analysis (EEM-PARAFAC) method. The binding interactions of CSM fluorescent components with heavy metals were quantified using fluorescence quenching titration and the Stern-Volmer model. Competitive binding studies were also conducted using one heavy metal as the quenching agent in the presence of competing heavy metal ions. Unconstrained PARAFAC modelling with two to four components was performed separately on 61 EEMs obtained from different concentrations of CSM samples, and the final component scores were determined through core consistency analysis, split-half analysis, and examination of the explained variance percentages. Protein-like (tryptophan & tyrosine) substances were the main fluorescent components identified by EEM-PARAFAC. The quenching titration results showed that the fluorescence intensity of CSM fluorescent components decreased with increasing heavy metal concentration under various environmental conditions. This strong quenching effect implies the binding ability of CSM to heavy metals and its significance in understanding metal toxicity, bioavailability, and transport in soil and natural waters.