Phytoremediation of Mercury-Contaminated Salvinia natans: Toxicity Thresholds and Sustainable Use of Spent Phytoremediation Biomass

The use of mercury in industry causes its continuous increase in nature. A pro-ecological technology that can reduce mercury levels in aquatic environments is phytoremediation using the plant Salvinia natans. The study aimed to determine the maximum mercury concentration for effective phytoremediation using Salvinia natans. The study aimed to determine the threshold for effective phytoremediation using Salvinia natans. A Microtox screening test was performed for concentrations ranging from 0.15 to 0.50 mg Hg·L−1. For the same concentrations, the effect of contamination on the physiological condition of the plant was tested by observing changes in the presence of chlorosis and necrosis. Analysis of enzymatic activity using the API ZYM test for plants exposed to mercury did not show any significant changes. The phytoremediation process produces a significant amount of spent phytoremediation biomass containing large amounts of mercury. Sustainable management in the form of a mixture with soil substrate, uncontaminated with mercury, was proposed. Microtox toxicity analysis of water extracts from soil containing biomass, with a final mercury content in the substrate of 1 mg Hg·kg−1 of soil, showed no toxicity to the environment. However, microbiological analysis of the same soil substrate showed changes in the total number of bacteria, actinomycetes, fungi, moulds, and yeasts compared to the control samples.