A variety of plant-based materials can be used in innovative methods to treat water pollution through bio-adsorption. This work evaluated, under lab conditions, the presence of native microorganisms in orange peel (OP) and elodea (Egeria densa, ELO), the aerobic degradation and biostability of the bio-adsorbents, and the contribution of microorganisms to the bio-adsorption of Pb (II) and Cr (III). The microbial characterization and biostability of OP and ELO were conducted using 2 g of dried bio-adsorbent and a solution of the metallic ions at 450 mg/L. ELO had a larger number of bacteria, fungi, and yeast than OP. After 2 hours of contact with a 450 mg/L Pb (II) and Cr (III) solution, this value decreased by 80-86% in both bio-adsorbents. After 25 days, the microorganisms showed adaptation to the Pb (II) and Cr (III) concentrations. According to the bio-degradation test, OP had a stability of over 7,01 months, while that of ELO was 2,61 months, with a CO2 value of 1 439,9 mg after 46 days of incubation. The microorganisms tolerated a high metal concentration, but they did not contribute significantly to Cr (III) bio-adsorption in ELO. The microorganisms present in the adsorbents affect the stability of the materials, as the bio-adsorbents provide a nutrient-rich substrate. OP had higher bio-stability and could be used in pilot tests for the treatment of metal-polluted water.