Toxicity of nZVI in the growth of bacteria present in contaminated soil

The use of nano zero-valent iron (nZVI) for the remediation of degraded areas is a consolidated practice. However, the long-term reactions that occur in the environment remain unknown. This study aimed to evaluate the potential toxic effects on the growth of colony-forming units (CFUs) of Bacillus cereus and Pseudomona aeruginosa present in soil contaminated with hexavalent chromium (Cr⁶⁺) and pentachlorophenol (PCP) nanoremediated with nZVI. The treatments were natural soil (control), soil contaminated by Cr⁶⁺, soil contaminated by PCP, and soil contaminated by Cr⁶⁺ and PCP (Cr⁶⁺ and PCP), all in duplicate. The concentration of contaminants used was 100 mg/kg of soil. One of the drums of the duplicate received an injection of nZVI solution with a concentration of 50 g/kg. Analysis was performed 7, 15, 21, 30, 60, and 90 days after the nZVI injection. Temporary oscillations in the abundance of the microbiological community were observed, characterizing the adaptation of bacteria to the contaminants. The bacteria showed similar behavior. Ninety days after the injection of nZVI, the averages of the CFUs were statistically equal, with the lowest coefficient of variation and the highest concentration of CFUs occurring. The strains of B. cereus and P. aeruginosa were resistant to the concentrations of nZVI, Cr⁶⁺, and PCP. The nanoremediation of nZVI in soil contaminated by Cr⁶⁺ and PCP had no toxic effects on the population of the bacteria evaluated and did not present major disturbances in temperature, electrical conductivity, pH, and humidity over time.