Iohexol as an Emerging Contaminant Potentially Influencing Structural and Functional Changes in the Activated Sludge Microbiome

Iohexol (IOX) is one of the most commonly used iodinated contrast agents due to its relatively low toxicity. However, owing to its low biodegradability, it accumulates in wastewater and sewage sludge, ultimately reaching wastewater treatment plants. With increasing IOX loads, the activated sludge (AS) microbiome is exposed to its long-term effects. Therefore, this study aimed to determine the impact of IOX on the structure and functioning of AS. The results demonstrated that IOX at lower concentrations does not affect the functional parameters of AS, and only long-term exposure of the microbiome to a concentration of 20 mg/L results in functional changes. These changes themselves, among other effects, concerning amino acid and carbohydrate metabolism and the phosphorus cycle. Furthermore, the study demonstrated that despite the activated sludge microbiome's ability to transform 20 mg/L of IOX, long-term exposure to this concentration reduces the efficiency of this process. This indicates that although IOX is a relatively safe compound, prolonged exposure of the AS microbiome to high doses may lead to functional changes in AS and potentially impair wastewater treatment processes.