The effect of long-term exposure to diatrizoate on microbial communities in activated sludge.

Contrast agents are very persistent compounds that are detected in increasing concentrations in sewage and water. This study aimed to determine whether the presence of iodinated contrast agent - diatrizoate impacts microorganisms in activated sludge. During the 100-day experiment, an attempt was made to find the most sensitive microbial indicator that would inform about changes in the structure or activity of microbial communities as a result of exposure to diatrizoate. Biochemical and genetic factors were tested, and it was found that the most sensitive indicators were dehydrogenase activity and indexes related to the oxidation of specific substrates. On the last day of the experiment, the values of all analysed functional diversity indicators were worse when a higher concentration of diatrizoate was added. Dehydrogenase activity was half lower, the Gini coefficient was 0.15 higher and the Shannon and Richness indices were 0.31 and 6 lower, respectively, compared to the control. Simultaneously, an increased intensity of glycogen, α-cyclodextrin, α-ketobutyric and D-malic acid oxidation was revealed. In conclusion, the long-term exposition to diatrizoate, affects microbial metabolism and causes significant adverse changes in their functional diversity. This work demonstrates the importance of long-term studies of the impact of pharmaceuticals on microorganisms in aquatic ecosystems.