Constant UV Absorbance at 218 nm in Atrazine Degradation Experiment

The observation of a constant absorbance at 218 nm over time (24, 48, and 72 hours) during your atrazine degradation experiment using bacterial isolates in Mineral Salt Medium (MSM) is a significant finding. Since atrazine strongly absorbs at 218 nm, this constant absorbance strongly suggests that the concentration of atrazine in the solution is not decreasing.

This lack of change in atrazine concentration indicates that:

Possible Reasons for No Degradation:

Several factors could contribute to this lack of degradation:

• Incorrect Isolates: The bacteria may not be true atrazine degraders.
• Suboptimal Growth Conditions: Nutrient limitations, incorrect atrazine concentration, inappropriate pH, temperature, or oxygen availability.
• Inadequate Inoculum: Low cell density or inactive state of the initial inoculum.
• Atrazine Availability: Atrazine precipitation or adsorption.
• UV Spectrophotometry Limitations: Interference from other compounds or absorption by degradation products.

Suggestions for Troubleshooting:

To address this issue and determine the cause, consider the following steps:

• Verify Isolates: Re-screen isolates using more specific methods (e.g., clear zones, HPLC). Ensure culture purity.
• Optimize Conditions: Adjust nutrient levels, atrazine concentration, pH, temperature, and aeration.
• Increase Inoculum: Use a higher concentration of active cells.
• Confirm Atrazine Availability: Ensure atrazine is fully dissolved and not adsorbed.
• Use More Sensitive Analytics: Employ methods like HPLC or GC-MS for accurate quantification and metabolite detection.
• Consider Induction: Explore pre-exposing bacteria to atrazine.
• Research Pathways: Understand known atrazine degradation pathways to guide optimization.

In conclusion, the constant absorbance at 218 nm is a clear signal that your experiment is not proceeding as expected. Troubleshooting by addressing the potential reasons listed above is crucial to achieve successful atrazine degradation.

Perhaps the metabolites absorb at the same wavelength? Thus the metabolites would appear to be parent atrazine?