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Reagent-Free Prediction of Free-Ammonia Toxicity in Algal Systems Using Chlorophyll Fluorescence Transients and
Masatoshi Kishi1,2,3, Panagiota Karachaliou4, Tetsuichi Fujiki3
1Institute of Sustainable Processes, University of Valladolid, Valladolid 47011, Spain.
Environmental Science & Technology
|June 15, 2026
Summary
This study presents a novel, reagent-free method using chlorophyll fluorescence to accurately quantify ammonia toxicity in algae. The developed framework enables real-time monitoring of ammonia levels in effluents and algal cultures.
Area of Science:
- Environmental science
- Biotechnology
- Algal research
Background:
- Accurate free ammonia (NH3) monitoring is crucial for managing nutrient-rich effluents and algal systems.
- Conventional assays are reagent-intensive and unsuitable for real-time monitoring.
- Chlorophyll fluorescence (e.g., FV/FM) offers a rapid, reagent-free proxy but lacks specificity and quantitative NH3 data.
Purpose of the Study:
- To develop a reagent-free framework for predicting ammonia toxicity in microalgae using fast chlorophyll fluorescence transients (O-J-I-P; OJIP).
- To establish a quantitative biosensing platform for real-time ammonia assessment in algal cultures and effluents.
Main Methods:
- Exposed three microalgae species (Chlorella vulgaris, Acutodesmus obliquus, Arthrospira platensis) to varying ammonia levels for 35 hours.
- Monitored O-J-I-P fluorescence transients and analyzed data using interpretable sparse regression (Lasso).
- Optimized regression models using nested cross-validation for accuracy and transferability.
Main Results:
- Lasso regression achieved high accuracy (R2 = 0.93-0.98 within species) and good transferability across taxa (R2 = 0.81-0.87 for green algae).
- Selected OJIP parameters identified conserved fluorescence signatures of ammonia stress, outperforming FV/FM under photoinhibition.
- Model diagnostics provided transparent uncertainty quantification and identified extrapolative predictions.
Conclusions:
- The developed workflow translates routine OJIP measurements into real-time, quantitative ammonia toxicity data.
- This reagent-free biosensing platform enhances environmental risk assessment for algal systems and high-ammonia effluents.
- The method offers a transparent and efficient alternative to conventional ammonia assays.
