A rapid Lemna bioassay empowered by open-source image analysis

Aquatic ecosystems are increasingly affected by complex combinations of pollutants, underscoring the need for rapid, economical, and efficient phytotoxicity assays. Despite Lemna minor being a standardized test organism, traditional bioassays predominantly depend on frond counting and visual assessment, which are time-consuming and subjective. This study enhanced a smaller, plate-based Lemna bioassay through quantitative, open-source image analysis, creating an efficient digital ecotoxicology procedure that requires minimal test volume. Potassium dichromate (K_₂Cr_₂O_₇) served as a reference toxicant for assay optimization. An image-based concentration-response study (0-160 ppm) demonstrated a distinct, dose-dependent inhibition of growth. The negative control exhibited a significant increase in frond area (from 20.56 ± 5.01 to 52.03 ± 1.78 px), while exposure to 40 ppm K_₂Cr_₂O_₇ led to nearly total growth inhibition and net tissue loss (growth rate: - 0.66 ± 1.78; growth inhibition: 104.97 ± 13.40%). Forty parts per million (ppm) was identified as the appropriate positive control based on biological significance and statistical validity. In the optimized time-course assay, control plants demonstrated sustained exponential growth over six days, whereas chromium-treated plants showed negligible or adverse effects on frond area, with a noticeable difference between treatments by day six. The frond area was measured using available software (GIMP and ImageJ), yielding objective, reproducible results with interobserver variability not exceeding 5%. The suggested small-volume, image-based Lemna assay improves sensitivity, repeatability, and throughput, while minimizing reagent consumption and experimental costs and providing a reliable instrument for regular aquatic toxicity assessment.