Chemical and Ecotoxicological Assessment of Agricultural Drainage Water from a Maize Crop Area: A Case Study in the Tejo Basin (Portugal)

The use of agricultural drainage water (ADW) in irrigation is a great challenge, improving efficiency, nutrient circularity, and avoiding surface ground-water contamination. objective this study was to evaluate the chemical ecotoxicological characteristics an ADW analyze safety its reuse. An irrigated area with maize crops selected (Tejo Basin, Portugal), where subsurface structure for recovery installed, collecting pond recycling it crop irrigation. Water collected monthly during campaign 2021 (April August). Three herbicides two metabolites were quantified, reaching maximum concentration 0.74 µg L−1 S-metolachlor 0.48 terbuthylazine. lethal bioassays did not detect toxicity, except sample August toward Vibrio fisheri (EC50 = 25.2%). samples toxic Pseudokirchneriella subcapitata, growth inhibition rate less than 10%. low sublethal effects may be ascribed high (e.g., 1.76 mg P 98.9 NO3− L−1, July) that could have masked effects. Ecotoxicological responses support option reuse irrigation, offering safe sustainable solution management.