Abstract
The dairy industry is the fourth largest in the food sector in Brazil, posing substantial environmental risks due to the discharge of dairy wastewater (DWW) into environmental waters. The numerous small-sized dairy facilities (500 − 30,000 L of milk processed day(− 1)) in the country are particularly concerning as they are subjected to less stringent environmental regulations. This study presents a comprehensive ecotoxicological analysis of DWW from a small dairy industry by exploring acute and chronic effects of the wastewater to test-organisms from various trophic levels and discussing results in light of current national and State-level regulations. Sampling was conducted during the dry and wet seasons. Acute and chronic toxicity were assessed for Aliivibrio fischeri (bacteria), Raphidocelis subcapitata (algae), Daphnia similis (crustacean), and Danio rerio (fish) larvae and adults. Acute toxicity tests revealed that DWW was toxic to all organisms in the following order: Daphnia similis (Toxicity Factor (TF) = 32) > Danio rerio (larvae) (TF ≥ 16) > Danio rerio (adult) (TF = 2). Bioassays with Aliivibrio fischeri showed great variability, probably due to matrix turbidity and color effects upon luminescence measurement, thus being the least appropriate species among those tested. Chronic toxicity tests showed the following outcomes: Raphidocelis subcapitata (TF = 32) > Danio rerio (larvae) (TF ≥ 16). Bioassays were also conducted with surface water from the DWW receiving pond and indicated a hormesis effect to bacteria and algae. Raphidocelis subcapitata and Daphnia similis were the most adequate organisms for chronic and acute ecotoxicity assessment, respectively. Results underscore the need to raise data on the toxicity of DWW, particularly those submitted to simplified treatment, and provides insights into the sensitivity of test organisms to this matrix, thereby contributing to the development of a more specific approach in industrial wastewater discharge regulations. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10646-026-03088-7.