Preliminary Acute Ecotoxicological Screening of Dairy Final Effluent After Multistage Treatment in a Karst-Sensitive Setting

Site-specific ecotoxicological monitoring data on dairy final effluents in karst groundwater environments remain scarce. This preliminary site-specific case study combined physicochemical characterisation with a 24 h Daphnia magna immobilisation assay of three final-effluent samples collected after the complete treatment train in winter, spring and summer. The three sampling occasions were used as independent screening snapshots to test for an acute response at high effluent concentrations, not to estimate the seasonal variability or treatment-stage efficiency. Six effluent exposure groups (three samples × two concentrations) were tested at 80% and 100% (v/v), each in four vessels containing five organisms, together with three negative controls. Across samples, the pH was 8.1–8.4, the temperature was 11.5–26.4 °C, the dissolved oxygen was 7.89–9.75 mg/L, the TSS was 3–9 mg/L, the COD was 16.4–40.4 mg/L and the BOD5 was 3.3–4.0 mg/L. No immobilisation occurred, and the 24 h EC50 was reported as >100% (v/v); the potassium dichromate EC50 values were 1.07–1.18 mg/L. No detectable 24 h acute immobilisation was observed in any of the three tested final-effluent samples. These findings provide a quantified site-specific final-effluent profile linked to a standardised whole-effluent effect endpoint and indicate the absence of acute immobilisation under the tested conditions.