PARENT SESSION
MA2 Chemical, Biological and Combined Methods for the Detection of Pollutants.
to ,
Session Chair: Diego Santiago Laguna

(010) Toxicity potential of substances in the tannery wastewater.

Tišler, Tatjana¹, Zagorc-Končan, Jana², ^{1 2}

ABSTRACT- The effective evaluation of the quality of wastewater is nowadays based on chemical specific measurements as well as ecotoxicological assessment. In Slovenia, acute toxicity evaluation of effluents discharged into receiving streams is prescribed when toxic substances in the effluent are expected. We detected successive determinants of acute toxicity with daphnids in the samples of wastewater from the tannery during a one-year period. Further investigations on acute and chronic toxicity on bacteria and daphnids were performed and conventional chemical determinations as well as priority pollutants were measured. In our research we tried to find the main cause of wastewater toxicity; the potential toxic compounds used in the technological process of leather processing and in pretreatment of wastewater were tested for toxicity. The toxicities of individual compounds were compared with measured concentrations in the wastewater. Ammonium (48h EC50 = 135 mg/l, pH was 7.5), chloride (48h EC50 = 3.4 g/l), aluminum (48h EC50 = 4.5 mg/l), chromium (48h EC50 = 8.8 mg/l) and sulfide (48h EC50 = 6.5 mg/l) were found to be toxic for daphnids; the measured concentrations of ammonium, chloride and aluminum in the wastewater exceeded toxicity thresholds. We prepared a synthetic mixture of tested compounds using concentrations that individually caused inhibitory effects on daphnids. The obtained toxicity of synthetic mixture was higher than the sum of toxicities of the single toxic compounds. The reason for the higher toxicity of wastewater was probably the synergistic effects between compounds in the wastewater. In additional study it was established that organic pollution and undetected substances were also responsible for wastewater toxicity. The results clearly confirm the importance of applying ecotoxicological tests in the regulation of industrial wastewaters.

Key words: daphnid, tannery, toxicity, wastewater