Determination of the ecotoxicity changes in biologically treated cyanobacteria oscillatoria and microcystis using indicator organisms

Abstract

The response of biological indicators with ecosystem food web and agricultural relevance were examined in biologically treated cyanobacteria culture water. To assess bioindicator responses to variations in the toxicity measurements, a case study on the filtrate of treated cyanobacteria was conducted. Cyanobacterial cultures of dominant Oscillatoria and Microcystis were treated by adding four different, potentially predatory bacterial isolates (isolates 1, 3w, 3y and B) over 4 days. A total microcystin assessment of filtrate water from these exposures indicated that approximately 30% of toxicity had been reduced in Microcystis samples treated with isolate 1 and isolate B. With Oscillatoria, the toxicity was increased by 14% by treatment with isolate 3w; minimal changes occurred through treatment by other bacterial isolates. Lactuca sativa germination was insufficiently sensitive to the toxin concentration changes, while Allium cepa mitotic indices indicated moderate sensitivity to microcystin concentration changes. Acute exposure of Thamnocephalus platyurus was most sensitive to toxicity changes, with better survival in less toxic samples, indicating slight toxicity increases through higher mortality. Phosphates, copper and ammonia fluctuated between the treated and untreated sample water, indicating a possible impact on the total nitrogen and total phosphorous ratio. There was a close correlation between the Lactuca sativa and Allium cepa response, and the Thamnocephalus platyurus and Daphnia magna responses. DNA apoptosis occurred in Thamnocephalus platyurus, with DNA having better integrity in isolate B treated samples. Overall, isolate B was the most favourable bacterial treatment, based on bioindicator response. The present research confirmed the toxicity reduction in a mixed cyanobacterial bloom culture and the reliability of crustaceans such as Thamnocephalus platyurus as indicators of total biological toxicity in biologically controlled cyanobacteria.