Assessment of heavy metal toxicity in four species of freshwater ciliates (Spirotrichea: Ciliophora) from Delhi, India.

In vitro laboratory experiments were conducted to determine the toxicity (per cent survival and LC50) of essential and non-essential heavy metals (cadmium, copper, nickel, lead and zinc) in four spirotrich ciliates: Euplotes sp., Notohymena sp., Pseudourostyla sp. and Tetmemena sp. isolated from three different freshwater ecosystems in the Delhi region, India. The toxicity of the heavy metals was found to vary among the different ciliates. Copper was most toxic (24 h-LC50 value ranged between 0.125 and 0.74 mg/l) and zinc was least toxic (24 h LC50 value ranged between 46.98 and 144.32 mg/l) to each of the ciliates. Of the four ciliates, Notohymena sp. had the highest tolerance limit to three heavy metals (Cu, Cd and Pb) out of the five tested. This study shows the high potentiality of using freshwater ciliates for monitoring the intensity and potency of ecological damage caused by heavy metals in aquatic ecosystems. [ABSTRACT FROM AUTHOR]