Toxicity Assessment on Odonata Larvae Survivability in Monitoring Heavy Metal Contaminations

Abstract

The aquatic ecosystem has been suffering a continuous increase of metal contamination such as Cadmium (Cd), Zinc (Zn), and Manganese (Mn) due to their inadequate high potential to disturb the aquatic organism population. Meanwhile, some insects such as Pseudagrion microcephalum and Ischnura senegalensis can be used as biological indicators to determine stream health. Therefore, this study was conducted to determine the relationship between the heavy metal concentration and its effect on the survivability of two different species of damselfly larvae from the family Coenagrionidae; Pseudagrion microcephalum and Ischnura senegalensis. In this study, there is a significant effect of three heavy metal exposures on the survivability of P.microcephalum (F11,180=14.50, P=0.00) and I.senegalensis (F11,180 =15.10, P=0.00). Pseudagrion microcephalum is more tolerable towards Mn (F3,60=13.19, P=0.00) and Zn (F3,60=16.07, P=0.00) at different concentrations compared to I.senegalensis. In the meantime, I.senegalensis was tolerable to Cd exposure. The LC50 value of Cd was much lower than other heavy metals. Besides, the LT50 value of Cd at 200 mg/L was the lowest on P. microcephalum (31 hr) and I. senegalensis (36 hr) compared to other heavy metals. Cd was the most toxic to P.microcephalum and I.senegalensis larvae followed by zinc and manganese (LC50 & LT50=Cd > Zn > Mn). It is concluded that I.senegalensis was tolerant towards Cd, Mn, and Zn compared to P.microcephalum and Cd had the fastest-acting toxicity and significantly reduced the lethal time of mortality on both species.