Analyses on Toxicity of Pb²⁺ Towards Chlorophyll A, Total Soluble Protein And Caspase-3-Like Enzyme Activity of Scenedesmus Regularis

Heavy metal pollutions, including lead (Pb), has become an increasing concern to humans due to their adverse effects and the fact that they are not easily degraded or destroyed. Microalgae are aquatic organisms that can be used in metal bioremediation since they can accumulate and detoxify metals. This study reported on the responses of a freshwater microalga, which was Scenedesmus regularis, when exposed to the inhibitory concentrations (IC) of Pb²⁺ at 25 %, 50 % and 75 %. The tolerance level of S. regularis against Pb²⁺ at IC₂₅, IC₅₀ and IC₇₅ was determined to be 3.5 mg/L, 7.2 mg/L and 10.9 mg/L, respectively. Then, the microalga was treated with these inhibitory concentrations. The concentration of Chlorophyll A (Chl A) and total soluble protein (TSP), as well as caspase-3-like enzyme activity of the alga were analysed. It was observed that Chl A concentration of the alga significantly decreased as more cells were inhibited by Pb²⁺. The highest concentration of Pb²⁺ significantly reduced the TSP concentration of the alga. However, no changes were observed amongst the concentrations of Pb²⁺, which inhibited 25 % and 50 % of the alga population. Activity of caspase-3-like enzyme was significantly induced by more than 3-fold of control in IC₂₅ of Pb²⁺, while the activity of this enzyme was observed to be supressed in both the IC₅₀ and IC₇₅. In conclusion, the alga has the potential to be a good indicator for Pb²⁺ toxicity and the Chl A concentration and caspase-3-like enzyme activity can be applied as biomarkers. (author)