Influence of Binary Mixture of Heavy Metals and 2,4-Dichlorophenoxyacetic Acid on Phosphatase Activity of Desmodesmus Abundans

Authors : Onyeukwu, Ugochukwu Romanus; Edna Ifeoma Chukwura

Volume/Issue : Volume 7 - 2022, Issue 3 - March

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The impart of mixtures of metals and pesticide on the activity of algal hydrolytic enzyme was examined. Toxicity of unary, and binary combinations of Copper (Cu2+), Zinc (Zn2+), Lead (Pb2+), Chromium (Cr2+), Cadmium (Cd2+) ions and 2,4- dichlorophenoxyacetic acid (2,4-D) was assessed over inhibition of phosphatase enzyme activity of Desmodesmus abundans. The unary ions of Cu2+ , Zn2+ , Pb2+ , Cr2+, Cd2+ and 2,4- dichlorophenoxyacetic acid (2,4-D) effect on phosphatase activity of Desmodesmus abundanswas assessed by inhibition of conversion of pnitrophenylphosphate to p-Nitrophenol at optical density (OD) of 410nm. The results gathered from the study for experimental data points and model-predicted doseresponse data for inhibition of phosphatase enzymatic activity showed that all the metal ions were all toxic to algal phosphatase activity by the gradual reduction of the coloured p-Nitrophenol.The order of their toxicity ranking appeared in the following decreasing order: Zn2+>Pb2+>Cd2+>Cr2+>2,4-D>Cu2+ . The threshold inhibitory concentration (1C50) of Zn2+at 0.13±0.00, Pb2+ at 0.16±0.01 and Cd2+at0.16±0.01(mM) were most toxic against Desmodesmus abundans. However, the pesticide: 2,4-D exhibited a low inhibition of phosphatase activity with only 15% inhibition. The effects of the amalgamation of different ratios assessed via binary mixture, was determined.The IC50 for 50:50 binary mixture ratio were: 2,4-D/Cu2+(4.32±0.55):,2,4- D/Pb2+(6.23±0.79):,2,4-D/Zn2+(4.97±0.52):,2,4- D/Cr2+(4.33±0.55):,2,4-D/Cd2+(6.78±0.25) (mM), while IC50 for 60:40 binary mixture ratio : 2,4- D/Cu2+(4.33±0.55):,2,4-D/Pb2+(4.33±0.55):,2,4- D/Zn2+(4.97±0.52),2,4-D/Cr2+(6.73±0.07):,2,4- D/Cd2+(6.78±0.25) (mM).For toxicant binary mixture ratio 50:50: 2,4-D/Cu2+ and 2,4-D/Cr2+were more toxic than others, followed by 2,4-D/Zn2+ ,2,4-D/Pb2+ and 2,4- D/Cd2+ .Their toxicity ranking appeared in the following order: 2,4-D/Cu2+>2,4-D/Cr2+>2,4-D/Zn2+>2,4- D/Pb2+>2,4-D/Cd2+ . Similarly, from the 60:40 toxicant ratio:2,4-D/Cu2+and2,4-D/Pb2+were more toxic, followed by 2,4-D/Zn2+. the least toxic mixtures were 2,4- D/Cr2+and2,4-D/Cd2+ . Their ecological toxicity ranking appeared in the following order as well: 2,4-D/Cu2+>2,4- D/Pb2+>2,4-D/Zn2+>2,4-D/Cr2+>2,4-D/Cd2+ . The drop in the toxicity effect from unary state as compared in their mixture state, was probably due to the increase in the pesticide concentration. Consequently, the binary ratio of 60:40 components tend towards antagonistic effect due to the presence of 2,4-dichlorophenoxycetic acid. However, others showed the tendency for an additive effect.Generally, model predicted dose-response data fitted well in sigmoid 3, 4, 5 parameters and statistically significant difference (p<0.05) between IC50 of unary and binary mixtures. However, 2,4-D became less toxic due to its amalgamation with the heavy metals ions. These results indicate the risk which mixtures of pollutants represent in a freshwater environment as against their occurrence as unary toxicants.

Keywords : Toxicity: Desmodesmus abundans: 2,4 dichlorophenoxycetic acid:dose-response: p-Nitrophenol: Threshold inhibitory concentration (1C50).


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