Toxicity of single and ternary mixtures of heavy metals and 2,4-dichlorophenoxyacetic acid to Chlorella vulgaris alkaline phosphatase activity
1 Department of Industrial Microbiology and Brewing, Nnamdi Azikiwe University, Awka, Anambra State. Nigeria.
2 Department of Biological Sciences, University of Agriculture and Environmental Sciences, Umuagwo, Imo State, Nigeria.
3 Department of Microbiology, School of Biological Sciences, Federal University of Technology Owerri, Imo State, Nigeria.
Research Article
World Journal of Advanced Research and Reviews, 2023, 17(03), 206–223
Article DOI: 10.30574/wjarr.2023.17.3.0334
Publication history:
Received on 16 January 2023; revised on 27 Februay 2023; accepted on 02 March 2023
Abstract:
The influence of mixtures of metals and pesticide on the activity of algal hydrolytic enzyme alkaline phosphatase was investigated. Toxicity of unary and ternary combinations of Copper (Cu2+), Zinc (Zn2+), Lead (Pb2+), Chromium (Cr2+), Cadmium (Cd2+) ions and 2,4-dichlorophenoxyacetic acid (2,4-D) was assessed via inhibition of phosphatase enzyme activity of Chlorella vulgaris. The effects of the amalgamated ternary mixtures were studied in their fixed percentage ratio of 20:40:40 and 40:30:30. Results obtained showed that all the unary heavy metal ions were toxic to algal phosphatase activity, with a concentration dependent inhibition of alkaline phosphatase activity. The analysis of eco-toxicity concentration (EC50) of toxicant ternary mixtures of metals/ pesticides mixtures in 20:40:40 ratios show that the ternary mixtures 2,4-D/Pb2+/Cd2+and 2,4-D/Zn2+/Cd2+ were more toxic, followed by 2,4-D/Cu2+/Cr2+, 2,4-D/Pb2+/Zn2+, 2,4-D/Cu2+/Zn2+ and 2,4-D/Cu2+/Cd2+. Whereas among the 40:30:30 mixture ratios 2,4-D/Pb2+/Cd2+ and 2,4-D/Zn2+/Cd2+ were most toxic. The decline in the trend of their toxicity strength was followed by 2,4-D/Cu2+/Cr2+, 2,4-D/Cu2+/Zn2+, 2,4-D/Cu2+/Cd2+, 2,4-D/Cu2+/Pb2+ and 2,4-D/Pb2+/Zn2+. In addition, the least toxic amongst them were the 2,4-D/Pb2+/Cr2+, 2,4-D/Zn2+/Cr2+ and 2,4-D/Cr2+/Cd2+ ternary mixtures. Toxicity index analysis of the mixture interaction effect showed that the mixtures of heavy metals with 2,4, D were mostly antagonistic with toxic index (TI) >>1, However, exceptions were the 2,4-D/Pb2+/Cd2+ and 2,4-D/Pb2+/Cd2+mixture which were additive and synergistic with TI=1 and TI<1 respectively. From the foregoing study, the toxicity of the mixtures exhibited largely sigmoidal relationship, increased composition of heavy metal in the mixture resulted in a potentiation of 2,4-D toxicity. These results indicate that mixtures of heavy metals with largely non-toxic 2,4-D may pose ecological risk to freshwater microalgae Chlorella vulgaris, presenting antagonistic, additive and synergistic toxicity interactions based on their relative occurrence in the mixture.
Keywords:
Toxicity; Mixture; Alkaline phosphatase; 2,4-dichlorophenoxycetic acid; Heavy metals; Chlorella vulgaris
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