Joint toxicity of binary mixtures of surfactants and heavy metals on Micractinum pusillum isolated from Otamiri River

Mary Udochukwu Kalu 1, *, Justina Chibuogwu Orji 2, Christian Okechukwu Nweke 2 and Christopher Emmanuel Nwanyanwu 2

1 Department of Microbiology/Biochemistry, Federal Polytechnic Nekede Owerri, Imo State, Nigeria.
2 Department of Microbiology, Federal University of Technology Owerri, Imo State, Nigeria.
Research Article
World Journal of Advanced Research and Reviews, 2024, 22(03), 1325–1337
Article DOI: 10.30574/wjarr.2024.22.3.1802
Publication history: 
Received on 05 May 2024; revised on 18 June 2024; accepted on 21 June 2024
Toxicity of lead (Pb), cadmium (Cd), cobalt (Co), nickel (Ni), zinc (Zn), sodium dodecylsulphate (SDS), cetylpyridinium chloride (CPC) and their binary mixtures were evaluated based on the growth (OD610) inhibition of Micractinum pusillum. The responses of the organism to the toxicity of Pb2+, Cd2+, Co2+ and Ni2+ showed a dose-dependent inhibition to the microbial growth  while Zn2+ , SDS and CPC showed hormetic curves which were characterized by stimulation of growth at low concentrations and toxicity at high concentrations. Zinc showed hormetic effect up to 1.0 mM while SDS showed hormetic effect at concentrations up to 2.5 mM.  Relatively, CPC among other toxicants exhibited greater stimulatory effect on the growth of the alga at concentration up to 8.0 mM. At doses above the stimulatory range, the toxicants progressively inhibited the growth of the organism. The EC50 values were evaluated using monotonic and hormetic dose-response models. The EC50 of the toxicants ranged from 0.12±0.05 to 11.88±1.60 mM. Statistically, the results obtained from the Tukey HSD POSTHOC test showed that the EC50 values of the toxicants were significantly different (P<0.05) and the order of decreasing toxicity is Co2+>Pb2+>Ni2+>Cd2+>Zn2+>SDS>CPC. The results of the joint effect of the mixtures on the growth of the test organism indicated additive, antagonistic and synergistic interactions for the mixtures analyzed. The chemicals may accumulate in the biota and get bio-magnified in the food chain, ultimately affecting man. Therefore, the results have the potential to inform decision-making processes related to environmental protection, chemical management, and public health.
Joint toxicity; Surfactant; Heavy metal; Microalgae; Effective concentration; Toxic index
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