Toxicity of pesticides and heavy metals to bacterial isolates from aquatic ecosystem
Date
2024-02
Authors
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Journal ISSN
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Publisher
Federal University of Technology, Owerri
Abstract
The research work was carried out to determine the effect of pesticides and heavy metals on bacterial isolates from an aquatic ecosystem using Otamiri River as a case study. Otamiri River is the major river in Owerri metropolis and its environs, thus most of the drainages empty into the River. A total of seventy-two (72) water and twelve (12) soil samples were collected from the River. The physiochemical and bacteria diversity of Otamiri River was analyzed using standard microbiological methods, equally the heavy metal and pesticides content of the River was analysed. Finally, the toxicity assay was carried out using the preponderant organisms. Among the physio-chemical parameters analyzed in the River water and soil samples, pH was between 5.3 and 6.11. The BOD was 3-5mg/L which was above the recommended standard by World Health Organization (WHO). From the heavy metals and pesticides content of the river, Cd and Pb recorded the highest value of 0.03mg/l and 0.1 mg/l respectively while Hg was absent in most sampling site, it has its highest deposit at Umezuruike hospital sample site (0.1mg/l). The pesticides content analyses reveals the presence of Athrazine, Butachlor, Glyphosate DDVPandAlachlor in the River, The results of the standard plate count showed that heterotrophic bacteriacount ranged from 1.0×106Cfu/ml to 9.7×10 6Cfu/ml, fecal coliform count 2.0×10 5Cfu/ml to9.0×10 6Cfu/ml, almonella/Shigella count 3.5×10 5Cfu/ml to 1.5×10 7Cfu/ml, Staphylococcuscount 2.0×10 5 Cfu/ml to 1.8×10 7 Cfu/ml, coliform count 3.5×10 5 Cfu/ml to 4.6×10 8 Cfu/ml, Vibrio count 1.5×10 5 Cfu/ml to 3.5×10 7 Cfu/ml. Anaerobic bacteria count ranged from2.0×10 5Cfu/ml to 2.9×10 6Cfu/ml. The percentage occurrence of the bacterial isolates in the water and soil samples showed that Alcaligens sp had the highest 68(94.44%), 24(100%), followed by Lysinibacillus 54(75%), 21(87.5%) while Lactobacillus sp had the least in water sample 6(8.33%), Klebsiellasphad the least in soil 6(25%). The five highest occurring isolates were subjected to molecular identification using 16SrRNA and were confirmed to be Lysinibacillus macrolides (OK298881), Pseudomonas aeruginosa (CP058331), Klebsiella pneumonia (MK641337), Alcaligenes faecalis(KX302624), Proteus mirabilis (MZ067158). Lysinibacillus macrolides and Alcaligenes faecaliswere futher subjected to toxicity assay using five heavy metal ions (Pb(II), Zn(II), Co(II), Ni(II) and Cd(II)) and two pesticides fomulations (Glyphosate and DDVP -(2,2- dichlorovinyldimethyl phosphate)). This analysis was done in singles, as well as mixtures (binary, ternary and septenary)using inhibition of dehydrogenase activity as a response. The EC50 equieffect concentrationratio(EECR-50) and fixed ratio ray design (Arbitrary concentration ratio- ABCR) were used to evaluate the toxicity of the mixtures to the bacterial isolates. The effects of the mixtures on the dehydrogenase activities of the preponderant organisms were assessed using toxic index (TI) and isobolographic analyses. The EC50s were compared statistically by two way ANOVAusingPOSTHOC= TURKEY ALPHA at P<0.05 level of significance. The results of the experimental toxicity thresholds of single metal ions to the total dehydrogenase activity of L. macrolides (OK298881) and A. faecalis (KX302624) showed that the EC50S of the toxicant on L. macroides(OK298881) ranged from 20.49 - 713.57mg/L while that of A. faecalis (KX302624) ranged from 58.87 – 624.41 mg/L. The order of increasing toxicity on L. macroides (OK298881) was Co(II) < Cd (II) < Ni(II) < Pb (II) < Zn(II) while that of A. faecalis(KX302624) was Ni (II) <Cd(II) <Co(II) < Pb(II) < Zn(II). Glyphosate had an EC50 value of 893.23mg/L. on L. macroides (OK298881) while on A faecalis (KX302624) it had an EC50 value of 593.98mg/L. The DDVP inhibitedthetotal dehydrogenase activity of L. macroides (OK298881) and A. faecalis (KX302624) at EC50 values 893.23mg/L. and 593.98mg/L respectively. The statistical analysis indicates that the EC50 of the toxicant were significantly different from each other (P<0.05) and the order of decreasing toxicity is DDVP> GLY. The toxic index of the mixture analyses showed that the toxic effect was increasing progressively as concentrations were increased.
Description
This thesis is for the award of Doctor of Philosophy (Ph.D) in Environmental Microbiology
Keywords
Heavy metals, pesticides, toxicity, dehydrogenase, EC50 ratio, toxic index, Department of Microbiology
Citation
Frank-Ogu, N. (2024). Toxicity of pesticides and heavy metals to bacterial isolates from aquatic ecosystem (Unpublished Doctoral Thesis). Federal University of Technology, Owerri, Nigeria