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Toxicity of Herbicide, Paraquat Dichloride and Insecticide, Lambda-cyhalothrin on Phosphate Solubilizing Bacteria, Pantoa dispersa in Aquatic Ecosystems

Aim: The study was aimed to determine the toxicity of paraquat dichloride and lambda-cyhalothrin on phosphate solubilizing bacteria, Pantoa dispersa in aquatic ecosystems. 
Study Design: This study employs randomized block design, statistical analysis of the data and interpretation. 
Place and Duration of the Study: Soil sample was collected from the root nodules of leguminous plants in a sterile polythene bag from the Elele, in Etche L.G.A, Rivers State. The fresh water sample was collected from Bane town in Khana L.G.A, brackish water sample was collected from Choba river in Obio/Akpor L.G.A while the marine water was collected from Bonny River of Bonny L.G.A., all of Rivers State, Nigeria. The samples were collected aseptically and transported in an ice-pack immediately to the Rivers State University, Microbiology laboratory for analysis. The study lasted for three months. 
Methodology: The bacterium, Pantoa dispersa was isolated and identified based on conventional and molecular characterization from water and soil samples. Different concentrations (3.13%, 6.25, 12.50, 25.00%, 50.00% and 75.00%) and the control (0%) of the herbicide (paraquat dichloride) and insecticide, Lambda-cyhalothrin were prepared using fresh, brackish and marine water samples and 10ml of the test organism, Pantoa dispersa was introduced and the survival count was determined at 0, 4hr, 8hr, 12hr and 24hr. The Mean Lethal Concentration (LC50) of the insecticide and herbicide on Pantoa dispersa in the three aquatic ecosystem was determined. 
Results: The LC50 of the herbicide (Paraquat dichloride) was recorded as 15.8% in brackish water, 17.37% in fresh water and 27.44% in marine water. While the LC50 of the insecticide, Lambda-cyhalothrin to Pantoa dispersa was 26.84% in fresh water, 27.26% in brackish water and 32.33% in marine water. 
Conclusion: From the study, the herbicide, Paraquat dichloride was more toxic in the three aquatic ecosystems compared to the insecticide, Lambda-cyhalothrin. The use of these agrochemicals should be monitored as they result in the mortality of beneficial soil bacteria like Pantoa dispersa which is phosphate solubilizing bacteria in aquatic ecosystems.