ABSTRACT
Aim: To assess the effect of the hydrocarbon discharges from the artisanal refineries on the community structure of microbial mats in an aquatic environment Study Design: The study employs experimental design, statistical analysis of the data and interpretation. Place and Duration of Study: The microbial mats, surface water and sediments samples were collected from four hydrocarbon polluted stations (A, B, C and D) and a control sampling station in Yellow island (Iyalla kiri) in Degema Local Government Area, in Rivers state Nigeria. The samples were immediately transported with ice packs to the Microbiology Laboratory of Rivers State University, Port Harcourt. The study lasted from March 2020 to February 2021, covering both wet and dry seasons. Methodology: Different concentrations of fresh effluent (0, 1.625, 3.25, 6.5, 12.5, 25, 50 and 75%) were prepared in test tubes to final volume of 10ml. Each of the test tubes was inoculated with one milliliter (1ml) of the test organism. Five sets of concentrations were prepared for the five test organisms (Bacillus subtillis MW808817, Enterobacter ludwigiiMW767009, Amorphotheca resinae EU040230, Cladosporium cladosporioides MW793722 and Penicillium chrysogenum MN184857). The organisms were exposed to the pollutant for duration of 0, 4, 8, 12 and 24 hours and plated out using spread plate technique. The cultures were incubated for 24 hours for bacteria and five days for fungi. Median lethal concentration (LC50) was determined using SPSS version 20. Results: The results showed that the percentage logarithm survival of the test organisms decreased with increase in exposure time and concentration. The LC50 of Bacillus subtillis MW808817 was 30.93%, Enterobacter ludwigii MW767009 was 29.74%, Amorphotheca resinae EU040230 was 19.65%,Cladosporium cladosporioides MW793722 was 20.08% and Penicillium chrysogenum MN184857 was 17.77%, (noting; the lower the LC50 the more toxic the pollutant). Conclusion: The effluent discharge was more toxic on Penicillium chrysogenum MN184857 than the other test organisms. Also, the ecotoxicological evaluation of the effluents on the test organisms isolated from the study area showed that LC50 of the effluent was slightly toxic on the microbial population when the results obtained were compared to GESAMP Standard for Toxicity Ranking of Chemicals/Effluents in Marine Environment.