Toxicity of Local and Industrial Refined Diesel on Nitrobacter Species a Key Environmental Pollution Bio-marker

Aim: Hydrocarbon toxicological effect on nitrogen fixing bacterium Nitrobacter sp. is of prime importance as it affects the nitrification process which negatively and adversely affects aquatic flora. In view of the significance of this process, the toxicity of local and industrial refined diesel on a key environmental pollution bio-marker, Nitrobacter was investigated.

Study Design: Semi-static ecotoxicological bioassay was used to study the effect of varying concentrations of toxicants local and industrial refined diesel on aquatic bacterium Nitrobacter sp.

Place and Duration of Study: Sample: marine water samples were collected from bonny sea, bonny, freshwater from a stream in MuuBagia in BiaraGokana and brackish water from sand-field in Port Harcourt, Nigeria.

Methodology: Winogradsky medium, nutrient agar, and King agar B base was used for the isolation of bacteria species by spread plate techniques. Standard toxicity procedure was carried out using diesel prepared at different concentrations (%) 0, 3.25, 6.5, 12.5, 25 and, 50; tested with Nitrobacter sp. for 0 h, 4 h, 8 h, 12 h, and 24 h separately for each toxicant. Median lethal concentration (LC50) was employed to compute the toxicity of different concentration to the test organism.

Results: The median lethal concentration (LC50) of the diesel used were calculated mean mortality of the test organism Nitrobacter sp. with industrial diesel in fresh water was (43.85%) >Nitrobacter with industrial diesel using brackish water (30.23%) >Nitrobacter with industrial diesel in marine water was (15.93%). Nitrobacter with locally refined diesel in fresh water (34.76%) >Nitrobacter with locally refined diesel in brackish water (26.81%) >Nitrobacter with locally refined diesel in marine water (29.77%). [Noting that the lower the LC50, the more toxic the toxicant].

Conclusion: The study shows that local refined diesel has more toxic effect in brackish and freshwater than industrial refined diesel whereas in marine water a reverse trend occurs; industrial refined diesel being more toxic than local refined diesel. In view of the sensitive nature of Nitrobacter sp. to slight variation in toxicity quotient and its role in biogeochemical cycle; it could serve as a potential tool for eco-toxicological assay and pollution bio-marker.