Comparative Eco-toxicological Effect of Corrosion Inhibitors on Aquatic Nitrogen Fixing Bacterium in Fresh and Brackish Water Ecosystem

Aquatic nitrogen-fixing bacteria play a crucial role in maintaining the nitrogen cycle and supporting primary productivity in freshwater and brackish water ecosystems. The activities of oil and gas industries operating within the coastal region of PortHarcourt releases effluents that contain various chemicals including corrosion inhibitors into the aquatic environment which can significantly affect the aquatic organisms including the nitrogen-fixing bacteria. Hence, this study was aimed to determine the comparative eco-toxicological effect of corrosion inhibitors on aquatic nitrogen fixing bacterium (Nitrosomonas sp.) in Fresh and Brackish water ecosystem. Fresh water and brackish water samples were collected from Chokocho stream in Etche Local Government Area and Eagle Island Port Harcourt, all in Rivers State, Nigeria. Standard toxicity procedure was applied on rectangular cut-out crude oil pipeline metal (ME) coated with corrosion inhibitors: Ambercil (AMB) and X-PRO 99 inhibitor (XPRO) immersed in freshwater (FW) prepared at concentrations of 25%, 50%, 75% and 100% for Nitrosomons sp. These inhibitors were tested with Nitrosomonas sp. at 0, 4, 8, 12 and 24hrs separately for each toxicant. The median lethal concentration (LC50) was employed to compare the toxicities of the different toxicants on the test organisms. The result for percentage survival of Nitrosomonas sp decreased when exposed to various concentrations listed above for 24. The LC50 (%) result (noting, that the lower the LC50, the more toxic the toxicant): of Nitrosomonas sp decreased in the following order: FW + ME (85.5) > BW + ME (86.7) > Both FW + AMB & FW + XPRO (86.8) > BW + XPRO (87.9) > BW + ME + XPRO (89.1) > BW + AMB (89.7) > FW + ME + XPRO (94.9). The above results revealed that Nitrosomonas sp decreased in percentage survival with an increase in concentration. The result showed that the effluents of metals coated with corrosion inhibitors (ME + AMB & ME + XPRO) were more toxic to Nitrosomonas sp in brackish water than freshwater while the effluents of XPRO & AMB not coated on metals were more toxic in freshwater than in brackish water. In conclusion, corrosion inhibitors when coated on metals, AMB corrosion inhibitor was more toxic than XPRO corrosion inhibitors in brackish and freshwater. Based on the findings, the use of XPRO corrosion inhibitor should be a best option for coating crude oil pipeline due to its relative low toxicity in upstream sector of the Nigeria petroleum industry.