Abstract

Detergents including biodegradable detergents can be toxic to aquatic life and hazardous to human health and the environment due to their properties. The aim of this study was to evaluate the acute toxicity of domestic detergents on Nitrobacter sp. (NS) isolated in marine water (MW), brackishwater (BW) and freshwater (FW). Fresh water was collected from Chokocho stream in Etche local Government Area; brackish water from Eagle Island, Port Harcourt; and marine water from Bonny River, all in Rivers State, Nigeria. Microbiological and physicochemical parameters of the water samples were analysed using standard methods. The pH of the water ranged from 5.96 to 8.23 while the temperature of the samples ranged from 27.9^oC to 31.2^oC.  The total dissolved solid (TDS) ranged from 520mg/l to 26700mgl and the total soluble solid (TSS) ranged from 0.01 to 0.003mg/l. The electrical conductivity of the samples ranged from 1040-12840 uS/cm. The toxicity of some domestic detergents including Branded Liquid soap – Morning fresh (MF), mama lemon (ML); Unbranded Liquid Soap: green soap (GS), and orange soap (OS) at 0%, 1.625%, 3.26%, 12.5%, 25%, 50% and 75% were tested against  Nitrobacter species in fresh, marine, and brackish water for 0, 2,8 ,12, 24, and 48 hours. The Median Lethal Concentration (LC₅₀) was employed to compare the toxicities of the detergents on the test organism. The process was monitored to determine frequency of mortality and survival for 48 hours using standard ecotoxicological methods. Results of Total heterotrophic bacterial count ranged from 9.6 x10⁶ to 1.15 x10⁷ cfu/ml with marine water  recording the lowest counts; while Nitrobacter counts ranged from 2.5×10⁴ to 7.3 x10⁴ cfu/ml. The percentage log survival of Nitrobacter sp decreased in marine water followed by fresh water and then brackish water.  The Median Lethal Concentration (LC₅₀) (%) for Nitrobacter decreased in the following order (noting that the lower the LC₅₀, the more toxic the toxicant). For branded liquid soap; Morning Fresh: BW (33.27) > FW (42.75) > MW (47.25), Mama Lemon: FW (23.82) > MW (32.57) > BW (33.10) while Unbranded Soap; Orange soap: BW (26.86) > FW (28.97) > MW (33.82), Green Soap: MW (22.94) > BW (26.77) > FW (36.10). The result of the mean lethal concentration showed the highest toxicity of soap/ detergent to test organism (Nitrobacter) in brackish water (30.00%) followed by Freaswater (32.91%) and marine water (34.15%). The use of detergents in aquatic ecosystems should be regulated to reduce their toxicity and to ensure safety of aquatic ecosystem.