Abstract

Aquatic ecosystems have been shown to be adversely affected by pesticides such as Gammalin 20, which can have an adverse effect on primary and secondary producers. This study investigated the ecotoxicity of gammalin 20 on Nitrobacter vulgaris and Nitrosomonas halophila in Freshwater, Marine water and Estuarine water samples collected from Adoni Local Government Area, Rivers State. The test isolates were isolated from roots of aquatic plants on Winogadsky agar using standard microbiological method. Various concentrations (0, 5, 15, 25, 50 and 75%) of the toxicant were prepared and transferred into conical flasks containing different measurements of the various water samples. The toxicity test and determination of Lethal concentration (LC₅₀) of the toxicant on the isolates was conducted at 4 hours intervals for 24 hours. The mean percentage survival of Nitrobacter vulgaris in different aquatic environments exposed to different concentrations of gammalin 20 after 24 hours in marine, estuarine and freshwater were 5.013±11.21 to 100±0.0, 24.84±25.75 to 100±0.0 and 14.52±13.26 to 100±0.0%, respectively. There was a significant difference (P<0.05) in the percentage survival of test organisms in all the aquatic environments. The mean percentage survival of Nitrosomonas halophila in known aquatic environments mixed with known concentrations of gammalin 20 after 24 hours in marine water, estuarine water and freshwater ranged from 4.86±10.87 to 100±0.0, 0.00±000 to 100±0.0 and 6.85 ±15.32 to 100±0.0%, respectively. The Nitrosomonas load of the control in all the aquatic environments was significantly (P < 0.05) higher than other concentrations with the 75% concentrations having the lowest survival counts. The LC₅₀ for Nitrosomonas halophila ranged from 13.40 to 16.89 while that of Nitrobacter vulgaris was 13.10 to 27.88. Thus, gammalin had low LC₅₀ on both isolates in freshwater than in other aquatic environments. Therefore use of Gammalin 20 in aquatic environment is not recommended.