Toxicity of substituted benzene derivatives to four chemolithotrophic bacteria isolated from the New Calabar River

Abstract

The toxicity of benzene, hydroxylbenzene (phenol), chlorobenzene, methylbenzene (toluene) and dimethylbenzene (xylene) to four chemolithotrophic bacteria (Nitrosomonas, Nitrobacter, Thiobacillus and Leptothrix isolated from the New Calabar River water was investigated. The static method for acute toxicity assessment was employed. Mortality within a period of 5 hours exposure to toxicant was the index for assessment. Toxicity of the chemicals to the bacteria decreased in the following order: phenol > xylene > benzene > chlorobenzene > toluene for Nitrosomonas, chlorobenzene > phenol > benzene > toluene > xylene for Nitrobacter, phenol > chlorobenzene > benzene > xylene > toluene for Thiobacillus, while phenol > chlorobenzene > xylene > toluene > benzene was for Leptothrix. Combining the results above the toxicity of the chemicals to the test organisms decreased in the order phenol > chlorobenzene > benzene > xylene > toluene. Sensitivity of the bacteria to the test chemicals decreased in the order Nitrosomonas > Leptothrix > Thiobacillus > Nitrobacter. Toxicity of the methyl and dimethyl substituted derivatives of benzene was probably a function of the genetic make up of the bacteria. The toxicity generally decreased with increased methyl substitution in the case of Nitrobacter and Thiobacillus, but increased with increased methyl substitution in the case of Nitrosomonas and Leptothrix. Hydroxyl and halogenated substituted derivatives were more toxic than methyl substituted derivatives. These results indicate that wastes containing hydroxyl and chlorosubstituted derivatives of benzene may pose a greater toxicity problem to microbiota in the New Calabar River than wastes containing methyl-substituted derivatives. The nitrification stage of the nitrogen cycle will also be greatly impaired in the presence of these groups of chemicals in the river.



Key Words: Chemolithotrophic bacteria, Toxicity, Sensitivity, Benzene derivatives, New Calabar River.

[Global Jnl Environ Sci Vol.2(2) 2003: 72-77]