Toxicity Evaluation of Monochloramine and Chlorinated Sewage Effluents by a Phytoplankton Growth Test

Abstract

Monochloramine (NH₂Cl) which is a highly toxic pollutant is usually contained in chlorinated sewage effluents. Effects of NH₂Cl and chlorinated sewage effluent on freshwater ecosystem were investigated by an algal growth test using a green alga Selenastrum capricornutum.
Toxicity of NH₂Cl for the alga was stronger than that of free chlorine, and NH₂Cl was extremely stable in freshwater. Lowest-observed-effect concentration (LOEC) of NH₂Cl after 96 hours exposure was 0.01 mg-Cl₂l^-1. Comparison of chlorinated effluents with non-chlorinated effluents, the algal growth was inhibited significantly in chlorinated effluents. The final chlorinated effluents collected from the sewage treatment plant also affected the growth of alga, and about 80% of total residual oxidants in the effluents was detected as NH₂Cl. On the contrary, the algal growth was not inhibited in dechlorinated effuents with Na₂SO₃ because of disappearance of the residual oxidant. Judging from these results, it was clear that NH₂Cl was the most important pollutant in chlorinated wastewater effluents for aquatic organisms.