The toxic effects of the herbicide Atrazine, its degradation products deethyl-atrazine and deisopropylatrazine,
and the herbicide metolachlor were examined in unialgal cultures of Chlorella fusca var-fusca.
The toxicity of a mixture of atrazine and metolachlor was also evaluated using the same bioassay system.
Cell numbers were determined daily and growth rates were calculated for a period of 4 days. The order of
toxicity of chemicals was atrazine>metolachlor>deethyl-atrazine>deisopropyl-atrazine. The presence of a
mixture of atrazine and metolachlor in toxic concentrations lower than the EC50 resulted in reduced toxicity
(antagonism) in comparison with the toxicity caused by the sum of toxic actions of the same levels of
concentration from single chemicals.