Comparative toxicity of two organophosphorus insecticides on membrane integrity of Chlorella vulgaris. I. Effect on membrane permeability

The organophosphorus insecticides dimethoate and quinalphos caused reductio n in accumulation of uranine by Chlorella vulgaris Beijerinck cells with in crease in their concentrations (0-500 mu M L-1) in growth medium. On the ot her hand, there was increase in the loss of metabolites and non-metabolizab le compounds like 2-deoxyglucose and 2-aminoisobutyric acid (AIBA) from the treated cells during 2 hr of treatment period. But significant loss of pro tein from cells was observed only at concentrations greater than or equal t o 350 mu M L-1 of the insecticides. The toxic effect of quinalphos on membr ane permeability was more pronounced at each selected concentration compare d to that of dimethoate. With dimethoate treatment the loss of 2-deoxygluco se, AIBA and other cellular metabolites was observed at greater than or equ al to 350 mu M L-1 concentration while with quinalphos treatment such effec t was reported at greater than or equal to 10 mu M L-1 concentration. Incre ased permeability of the plasma membrane of intact cells is expected to be caused by the reduction in integrity of membrane lipids. The results are di scussed to arrive at the conclusion on mechanism of action of insecticides on actively growing autotrophic cells.