Single soil – column studies were carried out to understand the influence o harmaceutical effluent (industrial type) on the physico – chemical behaviour and on the index and strength properties of five soils (two commercial and three natural soils) due to artificial contamination extending to nearly 250 days period. Two modes of operation, two HRTs and two concentrations of effluents, were the parameters considered. The unique role played by the above ‘organic and toxic’ effluent in influencing the physico – chemical behaviour and the index properties of soils are highlighted. It is found that the strengths of the soils have reduced by about 20%, within the period of concentration. Great caution need to be exercised by Geotechnical Engineers and by the various industries, when an ‘organic and toxic’ effluent, is allowed to discharge on a soil mass, containing at least 35% of clay content, when such soil/(s) are to be used for Engineering purposes.