INHIBITION EFFECT OF THE ANIONIC SURFACTANT SDS ON DUCKWEED, LEMNA-MINOR WITH CONSIDERATIONS OF GROWTH AND ACCUMULATION

The growth inhibiting and accumulation effects of sodium dodecyl sulphate (SDS) on Lemna minor L. were tested at 1-300 ppm levels both in the full-strength and 1/10-diluted Jacob's nutrient media under continuous illumination at 26-30 degrees C for a 7-day experimental period. The growth of Lemna minor L. was enhanced by increasing concentrations of SDS between 1 and 40 ppm and inhibited thereafter, while no response was observed when the concentration reached a value of 100 ppm. On the contrary, the growth in 1/10-diluted medium was observed to be slightly enhanced up to concentrations of 40 ppm, but more so between 40-80 ppm SDS; exhibiting a sharp inhibition, thereafter. The accumulation of SDS by Lemna minor L. (expressed on dry weight basis) increased with increasing concentrations of SDS between 1-90 ppm, both in full-strength aid 1/10-diluted media. The correlation of increasing SDS concentrations with growth and accumulation were determined by using linear and non-linear regression analysis. The statistical significance of observed differences in full-strength and diluted media were also investigated. pH of both full-strength and diluted media at 1-90 ppm of SDS levels increased during the test: period and remained constant at higher SDS concentrations. This indicated that the biodegradation of SDS generated the alkaline intermediates in the medium.