Inhibition effect of the anionic surfactant SDS on duckweed, 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 Jacobʹs nutrient media under continuous illumination at 26–30°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 and 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.