Formation of Purple Reddish Colour in Salt Pans

Abstract

Sudden appearance of a whitish scum appeared during the seasonal pinkish coloration of the salt pans in the C area (evaporation area at salinity 6%to 11%) of Lanka Salt Ltd., Hambantota during October 2021, and this study was conducted to study the causative factors on this sudden color change. Water samples were taken from inlet of C area (n=3), C area salt pans (n=5) and outlet (n=3) of C area salt pans. The salinity level of the water samples was approximately in the range of 6% and 11%. Collected water samples were filtered through 30 μm mesh and the filtrate was examined under light microscope. Algae observed under the microscope were isolated using a dropper and those algae were cultured in BG-11 culture medium for subsequent identification. Absorbance of the samples at the wavelengths of 200 nm to 800 nm was detected using a UV visible spectrophotometer. The dominant planktonic organism was Dunaliella sp. (500 cells/mL) followed by Euplotes sp. (150 cells/mL) and Fabrea salina (100 cells/mL) respectively. The optimum population density of Dunaliella was observed in the laboratory culture after ten days of inoculation. The absorbance spectrum of both water samples collected from the salt pans and laboratory cultures exhibited a peak absorbance at the wave length of 400 to 600 nm, which has been identified as the range that includes the peak for carotenoids. Therefore, the observed reddish colour in the samples was explained by the presence of Dunaliella cells. Furthermore, this could be the reason for the pink coloration which appears in the normal salt crystallizer pans at the harvest. Present study identified a potential to extract carotenoids using Dunaliella and thus, further studies are recommended to develop procedures to extract carotenoids.