Light intensity can significantly regulate cadmium transformation into CdS nanoparticles in microalgae (Dunaliella salina and Phaeodactylum tricornutum)

Abstract

Light is a critical factor influencing algal growth and contributes to the uptake of metal elements by algae. However, the impact of light on the bioavailability and transformation of heavy metals requires further exploration, particularly in the context of bioremediation efforts. This study explores how varying light intensities (1000, 2000, and 3000 lux) influence the ability of these algae to absorb Cd, distribute it within cells, and transform Cd (II) into CdS NPs. By using ICP-MS, it was found that increasing the light intensity to 2000 lux could increase the Cd uptake capacity of Dunaliella salina and Phaeodactylum tricornutum by 28 % and 14 %, respectively. Changes in the percentage of Cd (II) in each component (medium, intracellular, and adsorption on cell surface) with the different light intensities supported the interpretation that the increase in Cd uptake by algal cells was a result of increased cellular adsorption and accumulation. Further analyses by HRTEM-EDS and SEC-ICP-MS showed that increasing light intensity not only influenced the size of CdS NPs but also significantly enhanced the algae's efficiency in transforming Cd(II) into CdS NPs. It is found that the transformation ratio of CdS NPs by D. salina and P. tricornutum increased to 16 % and 52 % respectively, after 10 days of Cd exposure under 2000 lux light intensity. These findings underscore the significance of light intensity as an environmental factor in the uptake and transformation of Cd by algae, with profound implications for its application in bioremediation.