Potential of the green microalgae Tetraselmis viridis and Dunaliella salina for bioremediation of aquatic ecosystems from the organophosphorus herbicide glyphosate

Abstract

Agricultural activities in Crimea and Sevastopol lead to contamination of aquatic ecosystems with herbicides, particularly glyphosate. A comparative assessment of the physiological response of the green microalgae Tetraselmis viridis and Dunaliella salina to glyphosate exposure (0–2100 μg/L) under optimal (45 μE m⁻² s⁻¹) and high (500 μE m⁻² s⁻¹) irradiance was conducted. The dynamics of algal abundance, physio-biochemical parameters of cells (chlorophyll a content, photosynthetic apparatus efficiency, cell size and granularity, reactive oxygen species production), and the abundance of associated bacteria were evaluated using microscopy, flow cytometry, and PAM fluorometry. It was found that glyphosate stimulates the growth of T. viridis and D. salina, which is reflected in high photosynthetic activity of cells, low oxidative stress levels, and increased biomass production. Under optimal irradiance, T. viridis exhibits growth stimulation at low and intermediate glyphosate concentrations (up to 700 μg/L) and inhibition at high doses. In contrast, D. salina demonstrates exceptional tolerance over a wide range of herbicide concentrations (up to 2100 μg/L). High irradiance enhances both the stimulatory and toxic effects of glyphosate on T. viridis while narrowing the tolerance range of D. salina, reducing the toxicity threshold of cells to the herbicide. It was shown that glyphosate addition stimulates the growth of associated bacteria. However, intensive algal growth outpaces bacterial population growth, indicating direct glyphosate uptake by microalgae as a nutrient source. The ability of both species to directly metabolize glyphosate and the possibility of controlling their physiological state through light conditions determine the high potential of these microalgae for application in biological wastewater treatment systems contaminated with herbicides. The feasibility of using T. viridis for rapid removal of low to moderate glyphosate doses (up to 700 μg/L) is demonstrated. D. salina can be used for the treatment of waters contaminated with high glyphosate concentrations.