Assessment of the toxic effects of the herbicides atrazine and glyphosate on the phytoplankton community of the Black Sea

The impact of glyphosate and atrazine herbicides on the growth and photosynthetic activity of the Black Sea phytoplankton community in spring was assessed. It has been shown that atrazine is more toxic to phytoplankton than glyphosate. The size structure of the phytoplankton community is an important factor determining its sensitivity to herbicide exposure. Pico-phytoplankton is more sensitive to pollutants than micro-nano-phytoplankton. Atrazine inhibits phytoplankton growth after 24 hours of exposure, with the greatest negative impact on pico-phytoplankton (EC50=16 μg/L). Micro-nano-phytoplankton exhibits high resistance to atrazine (EC50=22-32 μg/L). Unlike atrazine, glyphosate has a delayed effect on microalgae. For micro-nano-phytoplankton, the effect of glyphosate exposure is observed after 4 days. Pico-phytoplankton reacts quickly to glyphosate: on the 3 day at 50 μg/L, a twofold decrease in abundance was recorded. The use of pico-phytoplankton as a bioindicator for monitoring aquatic ecosystems and fluorescence parameters as early stress markers is recommended. Safe concentrations of atrazine and glyphosate for aquatic ecosystems do not exceed 5 and 10 μg/L, respectively.