Dual stressors in freshwater ecosystems: A critical review of the independent and combined effects of pesticides and road salts on phytoplankton

Freshwater ecosystems rely heavily on phytoplankton, which are primary producers and play a crucial role in regulating nutrient processes. The health and productivity of phytoplankton are facing increasing threats from human-induced environmental stressors, including pesticides and road de-icing salts. The study reviews the individual and combined effects of these stressors on freshwater phytoplankton, with a focus on chlorophyll production, as well as changes in growth and biomass. Experimental and field-based studies demonstrate that pesticides disrupt photosynthesis and cause growth inhibition, while salts trigger osmotic imbalances and disrupt critical ion equilibrium. The existing research establishes that these independent stressors expose sensitive phytoplankton species to distinct threats. The combined effects of pesticides and salinity exposure on phytoplankton need further scientific investigation. The growing studies demonstrate that these stressors interact and result in synergistic or antagonistic effects. The key interacting mechanisms between these stressors include membrane permeability changes and pesticide solubility variations, combined with oxidative stress production. Phytoplankton communities exposed to compounded challenges will likely experience shifts in species composition where tolerant species dominate sensitive ones, which could affect ecosystem functions. The present review underscores the urgent requirement to explore the intricate relationships between pesticide exposure and road salt while examining their cumulative effects on freshwater habitats. Scientists need targeted studies to investigate critical knowledge gaps that encompass both long-term ecological effects and the biological mechanisms that govern stressor interactions.