Differential Toxicity of Fungicides and their Binary Mixtures on Raphidocelis Subcapitata: Predictive Assessment of Aquatic Ecological Risk

<title>Abstract</title> <p> Aquatic ecosystems are frequently exposed to complex mixtures of contaminants at sublethal levels, often leading to long-term negative consequences. Interactions among chemicals within these mixtures can magnify or diminish their overall toxicity, resulting in synergism, antagonism, or additivity. This study investigated the acute algicidal effects of 44 individual fungicides and their combinations on the green alga <italic>Raphidocelis subcapitata</italic> . The respective median effective concentration causing a 50% reduction in algal growth (EC ₅₀ ) was determined for each compound, and dose-response relationships were analyzed. Furthermore, to evaluate the combined effects of mixtures, the estimated toxic unit (TU) of binary mixtures and their joint action were then evaluated using the two-mixture approach. The study found significant cases of additive, antagonistic, and/or synergistic interactions between the fungicides. The data also provided detailed hazard characterization parameters, including no observed effect concentration (NOEC), lowest observed effect concentration (LOEC), maximum allowable toxicant concentration (MATC), predicted no-effect concentration (PNEC), chronic value (ChV) and concentration of concern (COC) values, due to exposure to the fungicides as aquatic stressors. These findings contribute to the establishment of Benchmark values and concentrations of concern due to exposure, which can be used by stakeholders to alleviate the ecotoxicological risk, protect surface waters, and maintain the health of the aquatic ecosystem. </p>