Acute toxicity of Nicosulfuron- and S-metolachlor-based herbicides in mixture to Artemia salina

Introduction: The combined use of two or more pesticides in the field has become an increasingly common practice. Herbicides based on Nicosulfuron and S-metolachlor are an example as they have complementary modes of action. However, mixing these substances can cause environmental problems and may pose a threat to aquatic ecosystems. The objective of this study was to evaluate the acute ecotoxicological effects of the mixture of Nicosulfuron- and S-metolachlor-based herbicides to Artemia salina. Methods: The bioassay was conducted in accordance with ABNT NBR 16530:2021. Assessments were performed at 24 h and 48 h. For each treatment, four replicates were performed, consisting of ten nauplii in 10 mL of solution. Five treatments were tested. Concentrations were established based on previous research, in which the NOEC of Nicosulfuron (2.67 mg/L) and S-Metolachlor (29.7 mg/L) were determined. Thus, the treatments consisted of mixtures of the herbicides in proportional amounts (100%, 75%, 50%, and 25%). The interaction of the mixtures was analyzed using the Colby model (1967). Results: Nauplii immobilization was observed only at 48 h. Values ranged from 5% to 35%, but none of the concentrations differed statistically from the control (Tukey, p > 0.05). Furthermore, application of Colby’s model (1967) revealed an additive interaction among the mixtures. This indicates that the effects of the mixtures are equivalent to the effects of the individual compounds. Conclusions: The purpose of using the NOEC was to determine whether combining two concentrations that had no effect when tested alone could produce an effect when mixed. However, the absence of a significant difference demonstrates that the results are positive from the perspective of developing safe mixtures. Thus, this mixture may not pose a danger to other aquatic organisms such as A. salina. However, the behavior of mixtures is not fixed, and a case-by-case evaluation is necessary.