Fate and toxicity of 2,4-D and fipronil in mesocosm systems.

2,4-D and fipronil are among Brazil's most used pesticides. The presence of these substances in surface waters is a concern for the aquatic ecosystem health. Thus, understanding the behavior of these substances under environmentally relevant conditions is essential for an effective risk assessment. This study aimed to determine the degradation profiles of 2,4-D and fipronil after controlled application in aquatic mesocosm systems under influencing factors such as environmental aspects and vinasse application, evaluate pesticide dissipation at the water-sediment interface, and perform an environmental risk assessment in water and sediment compartments. Mesocosm systems were divided into six different treatments, namely: control (C), vinasse application (V), 2,4-D application (D), fipronil application (F), mixture of 2,4-D and fipronil application (M), and mixture of 2,4-D and fipronil with vinasse application (MV). Pesticide application was performed according to typical Brazilian sugarcane management procedures, and the experimental systems were monitored for 150 days. Pesticide dissipation kinetics was modeled using first-order reaction models. The estimated half-life times of 2,4-D were 18.2 days for individual application, 50.2 days for combined application, and 9.6 days for combined application with vinasse. For fipronil, the respective half-life times were 11.7, 13.8, and 24.5 days. The dynamics of pesticides in surface waters resulted in the deposition of these compounds in the sediment. Also, fipronil transformation products fipronil-sulfide and fipronil-sulfone were quantified in water 21 days after pesticide application. Finally, performed risk assessments showed significant potential risk to environmental health, with RQ values for 2,4-D up to 1359 in freshwater and 98 in sediment, and RQ values for fipronil up to 22,078 in freshwater and 2582 in sediment.

Fipronil and 2,4-D effects on tropical fish: Could avoidance response be explained by changes in swimming behavior and neurotransmission impairments?

Brazil is the largest producer of sugarcane, a crop largely dependent on chemical control for its maintenance. The insecticide fipronil and herbicide 2,4-D stand out among the most commonly used pesticides and, therefore, environmental consequences are a matter of concern. The present study aimed to investigate the toxicity mechanisms of Regent® 800 WG (a.i. fipronil) and DMA® 806 BR (a.i. 2,4-D) pesticides using forced and non-forced exposures through an integrative approach: firstly, to assess whether contamination by fipronil and 2,4-D can trigger the avoidance behavior of the fish Danio rerio (zebrafish) and Hyphessobrycon eques (serpae tetra or mato-grosso). Additionally, the effects on fish were analyzed considering the swimming behavior together with a biomarker of neurotoxicity, the activity of acetylcholinesterase (AChE). In avoidance tests with pesticide gradients, D. rerio avoided the highest concentrations of the two compounds and H. eques avoided only the highest concentration of 2,4-D. The swimming behavior (distance moved) was reduced and AChE was inhibited when D. rerio was exposed to fipronil. The 2,4-D affected the swimming (maximum speed) of H. eques, but AChE was not altered. Avoidance response seemed not to have been affected by possible effects of contaminants on swimming behavior and Ache activity. This study showed the importance of knowing the avoidance capacity, swimming behavior and neurotoxic effects of pesticides on fish in an integrated and realistic context of exposure in environments contaminated with pesticides and can be useful as ecologically relevant tools for ecological risk assessment.