Impact of Simulated Pesticide Spray Drift and Runoff Events on the Structural and Functional Zooplankton Diversity in Tropical Freshwater Microcosms

In conventional agriculture, several pesticides can be applied at the same stage of plant development, either individually or in mixtures and these compounds also reach aquatic ecosystems. The aim of the present study was to investigate the short-term effects of the insecticide Kraft® 36 EC (active ingredient — a.i. abamectin) and the fungicide Score® 250 EC (a.i. difenoconazole) on the zooplankton community in outdoor freshwater microcosms. The potential risks related to the exposure to both compounds, isolated and in mixture, likely to occur in the field after runoff and spray drift events of their recommended doses were assessed in these microcosms through integrative analyses of the effects on the composition, density, and functional diversity of zooplankton. Namely, these endpoints were evaluated for eight different exposures, which were (1) Runoff control — RC; (2) Kraft-contaminated runoff — RK; (3) Score-contaminated runoff — RS; (4) Kraft and Score-contaminated runoff — RKS; (5) Spray drift Control — SC; (6) Kraft spray drift — SK; (7) Score spray drift — SS; and (8) Kraft and Score spray drift — SKS. Zooplankton taxa responded quickly to physical, chemical, and biological changes in the aquatic ecosystems. The principal response curves (PRC) analyses of the zooplankton community in the microcosms indicated significant effects after all insecticide treatments, both when applied individually and in a mixture with the fungicide. The insecticide treatment (RK and SK) demonstrated a decrease in the number of unique species (sing.sp) of zooplankton in the microcosms, and RK also decreased the functional divergence (FDiv). However, it was the treatment of mixtures (SKS) that caused a decrease in functional diversity (FD) and in the functional diversity indexes (divergence and richness) and sing.sp. Thus, the results showed the risk of the insecticide and their mixture to aquatic ecosystems.