RESUMO
Sugarcane expansion has been associated with soil contamination by agrochemicals. Pesticides can affect plant growth, and their mixture might have potentiated effects on exposed species. This research aimed to evaluate the influence of fipronil on the phytotoxicity of 2,4-D on three green manure plant species: Canavalia ensiformis, Dolichos lablab, and Lupinus albus. Plants were exposed (for 21 days, at 25 °C) to a control soil and five concentrations of each pesticide and their combinations (36 treatments, considering a full-factorial approach). Effect concentrations of 50% growth inhibition (EC50) were estimated. No phytotoxicity effects were identified when plants were exposed to different fipronil concentrations (up to 0.12 mg kg-1). All species exposed to 2,4-D showed a decrease in shoot and root length and fresh/dry biomass. L. albus and D. lablab roots showed the highest sensitivity when exposed to 2,4-D among the endpoints (EC50 = 0.02 and 0.05 mg kg-1, respectively), while C. ensiformis roots were the most tolerant (EC50 = 0.98 mg kg-1). However, the interference of fipronil on the toxicity of 2,4-D was not detected in different mixture proportions, indicating no interaction between pesticides. Residues of 2,4-D might also impair other crops' growth, compromise productivity, and limit phytotechnologies for soil recovery.
Assuntos
Praguicidas , Poluentes do Solo , Esterco , Praguicidas/toxicidade , Pirazóis/toxicidade , Solo/química , Poluentes do Solo/toxicidade , Poluentes do Solo/análiseRESUMO
Improper disposal of mining waste is still considered a global problem, and further details on the contamination by potentially toxic metals are required for a proper assessment. In this context, it is important to have a combined view of the chemical and biological changes in the mining dump area. Thus, the objective of this study was to evaluate the Pb, Zn and Cd contamination in a slag disposal area using the integration of geochemical and microbiological data. Analyses of soil organic matter (SOM), pH, Eh, pseudo-total concentration of metals, sequential extraction and microbial community by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) were conducted. Metal availability was evaluated based on the geoaccumulation index (I geo), ecological risk ([Formula: see text]), Risk Assessment Code (RAC) and experimental data, and different reference values were tested to assist in the interpretation of the indices. The soil pH was slightly acidic to neutral, the Eh values indicated oxidized conditions and the average SOM content varied from 12.10 to 53.60 g kg-1. The average pseudo-total concentrations of metals were in the order of Zn > Pb > Cd. Pb and Zn were mainly bound to the residual fraction and Fe-Mn oxides, and a significant proportion of Cd was bound to the exchangeable and carbonate fractions. The topsoil (0-20 cm) is highly contaminated (I geo) with Cd and has a very high potential ecological risk ([Formula: see text]). Higher bacterial diversity was mainly associated with higher metal concentrations. It is concluded that the integration of geochemical and microbiological data can provide an appropriate evaluation of mining waste-contaminated areas.