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Fipronil is a phenylpyrazole pesticide widely used to protect sugar-cane crops from insect pests. After reaching the environment, this insecticide may have several fates. This research aimed to propose a kinetic model to describe the fate of commercial fipronil Regent 800WG in the sediment-water interface of the Oleo Lagoon in the Mogi-Guaçu river floodplain, situated within the Jataí Ecological Station, by means of a microcosm scale experiment. Results showed that a small fraction of the pesticide is quickly dragged to the sediment while most of it remains in the water column. Biodegradation proves to be an important fipronil degradation route, especially when microorganisms capable of using fipronil as sole carbon source increase their population, as a function of exposure time. Biodegradation rates were higher in the sediment than in the water column.

In this study, we proposed a straightforward approach that could be used for Cr redox speciation in soil samples from remote places. For this aim, soil samples under strong anthropogenic impact, from the vicinity of the Brazilian Antarctic Station were studied. Control samples with no direct impact, were also collected further (4 km) from the station. A preliminary laboratory evaluation for Cr (VI) presence was performed using X-ray absorption spectroscopy. The proposed method was based on a hot alkaline extraction to promote the quantitative extraction of Cr (VI) from soil samples. The colorimetric reagent 1,5-diphenylcarbazide (DPC) was added to the extracts to form a violet complex with Cr (VI). A simple and inexpensive commercial scanner was used to acquire the digital images of the formed complex. Partial Least Squares models were constructed with the following average color descriptors: red (R), green (G), blue (B), hue (H), saturation (S), value (V), relative color descriptors (r, g and b) and luminosity (L). The results obtained with this scanner approach were consistent with the official method that uses a spectrophotometer at 540 nm. Besides that, this is the first study that reports Cr redox speciation in soils from Antarctica, which is regarded as the less polluted place on the Earth.

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