Determining pyroxasulfone herbicide in honey samples using liquid-liquid extraction with low temperature purification (LLE-LTP).

Pyroxasulfone is a selective, systemic, pre-emergence herbicide which acts to inhibit weeds in potato, coffee, sugar cane, eucalyptus, and soybean plantations, among others. This active ingredient was classified by Brazilian legislation as a very dangerous product for the environment, and to date there are no studies involving the development of extraction methods for monitoring this compound in environmental matrices. Therefore, the objective of this study was to optimize and validate liquid-liquid extraction with low temperature purification followed by a gas chromatography coupled to mass spectrometry analysis to determine this herbicide in honey samples. The results showed that the best extractor phase was acetonitrile and ethyl acetate (6.5 mL:1.5 mL), with recovery rates close to 100% and relative standard deviations below 11%. The validation proved that the extraction method was selective, precise, accurate and linear in the range of 3-225 µg kg-1, reaching a limit of quantification of 3 µg kg-1, with a -25.95% matrix effect. Monitoring on real samples did not reveal episodes of environmental contamination with pyroxasulfone residue.

Metal Contamination of Water and Sediments of the Vieira River, Montes Claros, Brazil.

Vieira River is the main recipient of domestic and industrial wastewater in the city of Montes Claros, MG, Brazil. Until 2010, domestic sewage was dumped in it without any kind of treatment. Concentrations of arsenic (As), chrome (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) were determined in water and sediment samples in eight locations along the Vieira River during the dry season of 2015. Concentrations of Cu, Ni, and Zn detected in the water at some sites along the Vieira River were superior to the reference limits for toxicity. The concentration of Cu and Ni restricts the use of water for irrigation in some sites of the river. The level of sediment contamination was assessed by five approaches, including contamination factor (CF), pollution load index (PLI), geo-accumulation index (Igeo), cluster analysis (CA), and principal component analysis/factor analysis (PCA/FA). The results showed that Cr and the downstream sampling site nearest to the Wastewater Treatment Plant of the city of Montes Claros had the highest values of PLI, Igeo, and CF, which reinforces the influence of domestic and industrial wastewater discharge in pollution of the Vieira River. In addition, CA and PCA/FA reinforced the assumption that Cr comes from anthropogenic pollution sources.