Products and mechanisms of the heterogeneous reaction of three suspended herbicide particles with NO₃ radicals

Effects of the herbicide trifluralin in the initial development of Piptadenia gonoacantha (Fabales: Fabaceae)

Trifluralin, a pre-emergent herbicide, is widely used in Brazil in the weed grass management in restoration areas. The objective was to evaluate the tolerance of Piptadenia gonoacantha to trifluralin. The treatments had three trifluralin doses (445, 890, and 1335 g a.i. ha^-1), applied in pre-sowing, as well as the control, without herbicide. Visual intoxication, seed germination, survival rate, emergence speed index (EMI), mean germination period, seedling height, and diameter, micromorphometric parameters of plant roots collected at 60 d after sowing, root length (RL) and volume, leaf area (LA), leaf numbers, root and shoot dry matter, and fluorescence of chlorophyll a at 30, 45, and 60 d after sowing were analyzed. Visual intoxication values above 50% were observed only with 1335 g a.i. ha^-1. The herbicide did not affect seed germination, EMI, average germination period, seedling height, and diameter, root micromorphometric parameters, length, dry matter or root volume, and chlorophyll a fluorescence. The dose 1335 g a.i. ha^-1 caused a reduction of 41.5% in survival, 50.3% in the LA, 36.7% in the number of leaves (LN), and 59.8% in the aerial dry mass of seedlings. The trifluralin presents potential for restoration programs of degraded areas with this forest species.

Photocatalytic oxidation of diuron using nickel organic xerogel under simulated solar irradiation

In this study, a nickel organic xerogel (X-Ni) was used as semiconductor photocatalyst for the degradation of the herbicide diuron (DRN) in aqueous solution. The main objective of this work was to analyze and compare the effectiveness of solar irradiation to remove DRN from water both by direct photolysis and photocatalytic degradation. We examined the influence of the initial concentration of the herbicide, the solution pH, the presence of different ions in the medium, the chemical composition of the water, and the presence of a photocatalyst, after 240 min of irradiation. Direct photolysis achieved a low percentage of DRN degradation but was favored: i) by a reduction in the initial concentration of the herbicide (from 35.6% to 79.0% for 0.150 × 10^-3 mol/L and 0.021 × 10^-3 mol/L of DRN, respectively) and ii) at solution pHs at which diuron is positively charged (78.6% for pH 2 and 50.4% for pH 7), as suggested by DFT calculations carried out for DRN and its protonated form (DRN-H⁺). The corresponding mono-demethylated DRN derivative, 1-(3,4-dichlorophenyl)-3-methylurea (DCPU), was identified as a DRN degradation byproduct. In addition, the presence of certain anions in the medium significantly affected the overall degradation process by direct photolysis, due to the additional generation of HO radicals. We highlight that the presence of X-Ni considerably improved the photodegradation process under solar irradiation. The photocatalytic degradation rate constant was directly proportional to the xerogel concentration, because an increase in catalyst dose produced an increase in surface active sites for the photodegradation of DRN, enhancing the overall efficiency of the process. Thus, when 4167 mg/g of X-Ni was added, the DRN removal rate was 3-fold higher and both percentage of degradation and mineralization increased 88.5% with respect to the results obtained by direct photolysis.

Analysis of 62 synthetic cannabinoids by gas chromatography-mass spectrometry with photoionization

Gas chromatography–mass spectrometry (GC–MS) in electron ionization (EI) mode is one of the most commonly used techniques for analysis of synthetic cannabinoids, because the GC–EI-MS spectra contain characteristic fragment ions for identification of a compound; however, the information on its molecular ions is frequently lacking. To obtain such molecular ion information, GC–MS in chemical ionization (CI) mode is frequently used. However, GC–CI-MS requires a relatively tedious process using reagent gas such as methane or isobutane. In this study, we show that GC–MS in photoionization (PI) mode provided molecular ions in all spectra of 62 synthetic cannabinoids, and 35 of the 62 compounds showed only the molecular radical cations. Except for the 35 compounds, the PI spectra showed very simple patterns with the molecular peak plus only a few fragment peak(s). An advantage is that the ion source for GC–PI-MS can easily be used for GC–EI-MS as well. Therefore, GC–EI/PI-MS will be a useful tool for the identification of synthetic cannabinoids contained in a dubious product. To the best of our knowledge, this is the first report to use GC–PI-MS for analysis of synthetic cannabinoids.