Around one million metric ton of plastics is produced worldwide daily. Plastic contamination is aggravated when the particles reach sizes between 5 mm and 1 μm, giving rise to microplastics, which are omnipresent in the environment, especially in agroecosystems. To appreciate the magnitude of this problem, this review analyzes 177 scientific works to focus on the occurrence and effects of microplastics in agricultural soils. Firstly, the sources, behavior and fate of microplastics in agroecosystems are evaluated. Then, in the absence of a standard methodology for the study of microplastics in farmland soils, the procedures which have been employed for microplastic separation (density and floatation in 73% of the discussed works), identification and quantification (stereomicroscopy, 77%; infrared analysis, 62%) are addressed to provide a practical work guideline. Finally, we highlight the interaction between microplastics and soil microbiota, fauna and vegetation (negative effects reported in 83% of cases), including crop production (decrease in growth parameters in 63% of the reports). From this review, it can be inferred that microplastics may disrupt the biophysical environment of farmland soil, potentially leading to economic losses and to their entrance into the trophic food chain, affecting human feeding and health.

Bioplastics aim to substitute conventional plastics in most applications, a critical one being the collection of organic wastes for composting or anaerobic degradation. The anaerobic biodegradability of six commercial bags composed of PBAT or PLA/PBAT blends and certified as compostable [1] was studied using ¹H NMR and ATR-FTIR techniques. This study aims to elucidate if commercial bioplastic bags are biodegradable under conventional conditions found in anaerobic digestates. Results showed that all studied bags are hardly anaerobically biodegradable at mesophilic temperatures. The biogas yield resulting from the anaerobic digestion under laboratory conditions oscillated between 270.3 ± 45.5 L kgVS^-1 for a trash bag composed of 26.64 ± 0.03%/73.36 ± 0.03% PLA/PBAT and 36.7 ± 25.0 L kgVS^-1 for a bag composed of 21.24 ± 0.08%/78.76 ± 0.08% PLA/PBAT. The degree of biodegradation did not correlate with PLA/PBAT molar composition. However, ¹H NMR characterization showed that the anaerobic biodegradation occurred mostly in the PLA fraction. No bioplastics biodegradation products were detected in the digestate fraction (<2 mm). Finally, none of the biodegraded bags comply with the EN 13432 standard.

Salinity is a serious threat for global agriculture, especially in arid and semi-arid regions where its incidence leads to considerable damages in the crop growth and production. Carica papaya L. is currently one of the most cultivated fruit crops in the tropical and subtropical areas, and generally, papaya cultivars exhibit a moderate sensitivity to salinity, although such responses may depend on the genotypes. In the present study, papaya seedlings were subjected to salt stress (100 mM NaCl) for 41 d and to exogenous gibberellic acid (GA₃; 0.1 mM) and proline (10 mM) pretreatments to evaluate plant physiological variables linked to stress responses. Analysis of the data (P < 0.05) showed a general decrease of plant growth parameters induced by solely salt stress compared to control, such as stem height (47%) and thickness (33%) and plant fresh and dry mass (84% and 83%, respectively), as well as a reduction in the stomatal opening (93%), chlorophylls (40%) and carotenoids (71%) concentration. By contrast, a significant increase was found in foliar and radicular proline levels under stress (87% and 47%). Exogenous foliar GA₃ or proline respectively induced a better performance of plants under salt stress by increasing stomatal conductance (444% or 350%), stem height (142% or 144%) and plant biomass (49% or 41%) regarding solely stressed plants, and leading to pigments concentrations close to those from control plants. The results suggest that exogenous gibberellic acid and proline as growth regulator and osmo-regulator solute, respectively could increase papaya seedlings adaption against salt stress.

A direct and general method for the synthesis of naturally occurring 2,3,4,5,6-pentasubstituted tetrahydropyrans has been developed, employing β,γ-unsaturated N-acyl oxazolidin-2-ones as key starting materials. The combination of the Evans aldol addition and the Prins cyclization allowed the diastereoselective and efficient generation of the desired oxacycles in two fashions: a one-pot Evans aldol-Prins protocol, in which five new σ bonds and five contiguous stereocenters were straightforwardly generated, and a two-steps version, which additionally permitted the isolation of precursors β,γ-unsaturated alcohols bearing an N-acyl oxazolidin-2-one in the α position. From these alcohols were also obtained halogenated pentasubstituted tetrahydropyrans as well as 2,3,4,5-tetrasubstituted tetrahydrofurans, shedding light on the mechanism of the process. Computational studies were consistent with the experimental findings, and this innovative Evans aldol-Prins strategy conducted to the preparation of a battery of more than 30 densely substituted tetrahydropyrans, unprecedentedly fused to a 1,3-oxazinane-2,4-dione ring, both in a racemic and in a enantiomeric fashion. These novel molecules were successfully submitted to several transformations to permit a simple access to a variety of differently functionalized tetrahydropyrans. Most of these unique molecules were evaluated for their antimicrobial activity against Gram-positive and Gram-negative bacteria and the yeast Candida albicans and some structure/activity relationships were established.