Ozone tolerance in Phaseolus vulgaris depends on more than one mechanism

Two bean cultivars with different sensitivity to ozone, i.e. the O₃-sensitive Cannellino and the O₃-tolerant Top Crop, were exposed to acute O₃-stress (165 nL L⁻¹) with the aim of evaluating physiological and biochemical traits that may confer O₃-tolerance. Stomatal conductance was smaller and the ability to dissipate excess energy, via regulated and unregulated nonphotochemical quenching mechanisms was greater in Top Crop than in Cannellino. These morphological and physiological-traits allowed the O₃-tolerant cultivar to compensate for the light-induced declines in Φ_PSII, to preserve photosystem II from excitation-energy, and likely to prevent the generation of ROS to a superior degree than the O₃-sensitive cultivar. Furthermore, the potential capacities to reducing the superoxide anion and H₂O₂ were significantly greater in Top Crop than in Cannellino. These findings are consistent with the early accumulation of H₂O₂, the almost complete disruption of cell structure, and irreversible damages to the photosynthetic apparatus observed in the O₃-sensitive cultivar.     

Oxidative degradation of chlorophenol derivatives promoted by microwaves or power ultrasound: a mechanism investigation

Background, aim, and scope

Phenols are the most common pollutants in industrial wastewaters (particularly from oil refineries, resin manufacture, and coal processing). In the last two decades, it has become common knowledge that they can be effectively destroyed by nonconventional techniques such as power ultrasound (US) and/or microwave (MW) irradiation. Both techniques may strongly promote advanced oxidation processes (AOPs). The present study aimed to shed light on the effect and mechanism of US- and MW-promoted oxidative degradation of chlorophenols; 2,4-dichlorophenoxyacetic acid (2,4-D), a pesticide widespread in the environment, was chosen as the model compound.

Materials and methods

2,4-D degradation by AOPs was carried out either under US (20 and 300 kHz) in aqueous solutions (with and without the addition of Fenton reagent) or solvent-free under MW with sodium percarbonate (SPC). All these reactions were monitored by gas chromatography–mass spectrometry (GC–MS) analysis and compared with the classical Fenton reaction in water under magnetic stirring. The same set of treatments was also applied to 2,4-dichlorophenol (2,4-DCP) and phenol, the first two products that occur a step down in the degradation sequence. Fenton and Fenton-like reagents were employed at the lowest active concentration.

Results

The effects of US and MW irradiation were investigated and compared with those of conventional treatments. Detailed mechanisms of Fenton-type reactions were suggested for 2,4-D, 2,4-DCP, and phenol, underlining the principal degradation products identified. MW-promoted degradation under solvent-free conditions with solid Fenton-like reagents (viz. SPC) is extremely efficient and mainly follows pyrolytic pathways. Power US strongly accelerates the degradation of 2,4-D in water through a rapid generation of highly reactive radicals; it does not lead to the formation of more toxic dimers.

Discussion

We show that US and MW enhance the oxidative degradation of 2,4-D and that a considerable saving of oxidants and cutting down of reaction times is thereby achieved. The results support the interpretation of previously published data and improve the understanding of the factors of direct degradation along different pathways.

Conclusions

Oxidative pathways for 2,4-D, 2,4-DCP, and phenol were proposed by a careful monitoring of the reactions and detection of intermediates by GC–MS.

Recommendations and perspectives

The understanding of the factors that affect chlorophenols degradation along different pathways may facilitate the optimization of the treatment. Type of energy source (US or MW), power, and frequency to be applied could be designed in function of the operative scenario (amount of pollutant in soil, water, or oils).     

Ecotoxicological evaluation of industrial port of Venice (Italy) sediment samples after a decontamination treatment

This work assesses the ecotoxicological effects of polluted sediment after a decontamination treatment process using a new sediment washing technique. Sediment samples were collected from four sites in Marghera Port industrial channels (Venice, Italy). Ecotoxicological evaluations were performed with Vibrio fischeri and Crassostrea gigas bioassays. Whole sediment and elutriate were deemed as the most suitable environmental matrices for this study. Toxicity scores developed in the Lagoon of Venice for V. fischeri on whole sediment and for C. gigas on elutriate were considered for the final ranking of samples. Ecotoxicological results showed that the treated sediment samples presented both acute and sub-chronic toxicities, which were mainly attributed to the presence of some remaining chemicals such as metals and polyaromatic hydrocarbons. The acute toxicity ranged from low to medium, while the sub-chronic one from absent to very high, suggesting that treated sediments could not be reused in direct contact with seawater.     

Effects of long-term land use on arbuscular mycorrhizal fungi and glomalin-related soil protein

The maintenance of soil health and productivity is a central aim of sustainable agriculture. Arbuscular mycorrhizal fungi (AMF) are soil biota fundamental for soil fertility and plant nutrition, which may be used in the evaluation of the impact of agronomic practices on soil quality. In the present study we evaluated the influence of three different land uses on AMF populations and correlated glomalin-related soil protein (GRSP) content with AMF biomass parameters, such as spore density and biovolume. Among the differently managed sites – maize monoculture, grassland and poplar grove – maize soil showed the lowest AMF spore number and GRSP content. The same morphological taxa were found in the three sites, except for one additional morphotype in poplar grove. A good correlation between GRSP and spore biovolume was found, suggesting that GRSP may represent a useful biochemical parameter for the assessment of biological soil fertility in sustainable agriculture.     

Determination of the microscopic rate constants for the hydrolysis of diuron in soil/water mixture

A kinetic equation for the analysis of the degradation reaction of xenobiotic molecules in the soil/water mixture has been derived. By means of this equation we have evaluated the microscopic rate constant for the abiotic hydrolysis of the herbicide diuron in the water phase of a soil/water mixture assuming that the reaction occurs only in the water phase and that diuron is reversibly adsorbed by the soil with a higher rate. The soil catalytic capacity on the hydrolysis of diuron was evaluated.