We investigated the physiological responses of Lemna minor plants exposed to glyphosate. The deleterious effects of this herbicide on photosynthesis, respiration, and pigment concentrations were related to glyphosate-induced oxidative stress through hydrogen peroxide (H2O2) accumulation. By using photosynthetic and respiratory electron transport chain (ETC) inhibitors we located the primary site of reactive oxygen species (ROS) production in plants exposed to 500 mg glyphosate l−1. Inhibition of mitochondrial ETC Complex I by rotenone reduced H2O2 concentrations in glyphosate-treated plants. Complex III activity was very sensitive to glyphosate which appears to act much like antimycin A (an inhibitor of mitochondrial ETC Complex III) by shunting electrons from semiquinone to oxygen, with resulting ROS formation. Confocal evaluations for ROS localization showed that ROS are initially produced outside of the chloroplasts upon initial glyphosate exposure. Our results indicate that in addition to interfering with the shikimate pathway, glyphosate can induce oxidative stress in plants through H2O2 formation by targeting the mitochondrial ETC, which would explain its observed effects on non-target organisms.

Heavy metal pollution, as well as greenhouse effect, has become a serious threat today. Both heavy metal and heat stresses can arrest seed germination. What response can be expected for seed germination under both stress conditions? Here, the effects of heavy metals (Cu2+, Cd2+ and Hg2+) on maize seed germination were investigated at 20 °C and 40 °C. Compared with 20 °C, heat stress induced thermodormancy. However, this thermodormancy could be significantly alleviated by the addition of a low concentration of heavy metals. Heavy metals, as well as heat stress induced H2O2 accumulation in germinating seeds. Interestingly, this low concentration of heavy metal that promoted seed germination could be partly blocked by DMTU (a specific ROS scavenger), irrespective of temperature. Accordingly, H2O2 addition reinforced this promoting effect on seed germination, which was induced by a low concentration of heavy metal. Furthermore, we found that the NADPH oxidase derived ROS was required for seed germination promoted by the heavy metals. Subsequently, treatment of seeds with fluridone (a specific inhibitor of ABA) or ABA significantly alleviated or aggravated thermodormancy, respectively. However, this alleviation or aggravation could be partly attenuated by a low concentration of heavy metals. In addition, germination that was inhibited by high concentrations of heavy metals was also partly reversed by fluridone. The obtained results support the idea that heavy metal-mediated ROS and hormone interaction can finally affect the thermodormancy release or not.

Oil from the Exxon Valdez laden with polycyclic aromatic hydrocarbons (PAH) has persisted on some beaches in Prince William Sound, Alaska, >20years after these beaches became contaminated. The degradation rate of the total PAH (TPAH) is estimated at 1% per year. Low oxygen concentrations were found to be the major factor causing oil persistence, and bioremediation through the injection of hydrogen peroxide and nutrients deep into four beaches in PWS were conducted in the summers of 2011 and 2012. It was found that due to the treatment, the TPAH biodegradation rate was between 13% and 70% during summer 2011 and summer 2012. The results also showed high efficiency in the delivery of oxygen and nutrient to the contaminated areas of the beach. However, the approach has an environmental cost associated with it, and stakeholders would need to conduct a rigorous net environmental benefit analysis (NEBA) for pursuing the bioremediation of submerged contaminated sediments, especially in higher latitudes.

The petroleum production has been raised sharply over the past decades, whereas the petroleum exploitation has also caused serious environmental contamination. A pot experiment has been conducted to monitor the dynamic response of antioxidant defense system and the growth reaction of Amorpha fruticosa seedlings to soil petroleum contamination. The results show that (1) in 5 g kg⁻¹ contaminated soil, A. fruticosa removes reactive oxygen species (ROS) by increasing the activities of antioxidant enzymes (glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT)), while in 10–15 g kg⁻¹ long-term contaminated soil, A. fruticosa removes ROS by the cooperation of antioxidant enzymes and antioxidants (SOD, CAT, ascorbate peroxidase (APX), GR, ascorbic acid (AsA), glutathione (GSH), and proline (Pro)). In long-term 20 g kg⁻¹ contaminated soil, the defense ability of APX and AsA decreases sharply, and A. fruticosa removes the ROS by the synergistic effect of antioxidant enzymes (SOD and CAT) and antioxidants (GSH and Pro). Only in 20 g kg⁻¹ long-term petroleum contamination caused significant (P < 0.05) increase in H₂O₂ content in seedlings. (2) SOD, CAT, GR, GSH, and Pro exhibit increases in long-term severely contaminated soil, and these enzymes and antioxidants are the most important defender of A. fruticosa to ROS accumulation caused by petroleum contamination. (3) The growth of A. fruticosa seedlings is less affected in 5 g kg⁻¹ petroleum-contaminated soil, while it significantly decreases in 10, 15, and 20 g kg⁻¹ petroleum-contaminated soils (P < 0.05). (4) Considering comprehensively the response of antioxidant defense system and the growth reaction of seedlings to petroleum contamination, A. fruticosa could be utilized for phytoremediation in ≤15 g kg⁻¹ contaminated soil.

Sudan dyes are widely used as coloring agents in various solvents, waxes, and polishes. However, the dyes are environmental contaminants and Sudan I is a weak carcinogen, and its removal from wastewater remains challenging. Here, we developed a new strategy for Sudan dye degradation for use in the non-alkaline conditions typically found in wastewater. By combing glucose oxidase (GOD) and horseradish peroxidase (HRP), we avoided the hydrogen peroxide-induced HRP damage and inactivation. Moreover, the GOD-HRP-coupled degradation of Sudan dyes were enhanced by the addition of different kinds of phenols. Systematic investigations were carried out to determine the optimal process parameters (i.e., phenol concentration, pH value, temperature, and enzyme dose) for degrading Sudan I with GOD and HRP. Also, this strategy could be applied to degradation of Sudan II and Sudan III. We were also able to co-express GOD and HRP in a prokaryotic-like polycistronic expression system in Pichia pastoris, based on the internal ribosome entry sites (IRES). Therefore, this fermented liquid containing GOD and HRP might be used in the future to degrade pollutants in weakly acidic conditions.

Lignin-derived methoxyphenols (MPs) with Fe³⁺-reducing activity were used as potential mediators to increase the decolorization of dyes by classical Fenton (Fe²⁺/H₂O₂) and Fenton-like reactions (Fe³⁺/H₂O₂). In this study, several MPs such as vanillin, vanillic alcohol, syringaldehyde, ferulic, vanillic, and syringic acids were evaluated. The results showed that all MPs displayed similar prooxidant activities in the decolorization of methylene blue, chromotrope 2R, methyl orange, and phenol red. For example, the reaction performed with Fe³⁺/H₂O₂ decolorized 27 % of chromotrope 2R, whereas the treatments with Fe³⁺/H₂O₂/MP decolorized around 70 % of the same dye after 60 min. For Fe²⁺/H₂O₂ systems, two stages of decolorization were visibly observed. In the first stage, the MPs inhibited the treatments, and then they increased the decolorization rate in the second stage. Prooxidant and antioxidant properties were observed for decolorization of methylene blue performed in the presence of low and high concentrations of vanillin, respectively. Overall, the MPs increased dye decolorization without increasing the consumption of H₂O₂.

This research work evaluates the use of hydrogen peroxide for the removal of cyanide from coking wastewater deriving from the washing of gases in coal combustion furnace. The effect of the presence or absence of suspended solids and organic micropollutants on the efficiency of the treatment is analyzed. Various dosages of hydrogen peroxide (6.5–200 mg/L) were added to both aqueous solution (at pH 10.5) and industrial wastewater (at pH 10.3) samples. The influence of suspended solids in coking wastewater was analyzed by applying a coagulation–flocculation–decantation process before the hydrogen peroxide treatment. The preliminary cyanide removal treatment in aqueous solution showed that the maximum cyanide removal did not exceed 14 % using a mass ratio of hydrogen peroxide to cyanide of 11.6. The maximum cyanide removal obtained in coking wastewater was 47 % with a mass ratio of hydrogen peroxide to cyanide of 12.2 provided that a coagulation–flocculation–decantation pretreatment was applied to remove the suspended solids composed mainly of coal, calcium carbonate, and magnesium carbonate. On the other hand, the cyanide removal treatment in coking wastewater with hydrogen peroxide showed promising results in the removing of different organic micropollutants formed mainly by polycyclic aromatic hydrocarbons and quinolines.

Pilot scale thin film plate reactors (TFPR) were fabricated to study the solar photocatalytic treatment of wastewater obtained from the secondary treatment plant of a sugar refinery. Silver-impregnated titanium dioxide (TiO₂) was prepared by a facile chemical reduction method, characterized, and immobilized onto the surface of ceramic tiles used in the pilot scale reactors. On 8 h of solar irradiation, percentage reduction of chemical oxygen demand (COD) of the wastewater by Ag/TiO₂, pure TiO₂, and control (without catalyst) TFPR was about 95, 86, and 22 % respectively. The effects of operational parameters such as, flow rate, pH, and addition of hydrogen peroxide (H₂O₂) were optimized as they influence the rate of COD reduction. Under 3 h of solar irradiation, 99 % COD reduction was observed at an optimum flow rate of 15 L h⁻¹, initial pH of 2, and addition of 5 mM of H₂O₂. The results show that Ag/TiO₂ TFPR could be effectively used for the tertiary treatment of sugar refinery effluent using sunlight as the energy source. The treated water could be reused for industrial purposes, thus reducing the water footprint of the industry. Graphical Abstract Sugar refinery effluent treatment by solar photocatalytic TFPR

The study delineates the investigation to determine the adsorption and desorption behaviour of Pretilachlor in three soils of Punjab with varying physicochemical characteristics using batch equilibration techniques. Kinetics of adsorption followed a pseudo-second-order model (R ² > 0.99) and adsorption–desorption data fitted well to the Freundlich equation for the three soils. L-type isotherms were obtained for the adsorption process, which indicated high affinity between Pretilachlor and adsorption sites. The magnitude of logK Fₐdₛ values for the three soils ranged from 0.887–1.226 μg¹⁻¹/ⁿ g⁻¹ mL¹/ⁿ and the order of adsorption was clay loam > sandy loam > loamy sand. Desorption of Pretilachlor was concentration dependent and in three desorption cycles ranged from 5.04 to 56.03 % in loamy sand, 3.14 to 23.12 % in sandy loam and 1.63 to 18.64 % in clay loam soil indicative of difficulty in the release of strongly adsorbed Pretilachlor. The removal of organic matter by hydrogen peroxide (H₂O₂) oxidation increased the adsorption of Pretilachlor in three Punjab soils. Pretilachlor desorption was hysteretic in the original as well as H₂O₂-treated soils. It could therefore be concluded that the adsorption was controlled by clay minerals and desorption of Pretilachlor in soils was controlled by the organic matter.

Over the last few decades, the concentration of cadmium (Cd) in the environment has increased considerably in many countries due to anthropogenic activities. Cd is one of the most toxic pollutants in the environment and affects many metabolic processes in plants. The main objective of this study was to evaluate the response of the production, nutritional, and enzymatic antioxidant system of two tomato genotypes (Calabash Rouge and CNPH 0082) grown in tropical soils that were treated with doses of Cd. Soil samples were collected from the layer of earth at a depth of 0–0.2 m in areas subjected to a minimum of human disturbance. The concentrations of Cd applied to the soil samples were 0, 1, 2, and 4 times (0, 3, 6, and 12 mg kg⁻¹ of Cd) the agricultural intervention value adopted by current environmental legislation in the state of São Paulo, Brazil. Analysis of superoxide dismutase, catalase, glutathione reductase, guaiacol peroxidase, and ascorbate peroxidase activities, formation of stress indicator compound (malondialdehyde—MDA and hydrogen peroxide), parameters of production—dry mass of the shoot and root system (here in after “shoots” and “roots”), as well as nutrition, and both the bioavailable and total levels of this metal in the soil were performed. When the bioavailable content and total levels of Cd in the soil increased as a result of this metal doses applied, the biomass of both shoots and roots decreased in both genotypes (with the exception of the CNPH 0082 grown in clay soil) and displayed lower SPAD (relative chlorophyll index) values when exposed to contaminated environments with Cd concentrations. Cadmium treatment resulted in nutritional imbalances, mainly in terms of N, P, and Mn metabolism. Plants subjected to an elevated available content of metal in the soil exhibited increases in content of MDA and hydrogen peroxide and increased activity of catalase, ascorbate peroxidase, and guaiacol peroxidase in plant tissues when grown in both clay soil and sandy soil. Cadmium was phytotoxic to the plants causing a nutritional imbalance, especially on the metabolisms of N, P, and Mn. An oxidative stress condition was established in response to the Cd treatments applied, which led to changes in peroxidase activity.