Arsenic (As) pollution in aquatic environment may adversely impact fish health by disrupting their thyroid hormone homeostasis. In this study, we explored the effect of short-term exposure of arsenite (AsIII) on thyroid endocrine system in zebrafish. We measured As concentrations, As speciation, and thyroid hormone thyroxine levels in whole zebrafish, oxidative stress (H2O2) and damage (MDA) in the liver, and gene transcription in hypothalamic–pituitary–thyroid (HPT) axis in the brain and liver tissues of zebrafish after exposing to different AsIII concentrations for 48 h. Result indicated that exposure to AsIII increased inorganic As in zebrafish to 0.46–0.72 mg kg−1, induced oxidative stress with H2O2 being increased by 1.4–2.5 times and caused oxidative damage with MDA being augmented by 1.6 times. AsIII exposure increased thyroxine levels by 1.3–1.4 times and modulated gene transcription in HPT axis. Our study showed AsIII caused oxidative damage, affected thyroid endocrine system and altered gene transcription in HPT axis in zebrafish.

Dissolution of silver nanoparticles (AgNP with carbonate or citrate coating, total Ag 1–5 μM) was examined in the presence of the ligands cysteine, chloride and fulvic acids and of the oxidant hydrogen peroxide (H2O2) at low concentrations at pH 7.5. Dissolved Ag was separated from AgNP by ultrafiltration. Cysteine in the concentration range 0.2–5 μM resulted in an initial increase of dissolved Ag within few hours. Chloride (up to 0.1 mM) and fulvic acids (up to 15 mg L−1) had little effect on the dissolution of AgNP within hours to days. In contrast, very rapid dissolution within 1–2 h of both carbonate and citrate coated AgNP was observed in the presence of H2O2 in the concentration range 0.1–10 μM, under dark or light conditions. The high efficiency of H2O2 in dissolving AgNP is likely to be of importance in toxic effects of AgNP to algae, as H2O2 is produced and released into solution by algae.

Photosynthesis, the basal manufacturing process in the earth is habitually restricted by airborne micropollutants such as phenanthrene (PHE). Here, we show that 24-epibrassinolide (EBR), a bioactive plant steroid is able to keep higher photosynthetic capacity consistently for a long period under a shoot-imposed PHE stress in tomato. EBR-promoted photosynthetic capacity and efficiency eventually resulted in a 37.5% increase of biomass under PHE stress. As primary response, transcripts of antioxidant genes were remarkably induced by EBR in PHE-treated plants. Activities of antioxidant and detoxification enzymes were also enhanced by EBR. Notably, EBR-induced higher antioxidant potential was associated with reduced levels of H2O2 and O2—, resulting in a 32.7% decrease of content of malondialdehyde in the end of experiment and relatively healthy chloroplast ultrastructure in EBR + PHE treatment compared with PHE alone. These results indicate that EBR alleviates shoot-imposed PHE phytotoxicity by maintaining a consistently higher photosynthetic capacity and antioxidant potential in tomato.

The properties of carbon nanotubes (CNTs) functionalized with –OH and –COOH groups during simulated water treatment with H2O2 and/or UV were tested. There following properties of CNTs were investigated: specific surface area, elemental composition (CHN), dynamic light scattering, Raman spectroscopy, X-ray photoelectron spectroscopy and changes in the CNTs structure were observed using transmission electron microscopy. Treatment of CNTs with H2O2 and/or UV affected their properties. This effect, however, was different depending on the functionalization of CNTs and also on the factor used (UV and/or H2O2). H2O2 plays a key role as a factor modifying the surface of CNT-OHs, whereas the properties of CNT-COOHs were most affected by UV rays. A shortening of the nanotubes, exfoliation, the opening of their ends, and changes in the surface charge were observed as a result of the action of UV and/or H2O2. The changes in observed parameters may influence the stability of the aqueous suspensions of CNTs.

Perfluorooctanoic acid (PFOA) is widely used in the manufacture of many industrial and household products. To assess the potential environmental risk of PFOA, its accumulation, translocation and phytotoxic effects were investigated using the model plant species Arabidopsis thaliana. Exposure to 18 μM PFOA-F in agar plates did not affect plant growth, but 181–1811 μM PFOA-F inhibited root and shoot growth. PFOA was more phytotoxic on shoot growth than NaF at the equivalent F concentration, with the latter having 3.9–7.6 times higher EC50 for shoot biomass than PFOA. PFOA was efficiently translocated from roots to shoots, where it existed as intact PFOA molecules without transformation evidenced by the 19F NMR spectra. PFOA caused a significant increase in the concentration of H2O2 and malondialdehyde (MDA) in shoots, indicating that oxidative stress is a likely cause of PFOA phytotoxicity.

This study proposes an improved activation for hydrogen peroxide and persulfate using Fe-modified diatomite (MD) to favorably lead the reaction to generate hydroxyl and sulfate radicals to degrade the contaminants phenanthrene and anthracene. Diatomite was modified by impregnating it with a mixture of ferrous (Fe²⁺) and ferric (Fe³⁺) ions in the form of precipitated iron oxides and hydroxides. The raw and synthesized materials were characterized by powder X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size by laser diffraction, chemical microanalysis of the elements by energy-dispersive X-ray, and scanning electron microscopy (SEM). Batch experiments were performed to compare the new activator material (modified diatomite) with traditional methods of activation for these oxidants and to statistically study the optimum ratio between the amount of this material and the concentration of one oxidant to the degradation of the contaminants phenanthrene and anthracene. The characterization results showed that the materials are amorphous and that the Fe ion concentration was 4.78 and 17.65 % for the raw and modified diatomites, respectively. This result shows a significant increase in the amount of iron ions after synthesis. Comparing the traditional activation method with the modified diatomite, the results of batch experiments showed that the synthesized material presents significant catalytic activity for the oxidation of these contaminants, using sodium persulfate and hydrogen peroxide as oxidants. The analysis of the variables results showed that the concentration of the oxidant has higher significance than the amount of the catalyst.

To treat PCP-contaminated soil, abiotic methods for PCP degradation have been developed, where heme or powder hemoglobin acts as a catalyst and hydrogen peroxide as an oxidant. Degradation of PCP had the first-order kinetics, and rate coefficients, k, were 0.073 and 0.104/day for heme and hemoglobin, respectively, indicating that the hemoglobin was a more efficient catalyst than heme. Approximately 96 % of the initial PCP was degraded at day 35. Thus, hemoglobin might be recommended as the catalyst of choice, since it is much less expensive than heme.

Solar Photo-Fenton reaction, using FeSO₄ and H₂O₂, is an effective and energy-efficient advanced oxidation process (AOP) for degradation of pesticides. However, a major environmental concern is whether the net toxicity after the photo-Fenton process is within the tolerance limit of the aquatic plants and animals, since the unreacted pesticide and Fenton’s reagent may impart additional toxicity to the treated water. Here, we report the oxidative removal of dichlorvos pesticide in wastewater by solar photo-Fenton reaction along with the residual toxicity analysis of the treated water on an aquatic alga. It was found that at pH 3, dichlorvos, with an initial concentration of 6.9 × 10⁻⁵ mol L⁻¹, was observed to be fully degraded within a batch time of 120 min, though the corresponding reduction of chemical oxygen demand (COD) was about 53 % signifying incomplete mineralisation. In order to predict the transient concentration profiles of dichlorvos under different initial concentrations, a four-parameter mathematical model was formulated. Additionally, the resultant toxicity was also examined using a model blue-green alga Nostoc sp. Compared to the raw wastewater, the net biomass of chlorophyll-a was found to increase significantly. Respective estimate of the protein concentration also indicated the same trend. Therefore, sunlight-assisted photo-Fenton process may be regarded as an effective and safe technique for the treatment of pesticide-contaminated agricultural wastewater.

Under various abiotic stresses, plants overproduce reactive oxygen species (ROS) such as superoxide anion (O₂•⁻), hydroxyl radical (OH•), and hydrogen peroxide (H₂O₂). When in excess, these highly reactive molecules cause oxidative stress, thus damaging proteins, lipids, and DNA. Therefore, plants evolved an enzymatic defense machinery that involves such enzymes as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APOX). Various plant families, species and even specimens differ in their ability to withstand the abiotic stress. A study has been undertaken to assess the differences in response to trace metals between two species: a resistant hyperaccumulator Indiana mustard (Brassica juncea) and a metal-sensitive pea (Pisum sativum). We observed that trace elements (Cu, Zn, Cd, Pb) changed the activity of antioxidative enzymes (SOD, APOX, CAT) and the rate of ROS generation. However, in the control plants and at a point 0′ of the treatment, we have noticed a large disproportion in the hydrogen peroxide level, with B. juncea maintaining naturally higher H₂O₂level (up to 40 times higher). We believe that this may be a distinguishing trait common to plants being resistant to oxidative stress.

Bioindicators are useful in monitoring air pollution. This study assessed the efficacy of various tree leaf morphological, physiological and biochemical biomarkers in reflecting different intensities of air pollution. Leaves from Brachylaena discolor trees growing 0, 2.5, 6 and 11 km from an industrial hub (pollution source) in eThekwini, South Africa, were analysed for leaf area, chlorophyll (Chl) content, superoxide and hydrogen peroxide (H₂O₂) production, electrolyte leakage, total antioxidant activity and concentration of selected minerals. B. discolor saplings grown under greenhouse conditions served as an ex situ control. Surface SO₂ and NOₓ levels which were measured at the in situ and control sites declined significantly with increasing distance from the source but were below detectable limits at the control site. At the site closest to the source, leaf area was significantly lower and Chl, electrolyte leakage, and copper (Cu) and phosphorous (P) levels were significantly higher than the control. Leaf area was significantly positively, and Chl content significantly negatively, correlated with distance from the source, while H₂O₂ production, electrolyte leakage and Cu and P concentrations were all significantly negatively correlated with distance from the source. The aforementioned parameters represent potential biomarkers of air pollution in B. discolor and in some cases (e.g., H₂O₂ and electrolyte leakage; leaf area and leaf Chl content) should be measured in conjunction with each other to accommodate for interactive effects. Using B. discolor leaves as bioindicators of air pollution may represent a more viable option for monitoring air pollution than monitoring stations.