The present work reports microwave-assisted synthesis of SnO₂ nanoparticles via green route using Psidium Guajava extract. For the enhancement of catalytic activity, nanohybrids of SnO₂ were formulated using different ratios of polyaniline (PANI) via ultrasound-assisted chemical polymerization. Formation of nanohybrids was confirmed via IR and XPS studies. The UV–vis DRS spectra of PANI/SnO₂ revealed significant reduction in the optical band gap upon nanohybrid formation. Microwave-assisted catalytic efficiency of pure SnO₂, PANI, PANI/SnO₂ nanohybrids was investigated using DDT as a model persistent organic pollutant. The degradation efficiency of PANI/SnO₂ was found to increase with the increase in the loading of PANI. Around 87% of DDT degradation was achieved within a very short period of 12 min under microwave irradiation using PANI/SnO₂-50/50 as catalyst. The effect of DDT concentration was explored and the degradation efficiency of PANI/SnO₂-50/50 catalyst was noticed to be as high as 82% in presence of 100 mg/L of DDT. The effect of microwave power on the degradation efficiency revealed 79% degradation using the same nanohybrid when exposed to microwave irradiation for 5 min under 1110 W microwave power. Scavenging studies confirmed the generation of OH, O₂⁻ radicals. The fragments with m/z values as low as 86 and 70 were confirmed by LCMS analysis. Recyclability tests showed that PANI/SnO₂-50/50 nanohybrid exhibited 81% degradation of DDT (500 mg/L) even after the third cycle, which reflected high catalytic efficiency as well as remarkable stability of the catalyst. This green nanohybrid could therefore be effectively utilized for the rapid degradation of persistent organic pollutants.

Seedlings of Psidium guajava cv. Pedro Sato were distributed into four open-top chambers: two with ambient CO2 (∼390 ppm) and two with elevated CO2 (∼780 ppm). Monthly, five individuals of each chamber were collected, separated into root, stem and leaves and immediately frozen in liquid nitrogen. Chemical parameters were analyzed to investigate how guava invests the surplus carbon. For all classes of phenolic compounds analyzed only tannins showed significant increase in plants at elevated CO2 after 90 days. There was no significant difference in dry biomass, but the leaves showed high accumulation of starch under elevated CO2. Results suggest that elevated CO2 seems to be favorable to seedlings of P. guajava, due to accumulation of starch and tannins, the latter being an important anti-herbivore substance.

We aimed to verify whether hydrogen peroxide (H₂O₂) accumulation and cell death are detected early in three bioindicators of ozone (O₃), Nicotiana tabacum ‘Bel-W3’, Ipomoea nil ‘Scarlet O’Hara’ and Psidium guajava ‘Paluma’, and whether environmental factors also affect those microscopic markers. The three species were exposed to chronic levels of O₃ in a subtropical area and a histo-cytochemical technique that combines 3,3′-diaminobenzidine (DAB) with Evans blue staining was used in the assessments. The three species accumulated H₂O₂, but a positive correlation with O₃ concentration was only observed in N. tabacum. A positive correlation between O₃ and cellular death was also observed in N. tabacum. In I. nil and P. guajava, environmental factors were responsible for symptoms at the microscopic level, especially in P. guajava. We conclude that the most appropriate and least appropriate bioindicator plant for O₃ monitoring in the subtropics are N. tabacum ‘Bel-W3’ and P. guajava ‘Paluma’, respectively.

Psidium guajava 'Paluma' saplings were exposed to carbon filtered air (CF), ambient non-filtered air (NF), and ambient non-filtered air + 40 ppb ozone (NF + O3) 8 h per day during two months. The AOT40 values at the end of the experiment were 48, 910 and 12 895 ppb h-1, respectively for the three treatments. After 5 days of exposure (AOT40 = 1497 ppb h-1), interveinal red stippling appeared in plants in the NF + O3 chamber. In the NF chamber, symptoms were observed only after 40 days of exposure (AOT40 = 880 ppb h-1). After 60 days, injured leaves per plant corresponded to 86% in NF + O3 and 25% in the NF treatment, and the average leaf area injured was 45% in NF + O3 and 5% in the NF treatment. The extent of leaf area injured (leaf injury index) was explained mainly by the accumulated exposure of ozone (r2 = 0.91; p < 0.05). Psidium guajava 'Paluma', a tropical species widely used in Brazilian food industry, is a potential sensitive bio-indicator of ozone.

The study was conducted to investigate the presence of antibiotic resistant bacteria in guava, sold in the local markets of Patna. A total of twenty five fresh samples of guava were collected from five different market places in Patna city. Several microbiological tests were performed to assess the growth and type of bacteria. The colonies were isolated and identified as isolate 1 and 3 (identical to Staphylococcus spp.), isolate 2 (identical to Escherichia spp.) and isolate 4 and 5 (identical to Bacillus spp.) based on their cultural, morphological, Gram’s staining and biochemical characteristics. Antibiotic susceptibility tests were conducted to detect their actual resistance capability. In the present study, S1 and S3 were found resistant to ampicillin, chloramphenicol, ofloxacin and intermediate to gentamycin while S2 was found resistant to ampicillin, chloramphenicol, gentamycin, ciprofloxacin, cephalexin and intermediate to ofloxacin. The isolates S4 and S5 were found sensitive to gentamycin, intermediate to chloramphenicol and resistant to ciprofloxacin. Results of this study showed that the guava samples obtained from different markets of Patna possess multidrug resistant bacteria.

Solid wastes generated from industrial sponge iron plants (ISP) are categorized as hazardous waste due to their extremely fine, loose texture, toxic metal concentrations, and being wind borne in summer; their unscientific disposal leads to severe land degradation and environmental pollution. In the present study, phytorestoration of such a hazardous waste dump in central India was carried out through blanketing with forest soil (substratum for vegetation growth) followed by plantation with Psidium guajava (L.) saplings (2500 saplings/ha). The present study aimed to assess the efficiency of fruit orchards in restoring the soil health of waste dumps (WD) without causing any health hazards, allowing the possibility for an economically viable after use of the degraded land. Heavy metal concentration (Mn, Zn, Cu, Cr, Ni) in blanketed topsoil, plant tissues (roots, leaves, fruits), and its associated risk due to consumption of guava fruits were analysed. Soil health with reference to organic carbon (1.7%), total nitrogen (1727.7 mg kg⁻¹), and exchangeable potassium (162.3 mg kg⁻¹) at the 7-year-old restored site was significantly higher than that of the initial stage of revegetation. No probables of health risk was found due to consumption of guava fruit (growing on WD) as the target hazard quotient (THQ) of all the metals in fruit was <1. Restoration cost analysis of the present study showed that only 5% of total costs were responsible for the development of fruit orchards. Therefore, the study concluded that fruit orchards could be a sustainable alternative for phytorestoration of WD, which will also provide socio-economic return to stakeholders.

Guava leaves (Psidium guajava, GL), a high-phenolic- and flavonoid-containing plant resource capable of substituting the high-quality forage, may help in mitigating ruminal methane (CH₄) emission without adverse impact on nutrient degradability if supplemented at an appropriate level. In order to test this hypothesis, rumen fermentation, CH₄ production, and nutrient degradability of GL either solely or as a substitute of berseem hay (Trifolium alexandrinum, BH) were evaluated in a diet containing 50:50 concentrate to roughage. Five different levels of GL (0, 12.5, 25, 37.5, and 50%) were tested in vitro after 24 h incubation using a semi-automated gas production (GP) system. The current findings indicated that merely the presence of GL resulted in significantly lower values for cumulative GP (P < 0.001), CH₄ emission (P < 0.05), truly degraded dry matter (TDDM; P < 0.001), truly degraded organic matter (TDOM; P < 0.001), and ammonia nitrogen (NH₃-N) concentration (P < 0.001); however, pH (P < 0.001) and partitioning factor (P < 0.001) were higher. The total and individual volatile fatty acid (VFA) concentrations were drastically declined with GL as compared to BH (P < 0.05). A negative linear correlation was recorded between the levels of GL and GP including CH₄ production (P < 0.05). The addition of GL up to 25% did not pose any negative effect on both TDDM and TDOM values along with NH₃-N concentration. In addition, the inclusion of GL up to 25% did not affect the total or individual VFA concentration. Conclusively, in a medium concentrate diet, use of 25% GL and 25% BH in animal diet could be a promising alternative for mitigating the CH₄ production without any deleterious effect on nutrient degradability.

Phytotoxic ozone (O₃) levels have been recorded in the Metropolitan Region of São Paulo (MRSP). Flux-based critical levels for O₃ through stomata have been adopted for some northern hemisphere species, showing better accuracy than with accumulated ozone exposure above a threshold of 40 ppb (AOT40). In Brazil, critical levels for vegetation protection against O₃ adverse effects do not exist. The study aimed to investigate the applicability of O₃ deposition model (Deposition of Ozone for Stomatal Exchange (DO₃SE)) to an O₃-sensitive tropical tree species (Psidium guajava L. ‘Paluma’) under the MRSP environmental conditions, which are very unstable, and to assess the performance of O₃ flux and AOT40 in relation to O₃-induced leaf injuries. Stomatal conductance (g ₛ) parameterization for ‘Paluma’ was carried out and used to calculate different rate thresholds (from 0 to 5 nmol O₃ m⁻² projected leaf area (PLA) s⁻¹) for the phytotoxic ozone dose (POD). The model performance was assessed through the relationship between the measured and modeled g ₛₜₒ. Leaf injuries were analyzed and associated with POD and AOT40. The model performance was satisfactory and significant (R ² = 0.56; P < 0.0001; root-mean-square error (RMSE) = 116). As already expected, high AOT40 values did not result in high POD values. Although high POD values do not always account for more injuries, POD₀ showed better performance than did AOT40 and other different rate thresholds for POD. Further investigation is necessary to improve our model and also to check if there is a critical level of ozone in which leaf injuries arise. The conclusion is that the DO₃SE model for ‘Paluma’ is applicable in the MRSP as well as in temperate regions and may contribute to future directives.