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.

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.

This paper evaluates the biosorption of toxic metal ions onto the bioadsorbents derived from mango (Mangifera indica) and guava (Psidium guiag) barks and their metal fixation mechanisms. Maximum metal biosorption capacities of the mango bioadsorbent were found in the following increasing order (mg/g): Hg (16.24) < Cu (22.24) < Cd (25.86) < Pb (60.85). Maximum metal biosorption capacities of guava bioadsorbent follow similar order (mg/g): Hg (21.48) < Cu (30.36) < Cd (32.54) < Pb (70.25), but with slightly higher adsorption capacities. The removal mechanisms of heavy metals using bioadsorbents have been ascertained by studying their surface properties and functional groups using various spectrometric, spectroscopic, and microscopic methods. Whewellite (C₂CaO₄·H₂O) has been identified in bioadsorbents based on the characterization of their surface properties using X-ray techniques (XPS and XRD), facilitating the ion exchange of metal ions with Ca²⁺ bonded with carboxylate moieties. For both the bioadsorbents, the Pb²⁺, Cu²⁺, and Cd²⁺ are biosorbed completely by ion exchange with Ca²⁺ (89–94%) and Mg²⁺ (7–12%), whereas Hg²⁺ is biosorbed partially (57–66%) by ion exchange with Ca²⁺ (38–42%) and Mg²⁺ (19–24%) due to involvement of other cations in the ion exchange processes. Bioadsorbents contain lignin which act as electron donor and reduced Cr(VI) into Cr(III) (29.87 and 37.25 mg/g) in acidic medium. Anionic Cr(VI) was not adsorbed onto bioadsorbents at higher pH due to their electrostatic repulsion with negatively charged carboxylic functional groups.

In Aguascalientes, Mexico, there is a special concern about pesticides because of their intensive use on guava production areas, which are located in the vicinity of water reservoirs; thus, non-target organisms could be exposed. Thereafter, the aim of this work was to assess the effect of cypermethrin, Faena® (glyphosate), and malathion, which are the most used pesticides in Aguascalientes’ guava production, on the indigenous freshwater species Alona guttata (cladoceran) and Lecane papuana (rotifer). Acute 48-h toxicity tests were carried out, and LC₅₀ values were calculated. Then, five sublethal concentrations (1/80, 1/40, 1/20, 1/10, and 1/5 of the respective LC₅₀) were selected for the chronic assays: (a) intrinsic growth rate analysis in the rotifer and (b) partial life table analysis in the cladoceran. The results of the acute toxicity tests showed that A. guttata was more sensitive to malathion (LC₅₀ = 5.26 × 10⁻³ mg/L) at concentrations found in natural environments with continuous application on guava fields, whereas L. papuana was more sensitive to Faena® (LC₅₀ = 19.89 mg/L). The somatic growth of A. guttata was inhibited for the chronic exposure to cypermethrin. In addition, cypermethrin and Faena® seemed to exert endocrine disruptive effects on A. guttata. Moreover, malathion chronic exposure significantly decreased the survival of A. guttata. Moreover, L. papuana was affected chronically for the three pesticides.

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.

The phenol removal by adsorption through the guava tree bark has been studied in this research. The surface characterizations of the guava tree bark were assessed through BET, FTIR, and SEM apparatus. The phenol removal percentage was investigated in batch experiments taking phenol content (30–150 mg/L), time (30–180 min), pH (4–9), adsorbent dose (1–6 g/L), and temperature (30–50 °C). The maximum percentage of phenol removal was obtained at 90.67% at the phenol concentration of 30 mg/L, the contact time of 120 min, pH of 7, adsorbent dose of 4 g/L, and temperature of 50 °C. The kinetic study indicated that the second-order was superior to the first order. The isotherm study exhibited that the Freundlich isotherm fitted best among the Langmuir, D-R (Dubinin-Radushkevich), and Temkin isotherms. The value of adsorption energy evaluated by the D-R isotherm supported physical adsorption; however, the mechanism seemed to be weaker since the correlation coefficient of the D-R model was found to be quite less than the correlation coefficients of other isotherm models. The adsorption mechanisms through film diffusion and chemisorption were well established as tested by the Reichenberg model, the Elovich model, the Fick model, the Furusawa and Smith model, and the Boyd model. The adsorption thermodynamics concluded that the adsorption method supported endothermic, random, and spontaneous. The scale-up design, the procedure for safe disposal of spent adsorbent, and the regeneration of the adsorbent were deliberated in this research. The research determined that the guava tree bark is suitable for the removal of phenol from wastewater.

Three carbon samples were employed in this work, including commercial (1690 m² g⁻¹), activated carbon prepared from guava seeds (637 m² g⁻¹), and activated carbon prepared from avocado kernel (1068 m² g⁻¹), to study the adsorption of the following gadolinium-based contrast agents (GBCAs): gadoterate meglumine Dotarem®, gadopentetate dimeglumine Magnevist®, and gadoxetate disodium Primovist®. The activation conditions with H₃PO₄ were optimized using a Taguchi methodology to obtain mesoporous materials. The best removal efficiency by square meter in a batch system in aqueous solution and model urine was achieved by avocado kernel carbon, in which mesoporosity prevails over microporosity. The kinetic adsorption curves were described by a pseudo-second-order equation, and the adsorption isotherms in the concentration range 0.5–6 mM fit the Freundlich equation. The chemical characterization of the surfaces shows that materials with a greater amount of phenolic functional groups adsorb the GBCA better. Adsorption strongly depends on the pH due to the combination of the following factors: contrast agent protonated forms and carbon surface charge. The tested carbon samples were able to adsorb 70–90% of GBCA in aqueous solution and less in model urine. This research proposes a method for the elimination of GBCA from patient urine before its discharge into wastewater.

Environmental considerations require disposal of the contaminants in a safe manner without causing any harm. Accordingly, the contaminants should be removed and recovered as value or disposed without any burden to the environment. In this context, natural biodegradable adsorbents could possibly be an answer as they get biodegraded along with the organic contaminants including phenol. Having observed from literature that the natural guava leaf powder (NGLP) can be used as an adsorbent, experimental studies were carried out to investigate the potential of NGLP to remove phenol from aqueous solutions. Batch experiments were carried out using NGLP and the effect of different variables such as pH, NGLP dosage, contact time and agitation speed was studied using response surface methodology (RSM) with Box–Behnken approach and the significant parameters were optimized by subsequent experimentation. The optimized parameters obtained in our studies correspond to pH 5.85 for a NGLP dosage of 2.15 g/L, at an agitation speed of 140 rpm and a contact time of 9 h for the initial phenol concentrations ranging from 50 to 250 mg/L. The absorption of phenol onto NGLP was confirmed using FTIR and SEM-EDX. Thermodynamic, kinetic and equilibrium isotherm studies were conducted using the optimal parameters. The adsorption data fitted well with Langmuir isotherm (R²= 0.9982) for the batch equilibrium studies and the pseudo-second-order type model (R²= 0.9743–0.9921) depicted the phenol adsorption kinetics. The maximum adsorption capacity of NGLP for phenol was 10.85 mg/g. The results inferred the feasibility of using NGLP as a phenol adsorbent and Box–Behnken design as an effective tool for the optimization of process conditions. Even though the studies are not intended to reuse the adsorbent in view of abundance and biodegradability, the preliminary experiments have indicated the possible potential of desorption and reusability.

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.

Food safety is a major concern worldwide and human beings are frequently exposed to potentially toxic metals (PTMs) through consumption of vegetables, fruits, and cereal crops grown in contaminated areas. The present study investigates the concentrations of PTMs such as chromium (Cr), nickel (Ni), zinc (Zn), arsenic (As), cadmium (Cd), and lead (Pb) in the foodstuffs (fruits, vegetables, and cereals) collected from different markets of Khyber Pakhtunkhwa, Pakistan. Samples of fruits (banana, tangerine, apple, and guava), vegetables (tomato, onion, potato, pea, and lady finger), and cereals (rice, kidney beans, and chick peas) were acid-extracted and analyzed using ICP-MS. The concentrations of Cr, Zn, Pb, As, and Cd in fruits (54, 50, 50, 45, and 4% samples, respectively), vegetables (53, 43, 63, 80, and 46%), and cereals (37, 62, 25, 70, and 25%) exceeded their respective permissible limits set by FAO/WHO (2001). The results showed that the highest mean concentration was observed for Ni (14.95 mg/kg), Pb (0.57 mg/kg), and Cd (0.27 mg/kg) in vegetables followed by fruits and cereals. However, the highest mean concentration of As (0.44 mg/kg) was observed in cereal crops followed by vegetables and fruits. The individual health risk of PTMs via consumption of fruits, vegetables, and cereals were found within safe limits for adults and children. Nevertheless, the total HRI values (fruits + vegetables + cereals) for Ni, As, and Cd for both adults and children were observed > 1 and may posed potential risk for the community consuming these foodstuffs on a daily basis. Graphical abstract ᅟ