Plants are reservoir for potentially useful bioactive compounds, and owing to the rising occurrences of drug resistance to malaria parasites, there is a need to discover and develop new phytochemicals in plant that can be used as antimalarial agents. In this study, we gave a detailed description of the phytochemicals present in both ethyl acetate and methanolic extracts of Callistemon citrinus (C. citrinus) using Gas Chromatography-Mass Spectrometry (GC-MS) analysis; both extracts were also evaluated for their in vitro antimalarial, antitrypanosomal, and cytotoxicity activities against Trypanosoma brucei brucei (T. b brucei) parasites, Plasmodium falciparum (P. falciparum) malaria parasites 3D7 strain, and human cervix adenocarcinoma cells (HeLa cells); in addition, the antimicrobial and antioxidant efficacies were determined using standard methods. Both extracts were characterized by a high amount of fatty acids (52.88 and 62.48%). The ethyl acetate extract exhibited a greater activity with minimum inhibitory concentration (MIC) values ranging from 0.025 to 0.10 mg/mL while the methanol extract ranged from 0.025 to 0.15 mg/mL. Both extracts were bactericidal to Escherichia coli ATCC 35150 (E. coli) and Pseudomonas aeruginosa ACC (P. aeruginosa). Qualitative and quantitative phytochemical screenings conducted for both extracts revealed the presence of alkaloids, glycosides, saponins, steroids, and triterpenoids, fat and oils, flavonoids, phenols, and tannins in varying amounts. Both crude extracts exhibited antitrypanosomal potentials with an IC₅₀ of 6.6/9.7 μg/mL and antiplasmodial activities with an IC₅₀ of 8.4/13.0 μg/mL. Conclusion from this study indicates that apart from the folkloric uses of this plant in traditional settings, the extracts possess a broad spectrum of antimicrobial, antitrypanosomal, and antimalarial activities and some pharmaceutically essential bioactive components with remarkable antioxidant capacities that may be used in the synthesis of novel drugs for the management of different varieties of ailments.

In this study, we report on the biosynthesis of gold nanoparticles (AuNPs) by using Callistemon citrinus (C. citrinus) seed extract as both reducing and capping agent as well as its characterization. Likewise, the in vitro antiparasitic activities of both biosynthesized gold nanoparticles and crude seed extract of the plant were evaluated. The formation of biosynthesized AuNPs was confirmed by a color change immediately when the seed extract was added to the gold chloride (III) solution. Characterization of the AuNPs was done using analytical tools like ultraviolet–visible spectroscopy, X–ray diffraction, scanning electron microscopy (SEM), energy dispersive X–ray (EDX), transmission electron microscopy (TEM) and Fourier transformed infra–red (FTIR). FTIR showed an absorption peak at 230 nm consistent with the absorption band for gold nanoparticles, the morphology and composition of AuNPs was ascertained by SEM and EDX micrographs; uneven spherical-shaped nanoparticles was established by SEM analysis, and an average particle size of about 37 nm was confirmed by the TEM analysis. The crude seed extracts exhibited antitrypanosoma activities with an IC50 of 11.06 µg/mL. Both the crude seed extract and AuNPs were inactive against plasmodial parasite, while the antibacterial assay showed that AuNPs is potent against gram positive and gram negative bacterial strains. GRAPHICAL ABSTRACT

Volatile oil from aromatic plants has been used by ancient Egyptians in embalming for the inhibition of bacterial growth and prevention of decay, Callistemon citrinus is used in traditional therapies for the treatment of bronchitis, cough, inflammation and as an antimicrobial herbs. This study examines the essential constituents of the volatile oils obtained from the aerial parts of the plant as well as its antioxidant activity, free radical scavenging, phenolic content and the antibacterial potential of the oils. A portion of 500 g, 250 g and 150 g of the leaves, flowers and stems of this plant respectively were subjected to hydro-distillation process for three hours. The oils collected from the various plant parts were immediately subjected to GC-MS analysis. The overall phenolic content of the leaves oil, radical scavenging, antibacterial action and antioxidant activities of the essential oils of both the leaves and flowers of Callistemon citrinus were determined using standard methods, with free radical DPPH and ABTS as a reference antioxidant. Analyses of the three oils revealed a total of twenty-six components for the leaves oil representing 96.84% of the total oil composition, forty-one components for the flowers oil accounting for 98.92% of the whole composition and ten components for the stem oil amounting to 99.98% of the entire oil constituents. The dominant compounds in the leaves oil were eucalyptol (48.98%) and α-terpineol (8.01%), while α-eudesmol (12.93%), caryophyllene (11.89%), (−)-bornyl-acetate (10.02%) and eucalyptol (8.11%) were the main constituents of the flowers oil. In the same vein, the leading constituents in the stems oil were eucalyptol (56.00%) and α-pinene (31.03%). The antioxidant capacities of both the leaves and flowers oils of the plant were evaluated and their IC50 were (1.49 and 1.13) for DPPH and (0.14 and 0.03) for ABTS assay respectively. The antibacterial activities of the oils from the (leaves and flowers) were also examined and were found to have wide range of activities against the bacterial strains used in this study. Observations drawn from this experiment shows clearly that the leaves and flowers of Callistemon citrinus possess phenolic compounds and cyclic ether of several pharmacological behaviors.

Emerging contaminants (ECs), encompass both natural and synthetic chemicals that are present or transformed to new chemical compounds in water bodies across the globe. They are presently not checked in the environment but poses a serious health threat to human and ecosystem as well as environmental damage. ECs are released into environment during the anthropogenic activities such as water treatments, fumigation, farming etc. More than 1036 ECs and their biotransformation have been identified by the NORMAN project, established in 2005 by the European Commission. They were further classified into different categorizes/classes including disinfection by-products, pesticides, pharmaceuticals and personal care products, nanomaterials, benzotriazoles, benzothiazoles among others. The potential sources, path route and their health implication on human were also discussed. The presence of ECs in our environments is global issue that requires urgent attention.