Levels and Cytogenotoxicity of Phytochemicals and Heavy Metals in Guava (Psidium guajava L.) Leaves Obtained From Birnin Kebbi, Nigeria

Background: Psidium guajava (guava tree) is widely used in Nigeria to treat diseases. However, a paucity of information exists on the safety of the plant. Objectives: This study determined the safety of P. guajava leaves collected in Birnin Kebbi, Nigeria. Methods: The methanolic extract of the plant’s leaves was subjected to phytochemical and heavy metal screening using standard protocols, and thereafter, subjected to a cytogenetoxicity test using the Allium cepa toxicity assay. Twenty-one A. cepa bulbs divided equally into seven groups were grown over beakers containing distilled water (negative control), formaldehyde (positive control), as well as 0.25, 0.5, 1, 2, and 4 g of the extract, respectively, for five days. The root-tip cells of the A. cepa bulbs were treated and then examined for chromosomal aberrations. Results: The phytochemical screening revealed high levels of saponins, and moderate levels of phenols, tannins, and flavonoids, while quinones and terpenoids were sparingly available. The heavy metal analysis showed non-permissible levels of cadmium and zinc, while two other tested heavy metals (lead and copper) were undetected. Except for the A. cepa treated with 0.25 and 0.5 g, the extract induced dose-dependent root growth and mitotic index inhibition (P<0.05). The extract also induced cytogenetic effects, mainly sticky, vagrant, and fragmented chromosomes as well as anaphase bridges. Conclusions: It can be inferred from the results that low to medium doses of the extract are safe but may elicit harmful effects at high doses. Advice from a phytomedicine or phytotherapy expert should be sought before using it.