Effects of Copper Toxicity on the Phytochemical Composition and Antimicrobial Activity of Methanolic Extracts of Euphorbia hirta (Asthma Weed)

Abstract

Heavy metal contamination poses increasing risks to plant metabolic processes and the therapeutic value of medicinal species. Hence, the objective of this paper was to evaluate the effects of copper toxicity on the phytochemical composition and antimicrobial activity of methanolic extracts of Euphorbia hirta (Asthma weed) using appropriate standard methods of growing seedlings in tap water (control), 100 mM/L and 151 mM/L CuSO₄·5H₂O solutions. Qualitative phytochemical screening using standard protocols revealed the presence of saponins, tannins, flavonoids, glycosides, alkaloids, steroids, and phenols across all treatments, while tannins and phenols compounds show the greatest increase under high copper exposure. Terpenoids and anthraquinones were absent in all samples. Antimicrobial activity was assayed against Salmonella typhi, Staphylococcus aureus, Escherichia coli, and Candida albicans using the agar well diffusion method. Extracts from control plants produced the highest inhibition zones (13.67–21.00 mm), followed by low-copper plants (5.67–9.33 mm), while extracts from high-copper plants exhibited no antimicrobial activity. The results indicate that copper exposure increases certain phytochemicals but significantly reduces antimicrobial potential. The findings highlight the relationship between secondary metabolite accumulation and antimicrobial efficacy under heavy metal stress in E. hirta.