Phytochemical composition and health risk assessment of heavy metals in herbal remedies from semi-arid Nigeria

Herbal remedies are widely utilized as alternative medicine, especially in Nigeria’s semi-arid regions where medicinal plants are abundant. The study evaluated the phytochemical composition and heavy metal content of Cadmium (Cd), Cobalt (Co), Nickel (Ni), Lead (Pb), and Zinc ( Zn) in five herbal remedies sold in Dutse, Jigawa State. Ethanolic extracts were prepared using Soxhlet extraction, and phytochemicals were identified through standard analytical procedures. For elemental analysis, samples underwent wet digestion with HNO₃ and HCl, followed by quantification using atomic absorption spectrophotometry, a reliable technique for elemental analysis. Quality control measures such as instrument calibration, blank and standard sample analysis, and triplicate analysis were employed to ensure accuracy and precision. Health risk assessments—including estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI), and target cancer risk (TCR)—were conducted for both adults and children. Phytochemical screening revealed the presence of phenols, terpenoids, and saponins in all samples; steroids and alkaloids in 80%; and tannins and flavonoids in 40%. Heavy metal analysis indicated that lead (1.086–1.636 mg/kg) and cobalt (0.630–0.740 mg/kg) concentrations exceeded the WHO permissible limits of 1.0 mg/kg and 0.043 mg/kg, respectively. Cadmium (0.088–0.110 mg/kg), nickel (0.662–0.942 mg/kg), and zinc (0.686–5.086 mg/kg) levels were within acceptable limits. Statistical analysis revealed significant differences in Cd, Co, Ni, and Zn concentrations among the samples (p < 0.05), with no significant variation in Pb levels (p = 0.338). Post hoc Tukey’s HSD test identified HR-4 and HR-5 as having notably higher levels of Cd, Co, and Ni, while HR-5 exhibited an exceptionally high Zn concentration (5.086 mg/kg). The use of reliable analytical methods like atomic absorption spectrophotometry ensures accurate quantification of heavy metals, underscoring the urgent need for stringent quality control and regulatory frameworks to ensure the safety and efficacy of herbal formulations.