Heavy Metal Contamination and Associated Human Health Risks of Commercial Herbal Bitters Marketed in Port Harcourt, Nigeria

Abstract

Background: The increasing consumption of commercial herbal bitters raises concerns about potential heavy-metal contamination and associated health risks. This study determined the concentrations of lead (Pb), arsenic (As), chromium (Cr), cadmium (Cd), nickel (Ni), copper (Cu), and zinc (Zn) in commercially marketed herbal bitters in Port Harcourt, Nigeria, and evaluated their potential non-carcinogenic and carcinogenic health risks. Methods: A laboratory-based cross-sectional study was conducted on 15 herbal-bitter products purchased from two herbal-medicine outlets in Obio/Akpor, Rivers State, Nigeria, in December 2019. Heavy-metal concentrations were determined using atomic absorption spectrophotometry following acid digestion. Measured concentrations were compared descriptively with selected World Health Organization (WHO) and United States Environmental Protection Agency (USEPA) reference values used as screening benchmarks. Potential health risks were assessed using estimated daily intake (EDI), chronic daily intake (CDI), hazard quotient (HQ), hazard index (HI), and incremental lifetime cancer risk (ILCR). Results: Heavy-metal concentrations varied considerably among the investigated products. Total chromium recorded particularly elevated concentrations in Supa Akwara (7.0125 mg/L), Cleanser (2.349 mg/L), and Ozor (2.03695 mg/L). All calculated individual HQ and cumulative HI values were below the conventional threshold of 1, suggesting low estimated non-carcinogenic risks under the exposure assumptions applied. However, several products recorded modelled ILCR values exceeding the adopted reference level of 1 × 10⁻⁴, indicating potential carcinogenic concerns requiring further evaluation. These estimates should be interpreted cautiously because their reliability depends on the exposure assumptions, toxicological parameters, and chemical forms of the metals, particularly chromium. Conclusion: Commercial herbal bitters marketed in Port Harcourt exhibited substantial variation in heavy-metal concentrations, with elevated total chromium levels in selected products. Although estimated non-carcinogenic risks remained below the adopted benchmark, some modelled carcinogenic-risk estimates warrant further investigation. Routine quality surveillance, improved manufacturing controls, and chemical speciation of chromium are recommended to strengthen consumer safety assessments.