Determination of Trace Metals in Medicinal Herbs Sold at Herbalists Markets in Ogun State, South West Nigeria

Traditional herbal medicine remains prevalent across South West Nigeria, with markets serving as primary distribution points for a wide variety of plant-based remedies whose heavy metal safety profiles are rarely assessed by regulatory authorities. This study determines the concentrations of lead, cadmium, arsenic, mercury, and chromium in fifteen commonly sold medicinal herb samples purchased from three major herbalists markets in Ogun State. Samples are prepared by dry ashing and dissolved in dilute nitric acid for analysis by atomic absorption spectrophotometry. Results are compared against World Health Organization guidelines for permissible heavy metal levels in herbal medicinal products. The study also investigates potential contamination sources by interviewing herbalists about collection sites, drying methods, and storage practices. Statistical correlations between metal concentrations and collection environment are examined using Spearman rank correlation. Results are expected to identify lead and cadmium as the metals most frequently exceeding permissible limits, particularly in herbs collected near mining sites, roadsides, and industrial zones. The study highlights significant consumer safety risks and underscores the urgent need for standardised quality control, post-market surveillance, and good manufacturing practices within the traditional medicine sector. Findings contribute to evidence-based regulation of herbal medicines in the South West zone. Keywords: trace metals, medicinal herbs, heavy metal contamination, Ogun State, herbal medicine safety