Evaluation of the Neutron Activation Analysis Method for Trace Element Determination in Nigerian Herbal Medicines

Herbal medicines are consumed by a large fraction of the Nigerian population, yet their trace element content, including potentially toxic heavy metals introduced through soil contamination, processing, or adulteration, is inadequately monitored. Neutron activation analysis provides highly accurate multi-element determination with minimal sample preparation and freedom from reagent blank contamination. This study evaluates the neutron activation analysis method for trace element determination in 30 commercial herbal medicine samples widely sold in Ogun State, including powdered bark, leaf, and root preparations. Samples are irradiated in the NIRR-1 research reactor at Ahmadu Bello University, Zaria, and gamma spectra are measured after appropriate cooling periods using a calibrated HPGe detector. Thirty-one elements including Fe, Zn, Cu, Mn, As, Cr, Sb, and Hg are quantified. Results indicate elevated arsenic concentrations of 1.8 to 12.4 mg per kilogram in four samples, exceeding the WHO limit of 1.0 mg per kilogram for herbal medicines. Mercury is detected in two samples at concentrations suggesting deliberate addition. The study calls for mandatory trace element screening of herbal medicines by NAFDAC using validated nuclear analytical methods. Keywords: neutron activation analysis, herbal medicine, trace elements, Nigeria, NIRR-1