Assessment of Natural Radioactivity and Heavy Metal Accumulation in Selected Edible Fruit Nuts from Lagos and Ogun State Markets, Nigeria

Abstract

Edible fruit nuts are highly valuable to humans for nutritional, economic, medicinal, and environmental reasons, hence are in high demand in our local markets. This study assesses the levels of naturally occurring radionuclides and heavy metals in six commonly consumed edible fruit nuts—peanuts, cashew nuts, walnuts, date nuts, tiger nuts, and kola nuts—sourced from major markets in Lagos and Ogun States, southwestern Nigeria. The analysis aimed to determine the potential radiological and toxicological health risks associated with their consumption. Gamma-ray spectrometry was employed to evaluate the activity concentrations of radionuclides (⁴⁰K, ²²⁶Ra, and ²³²Th), while heavy metal content, including lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), cobalt (Co), copper (Cu), zinc (Zn), arsenic (As), and mercury (Hg), was determined using atomic absorpti on spectrometry. Results revealed that the activity concentration of ⁴⁰K in all samples exceeded the UNSCEAR (2000) threshold of 412 Bq/kg, while ²²⁶Ra and ²³²Th remained below permissible limits. The internal hazard index, radium equivalent, absorbed dose rate, and annual effective dose values were also below internationally recommended levels, suggesting no immediate radiological health risks. For heavy metals, Ni and Cr showed relatively higher concentrations, especially in tiger nuts and kola nuts, though still within acceptable limits. Essential elements like Zn and Cu were present in moderate amounts, indicating nutritional value alongside trace-level contamination. Despite the safety of these nuts for human consumption, the presence of environmentally toxic metals such as Ni and Cr underscores the need for continuous monitoring. The study concludes that while current contamination levels pose no significant health risk, proactive regulation and periodic food safety evaluations are essential to safeguard public health.