Trace metal concentration in selected medicinal plants in Abraka and Olomoro communities in Delta State, Nigeria

Abstract

The increasing interest in the therapeutic benefits of medicinal products has led to increased concern over the safety and toxicity of medicinal plants. Niger delta is the hotspot of oil exploration activities in Nigeria; this has caused different forms of pollution. Heavy metals like Iron (Fe), Maganese (Mn), Zinc (Zn), Chromium (Cr), Copper (Cu) and Lead (Pb) were analysed in four selected medicinal plants (Ocinum gratissimum, Vernonia amygdalina, Spinacia oleracea and Citrus aurantifolia) using Atomic Absorption Spectrophotometer (AAS). The results showed that the levels of metals were in the range of 7.33-8.37 mg/kg for Fe, 0.09-0.10 mg/kg for Pb, 0.18-0.36 mg/kg for Mn, 0.12-0.14 mg/kg for Zn, 0.01-0.12 mg/kg for Cu and below detectable limit ( – 0.02 mg /kg) for Cr. This shows that most of the metal concentration levels in the herbs were within the WHO maximum permissible limits of 15 mg/kg for Fe, 100 mg/kg for Zn, 10 mg/kg for Cu and Pb and 2 mg/kg for Mn. Heavy metal contents differed in the same medicinal plant collected from different sites. Vernonia amygdalina (from Abraka) had the highest concentration (8.37 mg/kg) of Fe while Ocimum gratissimum from Olomoro had the least concentration (7.30 mg/kg) of Fe. The highest content of Mn (0.36 mg/kg) was observed in Ocimum gratissimum from Olomoro while the least (0.18 mg/kg) was observed in Citrus aurantifolia. Chromium was below detectable limit in all the samples from Abraka while the highest concentration (0.02 mg/kg) was observed in Spinacia oleracea from Olomoro. The level of heavy metal concentration differed in the same medicinal plant collected from different sites, indicating the consequences of oil-related activities and other anthropogenic sources. Pharmaco-vigillance of medicinal products and further studies to determine long-term cumulative risks on consumers’ health is hereby recommended.