Effect of artificial fertilizers and pesticide use on heavy metal concentration and health risk of selected medicinal plants from Nyamira County‑Kenya

Abstract

Medicinal plants play a significant role in treatment of both animal and human diseases especially in rural Africa. In Kenya, majority of rural population depends on the medicinal plants and their formulations for healthcare needs as they are cheaper, accessible and believed to be safer. However, recent studies have shown some of these medicinal plants contain high concentrations of elements and other pollutants above WHO permissible limits. In this study the levels of Lead (Pb), Cadmium (Cd), Chromium (Cr), Zinc (Zn), Copper (Cu), Manganese (Mn) and Iron (Fe), in soils and seven commonly used medicinal plants (MP) in the management of diabetes and anemia in Nyamira County-Kenya were determined using flame atomic absorption spectrophotometer. The levels were used to evaluate the health risk and the carcinogenic health risks associated with their consumption. The levels of the heavy metals (HM) ranged from Cd to Fe with 0.56 to 11,093.03 and 0.58 to 11,122.22 mg kg− 1 in soils from Ekerenyo and Borabu respectively. The amounts of the HM in MP were: Fe (31.12–338.84), Cu (3.32–13.32), Zn (5.36–88.49), Cr (0.14–2.21), Mn (9.64–25.90) Cd (not detected—Nd-0.26) and Pb (Nd-1.04) mg kg− 1 and the levels of the heavy metals between Ekerenyo and Borabu medicinal plants were not statistically significant (P < 0.05). Most medicinal plants had the estimated daily intake (EDI) values for most heavy metals of below recommended oral reference dosage (RfD) except for Mn that was slightly above acceptable limits and the non-carcinogenic health risks assessment, target hazard quotient (THQ) were less than one for most heavy metals, indicating that the MP were safe for consumption. The combined effect of all the heavy metals (HI) in each medicinal plant was greater than one indicating that the non-carcinogenic health effects may be caused as a result of prolonged usage. Carcinogenic assessment (TCR) revealed that for all the heavy metals in each medicinal plant were greater than the threshold limit and the consumption of the MP from the study areas should be consumed with caution. Keywords Medicinal plants (MP) · Heavy metals (HM) · Estimated daily intake (EDI) · Health risk assessment (HRA)