Analysis of Selected Toxic Heavy Metals and Pesticide Residues in Catha Edulis from Selected Regions in Meru County, Kenya

Abstract

Heavy metal and pesticide pollutions on environmental matrices and their potential human toxicity have attracted considerable attention worldwide in recent years. The desire to increase food production to satisfy the ever rising population has resulted in the use of potentially toxic pesticides and fertilisers. The application of these chemicals in modern farming technologies is a source for potentially toxic heavy metals and pesticide residue levels in human consumables such as foodstuffs, which may ultimately trigger adverse health effects. Accordingly, this study focused on the concentration profiles of cadmium (Cd), lead (Pb), chromium (Cr), iron (Fe), nickel (Ni), and copper (Cu) and pesticide residues in 11 khat (Catha edulis) samples randomly sourced from 11 farms within regions of Meru County, Kenya. These analyses are meant to evaluate any associated human health risks through comparison with the World Health Organisation/ Food and Agriculture Organisation (WHO/FAO) safe limits. Human health risk assessment was done using target hazard quotient (THQ) and health index (HI). Inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis gave results of heavy metal concentrations (mg/kg) in dry khat samples as follows; Cd (7.81 ± 1.56), Cr (15.98 ± 2.22) and Pb (32.35 ± 9.95), indicating all was above the acceptable WHO/FAO limits. The levels of Ni, Cu and Fe heavy metals were below permissible limits and may benefit important human biological functions. The Pb and Cd THQ values and the HI of all investigated heavy metals in the khat samples exceeded the threshold value of 1.0. This suggests that the excessive consumption of Meru khat-based products, poses a potential health risk to the consumers. Besides, the gas chromatograph-mass spectrometry (GC-MS) results showed the detection and identification of pyrethroid and organophosphate pesticides representing 54.5% pesticide contamination prevalence rate of the sample size. The Ultraviolet-Visible (UV-Vis) quantification results revealed that acephate and cypermethrin residue levels in khat samples were below maximum residue limits (MRLs) thus, there is no acephate and cypermethrin pesticide contamination reported from this study. Consequently, Meru khat farmers should regularly be educated on safe post-harvest practices to protect consumers. Therefore, the results of this work are important in sensitizing khat farmers that the use of agro-chemicals should significantly be minimized or avoided on farms and encourage on alternative farming practices that do not potentially increase potentially toxic heavy metals and residues in khat. Regular monitoring and evaluation of pesticide residues and heavy metals in khat products is necessary to ensure public and environmental health.