Concentration, Reduction Efficancy and Degradation of Chlorothalonil and Lambda Cyhalothrin Pesticides in Vegetables Sold in a Nairobi City Market

Abstract

Vegetables are very essential in almost all the meals served in Kenya and worldwide. Therefore their production is driven by high demands in the Kenyan and the world markets. This pushes the farmers in Kenya to consistently use and sometimes overuse the pesticides so as to produce high yield of vegetables to meet the high demands as well as to maintain the quantity of the vegetables in the markets. This leads to contamination of the vegetables and fruits. Use of pesticides must ensure public food safety as well as safeguard the environment with regard to the chemicals used and their harmful metabolites. The study aimed at determining chlorothalonil and lambda-cyhalothrin pesticides residue levels in spinach, kales and African nightshade sold in Nairobi city park market, effectiveness of washing methods for their removal and their degradation process in the washing solutions. The washing was done using tap water, 0.9% NaCl, 0.1% NaHCO3, 0.001% KMnO4, 0.1% H2O2 and 0.1% CH3COOH. Degradation process of the pesticides was studied by mixing known concentration of the pesticides with the washing solution at ratio of 1:9. The mixture were then subjected to different condition of shaking and settling for different time durations, and then extracted for analysis. UV-Vis spectrophotometer was used for analysis of the pesticide residue levels. The mean chlorothalonil residue levels in spinach, kales and african nightshade were 0.140 ±0.013 mg/kg, 0.100 ±0.007 mg/kg and 0.002 ±0.001 mg/kg respectively. These values were above the maximum residue limits (MRL) of 0.04 mg/kg allowed and also above allowed daily intake (ADI) of 0.02 mg/kg in spinach and kales. The mean lambda cyhalothrin residue levels were found to be 0.034 ±0.003 mg/kg and 0.030 ±0.002 mg/kg in spinach and kales respectively. The concentration of lambda cyhalothrin was below detection limits (BDL) in the african nightshade. The concentrations were below MRL of 0.1ppm and 0.2 in spinach and kales respectively but above ADI of 0.007 mg/kg. 0.001% KMnO4 was the most effective washing solution at 65.67 ±3.73% to 70.23 ±3.82% removal of chlorothalonil and 81.68 ±3.03% to 85.98 ±4.19% for lambda cyhalothrin in all the three vegetables analyzed. Tap water was the least effective pesticides remover, ranging from 10.23 ±2.00% to 11.43 ±0.21% for chlorothalonil and 42.34 ±2.47% to 48.43 ±1.91% removal of lambda cyhalothrin in the three vegetables analyzed. 0.001% KMnO4 gave the highest degradation rate of 86.63 ±0.02% to 89.01 ±1.03% for lambda cyhalothrin and 81.52 ±1.02 % to 84.08 ±1.78% chlorothalonil. Agitation increased the degradation of 0.9% NaCl which surpassed that of both 0.001% KMnO4 and 0.1% CH3COOH with a degradation of 92.57 ±0.99% of lambda cyhalothrin and 86.97 ±1.36% chlorothalonil after 20 minutes of shaking.