Determination of karate and pyagro residue levels in fresh, black and brewed tea from tea farms in Kericho

Abstract

Karate and Pyagro are insecticides currently registered and used in Kenya for control of several insect and mite pests in diverse crops. They are emulsifiable concentrate formulations of the active ingredients lambda-cyhalothrin (Karate) and Pyrethrins (Pyagro). This study established residue levels for lambda-cyhalothrin and Pyrethrins in fresh tea leaves, black tea and brewed tea. The study evaluated the effect of tea preparation procedures on pesticide residue levels in tea and monitors the decline of pesticide residues under normal harvest time intervals. The samples were collected at various intervals after application of pesticides at maximum proposed application rates (i.e. worst-case conditions allowable) according to instructions on the label. The study was carried out at Timbilil estate of Tea Research Foundation of Kenya in Kericho. Two replicate plots of 6 by 15 tea bushes were treated with Karate 1.75 EC, another two replicate plots of 6 by 15 tea bushes were treated with Pyagro 4 EC and one untreated plot of 6 by 20 tea bushes at the field trial. Foliar applications were made to mature tea bushes, Karate was prepared by dissolving 3.0 mL of Karate concentrate in a litre of water and Pyagro was prepared by dissolving 5.0 mL of Pyagro concentrate in a litre of water. Extraction of lambda-cyhalothrin from Karate treated samples was accomplished using 50% acetone in hexane and Pyrethrins from Pyagro treated samples were extracted using acetonitrile then partitioned with petroleum ether. Analysis of the samples was done by Gas Chromatography (GC), employing the electron capture detector with a packed column. The pesticide residue concentrations in the tea samples were calculated using the power curve fit; y = bxm . Results show that the levels of the pesticide residues decrease with increase in the pre-harvest interval days. The results reveal that residues found in samples collected on the first day after application contain the highest residue levels and those collected fourteen days after application contain the lowest residue levels. The processing and brewing of tea appear to affect the residues of lambda-cyhalothrin (Karate) and Pyrethrins (Pyagro) most significantly i.e. for the same pre-harvest interval, the residues in fresh tea samples are higher than residues in the black tea samples which are also higher than the residues in the brewed tea samples. The study determined the maximum residue level and compared it with the suggested tolerances. The residue levels from the study are lower than the maximum residue levels allowed within the European Union. Therefore, if these pesticides are used according to the established pattern they will pose no risk to the consumers of tea.