Determination of chlorothalonil and copper fungicide residues in soil water and some annual food intercrop from Kiambu District in Kenya

Abstract

In the process of application to agricultural crops, fungicides spread into the surrounding environment, such as the soil surface, on food crops growing near the area of application and the water bodies. Copper bordeaux mixtures and chlorothalonil, an organochlorine fungicide, are most commonly used to fight fungal attack in coffee. If used repeatedly on coffee farms copper- based fungicides and chlorothalonil get deposited on, or are absorbed by the coffee plant, and on being processed get to the consumer. Chlorothalonil and copper pesticide residue levels in coffee beans and leaves, food intercrop (beans and potatoes), market coffee beverages, soil and water samples were detennined. A gas liquid chromatographic method was used for detennining the chlorothalonil residue levels while atomic absorption spectrometry method was used for copper detennination. Crop and soil samples for chlorothalonil analysis were extracted using phosphoric acid and recovered in hexane. Recoveries of chlorothalonil from soil fortified with l.O0ppm chlorothalonil were carried out and mean recovery of 74.1% recorded. Analysis of soil samples for detennination of total and extractable copper by nitric — perchloric acid and EDTA methods were done. The results of these analyses on soil showed levels of 0.037 — 3.186 ppm for chlorothalonil and 2.0 — 172.2 ppm and 0.30 — 50.61 ppm for Total and Available copper in soil respectively. An experiment involving sequential extraction of soil samples for copper cations using sodium oxychloride (NaOCl) and magnesium chloride (MgCl2) was carried out. Statistical analysis of data obtained from this experiment showed a positive correlation between Cu (I) in soil and total copper in plant tissue. This was an indication that application of Cu (I) sprays (Cu;O) unlike Cu (II) (CuO, Cu(OH)2) into coffee plantations could lead to high levels of copper in plant tissue and the possible build up to toxic levels. Market coffee beverages were found to have copper residue mean levels of 0.833 ppm. Mean chlorothalonil residue levels in different media were determined as follows: coffee beans 0.044 ppm, coffee leaves 0.803 ppm, leaves of potato intercrop 0.723 ppm, leaves of beans intercrop 0.677 ppm market coffee beverage 0.031 ppm, soil samples 0.542 ppm and water samples 0.457 ppm. The mean levels for both copper and chlorothalonil in marketable coffee were found to fall below the maximum recommended levels by the WHO and FAO and therefore posed no threat to health on consumption. SPSS was used for data analysis.