Distribution of fungicide-derived copper in a coffee farm in Kiambu district
Kariuki, James Keffa
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Copper is a key element in our health and our life-styles. It is one of the trace elements essential to healthy life of many plats and animals. Usually occurring as part of the prosthetic group of oxidizing enzymes. On the other hand, copper can be toxic in larger quantities, especially to the lower members of the food chain. Copper-based fungicides are widely used for the control of coffee berry disease (CBD) and coffee leaf rust, the two most common diseases of coffee encountered in Kenya. Continued use of these fungicides raises some concern about possible copper toxicity. The levels of copper in soils from inside and outside the coffee blocks of Oaklands and Nando Estates in Kiambu District were investigated. The levels of copper in the Mugutha River flowing in the valley separating the two estates were also investigated. Copper levels in both the flowing water and in the bottom sediments were investigated. The uptake of copper from the soils by blackjacks Bidens pilosa L. was also investigated. The pH and conductivity of the soil and water samples were measured. Analysis showed mean levels of copper up to 542 mg/kg in the soils inside the coffee blocks. While the soils outside the coffee blocks had mean levels of copper up to 25mg/kg. The highest level of copper in soils from a control site was 12 mg/kg. The mean level of the total copper in the flowing water of the Mugutha River was found to have reached 10.9 x10-2mg/1. While copper levels up to 130 mg/kg were found in sediments from the bottom of the Mugutha River. Blackjack samples inside the coffee blocks were found to have copper levels of up to 611 mg/kg. While those from a control site had copper levels up to 29 mg/kg. It was estimated that about 30% of the total amount of copper, which gets onto the land under coffee, which may directly affects the copper content of the Mugutha River. Is carried towards the Indian Ocean by the flowing water of the river. The rest of the copper may be accounted for by: (1) copper in the bottom sediments of the river. (2) copper taken up by other plants growing in the soils. (3) copper in the bark and wood of the coffee bushes, (4) copper in the coffee berries, (5) copper which may be absorbed on the clothes and bodies of people passing through the coffee bushes and (6) copper which may accumulate below a depth of 20cm. The results are discussed with references to the influence of a variety of factors namely: pH, conductivity, the rainy season, the spraying of the coffee, vegetation around sampling sites, and the river flow.