faculty of pure and applied sciences - The Department of Chemistry ...

O-13 THE PERSISTENCE OF MIRAL 500CS ON TWO COFFEEFARMS IN JAMAICADwight E. RobinsonDepartment of Life Sciences, MonaSerious outbreaks of the coffee leaf miner (CLM), Perileucoptera coffeella, during 1991 - 1995prompted the spraying of several insecticides, particularly Miral 500CS (isazofos), which wasfound to be quite effective in suppressing the CLM (Reid and Robinson, 1994). However, concernsabout its persistence in the environment and possible impact on non-target organisms prompted thefollowing study which was aimed at determining its persistence in two varied coffee cultivatingconditions of Jamaica.The study was carried out on a Blue Mountain plantation (Mavis Bank) and another in the highlandsof St. Catherine (Mountain Hill). Sample plots of 0.2 ha with about 250 trees were selected on eachfarm and treated with Miral 500CS at a concentration of 3 mL/L. A 625 m 2 area of soil under treeswas demarcated in a separate area and treated similarly. Thirty leaves and berries were randomlypicked from treated trees and a 100g sub-sample of soil taken from a mixture of ten 60-g soilsamples taken at random from the treated soil area. Samples were collected 2 hours and 1, 3, 7, 14and 21 days after treatment for extraction and analysis in the laboratory. Rainfall was also recorded.Samples were weighed, extracted in methylene chloride by shaking on a wrist action shaker, filteredand cleaned on a florisil column. Cleaned extracts were concentrated to 10 mL and analyzed on aShimadzu 9A gas chromatograph equipped with an FPD chromatopack data system. Analyticalconditions were: glass column, 1.6 m by 2 mm packed with OV-17; carrier gas; nitrogen, at a flowrate of 30 - 35 mL/min; temperature settings of 230 o C for the column and 260 o C for the injector anddetector. The detection limit for isazofos was 0.004 ng. Probit analysis was used to determine thehalf life of the insecticide on each substrate.The half life of Miral 500CS on coffee leaves and in soil was 7-fold greater in the Blue Mountainthan highland plantation (Table). This trend was reversed for the berries as the loss of Miral 500CSfrom the berries was 3-fold greater on the Blue Mountain than the highland plantation. Variations inpersistence of the insecticide on leaves and berries of the plantations may be attributed to differingenvironmental conditions such as precipitation, temperature, sunlight and wind velocity, whichwould all impact on the insecticide’s loss and degradation (Edwards, 1975; Hill and Wright, 1978).In addition to these factors, its persistence in the soil would also be influenced by soil properties suchas the organic matter content.There is a direct correlation between the persistence of insecticides in soil and organic matter contentof the soil (Arnold and Briggs, 1990) which would explain the greater persistence of Miral 500CS inMavis Bank than Mountain Hill soil which had 4.55 and 1.15% organic matter, respectively. Itshould be noted that the half-lives presented were obtained under conditions of high rainfall (94 and128 mm in Mountain Hill and Mavis Bank, respectively) which is indicative of the highenvironmental persistence of Miral 500CS. It is, therefore, obvious that encapsulation of the activeingredient, in an attempt to reduce its hazardous effects, has resulted in its increased persistence inthe environment, thus prolonging possible harmful effects.35