Persistence of Chlorpyrifos pesticide in leaves and stems of guava-tree (Psidium guajava L.).

The guava is a crop whose leaves and stems have high medicinal potential, but is attacked by the “Guava Cottony Scale” (Capulinia sp.), which colonizes the plant and cause his death, and farmers often employ Chlorpyrifos for combat. This study examined the persistence of Chlorpyrifos in leaves and stems of three types of guava: Red Native, Brazilian and Tamare, with a single application at the recommended dose by the manufacturer and determine their residual levels in time (1, 5, 9, 24, 48 and 72 hours post application). The samples were analyzed using gas chromatography with nitrogenphosphorus detection. There were high percentages of recovery in leaves and stems (88.29-105.48%) to addition levels between 0.025 and 0.250 μg.g, with low relative standard deviations (0.10-6.72%) and a low detection limit (0.0147 μg.g ). Chlorpyrifos dissipation in leaves and stems followed a first order kinetics. The half-life times in leaves of Red Native, Brazilian and Tamare were 9.42, 12.47 and 10.60 hours, respectively and in stems: 12.33, 13.18 and 11.87 hours, respectively. These results indicate that the persistence is greater in stems than in leaves (P Tamare>Red Native (P Red Native>Tamare (P<0.01).