Behaviour of acephate and its metabolite methamidophos in apple samples

Summary A study of the decay of acephate in apple samples was carried out, including penetration studies and the transformation of acephate in to its main metabolite, methamidophos. Sample treatment involved extraction with ethyl acetate and determination by gas chromatography with nitrogen—phosphorus detection (GC-NPD). Three different parts of the fruit were studied separately: apple surface, peel and pulp. Recoveries were measured at three spiked levels, ranging from 0.050 to 0.504 μg g⁻¹ for acephate and 0.049 to 0.492 μg g⁻¹ for methamidophos. Mean acephate recoveries were 93.0 to 115.5% from peel and 99.2 to 110.2% from pulp, while methamidophos recoveries were 77.2 to 104.2% and 77.5 to 98.6% from peel and pulp, respectively (n=6). Results showed that acephate penetrates into the fruit, where it is transformed to methamidophos. This transformation was not seen on the external apple surface.