Abstract

Chlorpyrifos is an organophosphate pesticide, widely used on fruit and vegetable crops. Here, we report on the oxidative degradation of standard chlorpyrifos by individual and combined effects of ultrasonic irradiation (US) and ozone (O₃). A standard chlorpyrifos solution (1 mg L^-1) was treated with 1 MHz US, O₃ and its combination (US/O₃) for 0, 10, 20, 30, 40, 50 and 60 min. Reduction of residual chlorpyrifos was determined by gas chromatography with flame photometric detection (GC-FPD) while ion chromatography (IC) was used to determine the concentration of anions as major degradation products. US/O₃ combined treatment had a synergistic effect in reducing chlorpyrifos concentrations, with the highest rate of degradation occurring within the first 10 min. Moreover, chloride, nitrate and sulphate anion concentrations obtained from chlorpyrifos treated with US/O₃ combination, were significantly higher, compared to those treated with ultrasonic irradiation or ozone alone. A sharp decrease in pH from 7.46 to 4.49 was also observed for the combined treatment. The degradation pathway of chlopyrifos, after treatment, was confirmed by gas chromatography mass spectrometry (GC-MS). All treatments resulted in similar main fragment ions at m/z 351, 314, 286, 258, 197 and 97. The lethal concentration (LC₅₀), over a series (0-100) mg L^-1 of standard chlorpyrifos solutions, was estimated and compared to the treated chlorpyrifos. All the treatments directly detoxified chlorpyrifos with LC₅₀ values against brine shrimps (Artemia salina L.) of 10.21, 103.54 and 234.09 mg L^-1 for US, O₃ and US/O₃ treated chlorpyrifos solutions, respectively. The brine shrimp test showed highest toxicity in standard chlorpyrifos with an LC₅₀ value of 7.22 mg L^-1.

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