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• Ultrasound and ultraviolet had synergistic effect on the degradation of chlorpyrifos. • The degradation mechanism mainly involves oxidation, hydrolysis and de-chlorination. • The toxicities of degradation products were lower than that of chlorpyrifos. • The combined treatment had little effect on the quality of the treated milk. The aim of this study was to compare the degradation kinetics of chlorpyrifos by treatment with ultrasound (US), ultraviolet radiation (UV) and a combination of both (US/UV), to evaluate the toxicity of the degradation products and the effect of the treatments on milk quality. US/UV markedly accelerated the degradation of chlorpyrifos. The half-life of chlorpyrifos by US/UV was 6.4 min, which was greatly shortened compared to the treatment with US or UV alone. Five degradation products were identified by GC–MS, and a degradation pathway for chlorpyrifos was proposed, based on density functional theory calculations. According to the luminescent bacteria test and predictions from a structure/activity relationship model, the toxicity of the degradation products was lower than that of chlorpyrifos. In addition, US/UV treatment had little effect on the quality of the treated milk. Therefore, US/UV can be used as a potential non-thermal processing method to degrade pesticide residues in milk. [ABSTRACT FROM AUTHOR]

• Lactobacillus plantarum can degrade 81.28% of dimethoate in milk rapidly. • Enzyme is the main mechanism for Lactobacillus plantarum to degrade dimethoate. • Five degradation products of dimethoate were identified by UPLC-QTOF/MS. Bioremediation of pesticides in contaminated foodstuffs using probiotics has attracted great attention in recent years, but some intermediate products may have profound effects on the toxicity of treated food. Therefore, this work studied the degradation mechanism of dimethoate in milk by L. plantarum, and analyzed the toxicity of degradation products. The results showed that under the optimal conditions, L. plantarum can degrade 81.28% of dimethoate. Dimethoate had high binding affinities to phosphatase with the free energy of –16.67 kcal/mol, and amino acid residues, Gln375 and SER415 played important roles in the catalysis process. Five degradation products were identified using UPLC-QTOF/MS, and their toxicity was estimated using quantitative structure–activity relationship models. Some intermediate products were predicted to be toxic, which should not be ignored, but the overall toxicity of milk decreased after fermentation. Furthermore, the pH and titratable acidity of the fermented milk were 4.25 and 85 ◦T, respectively. [ABSTRACT FROM AUTHOR]