Residue profiles and dietary risk assessment of pyraclostrobin in Brassica oleracea var. italica, Lactuca sativa , Cucumis melo, Pleurotus ostreatus , and Dendrobium officinale

This study established a QuEChERS-UPLC-MS/MS method for determination of pyraclostrobin residues in Brassica oleracea var. italica, Lactuca sativa, Cucumis melo, Pleurotus ostreatus, and Dendrobium officinale. The method showed good linearity over 0.001 ~ 0.1 mg L−1 (R2 ≥ 0.9681), with average recoveries of 84.40% ~96.30% and RSDs ≤ 8.20%. The LOQ was 0.01 mg kg−1 for all matrices. At 2 h after application, residues were 0.14 ~ 0.22 mg kg−1 in Brassica oleracea var. italica, 2.30 ~ 2.70 mg kg−1 in Lactuca sativa, 0.05 ~ 0.10 mg kg−1 in Cucumis melo, 1.20 ~ 1.80 mg kg−1 in fresh Dendrobium officinale, and 8.90 ~ 9.40 mg kg−1 in dried Dendrobium officinale. At recommended pre-harvest intervals, residues were: 0.02 ~ 0.08 mg kg−1 in Brassica oleracea var. italica at 7 ~ 10 d; 0.04 ~ 1.40 mg kg−1 in Lactuca sativa at 7 d; <0.12 mg kg−1 in Cucumis melo at 7 ~ 10 d; 0.50 mg kg−1 in Pleurotus ostreatus at 3 d and <0.04 mg kg−1 at 5 d; 0.11 ~ 0.56 mg kg−1 in fresh Dendrobium officinale at 45 ~ 60 d, and 0.64 ~ 1.60 mg kg−1 in dried Dendrobium officinale at 60 d. Degradation half-lives were 4.74 ~ 4.92 d (Brassica oleracea var. italica), 1.20 ~ 4.00 d (Lactuca sativa), 26.70 ~ 35.00 d (fresh Dendrobium officinale), and 17.10 ~ 21.20 d (dried Dendrobium officinale), indicating faster degradation on leafy vegetables and slowest on Dendrobium officinale. Dietary risk assessment gave acute risk quotient (RQa) of 0.77% ~12.44% and chronic RQc of 56.60%, both far below the 100% threshold. These results indicate that at recommended dosage, pyraclostrobin residues in the five crops pose an acceptable dietary exposure risk to the general population, though the concentration effect during drying of Dendrobium officinale should be noted. This study provides a scientific basis for rational use and MRL setting.