Pesticide Use by Rice Farmers and the Presence of Residues in the Rice Grain: an Evidence-Based Study in Selected Rice-Growing Districts in Sri Lanka

Rice is the major constituent in the Sri Lankan diet and the development of an analytical method for the analysis of the pesticide residues present in rice grain is important to ensure consumer safety in rice. This study attempted to investigate the use of pesticides by farmers and a random multi-pesticide residue analysis in rice grain samples. Overall, 57 pesticides in rice grain were validated according to the SANTE/12682/2019 using QuEChERS, as per AOAC official method 2012, and quantified by the Liquid chromatography separation with heated electrospray ionization and Triple Quadrupole Tandem Mass Spectrometry (LC-MS/ MS). LOD was 10 ppb while, recovery studies at three spiking concentration levels of 1 LOQ, 5 LOQ, and 10 LOQ showed recovery of 70-120% with RSD of <20% and R² of ≥0.995. Pre-tested questionnaires distributed among 60 farmers in Anuradhapura, Polonnaruwa, Kurunagala, Hambantota, and Ampara Districts were evaluated. Of all the farmers, 56.7% used pretilachlor as a weedicide while 26.3% used Carbosulfan and Thiamethoxam as insecticides. For real sample analysis, 62 rice grain samples grown in the above Districts were collected randomly from farmers from January to March 2020 and were evaluated against the 57 pesticides using LC-MS/MS. The harvested rice samples were extracted and cleaned using QuECHERs and AOAC 2012. Of 57 pesticides, only six pesticide residues were detected with 4.8%, 3.2%, 3.2%, 4.8%, 1.6%, and 1.6% for Thiamethoxam, Imidacloprid, 3-hydroxycarbofuran, Profenophos, Buprofezin, and Tebuconazole respectively. The highest contamination was reported as 108 ppb for Imidacloprid harvested at Ampara District and the total detection percentage was 0.33% while not exceeding the FAO MRL’s or Sri Lankan MRL’s. The results revealed that the presence of pesticide residues in rice is low.