Dissipation dynamics and dietary risk assessment of pyraclonil residues in rice (Oryza sativa L.)

Abstract

Pyraclonil is a highly efficient broad-spectrum herbicide, widely used for weed control in paddy fields, especially in Japan. However, pyraclonil residues remaining in soil after application pose a potential threat to human health. In this study, the QuEChERS (quick, easy, cheap, effective, rugged, and safe) and HPLC–MS (high-performance liquid chromatography–tandem mass spectrometry) methods were employed for residue analysis of pyraclonil in rice (Oryza sativa L.). Field experiments were conducted over two years (2018–2019) to monitor pyraclonil dissipation in four rice production areas (Jiamusi, Jining, Ningbo, and Nanchang) across China. The dissipation dynamics of pyraclonil in paddy water, paddy soil, and rice plants was well described by a first-order kinetic model. Dissipation dynamic tests indicated pyraclonil half-lives of 2.13–3.56, 5.45–8.66, and 3.08–3.97 days in paddy water, paddy soil, and rice plants, respectively. Pyraclonil was dissipated more rapidly in paddy water than in paddy soil and rice plants. The variation in pyraclonil dissipation rates across the different areas was mainly attributed to differences in rainfall during the rice growth period and in the organic matter content of soil. At an initial pyraclonil dosage of 420 g a.i.•ha−1, the highest levels of pyraclonil residues in brown rice were found in the Jiamusi area in 2018 (0.144 mg•kg−1) and in the Nanchang area in 2019 (0.147 mg•kg−1). Under standardized residual test conditions, the level of pyraclonil residues in rice prior to harvest was within the acceptable intake limits based on chronic dietary risk assessments for Chinese residents of different age groups. These results can guide the practical application of pyraclonil and help minimizing environmental risks associated to its worldwide use.