Analysis of wheat and soil cyproconazole dissipation under field conditions and risk for dietary residue intake

Currently, there is little research on the assessment of dissipation and dietary intake of cyproconazole in wheat and soil under field conditions. This paper developed a sensitive and simple method of analysis of cyproconazole based on gas chromato- graphy with nitrogen-phosphorus detector (GC-NPD). Calibration curves were derived for cyproconazole by plotting peak area against concentration range of 0.05 2.0 mg·L^-1 in a linear equation (y=266 482x + 2 296.7) with a correlation coefficient of r²=0.999 7. The limit of quantification (LOQ), defined as minimum spike level, was 0.05 mg·kg^-1. The average recoveries of five replicates fortified at 0.05 0.2 mg·kg^-1 were in the range of 79.2% 95.6% for soil, wheat crop and wheat grain and with relative standard deviation (RSD) range of 1.9% 10.0%. Based on the developed method, the dissipation and terminal residues of cyproconazole in wheat and soil in three experiment fields respectively in Henan, Jiangsu, and Heilongjiang Provinces were investigated under field conditions. The effects of application frequency, dosage and pre-harvest interval on terminal residues were also discussed. Based on first-order kinetic equations, half-life of dissipation of cyproconazole in wheat (3.0 5.5 days) was much shorter than in soil (18.1 34.5 days) in three experimental fields. The sequence of residue level was wheat grain < soil < wheat plant; which were respectively 0.415 mg·kg^-1, 0.696 mg·kg^-1 and 5.670 mg·kg^-1. Final residues of cyproconazole in wheat grains was less than 0.415 mg·kg^-1 under different application times, doses and pre-harvest intervals. When pre-harvest interval was 14 and 21 days, cyproconazole residues in wheat plants, grains and soil were not significant different among different application times, doses. However, when harvested at 7 days after application, residues in wheat plants, grains and soil were significantly different between 108 g hm^-2 cyproconazole spraying 2 times and 162 g hm^-2 cyproconazole spraying 3 times. Acceptable daily intake (ADI) of cyproconazole was 0.02 mg for per kilogram body weight. The supervised trial median residue (STMR) in wheat grain was 0.05 mg·kg^-1 and the estimated ADI of cyproconazole was 0.000 109 9 mg kg^-1 (body weight). Risk assessment analysis for supervised residue trial suggested that potential health risk posed by cyproconazole was insignificant. Comparison using the one-way Duncan analysis showed that when pre-harvest interval was 14 21 days, dosage and frequency of cyproconazole application had no effect on terminal residues. When pre-harvest interval was 7 days, dosage and frequency had a critical effect on terminal residues. The results showed that cyproconazole use was comparably safe under recommended application methods. This provided a guideline for safe and reasonable use of cyproconazole.