Evaluation of the disappearance of cyanogen and hydrogen cyanide in different soil types using gas chromatography–mass spectrometry

Abstract

Cyanogen (C2N2) is a new soil fumigant being tested worldwide for soil fumigation or sterilization before planting. This study established a multi-fumigant detection method for C2N2 and its degradation product hydrogen cyanide (HCN) by gas chromatography–mass spectrometry (GC–MS). The GC–MS method was then applied to investigate the degradation of C2N2 and HCN in eight different agricultural soils. The optimal headspace sampling conditions using a Box–Behnken experimental design were an extraction temperature of 60 °C, an extraction time of 0.7 h, and a solvent volume of 35 mL (30% H2SO4). Under these conditions, the extraction rates of C2N2 and HCN were 89.22% ± 0.65% and 92.50% ± 0.63%, respectively. The limits of quantification for both target compounds were 0.001 mg·kg−1. The recoveries of C2N2 and HCN ranged from 84.7% to 102.9% and from 80.18% to 95.34%, respectively, at spiked levels of 0.05, 0.2, and 1.0 mg·kg−1 with relative standard deviation ≤2.2%. A residual dynamics experiment showed that C2N2 and HCN disappeared rapidly in the soils. The first-order double-exponential decay model best described the decline of C2N2 and HCN concentrations in soil. The half-lives of C2N2 and HCN in soil were 8.553–27.964 h and 11.823–35.674 h, respectively. The GC–MS method provides a simple, fast, and organic solvent-free procedure to analyze multiple fumigants in the soil matrix. The proposed method is therefore recommended as a screening tool for the field investigation of C2N2- and HCN-fumigated sites.