| Fumigant is a kind of insecticide that uses the steam produced during volatilization to poison and kill harmful organisms.CSIRO Australia and the University of Canberra had developed cyanogen as a new fumigant and obtained an international patent for the application of cyanogen as a fumigant and its methods of use in 1995.It appeared to have a high toxicity for insect pests in stored grains,timbers and soils,and also have a high toxicity to pathogens in the soils.Cyanogen has the potential to replace hazardous methyl bromide,which is an ozone depleting substance,for fumigation purposes of timber and soils.The research in this report was focused on residual analysis of cyanogen and hydrogen cyanide,their sorption,desorption and degradation in grains and soils.The results will provide information for investigation and evaluation of cyanogen for fumigation purposes of soils.A method for the determination of C2N2 and HCN residues in eight different soils by headspace solvent extraction and gas chromatography mass spectrometry（GC-MS）was established.The optimum extraction process of HCN and C2N2 by headspace method was obtained by response surface analysis.The extraction rate of HCN and C2N2 was（92.50±0.63）%and（89.22±0.65）%respectively at 60℃,35 m L（30%H2SO4,relative to 20g soil sample）solvent volume and 0.7 h extraction time.The detection limits of C2N2 and HCN were 0.0012 mg·kg-1 and 0.001 mg·kg-1,respectively.The quantitative limits of C2N2 and HCN were 0.004 mg·kg-1 and 0.003 mg·kg-1,respectively.The recoveries of C2N2 and HCN in eight soils were 84.7%-102.9%and 80.18%-95.34%respectively.RSD of RSD was less than 1.2%and 2.1%respectively.At the same time,in the solvent headspace method,the distribution and stability of C2N2 and HCN in the headspace of closed system under different extraction matrix and temperature,as well as the influence of extraction time on the extraction effect were discussed.The results of the study on the adsorption,desorption and residue of C2N2 and HCN in soil showed that the top space decay of C2N2 and HCN in eight soils（Hebei brown soil,Heilongjiang black soil,Sichuan purple soil,Zhejiang paddy soil,Jiangxi red soil,Hubei yellow soil,Shandong brown soil,Hainan brick red soil）was faster than that in PH3.Soil has strong adsorption capacity for C2N2 and HCN.The adsorption capacity for C2N2 is slightly lower than HCN in the first 24 hours of fumigation,and higher than HCN in the 24-48 hours after fumigation.Water content has a certain influence on the adsorption of C2N2and HCN.Water content in soil is conducive to the adsorption of HCN,but has little influence on C2N2.At the same time,water content can accelerate the conversion of HCN to C2N2 and the degradation of C2N2 to HCN.In the closed system,the attenuation of C2N2 and HCN in soil is slow,and the adsorption of C2N2 and HCN in non sterilized soil is slightly higher than that in sterilized soil.In the first 4 hours of fumigation,the conversion rate of HCN to C2N2 in non sterilized soil is faster than that in sterilized soil,while the conversion rate of C2N2 to HCN is similar.The attenuation of C2N2 and HCN in sterilized soil is the same as that in non sterilized soil,but HCN in non sterilized soil is slightly faster than that in sterilized soil.No significant difference in the t1/2 was observed between sterilized and unsterilized soils,indicating that abiotic degradation was predominant in the degradation of C2N2 and HCN.This fact could be attributed to the low bioavailability of C2N2 and HCN for microbial degradation.HCN produced by C2N2 degradation in eight different soils increased sharply and then decreased gradually.In Heilongjiang black soil,HCN began to decrease slowly after the first two hours of rapid growth,while in Sichuan purple soil,HCN decreased gradually after the first two hours of slow growth.Compared with PH3,HCN has a higher residual level in the soil.After 96 hours of fumigation with 50 mg·L-1 HCN,Hebei brown soil,Heilongjiang black soil,Sichuan purple soil,Zhejiang paddy soil,Jiangxi red soil,Hubei yellow soil,Shandong brown soil and Hainan brick red soil still reach 0.158,0.335,0.212,0.321,0.251,0.381,0.198 and 0.198 mg·kg-1 respectively 165 mg·kg-1;half lives were 26.353,45.793,35.863,48.707,37.293,36.243,34.883 and 27.422 h,respectively.C2N2 is easy to degrade in soil,and the residual level in eight soils is low.HCN,the degradation product of C2N2,was slowly desorbed and remained in the soil at a high level,and its attenuation law was consistent with that of fumigation with HCN directly.Leaching experiments showed that C2N2 and HCN mainly diffused downward,and there was almost no residue in the soil.After 100 mg·L-1 C2N2 or HCN was injected,higher concentrations of C2N2,HCN,NH4+and NO3-were found within 15 cm from the top of Heilongjiang black soil.The values were 30,20,19.21 and 10.48 mg·kg-1,respectively.Further research shows that,compared with the laboratory,the establishment of more complex field environment to establish the minimum dose of C2N2 can be used to block hazards and effectively control pests and improve crop yield.The toxicity of cyanogen,hydrogen cyanide,emamectin benzoate and methomyl to Bursaphelenchus xylophilus was determined in this experiment.It was found that the corrected mortality of pine wood nematode increased with the increase of concentration.The adjusted mortality of pine wood nematode was 98.23%and 98.10%respectively after treated with 10 mg·L-1 cyanogen and hydrogen cyanide for 48 hours.At the concentration of 5mg·L-1,the corrected mortality of pine wood nematode was 99.00%and 88.04%,respectively.Among them,the nematicidal activity of carbendazim to pine wood nematode was the strongest,LC50and LC90 were 0.20 and 1.03 mg·L-1 at 48 h,followed by methomyl,LC50 and LC90 were 0.34 and 3.57 mg·L-1 at 48 h,respectively.Cyanogen and hydrogen cyanide also showed a certain linear killing activity,but compared with carbaryl salt and methomyl,their LC50 and LC90 were 0.58,0.57 mg·L-1,5.41 and 3.96 mg·L-1 at 48 h,respectively. |
