| Background:Semicarbazide(SEM)is a characteristic metabolite of nitrofurazone,which can form better stability in organisms through protein binding.After human ingestion of animal-derived foods with SEM residues,SEM is released from the stably bound proteins under the action of gastric acid and has toxic effects on the human organism.Because nitrofurazone and its metabolites SEM are potentially teratogenic,carcinogenic and neurotoxic to humans,nowadays it has been banned from detection in various countries,but its metabolite SEM is still detected in crustacean aquatic products,causing the source of its residues is still unclear,so the residues of SEM has been a key issue affecting the export of crustacean aquatic products and the regulation of nitrofurazone,according to the "China Procambarus clarkii Industry Development Report(2020),the total output value of China’s Procambarus clarkii industry in 2019 was as high as 411 billion yuan,the output value of Procambarus clarkii farming was about 71 billion yuan,the output value of the secondary industry,mainly processing industry,was about 44 billion yuan,the output value of the tertiary industry,mainly catering,was about 296 billion yuan,and the middle and lower reaches of the Yangtze River were the main production and consumption areas of Procambarus clarkii.In this paper,we used liquid chromatography-mass spectrometry(LC-MS)to detect and analyze the status of SEM contamination in Procambarus clarkii in the middle and lower reaches of Yangtze River;explored the distribution characteristics of SEM in Procambarus clarkii;determined the SEM content in Procambarus clarkii culture environment in the middle and lower reaches of Yangtze River and investigated the main factors causing its residues.Methods:(1)Based on liquid chromatography tandem mass spectrometry(LC-MS),a pre-treatment method was optimized for the detection of SEM in Procambarus clarkii.The in vivo SEM and the different links SEM exposure level of Procambarus clarkii in the middle and lower reaches of the Yangtze River was detected by LC-MS/MS.(2)The SEM levels of the main tissues(muscle,cephalic shell,dorsal shell,hepatopancreas)of the Procambarus clarkii in the middle and lower reaches of the Yangtze River were measured to investigate the distribution of SEM in the Procambarus clarkii.(3)The relationship between SEM residues and the culture environment of crayfish in the middle and lower reaches of the Yangtze River was investigated by Spearman correlation analysis.(4)The water column was exposed to different doses of nitrofurazone(10,50,200 mg/L),sodium hypochlorite(0.125%,0.25%,0.5% active chlorine)and azodicarbonamide(ADC)(50,500,5000 mg/L)for a short period of time(60 h)to simulate the effects of different factors(medication,disinfectant,transport packaging materials,etc.)on the SEM of crayfish.The effects of different factors(dosing,disinfectants,transport packaging materials,etc.)on the content and distribution characteristics of SEM in Procambarus clarkii.Results:(1)The detection rate of SEM in Procambarus clarkii from different regions was100%,the concentration of SEM ranged from 0.25 to 43.72 μg/kg,and the average levels in Shishou,Jianli,Honghu,Qianjiang,Shayang,Huoqiu,Huarong,Jianhu and Xuyi were 27.48,2.05,1.73,3.94,3.30,7.67,5.76,3.10,2.89 μg/kg,and the average content of SEM in the samples of Procambarus clarkii from different distribution stages in descending order was market shrimp > farmed shrimp > restaurant shrimp >semi-processed shrimp > processed shrimp.(2)The SEM content in the muscle of Procambarus clarkii ranged from 0 to8.45 μg/kg,with a detection rate of 90.2%;the SEM content in the back shell ranged from 1.47 to 12.94 μg/kg,with a detection rate of 100%;the SEM content in the head shell ranged from 0 to 8.38 μg/kg,with a detection rate of 97.6%;the SEM content in the hepatopancreas ranged from 0 to 6.11 μg/kg,with a detection rate of The detection rate was 92.7%.The mean contents of SEM in muscle,dorsal shell,cephalic shell and hepatopancreas were 0.26,4.71,3.63 and 1.66 μg/kg,respectively,indicating that the SEM content in Procambarus clarkii had tissue specificity and showed the tissue distribution characteristics of: dorsal shell > cephalic shell > hepatopancreas >muscle.(3)The correlation coefficient value between SEM content of Procambarus clarkii and cultured substrate in the middle and lower reaches of Yangtze River was-0.070,and the correlation coefficient value between SEM content of Procambarus clarkii and cultured water body was-0.144,which was close to 0,and the P values were all greater than 0.05,thus indicating that there was no correlation between Procambarus clarkii and cultured water body and cultured substrate.(4)The relationship between nitrofurazone and SEM formation in Procambarus clarkii: at 36 h,the SEM content in whole shrimp was highest in different dose groups(10,50,200 mg/L),with mean contents of 17.29 μg/kg,25.56 μg/kg,and 56.69 μg/kg,respectively.The highest levels of SEM in the dorsal shell were achieved at 36 h,with mean levels of 11.96 μg/kg,11.46 μg/kg,and 16.80 μg/kg in the low,medium,and high dose groups,respectively.The highest levels of SEM in the hepatopancreas were found at 60 h,with mean levels of 14.16 μg/kg,15.48 μg/kg,and 50.88 μg/kg in the low,medium,and high dose groups,respectively.(5)The relationship between sodium hypochlorite and SEM formation in Procambarus clarkii: at 36 h,the SEM content in whole shrimp was highest in different dose groups(0.125%,0.25%,0.5% active chlorine),with mean contents of17.29 μg/kg,25.56 μg/kg,and 56.69 μg/kg,respectively.the SEM content in muscle was highest at 24 h,with mean contents of 12.80 μg/kg and 21.38 μg/kg in low,medium,and high dose groups,respectively.The SEM levels in the dorsal shell were highest at 36 h,with mean levels of 11.96 μg/kg,11.46 μg/kg,and 16.80 μg/kg in the low,medium,and high dose groups,respectively.The highest levels of SEM in the hepatopancreas were found at 60 h,with mean levels of 14.16 μg/kg,15.48 μg/kg,and50.88 μg/kg in the low,medium,and high dose groups,respectively.residual SEM caused by sodium hypochlorite was mainly enriched in the hepatopancreas.(6)The relationship between ADC and SEM formation in Procambarus clarkii:SEM levels in whole shrimp were highest in different dose groups(50,500,5000mg/L)at 60 h,with mean levels of 14.48 μg/kg,21.82 μg/kg,and 27.65 μg/kg,respectively.SEM levels in muscle were highest at 36 h,with mean levels of 8.93μg/kg and 23.95 μg/kg in low,medium,and high dose groups,respectively.The highest levels of SEM in the dorsal shell were reached at 60 h,with mean levels of17.20 μg/kg,43.69 μg/kg,and 78.86 μg/kg in the low,medium,and high dose groups,respectively.The concentration of SEM in the hepatopancreas was highest at 36 h,with mean levels of 32.53 μg/kg,49.10 μg/kg,and 81.96 μg/kg in the low,medium,and high dose groups,respectively.SEM caused by ADC was mainly enriched in the hepatopancreas. |
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