Arson is classified as a violent crime,and often involves accelerants that significantly increase casualties and property damage.These accelerants,typically flammable liquids with low saturated vapor pressure,present volatile characteristic components in fire residues,making evidence preservation critical for accurate forensic analysis.In this study,the preservation performance of AMPAC(American KAPAC polyester sampling bags)and polyethylene(PE)evidence bags were evaluated under simulated field conditions(40 oC)through gas chromatography-mass spectrometry(GC-MS)technique,focusing on background interference,sealing integrity,and cross-contamination.The results demonstrated that AMPAC bags exhibited minimal background interference(C12?C14 alkanes detected after 3?7 days)and effective gasoline sealing,though slight losses of C2?C3 alkylbenzenes and trace cross-contamination were observed.In contrast,PE bags showed significant background hydrocarbons(C15?C19 alkanes)and pronounced gasoline component losses,including C2?C4 alkylbenzenes,naphthalenes,and indenes.Notably,severe cross-contamination of gasoline markers was detected in adjacent blank PE bags,with characteristic components such as C2?C4 alkylbenzenes,naphthalenes,methylnaphthalenes,dimethylnaphthalenes,indenes,indanes,methylindenes,and dimethylindenes identified,indicating substantial cross-contamination issues in PE evidence bags.Microstructural analysis revealed superior sealing in AMPAC bags attributed to their smooth,dense surface morphology compared to PE's rougher,porous structure.This study established a comprehensive evaluation framework for fire residue evidence containers,and found that PE bags were unsuitable for long-term gasoline evidence preservation due to compromised integrity.These findings provided critical references for forensic container selection in fire investigations.

Objective To assess the changes in iodine status and dietary iodine intake among Shanghai residents since common salt was iodized 20 years ago.Methods As-CE Catalysis spectrophotometry was used to determinate the urine iodine level in school-age children,pregnant women,wet nurse and adults of Shanghai between 1995 and 2015.B ultrasonic was used to determinate the thyroid volume of school-age children.And then the goiter rate was calculated.Direct titration or arbitration methods were applied to detect the household salt iodine level quantitatively.The survey was conducted by using 3 days 24-hour dietary questionnaire and condiment weighing methods to analyze the level of iodine intake and sources for the cases of all iodized salt consumption and all consumption of non-iodized salt.Results The median urine iodine concentration (UIC) of school age children was 72.3 μg/L in 1995,rose to 214-231 μg/L from 1997-1999,and then became stable between 100 μg/L and 200 μg/L since 2002.The goiter rate was below 5% among children aged 8-10 from 1995-2015 in Shanghai.The median urine iodine of pregnant women was between 126.5 μg/L and 139.8 μg/L.The median UIC of other populations were all between 100 μg/L and 200 μg/L: with adults,lactating women,infants and young children and women of childbearing age,the median urinary iodine was 138.4,123.1-131.1,150.1 and 125.6 μg/L.The qualified iodized salt at household consumption rate was 90% from 2001 to 2009,the percentage declined year by year from 2010.In the cases of all taking iodine salt,the median iodine intake volume for male aged 7-10,11-13,14-18 and over 18 was 200.3,235.5,252.7 and 215.4 μg/L;women aged 7-10,11-13,14-18 and over 18 was 193.0,213.8,208.3 and 186.1 μg/L.The contribution rate of iodine salt in the diet were 51.6%-54.1% and 49.1%-53% in men and women.Kelp,seaweed and fish and shrimp on the contribution of iodine are 7.6%-16.6% and 4.5%-7.4%.Conclusion In the past about 20 years,iodine nutritional status of residents in Shanghai has stabilized totally in a appropriate and safe level.However,the iodine nutrition of pregnant women was insufficient.As iodized salt is the major source of dietary iodine in coastal areas,it is still necessary to continue the policy of universal salt iodized in Shanghai to ensure residents'' needs for iodine and control the risk of iodine deficiency.