北京市售大米重金属含量监测及膳食风险评估

监测市售大米重金属含量,为北京市食品安全风险评估提供参考和数据支撑,采集了市售大米样品537件,分析其9种重金属(Cd、Cr、Cu、Fe、Mn、Ni、Pb、Sr和Zn)含量。采用内梅罗综合污染指数法评价市售大米的重金属污染水平,采用健康风险评价模型进行食用安全评估。结果如下:大米Cd、Cr、Cu、Fe、Mn、Ni、Pb、Sr和Zn含量平均值分别为0.02、0.02、2.27、2.63、9.10、0.15、0.07、0.17和14.27 mg/kg。大米重金属污染程度依次为:PbZnNiCuCdCr,其风险等级依次为:CuZnCdPbCrNi。结果表明,大米重金属的内梅罗综合污染指数较低,表明当前北京市售大米整体状况较好、处于安全水平;大米重金属对儿童的THQ贡献率高于成人,相关部门应加强有毒重金属监督与相应膳食指导。     

炭化-湿法消解-石墨炉原子吸收光谱法测定植物油中铅、镉和铬的研究

为了快速、准确、低成本地消解植物油,检测Pb、Cd和Cr含量,通过对比消解用酸和取样量,优化石墨炉原子吸收光谱仪(GFAAS)灰化温度和原子化温度,对比消解方法及ICP-OES、ICPMS和GFAAS等方法的精密度,采用炭化-湿法消解-GFAAS测定了12类219件植物油(134件食用油和85件调味油)Pb、Cd和Cr含量,同时利用加标回收进行质量控制。结果表明:取样量为0.200 0 g,消解用酸为硝酸13 m L、过氧化氢5 m L时,可将植物油消解彻底;采用氘灯背景校正法测定Pb和Cd,塞曼背景校正法测定Cr;测定Pb、Cd和Cr的灰化温度和原子化温度分别为400、300、1 400℃及1 100、800、2 000℃;加标回收率范围为94.6%~109.3%;食用油Pb、Cd和Cr含量平均值为0.052 2、0.001 0、0.331 7 mg/kg,调味油的Pb、Cd和Cr含量平均值为0.192 5、0.003 7、1.813 8 mg/kg。调味油Pb、Cd和Cr的含量普遍高于食用油中的含量;炭化-湿法消解-GFAAS测定Pb、Cd和Cr的精密度较高、方法可靠,是批量检测植物油Pb、Cd和Cr的优选方法。     

内蒙古锡林河流域羊草草原植物生长旺季呼吸的影响因素分析和区分

Based on the static opaque chamber method, the respiration rates of soil microbial respiration, soil respiration, and ecosystem respiration were measured through continuous in-situ experiments during rapid growth season in semiarid Leymus chinensis steppe in the Xilin River Basin of lnner Mongolia, China. Soil temperature and moisture were the main factor affecting respiration rates. Soil temperature can explain most CO2 efflux variations (R2=0.376-0.655) excluding data of low soil water conditions. Soil moisture can also effectively explain most of the variations of soil and ecosystem respiration (R2=0.314-0.583), but it can not explain much of the variation of microbial respiration (R2=0.063). Low soil water content (≤5%) inhibited CO2 efflux though the soil temperature was high. Rewetting the soil after a long drought resulted in substantial increases in CO2 flux at high temperature. Bivariable models based on soil temperature at 5 cm depth and soil moisture at O-10 cm depth can explain about 70% of the variations of CO2 effluxes. The contribution of soil respiration to ecosystem respiration averaged 59.4%, ranging from 47.3% to 72.4%; the contribution of root respiration to soil respiration averaged 20.5%, ranging from 11.7% to 51.7%. The contribution of soil to ecosystem respiration was a little overestimated and root to soil respiration little underestimated because of the increased soil water content that occurred as a result of plant removal.