Urinary Excretion of Chromium Following Ingestion of Chromite-Ore Processing Residues in Humans: Implications for Biomonitoring

Biomonitoring programs for urinary chromium (Cr) typically attempt to evaluate occupational exposure via the inhalation route. This study investigated whether Cr can be detected in the urine of people following the ingestion of soils that contain relatively high concentrations of chromium in chromite ore processing residue (COPR). To evaluate the reasonableness of using urinary monitoring to assess environmental exposure, six volunteers ingested 400 mg of soil/day (low-dose group), two others ingested 2.0 g of soil/day (high-dose group) for 3 consecutive days, and one person ingested a placebo on each of 3 days. The soil and COPR mixture contained concentrations of total chromium (Cr) and hexavalent chromium [Cr(VI)] of 103 ± 20 and 9.3 ± 3.8 mg/kg, respectively. Therefore, the low-dose group ingested 41 μg Cr/day [including 3.7 μg Cr(VI)] and the high-dose group ingested 206 μg Cr/day [including 18.6 μg Cr(VI)] on each of 3 consecutive days. All urine samples were collected and analyzed individually for total Cr on the day prior to dosing, during the 3 days of dosing, and up to the first void 48 h after the last dose. No significant increases in urinary Cr excretion were found when background excretion data were compared with data following each of the 3 days of dosing or in daily mean urine concentrations of the high- vs the low-dose groups. It appears that Cr present in a soil and COPR mixture at Cr doses up to 200 μg/day is not sufficiently bioavailable for biomonitoring of urine to be informative. These results are consistent with previously published findings suggesting that incidental exposure to dusts and soils containing comparable levels of Cr will not result in increased concentrations of Cr in urine.     

SERIES REPRESENTATION OF DOUBLY NONCENTRAL t DISTRIBUTION BY USE OF THE MELLIN INTEGRAL TRANSFORM

ABSTRACT

The Mellin integral transform is widely used to find the distributions of products and quotients of independent random variables defined over the positive domain. But it is hardly used to derive the distributions defined over both positive and negative values of the random variables. In this paper, the Mellin integral transform is applied to obtain the doubly noncentral t density and its distribution function in convergent series forms.     

局部环上欧氏空间中象对称表为对称的分解

局部环上欧氏几何中 ,正交变换表为对称问题 ,是环上欧氏几何的基本问题之一 .本文探讨的是如何将域上欧氏几何中 ,关于这一问题的结果 ,有效的转到环上来 .     

用中药渣制备天然碱泥用生物絮凝剂的研究

利用中药渣作为有机碳源和氮源，对从含中药渣的发酵泥土中筛选出的具有较好产生絮凝剂能力的乳酪杆菌TC-1．进行了最佳培养基的选择和影响絮凝剂絮凝能力的研究．得出了菌生长量与絮凝活性的正相关关系和絮凝剂澄清悬浊液的适用pH值范围．由TC-1所产絮凝剂特别适合强碱性的天然碱泥悬浊液的澄清．试验结果还表明．在培养基中以中药渣作为有机碳源和氮源，可以降低微生物絮凝剂的生产成本．提高絮凝活性．具有广阔的应用前景．     

国外技术性贸易措施对我国农产品出口的影响——以我国苹果及大蒜出口为例

技术性贸易措施正逐步取代关税和配额,成为我国加入WTO后农产品出口面临的主要障碍。以我国苹果及大蒜出口为例,以国外农药最大残留限量标准作为技术性贸易措施的量化指标,利用HMR两阶段模型研究国外技术性贸易措施对我国农产品出口的影响。研究表明：国外农药最大残留限量标准对我国苹果及大蒜的出口概率有显著的抑制作用,对我国苹果的出口贸易量也有显著的抑制作用。具体而言,与发达国家相比,发展中国家的农药最大残留限量标准更为显著地抑制了我国苹果及大蒜的出口概率;与发展中国家相比,发达国家的农药最大残留限量标准则更为显著地抑制了我国苹果及大蒜的出口贸易量。     

“肯定列表制度”对中国输日农产品的经济效应

通过运用局部均衡模型研究发现,“肯定列表制度”在短期会使中国贸易福利减少,贸易条件恶化,存在负经济效应;在中长期则有利于出口企业提高技术水平,存在贸易促进作用。应用中国农产品最新出口月度统计数据进行实证分析,并选取代表产品——烤鳗,用计量经济学方法和EVIEWS软件建立多元线性回归模型。在剔除相关因素的影响后,“肯定列表制度”的实施使中国对目烤鳗出口数量减少607．6361个单位,短期负面影响显著。     

农药残留快速检测生物传感器研究进展

迄今为止,农药残留快速检测用途生物传感器主要有酶生物传感器和免疫生物传感器两大类,农药残留快速检测用途酶生物传感器又包括胆碱酯酶、酪氨酸酶、碱性磷酸酶、酸性磷酸酶、过氧化物酶、有机磷水解酶和谷胱甘肽巯基转移酶等七种类型主要用于蔬菜、水果,以及食晶中农药残留的快速检测.农药残留快速检测用途免疫生物传感器主要包括电化学、光学、压电和微机械悬臂梁四种类型,可以直接用于饮用水、果汁和葡萄酒等农药残留快速检测.     

多维Laplace变换及其应用

提出了多维Ｌａｐｌａｃｅ变换的概念，并讨论它在解微分方程中的应用．     

加强计算机仿真在数学物理方法教学中的应用

计算机仿真可广泛应用于复变函数的积分计算、级数展开、留数计算、积分变换以及特殊函数的计算及图形显示中,而且对于三类典型的数学物理方程的求解也显得简单明了,尤其对于波动方程、热传导方程能动态地演示方程的解随时间的变化规律。计算机仿真方法对培养同学们的数学建模能力、编程实践能力、创新思维能力具有重要作用和指导意义。在本科的教学实践中应切实加强计算机仿真的地位和作用。     

求常系数线性非齐次方程特解的一种简捷而实用的方法

本文借助于Laplace变换,以及复变函数的积分,给出了计算常系数线性非齐次方程特解的公式。该公式简单易记,简便实用,不失为求特解的一种简捷方法。