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Distributions of Metal Levels in the Blood of Preschool Children in Taiwan and the Relevant Affecting Factors
blood,lead,arsenic,mercury,biological monitoring,trace metal,inductively coupled plasma-mass spectrometry,
|Publication Year :||2012|
若以各血中金屬濃度平均值正負兩個標準差範圍內為常模，本研究結果顯示臺灣地區學齡前孩童血中金屬濃度常模分布範圍分別為：鉛0.774~4.47 μg/dL、鈹<1.47μg/L、鍶7.75~38.0 μg/L、鉬<2.47 μg/L、鎘<0.340 μg/L、銻1.49~6.24 μg/L、銫0.752 ~4.12μg/L、鈾<0.0170 μg/L、釩<0.674μg/L、錳6.00~22.1 μg/L、鈷0.0481~0.917μg/L、銅674~1397 μg/L、鋅2623~6315 μg/L、砷0.745~11.4 μg/L、硒79.7~154 μg/L、銣1140~3059μg/L、錫<1.44 μg/L、汞1.04~17.7 μg/L。
全台灣學齡前孩童血中鉛濃度分布曲線呈現右偏，血中鉛值最多分布在1~2μg/dL 之間。與美國4 到7 歲孩童比較，台灣學齡前孩童血中鉛的累積分佈圖形與美國2003-2004 年和2005-2006 年最為類似；預期再過4 至6 年，台灣學齡前孩童血中鉛可以更接近美國當代的學齡前孩童血中鉛濃度分布。
此外，以2 μg/dL 和3 μg/dL 為高低血鉛濃度之切分點的羅吉斯回歸模式分析結果顯示，主要的顯著影響因素是孩童家庭背景資料相關的變項。以4 或5μg/dL 為高低血鉛濃度之切分點的羅吉斯回歸模式分析結果則顯示主要的顯著影響因素是與父親職業與居住環境相關的變項。以衛生單位的角度來看，考量台灣孩童血中鉛常模值分布範圍，以及有限的行政資源，孩童血中鉛警戒值可訂在5μg/dL，以便能針對少部分高血中鉛濃度孩童進行重點式鉛暴露防治工作。
Biological monitoring of metals in blood is important in characterizing human’s exposure to metals. The aim of this study was set to establish the norm of metal levels in blood of the preschool children in Taiwan as well as to explore their determinants in order to set forth the benchmarks for further toxic metal exposure prevention.
Stratum random sampling was adopted based on administrative area and in total 44 districts, cities, towns, and villages were selected. Within these areas, after being invited in sequence, 85 kindergartens agreed to participate in this study. All the parents of children of the participating kindergarten were informed the study goals and processes, and asked to sign a statement of consent once they agreed to take part in this study. Questionnaires were administrated through help of the kindergarten teachers, while blood samples were collected by pediatric nurses or doctors. From April to October 2011, in total, 932 blood samples were collected from the volunteering kindergarten children, and stored in tubes with heparin at 4℃ until laboratory analysis with inductively coupled plasma mass spectrometry for 18 trace metals, including beryllium, lead, strontium, molybdenum, cadmium, antimony, cesium, uranium, vanadium, manganese, cobalt, copper, zinc, arsenic, selenium, rubidium, tin, mercury.
As being defined as mean plus/minus two times the standard deviation, the norms of metal levels in blood of preschool children were set as 0.774 to 4.47 μg/dL for lead, less than 1.47μg/L for beryllium, 7.75 to 38.0 μg/L for strontium, less than 2.47μg/L for molybdenum, less than 0.340μg/L for cadmium, 1.49 to 6.24 μg/L for antimony, 0.752 to 4.12 μg/L for cesium, less than 0.0170 μg/L for uranium, less than 0.674 μg/L for vanadium, 6.00 to 22.1μg/L for manganese, 0.0481 to 0.917 μg/L for cobalt, 674 to 1397 μg/L for copper, 2623 to 6315 μg/L for zinc, 0.745 to 11.4 μg/L for arsenic, 79.7 to 154 μg/L for selenium, 1140 to 3059 μg/L for rubidium, less than 1.44 μg/L for tin and 1.04 to 17.7 μg/L for mercury, respectively.
Except for cadmium and antimony, levels of all study metals in children’s blood were significantly different among geographical zones, i.e. northern, central, southern, eastern Taiwan, and off-shore islands (p<0.025). The highest levels of lead and tin in children’s blood were found in off-shore islands; the highest levels of beryllium, molybdenum, cesium, manganese, arsenic, rubidium and mercury were found in eastern Taiwan; the highest level of strontium was found in central Taiwan; the highest levels of vanadium, cobalt, copper, zinc and selenium were found in southern Taiwan. The lowest levels of lead, manganese, zinc, rubidium and mercury in children’s blood were found in northern Taiwan; the lowest levels of beryllium, strontium, cesium, vanadium, copper and selenium were found in off-shore islands; the lowest levels of cobalt and tin in children’s blood were found in eastern Taiwan; the lowest level of arsenic was found in southern Taiwan.
The distribution of blood lead level of the preschool children in Taiwan was skewed to right with most blood lead levels ranging from 1 to 2 μg/dL. Such a distribution was similar to the findings in the surveys on American children aged 4-7 years in 2003-2004 and 2005-2006, respectively. It is expected that the blood lead level distribution of the preschool children in Taiwan will get close to the contemporary blood lead level of same age children of the United States in the upcoming four to six years.
It was found that incense burning at home was associated with arsenic, mercury and lead levels in children’s blood samples. Especially, there was a dose-response relationship between frequency of incense burning at home and lead level in children’s blood samples, indicating incense burning probably a lead exposure source for children. Besides, factories located in the vicinity of the study subject’s residence is positively correlated with lead level in children’s blood samples; smell of odor in the vicinity of study subject’s residence was also positively correlated with antimony level in children’s blood samples. Lead level in children’s blood samples was negatively correlated to family income, and blood strontium and tin levels in children’s blood samples were also negatively correlated to parental education levels. These relevant metals are generally used in the manufacturing industry, implying parental occupational exposure could indirectly lead to children’s metal exposure.
With different cut-points applied in categoring high-low blood lead level groups, results of logistic regression model showed that the major variables for high blood lead level group were demographic related factors as cut-point set at 2 or 3 μg/dL, while the major affecting factors for high blood lead level group were parental occupation and general living environmental related factors as cut-point set at 4 or 5 μg/dL. Therefore, from the viewpoint of health administration, considering the norm of blood lead level of preschool children and limited administrative resources, the alert for blood lead level of preschool children could be set at 5 μg/dL, in order to launch lead exposure prevention by focusing on the small part of children with relatively high level of lead in blood.
As compared to the traditional hazardous metal exposure environment with conspicuous pollution sources and high levels of pollutant contents, the hazardous metal exposure nowadays becomes low level multi-elements exposure with obscure sources, and was reflected by low social economic status, low educational level and culture heritage. This phenomenon suggested that the exposure prevention for hazardous metals in the future should focus on the disadvantaged minority.
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