Summing Nondetects: Incorporating Low-Level Contaminants in Risk Assessment
Summing Nondetects: Incorporating Low-Level Contaminants in Risk Assessment
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DOI：
10.1002/ieam.31
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发表时间：
2010-07-01
影响因子：
3.1
通讯作者：
Helsel, Dennis R.
中科院分区：
文献类型：
--
作者：
Helsel, Dennis R.
低水平污染物通常低于实验室的检测限或报告限，导致报告的值为未检出或小于。如何将这些值与检出浓度沿着相加以获得总量，特别是当使用毒性等效因子（TEF）等加权因子时？环境科学家将未检出值沿着检出值相加时，最常用的方法是用检出限的一半代替每个未检出值。这种替代允许最不精确的测量，具有高检测限的数据，对所得的总量有很大的影响。在过去20年的研究中，替代方法一再显示出不合格的结果。在这里，一种替代方法，Kaplan-Meier（KM）方法用于整个医疗和工业统计领域，用于获得总数。KM估计值受最不精确数据的影响远小于使用替代计算的估计值。不需要对数据的分布（无论它们遵循正态分布还是其他分布）做出任何假设。直接应用KM计算的毒性当量浓度（TEC）。Integr Environ Assess Manag 2010;6：361-366. (C)2009年SETAC
Low-level contaminants often are present below the detection or reporting limits of a laboratory, resulting in values reported as a nondetect or less than How can these values be summed along with detected concentrations to obtain a total, particularly when weighting factors such as toxic equivalence factors (TEFs) are used? The most common method employed by environmental scientists for summing nondetects along with detected values is to substitute one-half the detection limit for each nondetect. This substitution allows the least precise measurements, data with high detection limits, to have a strong influence on the resulting total amount. Substitution methods have repeatedly been shown to provide substandard results in studies over the last 2 decades. Here an alternative, the Kaplan-Meier (KM) method used throughout the fields of medical and industrial statistics, is used to obtain the total. KM estimates are far less affected by the least precise data than are estimates computed using substitution. No assumptions about the distribution of data (whether they follow a normal or other distribution) need be made. Direct application of KM to computation of toxicity equivalence concentrations (TECs) is shown. Integr Environ Assess Manag 2010;6:361-366. (C) 2009 SETAC