Monitoring the aftermath of Flint drinking water contamination crisis: Another case of sampling bias?
Monitoring the aftermath of Flint drinking water contamination crisis: Another case of sampling bias?
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DOI：
10.1016/j.scitotenv.2017.02.183
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发表时间：
2017-07-15
影响因子：
9.8
通讯作者：
Goovaerts, Pierre
中科院分区：
文献类型：
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作者：
Goovaerts, Pierre
在弗林特市改用弗林特河作为供水后，弗林特饮用水含铅量高的报告出现延误，部分原因是抽样地点的选择偏离了铅管网络。自从弗林特恢复危机前的饮用水源以来，该州一直在选定的“哨点”监测水铅含量。在为期两个月的第一阶段，对739个住宅进行了抽样调查，其中大多数是每两周一次，以确定配电系统的总体健康状况，并跟踪铅含量的时间变化。在同一时期，还通过一项自愿方案收集了水样，有关公民获得免费检测工具包，并自行进行采样。州政府官员依靠以前的数据来证明水质的稳步改善。然而，最近对自愿抽样收集的数据进行的一项分析显示，铅含量随着时间的推移而增加，这是一个相反的趋势。本文着眼于潜在的抽样偏差来解释这种差异。虽然房子较高的WLL更有可能被反复抽样，自愿抽样结果相当好地再现弗林特住房存量的主要特征（即存在的铅服务线（LSL），建设年）。国家控制抽样的代表性较低;例如，具有LSL的哨点大多建于1935年至1950年之间的较低贫困地区，这可能会妨碍我们理清LSL和房屋管道（旧房屋内的铅固定装置和管道）对WLL的影响。此外，在两个最贫困的病房中没有LSL的哨点，包括在供水切换后血铅水平升高的儿童百分比增加了两倍的地方。校正采样偏差缩小了采样程序之间的差距，但总体时间趋势仍然相反。(C)2017爱思唯尔B. V.保留所有权利。
The delay in reporting high levels of lead in Flint drinking water, following the city's switch to the Flint River as its water supply, was partially caused by the biased selection of sampling sites away from the lead pipe network. Since Flint returned to its pre-crisis source of drinking water, the State has been monitoring water lead levels (WLL) at selected "sentinel" sites. In a first phase that lasted two months, 739 residences were sampled, most of them bi-weekly, to determine the general health of the distribution system and to track temporal changes in lead levels. During the same period, water samples were also collected through a voluntary program whereby concerned citizens received free testing kits and conducted sampling on their own. State officials relied on the former data to demonstrate the steady improvement in water quality. A recent analysis of data collected by voluntary sampling revealed, however, an opposite trend with lead levels increasing over time. This paper looks at potential sampling bias to explain such differences. Although houses with higher WLL were more likely to be sampled repeatedly, voluntary sampling turned out to reproduce fairly well the main characteristics (i.e. presence of lead service lines (LSL), construction year) of Flint housing stock. State-controlled sampling was less representative; e.g., sentinel sites with LSL were mostly built between 1935 and 1950 in lower poverty areas, which might hamper our ability to disentangle the effects of LSL and premise plumbing (lead fixtures and pipes present within old houses) on WLL. Also, there was no sentinel site with LSL in two of the most impoverished wards, including where the percentage of children with elevated blood lead levels tripled following the switch in water supply. Correcting for sampling bias narrowed the gap between sampling programs, yet overall temporal trends are still opposite. (C) 2017 Elsevier B.V. All rights reserved.