评估自来水中消毒副产物估计水平的空间波动、时间变异性和测量误差：对暴露评估的影响。
Assessing spatial fluctuations, temporal variability, and measurement error in estimated levels of disinfection by-products in tap water: implications for exposure assessment.
作者信息
Symanski E, Savitz D A, Singer P C
机构信息
Environmental Sciences, University of Texas School of Public Health, Houston, Texas 77030, USA.
出版信息
Occup Environ Med. 2004 Jan;61(1):65-72.
AIMS
To assess spatial fluctuations, temporal variability, and errors due to sampling and analysis in levels of disinfection by-products in routine monitoring tap water samples and in water samples collected in households within the same distribution system for an exposure assessment study.
METHODS
Mixed effects models were applied to quantify seasonal effects and the degree to which trihalomethane (THM) levels vary among households or locations relative to variation over time within seasons for any given location. In a separate analysis, the proportion of total variation due to measurement error arising from sampling and analysis was also quantified.
RESULTS
THM levels were higher in the summer relative to other seasons. Differences in the relative magnitude of the intra- and inter-household components of variation were observed between the two sets of THM measurements, with a greater proportion of the variation due to differences within seasons for the routine monitoring data and a greater proportion of the variation due to differences across locations for the exposure assessment study data. Such differences likely arose due to differences in the strategies used to select sites for sampling and in the time periods over which the data were collected. With the exception of bromodichloromethane, measurement errors due to sampling and analysis contributed a small proportion of the total variation in THM levels.
CONCLUSIONS
The utility of routine monitoring data in assigning exposure in epidemiological studies is limited because such data may not represent the magnitude of spatial variability in levels of disinfection by-products across the distribution system. Measurement error contributes a relatively small proportion to the total variation in THM levels, which suggests that gathering a greater number of samples over time with fewer replicates collected at each sampling location is more efficient and would likely yield improved estimates of household exposure.
目的
在一项暴露评估研究中，评估常规监测的自来水样本以及同一供水系统内家庭采集的水样中消毒副产物水平的空间波动、时间变异性以及采样和分析导致的误差。
方法
应用混合效应模型来量化季节效应，以及相对于任何给定位置在季节内随时间的变化，三卤甲烷（THM）水平在家庭或地点之间变化的程度。在另一项分析中，还量化了采样和分析产生的测量误差在总变异中所占的比例。
结果
夏季的THM水平高于其他季节。在两组THM测量值之间观察到家庭内和家庭间变异成分相对大小的差异，对于常规监测数据，季节内差异导致的变异比例更大，而对于暴露评估研究数据，不同地点差异导致的变异比例更大。这种差异可能是由于用于选择采样地点的策略以及收集数据的时间段不同所致。除溴二氯甲烷外，采样和分析导致的测量误差在THM水平总变异中所占比例较小。
结论
常规监测数据在流行病学研究中用于确定暴露的效用有限，因为此类数据可能无法代表整个供水系统中消毒副产物水平的空间变异性大小。测量误差在THM水平总变异中所占比例相对较小，这表明随着时间推移收集更多样本，每个采样地点收集较少的重复样本更有效，并且可能会改进对家庭暴露的估计。
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