Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, United States.
USDA-Agricultural Research Service, Environmentally Integrated Dairy Management Research Unit, 2615 Yellowstone Drive, Marshfield, Wisconsin 54449, United States.
Environ Sci Technol. 2020 Jan 7;54(1):137-145. doi: 10.1021/acs.est.9b03274. Epub 2019 Dec 9.
Lesser pathogen prevalence is well recognized in granular versus fractured aquifers; however, the impact of residence time (inactivation/death) versus removal (pore-scale delivery to surfaces) on pathogen prevalence remains unaddressed. The objective of this study was to examine the specific role of pore-scale delivery to surfaces (removal) as an explanation of contrasting pathogen prevalence in granular versus fractured media from Wisconsin. Inactivation/death was obviated by the use of nonbiological colloids in column transport experiments conducted in representative media from the two Wisconsin sites. Trends in retention as a function of colloid size were examined using nano- to microsized (0.1-4.2 μm) carboxylate-modified polystyrene latex microspheres that represented virus- to protozoa-sized pathogens. Several orders of magnitude greater removal of all colloid sizes were observed in granular relative to those in fractured media, whereas the size corresponding to minimum retention contrasted between the two media. Particle trajectory simulations in collectors (flow fields with surfaces) representing granular versus fractured media captured the observed contrasting retention and trends with colloid size. These results demonstrate that flow impingement on surfaces at forward flow stagnation zones drives contrasting pore-scale delivery to surfaces in granular versus fractured media and potentially the observed contrasting pathogen prevalence in granular versus fractured aquifers.
颗粒状含水层中的病原体流行程度较低，这一点已得到广泛认可；然而，关于停留时间（失活/死亡）与去除（通过孔隙尺度到达表面）对病原体流行程度的影响，仍有待解决。本研究的目的是考察通过孔隙尺度到达表面（去除）这一特定机制，能否解释在来自威斯康星州的颗粒状和裂隙状介质中，病原体流行程度存在差异这一现象。在两个威斯康星州地点的代表性介质中进行的柱状传输实验中，通过使用非生物胶体，避免了失活/死亡的发生。通过使用代表病毒到原生动物大小的病原体的纳米到微尺寸（0.1-4.2μm）羧酸修饰聚苯乙烯乳胶微球，考察了胶体尺寸与保留之间的关系。与裂隙介质相比，所有胶体尺寸在颗粒状介质中的去除量都要高出几个数量级，而在两种介质中，最小保留对应的尺寸则相反。在代表颗粒状和裂隙状介质的收集器（具有表面的流场）中进行的颗粒轨迹模拟，捕获了观察到的保留和胶体尺寸之间的对比趋势。这些结果表明，在向前流动停滞区，颗粒状介质中的流动冲击表面，会导致与裂隙状介质相比，出现不同的孔隙尺度到达表面的情况，这可能是颗粒状和裂隙状含水层中观察到的病原体流行程度存在差异的原因。
