Department of Earth and Environmental Sciences, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
Water Res. 2010 Feb;44(4):1235-45. doi: 10.1016/j.watres.2009.10.010. Epub 2009 Oct 22.
Polystyrene latex microspheres are widely used as surrogates for biocolloid transport in porous media; however, relatively few studies directly compare microsphere transport with that of the microorganism it is intended to represent, particularly at the field scale. Here, we compared the transport behaviour of a bacterium (Escherichia coli RS2g; 1.2 microm in diameter) and three different sized microspheres (1.1, 3.9, and 4.8 microm in diameter) within undisturbed agricultural field soil following infiltration under partially saturated conditions. The soil contained significant macroporosity. A tension infiltrometer was used to control the application of a transport solution containing Brilliant Blue FCF dye to two plots. A >2 log reduction in the concentration of all colloids was observed from the soil surface to 5 cm depth in both plots. The concentration of colloids in the soil was generally proportional to the intensity of soil dye staining; however, both the E. coli RS2g bacterium and the 1.1 microm microspheres appeared to be transported deeper than the other colloids and the visible dye along root holes at the bottom of the profile in both plots. The similarities in size and zeta potential of the 1.1 microm microspheres and the E. coli RS2g likely contributed to that outcome. Colloid concentrations in dyed soil by depth were similar between the two plots, despite differences in soil properties and infiltration patterns. The properties of the colloids and macropore density were the most important factors affecting colloid transport. These results suggest that microspheres with size and surface properties similar to the microbe of interest are useful surrogates to trace potential pathways of transport in the subsurface.
聚苯乙烯乳胶微球被广泛用作多孔介质中生物胶体运移的示踪剂；然而，很少有研究直接比较微球运移与它所代表的微生物的运移，特别是在野外尺度上。在这里，我们比较了一种细菌（大肠杆菌 RS2g；直径 1.2 微米）和三种不同大小的微球（直径 1.1、3.9 和 4.8 微米）在部分饱和条件下渗透进入未扰动农业土壤后的运移行为。土壤中含有大量的大孔隙。张力入渗仪用于控制含有亮蓝 FCF 染料的运移溶液在两个试验区的应用。在两个试验区中，从土壤表面到 5 厘米深度，所有胶体的浓度都观察到了>2 个对数的减少。胶体在土壤中的浓度通常与土壤染料染色的强度成正比；然而，在两个试验区中，大肠杆菌 RS2g 细菌和 1.1 微米的微球似乎比其他胶体和可见染料更深入地运移，沿着剖面底部的根孔。1.1 微米微球和大肠杆菌 RS2g 的大小和zeta 电位相似，可能导致了这种结果。尽管土壤性质和入渗模式存在差异，但两个试验区中染色土壤的胶体浓度随深度的分布相似。胶体和大孔密度的性质是影响胶体运移的最重要因素。这些结果表明，具有与感兴趣微生物大小和表面性质相似的微球是追踪地下潜在运移途径的有用示踪剂。
