Strong Retardation in the Transport of Burkholderia cepacia during Infiltration into a Volcanic Ash Soil

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Microbial contamination of groundwater by bacteria as a result of human activities has gained considerable attention because of public health concerns. The objective of this study was to examine the vertical transport and accumulation of bacteria during infiltration of water into an Andosol derived from volcanic ash with variable surface charge as well as a high organic matter content, which may enhance the adsorption of bacteria by soil particles. First, 70−720 ml of Burkholderia cepacia suspension containing 10⁷ cells ml⁻¹ was supplied to the upper surface of repacked soil columns (Kannondai Andosol and Sawara Gray Lowland soil for comparison), 5.0 cm in diameter and 17.5 to 100 cm long, at a negative pressure head of −5 cm using a disk permeameter. After terminating the infiltration, the columns were rapidly sectioned and profiles of the number of B. cepacia were determined using a selective medium containing tetracycline (10 mg l⁻¹), ampicillin (100 mg l⁻¹) and cycloheximide (300 mg l⁻¹). The distance traveled by B. cepacia in the Kannondai Andosol was found to be smaller than that of water derived from the infiltrated suspension, with B. cepacia heavily accumulated at a 0−5 cm depth of the soil in all columns. In contrast, B. cepacia moved deeper in the Sawara soil, and the travel distance increased with the volume of the suspension infiltrated. The observed difference in the bacterial transport could be due to the differences in the surface electrical properties and organic matter content, or alternatively, the pore size distribution of the two soils.