Transport and retention of bacteriophages in two types of willow-cropped lysimeters

Irrigation and fertilization of short-rotation willow coppice with wastewater is a new way of reusing wastewater in Sweden. To evaluate the possible impact of viruses on groundwater quality, the transport and retention of the bacteriophage Salmonella Typhimurium type 28B were studied in two types of willow-cropped field lysimeters containing clay or sand soil. Phages were applied to the soil surface and moderate irrigation was done daily under field-like conditions. In the clay, soil rapid transport of bacteriophages was recorded with breakthrough at 1.2-m depth after 2-24 hours indicating macropore flow through the soil. Phage transport through the sand soil varied considerably, but was in general much slower and the phage retention much higher compared with the clay soil. The willow plants were not found to facilitate phage leaching. Instead, the results indicate the presence of phage retaining processes in the rhizosphere.