VIRUS SURVIVAL IN SEWAGE-SLUDGE AMENDED DESERT SOIL

Currently Pima County, Arizona, disposes all of its anaerobically dige sted sewage sludge in liquid form (1.5% solids) on agricultural land u sed for non-food crop production by subsurface injection or surface sp reading. Present in these sludges are human enteric viruses in concent rations as high as 1,000 per liter of sludge. These viruses could pote ntially contaminate surface and groundwater sources during periods of irrigation or extended rainfall. This study was designed to assess the survival of viruses under field conditions typical of the arid Southw estern United States during the winter and summer months. This study w as also conducted in the laboratory to simulate field conditions. Soil samples taken from freshly amended fields were seeded with poliovirus type 1 (stock titer = 10(6)/ml) and bacteriophage MS2 (stock titer = 10(10)/ml) and thoroughly mixed with the sludged soil. The seeded samp les were put into containers and buried 10 cm below the soil surface, and samples were taken at pre-determined time intervals. Average soil temperature (measured at the 10 cm depth) ranged from 15-degrees-C in the winter to 33-degrees-C in the summer. Soil moisture decreased from 25% to 15% in the winter and from 40% to less than 5% in the summer. During the winter study, no inactivation of poliovirus was observed af ter 7 days, while greater than a 90% reduction was observed for MS-2. During the summer study, no poliovirus was recovered after 7 days, and no MS-2 was recovered after 3 days. The results of this study suggest that high soil temperature and rapid loss of moisture limit the survi val of viruses in desert soils.