Review: Indicator bacteriophages in sludge, biosolids, sediments and soils

Solid or semisolid matrices polluted with fecal remnants can be highly loaded with pathogens, especially viruses, and play a substantial role in the persistence and dispersion of pathogens in the water cycle. Water quality regulations and guidelines are increasingly including bacteriophages infecting enteric bacteria as indicators of fecal and/or viral pollution. However, more data are needed about viral indicators in contaminated solids to develop effective sanitation strategies for the management of raw and treated sludge, fecal sludge, manures and slurries. Also, the exact role of sediments and soil in the transmission cycle of viral pathogens still needs to be determined. This review aims to provide an update on available data for concentrations of indicator bacteriophages in different solid matrices as well as their resistance to treatments and persistence in solids. The conclusion reached is that there is a need for improved and standardized methodologies for bacteriophage extraction, detection and enumeration in solids. Reports indicate that these contain higher levels of somatic coliphages in comparison with traditional bacterial indicators and F-specific RNA coliphages. Water body sediments and soil have been found to be notable reservoirs of somatic coliphages, which are more persistent in nature and resistant to sludge treatments than Escherichia coli and fecal coliforms and F-specific RNA coliphages. Thus, somatic coliphages show up as excellent complementary indicators for the prediction of pathogenic viruses in solids.