Currently about 60% of all biosolids are land applied in the United States, with most of the land receiving Class B biosolids.  Class B biosolids may contain pathogenic viruses, bacteria, protozoan parasites and helminths, and although the type of land and crops to which Class B biosolids is applied is controlled, public concern in some areas of the United States has resulted in the banning of Class B biosolids.  Much of the concern is due to the limited amount of data on the fate and transport of pathogens after land application.  Specifically, indirect routes of exposure such as contact with bioaerosols away from the land application sites, or consumption of groundwater contaminated with pathogens, have warranted attention.  However, recent research conducted at the University of Arizona has addressed many of these issues.

We have also evaluated the overall benefits and risks of biosolids on the soil microbial community following 20 years of land application of liquid Class B biosolids.  Having an agricultural field with a 20 year history of biosolids application provided a unique opportunity for the evaluation of the long- term effects of biosolids on various biological parameters. In this work we evaluated the effect of long-term application of biosolids on soil microbial numbers (including bacteria, fungi and actinomycetes), microbial diversity and microbial activity.  In addition we determined if microbial indicator organisms and pathogens found in the original biosolids persisted in the field soil following land application.