THERMOTOLERANT CLOSTRIDIA AS AN AIRBORNE PATHOGEN INDICATOR DURING LAND APPLICATION OF BIOSOLIDS

Since biosolids could harbor a variety of potentially infectious micro organisms, there are concerns of human exposure to these microbial pat hogens in population centers surrounding sites where biosolids are lan d applied. A field study was conducted at a large commercial biosolid application site to determine if thermotolerant clostridia could be em ployed as a microbial indicator in determining the presence of such fe cal contamination in aerosols. Even though the applied biosolids harbo red as much as 10(7) MPN fecal and total coliforms per gram wet weight , these traditional indicators were undetectable at locations having t he greatest potential for aerosolization. Thermotolerant clostridia an d bacteriophages, however, were detectable in 73% and 53% of the sampl es, respectively. Hydrogen sulfide producing bacteria as a group, were detected in 93% of the samples. Even at sites directly in the vicinit y of the biosolid application, thermotolerant clostridia were detected in 26% of the samples, as compared with the fecal and total coliforms which were detected in only 1 out of 15 (6.6%) samples. Since municip al sewage sludges usually undergo anaerobic digestion before land disp osal, it would favor the selection of thermotolerant clostridia within these biosolids. Moreover, clostridia also could be ribotyped using t he 16S-23S interspacer region length polymorphism to identify the orig ins or sources of aerosol contamination. Thermotolerant clostridia cou ld thus serve as a reliable indicator to determine the presence of mic robial pathogens and biosolid derived microbial populations in aerosol s being generated from biosolid application programs.