Human pathogenic and lung inflammatory aerosol exposures associated with the land application of biosolids.

摘要

Land application of biosolids (treated sewage sludge) to agricultural fields generates a significant emission of respirable aerosols that can move off-site and expose downwind communities to biosolids constituents. Accurate estimation of infectious and respiratory health risks associated with this practice requires better knowledge of pathogen content and lung inflammatory potential for biosolids of class A and class B quality. Biosolids from twenty-nine U.S. utilities were surveyed for resistant bacterial and viral pathogens, associated indicators, and lung inflammatory agents (e.g. endotoxins)---four stabilization processes were targeted including class B mesophilic anaerobic digestion, and class A temperature-phased anaerobic digestion, composting, and heat pelletization. Both culturable indicator and qPCR-based concentrations of human adenovirus spp., Legionella pneumophila, Staphylococcus aureus, and Clostridium difficile were significantly lower and detected less frequently in class A biosolids, while lung inflammatory agents were comparable between the two classes. Enterococci qPCR was more indicative of pathogen inactivation behavior than fecal coliforms through biosolid treatment and could circumvent specificity issues associated with using multi-species indicators when monitoring in complex biosolid microbiological communities.;Pathogen densities in bulk biosolids were translated to an aerosol inhalation dose for a land application event using previously calibrated aerosol reconstruction, Gaussian aerosol transport, and intermittent exposure time models. Pathogen aerosol dose was affected more by biosolid treatments than separation distance from the biosolid field---using class A composting over class B MAD resulted in 2.6 log exposure reductions, while 165--500 m separation distances reduced exposure by 0.5--1.3 logs for a worst-case aerosol scenario. To further elucidate human health effects from a biosolid aerosol exposure, in vitro experiments exposed bronchial epithelial cells to respirable biosolids, animal manure, and soils. Lung cell cytotoxicity and induction of inflammatory cytokines were significantly increased in biosolid and animal manure exposures compared to agricultural soils---lung cytotoxicity results followed pathogen content trends, with MAD biosolids showing the highest cytotoxicity. Research outcomes provide a scientific basis for updating U.S. biosolid regulations---biosolid aerosol exposures could be decreased by 4-logs through mandating class A composting or similar treatment and requiring a minimum of 150 m separation distance between biosolid-applied fields and downwind communities.