Bioaerosol Deposition to Food Crops near Manure Application: Quantitative Microbial Risk Assessment.

Production of both livestock and food crops are central priorities of agriculture; however, food safety concerns arise where these practices intersect. In this study, we investigated the public health risks associated with potential bioaerosol deposition to crops grown in the vicinity of manure application sites. A field sampling campaign at dairy manure application sites supported the emission, transport, and deposition modeling of bioaerosols emitted from these lands following application activities. Results were coupled with a quantitative microbial risk assessment model to estimate the infection risk due to consumption of leafy green vegetable crops grown at various distances downwind from the application area. Inactivation of pathogens ( spp., spp., and O157:H7) on both the manure-amended field and on crops was considered to determine the maximum loading of pathogens to plants with time following application. Overall median one-time infection risks at the time of maximum loading decreased from 1:1300 at 0 m directly downwind from the field to 1:6700 at 100 m and 1:92,000 at 1000 m; peak risks (95th percentiles) were considerably greater (1:18, 1:89, and 1:1200, respectively). Median risk was below 1:10,000 at >160 m downwind. As such, it is recommended that a 160-m setback distance is provided between manure application and nearby leafy green crop production. Additional distance or delay before harvest will provide further protection of public health.

Emission and Dispersion of Bioaerosols from Dairy Manure Application Sites: Human Health Risk Assessment.

In this study, we report the human health risk of gastrointestinal infection associated with inhalation exposure to airborne zoonotic pathogens emitted following application of dairy cattle manure to land. Inverse dispersion modeling with the USEPA's AERMOD dispersion model was used to determine bioaerosol emission rates based on edge-of-field bioaerosol and source material samples analyzed by real-time quantitative polymerase chain reaction (qPCR). Bioaerosol emissions and transport simulated with AERMOD, previously reported viable manure pathogen contents, relevant exposure pathways, and pathogen-specific dose-response relationships were then used to estimate potential downwind risks with a quantitative microbial risk assessment (QMRA) approach. Median 8-h infection risks decreased exponentially with distance from a median of 1:2700 at edge-of-field to 1:13 000 at 100 m and 1:200 000 at 1000 m; peak risks were considerably greater (1:33, 1:170, and 1:2500, respectively). These results indicate that bioaerosols emitted from manure application sites following manure application may present significant public health risks to downwind receptors. Manure management practices should consider improved controls for bioaerosols in order to reduce the risk of disease transmission.

Effects of growth conditions and NAPL presence on transport of Pseudomonas saccharophilia P15 through porous media.

Extensive research has been done to characterize transport of bacteria in porous media; however, little is understood on how the presence of non-aqueous phase liquids (NAPLs) coupled with the growth state and carbon source of bacteria affect bacterial transport. The objective of this research is to quantify the bacterial adhesion of Pseudomonas saccharophilia P15 (P15), which is known to biodegrade polycyclic aromatic hydrocarbons (PAH) and to interact with coal tars, within a NAPL-water-mineral system. Through a series of short-pulse column experiments, the transport and deposition of P15 in porous media (quartz sand) as a function of growth state and carbon sources (peptone and naphthalene), and in the presence and absence of residual NAPL (hexadecane), is measured and evaluated. Coating 20% of the quartz grain with hexadecane as a model NAPL increased the retention of P15 by as much as a factor of 26 as compared to the retention exhibited in quartz sand with no NAPL present. P15 grown on peptone and in the late exponential growth state exhibited a greater amount of deposition within the hexadecane column than when it was grown on naphthalene or was in early exponential growth phase. During early growth stage P15 grown on naphthalene adhered stronger to the porous media compared to when grown on peptone. Results were compared with results of MATH assays, where P15 partitioning to hexadecane was evaluated as a function of carbon source and growth state.

Characterization of DNAPL from the U.S. DOE Savannah River Site.

The composition of chlorinated hydrocarbon DNAPLs (dense non-aqueous phase liquids) from field sites can be substantially different than the material originally purchased for use as a solvent. Waste management practices at the U.S. Department of Energy's (DOE) Savannah River Site (SRS) included co-disposal of a wide range of organic and inorganic wastes. In 1991, a clear, orange-colored DNAPL was found in two wells near the SRS M-area settling basin. Waste effluent from the fuel and target fabrication facilities that were discharged to this settling basin included acids, caustics, metals and chlorinated solvents. The characterization of the SRS DNAPL suggests that numerous constituents partitioned into the DNAPL during its use as a solvent, co-disposal and ultimate migration through the subsurface. Trace constituents in the DNAPL include metals, from processing operations or co-disposal practices and subsurface minerals, high molecular weight hydrocarbons and alkyl esters, and acids. This complex mixture results in DNAPL-water interfacial properties that are substantially different than would be expected from a simple mixture of PCE and TCE. Under conditions when there is a high DNAPL to water volume ratio, a semi-rigid film accumulates on water droplets suspended in the DNAPL. It is concluded that the array of precipitated metal species comprising this film contributes to the interfacial tension that is over an order of magnitude lower than expected for a "clean" PCE/TCE mixture.