Bioaerosols
The transportation, management, and application to land of fertilizers, animal manures, biosolids, or other materials can stir up dust and create small particles that may contain microorganisms (e.g. bacteria), some of which might be pathogenic (disease-causing). This can happen in enclosed facilities (e.g. compost facilities) as well as outside at farm sites.
In the late 1990s, there was concern and research regarding the possibility that pathogens and/or other emissions from Class B biosolids land application activities or biosolids composting facilities may cause health impacts to neighbors. (Note that there are few concerns about Class A biosolids, because they have been treated so levels of pathogens are similar to background soils or less.)
Research has found measurable health impacts in workers at confined feeding operations (e.g. hog farms) and compost facilities that process food waste, yard waste, and/or wastewater solids (sewage sludge). Apparently, exposure to high levels of organic dusts for extended periods of time - such as at composting facilities - can trigger measurable health impacts in some people.
The effects of exposure to unstabilized (raw) or Class B biosolids - which contain viable pathogens and may generate bioaerosols and dust - are not as clear. Research regarding the health of workers at wastewater treatment facilities, who are most highly exposed to unstabilized wastewater solids, has not found significant health impacts. Such workers are generally not considered to be in hazardous work conditions. Still, those managing large volumes of Class B biosolids or unstabilized wastewater solids (including workers at wastewater treatment facilities) are advised to use personal protective equipment, wash hands frequently, and avoid hand-to-mouth contact during work (see the NIOSH guidance). The same precautions are advised when working with untreated animal manures that also contain pathogens.
There are reports in newspapers and on the Internet of health impacts - mostly respiratory and headaches - to neighbors of Class B land application sites. However, research showing a causal relationship between Class B biosolids and the health impacts is lacking. Often, intense malodors are also present when impacts are reported, and there is evidence that odors cause physiological impacts. This complicates the situation. Some biosolids have the potential to create malodors, and some people feel ill when exposed to bad odors, be they from biosolids or animal manures.
Researchers at the University of Arizona have collected air samples at Class B land application sites (photo) during actual land application activities around the country (Univ. of AZ news release, 2010). They concluded that risks to neighbors from bioaerosols from Class B land application are minimal.
A health study of neighbors to permitted land application sites in Ohio published in 2008, appeared to find health impacts. However, the study's conclusions were subsequently challenged and the authors released a clarification that they had found no causal relationship between biosolids and people’s self-reported health concerns (contact NEBRA for copies of these documents).
U. S. EPA conducted an evaluation of the potential for impacts from bioaerosols and other parameters (e.g. soil microbial population impacts, pathogens, and trace chemical fate in soils) at a land application site in North Carolina. The project summary states: "While in some cases microbes were detected, no bacterial pathogens or viruses were detected in the air samples collected. This study was not able to determine whether this result was because microbes were absent, or present and not detected. Approximately 20% of the soil samples contained detectable concentrations of enteric viruses, Salmonella spp. and viable helminth ova. Odors were detected in the air after biosolids application, but dissipated after 4 days. The summary and report were published in 2012.
Given the hundreds of biosolids land application programs around the continent, many of which have been ongoing for a decade or more, and relatively few complaints of health impacts, this concern seems to be minimal and possibly localized.
In the meantime, those managing Class B biosolids are required by all Northeast state and provincial regulations to maintain setbacks from neighbors for Class B biosolids management activities, and public access to Class B land application sites is restricted. In recent years, there have been few complaints in this region.
Those managing biosolids land application programs strive to manage odors and take measures to reduce the potential for bioaerosol emissions or other exposures to pathogens. For example, biosolids that have been anaerobically digested tend to have low potential for odors, and injection of biosolids or incorporation in the soil immediately after application dramatically reduces any risk of pathogen exposure.
Similar measures are not required for the use of animal manures, of which there is a far greater amount being used on farms. And animal manures also contain trace elements (e.g. heavy metals), chemicals, including microconstituents (e.g. antibiotics), and pathogens.
In summary, ...
...a literature review on this topic, conducted by Solinov for the Quebec environment ministry, concluded: “the risks for exposed workers, such as farmers, are relatively low and even extremely low for people living in the vicinity of the sites where biosolids are being applied. Available information also suggests that the potential health risks are relatively lower than those associated with the management of manure” (Forcier, Francoise, 2002: Biosolids and Bioaerosols: The Current Situation).
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