RD14 - Land Applied Biosolids Epidemiological Pilot Study and Pathogen Content Analysis – December 12, 2019
The 2018 General Assembly appropriated $100,000 to the Virginia Department of Health (VDH) to study land-applied biosolids in Virginia, specifically health risks and pathogen content. Fifty thousand dollars ($50,000) was appropriated to conduct a pilot epidemiological study of the human health effects of land application of biosolids, following which VDH must submit its findings and a proposed design for a full-scale epidemiological study, if needed. Fifty thousand dollars ($50,000) was appropriated to perform sample testing of Class B biosolids that are land applied in Virginia to determine their pathogen content. VDH used test results to inform its epidemiological pilot study and assessment of aerosol infection risks.
VDH mailed health based surveys to addresses determined to be within 1,000 feet of sites where the Department of Environmental Quality (DEQ) received notification that Class B biosolids were going to be land applied. VDH received completed surveys and participants were put into two groups: those living within 200 feet of fields where Class B biosolids was land applied and those living between 200 and 1,000 feet of fields where Class B biosolids was land applied. VDH mailed 2,670 surveys between April and June 2019 and received a combined total of 68 responses from the two study populations. The majority (96%) of all survey participants reported that their health was fair or better with 20 (29%) reporting that they were ill or had symptoms in the past two weeks. Seven of the 20 with symptoms or illnesses reported they required medical care. The most reported symptom or illness in the past two weeks included runny nose and congestion (14), sore throat (9), and headache (8). Forty-five (66%) reported detecting biosolids odor in the past two weeks with seven reporting the level of odor as faint, 24 not providing an answer, and 38 reporting the level of odor as moderate or strong. When asked about biosolids impact on quality of life, of the 68 that provided an answer 32 (47%) reported that biosolids land application affected their quality of life.
Biosolids samples were collected from 34 application sites, four storage facilities, and two wastewater treatment facilities between March and May 2019. VDH contracted with the University of Arizona to test biosolids samples for pathogens which included seven microorganisms or classes of microorganisms. Pathogens tested included bacteria, viruses, and helminth ova. A total of 40 biosolids samples including 39 Class B biosolids and one Class A biosolids samples were sent to the University of Arizona. The biosolids treatment type identified for the 40 samples included: aerobic digestion (10), anaerobic digestion (12), lime stabilization (16), pasteurization/digestion (1), and thermal hydrolysis (1).
Fecal coliform bacteria can be used as a measure of treatment effectiveness for Class B biosolids. The Class B biosolids fecal coliform standard for effective treatment is a geometric mean of 7 samples <2,000,000 most probable number/gram (MPN/g), for biosolids producers opting to use this monitoring requirement. Five anaerobically digested biosolids from different producers had fecal coliforms greater than 2,000,000 MPN/g.
The number of samples with measurable concentration of Salmonella by treatment type reported: aerobic digestion (6), anaerobic digestion (8), and lime stabilization (1). There is no Salmonella standard for Class B biosolids; however, the Salmonella standard for Class A biosolids generated for unrestricted use is 3 MPN/4g. One lime stabilization treated sample Salmonella content was reported as 5 MPN/4g compared to six aerobic and seven anaerobically digested biosolids samples that were reported to have Salmonella content greater than 3 MPN/4g. Measurable concentration of pathogenic viruses were reported in five aerobic and one anaerobic digested biosolids samples. Ascaris was not detected in any samples.
VDH used quantitative microbial risk assessment to calculate the probability of aerosol infection by each pathogen using the laboratory results. The risk of aerosol infection was calculated using 6.5 feet, 200 feet, and 400 feet as the distance from the land application site and the measured pathogen concentrations. The aerosol risk of infection from Salmonella measured in collected samples was only considered elevated at 6.5 feet and 200 feet for one sample. However, there is no elevated risk to Salmonella if the geometric mean concentration of all samples is used in the risk calculation. The aerosol risk of infection from rotavirus and adenovirus aerosol infection at 6.5 feet from the biosolids application site was elevated. There was also an increased risk of rotavirus and adenovirus aerosol infection at 200 feet when calculating the risk using the sample with the maximum concentration. There was an increased risk of listeria aerosol infection at 6.5 feet from the biosolids application site when calculating the risk using the maximum and geometric mean concentrations of samples. There was also an increased risk of Listeria aerosol infection at 200 feet from the biosolids application site. There was no increased risk for any of the above pathogens at 400 feet from the biosolids application site.
The pathogen study shows that Class B biosolids generated by lime stabilization have fewer pathogens than aerobic or anaerobically generated Class B biosolids. Therefore, additional health studies to evaluate symptom onset related to pathogens do not need to include fields where Class B biosolids generated by lime stabilization is applied. The quantitative risk assessment performed using the pathogen results indicate that there is no aerosol risk to any pathogen analyzed at a distance of 400 feet from the application site. The epidemiological survey response rate was low and additional resources and employee hours are necessary to adequately study the impact on health. The survey responses received suggest that the quality of life is impacted and can be attributed to the odor.