Biosolids Case Study
- Hazard ID
- Exposure Assessment
- Dose Response
- Risk Characterization
- Risk Management
Our group focuses on two pathogens: one from bacteria group and one from virus group. The bacteria group that we are focusing on are: Campylobacter jejuni and the virus group is Adenovirus.
The Problem Significance In the yesteryears, wastes were often discharged into surface waters and polluted streams and rivers. The technology of widespread collection, treatment and disposal of wastewater effluent evolved in the mid-to late 19th century. The technology of waste systems has improved tremendously; thereby reducing the threat to our environment. Wastewater effluent has become much cleaner today. However, in the process of producing clean effluent, the process itself accumulates residues or solids. These solids are called sewage sludge or commonly biosolids (Ogg, 2014). The word biosolids is a new term used to describe municipal treatment plant solids which are tested and determined to be safe for land application. On the other hand, the word sludge is a generic term that most people use to refer to some type of unprocessed waste material. According to USEPA, Biosolids are defined as nutrient-rich organic materials resulting from the treatment of domestic sewage in a treatment facility. These residuals can be recycled and applied as fertilizer to improve and maintain productive soils and stimulate plant growth. In a nutshell, biosolids are treated sewage sludge. These must be carefully treated and monitored and must be used in accordance with regulatory requirements (United States Environment Protection Agency [USEPA], 2012). Biosolids management practices primarily involve land application, which can include the use of compost or other highly treated biosolids. Land application is defined by EPA as “the spreading, spraying, injection, or incorporation of sewage sludge, including a material derived from sewage sludge (e.g., compost and pelletized sewage sludge), onto or below the surface of the land to take advantage of the soil enhancing qualities of the sewage sludge” (Jenkins, Armstrong, & Monti, 2007). Biosolids contain significant amounts of nitrogen (N), phosphorus (P), and organic matter that can benefit crop production. The benefits of biosolids as soil amendments are similar to those provided by animal manures—they provide important plant nutrients and organic matter (College of Agricultural Sciences, Penn State University, 2014). Even though biosolids have enormous amounts of nutrients, beneficial for crop growth, their use is hindered due to concerns about pollutants in them, risk of disease, and nuisance issues such as odours. When properly treated and managed in accordance with existing regulations and standards, biosolids are safe for the environment and human health (USEPA, 1999). Hundreds of scientific studies have been conducted to investigate possible environmental and human health risks from the use of biosolids as soil amendments. Short-term risks would occur within a relatively short period after biosolids application. Such risks include excessively high soil pH, nutrient leaching or runoff, and transfer of pathogens to farm animals or humans. Long-term risks are those that result from repeated biosolids applications over many years and are associated primarily with the buildup of trace elements in soils (College of Agricultural Sciences, Penn State University, 2014). Pollutants that are found in biosolids can generally be divided into three categories namely inorganic contaminants, organic contaminants and pathogens (e.g., bacteria, viruses and parasites). For this particular paper, we would be focussing on the presence of pathogens in biosolids. Four major types of human pathogens can be found in biosolids: bacteria, viruses, protozoa, and helminths. Some references also include fungi. Potential transmission pathways of human pathogens from biosolids include air, soil, and water. In addition, it is possible that vectors, such as flies, could transmit pathogens from biosolids (Straub, Pepper, & Gerba, 1993; Gattie & Lewis, 2004). There are two different classes of biosolids; Class A biosolids, which contain no detectible concentrations of pathogens and Class B biosolids have detectable concentrations of pathogens (USEPA, 2012 as cited in Jenkins, Armstrong, & Monti, 2007).
When considering human health effects from biosolids, risk assessment is key to providing appropriate protection to the public. It is a process for identifying potential adverse consequences along with their severity and likelihood. The present paper, therefore, tries to evaluate the existing literature to identify the data gaps for microbial risk assessment. Risk assessment is the process of analyzing potential losses from a given hazard using a combination of known information about the situation. The risk assessment for a particular issue forms the foundation for making a decision about future actions. That decision may be to perform additional analyses, to perform activities that reduce the risk, or to do nothing at all. Problem Formulation People can come in contact with land applied biosolids on through the following pathways: • Inhalation of aerosols from land application sites • Consumption of groundwater contaminated by land-applied biosolids • Direct ingestion of biosolids-amended soils • Ingestion of plants contaminated by land-applied biosolids • Consumption of surface water contaminated by runoff from a land application site For this particular paper, the focus, however, has been on incidental ingestion of four pathogens from hand-mouth transfer. The risk of illness from pathogens found in biosolids when people come in direct contact with them, and how do the various studies under consideration deal with them in terms of defining the risk estimates, assumptions, creating models etc. has been studied. A comparison among the various studies would be drawn towards the end to comment upon which model should be chosen over other and why. Also to suggest changes to be made to the spread sheet risk assessment tool.
Hazard Identification Cryptosporidium Cryptosporidium is a parasitic coccidian protozoan found in the intestinal tract of many vertebrates. The organism was first described in 1907 by Tyzzer, who recognised it was a coccidian. It is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are commonly known as "Crypto." The parasite is protected by an outer shell for it to survive outside the body for long periods and makes it tolerant to chlorine disinfection. Water is the most common method of transmission of this pathogen (CDC, 2013). Cryptosporidium is found in soil, food, water, or surfaces that have been contaminated with infected human or animal faeces. Transmission occurs through animal-to-human or human-to-human contact. People may also be infected by consuming contaminated water or food, or by swimming in contaminated water (for example in lakes or rivers) (Public Health England, 2013).
Enterovirus are any of a group of RNA viruses (including those causing polio and hepatitis A) which typically occur in the gastrointestinal tract, sometimes spreading to the central nervous system or other parts of the body. Enteroviruses are a genus of positive-sense single-stranded RNA viruses associated with several human and mammalian diseases. On the basis of their pathogenesis in humans and animals, the enteroviruses were originally classified into four groups, namely polioviruses, Coxsackie A viruses (CA), Coxsackie B viruses (CB), and echoviruses. Enteroviruses isolated more recently are named with a system of consecutive numbers: EV68, EV69, EV70, and EV71, etc. Enteroviruses affect millions of people worldwide each year, and are often found in the respiratory secretions (e.g., saliva, sputum, or nasal mucus) and stool of an infected person. Historically, poliomyelitis was the most significant disease caused by an enterovirus, poliovirus. There are 62 non-polio enteroviruses that can cause disease in humans: 23 Coxsackie A viruses, 6 Coxsackie B viruses, 28 echoviruses, and 5 other enteroviruses. Poliovirus, as well as coxsackie and echovirus are spread through the fecal-oral route. Infection can result in a wide variety of symptoms ranging from mild respiratory illness (common cold), hand, foot and mouth disease, acute hemorrhagic conjunctivitis, aseptic meningitis, myocarditis, severe neonatal sepsis-like disease, and acute flaccid paralysis (Oberste, Maher, Kilpatrick, & Pallansch 1999). Adenovirus Adenovirus infections most commonly cause illness of the respiratory system; however, depending on the infecting serotype, they may also cause various other illnesses. Illnesses of adenovirus also include gastroenteritis, conjunctivitis, cystitis, and rash illness. Symptoms of respiratory illness caused by adenovirus infection range from the common cold syndrome to pneumonia, croup, and bronchitis. Patients with compromised immune systems are especially susceptible to severe complications of adenovirus infection (Wadell et al., 1987). Adenoviruses are transmitted by direct contact, fecal-oral transmission, and occasionally waterborne transmission. Some types are capable of establishing persistent asymptomatic infections in tonsils, adenoids, and intestines of infected hosts, and shedding can occur for months or years. Epidemics of febrile disease with conjunctivitis are associated with waterborne transmission of some adenovirus types, often centering around inadequately chlorinated swimming pools and small lakes. For some adenovirus serotypes, the clinical spectrum of disease associated with infection varies depending on the site of infection; for example, infection with adenovirus 7 acquired by inhalation is associated with severe lower respiratory tract disease, whereas oral transmission of the virus typically causes no or mild disease. Outbreaks of adenovirus-associated respiratory disease have been more common in the late winter, spring, and early summer; however, adenovirus infections can occur throughout the year (Gracy, 2006).
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