Types of Wastes
Wastes can be classified as follows-
Type 1
The liquid wastes comprise of PCB-based dielectric fluids removed from transformers and other equipment, PCB-based heat transfer and hydraulic fluids, PCB-contaminated solvents; washings of PCB-contaminated materials; and leakages, spillages and splashes of PCB-based fluids due to mishandling or accidents. The fluids removed from retro filled transformers should be regarded as Type 1 waste if the PCB concentration in the fluids exceeds 50 ppm.
Type 2
The combustible solid wastes contain the materials used in cleaning PCB equipment or absorbing the spillages such as rags, sawdust, contaminated clothing, gloves and gaskets, etc.
Type 3
Non-combustible solid waste include redundant PCB equipment such as capacitors, transformers, switchgears, circuit breakers, heat transfer systems etc., and the contaminated components removed from the equipment such as windings; PCB-contaminated containers and equipment such as metal drums, tanks, pumps and metal filters etc. Scrap transformers retro filled with substitute fluids should be regarded as Type 3 waste, if the PCB concentration in the fluid exceeds 50 ppm.
Wastes, which may contain PCBs, should be treated as hazardous unless and until laboratory tests provetheir absence. A simple test to differentiate PCBs from mineral oil is to make use of their difference in density. PCBs are heavier than water where as mineral oils are lighter. For equipments and products with proper name plates, the presence of PCBs could be easily verified by checking of the trade names, which appears, on the nameplates. If identification by trade names is not possible, the supplier or manufacturer should be contacted for details, or arrangement could be made with a qualified laboratory to undertake analysis. If the concentration of PCBs in the product or the waste is greater than 0.005% by weight (50 ppm), then the waste should be regarded as PCB waste. As PCBs decompose thermally to dioxins and dibenzofurans which are extremely toxic, great care must be taken in collecting samples for analysis, and the samples should be stored in a fire resistant room with a fixed fire suppression system. Further advice on PCB analysis may be obtained from the Environmental Protection Department (EPD).
Capacitors are hermetically sealed to reduce leakage risk and thus, cannot be tested to verify their contents. Most electrical capacitors manufactured since the 1930s were, however, filled with PCB liquids. It should be assumed, therefore, that all power capacitors regardless of size or use contain PCBs except where alternative (non-PCB) liquids are clearly indicated on the nameplate.
Small PCB capacitors have also been used in the starter units of fluorescent lights and fractional horse-power motors of the type used in domestic and light-industrial electrical equipment. Typically, they contain about 50 g of the lower chlorinated PCBs, mostly absorbed in the windings. They normally carry no label identifying the PCB content, and they are usually disposed of as part of the redundant appliances at landfill sites. Further, no special precautions need to be taken in the disposal of small capacitors unless the landfill operator advises that there is undue concentration at the landfill site. However, if sufficient quantities are located, they should be handled in the same manner as the larger electrical capacitors but need not be packaged as carefully because they contain no free fluids. It is understood that non-PCB materials are gaining wider use in capacitors for fluorescent light fittings, and the use of capacitor start motors in domestic appliances is diminishing due to design changes.
Under the Regulation, PCB waste is classified as chemical waste. Any person who produces or causes to be produced PCB waste is required to register with EPD as a chemical waste producer. Any chemical waste producer who fails to comply with the registration requirement commits an offence. A waste producer who intends to dispose of any PCB waste including old PCB equipment must therefore register with EPD. For more details, please refer to A Guide to the Registration of Chemical Waste Producer published by EPD. The Copies of the Guide and Registration forms can be procured from EPD.
Waste collectors who collect and transport PCB waste to an off-site facility for disposal have to be licensed by EPD. A registered waste producer must engage a licensed collector to transport the waste to an off-site disposal facility. Any registered waste producer who wishes to transport his own waste also has to be licensed. The details on the licensing requirements and the application procedures can be obtained from EPD.
Type 1 waste should be contained in adequately sealed and well labeled new or good condition steel drums of No.16 gauge or heavier and fitted with double bung fixed ends. The drums should be clearly marked DANGER CHEMICAL (PCB) WASTE in both English and Chinese, together with a chemical waste label. The drums should never be fully filled,and a 100 mm air space should be allowed between the top of the drums and the level of the liquid contents.
Type 2 waste should be packed in heavy duty and leak-proof polythene sacks and placed into new or good condition steel drums of No.16 gauge or heavier and fitted with removable lids. The drum should be properly sealed and labeled DANGER CHEMICAL (PCB) WASTE in both English and Chinese, together with a chemical waste label.
Type 3 waste, excluding large capacitors and transformers, should be packed in heavy duty, and leak-proof polythene sacks, and placed into new or good condition removable lid steel drums of No.16 gauge or heavier. The drums should be properly sealed and labeled DANGER CHEMICAL (PCB) WASTE in both English and Chinese, together with a chemical waste.
The capacitors should be left in their cases unopened, and stored with their terminals pointing upwards to prevent leakage from the capacitor bushings. The drums should be packed with non-combustible absorbent material such as vermiculite so that any leakage will be absorbed.
The large PCB capacitors, which do not fit into drums, should be inspected for leakage before packaging. If they are in poor physical condition, they should be packaged in heavy duty.
A. Livestock farm wastes
Concentrated, large-scale livestock production often creates great environmental problems. The large industrial farms bring in massive quantities of nutrients in the form of concentrate feed. And they produce far more waste than can be recycled as fertilizer and absorbed on nearby land. When intensive livestock operations are crowded together, the pollution can threaten the quality of the soil, water, air, biodiversity and ultimately public health.
The pollution damage is especially harmful when large numbers of animals are concentrated in sensitive areas around cities or close to water resources. The effluents are commonly discharged into the environment or stored in vast “lagoons” from, which waste may spill or leak into nearby streams, and ground water supplies. Noxious gases escape into the atmosphere, subjecting downwind neighbours to sickening odours and contributing to atmospheric aerosol formation, build-up of greenhouse gases and acid rain.
Much of the increased risk of pollution is caused by rupturing the traditional “short cycle” between livestock production and crop production. In less intensive, mixed farming systems, animal wastes are recycled as fertilizer by farmers who have direct knowledge and control of their value and environmental impact. Industrial production leads to a longer cycle, in which large quantities of wastes accumulate far from croplands where they could be safely and productively recycled. Therefore, even though intensive systems tend to make more efficient use of resources, with lower levels of water use, nutrient excretion and gas emissions per kilogram of meat or milk produced, they often generate more pollution than less intensive farms where manure is better managed.
North America. Therefore, major threats occur to the water, soil and air from concentrations of animal wastes.
Major forms of pollution associated with manure management in intensive livestock production include the following:
Eutrophication of surface water, as nitrogen, phosphorus and other nutrients are discharged or run off into streams, damaging wetlands and fragile coastal ecosystems, and fueling algae “blooms” that use up oxygen in the water, killing fish and other aquatic life. The livestock production has been identified as the major source of land-based nutrient pollution that has caused massive algae blooms in the South China Sea, including one in 1998 that killed more than 80 percent of the fish in 100 square kilometers along the coast of Hong Kong and Southern China. Leaching of nitrates and pathogens into ground water, threaten drinking water supplies. A 1998 study of 1600 wells located near factory farms in the United States, for example, found that 34 percent of the wells had been contaminated by nitrates, with 10 percent registering nitrate levels above the drinking water standard.
Buildups of excess nutrients and heavy metal in the soil, damaging soil fertility and shrinking arable land resources already strained by population growth, rising demand for food and conversion to other uses. In several Asian countries, fully one quarter of the total crop area suffers from significant nutrient overloads. Almost half the excess phosphorous supply comes from the livestock.
The contamination of soil and water resources can occur with pathogens. This can be another common result of breaking the “short cycle” for nutrient recycling. When wastes are discharged into the environment or transported from industrial livestock operations for use on specialized crop farms, distance often erodes farmers’ ability, and incentive to manage risks from bacteria, heavy metals or drug residues.
The release of ammonia, methane and other gases result into air pollution. Ammonia emissions contribute to acid rain and nitrogen deposition that damage crops and natural ecosystems, as well as to aerosol formation, which can cause health hazards. The livestock and manure management are also major contributors to greenhouse gas releases. Emissions of methane from ruminants digesting fibrous feeds and from manure storage facilities add up to nearly 90 million tons per year, accounting for about 16 percent of global annual production. Manure also produces nearly seven percent of total global emissions of nitrous oxide, which ranks among the most damaging green house gas of all with an impact 296 times greater than carbon dioxide.
The destruction of fragile ecosystems such as wetlands, mangrove swamps, and the coral reefs – irreplaceable reservoirs of biodiversity, that are the last refuge of many endangered species. The threatened coastal areas of the South China Sea, for example, have provided the habitat for 45 of the world’s 51 mangrove species, almost all of the known coral species, and 20 of 50 known sea grasses.
Proven policies and technologies exist that could manage and reduce the environmental damage caused by industrial livestock production. Zoning regulations and taxes can be used, for example, to discourage large concentrations of intensive production close to cities and far from cropland where nutrients could be recycled. And taxes, certification programmers and other policy instruments can be used to support best practices in livestock production. Building of barns and manure storage facilities to meet rigorous sitting and construction standards can reduce effluent discharges. The use of quality feed, and careful monitoring of nutrient inputs, and outputs can help minimize releases of nitrates, phosphates and heavy metals. The recycling of manure and compost can provide livestock producers with an outlet for their waste and farmers with an inexpensive supply of organic fertilizer. Biogas generators can improve manure management while providing a valuable source of renewable energy.
Over the past century, agriculture has shifted from extensive, independent farms to concentrated and integrated operations. This shift has resulted in numerous changes, particularly in the area of farm waste management. Previously, the method of disposal of animal wastes was simply to allow the environment to absorb and utilize them, as it does with the waste of wild animals. However, as the production of meat, poultry, milk, and eggs has become more concentrated, so too have the byproducts of that production, namely animal waste and carcasses. If left to the age-old methods of disposal, these extremely concentrated wastes quickly overwhelm the ecosystem’s ability to deal with them, resulting in severe environmental degradation. This is the reason that appropriate management of waste is a key aspect of animal agriculture today.
There are many types of waste management systems, and the type of system used is largely determined by the type of housing utilized (open lot versus partially or completely enclosed) as well as the consistency (liquid, semisolid, or solid) and method of removal of waste. The standard components of any waste management system include collection, storage, treatment, transportation, and utilization. The most common types of waste management systems are liquid retention and storage ponds, and anaerobic waste treatment lagoons. The liquid retention and storage ponds simply retain the wastes until they can be utilized, usually via application to croplands.
Anaerobic treatment lagoons are engineered to degrade waste materials into less substantive solids, methane, and carbon dioxide. A certain temperature is required for the bacteria performing this degradation, so lagoons must be located in areas of moderate temperature to function optimally. The final step in most management systems is land application as fertilizer.
Historically, the land application was based solely on the amount of nitrogen (N) required by the crops and cropland to which the waste was being applied. However, this often results in an over-abundance of phosphorus (P), as well as other compounds such as heavy metals. Regulations that are more recent may require consideration of P levels and needs, to avoid ground and surface water contamination with phosphorus. The contamination with high levels of phosphorus may result in severe ecosystem depletion, such as the large “dead zone” in the Gulf of Mexico. Besides nitrogen, phosphorus, and heavy metals, other chemical and biological residues can be found in farm animal waste, including antibiotics and other antimicrobials.
In addition, the animal wastes are known to be a primary source of pathogens that can lead to disease outbreaks. There may be very high concentrations of zoonotic pathogens in animal wastes. For some agricultural animals, such as cattle and swine, faecal production equals or far exceeds that of humans, and because industrial production facilities house thousands to tens of thousands of animals in confined areas, industrial food animal production (IFAP) produces large quantities of concentrated faecal, and other wastes that require effective management in order to minimize environmental, and public health risks.
Zoonotic pathogens are those infectious agents, which cause disease in humans as well in a wide variety of animals. Presently, over 300 zoonotic pathogens are reported which produce high morbidity and mortality in humans and animals. Zoonotic agents in animal wastes include bacteria, such as E. coli O157:H7; viruses, such as avian influenza; parasites, such as Cryptosporidium; and even fungi, which may be prevalent in air samples from IFAP facilities. The common waste management systems may be able to significantly reduce microbial contamination. For example, the typical anaerobic, aerobic, or facultative (both anaerobic and aerobic) systems used on many industrial farms can reduce microbial contamination by 90–99%. Additional stages of waste treatment can improve on that number, depending on the type of pathogen. Despite this, changes in pathogens themselves, environmental disruptions, and lack of standards and regulations can and do lead to public health issues and environmental degradation.
To protect human health and the environment, there is a need for greater measurement and regulation of microbial, and chemical contaminants in farm waste. In addition to reducing microbial contaminants, ideal waste management systems would reduce the level of harmful chemical components, create a useful product, and perhaps even capture energy from the process. If meat, milk, and egg consumption continues to rise, the increased number of concentrated farms will require greater regulation of waste disposal to protect the environment and public health. As animal agriculture becomes less of a pastoral endeavor and more of an industry, the level of regulation must also become more industrial.
Current Methods for Disposal of Livestock Mortalities
Burial
The traditional methods of on-farm burial of livestock mortalities include burial in graves, trenches, or in open bottomed containers referred to as mortality or disposal pits.The burial of livestock has been banned in the EU due to fears that infectious agents may inadvertently enter both the human food, and animal feed chains or lead to environmental pollution. Outside of the EU, some concern has been raised that improper burial may lead to contamination of ground and surface water with pathogens and the chemical products of decomposition. However, no studies could be found that reported any serious environmental impact from routine disposal via burial. It was concluded that the pollution from burial pits was similar to that of domestic septic tanks, and could be controlled with legislation synonymous with on-site wastewater treatment regulation. Many of the assumptions about the environmental impact of the burial of fallen (dead) stock have been made following mass burial at incidences of high mortality. However, it is unlikely that the findings of such studies provide an accurate representation of the typical risks posed by routine burial of on-farm mortalities. For instance, weekly disposal of dead animals from an American turkey farm typically equates to approximately 2000 kg, whereas one investigator evaluated the environmental impact of burying 28,000 kg of turkeys in two pits following a barn ventilation failure. Similarly, numbers of dead sheep from a typical European farm will be significantly less than those generated following mass-disease outbreaks. During the UK foot and mouth disease (FMD) outbreak in 2001, approximately 61,000 tons of carcasses were disposed of at four mass-burial sites. It is inevitable that such mass burial would pose considerably greater environmental and biosecurity risk than burial of routine mortalities, and hence extrapolation of the results from studying such extreme events may be erroneous. Indeed, investigators concluded that the concentrations of E.coli and Cryptosporidium in ground and surface water were affected to a greater extent by excretion from live animals than they were from the burial of a small number of carcasses. The risk posed by routine burial should therefore be balanced against other widespread agricultural practices (e.g. farm wasteland spreading) so that the threat is realistically evaluated in relative terms. In addition to the potential introduction and subsequent survival of pathogenic bacteria in soil and water arising from carcass burial, concern has also arisen that burial may lead to propagation of pathogens and subsequent pollution of groundwater and drinking water. Many factors affect the movement of pathogens through soil to groundwater, including soil type, permeability, water table depth and rainfall. However, adsorption, filtration and predation by natural microbial populations significantly reduce the amount of pathogens that eventually reach underlying groundwater. Within an aquifer, there are also many factors that govern the inactivation of the pathogens, e.g. pH, water flow rate, and substrate grain size. Considering all these factors, it is possible that the numbers of pathogens reaching any drinking water source due to routine burial are likely to be low; particularly if boreholes and wells are deep, thereby increasing the time taken by pathogens to reach the underlying aquifer and thus the likelihood of their demise before reaching the water. In support of this, scientists reported low concentrations of coliforms, and Salmonella in observation wells surrounding disposal pits, concluding that bacteria did not move more than 30 m laterally in groundwater. Similarly, in a survey of poultry disposal pits, investigators found the average concentrations of faecal coliforms, and faecal streptococci in water samples to be relatively low (24 CFU 100 ml and 3 CFU 100 ml, respectively); with many samples testing negative. Indeed, no studies have been reported in the literature linking the burial of animal carcasses to detrimental effects on either human or animal health, although burial of humans within a water table has led to incidences of contaminated groundwater. Furthermore, the addition of hydrated lime (CaOH2) to the base of burial pits has shown to effectively reduce the survival of pathogens and the possibility for off-site pathogen transfer. The use of a chemical barrier to minimize risk is supported by the investigators who found no viable E. coli O157 cells in contaminated abattoir waste treated with lime applied at a rate of 10 g of CaO lime l waste. Applying lime both during the construction,and during subsequent operation of burial sites may impede the growth of all microorganisms and hence slow the process of decomposition. However, in the context of improving biosecurity, it is a simple and cost effective procedure that would be accessible to many farmers; justifying the case for further research to enable the scientific basis of current legislation to be critically evaluated. Despite the seemingly low incidence of drinking water contamination with enteric pathogens arising due to burial of carcasses, some infectious material such as anthrax spores or prions can reside within the soil after carcass decomposition. This may lead to animals inadvertently ingesting contaminated soil and the infectious agents and hence may lead to development of neurodegenerative disease such as BSE or scrapie in the case of prions, or the reintroduction of anthrax. Waste management events pose real risks, and therefore, measures can be implemented to reduce the risk of prion transmission and propagation arising through burial of carcasses. Primarily, animals suspected of dying from neurodegenerative disease or a veterinary practitioner should automatically send anthrax for incineration following examination. The burial sites could also be located away from the livestock fields, and at sufficient depth so that the potential for transfer of infectious agents back to the surface (e.g. through earthworm activity) is very low. Indeed, burial of carcasses at depth may stimulate prion-degrading enzyme production by indigenous microbial populations, thus further reducing any threat. The use of soil additives incorporating prion degrading proteases or microbes known to degrade prions could also stimulate prion degradation, and is a potential area for future research. The risk assessments undertaken in 1997 after the UK BSE crisis concluded that the leachate from the landfill used to dispose of BSE-infected cattle was not likely to cause a significant risk to local inhabitants. However, the burial at depth may induce hypoxic conditions, particularly in soils with very high moisture content (e.g.when water logged). This may impede microbial degradation of prions, and ultimately sustain infectivity and thus pose a biosecurity threat if pits are inadvertently exposed later. Nevertheless, the associated probability of TSE transmission through burial of carcasses in Europe is clearly reduced given that the number of livestock infected with prions has decreased dramatically over the last decade. In the UK, ground water vulnerability maps were used during the 2001 FMD outbreak to locate suitable mass burial sites, and are currently used to locate suitable human cemetery site. A similar risk assessment method could be employed to reduce the risk of contamination to ground water from routine livestock burial using additional datasets, including locations of boreholes and wells, topography, and land use. Such methods could identify potential on farm burial sites that minimize the risk of environmental pollution whilst proving to offer a viable and practical option for farmers to dispose of on farm mortalities. It is deduced that more evidence is needed to definitively test the environmental impact of burial of routine mortalities.
Human Pathogens in Animal Agriculture Production Systems
A wide variety of animal pathogens which include viruses, bacteria, fungi, Chlamydia, Rickettsia, protozoa,and helminthes pose potential risks to human health. Some of which are endemic in commercial livestock and difficult to eradicate from both the animals and their production facilities. Hence, pathogens in animal manure and other wastes pose potential risks to human and animal health both on and off animal agriculture production facilities if the wastes are not adequately treated and contained. There are also growing public health concerns about the high concentrations of antibiotic-resistant bacteria in agricultural animals resulting from the therapeutic and growth-promotion use of antibiotics in animal production.
Newly recognized or emerging livestock animal pathogens with uncertain host ranges continue to be discovered, and there are concerns that these pathogens, such as hepatitis E virus and orthomyxo viruses (influenza viruses), may be able to infect human beings.
Animal pathogens posing potential risks to animal and possibly human health include a variety of viruses such as swine hepatitis E virus, bacteria, Salmonella species, and parasites such as Cryptosporidium parvum. Some of these pathogens, such as the ones just mentioned, are endemic in commercial livestock and are difficult to eradicate from both the animals and their production facilities. Because these pathogens are so widely prevalent in animals, they are often present in fresh animal manure and other animal wastes. Therefore, the pathogens in animal manure, and other wastes pose potential risks to humans, and animal health both on and off animal agriculture production facilities if the wastes are not adequately treated and contained. Manure and other animal waste management technologies must be capable of reducing, and containing these pathogens in order to prevent or minimize human, and animal exposures to them that would pose health risks. In addition many animal pathogens have the ability to pose health risks to exposed humans and animals.
There are also growing concerns about the presence of high concentrations of antibiotics and antibiotic resistant bacteria in agricultural animal manures. Antimicrobials are widely used therapeutically and subtherapeutically in animal production for disease prevention, and growth promotion, respectively. Sub-therapeutic antimicrobial use is associated with increased antibiotic resistance (AR) and multiple AR in enteric bacteria in swine and other animals. Furthermore, E. coli has been implicated in AR gene transfer to other enteric bacteria. Enteric bacteria with AR genes can spread from farm animals to other animals and to farm workers. Research and outbreak data have shown that AR Salmonella have lower infective doses, and cause increased incidence of human salmonellosis. Therefore, the presence of antibiotic resistant bacteria in animal manures is another potential health risk of concern from both on-farm exposure and off-farm contamination. Of the many potentially antimicrobially resistant bacteria, Salmonella spp. are a particular concern.This is because they are important human pathogens, they are wide spread in agricultural animals, and they have developed a wide range of antimicrobial resistance of considerable public health concern.
Viruses
A variety of different viruses can be present in animal fecal wastes and manures, especially important are a variety of enteric and respiratory viruses, including animal enteroviruses, rotaviruses, adenoviruses, hepatitis E viruses, caliciviruses, reoviruses, parvoviruses, and other non-enveloped viruses. The animal viruses are primarily of concern to agricultural animal health, and productivity because the animal diseases they caused are responsible for high morbidity and mortality, and reduced food animal production. However, the impacts of some of these viruses, such a swine HEV and caliciviruses, on animal health and productivity are uncertain and perhaps have minor impacts. Because many of these viruses are non-enveloped, they are relatively persistent in the environment and resistant to treatment processes. However, some enveloped viruses also can be present in animal manures at high concentrations, and they may persist for considerable periods of time in the manure and intreatment and storage processes. Many of these enveloped viruses of concern are not endemic in the U.S. Vesicular stomatitis virus is an enveloped virus endemic in the U.S., but it is not present at high concentrations in manure. Instead, it is transmitted primarily by direct contact with infected animals, by aerosols and perhaps by the bites of flies.
Some of the viruses, notably the caliciviruses, rotaviruses, myxoviruses, and hepatitis E viruses, are or may be capable of infecting humans. On rare occasions some viruses, notably myxoviruses such as swine influenza virus, have caused human illness. The extent to which animal caliciviruses, rotaviruses, and animal HEV strains pose risks to human health remains uncertain but appears to be low in terms of documented risks of severe illness. However, epidemiological investigations of the human health risks of these viruses are limited. Therefore, the extent of such risks remains uncertain and needs further study.
Infections and diseases caused by human enteric, and respiratory viruses that are transmitted through facally contaminated food and water have been well documented. However, the transmission of fecally associated viruses of animal origin to a human host is not common. This is may be the result of the relative specificity of the viruses to their host. Three virus groups associated with fecal-oral transmission, astroviruses, reoviruses and rotaviruses, infect a wide range of hosts. However, rotaviruses and astroviruses are thought to be relatively host specific. Some reoviruses, notably type 3, have a wide host range including humans. Recently, hepatitis E viruses of swine, and possibly other animal species have become of increasing concern with respect to human health because these viruses are prevalent in swine and present in swine wastes. Swine HEV has been shown to be experimentally transmissible to primates and human HEV is infectious for swine. Furthermore, swine and human HEV strains are genetically very similar on a country or regional basis. For example, in the U.S., human and swine HEV are very similar genetically and the same is true for the human and swine HEVs in Taiwan. To date, swine, sheep, and rats have been found to be carriers of hepatitis E but only swine have been implicated in possible zoonoses. In general, it is believed that animal-to-human transmission via animal wastes is not as high a risk as bacterial transmission. However, animal-to-animal transmission or herd-to-herd transmission of viruses is a concern.
Rodent urine and faeces contain viruses that may be transmitted to humans via aerosols such as arenavirus (located in West Africa), and Hantavirus. Aphthovirus (foot and mouth disease), and swine vesicular disease virus (SVDV), members of the Picornaviridae family, are transmitted to humans through aerosols containing the virus or ingestion of contaminated food products from infected cattle and pigs. However, the disease incidence is low, and these viruses are not considered important risks due to eradication and importation restriction measures. Vaccinations for aphthovirus and SVDV are an effective means of control for these diseases within the animal population. However, some of these viruses are of concern as bioterror agents, and greater vigilance is now being exercised to prevent their introduction and spread in the U.S.
Zoonotic transmission of animal viruses to humans via the faecal-oral route is believed to be limited in the U.S. However, some enteric viruses, such as swine HEV, are of increased concern in this respect because of serological evidence for higher levels of infection in swine workers than in the general population or in similar, but non-animal, agriculture occupations. Virus transmission between animals and humans also may occur through direct contact with the infected animal or by a vector such as ticks or mosquitoes. Therefore, viral zoonoses also are a concern for occupational workers who come into direct contact with animals and their waste. For example, poxviruses associated with sheep are commonly transmitted to humans working with domestic sheep. Prevention of zoonotic viruses via direct contact is accomplished by good hygienic, and sanitation practices.
Persistence and Survival of Viruses and Other Pathogens
A variety of physical, chemical and biological factors can influence the persistence and stability of viruses in animal waste treatment and management systems. Many if not all of these same factors also influence the survival of bacteria and parasites in animal wastes and environmental media. Virus survival in animal manures is probably most directly influenced by temperature, pH (either very high or very low levels), microbial activity, ammonia, and indirectly by solids-association and other physical conditions of viruses (aggregation, encapsulation or embedding, etc.). Differences in the values of or conditions for these variables have been shown to dramatically influence virus survival in manures, biosolids and other matrices.
However, it is not possible to rank these factors for their effects on virus survival, because the nature and magnitude of their effect depends on the actual level or state of the factor and the levels or states of the other factors. Overall, viruses survive longer than bacteria inthe environment. For example, enteric viruses have been observed to survive for greater than 6 months in semiliquid cattle manure.
Pathogen Reductions during Waste Treatment
Commercially raised farm animals can be infected with numerous pathogens that are also pathogenic to humans. Thus, farm animals can shed human pathogens which can subsequently be found in animal waste that is further managed on the farm. Waste management techniques that may be effective for reducing pathogen concentrations in farm animal waste should be used. Improved animal management and housing techniques can also be effective in reducing pathogen levels in animal waste. These techniques generally include vaccination, prophylactic antibiotic therapy, animal diet modifications, on-farm hygienic and sanitation measures, herd management, and housing designs.
The persistence and fate of pathogens in animal waste treatment processes and management systems have not been adequately characterized and quantified. Only limited studies have been reported and most have been laboratory studies. Most studies have attempted to quantify reductions of microbial infectivity (inactivation) in animal manure slurries or mixtures of these with other constituents under controlled temperature conditions and maintenance of either aerobic or anaerobic conditions. Studies on the fate of pathogens after land application of animal manures, liquids or solids have not been reported. The term “reduction” includes pathogen inactivation (loss of infectivity), and well as physical removal of the microbe.
Some processes cause primarily pathogen inactivation, such as thermophilic processes. Others cause both inactivation and physical removal, such as many of the mesophilic biological processes (e.g., lagoons and constructed wetlands). Estimates of
pathogen reductions are uncertain and based on limited lab studies or pilot field studies with few pathogens, including indicator microbes (primarily faecal coliform bacteria), being investigated.
MANURE SOLIDS WASTE
Manure can contain high concentrations of pathogens. Over time, a decrease in pathogens in untreated manure will occur without intervention but the die-off of microbes may not be extensive and depends on factors such as microbe type, manure physicochemical characteristics and environmental conditions. E. coli O157:H7 has been found to survive for over a year in non-aerated sheep manure. Salmonella inoculated into cattle slurry were observed to survive for 2-4 months when storage temperatures were 20ºC or less. Enteric viruses have been observed to survive for greater than 6 months in semi-liquid cattle manure, with lower virus survival times observed for samples having lower fractions of manure solids. Ascaris eggs can survive for greater than two years in biosolids held at 4°C. Increased pathogen inactivation rates in manure can be achieved using manure treatment techniques, especially those that involve aeration or elevated temperatures. When air drying alone is used as a method for sludge treatment, the sludge must rest on sand beds for a minimum of 3 months with 2 months at temperatures above 0°C. This process only inactivates bacteria while viruses and helminths remaining detectable. The time required in various processes and their effectiveness for reductions of pathogens influence the development of methods to achieve pathogen reductions in manure or animal waste treatment systems. Treatment methods selected are based on the potential for pathogen exposure to humans, management of byproducts, the types of waste treated, cost, ease of application, and area required for the process.
Dry Techniques: Composting
Composting depends primarily on indigenous microorganisms to degrade manure waste materials under aerobic and warm conditions. Yet factors such as the heterogeneity of the material, the moisture content, and temperature stability and uniformity throughout the process determine the success for reducing pathogens. Additionally, aeration, presence of bulk organic material (e.g., wood chips, bark mulch, etc.), carbon/nitrogen content, and pH contribute to the efficiency of indigenous microbes in breaking down the waste materials.
Three main types of composting are utilized: pile, windrow, and in-vessel. The pile process consists of mixing the waste with a bulking agent that encourages aeration. Air is blown into the mixture for approximately 21 days followed by a 30-day curing period. During the windrow process, the sludge is also mixed with a bulking agent and then piled into rows 1-2 m high. The rows are turned every few days for 30-60 days. In-vessel, composting consists of mixing sludge in a composting vessel while air is forced through the waste materials.
Some agricultural practices utilize composted materials to amend soils with nutrients or conditioners, therefore, much of the research on composting is related to the nutrient and soil conditioning properties of the biosolids. Concern about the possible survival of pathogens in composted materials has led to research on the survival of pathogens in these materials, transport of pathogens through manure-amended soils, and the possibility of runoff from land application fields. Pathogens originally present in the feedstock materials may remain in the finished compost if the composting process is not adequately controlled and monitored. Additionally, certain bacterial pathogens present in the original biosolid materials, such as Salmonella, may undergo proliferation during or at the end of the composting process, if the reactor or storage conditions are not adequately controlled. The superficial layers of a compost pile will not reach elevated temperatures unless the material is constantly or periodically turned. Under such circumstances, improper temperature regimes within the compost pile can lead to pathogen re-growth due to the sudden increase in available carbon and nitrogen nutrients. Optimization of composting conditions is necessary in an effective method for the reduction of bacteria, viruses, protozoan cysts, and helminth eggs. In a static pile process, a temperature of 55°C or higher must be maintained for 3 days or longer to achieve effective pathogen inactivation. Frequent turning or mixing, on a daily to weekly basis, is important for providing oxygen to the aerobic compost microorganisms, keeping temperatures elevated, and removing excess moisture. However, composting conditions that are effective for inactivating some pathogens (e.g., pathogenic bacteria such as Salmonella), and may not be effective for inactivating more persistent pathogens (e.g., helminths and viruses).
Viruses, helminth eggs and protozoan parasite cysts and oocysts are generally thought to be the most resistant pathogens to typical composting conditions, but can be completely inactivated when composted at >60°C for 1 hour. In one study, faecal coliforms, faecal streptococci, and Salmonella were reduced by 5 log10, 4 log10, and 3 log10, respectively, after 14 days of treatment in a combined windrow-static pile composting system. An aerobic static pile compost system treating swine manure was reported to reduce enterococci concentrations by 4 log10 after 15 days of treatment. Salmonella is the focus of many composting studies due to its ability to survive and re-grow in composted materials. The windrow process effectively eliminates Salmonella when temperatures of 64-67°C were maintained for 21 days. However, Salmonella re-growth can occur if there is incomplete disinfection of the biosolids during the composting process. It is thought that this re-growth is facilitated by the inactivation of competitive, non-pathogenic native microflora in the biosolids. Additionally, storage alone or after composting does not ensure elimination of Salmonella in the compost. Composting of sludge for two weeks has been reported to be seven times more effective for inactivating Salmonella than sludge storage for 117 weeks. Although windrow composting can be effective for reducing Salmonella concentrations, research has shown that more persistent pathogens, such as Giardia cysts can remain at relatively high concentrations (200-600 cysts/g dry weight) in windrow composted material. It was found that storage of the windrow compost for an additional 30 weeks was needed to reduce Giardia cyst concentrations to below their detection limit. Although mechanical agitation of biosolids during the various stages of composting is crucial to maintaining effective composting conditions, the mixing process may aerosolize pathogens. It was reported that mechanical agitation of compost material was a major source of airborne emissions. Scientists monitored airborne microorganisms for 12 months around two different composting facilities (open and closed) in Germany, and found that the emission levels of aerosolized molds were higher around the closed composting facility as compared to the open facility. These researchers suggested that additional fungal microbes such as Saccharopolyspora spp. and Thermoactinomyces spp. should be included in air monitoring programs of composting facilities. Although there are studies documenting the presence of Aspergillus fumigatus spores around composting facilities, few studies have been published regarding the presence of specific pathogens such as Salmonella spp. Investigators have reported finding airborne A. fumigatus spores in close proximity to a composting facility. It is mentioned that total numbers of microorganisms in composting plants can range between a 500 CFU/m3 and 105 CFU/m3 while Gram-negative bacteria can range between 200 CFU/m3, and 50000 CFU/m3. The increased occupational risk to compost workers in such settings have been recorded. Researchers have described on the upper airway based occupational exposure of compost workers to microbial agents (endotoxin and beta 1,3 glucan). Scientists have also reported that high exposure to bioaerosols in compost workers is significantly associated with higher frequency of health complaints, and diseases as well as higher concentrations of specific antibodies against molds and actinomycetes. Thus, while composting can be an effective method for reducing pathogen concentrations in animal manure, appropriate process controls and safety measures should be maintained to protect worker health and minimize environmental contamination in the vicinity of composting facilities.
Manure Slurry Treatment Techniques
Manure and other animal wastes are often removed from production areas using water. The resultant manure slurry can then be stored prior to land application, or further treated. Anaerobic lagoons are a popular alternative for liquid manure storage and biological treatment. Due to concerns regarding the extent of waste treatment in anaerobic lagoons, gas emissions from lagoons, and the potential for waste releases during lagoon failures, substantial effort is being focused on developing and evaluating alternative treatment systems for animal waste. Available information is often insufficient to fully evaluate the efficacy of many of these treatment techniques for reducing pathogen concentrations in manure slurry. However, comparatively more relevant data may be available from research on these techniques for treating municipal wastewater.
Physical Treatment Techniques
Physical treatment techniques for flushed manure include sedimentation, screening and filtration to separate solid particles from bulk liquid. Filtration is not a common physical separation technique for animal waste management systems, but techniques such as sand filtration and drying beds may be effective for separating solids in flushed animal waste. However, labour requirements to maintain and operate such systems may be a limiting factor. The primary purpose of sedimentation and screening in animal waste management systems is to reduce the organic and solids loadings to subsequent treatment systems, thereby improving their potential performance and minimizing operation and maintenance problems. Increasingly, solids separation is being investigated for recovery of biosolids as commercial fertilizer or soil amendment. Little data is available to estimate potential pathogen reductions in solids separation units for animal waste. In municipal waste systems, many studies have investigated pathogen removals in primary sedimentation tanks. In general, removals of viruses, bacteria, and protozoa can all be expected to be less than 90% (1 log10). For the most part, the solids separation process does not destroy pathogens but only partitions them into the two resulting waste streams, solids and liquids, with about equal numbers in both of them.
Biological Treatment Techniques
Lagoons traditionally are built for wastewater to flow through at specified retention times, resulting in the decrease of biological oxygen demand (BOD), chemical oxygen demand (COD), various nutrients such as phosphorous and nitrogen, and pathogens. Lagoons, also referred to as stabilization ponds in municipal treatment systems, vary based on the type of oxygen environment maintained throughout the reactor water column. Three primary classifications exist for lagoons: aerobic lagoons, anaerobic lagoons, and facultative lagoons. Aerobic lagoons are those in which measurable levels of dissolved oxygen are present throughout the lagoon depth. In multi-cell municipal waste lagoon systems, the final lagoon is often naturally aerobic. In lagoon systems such as those typically found in concentrated animal feeding operations (CAFOs), organic loadings to the lagoons are sufficiently high such that aerobic conditions in the lagoons can only be achieved by forced introduction of air into the lagoons (e.g., by mixing, air blowers, bubble aerators). Facultative lagoons maintain aerobic, and anaerobic zones simultaneously. The anaerobic zone occurs deeper in the lagoon while the aerobic zone is closer to the surface. A zone that oscillates between anaerobic and aerobic classifies this type of lagoon as facultative. Anaerobic lagoons are those in which anoxic conditions are maintained throughout the lagoon depth, with the exception of the small surface layer in contact with ambient air. In general, greater pathogen reductions are expected in aerated or facultative lagoons, due to conditions related to the higher metabolic activity present in aerobic biological treatment systems, and the toxic effects of oxygenic compounds.
The treatment purpose for a lagoon varies from treating sludge and wastewater to serving as storage or overflow area for other treatment systems. Several considerations must be given prior to utilizing lagoons as a method for waste treatment. The land area, climate, loading rates, and subsurface soil conditions are major considerations for lagoon design.
Anaerobic Lagoon Treatment
Lagoon storage is a common management technique for flushed animal waste because of its cost effectiveness. Lagoons receiving untreated flushed animal excreta (manure and urine) are typically anaerobic throughout their reactor water volume due to the high organic loading that they receive. Under normal conditions, non-aerated animal waste lagoons built, and operated according to Natural Resource Conservation Service (NRCS) Code 359 are anaerobic and have hydraulic residence times (HRTs) of over 3 months. Anaerobic swine waste lagoons have been shown to reduce enteric bacterial and viral indicator microbes by 1-2 log10, but concentrations of fecal coliform concentrations on the order of 100,000 cfu/100 ml remain in swine lagoon liquid . Salmonella and faecal coliforms have been found at geometric mean concentrations of 140-260 MPN/100 mL and 320,000-820,000 CFU/100 ml, respectively, in anaerobic swine waste lagoon. Cryptosporidium parvum oocysts have been found at concentrations of 1200-2200 oocysts/L in commercial swine waste lagoons in Iowa. Overall, reductions of enteric bacteria and viruses in anaerobic animal waste lagoons can be substantial (up to 3 log10), but the effectiveness of these systems is not consistent (e.g., reductions below 1 log10), and can be affected by seasonal changes in climatic conditions like ambient temperature.
Multiple Lagoon Systems
It is well established for municipal waste stabilization pond systems that the use of multiple ponds in series is more effective for reducing nutrient and enteric microbe concentrations than the use of a single pond with the same overall reactor volume. Recently, researchers have linked the concept of multiple lagoon systems to recommendations they made for revisions to the World Health Organization’s microbiological quality guidelines for the use of treated wastewater in agriculture. Faecal coliform reductions as high as 4-6 log10 have been achieved in municipal stabilization pond systems having 4-5 ponds in series and overall HRTs of approximately 20-30 days, a range of HRTs that is substantially lower than is typical in CAFO lagoons. Salmonella were found to be reduced by 2-4 log10 in a series of 3 municipal waste lagoons, compared to reductions of 1-2 log10 in single-stage ponds operated at the same HRT as the in-series system. Swine waste lagoon systems having two lagoons in series have been found to achieve sub-stantially higher reductions of Salmonella and enteric microbial indicators than single-lagoon systems. Additional reductions of up to 3 log 10 can be achieved in secondary lagoons, depending on enteric microbe type and ambient conditions.
Aerated Lagoons and Oxidation Ponds
Aeration of manure slurry, whether in traditional lagoons or alternative designs such as oxidation ponds, can substantially increase metabolic activity beyond the extent achievable in anaerobic systems. In addition to increased nutrient removal, it is likely that aeration off lushed waste would increase pathogen reductions. Enteric viruses, Salmonella, Yersinia, and E. coli have been shown to be more effectively reduced in aerated pig or cattle slurry than in non-aerated slurry. Faecal coliform, and faecal streptococci reduction rates have been observed to be higher in municipal oxidation ponds than in non-aerated stabilization ponds. Viruses can be reduced by 2-log10 in aerated ponds, but treatment efficiencies are temperature dependant. In cool weather, the time to achieve a 2-log reduction of viruses was found to be five times as long as in warm weather. Bacteria can be reduced by 1-2 log10 in oxidation ponds, with the primary factors influencing inactivation being hydraulic residence time, reactor pH, temperature, predation, and sunlight. Most of the data available regarding pathogen reductions in aerated lagoons and oxidation ponds are from the studies of municipal waste treatment systems. Insufficient data is currently available to fully evaluate the effectiveness of these aeration technologies for achieving pathogen reductions in CAFO wastes.
Aerosolization of Pathogens
With the use of spray irrigation and waste treatment systems to recycle waste, aerosolization of pathogens has become a concern. This section covers the concepts and state of the knowledge regarding pathogen aerosolization as it relates to waste management. Bioaerosols are defined as a collection of aerosolized biological particles.
The composition, size and concentration of the microbial populations comprising the bioaerosol vary with the source, dispersal mechanisms in the air, and more importantly, the environmental conditions prevailing at the particular site. Bioaerosols generated from water sources (such as during splashing and wave action) are different from that generated from soil or non-aqueous surfaces in that they are usually formed with a thin layer of moisture surrounding the microorganisms. They often consist of aggregates of several microorganisms. Bioaerosols released into the air from soil surfaces such as those surrounding biosolid and composting facilities are often single units or associated with particles. In many instances, the presence of these particulate matter serves as “rafts” for microorganisms. The extent of dispersal (transport) and the settling of a bioaerosol are affected by its physical properties and the environmental parameters that it encounters while airborne. The size, density, and shape of the droplets/particles comprise the most important physical characteristics, while the magnitude of air currents, relative humidity, and temperature are the significant environmental parameters. It must be emphasized that bioaerosols vary greatly in size ranging from 0.02 to 100 µm in diameter. Aerosols can be launched from either “point” sources, “linear” or “area” sources. A biosolid pile is an example of a point source while an agricultural field that has been spread with biosolids is an example of an area source. The transport of bioaerosols can be defined in terms of distance and time. Submicro scale transport involves very short periods of time under 10 minutes, as well as relatively short distances under 100 m. This type of transport is common within indoor environments. Micro scale transport ranges from 10 minutes to 1 hour and from 100m to 1km and is the most common and significant type of bioaerosol transport from a human health standpoint.
Mesoscale and macroscale transport refers to longer duration bioaerosol transport patterns. The diffusion of bioaerosols during their transport is one of the primary means by which their concentration decreases. Atmospheric turbulence significantly influences the diffusion of bioaerosols. Thus, with biosolid based composting, the storage conditions of the feed-stock, the length and size of the open windrows, the atmospheric conditions during storage and windrow “turning,” and the distance to the closest population center have to be taken into careful consideration when evaluating whether composting associated bioaerosols can have public health implications.
Inhalation, ingestion and dermal contact are routes of human exposure for aerosolized microorganisms. Large aerosolized particles are lodged in the upper respiratory tract (nose and nasopharynx). Particles < 6µm in diameter are transported to the lung with the greatest retention of 1-2 µm-sized particles in the alveoli.
Human microbial pathogens such as Legionella pneumophila, Mycobacterium tuberculosis, and Hantavirus infections are known to be aerosol transmitted, and are capable of causing severe infections. Asthma, hypersensitivity pneumonitis and other respiratory illnesses are also associated with exposure to bioaerosols containing respiratory pathogens. The typical route of exposure for organisms that are primarily associated with intestinal infections such as Salmonella spp., Campylobacter spp, and enteric viruses is based upon the inhalation of bioaerosols containing these pathogens, which are then deposited in the throat and upper airway and swallowed. Additionally, the inhaled enteric pathogens may establish throat and respiratory infections that can in turn, increase the risk of swallowing an infectious dose. This could possibly explain why the infectious dose of enteric organisms is lower when these organisms are inhaled as opposed to ingestion.
A number of publications over the last few years have documented that aerosolization of microbial pathogens is strongly linked to waste application practices, biosolids handling, wind patterns and micrometeorological fluctuations. The very process of “turning over” or mechanical agitation of biosolids material at the initial stages of the composting process or during the process itself can generate large amounts of microbial pathogens. Studies conducted around biosolids land application processes have shown that when the biosolids material is physically agitated Salmonella and faecal indicator viruses can be released into the surroundings. At an arid location in the U.S., scientists detected bioaerosols averaging 300 most probable number (MPN) of Salmonella cells /m3 or air at biosolids loading and application sites. The levels of faecal indicator viruses averaged around 1000 virus particles (PFU)/m3. On occasions, Salmonella at levels up to 3000 MPN/m3 were detected four miles down-wind. The detection of microbial pathogens at distances away from the point source is indicative how wind gusts and wind patterns can transport bioaerosols over distances. The amount of pathogens bioaerosolized and transported are dictated by the source material, wind patterns and mechanical agitation of the biosolids material. In addition to bacteria, poultry litter contains bacteriophages, and fungi. Both bacteria and fungi produce endotoxins that have been identified to be key respiratory irritants. Thus, any off-site migration of bioaerosols and dust will potentially lead to the dissemination of either specific microbial pathogens or end toxins. It has been shown that airborne microbial counts in poultry processing plants were highest around the shackling areas and decreased towards the packaging areas.
Not only do outdoor aerosols carry pathogens but indoor particulate matter carries human health concerns. Scientists have reported on the concentration and emission of endotoxins in different types of animal (cattle, pig, and poultry) facilities in North Europe. Cattle had the lowest concentration, while the highest concentration was detected within poultry houses. End toxin concentration was generally higher in the day than in the night. The high daytime concentration implied that it could be a significant occupational health issue. The mean emission rates from poultry houses were higher than that found in cattle barns. The indoor concentration of heterotrophic bacteria were however higher in cattle barns as compared to poultry houses. Airflow within poultry houses have been shown to influence the transmission of Salmonella enteriditis between birds. The contamination of feed, and water never preceded the appearance of positive faecal droppings suggesting that bird inhalation was the primary route.
One report mentioned that environmental and nuisance problems occur in Europe from poultry operations. They listed odour concentration, ammonia concentration, noise, dust, pathogen concentration in dust, and sulfur gas as the key air quality parameters. It has been reported that dust concentrations in poultry houses varied from 0.02 to 81.3 mg/m3 for inhalable dust and from 0.01 to 6.5 mg/m3 for respirable dust. Houses with caged laying hens showed the lowest dust concentration
(< 2 mg/m3) while dust concentrations in other housing systems were often four or five times higher. The most important source of dust was found to be feathers and faecal material. Thus dissemination and depositing of pathogens by aerosols are other areas of research where the magnitude of impact needs to be discovered.
Microbial Detection Analysis Techniques
The detection and characterization of microbial pathogens in animals and wastes depends significantly on the “age” of the waste material in question. Previous studies have shown that the concentration of the pathogen can decrease depending on the environmental conditions that the waste material is exposed to. Thus, it is theoretically easier to detect specific pathogens from fresh wastes because the numbers of organisms in fresh wastes are generally higher than stored wastes. However, for an “aged” waste, the assay has to be not only sensitive to detect the low numbers of target organisms but has to be able to detect organisms that may have undergone stresses such that they are no longer cultivable or detectable if conventional methods are employed. Thus, in such situations it is quite impossible to know what the actual detection sensitivity of an assay (molecular or conventional) is or whether the sample does indeed contain any pathogen. Selection of a measurement technique requires identification of the questions to be answered and timeliness of tolerated, such as during outbreak investigations. Methods employed for microbial detection represent a myriad of culture, molecular, and chemical techniques. Mass spectrometry, high performance liquid chromatography, and radioimmunoassay, although rapid, require extensive sample preparation, specialized skills, and instrumentation, are limited to detection of single pathogenic species and do provide information on viability or infectivity. Molecular methods targeting nucleic acids, such as DNA/RNA fingerprinting, hybridization, or PCR, are still more expensive than traditional culture techniques, may be labor intensive and time consuming, and also do not provide definitive information on viability and infectivity. Although molecular methods such as PCR are theoretically very sensitive, may not always be applicable to the samples of interest. Inhibitory components in the sample may prevent the enzymatic process needed to amplify the target nucleic of the microbe, thus leading to false negative results. Additionally, molecular techniques do not indicate the infectious state of the organism if culturing is not performed prior to analysis. To address these problems, hybrid protocols that involve a combination of culture-based enrichment, and molecular assays have been developed and are now commercially available (BAX assays, Qualicon, DE).These assays have now been approved for use in food samples. Although not yet commercially available, researchers have also applied the same culture enrichment and molecular assay technique to water and wastes. However, commercially available assays for on-farm use have not become a reality yet. To develop assays that are applicable to animal waste management, concerted efforts have to be undertaken to ensure that the protocols are tested (to the extent possible) on naturally contaminated samples, on samples that have varying numbers of target organisms, on samples that show marked differences in physical, and chemical composition, and wastes from different animal species. Sampling regimes and protocols have to consider the heterogeneity of the sample and the potentially “patchy” distribution of the pathogens. There is a need for the development of rapid and effective sample processing protocols to detect specific pathogens that may be in low numbers, and tightly bound to particulates in waste.
Three main steps are necessary for detection of pathogens in waste and environmental samples: capturing, concentrating or culturing of pathogen in a representative, detecting, identify or quantifying the pathogen, and finally characterizing or confirming the identity and properties of the pathogen. Culture techniques typically used for bacterial detection are less expensive but have a limited range for the types of organisms that can be cultured at this time. The issue of viable but non-culturally microorganisms is still a major limitation of culture based analytical methodologies.
Microbial cells during transport, deposition and sampling are exposed to a variety of inactivating/desiccating which could injure the bacterial cells. These “injured” cells maybe incapable of being cultured on routine microbiological media. Thus, assays relying on culture-based enumerations can be underestimating the actual number of viable cells within waste and environmental samples. Molecular methods are an alternative to culturing since many bacteria cannot be cultured and molecular methods increase the specificity of detection. Capturing of bacteria for molecular methods can be by filtration or centrifugation of a water sample or extracting from solid samples, and then either direct nucleic acid extraction or isolation on media prior to nucleic acid extraction. Though molecular biology-based assays such as gene probe hybridization and gene amplifications have the promise to detect and characterize specific microbial groups within waste and environmental samples, the methods still suffer from some technical shortcomings such as inhibitory sample effects, sample processing deficiencies, and laborious protocols, and possible laboratory based contamination.
Scientists have reported on the detection of Salmonella specific nucleic acids within thermophilic compost piles suggesting that microbial nucleic acids can be resistant to degradation even at the elevated temperatures found within compost piles. The detection of stable nucleic acid sequences does not imply viable or infectious organisms and so, caution is required when interpreting the public health significance and health risks of molecular analyses, such as gene probe hybridizations and gene amplifications. Because viruses and parasites in many samples occur in low numbers, concentration of the sample is required prior to molecular or culture analysis. The method of concentration may consist of either capturing microbes on a filter, concentrating by size exclusion filtration, antibody capture, flocculation or centrifugation. Size exclusion filtration selects for the larger particles to remain in the sample while allowing smaller molecules such as water pass through the filter. Antibody capture uses an antibody specific for a microbe to retain the specific microbe on a solid phase, such as a column. The microbe is subsequently released from the column by elution or extraction. The concentrated sample or captured pathogens are then subjected to a method for detection. The detection methods consist of either an antigen/protein based detection system (i.e. ELISA), molecular detection system (i.e. PCR or hybridization) or culturing method (e.g., infection of cell monolayer). Some viral (hepatitis E virus) and protozoan (Giardia lamblia) pathogens at this time cannot be cultured. Therefore, microscopic, immunological or molecular methods are the only ones available of detection.
Detection by of viruses and parasites by most available methods identify only at the major group or genus level. Therefore, additional tests are needed to determine the species. Integrated cell culture PCR (ICC-PCR) is a promising application for the detection and identification of viable oocysts, and infectious viruses in environmental samples. The major disadvantage of these methods is that they are not adapted for on-site detection at this time and require days for analysis. An increasing demand for high-throughput screening in the clinical and pharmaceutical industries has produced several technological developments in methods for detecting and analyzing biomolecules, many of which could be applied to the detection of pathogens in the agriculture environment. These emerging technologies include real-time polymerase chain reaction (PCR) and hybridization, flow cytometry, molecular cantilevers, matrix-assisted laser desorption/ionization, immune magnetics, artificial membranes, ELISA (enzyme-linked immunosorbent assay), gas-phase detection (electronic nose), spectroscopy, and evanescent wave technologies. For farm and environmental applications, three technologies have potential applications: electronic nose, spectroscopy, and evanescent wave technology, particularly the surface plasm on resonance (SPR) technique.
On-farm Verification of Microbial Reduction by Corrective Measures
Electronic nose instrumentation has advanced rapidly during the past 10 years, with the majority of the applications in the foods and drink industry, and for environmental monitoring. Electronic noses have also been reported to identify microorganisms. Moreover, electronic nose is able to identify and differentiate in vitro bacterial cultures of Staphylococcus aureus,
and Escherichia coli with nearly 100% accuracy. Scientists have shown the effectiveness of electronic nose in recognizing early infection of potato tubers from the bacterium Erwinia carotovora. It has been recorded that an electronic nose can differentiate between E. coli O157:H7 from non-O157:H7 strains.
An electronic nose is a device usually consisting of metal oxide gas sensors coupled with an artificial neural network (ANN). The gas sensors detect the gases and generate a gas signature or pat-tern; the ANN interprets the pattern. An artificial neural network (ANN) is an information processing paradigm that is inspired by the way biological nervous systems, such as the brain, process information. It is composed of a large number of highly interconnected processing elements (neurons) working in unison to solve specific problems. ANNs, like people, learn by example. An ANN is configured for a specific application, such as pattern recognition, data classification, and forecasting, through a learning process. The most important advantage of ANNs is in solving problems that are too complex for conventional technologies. ANNs have already been successfully applied to various areas of food safety and medical diagnosis, such as diagnostic aides, biochemical analysis, image analysis, and drug development. The ANN approach to food and water safety information processing has several benefits:
(1) It is trained by example instead of rules.
(2) It is automated.
(3) It eliminates issues associated with human fatigue.
(4) It enables rapid identification.
(5) It enables analysis of conditions and diagnosis in real time.
(6) It is reagent less.
(7) It is inexpensive.
The electronic nose technology can be used to develop a “microbial sniffer” to provide an economically viable, reagent less, easy-to-use tool for identifying possible sources of contamination in the farm before infection spreads to unmanageable proportions or enters the food or water supply. Recently, a technique has been developed to detect the gastric ulcer-causing bacteria Helicobacter pylori in humans, and rhesus monkeys through breath samples.
Diagnosis through this simple, noninvasive, inexpensive technique has been 85-100% accurate.
Real-Time Measurement Techniques
Evanescent wave technology is a state-of-the-art system that couples antigen-antibody interactions with signal generation. The system used is based on the principle of surface plasmon resonance (SPR). SPR is an optical surface sensing technique that can be used to probe refractive index changes that occur within the immediate vicinity of a sensor surface. A surface plasmon is a charged density wave that oscillates along the surface of a metal. A metal film is layered over a high refractive index medium such as glass or epoxy. Using the Kretschmann geometry, light can be coupled into the surface plasmon mode, and monitored as the analytical signal. In this geometry, light passes through a prism and is incident (at a certain angle of incidence) onto a thin metal film. An evanescent wave propagates through the metal and excites surface plasmons on the other side of the film, which is immersed in the liquid sample. SPR can be achieved by varying the frequency of the light, or by varying the angle of incidence. Either way, at some point resonance occurs: the reflected intensity of the light drops dramatically. The position of the SPR is extremely sensitive to the refractive index of the sample, which is unique to different types of bacteria. Many medical applications, such as the human enzyme creatine kinase (CK), the anti-convulsant drug phenytoin, human chorionic gonadotrophin (hCG), and various other biological contaminants in matrices such as blood, serum, plasma, saliva and urine have been measured with success using SPR. This technology is currently being used in bringing medical diagnostics out of the laboratory to the point-of-care. Detection can be performed in a matter of minutes. Recent developments in SPR technology have produced inexpensive (less than US $3,000) miniaturized units that can be held in the palm of a person’s hand, allowing for easy and convenient use in the field and point-of-diagnosis. The potential for using the technology for on-farm and onsite analysis is tremendous. Chemiluminescence is one optical technique that can be used to detect the presence of pathogens in the food matrix. Chemiluminescence is the production of light by a chemical reaction in which a substrate reacts with an activating enzyme producing an instantaneous release of light energy. It uses quantitative measurements of the optical emission from excited chemical species to determine analyte concentration. Chemiluminescence is usually emission from energized molecules instead of simply excited atoms. The bands of light determined by this technique emanate from molecular emissions and are therefore broader and more complex than bands originating from atomic spectra. Furthermore, chemiluminescence can take place in either the solution or gas phase. Chemiluminescence takes its place among other spectroscopic techniques because of its inherent sensitivity and selectivity. It requires no excitation source (as does fluorescence and phosphorescence), only a single light detector, no monochromator, and often not even a light filter. Its strength lies in the detection of electromagnetic radiation produced in a system with very low background. Because the energy necessary to excite the analytes to higher electronic, vibrational, and rotational states does not come from an external light source like a laser or lamp, the problem of excitation source scattering is completely avoided. Most chemiluminescence techniques need only a few chemical components to actually generate light. Luminol chemiluminescence, which has been extensively investigated,and peroxyoxalate chemiluminescence are both used in bioanalytical methods. In each system, a “fuel” is chemically oxidized to produce an excited state product. In many luminol methods it is this excited product that emits the light for the signal. In peroxyoxalate chemiluminescence, the initial excited state product does not emit light at all but reacts with another compound; it is this fluorophore which becomes excited, and emits light. The oxalate reactions require a mixed solvent system (buffer/organic solvent) to assure solubility of the reagents, optimized pH, and allow compatibility with the analytes. In luminol chemiluminescence system, the chemiluminescent emitter is a “direct descendant” of the oxidation of luminol (or an isomer like isoluminol) by an oxidant in basic aqueous solution.
Hydrogen peroxide is probably the most useful oxidant in luminol chemiluminescence; however, other oxidants have also been used, such as hypochlorite, and iodine. The presence of a catalyst is paramount to this chemiluminescent technique as an analytical tool. Many metal cations catalyze the reaction of luminol, H2O2, and OH in aqueous solution to increase light emission or at least to increase the speed of the oxidation to produce the emitter and therefore the onset and intensity of light production. The availability of highly specific and sensitive detection tools may not be the final answer. The assays should be cost-effective and simple so that they can be employed at the production farm level. The profit margin at the production level is so narrow that any assay unless it is cheaper than the conventional methods will not be employed. Alternatively, these assays could be used by the animal or bird breeder. An issue that is a major impediment to the adoption of molecular pathogen detection techniques is the lack of vertical integration within the industries. Except for the poultry industry, which is highly integrated, the rest of the animal industry is not vertically integrated and so the adoption of these methods by small-scale growers and producers is highly uncertain. It is, however, obvious that DNA or RNA based assays will not totally replace culture based methods. Nevertheless, molecular assays will significantly improve the questions and answers that one can obtain from such pathogen detection assays. More research is needed in this area to integrate detection technologies that can be utilized at the farm level.
Public Health Hazards due to Wastes
The generation of waste and the collection, processing, transport and disposal of waste, the process of ‘waste management’, is important for both the health of the public and aesthetic, and environmental reasons. Waste is anything discarded by an individual, household or organization. As a result waste is a complex mixture of different substances, only some of which are intrinsically hazardous to health. The potential health effects of both waste itself and the consequences of managing it have been the subject of a vast body of research.
The UK Environment Agency classifies waste as either controlled waste or non-controlled waste from households (municipal solid waste), commercial and industrial organizations and from construction and demolition. Non-controlled waste includes waste generated from agriculture, mines and quarries and from dredging operations. In 1998–99, over 470 million tons of waste were generated in the UK. The mean production of daily household and commercial waste in EU Member States in 1993–96 was approximately 370 kg/capita/annum, ranging from 350 to 430 kg. Municipal solid waste (MSW) consists of many different things including food and garden waste, paper and cardboard, glass, metals, plastics and textiles. These are also generated by commercial and industrial organizations although large volumes of chemical and mineral waste are produced in addition,
depending on the sector. Agricultural waste comprises mainly slurry and farmyard manure with significant quantities of straw, silage effluent, and vegetable and cereal residues. Most of this is spread on land. Certain types of waste are defined as hazardous because of the inherent characteristics (e.g. toxic, explosive). The three largest waste streams in this category are oils and oily wastes, construction and demolition waste and asbestos, and wastes from organic chemical processes.
Controlled waste includes waste generated. The most common public health threat hazardous waste poses is the contamination of our drinking water supplies. In Woburn, contaminated drinking water caused a cluster of leukemia cases in children. Contaminated soil also poses a problem. At Love Canal, toxins oozing out of the dump caused rashes, burns and other problems to both children and adults coming in contact with it. Toxins can also seep into buildings built above hazardous waste sites, causing indoor air problems, respiratory diseases and chemical sensitivity. Hundreds of people across New England are trapped in their contaminated homes waiting for the polluters or the environmental agencies to clean-up the contamination. The experience of living in a contaminated home not only ends normal life, but also can cause serious psychological illnesses.
