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Emission of Airborne Particulates from Animal Production

 

 

J. Seedorf and J. Hartung
Institute for Animal Hygiene and Animal Welfare of the
School of Veterinary Medicine Hanover,
Bünteweg 17 P, 30559 Hanover
Abstract

The air in animal housing contains gases, odours, dust particles and microorganisms which are discharged by way of the ventilation system into the environment. There is increasing concern within parts of the population that these compounds may affect the respiratory health of people living close to livestock enterprises. Particularly compounds like dust, microorganisms and endotoxins, which are also addressed as bioaerosols, are supposed to play a role in the prevalence of respiratory affections in receptive humans as it is known from occupational health reports of farm workers in animal houses. A brief survey is presented on airborne particulate emissions from livestock buildings. The concentrations of airborne microorganisms in livestock buildings are between some 100 and several 1000 per liter. Staphylococcae, streptococcae, colilike bacteria, fungi, moulds and yeasts are regularly found. The 24 h average concentrations of dust in animal barns vary considerably. In poultry houses the highest inspirable resp. respirable dust concentrations (up to 10 mg/m3 resp. 1.2 mg/m3 ) were found, followed by pig houses (5.5 mg/m3 resp. 0.46 mg/m3 ) and cattle barns (1.22 mg/m3 resp. 0.17 mg/m3 ). The concentrations of endotoxins in the airborne dust can range from 0.6 ng/m3 (cattle, respirable dust) to 860 ng/m3 (laying hens, inspirable dust). The presently discussed occupational health threshold at the workplace is around 5 ng/m3 (50 EU/m3 ). The emission rate for respirable dust from piggeries is at about 60 mg/h, from poultry houses nearly 300 mg/h and from cattle barns at 20 mg/h, related to 500 kg liveweight of the animals. Little is known about the distances these particles are transported through the air outside the animal buildings. There is a further need for reducing the emission of environmentally harmful substances by implementing recognized abatement techniques. Urgent actions are required to investigate the travel distance of bioaerosols and whether and how particulate emissions from animal farming can cause health effects in residents living in the rural environment.

Introduction

Modern animal production is increasingly regarded as a source of air pollutants which can be both aggravating and environmentally harmful. The pollutants can give cause for concern for several reasons. There is epidemiological evidence that the health of farmers working in animal houses may be harmed by regular exposure to air pollutants such as gases, dust, microorganisms and endotoxins (DONHAM, 1987; WHYTE et al., 1993; NOWAK, 1998). Equally, animal respiratory health may be compromised by these pollutants (e.g. BAEKBO, 1990; HAMILTON et al., 1993). ELBERS (1991) found in about 50 % of the lungs of slaughter pigs signs of freshly or earlier suffered pneumonia, pleuritis or other respiratory affections. In broilers about 30 % of the birds which are rejected at meat inspection showed lung lesions (VALENTIN et al., 1988). The third reason of concern is the fact that livestock buildings, manure storage facilities, spreading and even grazing cattle are major sources of pollutants which contribute to soil acidification and global warming (JARVIS and PAIN, 1990, HARTUNG et al., 1990, ECETOC, 1994, WILLIAMS, 1994). Fourthly, particulate emissions such as dust and microorganisms from buildings are supposed to play a role in respiratory affections in people living in the vicinity of animal enterprises. MÜLLER and WIESER (1987) calculated the travel distance of viable bacteria from a laying hen house of 200 to 300 m downwind. Little is known about the emission amounts and the distribution characteristics of dust particles in the surrounding of animal houses. Tentative experiments using high volume sampling and a Lidar technique around a piggery revealed distinctly higher particle concentrations and endotoxins 115 m downwind the building as compared to the reference sampling point upwind (HARTUNG et al., 1998). However many factors such as wind and weather conditions can have a considerable influence.

This paper summarizes the most important airborne particulate emissions from animal farming and discusses aspects of the environmental risks for nearby residents and the farer environment.

Dust emissions

The dust in animal housing originates from the feed, the bedding material and from the animals themselves. A small amount enters the animal house with the incoming ventilation air. The dust particles are carriers for gases, microorganisms, endotoxins and various other substances such as skin cells and manure particles (DONHAM, 1989). Animal house dust consists up to 90 % of organic matter (AENGST, 1984).

The amount of airborne dust fluctuates greatly both in the course of a day and according to the type of animal. Recent investigations carried out in 329 animal houses in four different EU countries revealed the dust concentrations given in Table 1. The results are given in 24 hours mean values for inhalable and respirable dust (TAKAI et al., 1998). The highest dust concentrations are found in poultry housing followed by pig and cattle.

Most of this dust may leave the animal houses by way of the exhaust air and is distributed in the surroundings. Assuming a mean dust concentration of 2 mg/m3 in the exhaust air of a piggery housing 1000 fattening pigs and a mean ventilation rate of 200 m3 /LU per hour (LU = livestock unit equals 500 kg live weight) throughout the year the total dust emission per year will be about 500 kg. In Figure 1 the mean dust emissions of the 329 animal houses are given as average values to elucidate the amounts of bioaerosols which are regularly emitted into the environment. The emission rate of respirable dust from piggeries is about 60 mg/LU and hour. Presently it is unknown how far these fine particles are distributed in the environment of animal houses (HARTUNG, 1998).

The health effects of dust particles depend very much on the nature of the dust (organic, not organic), the compounds the particles are carrying (bacteria, toxins) and the diameter of the particles. Particles with aerodynamic diameters smaller than 5 Ám can penetrate deep into the lung. The larger particles are deposited in the upper airways. High dust concentrations can irritate the mucous membranes and overload the lung clearance mechanisms. Together with the dust particles microorganisms can be transported into the respiratory system causing infections. Endotoxins can trigger allergic reactions in the airways of susceptible humans, even in low concentrations.

Microorganisms and endotoxins in animal houses

Microorganisms and endotoxins belong to the prominent aerial pollutants in farm animal housings which have been linked with several production diseases (WATHES, 1994; HARTUNG, 1994) and which are assumed to pose a risk for the health of farmers and workers in the farms (DONHAM, 1990) and to the neighbouring residential areas around intensive livestock enterprises. Concentrations of airborne microorganisms are particularly high in pig and poultry houses (CLARK et al., 1983; CORMIER et al., 1990; EWERTH et al., 1983).

Usually microorganisms and endotoxins (lipopolysaccharides, LPS) are associated with dust particles and present a biologically active aerosol (bioaerosol).

The quantities eg of bacteria in animal house air can be very high at times but show vast variations which depend on daily and seasonal influences as well as on the animal species and on the keeping and management system (MÜLLER and WIESER, 1987). Another crucial problem when measuring airborne microorganisms is the sampling method. At present there is no generally accepted standard sampling procedure available.

The concentrations of airborne microorganisms shown in Figure 2 give a current overview of the microbiological status of the air in animal houses in Germany (SEEDORF et al., 1998). Total counts of bacteria, Gram3 negative bacteria (Enterobacteriaceae) and fungi and yeasts were of general concern. The results of 61 daily and 25 nightly measurements are shown, expressed as average log value for each animal type.

The highest bacteria concentrations were detected in broiler houses. Concentrations of about 6.43 log CFU per m3 air on average were found during the day as well as during the night. In contrast to broiler houses, houses for laying hens had lower concentrations of between 4 and 5 log CFU per m3. For pigs, average concentrations of 5.1 log CFU per m3 and for cattle of 4.3 log CFU per m3 were detected. In all cases the concentrations were greater in the day than at night. This diurnal distribution was also observed for Enterobacteriaceae with the exception of layers. The overall concentrations differed during the day between 3 and nearly 4 log CFU per m3. Only fattening pigs and layers had higher yields of Enterobacteriaceae, ranging between 4.2 and 4.7 log CFU per m3. In cattle houses, concentrations of 2.3 log CFU per m3 and in pig and poultry houses 3.9 log CFU per m3 were measured during the night. The mean daily fungi concentration was 3.8 for cattle, 3.7 for pigs and 4.0 for poultry log CFU per m3 , respectively. During the night, the mean fungi concentration was 3.6 for cattle, 3.8 for pigs and 3.7 log CFU per m3 for poultry.

Based on the concentration of airborne microorganisms, the measurements were ranked by animal type. During the day and night, broiler houses had the highest concentrations of total bacteria and of fungi, while the highest concentrations of Enterobacteriaceae were recorded during the day in fattening pig units. The highest concentration was found during the night in houses for laying hens.

The results of endotoxin (ET) measurements are summarised in Tables 2 and 3. Compared with pigs and poultry the ET concentration in cattle houses was clearly low. For inhalable ET, mean concentrations ranged between 7.4 and 63.9 ng m-3 and for respirable ET, concentrations ranged between 0.6 and 6.7 ng m-3 . Mean ET concentrations were higher for pigs. Inhalable ET concentration ranged between 52.3 and 186.5 ng m-3 with related respirable ET concentrations of between 7.4 and 18.9 ng m-3 . Concentrations were highest for poultry; mean values ranged between 338.9 and 860.4 ng ET m-3 air in inhalable dust fractions and from 9.6 to 58.1 ng ET m-3 air in respirable dust. The overall percentage of the RD/ID ratio differed between species, ie. 8.6 % for cattle, 8.8 % for pigs and 5.7 % for poultry. For the RN/IN ratio, values of 13.9, 12.2 and 9.0% were calculated, respectively.

The results of the statistical analysis showed that poultry had the highest ET concentrations in each of the four dust fractions (p<0.001), followed by pigs and cattle. Calves had higher ET concentrations in the ID (p<0.0005) and IN (p<0.001) fractions than dairy cows and beef cattle. For the same dust fractions significant variations between the different housing types were estimated. For ID samples, the ET concentration was higher in cattle buildings with litter (p<0.01), while cattle houses with slats showed higher ET concentrations for IN samples (p<0.04).

Pig houses in The Netherlands had the highest ET concentrations in the RN fraction (p<0.03). The highest ET concentrations for ID (p<0.007), IN (p<0.007), RD (p<0.0004) and RN (p<0.0002) in weaner houses were detected with mesh or slat flooring. As a consequence, for nearly all dust fractions the ET concentration was higher in the mesh/slats housing type (p<0.03) than in buildings with litter or slats alone. Housing types with litter showed the highest ET concentrations (p<0.002) only for ID. Differences between poultry houses were observed. Poultry houses in the UK showed the highest ET concentrations for ID (p<0.0005), IN (p<0.0008), RD (p<0.004) and RN (p<0.008). Except for ET in IN, aviaries showed the highest ET concentrations for ID (p<0. 04), RD (p<0. 007) and RN (p<0. 0 1). Significant seasonal interactions with aerial ET concentrations were not observed for cattle, pigs and poultry.

Significance for animal and human health

Airborne microorganisms and endotoxins are supposed to contribute to respiratory disorders, in particular of the "multifactorial-type" such as shipping fever in cattle, atrophic rhinitis in pigs or infectious bronchitis in poultry (WEBSTER, 1985). Together with dust microorganisms can stress the defence mechanisms of animal or man and can reduce resistance. Over-sensitivity reactions and toxic effects by allergens and toxins are also possible (ZEITLER, 1988). There are numerous reports on complaints on respiratory problems among farmers and farm workers. In some investigations up to 70 % of the farmers respond with respiratory symptoms after working in the animal house atmosphere (HEEDERIK et al., 1991). Which of the compounds are responsible is still unclear. Experiments using nasal lavage show that pig house dust containing endotoxins increases the inflammatory reaction of the nasal muceous membranes of humans distinctly (NOWAK et al., 1994). Even dusts with low endotoxin concentrations provoke prominent reactions whereas the application of dust which was free of endotoxins was not followed by signs of inflammation. It seems that the role of airborne endotoxins from livestock housing should be given more attention.

Emission of airborne bacteria, fungi and endotoxins

The microorganisms and endotoxins in the air of animal houses are emitted into the environment by way of the exhaust ventilation system. The amount of these emissions is calculated on the base of the ventilation rate and the indoor concentrations. A common method to estimate the air exchange is the carbon dioxide balance method (van OUWERKERK, 1994). The principle is based on the assumption that at a given carbon dioxide production indoors, mainly by the animals, and at a constant level outdoors the indoor concentration is only influenced by the air exchange which is expressed eg as ventilation rate usually related to 500 kg live weight of the animals kept in the animal house (m3 per 500 kg and h). The following data are mainly given as an average over 24 hrs.

The emission rates for airborne microorganisms were calculated and expressed as log CFU per h and 500 kg live weight (LW). The mean emission levels over 24 h are shown for all livestock buildings and microbial type in Figure 3. The highest emission rates of total bacteria were measured in broiler houses, namely 9.5 log CFU per h and 500 kg LW but the range of emission rates amongst the other species and housing types was much less and the average rate was approximately 7 log CFU per h and 500 kg. The emisson rates of Enterobacleriaceae were much lower. Layers had the highest emission rate of 7.1 log CFU per h and 500 kg, sows had the lowest emission rate of 6.1 CFU per h and 500 kg. For fungi the range of emission rates was from 7.7 log CFU per h and 500 kg for broilers to 5.8 log CFU per h and 500 kg for weaners.

In contrast with inert pollutants, emission calculations for microbes have to take into account the biological half-life period of microorganisms under varying environmental conditions. This is especially important when estimating both the number and dispersion of viable microbes. These calculations are the theoretical basis for epidemiological and environmental risk assessments. Broiler houses showed the highest emission rates on average. Compared with emission rates from other animal types, the release of total bacteria was more than a 100 fold higher. The health hazard of such high emissions is relevant to the design of ventilation systems. The position of air outlets on the roof or in the wall determine the potential transmission of such pollutants. Furthermore, the weather conditions and the nature of the surrounding area (forest, meadows) also has to be taken into account. A pig unit surrounded by meadows and with roof outlets and relatively low emission rates may distribute the compounds farer than a broiler house surrounded by many trees and with wall outlets.

Recent studies have shown, that emissions can be reduced by installing biofilters or bioscrubbers. These devices have been developed to reduce odour and ammonia emissions but they can also control emissions of bioaerosols. This however deepends very much on the quality and management of the filter and of the contamination of the washing water which used to remove most of the dust from the air before entering the filter. The microbial emission from the filter can be several magnitudes higher for certain microorganism species than in the animal house air (SEEDORF et al., 1999). High energy costs and frequent maintenance to guarantee cleaning efficiency are crucial when using such devices.

Role of airborne emissions in the environment

There is increasing concern that bioaerosols which are emitted into the ambient air may pose a health risk to humans living nearby. Investigations on pig farms have shown that the concentrations of airborne bacteria about 100 m off pig farms are around 1700 CFU m-3 in winter and 930 CFU m-3 in spring (PLATZ et al., 1995). The indoor concentrations were at 6.04 log CFU per m3 in winter and 5.76 log CFU per m3 during summer. Investigations during a whole year at 8 different sampling places in an area with high livestock density revealed pronounced distance dependend bacteria concentrations and a huge seasonal influence on the fungi concentrations in particular. Higher concentrations were found at distances up to 150 and 250 m from the source (HARTUNG, 1992). Similar results for bacteria are also reported earlier (MÜLLER and WIESER, 1987). Some recent experiments showed distinctly higher particle densities about 115 m downwind of a piggery using a Lidar detection device (HARTUNG et al., 1998). However, there is still a considerable lack of knowledge on the travel distances of both viable and non viable particles from animal houses.

Table 5 summarizes our present knowledge where the emissions may develop effects in the closer and farer environment of animal enterprises. Concerning odours and ammonia sufficient knowledge is available, to give an estimation. Odours are relevant in the near of animal houses only. Ammonia can cause damages close to the sources when high amounts are released. It also acts in the farer environment by overfertilizing soils and water and contributes to the decay of forests (acid rain problem). Methane, nitrous oxide and carbon dioxide contribute to the greenhouse effect, they don't develop significant problems indoors or close to the animals. Hydrogen sulphide is noticed as a prominent odourous compound outside the animal houses. Little is known about the fate of the microorganisms and endotoxins outside the buildings, although there is increasing concern that these compounds may cause harm to the population living in the vicinity of animal enterprises, particularly in areas with high animal densities. From epidemiological studies it is assumed that the virus causing Mouth and Foot Disease can travel airborne more than 50 miles. For the bioaerosols from animal production such as fine dust, endotoxins, bacteria, fungi and their spores similar dispersion models are still lacking.

Conclusions

  • There are loads of dusts, microoganisms and endotoxins present in animal house air.
  • There seem to be a health risk for animal and man indoor caused by these substances.
  • These substances are emitted in considerable amounts from buildings and manure stores into the environment.
  • Suitable abatement techniques for gases such as ammonia and particulates are available. They should be employed in practice.
  • There is still a considerable lack of knowledge on the distribution and health effects of airborne particulate emissions from livestock sources in the environment.
  • For licensing new animal farms as well as residential areas in the farming environment more precise informations on the travel distance of harmful particles and compounds are required.
  • For the realization of these aims the cooperation of farmers, agricultural engineers, veterinarians and governmental agencies is necessary.

    Acknowledgements

    The authors thank Deutsche Bundesstiftung Umwelt for financial support.

    Much of the work described was funded by the Commission of the European Union under Project No PL900703. Supplementary funding was also received from the Ministry of Agriculture, Fisheries and Food of Lower Saxony, Germany.

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    Correspondence:

    Prof. Dr. J. Hartung,
    Institut für Tierhygiene, Tierschutz und Nutztierethologie,
    Tierärztliche Hochschule Hannover,
    Bünteweg 17p, 30559 Hannover, Germany

    Tab. 1: Mean dust concentrations in the air of livestock housings, mg/m3 , n = 329

    Tab. 2: Means of airborne endotoxin (ET) concentrations (ng ET m-3 ) for different animal types and daily and nightly ratio (%) between respirable and inhalable ET

    Tab. 3: Mean endotoxin (ET) concentrations (ng ET m-3 ) in ID, IN, RD and RN samples in relation to country, animal type and housing type and the ET ratio (%) between RD/ID and RN/IN

    Tab. 4: Environmental impact of some emissions from livestock sources.

     

    Fig.: 1: Dust emissions from cattle, pig and poultry barns

    Fig. 2: Concentration of airborne microorganisms in livestock buildings. Day: n = 61; Night: n = 25

    Fig. 3: Emission rates of microorganisms. n = 61

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