Bunger et a/.118 carried out a cross sectional study, in Germany, to look at work related health complaints and immunological markers of exposure to bioaerosols among biowaste collectors and compost workers. 58 compost workers (mean duration of employment 3 years), 53 biowaste collectors (mean duration of employment 1.5 years) and 40 controls took part. The levels of specific IgG antibodies to fungi and bacteria were measured as immunological markers of exposure to bioaerosols. At the composting plants non-compostable materials were removed by manual sorting, the biowaste was mixed with shredded garden waste and piled in rows and the finished compost was sieved.
The levels of specific IgG antibodies to A. fumigatus, A. nidulans, A. niger, A. versicolor, Penicillium spp. Saccharopoylyspora hirsuta, Saccharopolyspora rectivirgula, Saccharomonospora viridis and Streptomyces thermovulgaris were measured.
The compost workers were found to have significantly more symptoms and diseases of the airways and skin than the control subjects. These included tracheobronchitis, mucous membrane irritation, sinusitis, eczema, dermatomycosis, pyoderma, nausea and ear inflammation. One compost worker complained of typical ODTS symptoms. Severe cases of infection or EAA or asthma were not found. Twenty compost workers had one or several increased antibody concentrations compared with only three biowaste collectors and one control. Significantly higher antibody titres to A. fumigatus were measured in workers at the composting plants. Compost workers also had higher titres to the other
116 A. Neef, A. Albrecht, F. Tilkes, S. Harpel, C. Herr, K. Liebl, T. Eikmann and P. Kampfer, Schriftenr. Ver. Wasser Boden Lufthyg., 1999, 104, 655-664.
117 R. Hofman, R. Böhm, G. Danneberg, S. Gerbi-Rieger, E. Gottlich, A. Koch, M. Kuhner, V. Kummer, K. Leibi, W. Martens, T. Missel, A. P. U. Neef, R. Rabe, B. Schilling, F. Tilkes and P. Wieser, Schriftenr. Ver. Wasser Boden Lufthyg., 1999, 104, 1-80.
118 J. Bunger, M. Antlauf-Lammers and T.G. Schulz, Occup. Environ. Med., 2000, 57, 458-464.
fungal antigens compared to biowaste collectors and control subjects. Significantly increased antibody titres were also obtained for Saccharopolyspora rectivirgula and Streptomyces thermovulgaris. The concentrations for Saccharopolyspora hirsuta were also increased. There was a significant association between diagnosed diseases and increased IgG antibodies in the compost workers. There was also significant association between the duration of employment of the compost workers and the increased IgG titres, suggesting progressive development of IgG antibody responses with duration of exposure.
The workers involved in this study had been in the industry for a relatively short length of time (three years). Longitudinal studies into the long-term health effects of exposure to compost bioaerosols are needed to investigate whether workers who develop IgG against the allergens to which they are occupationally exposed go on to develop occupationally related symptoms.
Brown et a/.119 reported a case study of a man who developed hypersensitivity pneumonitis after working on the compost in his garden. Symptoms included respiratory difficulty about two hours after commencing work, fatigue, a non-productive cough, fever, chills, and pain in the joints. The patient made a full recovery within a few days, but the symptoms reoccurred on two subsequent occasions. The patient was found to have precipitating antibodies to Thermoac-tinomyces vulgaris and positive skin prick test to Aspergillus. The patient also had precipitating antibodies against an extract made from his compost pile. The patient had spent some considerable time gardening with the compost, working long hours every weekend. However, no information was reported on his possible exposure levels.
Douwes et a/.47'120 carried out a small study on 14 Dutch compost workers and 10 controls. For the duration of the study, nasal lavage was performed before and after the work shift on Mondays and Fridays. Mean personal dust and endotoxin exposures ranged from 0.4 to 3.1 mg m ~3 and 50 to 100 EU m ~3 respectively, and glucans ranged from 0.36 to 4.85 jug m-3. Fungi levels were indicated to be over 106 cfu m"3, total bacteria 109 cfu m-3 and Gram-negative bacteria 104 cfu m "3. There was a cross shift increase in total cells and inflammatory mediator levels in the workers and a decrease in the controls. Total cells and inflammatory mediator levels in the workers were elevated pre-shift on Mondays compared to controls, and were more elevated at higher than lower endotoxin exposures. Occupational exposure in the compost workers was found to cause acute and (sub-)chronic non-immune or type III allergic inflammation in the upper airways. The authors suggest this is induced by non-allergic pro-inflammatory agents such as endotoxins and /?(l-»3)-glucans.
119 J. E. Brown, D. Masood, J. I. Couser and R. Patterson, Ann. Allergy, Asthma Immunol., 1995, 74, 44-47.
120 J. Douwes, H. Dubbeld, L. van Zwieten, I. Wouters, G. Doekes and D. Heederik, Ann. Agric. Environ. Med., 1997, 4, 149-151.
J. R. M. Swan, B. Crook and E. J. Gilbert Cytotoxic Effect of Compost
Non-immunological factors, such as cytotoxic effects, can also cause inflammatory responses. Cytotoxic responses have been linked to work related ill health in workers exposed to organic dusts. Roepstorff and Sigsgaard121 used a cytotoxic assay to test a range of organic dusts and found that the most aggressive dusts tested were those with a high microbial content. Compost dust (5 week old organic household waste compost) and grain dust exerted an effect at very low concentrations after two hours incubation with monkey kidney cells and human lung carcinoma cells. The dusts tested, in order of decreasing cytotoxic effect, were compost, grain, swine and cotton. Further tests confirmed that the greatest cytotoxic potential occurred when the microbial activity was at its height in the composting process. However, pure endotoxin did not show any cytotoxic activity in the assay.122 Further investigations are required to find out which microbially associated components are responsible for the cytotoxic potential.
The outcome of a large study on the health of a population living near to a grass and leaf composting plant at Islip, New York was recently reported.106 Sixty-three people living near the site and 82 controls were asked to keep a symptom diary. Individual personal exposure data were not collected, but bioaerosols were measured at fixed sites. Daily maximum A. fumigatus counts ranged from 30 to 19000 spores m~3. Average counts were 50 spores m"3 at the control neighbourhood, 100 spores m~3 in the study neighbourhood and 500 spores m~3 at the composting facility. Elevated spore counts (counts exceeding 300 spores m~3) occurred in 15% of the counts in the study neighbourhood, in nearly 20% of the counts at the composting facility and in less than 5% of the counts at the control sites. When the study neighbourhood was downwind of the composting facility spore counts averaged four times the average background level. There was no evidence of A. fumigatus being associated with increases in respiratory or irritative symptoms, but there was an association with ragweed pollen (a common inhalant allergen), ozone, temperature, and time since the start of the study. Within the size limitation of the study, it was concluded that any major increase in allergy and asthma symptom prevalence in people living near the site was too small to detect, even though residents were exposed to elevated concentrations of A. fumigatus as a result of operations at the compost facility. Recer et al.,123 reporting on the same study, recommend that since composting facilities are a permanent source of A. fumigatus spore emissions, this should be considered when siting open air composting sites in heavily developed areas.
Cobb et al.124 investigated health complaints associated with commercial processing of mushroom compost. They could not demonstrate a significant health hazard. A comparison group, with no exposure to compost, had similar
121 V. Roepstorff and T. Sigsgaard, Ann. Agric. Environ. Med., 1997, 4, 195-201.
122 V. Roepstorff and T. Sigsgaard, Waste Manage. Res., 1997, 15, 189-196.
123 G. Recer, E. Horn, K. Hill and W. Boehler, Aerobiologia, 2001, 17, 99-108.
124 N. Cobb, P. Sullivan and R. Etzel, J. Agromed., 1995, 2, 12-25.
symptoms to those living within 3000 feet [914 m] of the site.
Marth et al.125 examined the occupational health of 137 employees at different waste handling facilities, including two composting facilities and three waste sorting plants. A medical examination, questionnaire and IgE measurements were carried out. No statistically significant increase of allergic diseases was found. There were no differences in lung function between workers and a control group. However, workers complained of hoarseness (38%), cough (35%), respiratory infections (23%), diarrhoea (18%), joint and muscle disorders (13%) and conjunctivitis (12%).
Aspergillosis. Under extreme circumstances, such as immunosuppression, A. fumigatus, an opportunistic pathogen, can cause infection.
Leenders et al.126 found that an increase in numbers of patients with invasive aspergillosis could not be explained by an increase in the number of Aspergillus conidia in the outside air. They found that the outside air contained 0-9 cfu m ~3 with A. fumigatus numbers relatively constant, decreasing only from January to April.
Gastric infections. Ivens etal.121 carried out a telephone questionnaire survey of 28 composting employees working at seven plants covering household and garden waste. 11 % reported nausea and 11 % reported diarrhoea, and there was a non-significant association between working with compost and diarrhoea. Among waste collectors the groups with highest exposure to total fungi or total micro-organisms reported fewer symptoms compared to the lower exposed groups. No positive trend was found, although there was an association between fungal exposure and diarrhoea.
I vens etal.128,129 further investigated the relationship between the gastrointestinal problems and bioaerosol exposure among waste collectors. An exposure-response relationship was found between nausea and endotoxin exposure and between diarrhoea and exposure to both endotoxins and viable fungi. Viable fungal spores reached levels greater than 107 cfu m~3, total fungal spores (viable and non-viable) reached levels greater than 2 x 107 cells m-3 and endotoxin levels reached more than 500 EU m~3. Bacteria levels were also very high, with total (viable and non-viable) micro-organisms exceeding 6 x 107 cells m~3.
Sigsgaard et al.38 investigated the health of eight compost workers. None had any skin problems and only one tested positive to a skin prick test against 10 common inhalant allergens. Mean total dust, total micro-organisms and endotoxin were 0.62 mg m~3, 5.44 x 103 cfu m-3 and 0.8 ng m-3 respectively.
125 E. Marth, F. F. Reinthaler, K. Schaffier, S. Jelovcan, S. Haselbacher, U. Eibel and B. Kleinhappl, Ann. Agric. Env. Med., 1997, 4, 143-148.
126 A. Leenders, M. Behrendt, A. Luijendijk and H. Verbrough, J. Clin. Microbiol., 1999,1752-1757.
127 U. Ivens, O. Poulsen and T. Skov, Ann. Agric. Environ. Med., 1997, 4, 153-157.
128 U. Ivens, N.O. Breum, N. Ebbehoj, B.H. Nielsen, O. Poulsen and H. Wurtz, Scand. J. Work Environ. Health, 1999, 25, 238-245.
129 U. Ivens, J. Hansen, N.O. Breum, N. Ebbehoj, M. Nielsen, O. Poulsen, H. Wurtz and T. Skov, Ann. Agric. Environ. Med., 1997, 4, 63-68.
Gastrointestinal symptoms, and ever having experienced vomiting or diarrhoea in relation to work, were significantly more common in the composting industry than in controls.
There is a low incidence of serious chronic work related disease in compost workers (i.e. asthma, extrinsic allergic alveolitis). However, several of the studies show the 'early' responses to the microbial exposures of development of raised levels of IgG and inflammatory mediators in the workers.118'130 Several have also reported a link between gastrointestinal symptoms and working with compost.38'128 More information is required on whether compost workers who have developed raised levels of IgG and inflammatory mediators go on to develop work related diseases/ill health.
Although several of the studies reporting ill health among compost workers also recorded very high exposure to bioaerosols, few studies have looked at the personal exposure levels of the workers on the site. More personal monitoring is needed to establish peak exposure levels which could trigger allergic response and to provide some dose-response data for this industry.
There is not enough information available on the dose-response relationships between microbial exposure and development of ill-health. The differing susceptibility of individuals exposed also confuses the matter. Different people have differing susceptibility to microbially induced ill health. Some people, e.g. atopics, have a higher risk of becoming sensitised to allergens in the workplace even at 'low' concentrations.
It must be noted that in many of these studies, only viable micro-organisms were counted. Non-viable micro-organisms can also cause allergic reactions and this can be a complicating factor when trying to estimate dose-response effects. Eduard131 estimated that IgG antibodies can be detected in response to 105 viable spores and 104 non-viable spores. The results from the airborne micro-organism surveys reported here show that the workers involved in composting are potentially regularly exposed to more than 105 viable spores.
Very high levels of airborne endotoxin were recorded at some sites.82'91'128 Darragh et al.91 recorded levels up to 59 306 EU m~3. Some were well over the levels shown to cause acute ill health responses and with the potential to contribute to the development of chronic diseases.69 At present there are no occupational exposure limits for endotoxin. The Dutch recommended health based occupational exposure limit for airborne endotoxin is 50 EU m-3 (4.5 ng m"3) based on personal inhalable dust exposure measured as an eight hour time weighted average.132 Rylander69 recommends a no-effect level of 10 ngm-3 (100 EU) endotoxin. Microbial emissions from composting sites are a complex mixture and there is the potential of adjuvant effects when inhaling this mixture of toxins and allergens.
As the micro-organisms associated with compost are such common environ-
130 j. Douwes and D. Heederik, Int. J. Occup. Environ. Health, 1997, 3, S37-S41.
131 W. Eduard, Ann. Agric. Environ., 1997, 4, 179-186.
132 DECOS (Dutch Expert Committee on Occupational Standards), Gezondheidsraad, 1998.
mental contaminants that the general population are exposed to in low levels during their normal daily activities, it is very important that control populations - non-occupationally exposed populations, or populations sited some distance from composting activities - are included in studies aiming to collect dose-response data.
Containing the compost in buildings or vessels decreases emissions to the general population but potentially increases compost worker exposure. There is very little data publishe d on exposure of workers and the public due to premises that use in-vessel composting methods.
Few health based studies have recorded the duration of employment of the workers. Large-scale composting is a relatively new, rapidly expanding industry and some ill health effects may not yet have had time to develop. There is also some evidence of a healthy worker effect occurring. It may be that we are not yet seeing the health effects of long term exposure to low/medium levels of microbial emissions of this type.
The people working directly with the compost are exposed to significantly higher levels of bioaerosols but there is, as yet, very little evidence that this is causing ill health. If the workers who have a somewhat higher exposure to the microbial emissions generated by compost are not suffering from ill health effects then the general public who receive a much lower exposure are unlikely to suffer ill health effects. There is very little evidence that people living more than 250 m from composting sites are exposed to microbial emissions that are significantly higher than can be reached 'normally'. However, there are a few recordings of high levels. In one study, increased concentrations were detected 500 m away from a composting site, with concentrations of thermophilic actinomycetes reaching 106 cfu m"3 200m away.116 Due to the A. fumigatus content of the emissions there may be an increased risk to immunocompromised persons sited downwind of a composting site.
Millner et a/.,105 reporting on the discussions at a workshop of experts, posed the question 'Do bioaerosols associated with the operation of biosolids or solid waste composting facilities endanger the health and welfare of the general public and the environment?'. They concluded that 'Composting facilities do not pose any unique endangerment to the health and welfare of the general public'. These conclusions were based on data showing that compost workers, who are exposed to the more concentrated bioaerosols, suffer from very few work related ill health effects. The airborne micro-organism level for most compost sites, whilst several fold higher than normal outdoor levels, are generally lower than in some occupational industries such as the grain industry where exposure to airborne micro-organisms can regularly be well over one million cfu m ~3.13 3'134 However, any exposure to airborne micro-organisms must consititute some risk to respiratory health and there is a need to assess the risks posed by composting facilities, whether actual or perceived, in the context of risks presented by other environmental hazards. Clearly further monitoring and epidemiological data are required.
133 J.R.M. Swan and B. Crook, Ann. Agric. Environ. Med., 1998, 5, 7-15.
134 J. Dutkiewicz, Eur. J. Resp. Dis., 1987, 71, 71-88.
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