Health complaints and immunological markers of exposure to bioaerosols among biowaste collectors and compost workers

OBJECTIVES—In a cross sectional study, work related health complaints and diseases of 58 compost workers and 53 biowaste collectors were investigated and compared with 40 control subjects. Levels of specific IgG antibodies to moulds and bacteria were measured as immunological markers of exposure to bioaerosols.
METHODS—With a standardised protocol, the participants of the study were interviewed for work related symptoms, conditions of exposure to bioaerosols at their workplaces, exposure to bioaerosols from other sources, atopic diseases, and smoking habits. They were clinically examined by physicians specialised in occupational medicine. Also, concentrations of specific IgG antibodies against antigens of moulds and actinomycetes occurring regularly at these workplaces were measured and compared with the health complaints of the workers.
RESULTS—Compost workers had significantly more symptoms and diseases of the airways (p=0.003) and the skin (p=0.02) than the control subjects. Health complaints of biowaste collectors did not differ significantly from those of the control group. Subjects with atopic diseases were underrepresented in the compost workers (p=0.003). Significantly increased antibody concentrations against fungi and actinomycetes were measured in workers at composting plants. The concentrations in biowaste collectors did not differ significantly from those in the control subjects. A significant association between the diseases and increased antibody concentrations were found in the compost workers.
CONCLUSION—The high exposure to bioaerosols of compost workers is significantly associated with a higher frequency of health complaints and diseases as well as higher concentrations of specific antibodies against moulds and actinomycetes. A healthy worker effect is indicated by the underrepresentation of atopic diseases among the compost workers compared with biowaste collectors and the control group.


Keywords: exposure to bioaerosols; organic dust; IgG antibodies; moulds; actinomycetes     

Comparative Investigations of Airborne Culturable Microorganisms in Selected Waste Treatment Facilities and in Neighbouring Residential Areas

The evaluation of airborne microorganisms in waste treatment facilities is complicated by different measuring systems, a lack of measuring standards and large variations between individual counts. In the present study, different sectors of the waste management industry were compared by determining median values of airborne culturable microorganisms from numerous parallel counts over a prolonged time period. The samples were taken during the warm season using the six-stage Andersen volumetric sampler in a large composting plant and its immediate vicinity, in an agricultural composting plant, a waste disposal site, and a sorting facility for recyclable materials. Control samples were taken at a site not influenced by the waste management industry in an open and largely uninhabited area. The highest median values for culturable bacteria (37°C) found were 1,1×10⁵ CFU/m³, for moulds (25°C) 1,4 ×10⁵ CFU/m³, and for A. fumigatus (37°C) 1,7 ×10⁴ CFU/m³ in the sorting cabins of the sorting facility (p<0.001). The highest median values for thermophilic bacteria (actinomycetes and bacillaceae, 50°C) were 7,3×10³ CFU/m³ in the large composting facility. In all other facilities as well as in the neighbouring residential areas of all facilities investigated, all median values were significantly lower and corresponded to the naturally occurring levels: approx. 10² CFU/m³ for bacteria, approx. 10³ CFU/m³ for moulds and approx. 10¹ CFU/m³ for A. fumigatus and thermophilic bacteria. Only in the neighbouring residential area of the large composting plant, the median values for thermophilic bacteria were approx. 10² CFU/m³, but an additional impact from farms cannot be excluded in this case. These results show permanent increased loads of the investigated microorganisms inside large composting facilities and especially in the sorting cabins for recyclable materials. The increasing number of reports on potential health hazards in these areas require adequate measures on the part of occupational medicine in order to limit the health risk to a minimum. The most important task is the automatization of the sorting process for recyclable materials.     

Critical working tasks and determinants of exposure to bioaerosols and MVOC at composting facilities

Airborne bioaerosols and Microbial Volatile Organic Compounds (MVOC) concentrations were simultaneously monitored at a composting facility and the main determinants of atmospheric concentrations were characterised, in order to help protect workers from potential adverse health effects. Microorganisms and MVOC were sampled during various process stages and working tasks, both on site at the two units (green waste and biowaste), and at the border of the composting facility. Ambient monitorings were performed at sampling points deemed representative of occupational exposures for critical working tasks, and additional individual samplings were done on workers for MVOC. A linear regression model was used to estimate the determinants explaining exposure variability to bioaerosols and volatile compounds. Bioaerosol concentrations ranging from 10² to 1.8 × 10⁵ cfu/m³ were observed, with peak exposures in the shredding and waste sieving phases. Shredder and siever adjustments, cleaning and maintenance of aeration systems/composting containers were associated with the highest bioaerosols ambient concentrations. MVOC concentration profiles were highly variable depending on the composting unit. Shredding/rotting phases were associated with the highest levels at respectively green waste/biowaste units. Terpenoids and alcohols were the most predominant compounds, and total MVOC levels reached up to 40 mg/m³. Individual and ambient MVOC concentrations did not show significant differences. “Season”, “waste turning”, “process stage” and “sampling location” were the main determinants of bioaerosols and MVOC concentrations variability. Moderate or no correlation was found between microorganisms and volatile organic compounds concentrations. The high bioaerosol and MVOC levels observed as well as the potential of additive irritative effects resulting from these exposures justify the wearing of personal protective equipments for the associated working tasks. On the other hand, low concentrations recorded in the immediate vicinity of the facility suggested a limited environmental impact from the composting activity. Simultaneous monitoring of bioaerosols and MVOC exposures at various sampling locations and during main working tasks (including cleaning/maintenance tasks) seems of importance for improving health risk assessments at composting facilities.     

Assessment of airborne bacteria in selected occupational environments in Quezon City,Philippines

Exposure to bioaerosols has been associated with health deterioration among workers in several occupational environments. This highlights the need to study the microbiological quality of air of workplaces as no such study has been conducted yet in the Philippines. To detect and characterize the culturable mesophilic airborne bacteria in selected occupational environments we used passive sedimentation technique. It was observed that the number of colony-forming units was highest in junk shop, followed by the light railway transit station and last the office. By contrast, the bacterial composition was similar in all sites: Gram-positive cocci > Gram-positive bacilli > Gram-negative bacteria. Staphylococcus aureus and Bacillus spp. were also detected in all sites. These findings suggest that the presence of airborne bacteria may be a potential health hazard in urban occupational environments in the Philippines.     

Assessment of airborne microorganism contamination in an industrial area characterized by an open composting facility and a wastewater treatment plant

In order to assess the potential exposure hazard to workers and people living in the immediate surroundings of an area characterized by an open composting facility and a wastewater treatment plant, a quantitative and a qualitative analysis of airborne microorganisms were carried out. Air sampling was performed once a week for four consecutive weeks in summer and winter. Six sites were selected as air sampling sites: one was upwind at approximately 40 m from the facilities; the other five were downwind at increasing distances from the facilities, with the furthest at 100 m away. Monitoring permitted us to verify the influence that the composting activities and wastewater treatment had on the bacterial and fungal contamination of the air. The results obtained have been expressed by means of contamination indexes that have already been used in previous works: a major microbiological contamination near the plants was evidenced. Near the facilities, mesophilic bacteria, psychrophilic bacteria and microfungi showed the highest median concentrations, respectively, of 307.5, 327.5 and 257.5 CFU/m³. Moreover, the season generally influenced the concentration of the bacteria as well as of the fungi; higher in summer than in winter. The contamination index global index of microbial contamination (GIMC/m³) showed mean values of 4058.9 in summer and 439.7 in winter and the contamination index—amplification index (AI) showed values of 4.5 and 1.1 in the same seasons, respectively. Controlling the seasonal effect, mesophilic bacteria, Pseudomonas spp. and Enterobacteriaceae showed a significant decline in concentration with respect to upwind air samples and with increasing distance. Both GIMC and AI showed a significant decline with respect to upwind air samples by increasing the distance from facilities after adjusting for the seasonal effect. In conclusion, even if these plants do not represent a potential risk for nearby populations, they may pose a potential health risk for workers.     

Exposure to Airborne Culturable Microorganisms and Endotoxin in Two Italian Poultry Slaughterhouses

Even if slaughterhouses’ workers handle large amounts of organic material and are potentially exposed to a wide range of biological agents, relatively little and not recent data are available. The main objective of this study was to characterize indoor concentrations of airborne bacteria, fungi, and endotoxin mod = Im (endotoxin～Gram-negative*plant*filter) in two Italian poultry slaughterhouses. Air samples near air handling units inlets were also collected. Since there are not standardized protocols for endotoxin sampling and extraction procedures, an additional aim of the study was to compare the extraction efficiency of three different filter.. The study was also aimed at determining the correlation between concentrations of Gram-negative bacteria and endotoxin.

In Plant A bacterial levels ranged from 17.5 to 2.6×10³ CFU/m³. The highest concentrations were observed in evisceration area of chickens, between the automatic detachment of the neck and washing offal, and near birds coupling before hair-chilling. The highest mean value of Gram-negative (266.5 CFU/m³) was found near the washing offal of turkeys. In Plant B bacterial concentration ranged from 35 to 8×10³ CFU/m³. The highest concentration. with the highest value of Gram-negative (248 CFU/m³), was found after defeathering. Fungal concentrations were overall lower than those found for bacteria (range: 0–205 CFU/m³ in Plant A and 0–146.2 CFU/m³ in Plant B).

The microbial flora was dominated by Gram-negative and coagulase-negative staphylococci for bacteria and by species belonging to Cladosporium, Penicillium and Aspergillus genera for molds. The highest endotoxin concentrations were measured in washing offal for Plant A (range: 122.7–165.9 EU/m³) and after defeathering for Plant B (range: 0.83–38.85 EU/m³).

In this study airborne microorganisms concentrations were lower than those found in similar occupational settings and below the occupational limits proposed by some authors. However, these microorganisms may exert adverse effects on exposed workers, in particular for those engaged in the early slaughtering stages, as evidenced by the presence of pathogenic species. The detection of pathogenic bacteria near AHU inlet may constitute a risk to public health and environmental pollution.     

Spatial variations in airborne microorganism and endotoxin concentrations at green waste composting facilities

The emission and dispersal of bioaerosols from open-air commercial composting facilities continues to be contentious. A meta-dataset enumerating cultivable microorganism emission and downwind concentrations is not yet available. A dataset derived from repeated and replicated field studies over a period of two years at two commercial composting facilities is presented. The data characterises patterns in Aspergillus fumigatus, actinomycetes, Gram-negative bacteria and endotoxin emission and downwind concentrations. For all bioaerosols, compost agitation activities had a significant impact on concentrations; levels were variable up to 600 m downwind from site. Bioaerosols declined rapidly from source and exhibited a secondary peak 100–150 m from site boundary. All bioaerosols were found downwind from site in elevated concentrations. Compared to those found 100 m upwind, levels were significantly higher at 180 m downwind for A. fumigatus; at 300–400 m for actinomycetes and Gram negative bacteria, and at 100 m for endotoxins. Periodically, elevated concentrations could be found for all bioaerosols at distances further downwind. The evidence provided by this data set provides operators and regulators of facilities with reliable data to inform the location, risk assessment and bioaerosol sampling strategies of commercial composting facilities.     

Evaluation of exposure–response relationships for health effects of microbial bioaerosols – A systematic review

Studies suggest adverse health effects following exposure to bioaerosols in the environment and in particular at workplaces. However, there is still a lack of health-related exposure limits based on toxicological or epidemiological studies from environmental health or from the working environment. The aim of this study was to derive health-based exposure limits for bioaerosols that can protect the general population as group “at risk” via environmental exposure using analysis of peer-reviewed studies related to occupational medicine, indoor air and environmental health. The derivation of exposure limits should be conducted by the members of a bioaerosol expert panel according to established toxicological criteria. A systematic review was performed in Medline (PubMed) including studies containing both data on exposure measurements and observed health outcomes. In addition, literature recommended by the experts was considered. A comprehensive search strategy was generated and resulted in a total of n = 1569 studies in combination with the literature recommendations. Subsequently, abstracts were screened using defined exclusion criteria yielding a final number of n = 44 studies. A standardized extraction sheet was used to combine data on health effects and exposure to different bioaerosols. After full-text screening and extraction according to the defined exclusion criteria n = 20 studies were selected all related to occupational exposures comprising the working areas wood processing, farming, waste processing and others. These studies were analyzed in collaboration with the bioaerosol expert network in terms of suitability for derivation of health-related exposure limits. The bioaerosol expert network concluded that none of the analyzed studies provided suitable dose–response relationships for derivation of exposure limits. The main reasons were: (1) lack of studies with valid dose–response data; (2) diversity of employed measuring methods for microorganisms and bioaerosol-emitting facilities; (3) heterogeneity of health effects; (4) insufficient exposure assessment. However, several indicator parameters and exposure concentrations could be identified for different bioaerosol-emitting facilities. Nevertheless, health-related exposure limits are urgently needed especially in approval procedures of facilities like composting plants or livestock farms emitting bioaerosols in the neighbourhood of residents. In the regulatory toxicology framework, it is common to use animal experimental studies for derivation of general exposure limits if appropriate environmental epidemiological studies on harmful substances are lacking. This might be another possibility to obtain health-related exposure limits for specific bioaerosol parameters. Furthermore, we recommend to use suitable measurable outcome parameters related to bioaerosols; to measure bioaerosols according to a protocol representative for exposure pattern and duration at the particular work place; to develop standardized detection methods for indicator parameters; to combine different detection methods to compensate for the limitations of each method; to apply new analysis methods to identify the real risk potential.     

A 5-year follow-up study on respiratory disorders and lung function in workers exposed to organic dust from composting plants

Objectives To evaluate acute and chronic effects of long-term exposure to organic dust on respiratory disorders and lung function among employees at 41 composting facilities in Germany. Methods A total of 218 compost workers and 66 control subjects were enrolled in the cohort. They were evaluated using a standardized questionnaire, a clinical examination, and spirometric measurements. Changes of symptoms, respiratory disorders, and lung function were determined in a first survey after 5 years of exposure in 123 compost workers and 48 controls. Exposure measurements were performed at six composting facilities for respirable dust, cultivable microorganisms, and endotoxins. Results Exposure measurements revealed high concentrations of thermo-tolerant/thermophilic actinomycetes and filamentous fungi in the bioaerosols at the composting sites. A significantly higher job fluctuation was observed among the compost workers compared to control subjects (95 vs. 18; p < 0.05). Compost workers reported a significantly higher prevalence of mucosal membrane irritation (MMI) of the eyes and upper airways than control subjects. Conjunctivitis was diagnosed significantly more often in compost workers. Forced vital capacity in percent of predicted (FVC%) of the non-smoking compost workers declined significantly (−5.4%) during the observation period compared to control subjects. The decline of FVC% in 16 compost workers exceeded 10% of initial values. A significant increase was observed in the number of compost workers suffering from chronic bronchitis (RR = 1.41; 95% CI = 1.28–1.55). Allergic alveolitis was diagnosed clinically in two compost workers. Conclusions The exposure to organic dust at workplaces of composting facilities is associated with adverse acute and chronic respiratory health effects, including MMI, chronic bronchitis, and an accelerated decline of FVC%. The pattern of health effects differs from those at other workplaces with exposures to organic dust possibly due to high concentrations of thermo-tolerant/thermophilic actinomycetes and filamentous fungi at composting plants.     

Farmers' exposure to airborne microorganisms in composting swine confinement buildings

Farmers' exposure to airborne microorganisms was studied in 12 composting swine confinement buildings and in 7 buildings with traditional slatted-floor pit systems. Airborne cultivable mesophilic, xerophilic, and thermotolerant fungi, mesophilic bacteria, and thermophilic actinobacteria were determined with a six-stage impactor. Furthermore, the total concentrations of microorganisms were determined with filter sampling and direct count using a microscope. In swine confinement buildings where the composting system was functioning properly, the concentrations of microorganisms were 10-1000 times higher than in traditional swine buildings. High concentrations of thermotolerant fungi and thermophilic actinobacteria (up to 10(5) CFU/m(3)), which have been considered to be the main causative agents of farmer's lung, were found in the composting swine confinement buildings that were studied. The conclusion was reached that farmers are exposed to high concentrations of fungal and actinobacterial spores also in swineries, at least in composting confinement buildings. Therefore, personal protection is strongly recommended in composting swineries, especially during the turning of the compost bed.     

Evaluating bioaerosol exposure among bus drivers in the public transport sector

Occupational hazards and consequent health problems suffered by drivers in the public transport sector require preventive measures. The aim of this study was to assess the exposure of drivers to microbiological air contamination (airborne bacteria and fungi) in buses. The air in public transport vehicles was examined in autumn, winter and spring. To evaluate the exposure of drivers to bioaerosols, air samples were collected and examined for the total number of bacteria and fungi in the air, the number of mesophilic aerobic bacteria specified by the number of colony forming units (CFU) per 1 m³ of air. The results of the research show that public transport as a workplace can be considered to be a significant risk to health.     

Bioaerosol exposure from composting facilities and health outcomes in workers and in the community: A systematic review update

Background

Rapid population growth and urbanisation around the world has led to increasing waste generation rates. Composting of organic waste in large-scale facilities is part of a growing trend in the UK, and elsewhere, to better manage and re-use the organic waste. However, composting inevitably generates bioaerosols, which have been associated with human health effects. In 2015, we reported that there was some, albeit limited, qualitative evidence linking bioaerosol emissions from composting facilities to poor respiratory health in nearby residents. However, the limited evidence precluded any quantitative assessment. Since then, the number of operational industrial-scale composting facilities in England has increased by 9% - nearly twice the growth from 2012 to 2014. At the same time, rapid urbanisation has led to expansion of city borders with more people living near large composting facilities and exposed to bioaerosol pollution. It is essential that regulatory authorities have access to the most up to date and accurate information.

Effects of bioaerosol exposure on work-related symptoms among Swiss sawmill workers

Objective Exposure to bioaerosols in the occupational environment of sawmills could be associated with a wide range of health effects, in particular respiratory impairment, allergy and organic dust toxic syndrome. The objective of the study was to assess the frequency of medical respiratory and general symptoms and their relation to bioaerosol exposure. Method Twelve sawmills in the French part of Switzerland were investigated and the relationship between levels of bioaerosols (wood dust, airborne bacteria, airborne fungi and endotoxins), medical symptoms and impaired lung function was explored. A health questionnaire was distributed to 111 sawmill workers. Results The concentration of airborne fungi exceeded the limit recommended by the Swiss National Insurance (SUVA) in the twelve sawmills. This elevated fungi level significantly influenced the occurrence of bronchial syndrome (defined by cough and expectorations). No other health effects (irritations or respiratory effects) could be associated to the measured exposures. We observed that junior workers showed significantly more irritation syndrome (defined by itching/running nose, snoring and itching/red eyes) than senior workers. Lung function tests were not influenced by bioaerosol levels nor dust exposure levels. Conclusion Results suggest that occupational exposure to wood dust in a Swiss sawmill does not promote a clinically relevant decline in lung function. However, the occurrence of bronchial syndrome is strongly influenced by airborne fungi levels.     

Exposure levels of airborne bacteria and fungi in Korean swine and poultry sheds

There is a limited amount of information available on stock farmers' exposure to airborne bacteria and fungi. In this study, the authors measured the airborne bacteria and fungi concentrations 46 times inside two swine sheds and four poultry sheds. Aspergillus, Cladosporium, and Penicillium were the most prevalent fungal genera, as most of the fungi belonged to these groups. Many microbial concentrations exceeded the Korean indoor bioaerosol guideline 800 CFU m(-3) (i.e., colony-forming units per cubic meter of air). This finding suggests the need for a strategy to reduce stock farmers' occupational exposure to the microorganisms in swine and poultry sheds, and the necessity of performing a longitudinal survey to better examine farmer exposure levels and their variability. Another finding was that the use of a sanitary mask may reduce stock farmers' exposure to bioaerosols.     

Airborne bacteria and fungi associated with waste-handling work

Abstract

Background: Municipal workers handling household waste are potentially exposed to a variety of toxic and pathogenic substances, in particular airborne bacteria, gram-negative bacteria (GNB), and fungi. However, relatively little is known about the conditions under which exposure is facilitated.

Methods: This study assessed levels of airborne bacteria, GNB, and fungi, and examined these in relation to the type of waste-handling activity (collection, transfer, transport, and sorting at the waste pre-processing plant), as well as a variety of other environmental and occupational factors. Airborne microorganisms were sampled using an Andersen single-stage sampler equipped with agar plates containing the appropriate nutritional medium and then cultured to determine airborne levels. Samples were taken during collection, transfer, transport, and sorting of household waste. Multiple regression analysis was used to identify environmental and occupational factors that significantly affect airborne microorganism levels during waste-handling activities.

Results: The “type of waste-handling activity” was the only factor that significantly affected airborne levels of bacteria and GNB, accounting for 38% (P?=?0·029) and 50% (P?=?0·0002) of the variation observed in bacteria and GNB levels, respectively. In terms of fungi, the type of waste-handling activity (R²?=?0·76) and whether collection had also occurred on the day prior to sampling (P<0·0001, R²?=?0·78) explained most of the observed variation. Given that the type of waste-handling activity was significantly correlated with levels of bacteria, GNB, and fungi, we suggest that various engineering, administrative, and regulatory measures should be considered to reduce the occupational exposure to airborne microorganisms in the waste-handling industry.     

Microbial contamination of coffee during postharvest on farm processing: A concern for the respiratory health of production workers

Abstract

Coffee workers respiratory health problems, found to be associated with dust exposure in the coffee factories, but the content of the dust is not well known. A cross-sectional survey was conducted to assess the microbial contamination of coffee in dry and wet coffee process, from four farms in two regions of Ethiopia. A total of 36 samples of coffee were collected for laboratory investigation. The microbial load in the dry process ranged from 6.9?×?10² to 7.2?×?10⁵ colony forming units (CFU)/mL while the microbial load in wet process ranged from 2.5?×?10² to 4.6?×?10⁵ CFU/mL. The results indicate the presence of gram negative bacteria in dried and stored beans from both the wet and dry process. During further coffee processing possible release of endotoxin from coffee contaminated by gram negative bacteria might affect coffee workers respiratory health. Further studies are required to assess the relation between bacterial contamination of coffee and endotoxin level in coffee factories.     

Bioaerosol exposure in waste collection: A comparative study on the significance of collection equipment,type of waste and seasonal variation

Recent Danish studies on waste collectors' bioaerosol exposure are summarized. Generally the median exposure levels ranged from 10⁵ to 10⁶ cells m⁻³ (total microorganisms), 10⁴ to 10⁵ cfu m⁻³ (culturable fungi) and 10³ to 10⁴ cfu m⁻³ (culturable bacteria). The type of waste was a governing factor for exposure. Garden waste collectors frequently experienced concentrations exceeding 10⁵ cfu m⁻³ for mesophilic fungi and 10⁴ cfu m⁻³ for the thermophilic fungus Aspergillus fumigatus. Workers collecting compostable, mixed and sorted waste occasionally experienced similar concentrations of the fungal groups while workers collecting ‘bulky waste’ and paper had low exposure. Type of collection vehicle was identified as another governing factor for exposure. Vehicles loaded from the top (approximately 3 m above the ground) caused lower exposure (by a factor of 25) to fungi than vehicles loaded at the level or the breathing zone of the workers. Exposure was also affected by season of the year—the concentration of total microorganisms, culturable fungi, Aspergillus fumigatus and endotoxin was low in winter. Exposure to total microorganisms counted by microscopy was found to have a fairly high validity (Va) as an indicator of exposure to culturable fungi (Va = 1.45) or culturable bacteria (Va = 1.25). Likewise, dust may also be used as an indicator of exposure to total microorganisms (Va= 1.36), culturable fungi (Va= 1.31) and culturable bacteria (Va = 1.35).     

Influence of seasons and sampling strategy on assessment of bioaerosols in sewage treatment plants in Switzerland

An assessment of sewage workers' exposure to airborne cultivable bacteria, fungi and inhaled endotoxins was performed at 11 sewage treatment plants. We sampled the enclosed and unenclosed treatment areas in each plant and evaluated the influence of seasons (summer and winter) on bioaerosol levels. We also measured personal exposure to endotoxins of workers during special operation where a higher risk of bioaerosol inhalation was assumed. Results show that only fungi are present in significantly higher concentrations in summer than in winter (2331 +/- 858 versus 329 +/- 95 CFU m(-3)). We also found that there are significantly more bacteria in the enclosed area, near the particle grids for incoming water, than in the unenclosed area near the aeration basins (9455 +/- 2661 versus 2435 +/- 985 CFU m(-3) in summer and 11 081 +/- 2299 versus 2002 +/- 839 CFU m(-3) in winter). All bioaerosols were frequently above the recommended values of occupational exposure. Workers carrying out special tasks such as cleaning tanks were exposed to very high levels of endotoxins (up to 500 EU m(-3)) compared to routine work. The species composition and concentration of airborne Gram-negative bacteria were also studied. A broad spectrum of different species within the Pseudomonadaceae and the Enterobacteriaceae families were predominant in nearly all plants investigated.     

Pneumoproteins in sewage workers exposed to sewage dust

Purpose

The association between exposure to bacteria and endotoxins in sewage dust and the serum concentrations of pneumoproteins in sewage treatment plant workers were studied.

Methods

Forty-four workers from eight sewage treatment plants and 38 reference workers participated in the study. Microbial aerosol was collected by personal inhalable samplers. The concentrations of bacteria and endotoxins were determined by fluorescence microscopy and the Limulus assay, respectively. Pneumoproteins (Clara cell protein: CC16, and Surfactant proteins A and D: SP-A, SP-D) were determined by ELISA in blood samples collected post-shift.

Results

The exposure to dust ranged from 0.02 to 9.3 (geometric mean (GM) 0.3 mg/m³, of bacteria from 0.3 to 4,900 × 10³ (GM 27 × 10³) cells/m³ and endotoxins from 1 to 3,160 (GM 28) EU/m³. The exposed workers had lower CC16 [arithmetic mean (AM) 4.9 ng/ml] compared to the referents (AM 6.4 ng/ml, p < 0.01). No significant difference was observed for SP-D and SP-A. Exposure to bacteria was positively associated with CC16 (p < 0.05) and SP-D (p < 0.05), adjusting for possible confounders.

Conclusions

This study showed that exposed workers had lower serum concentration of CC16 as compared to the referents, which may reflect a long-term effect on secretion of these pneumoproteins. The positive association between exposure to bacteria and the serum concentrations of CC16 and SP-D may be explained by a transient increased permeability of the lung–blood barrier.