An Assessment of Dust, Endotoxin, and Microorganism Exposure during Waste Collection and Sorting

ABSTRACT

This study was conducted to assess inhalation exposure to dust, endotoxin, and microorganisms (including viable bacteria, Gram-negative bacteria [GNB], and fungi) during waste collection and sorting; to identify factors affecting this exposure; and to estimate the gastrointestinal exposure to microorganisms. A total of 48 or 49 workers involved in collecting and sorting waste from households or the street were studied. Each worker carried two personal samplers in which filters were placed in the breathing zone for estimation of inhalation exposure. To assess the possibility of gastrointestinal exposure, microorganisms on the workers' faces were collected before and after work and compared with those collected from office workers. Inhalation exposure levels were categorized according to job title, waste type handled, and working conditions and were compared using analysis of variance. Multiple regression models were developed to identify those factors that substantially affected inhalation exposure. The average exposure level to total dust was 0.9 mg/m³ (range = 0.05 to 4.51 mg/m³), and the average exposure to endotoxin was 1123 EU/m³. The average respective exposure levels to bacteria, GNB, and fungi each exceeded 10⁴ colony forming units (CFU)/m³. The multiple regression models found several factors that significantly explained the variation in levels of inhalation exposure to endotoxin and microorganisms; namely, sex (dust, bacteria, and GNB), job title (GNB and fungi), collection day (dust, bacteria, and GNB), temperature (endotoxin and GNB), humidity (endotoxin and fungi), and region (endotoxin) were significantly associated with exposure to these agents. In addition, the workers' faces were highly contaminated with microorganisms. In conclusion, inhalation exposure to endotoxin and microorganisms was high during waste collection and sorting, which may place workers at risk of developing various health problems, including respiratory complaints.

IMPLICATIONS

This paper reports that waste handlers, including the drivers of waste vehicles, had high inhalation exposures to dust, endotoxin, and microorganisms, and several signifi-cant factors that influence the exposure were identified. Waste handlers' faces, hands, and clothes were extremely contaminated with microorganisms. The results indicate that waste handlers may be at risk of developing various health problems, including respiratory and gastrointestinal complaints. To prevent occupational health risks to waste handlers, government legal support and engineering control measures should be required to control the major factors found in this study.

INTRODUCTION

In Korea, waste collectors are involved in collecting, transporting, sorting, and disposing of various types of biodegradable and nonbiodegradable waste originating from households and the street; industrial waste is handled by another collection system. When biodegradable waste is handled, organic dust including microorganisms can become aerosolized, and waste handlers may be exposed to multiple biological agents containing bacteria, endotoxins, mold spores, glucans, microbial volatile organic compounds, and even infectious materials.1

Exposure to this multitude of bioaerosols may present a high risk of occupational health problems for waste handlers. A high incidence rate of respiratory complaints, gastrointestinal problems, eye and skin irritation, and symptoms of toxic organic dust syndrome have been reported among workers collecting the organic fraction of household waste.2–4 However, few studies have assessed inhalation and gastrointestinal exposure to microorganisms and their toxins. To the authors' knowledge, occupational characteristics affecting exposure to dust, micro-organisms, and their toxins during waste collection and sorting have not been fully examined. The purpose of this study was (1) to assess inhalation exposure to dust, endotoxin, and microorganisms (including viable bacteria, Gram-negative bacteria [GNB], and fungi) during waste collection and sorting; (2) to identify factors affecting inhalation exposure to these agents; and finally (3) to estimate gastrointestinal exposure to microorganisms by assessing microorganism contamination of the face and clothes.

METHODS

Description of Waste Type, Waste Collection, and Sorting

Household waste includes biodegradable food, paper and cardboard; nonbiodegradable waste such as plastic materials, metals, and glass; and nonseparated general waste. In general, source-separated food garbage in Korea is stored in plastic bags or plastic vinyl containers of various sizes and transferred by vehicle to a plant where it is processed for uses including organic fertilizer and animal food. Most source-separated nonbiodegradable waste represents a recyclable fraction composed of, for example, paper, cardboard, plastic materials, wood, glass, and metals. These wastes are sorted at refuse transfer stations to produce raw materials for recycling, and this may require direct waste contact. Nonsepa-rated household waste such as leaves, vegetables, dead animals, and feces contained in vinyl is directly transported to the landfill without sorting. Street waste is composed of a mixture including cigarette butts, leaves, paper, and various types of mixed waste from stationary refuse containers; this waste is manually collected and transported to a landfill or an incinerator.

Inhalation Exposure Assessment Strategy

This study encompasses not only household and street waste collectors, but also workers at the refuse transfer station who sort recyclable, nonbiodegradable waste collected from households. In Korea, the time from beginning to end of waste collection differs among regions. The sampling duration to assess inhalation exposure was determined to cover the whole process of waste collection and ranged from 1.9 to 8.7 hr (mean 5.9 hr); this was considered sufficient time to include inhalation exposure during waste collection and sorting. After categorizing workers who were involved in collecting and sorting waste into similar exposure groups (SEGs) classified according to job title and waste-handling practices, waste handlers representing each SEG were randomly selected to assess inhalation exposure. A total of 48 or 49 workers were each monitored for one entire work session during a specific day. Each worker carried two pieces of personal sampling equipment in which filters were placed in the breathing zone for estimation of inhalation exposure during the entire period of work. One sampler was used for collection of total dust and endotoxin, whereas the other was used for collection of airborne microorganisms including viable bacteria, GNB, and fungi. The personal pumps (part no. 497701, Escort ELF, MSA) were calibrated to approximately 2 L/min for the collection of airborne dust, endotoxin, and microorganisms.

Total Dust

Levels of airborne aerosols were measured using analytical method 0500 of the National Institute for Occupational Safety and Health.5 Glass fiber filters (37-mm diameter, 1-μm pore size, catalog no. 225-7, SKC, Inc.) were desiccated for 1 day and preweighed using a semi-micro electrobalance (model ANALYTICAL, accuracy = 10⁻⁵ g, bias = 0.01%) in a room with a controlled environment (temperature = 23.5 ± 3 °C, relative humidity [RH] = 50 ± 15%). The amount of collected total airborne dust was determined by weighing the filter before and after sampling.

Endotoxin

Concentrations of airborne endotoxin were determined from kinetic turbidimetric analyses of aqueous extracts of the collected airborne dust, using the Limulus amoebocyte lysate (LAL) method (Pyrogent-5000, Lonza) and the time-of-onset protocol as described here. The Pyrogent 5000 reagent was chosen because the lysate was modified to be less reactive to the glucan-sensitive pathway of the LAL assay. All glassware was made pyrogen-free by baking at 200 °C for 1 hr. None of the glassware, pipet tips, or MICROTEST plates (96-well, flat-bottomed, Polystyrene, Falcon, No. 353072) had been previously used. A stock solution of endotoxin (Escherichia coli O55:B5, Lot No. 0000114805, Lonza) was prepared by reconstituting the supplied 50 ng of endotoxin with 2.4 mL of LAL reagent water to produce a concentration of 100 EU/mL (giving a conversion factor of 4.8 EU/ng). The stock solution was shaken vigorously for 15 min at high speed on a vortex mixer. Serial dilutions of the stock solution produced a range of standard concentrations from 0.01 to 100 EU/mL. All extracted samples were vortexed for 30 sec and diluted by serial dilutions of 1:10 and 1:100 using 900-μL LAL reagent water blanks in depyrogenated 13- by 100-mm test tubes. Next, 100-μL volumes of all samples were diluted, spiked, and along with the standards were dispensed into 96-well MICROTEST plates. The assay plates were incubated at 37 °C in a plate reader (Cambrex Elx808, Bio-tek, Inc.) for 10 min. The kinetic turbidimetric assay measured the time of onset of the clotting reaction of the lysate initiated by the presence of endotoxin in the samples and standards. The increase in turbidity was measured as an increase in optical density at 340 nm. Computer software (Lonza, WinKQCL, version 3.1) was used to calculate a standard curve and to assign endotoxin concentrations to the unknown samples. The standard curve showed a strong linear correlation (Pearson r >0.99) between the log endotoxin concentration and the log mean reaction time.

Cultivatable Total Bacteria, GNB, and Fungi

Microorganisms were quantified using the Collection of Airborne Microorganisms on Nuclepore Filters, Estimation, and Analysis method, which includes determination of levels of cultivatable bacteria, GNB, and fungi.6 Nucle-pore filters (37-mm diameter, 0.4-μm pore size, catalog no. 225-5, SKC, Inc.) were used to collect airborne micro-organisms including bacteria, GNB, and fungi. Sterile 0.05% Tween-80 (5 mL) was added to each filter cassette, which was then subjected to orbital shaking for 15 min at room temperature, after which the aqueous extract was decanted and diluted 10-fold in resuspension medium. Aliquots (0.1 mL) of the diluted extracts were plated onto the following solid media obtained from Hanil Komed Corporation: for bacteria, Tryptic soy agar; for GNB, Mac-Conkey agar; and for fungi, Sabouraud dextrose agar with chloramphenicol. The agar plates were incubated at 35 °C for 2 (bacteria and GNB) or 4 days (fungi). For all media, the minimum detectable number of colony forming units (CFU) was 50 per sample. The airborne concentration of microorganisms was expressed as CFU per air volume (m³) taken.

Wipe Sampling Strategy

Contaminating microorganisms from the face and from several areas of clothing were collected by wiping with a sterile swab tester (no. 6437; 3M China), which was then immersed in buffered peptone water, followed by incubation. The area wiped was 3 × 5 cm² of the template (SKC, Inc.). Microorganisms on the workers' faces were collected just before and after work and compared with those collected from office workers. In addition, among 49 waste handlers, certain areas of the clothes such as the pants (n = 27), shoulders (n = 8), sleeves (n = 8), navel (n = 2), gloves (n = 7), and handkerchiefs (n = 1) were randomly wiped at the end of the working shift. The concentration of microorganisms obtained from the face and from clothing was expressed as CFU per surface area wiped.

Data Analysis

The data associated with the waste handlers were categorized according to the handler's sex, job title, waste type handled, company type, and weather conditions during waste collection, all of which were presumed to influence inhalation exposure to dust, total bacteria, endotoxin, and microorganisms (Table 1). Mean exposure levels were compared between categories using analysis of variance. Factors with P values less than 0.25 were selected7 for multiple regression analysis, which was developed to identify those factors that significantly affected exposure to dust, endotoxin, and microorganisms. The respective distributions of the various exposure levels were skewed, and to improve the model the exposure data used as dependent variables in the multiple regression model were log-transformed. Workers associated with one of each pair of dichotomized factors served as a reference group for comparison with other groups. Each descriptive factor was given a value of zero if it was used as a reference variable or a value of one if not. Descriptive statistics, correlations, t tests, and simple linear regressions were conducted using Stata version 10 software (Stata Corporation).

Table 1. Categorization of variables related to waste collection and sorting activities

Variable	Classification
Sex	Male
	Female
Job title	Street cleaner to collect street waste
	Handlers of residential waste including driver of waste
	vehicle
Type of company	Private
	Government
Day during waste collection	Weekday
	Weekend
Temperature	≤20 °C
	>20 °C
Humidity	<50%
	>50%
Region	Seoul
	Other cities in Korea

RESULTS

Dust Exposure

The average dust exposure level was 0.9 mg/m³ (SD = 0.9 mg/m³, range = 0.05 to 4.51 mg/m³) (Table 2). Four of 48 workers were found to be exposed to levels higher than the 3 mg/m³ of organic dust recommended as the occupational exposure limit (OEL) in Denmark.2

Table 2. Inhalation exposure level to dust, endotoxin, and microorganisms during waste collection and sorting

Hazardous Agent	n	Mean	SD	GM	Median	Range
Dust, mg/m^3	48	0.9	0.9	0.6	0.5	LOD–4.5
Endotoxin, ×10^2 EU/m^3	48	11.2	15.1	2.2	4.2	0.04–68.7
Viable total bacteria, ×10^5 CFU/m^3	49	1.9	4.8	0.2	0.2	0.13–23.5
Viable GNB, ×10^4 CFU/m^3	49	7	15.4	0.4	0.4	0.4–58.3
Viable fungi, ×10^4 CFU/m^3	49	2.2	2.8	0.9	0.9	2.4–0.8
Notes: n = Number of waste handlers, SD = standard deviation, GM = geometric mean.

Exposure among workers who sorted nonseparated household waste ranged from 1.37 to 2.69 mg/m³, which was significantly higher than the exposure levels of other workers (P ≤ 0.0001). Significant differences in dust exposure levels were also found among categories of day, humidity, and region (P < 0.05) (Table 3). Household waste handlers were exposed to slightly greater levels of dust (0.9 mg/m³) than were drivers of waste vehicles (0.6 mg/m³), although the difference was not statistically significant. Across all categories, dust exposure level was found to be significantly correlated with inhalation exposure to endotoxin, bacteria, GNB, and fungi (P < 0.01) (Table 4). In the full regression model, in which sex, company type, collection day, humidity, and region were adjusted, sex and day were significant (adjusted R ² = 31.8%, P = 0.0034). Female workers had a higher level of inhalation dust exposure than did male workers, and dust exposure was higher during weekdays than during weekends (Table 5).

Table 3. Comparison of inhalation exposure to dust, endotoxin, and microbes during waste collection and sorting according to the categorization of work characteristics

	Dust, mg/m^3			Endotoxin, EU/m^3			Bacteria, CFU/m^3			GNB, CFU/m^3			Fungi, CFU/m^3
Categorization of Variables	n	Mean (SD)	ANOVA	n	Mean (SD)	ANOVA	n	Mean (SD)	ANOVA	n	Mean (SD)	ANOVA	n	Mean (SD)	ANOVA
Sex			P = 0.242			P = 0.236			P < 0.001			P = 0.214			P = 0.024
Male	44	0.7 (1.0)		44	1.0 × 10^3 (1.5 × 10^3)		45	1.2 × 10^5 (3.6 × 10^5)		45	4.0 × 10^4 (1.2 × 10^5)		45	1.9 × 10^4 (2.6 × 10^4)
Female	4	2.6 (1.0)		4	2.0 × 10^3 (1.1 × 10^3)		4	1.0 × 10^6 (8.9 × 10^5)		4	4.1 × 10^5 (1.2 × 10^5)		4	5.1 × 10^4 (3.5 × 10^4)
Job title			NS			NS			NS			P = 0.248			P = 0.186
Driver	6	0.6 (0.4)		6	1.1 × 10^3 (1.2 × 10^3)		7	1.8 × 10^4 (1.8 × 10^4)		7	7.2 × 10^3 (8.6 × 10^3)		7	8.7 × 10^3 (1.3 × 10^4)
Waste handler	42	0.9 (1.0)		42	1.1 × 10^3 (1.6 × 10^3)		42	2.2 × 10^5 (5.2 × 10^5)		42	8.1 × 10^4 (1.6 × 10^4)		42	2.4 × 10^4 (3.0 × 10^4)
Company type			P = 0.228			NS			NS			NS			P = 0.157
Private	42	0.8 (1.0)		42	1.2 × 10^3 (1.6 × 10^3)		43	2.1 × 10^5 (5.1 × 10^5)		43	7.8 × 10^4 (1.6 × 10^5)		43	2.4 × 10^4 (2.9 × 10^4)
Government	6	1.3 (1.0)		6	7.0 × 10^2 (8.9 × 10^2)		6	8.0 × 10^4 (7.6 × 10^4)		6	1.2 × 10^4 (1.6 × 10^4)		6	6.5 × 10^3 (4.8 × 10^3)
Day			P = 0.011			P = 0.008			P = 0.214			P = 0.089			P = 0.188
Weekday	38	1.1 (1.0)		38	1.4 × 10^3 (1.6 × 10^3)		38	2.4 × 10^5 (5.4 × 10^5)		38	9.0 × 10^4 (1.7 × 10^5)		38	2.4 × 10^4 (3.0 × 10^4)
Weekend	10	0.2 (0.2)		10	2.5 × 10 (3.0 × 10)		11	3.3 × 10^4 (8.6 × 10^4)		11	3.3 × 102 (2.3 × 102)		11	1.2 × 10^4 (1.3 × 10^4)
Temperature			NS			P = 0.027			NS			P = 0.187			P = 0.079
≤20 °C	8	0.6 (0.5)		8	5.6 × 10 (6.3 × 10)		8	2.5 × 10^4 (2.8 × 10^4)		8	3.8 × 10^3 (6.4 × 10^3)		8	5.8 × 10^3 (3.8 × 10^3)
>20 °C	40	0.9 (1.1)		40	2.4 × 10^3 (1.4 × 10^3)		41	2.2 × 10^5 (5.2 × 10^5)		41	4.5 × 10^5 (1.2 × 10^5)		41	2.5 × 10^4 (2.9 × 10^4)
Humidity			P = 0.019			P < 0.001			P = 0.001			P < 0.001			P = 0.001
≤50%	16	1.4 (1.4)		16	2.6 × 10^3 (1.6 × 10^3)		16	5.1 × 10^5 (7.6 × 10^5)		16	2.0 × 10^5 (2.2 × 10^5)		16	4.8 × 10^4 (3.2 × 10^4)
>50%	32	0.7 (0.6)		32	3.8 × 10^2 (7.7 × 10^2)		33	3.7 × 10^4 (6.3 × 10^4)		33	8.8 × 10^3 (1.7 × 10^4)		33	9.0 × 10^3 (1.3 × 10^4)
Region			P = 0.021			P = 0.018			P = 0.014			P = 0.091			P = 0.188
Seoul	10	0.2 (0.2)		10	2.5 × 10 (3.0 × 10)		11	3.3 × 10^4 (8.6 × 10^4)		11	3.3 × 10^2 (2.3 × 10^2)		11	1.2 × 10^4 (1.3 × 10^4)
Other cities in Korea	38	1.1 (1.0)		38	1.4 × 10^3 (1.5 × 10^3)		38	2.4 × 10^5 (5.4 × 10^5)		38	9.0 × 10^4 (1.7 × 10^5)		38	2.4 × 10^4 (3.1 × 10^4)
Notes: n = number of samples, NS = nostatistically significant differences with any other groups (P ≤ 0.25).

Table 4. Correlation matrix among dust, endotoxin, bacteria, GNB, and fungi level (P value)

	Dust	Endotoxin	Bacteria	GNB	Fungi
Dust	1
Endotoxin	0.38 (P = 0.0071)	1
Bacteria	0.69 (P ≤ 0.0001)	0.43 (P = 0.0026)	1
GNB	0.76 (P ≤ 0.0001)	0.52 (P = 0.0001)	0.74 (P ≤ 0.0001)	1
Fungi	0.40 (P = 0.0047)	0.59 (P ≤ 0.0001)	0.62 (P ≤ 0.0001)	0.55 (P ≤ 0.0001)	1

Table 5. Factors significantly affecting inhalation exposure to dust, endotoxin, and microorganisms during waste collection and sorting

	Coefficient (95% confidence limit)
Independent Variables	Dust	Endotoxin	Bacteria	GNB	Fungi
Full model adjusted R ^2, % (P)	31.8 (P = 0.0034)	71.8 (P ≤ 0.0001)	39.2 (P ≤ 0.0001)	64.2 (P ≤ 0.0001)	49.6 (P ≤ 0.0001)
Constant	−0.24 (−1.35 to 0.87)	2.42 (0.50–4.34)	10.98 (10.08–11.88)	5.99 (3.74–8.25)	9.26 (7.46–11.07)
Sex
Male (reference)
Female	1.70 (0.55–2.85)	−0.34 (−1.77 to 1.10)	2.62 (0.82–4.42)	2.47 (0.58–4.36)	−0.02 (−1.26 to 1.21)
Job title
Driver (reference)
Waste collector	NS	NS	NS	1.99 (0.57–3.42)	1.39 (0.45–2.34)
Company type
Government (reference)
Private	−0.54 (−1.49 to 0.42)	NS	NS	NS	−0.03 (−1.07 to 1.00)
Day
Weekday (reference)
Weekend	−0.98 (−1.88 to −0.08)	NS*	−1.28 (−2.43 to −0.13)	−3.78 (−5.14 to −2.42)	0.31 (−0.61 to 1.24)
Temperature
<20 °C (reference)
>20 °C	NS	2.35 (1.25–3.46)	NS	2.42 (0.94–3.91)	0.10 (−0.88 to 1.08)
Humidity
<50% (reference)
>50%	0.17 (−0.59 to 0.93)	−2.02 (−3.00 to −1.04)	−1.04 (−4.59 to −1.89)	−1.01 (−2.27–0.26)	−2.21 (−3.07 to −1.35)
Region
Seoul (reference)
Other cities in Korea	NS	3.02 (1.99–4.05)	NS*	NS*	NS*
Notes: NS = not statistically significant factor (P > 0.25), which was already removed through ANOVA test (Table 3). NS* = not statistically significant factor in final model (P > 0.05). P value (dependent variables = log-transformed value, independent variables = categorical).

Endotoxin Exposure

The average exposure to endotoxin was 1123 EU/m³ (Table 2), which is much higher than the 50 EU/m³ recommended by the Dutch Expert Committee on Occupational Exposure Standards (DECOS).8 Of the 48 waste handlers, 35% were found to be exposed to levels higher than 1000 EU/m³, which is generally regarded as the level indicating dangerous exposure. Furthermore, workers sorting nonseparated recyclable wastes were exposed to levels over 2000 EU/m³. Significant differences in endotoxin exposure were observed among the classifications of day, temperature, humidity, and region (P < 0.05) (Table3). The final multiple regression model indicated that temperature, humidity, and region were significantly associated with endotoxin exposure (adjusted R ² = 71.8%, P < 0.0001). Endotoxin exposures were significantly higher when the temperature exceeded 20 °C and when the RH was less than 50% (Table 5).

Inhalation Exposure to Viable Microorganisms

The average degree of exposure to microorganisms, including bacteria (1.9 × 10⁵ CFU/m³), GNB (7 × 10⁴ CFU/m³), or fungi (2.2 × 10⁴ CFU/m³) (Table 2), was greater than 10⁴ CFU/m³. In particular, nine workers were exposed to total bacteria levels greater than 10⁶ CFU/m³, which is associated with development of respiratory or gastrointestinal disease. Levels of exposure to bacteria, GNB, and fungi were significantly different (P < 0.25) among classifications of all independent factors, except for company type (Table 3). In particular, humidity was significantly related to exposure to bacteria and fungi (P ≤0.0001). The results of the multiple regression analysis for each type of microorganism are summarized in Table 5. Waste handlers had a greater exposure to GNB and fungi than did drivers of waste vehicles, although there was no significant difference between them with respect to bacterial exposure. Exposure to GNB and fungi was higher when the RH exceeded 50%, and exposure to bacteria and GNB was significantly greater during weekdays than during weekends.

Microorganism Contamination of Facesand Clothes

The level of microorganisms obtained from workers' faces after work was higher than that obtained before work, and the contamination was markedly higher than the level obtained from the faces of office workers (Table 6). No significant difference was found in the level of microorganisms collected after work from workers of various job titles, indicating that the workers' faces were severely contaminated regardless of work type. High levels of microorganisms were also detected from several areas of clothing.

Table 6. Level of microorganisms collected from faces and from several parts of clothing of waste collectors

			Bacteria, CFU/cm^2		GNB, CFU/cm^2		Fungi, CFU/cm^2
Type of Worker	Part Exposed/Wiped	n	Mean	SD	Mean	SD	Mean	SD
Waste collector ^a
Before work	Face	49	1.3 × 10^2	1.9 × 10^2	3.5 × 10^1	1.2 × 10^2	1.4 × 10^2	2.9 × 10^2
After work	Face	49	3.1 ×10^4	5.6 × 10^4	5.5 × 10^4	1.9 × 10^5	2.7 × 10^5	6.5 × 10^5
Street cleaner	Face	6	9.2 × 10^3	9.1 × 10^3	3.6 × 10^4	8.4 × 10^4	8.2 × 10^3	1.0 × 10^4
Driver	Face	7	5.1 × 10^4	9.3 × 10^4	8.9 × 10^3	1.8 × 10^4	3.2 ×10^5	8.1 × 10^5
Waste separator	Face	6	1.4 × 10^4	3.1 × 10^4	5.5 × 10^4	8.6 × 10^4	1.6 × 10^4	1.3 ×10^4
Waste collector	Face	30	3.3 × 10^4	5.4 × 10^4	6.9 × 10^4	2.3 × 10^5	3.7 × 10^5	7.3 × 10^5
ANOVA P value	–	–	NS	–	NS	–	NS	–
Office worker
Before work	Face	10	3.8 × 10^1	7.3 × 10^1	ND	ND	4.4 × 10^1	8.6 × 10^1
After work	Face	10	1.0 × 10^2	1.6 × 10^2	ND	ND	9.3 ×10^1	1.0 × 10^2
Waste collector/after work	Pants	24	5.4 × 10^6	9.3 × 10^6	3.2 × 10^6	7.1 × 10^6	4.2 × 10^6	8.8 × 10^6
	Gloves	7	2.4 × 10^6	3.0 × 10^6	1.5 × 10^6	2.2 × 10^6	6.5 × 10^6	8.4 × 10^6
	Palm	3	1.4 × 10^7	6.9 × 10^6	1.4 × 10^7	6.9 × 10^6	6.4 ×10^6	2.1 × 10^6
	Back of hand	4	2.3 × 10^6	2.9 × 10^6	3.4 × 10^5	7.4 × 10^4	2.6 ×10^6	2.8 × 10^6
	Sleeve	8	3.5 × 10^7	6.7 × 10^7	2.3 × 10^7	2.8 × 10^7	3.2 × 10^6	3.6 × 10^6
	Shoulder	8	1.4 × 10^6	2.7 × 10^6	6.7 × 10^4	1.2 × 10^5	1.6 ×10^5	2.1 × 10^5
	Handkerchief	1	1.3 × 10^5	NA	1.2 × 10^6	NA	3.3 ×10^5	NA
	Navel	2	3.7 × 10^5	2.6 × 10^5	7.7 × 10^4	5.8 × 10^4	7.9 ×10^4	6.3 × 10^4
Notes: n = number of samples, NS = not statistically significant (P > 0.05), ND = 50 CFU/sample, P value = multiple comparison mean test among job titles (dependent variables = log-transformed value).
^aIncludes driver.

DISCUSSION

These findings could be useful in several respects, not only to characterize the exposure to dust, endotoxin, and microorganisms during waste collection and sorting, but also to identify which factors may significantly influence inhalation exposure to these agents. In addition, micro-organism levels measured from workers' faces and clothes could be used to estimate gastrointestinal exposure to these microorganisms.

First, exposure to endotoxin and microorganisms was greater than that reported for other refuse collectors.2,9 These high exposure levels were observed irrespective of the waste type handled, which agrees with the results reviewed by Kuijer and Frings-Dresen.10 The endotoxin results were also greater than those reported in Sweden (compostable waste, 0.5 ng/m³ = 5 EU/m³; unsorted waste, 0.7 ng/m³ = 7 EU/m³),11 but they were below the concentration range12 of 4800–9900 EU/m³ that can cause acute pulmonary effects.13 The average levels observed (bacteria ≤3 ×10⁵ CFU/m³, GNB = 4 ×10⁴ CFU/m³, fungi = 10⁵ CFU/m³) were also greater than those measured for workers sorting household garbage.12 In particular, the highest exposure was recorded for work processes in which nonseparated waste was received and sorted into fractions for incineration, recycling, or other uses (e.g., magnetic metals and inorganic materials such as sand and glass fragments). A possible reason for this high exposure from nonseparated waste may be that even small amounts of contaminated water, food, or milk left in various wastes could provide excellent nutrients for microbial growth. Moreover, in general there was no facility for ventilation or the ventilation was inefficient. Consequently, continuous manual handling of various types of waste contaminated wit microorganisms, combined with a lack of measures for reducing exposure and other unique work characteristics related to waste sorting, could be major factors leading to excessively high levels of exposure among workers sorting nonseparated wastes. Exposure levels among vehicle drivers were also high because most drivers are also involved in actual waste collection as a helper.

Second, the average level of inhalation exposure to microorganisms and endotoxin was greater than the recommended OEL. Because no OEL is in place for airborne microorganisms or microbial toxins, the results presented here could be compared only to the existing proposed recommendations. The average exposure to endotoxin(1.1 × 10³ EU/m³) was approximately equal to the OEL values proposed by Rylander (1000–2000 EU/m³)13 and Clark (1000 EU/m³),14 but it was greater than the exposure levels reported for human volunteers exposed to cotton dust that contained more than 50 ng/m³ (500 EU/m³), which led to a significant reduction in forced expiratory volume (1%).15

The average exposure to viable airborne bacteria(1.9 × 10⁵ CFU/m³) exceeded the OEL (10⁴ CFU/m³) proposed by Malmros et al.12 No worker was exposed to more than the 10⁶ CFU/m³ reported by Eduard et al.16 to be associated with respiratory symptoms, mucous membrane irritation, and organic dust toxin syndrome-like symptoms in workers at saw mills. The OEL for GNB (1000 CFU/m³) recommended by Clark14 and Malmros et al.12 was greatly exceeded in 71% of the 49 workers. The average exposure to GNB (7 × 10⁴ CFU/m³) was also greater than the OEL (2 × 10⁴ CFU/m³) recommended by Gorny and Dutkiewicz.17

The fungi exposure level ranged from 2.4 × 10⁴ CFU/m³ to 10.8 × 10⁴ CFU/m³ (mean = 2 × 10⁴ CFU/m³) and was greater than the OEL (50 × 10³ CFU/m³) proposed by Gorny and Dutkiewicz17 in 12% of the workers. Several studies have indicated that refuse collectors are at increased risk of respiratory and influenza-like symptoms.2,11,18 These respiratory complaints in refuse collectors are likely to be associated with exposure to high levels of bioaerosols and organic dust. In particular, exposure to fungal spores and endotoxins probably results in a respiratory inflammatory response.19

Third, multiple regression models were developed to identify the significant variables influencing inhalation exposure to dust, endotoxin, and microorganisms during waste handling. Several factors could explain the variation in levels of endotoxin and microorganism inhalation exposure among waste collectors; namely, sex (dust, bacteria, and GNB), job title (GNB and fungi), collection day (dust, bacteria, and GNB), temperature (endotoxin and GNB), humidity (endotoxin and fungi), and region (endotoxin) were all significantly associated with exposure to these agents. The confidence levels of the regression models using the endotoxin data (71.8%) and GNB data (64.2%) were greater than those for the models using the dust data (31.8%), bacterial data (39.2%), or fungal data (49.6%) (Table 5). It may be helpful to identify strategies to reduce bioaerosol exposure through review of the occupational factors affecting such exposure. Poulsen et al.2 summarized the factors that may influence working conditions and hence the level of potentially health-damaging exposure in waste collectors; these included type of company, organization of work, type of equipment, type of district, type of waste, frequency of collection, and seasonal variations.

For household waste collectors, the degree of bioaerosol exposure probably depends on such factors as the microflora of the waste, the type of container, the truck, and the manner in which the work is carried out.19 Breum et al.20 reported that workers collecting garden waste were exposed to greater concentrations of bioaerosol than were workers who collected paper and cardboard (P < 0.05; Mann–Whitney test). Personal bioaerosol exposure when collecting household waste was also correlated with parameters that included the type of waste, the household collection unit, type of collection vehicle, and the waste collector's job description. In fact, exposure of waste collectors to bioaerosols may be determined by numerous parameters related to their work conditions such as the type of waste, season of the year, type of collection unit of the household, type of collection vehicle, and organization of work. Exposure levels in waste collectors may be difficult to generalize because of the many influencing factors mentioned above and differences between collecting systems throughout the country.

Fourth, a significant correlation matrix was detected among exposure levels to dust, endotoxin, and microorganisms (Table 4). In general, biodegradable organic material generated from households was kept in containers for different periods before collection, providing an ideal environment for excessive microbial growth. Collection, transportation, and manual handling of biodegradable waste may generate organic dusts containing high levels of microorganisms and their toxins, such as endotoxin and (1→3)- β-D-glucan, depending on the storage conditions.11 Consequently, airborne organic dusts contain bioaerosols including microorganisms and their toxins. In the environment, the level of airborne endotoxin is related to the incidence of GNB. Thus, GNB from waste collection and sorting could be a source of adverse endotoxin. Exposure to organic dust, including microorganisms and their toxins and byproducts, could therefore be most prevalent in waste collection and handling activity.

Finally, not only were the workers' faces contaminated with microorganisms but so also were most parts of their clothes. In particular, the levels of face contamination were markedly different not only between the periods before and after work, but also between waste-handling workers and office workers. These results indicate that inhalation exposure could be very common in workers handling waste. Little data are available on the possibility of gastrointestinal exposure to microorganisms, although a high frequency of gastrointestinal problems has been reported for refuse workers,2,11 especially in the summer.21

Kuijer and Frings-Dresen10 reported that the wet biological fractions of refuse (i.e., garden waste and the bio-degradable fraction of household refuse) were responsible for the gastrointestinal complaints in refuse collectors; these could be caused by absorption of endotoxin and infectious microbes contaminating the face, hands, clothes, and handkerchiefs of these workers. Among refuse collectors, an exposure-response relationship exists between diarrhea and exposure to endotoxin and viable fungi.3 It has been suggested that resuspension of accumulated dust in the clothing can be a source of inhalation exposure.22

Manual handling is to some degree unavoidable in the collection of waste. Most waste collectors had no opportunity to wash during working hours, which may place them at high risk of inhalation and gastrointestinal exposure. Applying administrative and engineering measures to reduce microorganism exposure is difficult because of the unique characteristics related to waste collection and sorting (e.g., manual handling of biodegradable fractions and materials contaminated with microorganisms) and because of the difficulty in establishing engineering control measures.

A major limitation of this study is the small number of waste handlers sampled (n = 48–49), who may or may not be representative of waste collection operations as a whole given the various types of collection, container, vehicle, and other factors. The effects of these various characteristics on inhalation exposure were not fully investigated. However, these results provide a basis not only for recognizing exposure to high levels of endotoxin and microorganisms during waste collection and sorting but also for estimating the risk of developing respiratory health problems. Further study is underway to examine the relationships between the occupational characteristics of waste collectors, their exposure to bioaerosols, and their respiratory and gastrointestinal symptoms. Another limitation of the study is its failure to fully assess the prework contamination of waste handlers' faces and clothes, which were already more contaminated with microorganisms than were those of office workers before work (Table 6). Some workers apparently wore the same clothing that they had previously worked in without laundering. The rooms where workers changed clothes and prepared for work were also contaminated with microorganisms. However, despite these limitations, the results reported here do indicate that waste handlers are exposed to specific environments containing high levels of microorganisms.