NIOSH HEALTH HAZARD EVALUATION REPORT:

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

TM

HETA #2003-0078-2918

Waste Management, Inc. Outer Loop Landfill

Louisville, Kentucky

November 2003

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports
ii

PREFACE

The Hazard Evaluations and Technical Assistance Branch (HETAB) of the National Institute for

Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the

workplace. These investigations are conducted under the authority of Section 20(a)(6) of the Occupational

Safety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of Health and

Human Services, following a written request from any employer or authorized representative of employees,

to determine whether any substance normally found in the place of employment has potentially toxic effects

in such concentrations as used or found.

HETAB also provides, upon request, technical and consultative assistance to federal, state, and local agencies;

labor; industry; and other groups or individuals to control occupational health hazards and to prevent related

trauma and disease. Mention of company names or products does not constitute endorsement by NIOSH.

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by Lisa Delaney, MS, of HETAB, Division of Surveillance, Hazard Evaluations and

Field Studies (DSHEFS). Field assistance was provided by Kevin L. Dunn of DSHEFS. Analytical support

was provided by Ardith Grote of NIOSH, Rhonda Halliday of Microbiology Specialists, Inc MSI, and

DataChem Laboratories. Desktop publishing was performed by Deborah Gibson and Shawna Watts. Review

and preparation for printing were performed by Penny Arthur.

Copies of this report have been sent to employee and management representatives at Waste Management Inc.

and the OSHA Regional Office. This report is not copyrighted and may be freely reproduced. Single copies

of this report will be available for a period of three years from the date of this report. To expedite your

request, include a self-addressed mailing label along with your written request to:

NIOSH Publications Office

4676 Columbia Parkway

Cincinnati, Ohio 45226

800-356-4674

After this time, copies may be purchased from the National Technical Information Service (NTIS) at

5825 Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may be

obtained from the NIOSH Publications Office at the Cincinnati address.

For the purpose of informing affected employees, copies of this report shall be

posted by the employer in a prominent place accessible to the employees for a period

of 30 calendar days.
iii

Highlights of the NIOSH Health Hazard Evaluation

Evaluation of Exposure to Microorganisms at 

Waste Management Inc. Outer Loop Landfill

In 2003, NIOSH assisted the Environmental Protection Agency (EPA) at the Waste Management Inc., (WMI)

Outer Loop Landfill in Louisville, Kentucky, to look at exposures during the disposal of sewage sludge

(biosolids). NIOSH evaluated exposures to bacteria and endotoxin. Workers did not report any health

problems. 

What NIOSH Did

# We met with WMI and EPA employees.

# We observed the unloading and compacting of

waste and sewage sludge.

# We took air samples to measure the levels of

bacteria and endotoxin (a component of some cell

walls of bacteria).

# We looked at work practices and personal

protective equipment (PPE).

What NIOSH Found

# Levels of culturable bacteria in samples

collected at the open face were much higher than in

samples we collected at other areas of the landfill.

# Bacteria that cause digestive tract illness were

identified in the samples.

# Endotoxins in two samples were at levels which

may cause illness.

# There are no shower facilities and employees do

not change work clothes before leaving work.

# No employees reported health problems. 

What WMI Managers Can Do

# Ensure PPE is provided and worn correctly.

# Conduct employee training on good hygiene

practices.

# Provide on-site showers and laundry services

for washing employee clothes to prevent

contaminating their vehicles or homes.

# Ensure employees wipe down and vacuum the

cabs of their equipment on a regular basis.

What the WMI Employees Can Do

# Wash your hands frequently and before eating,

drinking, or smoking.

# Wipe down and vacuum the cabs of your

equipment on a regular basis.

# Report possible work-related health effects to

management.

What To Do For More Information:

We encourage you to read the full report. If you

would like a copy, either ask your health and

safety representative to make you a copy or call

1-513-841-4252 and ask for

 HETA Report # 2003-0078-2918

Highlights of the HHE Report
iv

Health Hazard Evaluation Report 2003-0078-2918

Waste Management, Inc. Outer Loop Landfill

Louisville, Kentucky

August 2003

Lisa J. Delaney, M.S.

SUMMARY

On November 25, 2002, the National Institute for Occupational Safety and Health (NIOSH) received a

request for technical assistance from the U.S. Environmental Protection Agency (EPA) regarding a landfill

bioreactor study at the Waste Management, Inc. (WMI), Outer Loop Landfill in Louisville, Kentucky. The

request concerned landfill dozer and compactor operators’ potential exposures during the dumping and

spreading of biosolids and sewage sludge at the working face of the landfill. No health effects were reported.

In response to this request, NIOSH investigators conducted an initial site visit on December 3, 2002. During

a follow-up site visit on June 3-5, 2003, NIOSH conducted air sampling which included the collection of area

and personal breathing zone (PBZ) samples for culturable bacteria, endotoxin (a component in cell

membranes of Gram-negative bacteria), and volatile organic compounds (VOCs). Samples were collected

at the active site of the landfill where waste is disposed and at a capped site no longer receiving waste for

comparison.

Total bacteria concentrations for the comparison samples and active site samples ranged from 96 colony

forming units per cubic meter of air (CFU/m3

) to 144 CFU/m3 and from 108 CFU/m3 to >62,304 CFU/m3

respectively. The following enteric bacteria (bacteria present in the intestinal tracts of humans and animals)

were identified: Klebsiella oxytoca, Leclercia adecarboxylata, Enterobacter cloacae, and Citrobacter

freundii. Exposure to these enteric organisms may result in disease (e.g., gastroenteritis) or in a carrier state

in which an infection does not clinically manifest itself in the individual but can be spread to others.

Occupational exposure criteria for culturable bacteria have not been established. Area endotoxin samples

collected at the active site of the landfill ranged from 2.9 endotoxin units per cubic meter (EU/m3

) to 170

EU/m3

. The personal breathing zone (PBZ) time-weighted average (TWA) exposure of the dozer operator

was 27.9 EU/m3

. Occupational exposure criteria for endotoxin, based on observed health effects at measured

endotoxin levels, have been suggested at 200 EU/m3

 for airway inflamation with increased airway activity,

2000 EU/m3

 for over-shift decline in forced expiratory volume in one second, 3000 EU/m3 for chest tightness,

and 10,000-20,000 EU/m3

 for toxic pneumonitis. NIOSH has not established any recommended exposure

limits. 

Major VOCs detected were ethanol, various aliphatic hydrocarbons, toluene, ethyl benzene, xylenes, trimethyl

benzenes, styrene, limonene, and siloxanes. 

Employees working in the landfill did not report any health problems. A locker room for employees is

located in the maintenance shop. Shower facilities are not provided and employees wear their work clothes

home. An employee reported they received training on proper hygiene precautions. Suggestions to improve

personal hygiene, personal protective equipment, and training are provided in the recommendations section

of this report.
v

The environmental monitoring data show that exposure to culturable enteric organisms and

endotoxin may occur. Although exposure criteria to evaluate the health implications of these

exposures are lacking, reasonable precautions to minimize exposures should be taken.

Recommendations are provided to help minimize exposure to sewage sludge and to increase

employee awareness of the importance of good hygiene and the appropriate use of personal

protective equipment.

Keywords: 4953 (Refuse Systems), biosolids, sewage sludge, endotoxin, bioaerosol, bacteria, landfill, volatile

organic compounds, thermal desorption
TABLE OF CONTENTS

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Acknowledgments and Availability of Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Introduction ........................................................................ 1

Background ........................................................................ 1

Methods ........................................................................... 2

Culturable Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Endotoxin ...................................................................... 2

Volatile Organic Compounds ....................................................... 2

Evaluation Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Health Hazards Associated with Sewage Sludge ........................................ 3

Pathogens ....................................................................... 4

Bacterial Endotoxin ............................................................... 5

Microorganisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

VOCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Results /Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Culturable Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Bacterial Endotoxin ............................................................... 7

VOCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Health Hazard Evaluation Report No. 2003-0078 Page 1

INTRODUCTION

On November 25, 2002, the National Institute for

Occupational Safety and Health (NIOSH) received

a request for technical assistance from the U.S.

Environmental Protection Agency (EPA)

regarding a landfill bioreactor study at the Waste

Management, Inc., (WMI) Outer Loop Landfill in

Louisville, Kentucky. The request concerned

landfill dozer and compactor operators’ potential

exposures to bioaerosols during the dumping and

spreading of biosolids and sewage sludge at the

working face of the landfill. No health effects

were reported. In response to this request, NIOSH

investigators conducted an initial site visit on

December 3, 2002. During a follow-up site visit

on June 3-5, 2003, NIOSH conducted air

sampling. 

BACKGROUND

The Outer Loop Landfill is a waste disposal

facility that has been in operation for

approximately 35 years. WMI purchased the

landfill in 1984. Waste disposal occurs in discrete

areas of the 794-acres site; the total waste

footprint is approximately 390 acres. WMI

accepts residential waste, industrial special waste

(e.g., biosolids, latex paint, fly ash), and

autoclaved medical waste. In October 2000, WMI

partnered with the EPA under a Cooperative

Research and Development Agreement (CRADA)

to compare conventional Subtitle D designed and

operated landfills with bioreactor landfills.

Bioreactor landfills require more liquid additions,

such as biosolids, to create an environment that

allows anaerobic microorganisms to degrade the

waste more rapidly. It is thought that the

bioreactor process extends the life of the landfill.

The WMI Outer Loop Landfill has approximately

30 employees including office personnel. Heavy

equipment operators, mechanics, and maintenance

employees work an 8-hour shift. Hourly

employees are represented by the International

Brotherhood of Teamsters Local 783.

Large trucks containing sewage sludge enter the

site through the receiving area/weigh station.

Drivers are directed to the location of the cell

receiving waste on that particular day. The active

site of the landfill receiving waste is referred to as

the working face. The compactor and bulldozer

operators direct traffic from their equipment and if

necessary exit the equipment for additional

instruction. The drivers exit their trucks to open

the back gate of the truck to empty the contents of

the load. Once empty, the driver closes the back

gate and exits the facility. This process usually

takes 10 to 15 minutes. Multiple semi tractor

trailers, personal vehicles, and smaller trucks can

be at the working face unloading a variety of

wastes at the same time. WMI bulldozer operators

spread the recently unloaded waste across the

working face and a compactor compresses the

trash. Typically, 1 compactor and 2 to 3

bulldozers work the open face. 

Sewage sludges are the organic residues resulting

from the treatment of commercial, industrial, and

municipal wastewater (sewage). WMI accepts

sewage sludge in various stages of pathogen

reduction treatment. WMI accepts “wet” biosolids

and sewage sludge from the City of Louisville and

smaller municipalities in the area. The City of

Louisville has the ability to process their biosolids

to a small, dry pellet form which WMI also

accepts. On June 4, 2003, WMI received 1

truckload of wet sewage sludge (11.2 tons) in the

morning and 1 truckload of pellets (14.4 tons) in

the afternoon. On the morning of June 5, 2003,

WMI received 4 truckloads of pellets (69.38 tons)

and 1 truckload of wet sewage sludge (13.32 tons).

The volume of sewage sludge received varies by

season. Receiving records for the month of May

showed that WMI received 2,204 tons of

pelletized and 678 tons of wet sewage sludge.

Documentation from WMI verifying that the

sewage sludge was U.S. EPA Class B biosolids

was not available. 

METHODS
Page 2 Health Hazard Evaluation Report No. 2003-0078

Culturable Bacteria

To determine concentrations of culturable airborne

bacteria, an Anderson single-stage viable cascade

impactor set at a calibrated flowrate of 28.3 liters

per minute (Lpm) and a Surface Air System (SAS)

Super 100 microbial air sampler pre-programmed

to draw a volume of 100 L of air were used.

Samples were collected at the edge of the open

face of area 7 on Unit 7 of the landfill

approximately 30 yards from the location of the

sewage sludge. Samples were collected before,

during, and after sewage sludge unloading.

Comparison samples were collected at Unit 6

which is a capped landfill no longer receiving

waste. The Anderson single-stage impactor is

designed to collect particles 0.65 micrometers

(μm) or larger. Samples using the Anderson

sampler were collected over a 3-minute time

period. The SAS sampler is estimated to collect

particles 2 μm or larger and was programmed for

a total air volume of 100 L in one run.1

 Sample

collection times were approximately 1 minute.

Samples were collected in sets of three replicates

using buffered charcoal yeast extract agar,

trypticase soy agar, and columbia nalidixic acid

agar. The samples were shipped overnight to the

contract laboratory which is an American

Industrial Hygiene Association Environmental

Microbiology Accredited Laboratory. Samples

were incubated at 23" Celsius and colony count

readings were taken on day 4 and day 6. The

results are expressed as colony forming units per

cubic meter of air (CFU/m3

). Organisms were

isolated and morphological characteristics, gram

stain reaction, and oxidase or catalase reaction

were determined. 

Endotoxin

Two personal breathing zone (PBZ) and 5 area air

samples were collected for endotoxin (component

in cell membrane of Gram-negative bacteria). The

samples were collected on 1 dozer operator, at the

edge of the working face, and at a control site

(Unit 6). The samples were collected on tared 5.0

μm pore size, 37 millimeter (mm) polyvinyl

chloride filters using a calibrated flowrate of 2

Lpm. The samples were weighed and analyzed for

endotoxin content with the Kinetic-QCL

instrumentation using the Limulus amebocyte

lysate (LAL) assay. For these analyses, 10

endotoxin units (EU) are equivalent to one

nanogram of endotoxin. The limit of detection

(LOD) for the analyses was 0.005 EU per sample,

which equates to a minimum detectable

concentration of 0.02 EU/cubic meter (m3

) based

on a sample volume of 230 L.

Volatile Organic

Compounds

Area samples that screen for VOCs were collected

at the edge of the working face during sewage

sludge unloading and at the Unit 6 control site.

The samples were collected on thermal desorption

(TD) tubes attached by Tygon® tubing to

sampling pumps calibrated at a flow rate of 50

cubic centimeters per minute (cc/min). The TD

tubes contained three beds of sorbent material: a

front layer of Carbopack YTM, a middle layer of

Carbopack BTM, and a back section of Carboxen

1003TM. The TD tubes were analyzed by the

NIOSH laboratory in a Perkin-Elmer ATD 400

automatic thermal desorption system. The thermal

unit was interfaced directly to an HP5890A gas

chromatograph with an HP5970 mass selective

detector according to NIOSH method 2549.2

EVALUATION CRITERIA

As a guide to the evaluation of the hazards posed

by workplace exposures, NIOSH field staff

employ environmental evaluation criteria for the

assessment of a number of chemical and physical

agents. These criteria are intended to suggest

levels of exposure to which most workers may be

exposed up to 10 hours per day, 40 hours per week

for a working lifetime without experiencing

adverse health effects. It is, however, important to

note that not all workers will be protected from

adverse health effects even though their exposures
Health Hazard Evaluation Report No. 2003-0078 Page 3

are maintained below these levels. A small

percentage may experience adverse health effects

because of individual susceptibility, a pre-existing

medical condition, and/or a hypersensitivity

(allergy). In addition, some hazardous substances

may act in combination with other workplace

exposures, the general environment, or with

medications or personal habits of the worker to

produce health effects even if the occupational

exposures are controlled at the level set by the

criterion. These combined effects are often not

considered in the evaluation criteria. Also, some

substances are absorbed by direct contact with the

skin and mucous membranes, and thus potentially

increases the overall exposure. Finally, evaluation

criteria may change over the years as new

information on the toxic effects of an agent

become available.

The primary sources of environmental evaluation

criteria for the workplace are: (1) NIOSH

Recommended Exposure Limits (RELs),3

 (2) the

American Conference of Governmental Industrial

Hygienists’ (ACGIH®) Threshold Limit Values

(TLVs®),4

 and (3) the U.S. Department of Labor,

Occupational Safety and Health Administration

(OSHA) Permissible Exposure Limits (PELs).5

Employers are encouraged to follow the OSHA

limits, the NIOSH RELs, the ACGIH TLVs, or

whichever are the more protective criterion.

OSHA requires an employer to furnish employees

a place of employment that is free from

recognized hazards that are causing or are likely to

cause death or serious physical harm

[Occupational Safety and Health Act of 1970,

Public Law 91–596, sec. 5(a)(1)]. Thus,

employers should understand that not all

hazardous chemicals have specific OSHA

exposure limits such as PELs and short-term

exposure limits (STELs). An employer is still

required by OSHA to protect their employees

from hazards, even in the absence of a specific

OSHA PEL.

A time-weighted average (TWA) exposure refers

to the average airborne concentration of a

substance during a normal 8- to 10-hour workday.

Some substances have recommended STEL or

ceiling values which are intended to supplement

the TWA where there are recognized toxic effects

from higher exposures over the short-term.

Health Hazards Associated

with Sewage Sludge

Sewage sludge, also called wastewater residuals,

has been used as a fertilizer and soil conditioner

in the U.S. for many years. Biosolids is another

name for the beneficially treated residuals from

wastewater treatment. The use and disposal of

sewage sludge in the U.S. is regulated under 40

CFR Parts 257, 403, and 503- Standards for the

Use or Disposal of Sewage Sludge: Final Rules.6

Landfilling of biosolids with municipal solid

waste in a municipal solid waste landfill is

regulated under 40 CFR Part 258 Landfill Rule.7

The U.S. EPA is the lead agency that has

regulatory responsibilities for wastewater

treatment and sewage sludge disposal.

Pathogens

There are four major types of human pathogenic

organisms found in sewage sludge: (1) bacteria,

(2) viruses, (3) protozoa, and (4) helminths

(parasitic worms).8

 The levels of pathogens

present in sewage sludge depend upon the number

of microorganisms present in the waste stream and

the reduction in pathogenic organisms achieved by

the wastewater and sewage treatment processes.

Examples of pathogens potentially found in

wastewater and sewage sludge are presented in

Table 1. Several of these pathogens can cause

gastrointestinal illnesses. Some are present

infrequently, depending, in part, on geographic

area.

There are two separate pathogen reduction

requirements for sewage sludge- Class A and

Class B.8

The goal of Class A requirements is to reduce

pathogen levels to below detectable limits. The

goal of Class B requirements is to reduce pathogen
Page 4 Health Hazard Evaluation Report No. 2003-0078

levels to concentrations that are unlikely to pose a

health risk to the public and the environment.

There are site restrictions for land application of

Class B sludge. Crop harvesting, animal grazing,

and public contact are limited to allow

environmental factors to further reduce pathogen

levels.

Some epidemiological studies of wastewater and

sewage workers have shown an increased risk of

gastrointestinal symptoms.9,10,11,12,13 Lundholm and

Rylander found that skin disorders and diarrhea

and other gastrointestinal symptoms were more

prevalent among employees at six Swedish

wastewater treatment plants than among workers

at three water treatment plants.14 Scarlett-Kranz

and associates also found that sewage workers in

New York reported a significantly higher

frequency of diarrhea, dizziness, headache, skin

irritation, and sore throat than workers at water

treatment plants.15 

In a three-year, prospective epidemiologic study in

Ohio, the health status of farming families using

sludge on land was compared to families not using

sludge.15 The families using sludge were

randomly selected. Each family participated in a

monthly family and animal health questionnaire,

annual tuberculin skin testing, and quarterly blood

sampling for serological testing for 23 viruses.15

There was no significant difference in the

frequency of respiratory illnesses, digestive

illnesses, or general symptoms between the two

family groups. There were also no observed

differences in health status among the farm

animals. Viral serological test results were

similar, and there were no tuberculin skin test

conversions. According to the authors, farmers in

the study had a sewage sludge application rate

comparable to the practices allowed under the U.S.

EPA regulations, and the sewage sludge had

undergone accepted digestion procedures.

Several studies have evaluated concentrations of

airborne microorganisms at landfill operations.

One study evaluated exposures to airborne

microorganisms at a landfill receiving sewage

sludge. Samples collected for total bacteria at the

landfill site ranged from 70 CFU/m3

 to 58,000

CFU/m3

.

16 The following Gram-negative genera

were identified: Achromobacter, Acinetobacter,

Aeromonas, Enterobacter, Escherichia, Hafnia,

Klebsiella, Pseudomonas, Serratia, and Yersinia.

Another landfill study concluded that

concentrations of fungi and mesophilic bacteria

were 2 to 30 times higher than background

levels.17 

There is limited information on the presence of

airborne microbial pathogens resulting from the

application of sewage sludge. One study by Pillai

et al. measured airborne bacteria during the land

application process.18 Concentrations for

heterotrophic bacteria, which require nitrogen and

carbon food sources, averaged 105

 CFU/m3. One

location, where a major amount of physical

agitation of the sewage sludge occurred, had

detectable levels of hydrogen sulfide-producing

bacteria and Clostridium spp. (5 x 102

 CFU/m3) on

three of the four days monitored at that site. Fecal

coliforms, fecal streptococci, and Salmonella sp.

were not detected at any of the sampling sites.18

Bacterial Endotoxin

Gram-negative bacteria, and endotoxin (which are

found in the cell wall of Gram-negative bacteria)

are ubiquitous in nature. Endotoxin is released

when the bacterial cell is lysed (broken down) or

when it is multiplying.19,20 They are found in

water, soil, and living organisms. Endotoxin has

been found in various industrial settings and in

non-industrial environments associated with

bacterial contamination, cooling towers,

humidifiers, air-conditioners, and other waterassociated processes.20,21,22,23,24,25

Clinically, little is known about the response to

inhaled endotoxin at levels that would be found in

indoor environments. In animal studies, and at

workplaces with high levels of exposure to

endotoxin (such as animal feed production

facilities), researchers have been able to

demonstrate some acute changes in workers’

pulmonary function.20,21,22,23 A study by Mattsby

and Rylander found that approximately 40% of
Health Hazard Evaluation Report No. 2003-0078 Page 5

sewage treatment plant workers reported diarrhea,

fatigue, and headache after exposure to an aerosol

of sewage dust containing endotoxin.26 Liesivouri

and associates found airborne endotoxin

concentrations in wastewater treatment plants to

range from 8 nanograms per cubic meter (ng/m3

)

to 410 ng/m3

 (equivalent to 80 EU/m3 to 4,100

EU/m3

) of air.27

Currently, acceptable exposure concentrations to

endotoxin have not been established.

Occupational exposure criteria have not been

established for bacterial endotoxin by OSHA,

NIOSH, or ACGIH. The ACGIH Bioaerosols

committee has identified endotoxin as a

biologically derived agent under study and is

soliciting information and data that may assist

in establishing a TLV for this agent.4

 However,

Rylander has reported that sufficient toxicological

data exists to establish an occupational exposure

limit for endotoxin based on acute changes in

pulmonary function.24 The following eight-hour

time weighted average (TWA) concentrations

have been suggested: 200 EU/m3

 for airway

inflamation with increased airway activity, 2000

EU/m3

 for over-shift decline in forced expiratory

volume in one second (FEV1), 3000 EU/m3

 for

chest tightness, and 10,000-20,000 EU/m3

 for

toxic pneumonitis. Castellan et al. have reported

a calculated zero pulmonary function effect

concentration of 90 EU/m3

.

25

Microorganisms

Microorganisms (including fungi and bacteria) are

normal inhabitants of the environment. Fungi

comprise 25% of the biomass of earth;28 therefore,

human exposure to fungi is ubiquitous. Although

there are thousands of fungal species, reports of

human and animal diseases have involved fewer

than 100 species.28 Saprophytic fungi (i.e., those

utilizing non-living organic matter as a food

source) inhabit soil, vegetation, water, or any

reservoir that can provide an ample supply of

nutrients. Under the appropriate conditions

(optimum temperature, pH, and with sufficient

moisture and available nutrients) saprophytic

microorganism populations can be amplified.

Through various mechanisms, these organisms can

then be disseminated as individual cells or with

soil or dust particles or water droplets. 

Fungi can produce adverse health effects by

three known mechanisms: (1) immunologic

hypersensitivity to the fungus (allergy), (2) fungal

infection (i.e., mycosis), and (3) mycotoxicosis, a

reaction to toxins produced by the fungus.29

Health effects related to allergenic responses are

based, partly, on a genetic predisposition.30

Allergic diseases typically associated with

exposures in indoor environments include allergic

rhinitis (nasal allergy), allergic asthma, allergic

broncho pulmonary aspergillosis, and extrinsic

allergic alveolitis (hypersensitivity pneumonitis).31

Allergic respiratory diseases resulting from

exposures to microbial agents have been

documented in agriculture, biotechnology, office,

and home environments.32,33,34

VOCs

VOCs are a large class of organic chemicals (i.e.,

containing carbon) that have a sufficiently high

vapor pressure to allow some of the compound to

exist in the gaseous state at room temperature.

VOCs are emitted in varying concentrations from

numerous sources including, carpeting, fabrics,

adhesives, resins, solvents, paints, cleaners, waxes,

cigarettes, and combustion sources.

RESULTS/DISCUSSION

Culturable Bacteria

The results of the air sampling for bacteria are

given in Table 2. Total bacteria concentrations for

the control samples and working face samples

ranged from 96 CFU/m3

 to 144 CFU/m3 and from

108 CFU/m3

 to >62,304 CFU/m3 respectively.

Results from four samples, collected at the
Page 6 Health Hazard Evaluation Report No. 2003-0078

working face, were approximated due to the heavy

bacterial load on the sampling media. The

bacterial concentrations were highest for the

samples collected in the afternoon of June 4, 2003,

during the unloading and spreading of one load of

dry sewage sludge. The bacterial concentrations

were higher at the working face compared with the

control area. The following enteric bacteria

(bacteria present in the intestinal tracts of humans

and animals) were identified: Klebsiella oxytoca,

Leclercia adecarboxylata, Enterobacter cloacae,

and Citrobacter freundii. 

Exposure to these enteric organisms may

potentially result in disease (e.g., gastroenteritis)

or in a carrier state in which an infection does

not clinically manifest itself in the individual but

can be spread to others. These enteric organisms

are usually associated with self-limited

gastrointestinal illness but can develop into more

serious diseases in sensitive populations such as

immune-compromised individuals. The disease

risk is a function of the number and types of

pathogens in the sewage sludge relative to the

exposure levels and infective dose. Because data

are sparse on what constitutes an infective dose, it

is prudent public health practice to minimize

workers’ contact with sewage sludge and soil or

dusts containing enteric organisms.

We were unable to sample at the working face of

a landfill not receiving sewage sludge; as such, no

data are available for comparison purposes. Our

data consist of culturable bacteria and endotoxin

results originating from the sewage sludge and all

the other municipal waste present at the landfill at

the time of the evaluation. We were unable to

identify the contribution the sewage sludge alone

had on our sampling results. 

Bacterial Endotoxin

The results of endotoxin sampling are given in

Table 3. The PBZ TWA exposure of the dozer

operator was 27.9 EU/m3

 and the working face

area TWA concentration was 4.7 EU/m3

. The

morning and afternoon PBZ exposures were

65 EU/m3

 and 1.7 EU/m3 respectively. The

morning and afternoon area samples collected at

the working face of the landfill were 6 EU/m3

 and

2.9 EU/m3

 respectively. The work activities of the

dozer operator were the same in the morning and

afternoon of sampling. Sewage sludge was

received in the wet form in the morning and in

the dry, pellet form in the afternoon. There was

also variation in the type of waste disposed

of throughout the day. A similar higher

concentration of endotoxin was not measured in

the morning area sample. This variation in waste

is a possible explanation for the difference in

measured exposures. A wide range of endotoxin

concentrations were measured. Both control

samples measured concentrations less than the

minimum detectable concentration of 0.02 EU/m3

assuming a sample volume of 230 L.

These results are lower than those detected at

wastewater treatment facilities. Two samples

collected in this study were at concentrations

associated with acute health effects in previous

endotoxin exposure studies.22,26,27 In a previous

NIOSH HHE evaluating biosolids exposure during

land application, area and PBZ endotoxin levels

ranged from 20 EU/m3

 to 39 EU/m3. 

VOCs

Major compounds detected were ethanol, various

aliphatic hydrocarbons, toluene, ethyl benzene,

xylenes, trimethyl benzenes, styrene, limonene,

and siloxanes. Other compounds detected

included chlorofluorohydrocarbons, naphthalene,

pinenes, 4-vinyl-cyclohexene, methyl isobutyl

ketone, butyl cellosolve, and butyl alcohols. None

of these compounds were identified on the control

sample collected on the closed unit. This sample

contained water after the initial helium purge

which may have prevented the detection of traces

of low boiling components. 

Observations

Employees working in the landfill did not report

any health problems. Operators spent the majority

of their day inside the cabs of the dozers and
Health Hazard Evaluation Report No. 2003-0078 Page 7

compactors. These cabs are enclosed and are

equipped with heaters and air-conditioners.

Operators leave their cabs to clear debris from

their equipment, clean the windshield of the

equipment, or to direct traffic at the working face.

The dozers and compactors are not routinely

cleaned. WMI management reported that it is

common practice to pass down older dozers and

compactors to smaller landfills when they are no

longer suitable for use at large-scale landfills. The

heavy machinery used at this site is state-of-the-art

and therefore may represent the best case scenario

for cab air filtration and resulting lower employee

exposures. A locker room for employees is

located in the maintenance shop. Shower facilities

are not provided and employees wear their work

clothes home. One employee reported they had

received training on proper hygiene precautions.

This employee reported routine hand washing

prior to eating lunch. 

CONCLUSIONS

Employees may be exposed to airborne sewage

sludge during the disposal and subsequent

spreading of it at the working face of the landfill.

The detection of enteric bacteria in the air samples

collected in this HHE confirms the potential for

operators to be occupationally exposed to

organisms which have been associated with

gastrointestinal symptoms and illnesses. The total

bacterial and endotoxin concentrations detected in

the air were higher than those found in a previous

NIOSH HHE during biosolids land application.

Exposure criteria to quantitatively determine

health risks associated with these exposure levels

are not available. 

At the time this HHE was conducted, employees

operating heavy equipment at the working face of

the landfill did not report any health problems.

Based on conversations with employees and

workplace observations, work practices such as

wearing work clothing home and not cleaning the

cab of the equipment may increase exposures to

sewage sludge. Actions should be taken to reduce

potential exposures.

RECOMMENDATIONS

The following recommendations are provided to

help minimize exposure to sewage sludge and

increase employee awareness of the importance of

good hygiene and the appropriate use of personal

protective equipment (PPE).

1. On-site showers should be installed and

laundry services for washing work clothes should

be provided to prevent contaminating personal

vehicles or homes.

2. To reduce exposures to airborne

microorganisms and endotoxin, the heavy

equipment (dozers and compactors) used at the

working face should be retro-fitted with air

cleaning devices in conjunction with the airconditioning units.

3. Appropriate PPE, such as gloves and

coveralls, should be required for all job duties

likely to result in exposure to sewage sludge.

Management and employee representatives should

work together to determine which job duties are

likely to result in exposure and which type of PPE

is needed. A qualified health and safety

professional should provide training or retraining

in the use of appropriate PPE.

4. Periodic training regarding standard hygiene

practices should continue, reviewing issues such

as:

• Frequent and routine hand washing. This

is the most valuable safeguard in preventing

infection by agents present in sewage sludge.

• Removing soiled PPE (such as gloves)

after use, proper storage and disposal to avoid

contaminating other objects or parts of the facility

with soiled PPE, and hand washing after gloves

are removed.

• Work clothes and boots should not be

worn home or outside the immediate work

environment.

• Eating, drinking, or smoking should not

be done while working. Employees should always
Page 8 Health Hazard Evaluation Report No. 2003-0078

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activities or using the restroom.

• PPE, such as boots, hard hats, and gloves,

should either be properly cleaned after use or

discarded.

• Signs and symptoms of illnesses

potentially related to sewage sludge.

4. The compactor and bulldozer cabs should be

wiped down and vacuumed on a regular basis to

reduce potential exposure to contaminated

material.

5. Employees should report health effects

thought to be caused by work exposures to a

designated WMI employee. A mechanism by

which employees may report health effects or

concerns should be developed. Those employees

found to have potential work-related health effects

should be referred to a physician knowledgeable

in occupational medicine. 

6. Since employees are at risk for soilcontaminated injuries, management should insure

that all employees are up-to-date on tetanusdiptheria immunizations.

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Table 1

Principal Pathogens of Concern in Domestic Sewage and Sewage Sludge8

Waste Management, Inc. Outer Loop Landfill

HETA 2003-0078-2918

June 4-5, 2003

Organism Disease/Symptom

Bacteria

Salmonella sp. Salmonellosis (food poisoning), typhoid fever

Shigella sp. Bacillary dysentery

Yersinia sp Acute gastroenteritis (including diarrhea, abdominal pain)

Vibrio Cholerai Cholera

Escherichia coli Gastroenteritis (pathogenic strains)

Campylobacter jejuni Gastroenteritis

Enteric Viruses

Hepatitis A virus Infectious hepatitis

Norwalk and Norwalk-like viruses Epidemic gastroenteritis with severe diarrhea

Enteroviruses- Polioviruses Poliomyelitis

Enteroviruses- Coxsackieviruses Meningitis, pneumonia, hepatitis, fever, cold-like

symptoms

Enteroviruses- Echoviruses Meningitis, paralysis, encephalitis, fever, cold-like

symptoms, diarrhea

Heovirus Respiratory infections, gastroenteritis

Astroviruses Epidemic gastroenteritis

Caliciviruses Epidemic gastroenteritis

Protozoa

Cryptosporidium Gastroenteritis

Entamoeba histolytica Acute enteritis

Giardia lamblia Giardiasis (including diarrhea, abdominal cramps, weight

loss)

Balantidium coli Diarrhea and dysentery

Toxoplasm gondii Toxoplasmosis
Table 1 Continued

Principal Pathogens of Concern in Domestic Sewage and Sewage Sludge8

Waste Management, Inc. Outer Loop Landfill

HETA 2003-0078

June 4-5, 2003

Organism Disease or Symptom

Helminths

Ascaris lumbrcoides Digestive and nutritional disturbances, abdominal pain,

vomiting, restlessness

Ascaris suum May produce symptoms such as coughing, chest pain, and

fever

Trichuris trichiura Abdominal pain, diarrhea, anemia, weight loss

Toxocara canis Fever, abdominal discomfort, muscle aches, neurological

symptoms

Taenia saginata Nervousness, insomnia, anorexia, abdominal pain, digestive

disturbance

Taenia solium Nervousness, insomnia, anorexia, abdominal pain, digestive

disturbance

Necator americanus Hookworm disease

Hymenolepis nana Taeniasis
Table 2

Culturable Bacterial Air Sampling Results

Waste Management, Inc. Outer Loop Landfill

HETA 2003-0078

June 4-5, 2003

Activity Sampler Type Total Bacteria

Concentrations

(CFU/m3

)*

Enteric Bacteria

Concentrations

(CFU/m3

)*

Control samples; no sewage

sludge activity

Anderson 144 0

Anderson 96 0

SAS 110 0

SAS 110 0

 Unloading and spreading of

wet sewage sludge

Anderson 108 0

Anderson 564 0

SAS 423 20

SAS 635 50

Unloading and spreading of

dry sewage sludge

Anderson 7584 0

Anderson >62,304** 0

SAS >29,681** 0

SAS > 53,152** 0

Unloading and spreading of

two loads of dry sewage

sludge

Anderson > 38,753** 0

Anderson 7344 36

SAS 671 0

SAS 2863 0

Unloading of one truckload

of wet sewage sludge

Anderson 6348 0

Anderson 11,556 0

SAS 9805 0

SAS 6965 0

* CFU/m3

 = colony forming units per cubic meter 

** > indicates approximate concentrations due to heavy bacterial loading
Table 3

Waste Management, Inc. Outer Loop Landfill

Endotoxin Air Sampling Results

HETA 2003-0078-2918

June 4-5, 2003

Job Title Date Job Task Time

(minutes)

Sample

Volume

(Liters)

Concentration

(EU/m3

)†

Full-Shift Personal Breathing Zone Samples

Dozer

Operator

06/04/03 Spread sewage

sludge at

working face

and directed

traffic

8:30 - 11:36

(126)

252 65

12:47 - 15:45

(178)

356 1.7

TWA Exposure 27.9

Full-Shift TWA Area Sample

Unit 7 06/04/03 Disposal of

sewage sludge

and other waste

at working face

10:00 - 12:47

(167)

334 6

13:36 - 15:37

(121)

242 2.9

Area TWA 

4.7

Unit 6 06/04/03 Control 9:00 - ???* --- < 0.02

Unit 7 06/05/03 Disposal of

sewage sludge

and other waste

at working face

8:33 - 10:54

(115)

230 170

Unit 6 06/05/03 Control 8:50 - 10:45

(141)

282 < 0.02

† = Endotoxin units per cubic milligram

* = Pump failure

TWA = Time-weighted average

TWA Calculation = C1T1 + C2T2 + CnTn ,where C = concentration and T = time 

 T1 + T2 + Tn
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