U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

National Institute fo r Occu pational Sa fety and He alth

Workers Exposed to Class B Biosolids

During and After Field Application

! Workers may be exposed to disease-causing

organisms while handling, applying or disturbing

Class B biosolids on agricultural lands or mine

reclamation sites.

! Class B biosolids are sewage sludge that has

undergone treatment by processes that significantly

reduce pathogen concentrations. These processes

include aerobic and anaerobic digestion, air drying,

composting, and lime stabilization. According to the

U.S. Environmental Protection Agency (EPA), Class

B biosolids may contain pathogens in sufficient

quantity to warrant restricted public access and

special precautions for exposed workers.

! Class A biosolids are sewage sludge that has

undergone treatment by processes that further reduce

pathogen concentrations resulting in an end product

that is virtually pathogen-free. These processes

include irradiation, composting, heat drying, heat

treatment, pasteurization, thermophilic aerobic

digestion, and alkaline stabilization. Class A biosolids

do not contain pathogens in sufficient quantity to

warrant restricted access or special precautions and

may be applied the same way as commercial fertilizer.

! NIOSH collected air samples for bacteria and

endotoxin (a component of some bacteria), and bulk

sewage sludge samples for fecal coliform bacteria at

a Class B biosolids land application processing

facility. Potentially pathogenic bacteria were found in

bulk samples and in some air samples. Employee

gastrointestinal illnesses at that facility may have

been caused by ingestion or inhalation of Class B

biosolids.

! Whereas EPA rules restrict public access to treated

lands in order to protect public health, these rules do

not apply to workers involved with applying biosolids

to land. The recommendations in this document are

intended to provide guidance to employers and

workers to minimize occupational risks from Class B

biosolids through the use of engineering controls,

personal protective equipment, and worker training.

These recommendations are not intended to address

non-occupational exposure.

Sewage sludge is typically treated to Class B

requirements at the sewage treatment plant. Class B

biosolids, in a liquid or semi-liquid state, can be

transported by truck to a land application site where they

are directly applied to the land using tractors, tank

wagons, irrigation systems, or special application

vehicles. Biosolids may undergo dewatering using

polymers. Dewatered biosolids are often temporarily

stored at the treatment plant or application site before

being transported and applied to land using front end

loaders, trucks, tractors, orsludge-spreading equipment.

Workers may come into either direct or indirect contact

with biosolids during any phase of the treatment,

transport, or application process. The biosolids are

applied as fertilizer to improve and maintain productive

soils and stimulate plant growth. Biosolids have been

applied on agricultural lands and surface mine

reclamation sites.

About Biosolids

Key Points

HID 10
There are four major types of human pathogenic

organisms found in biosolids: (1) bacteria, (2) viruses, (3)

protozoa, and (4) helminths (parasitic worms). The

concentration of organisms in biosolids depends on the

type and concentration of pathogens present in the source

sewage and the degree to which those organisms are

removed or killed by the pre-treatment process.

The hazard that is associated with Class B biosolids is a

function of the number and type of pathogens in the

treated sludge relative to the minimum infective dose and

the exposure level. Under the EPA biosolids rule (40 CFR

503), Class B biosolids must contain less than two

million colony forming units (CFU) of fecal coliform per

gram of total solids (dry weight). To protect public

health, the EPA rule prescribes a restricted period of up

to one year to limit public access to lands where Class B

biosolids have been applied. These EPA restrictions do

not apply to occupational access. The risk of worker

exposure to infectious agents is likely greatest during and

immediately after land application of the biosolids.

Because the concentration of pathogens decays through

natural processes, the potential for pathogen exposure

decreases over time. 

In other settings, the association between poor hygiene,

raw sewage, and infectious disease is well established.

Most of the pathogenic bacteria and viruses in Class B

biosolids are enteric, which means they are present in the

intestinal tracts of human and animals. Enteric organisms

that may be found in Class B biosolids include, but are

not limited to, Escherichia coli, Salmonella, Shigella,

Campylobacter, Cryptosporidium, Giardia, and

enteroviruses. Exposure may potentially result in disease

(e.g., gastroenteritis), or in a carrier state (e.g., typhoid),

where 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

disea ses in sensitive popula tions such a s

immunocompromised individuals,infants,youngchildren,

and the elderly. Because data are sparse on what

constitutes an infective dose, it is prudent public health

practice to minimize workers’ contact with soil or dusts

containing Class B biosolids during the restricted periods.

During investigations at a Class B biosolids land

application and at a Class B biosolids storage site:

! NIOSH interviewed five employees at a Class B

biosolids land application operation. All five

employees reported at least one episode of

gastrointestinal illness after working with the

biosolids, either at the treatment plant or during land

application. The environmental sampling results

indicated that the gastrointestinal illnesses were

possibly of occupational origin.

! NIOSH collected bulk samples from different

locations within the biosolids storage site. The mean

fecal coliform concentration of the bulk samples was

220,000 CFU per gram of sample (wet weight). Fecal

coliforms are used as an indicator for the presence of

other enteric microorganisms. There remains a

significant exposure risk. This example illustrates the

importance of minimizing exposure to Class B

biosolids during the restricted period.

! NIOSH collected air samples at the Class B biosolids

land application and storage site. Enteric bacteria

were detected in the air. The presence of enteric

bacteria in air samples is sufficient justification to

implement engineering controls and work practices

that minimize employee exposure to biosolid aerosols.

The detection of enteric bacteria in a limited number of

air and bulk samples confirms the potential for workers

to be exposed to organisms which have been associated

with gastrointestinal symptoms and illness. Operations

where employees are potentially exposed to Class B

biosolids include transport, loading, unloading, and

application activities. Other potentially exposed workers

include compost workers, surface miners working around

reclamation sites, and farmers.

The recommendations contained in this document apply

to workers at Class B biosolids land application sites.

These recommendations are different from those required

for the general public which are regulated by Title 40,

Code of Federal Regulations, Part 503 (40 CFR 503).

! Class B biosolids should be incorporated (thoroughly

mixed) into the soil to prevent suspension into the air

during periods of dryness. After application,

mechanical disturbance and contact with Class B

biosolids should be avoided for the restricted period.

! Hand-washing stations with clean water, mild soap,

and paper (disposable) towels should be readily

available whenever contact with Class B biosolids

may occur. In the case of workers in the field,

portable equipment, including clean water and soap,

should be provided.

! Since employees are at risk of soil-contaminated

injuries, management should ensurethatall employees

are up-to-date on tetanus-diphtheria immunizations.

Description of Hazard

Recommendations for Prevention
! Current CDC recommendations do not support

hepatitis A vaccination for sewage workers. Data are

sparse; thus, this recommendation may be modified as

more data are developed.

! Periodic training regarding standard hygiene practices

and the use of personal protective equipment should

be conducted.

As a rule, the most effective control for occupational

safety and health hazards is to eliminate the hazard

through substitution. In this case the use of Class A

pathogen-free biosolids would eliminate the hazard;

however, this report addresses reducing worker risk

where Class B biosolids are used. When using Class B

biosolids, engineering controls and work practices should

be used to prevent exposures. Personal protective

equipment, including respiratory protection, should be

used when engineering controls are not feasible; before

engineering controls are installed; or when installed

engineering controls are being repaired or maintained.

Engineering Controls:

! The storage time for dewatered (filter cake) Class B

biosolids should be minimized at both the water

treatment facility and in the field to prevent the

growth of pathogens.

! The Class B biosolids should be incorporated

(thoroughly mixed) into the soil, where feasible.

Where incorporation is not feasible, workers exposed

to the land-applied biosolids should use personal

protective equipment during the restricted period.

! Mechanical disturbance of applied Class B biosolids

should be avoided during the restricted period.

! Heavy equipment used at storage and application

facilities for Class B biosolids should be equipped

with sealed positive pressure, air-conditioned cabs

that contain filtered air recirculation units to reduce

the potential for exposure to airborne microorganisms

and endotoxin.

Personal Protective Equipment:

Appropriate personal protective equipment should be

required for all job duties likely to result in exposure to

Class B biosolids. The choices of personal protective

equipment include goggles, splash-proof face shields,

respirators, liquid-repellant coveralls, and gloves. Face

shields (that fit over the employee’s hard hat) should be

made available for all jobs where there is a potential for

exposure to spray, high-pressure sewage leaks, or

aerosolized biosolids during land application. Gloves

should be used when touching biosolids or surfaces

exposed to biosolids. Management and employee

representatives should work together to determine which

job duties are likely to result in this type of exposure and

which type of equipment is needed. A qualified health and

safety professional should provide training or retraining

in the appropriate use of personal protective equipment.

Hygiene and Sanitation:

Hand-washing stations with clean water and mild soap

should be readily available whenever contact with Class

B biosolids may occur. In the case of workers in the field,

portable sanitation equipment including clean water and

soap should be provided. Biosolids should be removed

from shoes prior to entering enclosed vehicles, and cabs

should be wiped down and cleaned of residual mud (or

settled dust), after each use, to reduce potential exposure

to contaminated material.

Hazard Communication and Training:

Periodic training regarding standard hygiene practices for

working with Class B biosolids should be conducted

which covers issues such as:

! the frequent and routine hand washing (the most

valuable safeguard in preventing infection by agents

present in Class B biosolids), especially before eating

or smoking, and after contact with Class B biosolids

or surfaces exposed to biosolids;

! the use of personal protective equipment, such as

coveralls, boots, gloves, goggles, respirators, and face

shields;

! the removal of contaminated personal protective

equipment and the use of available on-site showers,

lockers, and laundry services;

! the proper storage, cleaning, or disposal of

contaminated personal protective equipment;

! the use of clean, dry bandages to cover cuts and

wounds;

! the instructions that work clothes and boots should

not be worn home or outside the immediate work

environment; and

! the prohibition of eating, drinking, or smoking while

working in or around biosolids.

Actions That Should Be Taken
Additional information about Class B biosolids and

preventive measures can be obtained from the following:

National Institute of Environmental Health Sciences

(NIEHS). The Beauty of Biosolids.Environmental Health

Perspectives, Vol. 104, No. 1, January 1997. On the

Internet at:

http://ehpnet1.niehs.nih.gov/qa/105-1focus/focusbeauty

.html

Environmental Protection Agency (EPA): Title 40 Code

of Federal Regulations Part 503. Homepage on the

Internet at:

http://www.epa.gov/owm/bio.htm

National Center for Infectious Diseases (NCID). Viral

Hepatitis Resource Center:

http://www.cdc.gov/ncidod/diseases/hepatitis.

To obtain more free information about this hazard or

other occupational safety and health issues:

The principal contributors to this publication are Joseph

Cocalis, P.E., DEE, CIH; Nancy Burton, CIH; Frank J.

Hearl, P.E, Ghazala Afaq, M.D., MPH., Douglas Trout,

M.D., Patrick Hintz, CMSP, and Molly Pickett-Harner.

Block JC, Havelaar AH, P L’Hermile (eds.) [1986].

Epidemiological studies of the risks associated with the

agricultural use of sewage sludge: knowledge and needs.

New York, NY: Elsevier Science Publishing Co., Inc.

Brugha et al. [1998]. Risk of hepatitis A in sewage

workers. Occup Environ Med 55(8):567-569.

CDC [1999]. Prevention of hepatitis A through active or

passive immunization. MMWR 48(RR-12).

Clark CS [1987]. Health effects associated with

wastewater treatment, disposal, and reuse. J Water Pollut

Control Fed 59(6): 436-440.

DeSerres et al. [1997]. Hepatitis A among workers from

a waste water treatment plant during a small community

outbreak. Occup Environ Med 54(1):60-62

Dorn RC, Reddy CS, Lamphere DN, Gaeuman JV,

Lanese R [1985]. Municipal sludge application on Ohio

farms: health effects. Environ Res 38:332-359.

Khuder SA, Arthur TA, Bisesi MS, Schaub EA [1998].

Prevalence of infectious disease and associated symptoms

in wastewater treatment workers. Am J Ind Med 33:571-

577.

Kowal NE, Pahren HR [1981]. Health effects associated

with wastewater treatment and disposal. J Water Pollut

Control Fed 53(6): 776-786.

Lundholm M, Rylander R[1983].Workrelated symptoms

among sewage workers. Br J Ind Med 40:325-329.

McCunney RJ [1986]. Health effects of work at waste

water treatment plants: a review of the literature with

guidelines for medical surveillance. Am J Ind Med 9:271-

279.

NIOSH [1982]. Hazard evaluation and technical

assistance report: Wastewater Treatment Plant, Brockton,

MA. Cincinnati, OH: U.S. Department of Health and

Human Services, Public Health Service, Centers for

Disease Control, National Institute for Occupational

Safety and Health, NIOSH Report No. 81-030-1102.

NIOSH [1999]. Hazard evaluation and technical

assistance report: Bio-Solids Land Application Process,

LeSourdsville, OH. U.S. Department of Health and

Human Services, Public Health Service, Centers for

Disease Control and Prevention, National Institute for

Occupational Safety and Health, DHHS (NIOSH)

Publication No. 98-0118-2748.

Scarlett-Kranz JM, Babish JG, Strickland D, Lisk DJ

[1987]. Health among municipal sewage and water

treatmentplantworkers. Toxicol Ind Health 3(3):311-319.

Trout D, Mueller MS, Venczel L, and Krake A. [2000].

Evaluation of Occupational Transmission of Hepatitis A

Virus Among Wastewater Workers. J Occup Environ

Med 42(1): 83-87.

U.S. EPA. [1999]. Environmental Regulations and

Technology: Control of Pathogens and Vector Attraction

in Sewage Sludge. Revised October 1999. Washington,

D.C. Report No. EPA/625/R-92/013 [See pages 9–10].

August 2000 DHHS (NIOSH) Publication No. 2000–158

For More Information

Call NIOSH at 1–800–35–NIOSH

(1–800–356–4674)

or visit the NIOSH Web site at

www.cdc.gov/niosh

References

Acknowledgments