The National Institute of Occupational Safety and Health (NIOSH) has released a report on the hazards of working with Class B biosolids, and recommends that workers use good personal hygiene practices and personal protective equipment to minimize exposure to residual microorganisms in Class B material.
In response, the Water Environment Federation (WEF) wrote a letter to Linda Rosenstock, NIOSH director, expressing concern that the report might be based on inadequate information and "may lead to misunderstandings about the potential risks to Class B biosolids workers."
However, the federation said that it agrees with the report's recommendations.
"Not only are the report's recommendations already routinely administered at the vast majority of publicly owned treatment facilities, they are measures WEF has actively supported and promoted for years," said Al Gray, WEF deputy executive director.
"Thousands of workers handle Class B biosolids every day across the United States, so the fact that NIOSH has been asked to review a single case at a lone facility is a testament to safety practices instituted at most of the country's 16,000 waste-water treatment plants," said Gray. "The body of scientific research and literature does not suggest any detrimental effects of properly managed biosolids on human health."
In preparing its report, 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, NIOSH said.
While EPA rules restrict public access to treated lands to protect public health, the rules do not apply to workers involved with applying biosolids to land.
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 exposure decreases over time.
According to NIOSH, there are four major types of human pathogenic organisms found in biosolids: bacteria, viruses, protozoa, and helminths (parasitic worms). 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).
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, Crypto-sporidium, Giardia, and enteroviruses.
Enteric organisms are usually associated with self-limited gastrointestinal illness but can develop into more serious diseases in sensitive populations such as immunocompromised individuals, infants, young children, and the elderly. The hazard 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.
"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," the NIOSH report states.
During its investigation, NIOSH interviewed five employees at a Class B biosolids land application operation. All five reported at least one episode of gastrointestinal illness after working with the biosolids, either at the treatment plant or during land application.
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), well below the federal standard for Class B biosolids. Fecal coliforms are used as an indicator for the presence of other enteric microorganisms. NIOSH also detected enteric bacteria in air samples collected at the site.
"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 report states.
NIOSH Recommendations
The NIOSH recommendations for workers at Class B biosolids land application sites include:
- 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 (up to one year).
- Hand-washing stations with clean water, mild soap, and paper towels should be 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 ensure that all employees are up to date on tetanus-diphtheria immunizations.
- Periodic training on standard hygiene practices and the use of personal protective equipment should be conducted. When using Class B biosolids, engineering controls and work practices should be used to prevent exposure. 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 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 biosolids should use personal protective equipment during the restricted period.
- Heavy equipment used at storage and application facilities 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. Protective equipment may include goggles, splash-proof face shields, respirators, liquid-repellent 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 jobs 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.
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, Training
Periodic training on standard hygiene practices for working with Class B biosolids should be conducted. Training should cover issues such as:
- Frequent and routine hand washing, especially before eating or smoking, and after contact with Class B biosolids or surfaces exposed to biosolids;
- Use of personal protective equipment, such as coveralls, boots, gloves, goggles, respirators, and face shields;
- Removal of contaminated personal protective equipment and the use of available on-site showers, lockers, and laundry services;
- Proper storage, cleaning, or disposal of contaminated personal protective equipment;
- Use of clean, dry bandages to cover cuts and wounds;
- Instructions that work clothes and boots should not be worn home or outside the immediate work environment; and
- Prohibition of eating, drinking, or smoking while working in or around biosolids.
