Composting is highly efficient at destroying pathogens if the composting process is fully completed. California regulations require the composting process be entirely finished and that compost products be tested for pathogens and metals. The allowable amounts of metals (14 CCR Section 17868.2) and pathogens (14 CCR Section 17868.3) are based on EPA Part 503 Biosolids Rule. Based on EPA’s risk assessment, consideration of end use, and other factors, there is a different standard in California for the allowable ceiling concentrations of selenium and chromium in compost products. California decided to retain the more stringent standard of 36 mg/kg of selenium, and 1200 mg/kg chromium on a dry weight basis. The US EPA ceiling concentrations include 100 mg/kg selenium and 3000 mg/kg chromium for sewage sludge. Because the EPA standard is for sewage sludge, California decided to retain the more stringent standard of 36 mg/kg for selenium and 1200 mg/kg chromium for compost products.


Composting is a biological activity which releases microorganisms, microbial products such as endotoxins, mycotoxins, microbial enzymes, β-1,2 glucans and other bacteria and fungi which becomes aerosols and chemical emissions. Odors are caused by chemical compounds. The Comprehensive Compost Odor Response Project provides extensive information and guidance on the subject of odor. Odors are generally a nuisance and do not present significant health risk to the community. Although odors are not directly associated with adverse public health effects, if a complainant claims illness due to odor from a composting facility/operations, the local environmental health department should advise the local Health Department.


Bioaerosols are airborne materials comprised of organisms or biological agents some of which may affect humans. Bioaerosols are naturally occurring in the environment and levels will be present even if no composting operations exist in the area. Composting activities which include any agitation of materials, screening, turning a windrow, etc., will produce bioaerosols. There is insufficient data to determine whether a relationship exists between different compost feedstocks and the type and concentration of bioaerosols emitted. Exposure limits are available for some contaminants such as wood dust. There are no ambient or occupational exposure limits for bioaerosols in the United States. Exposure limits for bacterial endotoxins have been proposed. Respiratory symptoms, mucosal membrane irritation, skin diseases and elevation of inflammatory markers are reported health effects. A literature summary which addresses air emissions and monitoring of bioaerosols and health effects from composting operation is available. Many bioaerosols are present throughout our environment, both in the home and in the workplace. Elevation above the background level had been reported in enclosed composting facilities and downwind of outdoor composting facilities (the elevated levels downwind do not necessarily correlate with adverse health effects) Monitoring exposure (sampling and analysis) is a big challenge. The most likely route of exposure is inhalation. . It is highly unusual for a community to be adversely impacted by bioaerosols from an outdoor compost facility. However, some immuno-compromised individuals may be negatively affected. To reduce potential exposure to workers, they should consider wearing half-facepiece respirator with disposable N95 filters when involved in dusty operations for an extended period of time.

Common types of bioaerosols that are linked to compost involve the following:

  • Aspergillus fumigatus, a member of the genus Aspergillus commonly present in the environment, is prevalently emitted during composting. This fungus not only induces allergic sensitization and symptomatic allergic lung disease, but can also cause infectious mycosis, especially in immuno-compromised people.
  • Endotoxins are encountered in composting, recycling and other solid waste handling facilities. Endotoxin is composed of lipopolysaccharides and is a non-allergenic cell wall component of Gram-negative bacteria. It has been recognized that the presence of endotoxin is an important factor in the etiology of occupational lung diseases including asthma, and Organic Dust Toxic Syndrome (ODTS). Occupational studies showed health effects may include acute and chronic respiratory symptoms including asthma, acute and chronic decline in lung function, non-allergic (neutrophilic) airway inflammation, increased bronchial hyper responsiveness.
  • Organic Dust Toxic Syndrome (ODTS) can develop when workers inhale dust contaminated with a large amount of organic material. The syndrome is characterized by fever occurring 4 to 12 hours after exposure and flu like symptoms such as general weakness, headache, chills, body aches, and cough. Shortness of breath may also occur. In 1995, the National Institute for Occupational Health suggested that endotoxin might be involved in the development of ODTS.

Other bioaerosols that are not present in significant quantities in composting facilities to cause concern include actinomycetes, glucans, and mycotoxins. A review report of the progress and prospects of bioaerosol health effects and exposure is available.

Bioaerosols and odor impacts can be reduced through best management practices utilized by the composting operation. To reduce exposure to bioaerosols, a combination of engineering controls, work practices, and personal protective equipment should be employed.