To All Local Enforcement Agencies:

Composting is a widely accepted process for converting yard waste and municipal solid waste into stable, agriculturally or horticulturally useful organic material. Recently, potential adverse health effects associated with airborne fungal spores, specifically Aspergillus fumigatus, have been raised as issues by some Californians during the siting or operation of composting facilities. The staff of the California Integrated Waste Management Board is providing a technical bulletin on this issue titled Aspergillus, Aspergillosis, and Composting Operations in California. Additional bulletins covering relevant health and safety issues are expected to follow.

California Integrated Waste Management Board staff prepared this technical bulletin in cooperation with the California Department of Health Services, and CalEPA's Office of Environmental Health Hazard Assessment. This document furnishes information on:

  • Aspergillus fumigatus and its life history,
  • the potential health risks and health effects,
  • the presence of Aspergillus fumigatus spore concentrations in ambient air and at composting operations,
  • an overview of current composting regulatory requirements, and
  • suggested operating practices to limit the production of airborne fungal spores

Summary of Findings

Aspergillus fumigatus spores are very common in our everyday environment in North America. The risk of disease or illness caused by Aspergillus fumigatus is negligible or very low for healthy people. Everyday activities account for most of the exposures to this fungus.

The majority of exposures to the fungus will not result in illness. Those most at risk of developing health complications if exposed to large concentrations of spores include people who already suffer from asthma, immunosuppressed people, or patients taking high doses of corticosteroids.

To mitigate occupational and community health risks, sludge composting/co-composting facility operators must follow existing federal standards. Green waste composting operators must comply with California's green waste composting facility regulations, California Code of Regulations, Title 14, Chapter 3.1. Additionally, compost facility operators must provide employees with appropriate personal protective equipment in accordance with OSHA regulations. Routine inspection and timely enforcement activities by the LEA's are also important mitigation measures; corrective action should not wait until complaints are generated.

A properly operated composting facility should not present a health risk from Aspergillus fumigatus. Sound management practices include maintaining moisture, temperature and pH levels, aerating, turning and mixing. Reducing the dispersal of dust and spores best controls exposure. The use of water sprays or mists while turning piles, and refraining from turning on windy days will help accomplish this.

Any further questions or comments concerning Aspergillus fumigatus should be directed to Diane Kihara. Questions concerning permitting or operational requirements should be directed to your CalRecycle permitting, inspection or enforcement staff contact.


Original signed by:

Deputy Director
Permitting and Enforcement Division


Aspergillus, Aspergillosis, and Composting Operations in California

Publication #200-93-005

The intent of the advisories is to provide guidance to Local Enforcement Agencies (LEA) in performing their duties. Guidance, for this purpose, is defined as providing explanation of the Board’s regulations and statutes.

Unless included by reference in the LEA's Enforcement Program Plan (EPP), advisories are not enforceable in the same manner as regulations because they have not been adopted through the formal rulemaking process (see Government Code sections 11340.5 and 11342.6). Advisories do not take precedence over statute or regulation.