Abstract
 
In the US recommended guidelines are given for comfort parameters in indoor air, but not for microbes such as fungal bioaerosols[i][i]^,[ii][ii].  The ACGIH Bioaerosol Committee has yet to give a numerical threshold limit value (TLV) for fungal bioaerosols most likely due to a lack of consensus and scientific evidence[iii][iii].  Other countries such as the UK, Germany, Sweden, and Finland also recognize the need for providing guidelines for indoor air comfort parameters[iv][iv].  Although there are no laws governing indoor fungal bioaerosol levels there is considerable agreement on the health risks caused by fungal growth in indoor spaces.  In the absence of a legal reference, a summary of the currently available guidelines for fungal bioaerosols, as well as fungal loading levels in indoor spaces are presented here.  These guidelines may aid the industrial hygienist and other professionals in the interpretation of fungal sampling results.
 
Introduction
 
Industrial hygienists, toxicologists, mycologists, and physicians recognize indoor fungal bioaerosols as potential human health hazards.  However, there are no rules, codes, laws, or regulations regarding indoor fungal bioaerosols or fungal loading levels.  There is a current set of available guidelines for indoor spaces and fungal levels promulgated by the following organizations: ACGIH, 1989 (Fewer than 100 CFU/m³ is considered of no concern, 200 CFU/m³ is recommended as a guideline for fungal bioaerosols), University of Minnesota Environmental Health & Safety, 2004 (Recommended guidelines in CFU/gram, low = 10,000 CFU/gram, medium = 10,000 to 100,000 CFU/gram medium to heavy = 100,000 to 1,000,000 CFU/gram, heavy > 1,000,000 CFU/gram), College of Chest Physicians, 2003 (1000 Count/m³ for indoors), US Public Health Service, 2003 (A 200 CFU/m³ guideline is recommended for fungal bioaerosols because 75% of indoor sampled fungal concentrations were less than 178 CFU/m³). CDC, 1993-1996, (Any level of Stachybotrys above outdoor levels is considered positive).  Health Canada Technical Guide, 1993, (if more than 50 CFU/m³,in either indoor outdoor air, of the same species other than Cladosporium or Alternaria are detected, there may be reason for concern).  Health Canada Technical Guide, (Up to 150 CFU/m³ is acceptable if there is a mixture of species reflected the outdoor air).  Health Canada Technical Guide, (Up to 500 CFU/m³ is acceptable in the summer, if the species present are primarily Cladosporium).  The Health Protection Act in Finland, 1999, (Defines indoor fungal bioaerosols as toxigenic material as hazardous to human health.  The owner of a fungal-contaminated building is required by law to take action to remedy the situation.  If the owner does not remediate the building then local, regional, or federal governmental agencies can evacuate and close the building until such time that remediation is accomplished). 

Findings
 
Summarized in Table 1 are all the currently available fungal bioaerosols, as well as fungal loading level guidelines.  Table 1 is a standalone reference source that can be used by the industrial hygienist, as well as other professionals in interpreting fungal sampling results.  These guidelines have been issued by the US, Canada, and Finland.  Two individual values standout for recommended guidelines for fungal bioaerosols from Table 1.  They are 200 CFU/m³ and
1000 Count/m³.  For fungal loading in CFU/gram the recommended guideline from Table 1 is 10,000 CFU/gram (light loading indicating the presence of fungal contamination).
 
Discussion
 
Although, there are no current laws governing fungal bioaerosol indoor levels, there is a general consensus among the scientific community on the detrimental health effects of fungal bioaerosols on humans.  Outlined in this article are the currently known guidelines for both fungal bioaerosols and fungal loading indoors.  These may be of some assistance to industrial hygienists and other professionals in interpreting fungal sampling results.  There seems to be both a need for a consensus agreement, as well as further scientific research in order to determine recommended limit values (TLVs) for both exposure assessment and health effects.

Table 1.  Summary of guidelines for fungal levels in indoor spaces.

Reference	Study focus	Principle	Guideline
ACGIH Guidelines for the assessment of bioaerosols in the indoor environment, 1989[v][v]	Bioaerosols of interest in indoor air, e.g. fungi, mycotoxins, bacteria, endotoxins	Medical Preassessment pp.1-9	Fewer than 100 CFU/m3 was considered of no concern, 200 CFU/m3 was recommended as a guideline for fungal bioaerosols-These guidelines were not given TLV values.
Indoor air quality in office buildings, Health Canada. Indoor air quality in office buildings: a technical guide, 1993[vi][vi]	General technical guideline	Occurrence based	If more than 50 CFU/m3 (in either indoor outdoor air) of the same species (other than Cladosporium or Alternaria) are detected, there may be reason for concern.  Up to 150 CFU m3 is acceptable if there is a mixture of species reflected the outdoor air.  Up to 500 CFU/ m3 is acceptable in the summer, if the species present are primarily Cladosporium.
Immunotherapy and allergen avoidance for allergic airway disorders. American College of Chest Physicians, Lesson 3, Vol. 12, 2003[vii][vii]	Provisional standards for allergenic exposures that lead to sensitization and symptoms	Threshold levels molds	Proposed limited of 1000 Count/m3 for fungal contamination for sensitive receptors.
Airborne fungal particles in non-residential buildings in the United States, Indoor Air, proceedings of the 6th international conference on indoor air quality, 1993[viii][viii]	Fungal bioaerosols in non-residential buildings	Occurrence based	Proposed limit of 200 CFU/m3 for fungal aerosols.
Guidelines on assessment and remediation of Stachybotrys  New York, 1993[ix][ix]	Stachybotrys contamination event	Chronic exposure to airborne Stachybotrys poses a risk of debilitating health effects	Any concentration of Stachybotrys exceeding outdoor levels should be considered positive.
University of Minnesota Environmental Health & Safety, 2004 [x][x]	Qualitative assessment of bulk contamination	Indoor loading levels when high can affect allergic individuals such as diabetics in this contaminated area	Recommended guidelines in CFU/gram, low = 10,000, medium = 100,000., high = 1,000,000.
US Public Health Service, 1993 [xi][xi]	Normal human respiration rate is 6 LPM.  Individuals are expected to breathe in 1 CFU/min. of fungal spores if the concentrations of airborne fungal spores are within the 200 CFU/m3 guideline	75% of indoor fungal aerosol concentrations in nonresidential environments were < 178 CFU/m3	A 200 CFU/m3 guideline is recommended for fungal bioaerosols.
Finnish Health Promotion Act, 1999 [xii][xii]	Fungal contamination of indoor spaces and resultant adverse health effects	Fungi is legally recognized as an indoor toxigenic material	The Health Promotion Act clearly defines the health risk associated with a building to be the owner’s responsibility.

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