H. WHO Indoor Air Quality Guidelines, 2010

The World Health Organisation IAQ guidelines aim to safeguard human health by providing health-based recommendations for appropriate fuels, technologies, and strategies within indoor environments, along with international exposure limits. Stressing the paramount importance of human health and potential indoor contaminants, the World Health Organisation has emphasised the significance of IAQ determinants in its technical documents and position papers¹⁰¹.

The World Health Organisation IAQ guidelines offer a comprehensive framework to protect public health from health risks posed by common indoor air pollutants. These guidelines result from rigorous evaluations of scientific evidence by a multidisciplinary group of experts. They encompass pollutants such as benzene, nitrogen dioxide, PAHs, naphthalene, carbon monoxide, radon, trichloroethylene, and tetrachloroethylene¹⁰². For carcinogenic pollutants like benzene, unitary risk values are defined for the general population, reflecting their presence in the air¹⁰³.

The guidelines are targeted at public health professionals, building designers, and authorities overseeing indoor materials and products, providing a consolidated reference to mitigate environmental exposure risks¹⁰⁴. Supported by robust evidence reviews, the guidelines evaluate indoor sources, concentrations, outdoor relationships, and health effects of selected pollutants¹⁰⁵.

Table1: WHO IAQ Guidelines Summary Table ¹⁰⁶ _.

Pollutant	Critical outcomes(s) for guidelines definition	Guidelines	Comments
Benzene	• Acute myeloid leukaemia (sufficient evidence on causality) • Genotoxicity	• No safe level of exposure can be recommended • Unit risk of leukaemia per 1 μg/m3 air concentration is 6 × 10–6 • The concentrations of airborne benzene associated with an excess lifetime risk of 1/10 000, 1/100 000 and 1/1 000 000 are 17, 1.7 and 0.17 μg/m3 , respectively
Carbon monoxide	Acute exposure-related reduction of exercise tolerance and increase in symptoms of ischaemic heart disease (e.g. ST-segment changes)	• 15 minutes – 100 mg/m3 • 1 hour – 35 mg/m3 • 8 hours – 10 mg/m3 • 24 hours – 7 mg/m3
Formaldehyde	Sensory irritation	0.1 mg/m3 – 30-minute average	The guideline (valid for any 30-minute period) will also prevent effects on lung function as well as nasopharyngeal cancer and myeloid leukaemia
Naphthalene	Respiratory tract lesions leading to inflammation and malignancy in animal studies	0.01 mg/m3 – annual average	The long-term guideline is also assumed to prevent potential malignant effects in the airways
Nitrogen dioxide	Respiratory symptoms, bronchoconstriction, increased bronchial reactivity, airway inflammation and decreases in immune defence, leading to increased susceptibility to respiratory infection	• 200 μg/m3 – 1 hour average • 40 μg/m3 – annual average	No evidence for exposure threshold from epidemiological studies
Polycyclic aromatic hydrocarbons	Lung cancer	No threshold can be determined and all indoor exposures are considered relevant to health • Unit risk for lung cancer for PAH mixtures is estimated to be 8.7 × 10–5 per ng/m3 of B[a]P • The corresponding concentrations for lifetime exposure to B[a]P producing excess lifetime cancer risks of 1/10 000, 1/100 000 and 1/1 000 000 are approximately 1.2, 0.12 and 0.012 ng/m3 , respectively	B[a]P is taken as a marker of the PAH mixture
Radon	Lung cancer Suggestive evidence of an association with other cancers, in particular leukaemia and cancers of the extrathoracic airways	• The excess lifetime risk of death from radon-induced lung cancer (by the age of 75 years) is estimated to be 0.6 × 10–5 per Bq/m3 for lifelong non-smokers and 15 × 10–5 per Bq/m3 for current smokers (15–24 cigarettes per day); among ex-smokers, the risk is intermediate, depending on time since smoking cessation • The radon concentrations associated with an excess lifetime risk of 1/100 and 1/1000 are 67 and 6.7 Bq/m3 for current smokers and 1670 and 167 Bq/m3 for lifelong non-smokers, respectively	WHO guidelines provide a comprehensive approach to the management of health risk related to radon
Trichloroethylene	Carcinogenicity (liver, kidney, bile duct and non-Hodgkin’s lymphoma), with the assumption of genotoxicity	• Unit risk estimate of 4.3 × 10–7 per μg/m3 • The concentrations of airborne trichloroethylene associated with an excess lifetime cancer risk of 1:10 000, 1:100 000 and 1:1 000 000 are 230, 23 and 2.3 μg/m3 , respectively
Tetrachloroethylene	Effects in the kidney indicative of early renal disease and impaired performance	0.25 mg/m3 – annual average	Carcinogenicity is not used as an endpoint as there are no indications that tetrachloroethylene is genotoxic and there is uncertainty about the epidemiological evidence and the relevance to humans of the animal carcinogenicity data

References

(101) Gaetano Settimo et al, “Indoor Air Quality: A Focus on the European Legislation and State-of-the-Art Research in Italy,” MDPI, 1 March 2020. Available online: https://www.mdpi.com/2073-4433/11/4/370#B6-atmosphere-11-00370

(102) Gaetano Settimo et al, “Indoor Air Quality: A Focus on the European Legislation and State-of-the-Art Research in Italy,” MDPI, 1 March 2020. Available online: https://www.mdpi.com/2073-4433/11/4/370#B6-atmosphere-11-00370

(103) Gaetano Settimo et al, “Indoor Air Quality: A Focus on the European Legislation and State-of-the-Art Research in Italy,” MDPI, 1 March 2020. Available online: https://www.mdpi.com/2073-4433/11/4/370#B6-atmosphere-11-00370

(104) The World Health Organisation, “WHO Guidelines for Indoor Air Quality,” the WHO regional office for Europe, 2010. Available online: https://www.who.int/publications/i/item/9789289002134

(105) The World Health Organisation, “WHO Guidelines for Indoor Air Quality,” the WHO regional office for Europe, 2010. Available online: https://www.who.int/publications/i/item/9789289002134

(106) The World Health Organisation, “WHO Guidelines for Indoor Air Quality,” the WHO regional office for Europe, 2010. Available online: https://www.who.int/publications/i/item/9789289002134