How much does the indoor environment contribute to cancer?

In addition to ambient air pollution, the potential contribution of indoor air pollution, particularly environmental tobacco smoke to the risk of lung cancer, has been increasingly recognized as important, given that, in developed countries, many people spend up to 90% of their time indoors.

Levels of substances in indoor air are related to levels outdoors, the

activities of the occupants (for example, smoking, cooking), fitting and furnishings (for example, formaldehyde in insulating materials), and the geographical location (for example, radon).

 

Radon

 

Radon is a natural radioactive gas which seeps into buildings from minute amounts of uranium that are present in all rocks, soils, brick and concrete.

Radon levels in homes vary during the day, from one day to the next, and from winter to summer, mainly because of temperature differences between indoors and outdoors. They are generally higher at night and during the winter.

Most people receive a larger radiation dose from radon indoors than from any other source, whether from the many industrial uses of radiation, nuclear power or medical exposures.

There is a great deal of evidence that exposure to radon, or rather its decay products, leads to lung cancer in miners.

Although the evidence from miners is clear, it is less easy to detect the effects of radon in houses because of the small number of people exposed at high radon levels in their homes, and the difficulty of measuring past exposures. Nevertheless, researchers are undertaking such studies. The most reliable are those that use individual data on radon exposures and smoking histories. Results from the largest domestic case-control study to date were recently published by researchers in Sweden. This study was based on 1360 lung cancer cases and roughly twice as many controls. The lung cancer risk was shown to increase to a statistically significant degree with increasing radon exposure and the risk estimates were consistent with those from the miner studies. The quantification of risk in studies of domestic exposure is, however, hampered by the lack of statistical power.

 

 

 

 

The contribution of environmental tobacco smoke and radon on the incidence of lung cancer has been estimated to be considerable. The source of formaldehyde, classed by IARC as a group 2A probable human carcinogen, in indoor air is mainly from furnishing materials and cigarette smoke. Levels indoors have been shown to be 10 times greater than levels outdoors.

 

 

 

Proportions of cancer deaths attributed to various different factors
Factor or class of factors	Percentage of all cancer deaths. Best estimate	Range of acceptable estimates
Tobacco		25-40
Alcohol		2-4
Diet		10-70
Reproductive and sexual behaviour		1-13
Occupation	4	2-8
Pollution	2	<1–5
Industrial products	<1	<1–2
Medicines and medical procedures		0.5–3
Geophysical factors		2–4
Infection	10?	1–?

 

(1) Regarding the causes of cancer:

(a) tobacco is the most important preventable cause

(b) occupational and environmental factors cause a high proportion of all cancers

(c) geophysical factors are responsible for a large number of non-fatal cancer cases

(d) all aspects of diet contribute to increased cancer rates (e) occupational exposures will continue to contribute a high proportion of future cancer incidence

(2) Air pollution

(a) air pollution has been associated with an increased risk of lung cancer

(b) lung cancer rates in urban areas are higher than in rural areas

(c) indoor air quality is not likely to contribute to cancer

(d) environmental tobacco smoke causes lung cancer

(e) air pollution definitely causes forms of cancer other than lung

 

(1) Which of the following is the correct defined size of ultrafine particles?

(a) > 100 µm

(b) < 100 nm

(c) < 1000 µm

(d) < 500 nm

(e) < 10 nm

(2) Are the following associated with increases in PM10?

(a) Deaths from respiratory causes

(b) Symptoms of fever

(c) Worsening of symptoms of asthma in patients with pre-existing asthma

(d) Deaths from heart attacks

(e) Attacks of chronic obstructive pulmonary disease (COPD)

(3) Which of the following is true of PM10 sampling convention measures?

(a) Mass of particles with a 50% efficiency for those with an aerodynamic diameter of 50 µm

(b) Mass of particles with 50% efficiency for those with an aerodynamic diameter of 10 nm

(c) Mass of particles with 10% cut off for those with an aerodynamic diameter of 50 µm

(d) Mass of particles with a 50% efficiency for those with an aerodynamic diameter of 10 µm

(e) Number of particles with 50% efficiency for those with an aerodynamic diameter of 50 µm

(4) Which of the following statements on ultrafine particles is not correct?

(a) They are found in large numbers in urban air

(b) They have a large surface area per unit mass

(c) The form aggregates

(d) They have a smaller surface area than the same mass of larger particles

(e) They can exert their effects through mechanisms other than transition metals

(5) Which of the following groups are susceptible to the adverse effects of PM10?

(a) Patients with asthma

(b) Patients with cystic fibrosis

(c) Patients with COPD

(d) Patients with cardiovascular disease

(e) Patients with hayfever