Biological Pollutants

As well as the chemical pollutants, various biological contaminants often contribute to illness. In fact, biological factors are reported to be behind the majority of cases. These biological pollutants can cause illness through three different mechanisms:


  • Infection
  • Allergy/Hypersensitivity
  • Toxicosis – symptoms caused by toxins produced by micro-organisms e.g. mycotoxins produced by mould/fungi

The following are the main sources of this form of pollution:

Toxic Black Mould

Reported to be the leading cause of sick building syndrome and building related illness. Mould grows rapidly in warm and damp environments. If the indoor environment is too humid or if water damage occurs through leaks or rising damp, mould growth is very likely to occur.

Viruses & Bacteria

Common in every building, especially high occupancy buildings such as offices and schools. These micro-organisms can make a significant contribution to causing illness. They become increasingly problematic if humidity levels are either too low or too high, as a result of how their growth is affected and the fact that our defences against them are also affected by humidity levels.

The House Dust Mite

‘Dust mite’ is the generic term for all the species of mite commonly found in homes. Thirteen species of mite have been found in house dust.

The mite family ‘Pyroglyphid’ produce a large range of particularly allergenic proteins, which have a direct causal and a dose-response relationship with asthma.

It is mainly their faecal matter that is responsible. The only regulating factor in their common habitats is the availability of moisture.

They have an ability to adapt and hibernate through non-optimum conditions.


Pollen is another allergy-causing substance that can accumulate in a building if proper ventilation and filtering are not maintained. Aside from being carried on breezes through open doors or windows, pollens can also be brought indoors on the occupants’ shoes and clothing.

Radon gas

Some homes and workplaces are known to be affected by high levels of Radon gas, primarily due to the geology of the area.

Radon is a gas that has no colour, odour or taste and comes from the natural radioactive breakdown of uranium in the ground.

You can be exposed to radon from two main sources:

  • Radon in the air.
  • Radon in drinking water.

Most of the radon in indoor air comes from the soil underneath properties. As uranium breaks down, radon gas forms and seeps into the property. Radon from soil can get into any type of building – homes, workplaces and schools and build up to high levels in the air inside the building.

Radon gas can also dissolve and accumulate in water from underground sources such as wells, springs or boreholes. When water that contains radon is used for showering, washing dishes and cooking, radon gas escapes from the water and goes into the air.

Why is radon a health concern?

Breathing radon in indoor air can cause lung cancer. Radon gas decays into radioactive particles that can get trapped in your lungs when you breathe it. As they break down further, these particles release small bursts of energy. This can damage lung tissue and increase your chances of developing lung cancer. Not everyone exposed to high levels of radon will develop lung cancer. However, radon in indoor air is the second leading cause of lung cancer. About 2,500 deaths a year in the United Kingdom are caused by breathing radon in indoor air.

Only about 1 to 2% of radon in the air comes from drinking water. Some radon stays in the water; drinking water containing radon also presents a risk of developing internal organ cancers, primarily stomach cancer. However, this risk is smaller than the risk of developing lung cancer from radon released to air from tap water.