HEALTH: Indoor Air Just as Polluted as Air Outdoors

By Marwaan Macan-Markar Reprint | | Print |

Marwaan Macan-Markar

MEXICO CITY, Mar 27 2001 (IPS) - Every weekday close to four million people descend into the belly of this enormous city to ride underground commuter trains, which run from dawn till after midnight along a network of tracks that add up to over 160 kilometres in length.

For passengers like Adriana Contreras Díaz, however, the daily journey from home to the office and back could mean spending well over two-and- a-half hours in Mexico City’s Metro, since the 29-year-old lives at the eastern end of this 1,479 square-kilometre megalopolis and works in the city’s centre.

But how clean is the air she breathes during the daily journeys in the Metro’s carriages? Are there times when the air is polluted and could lead to respiratory problems? What pollutants does such indoor air contain?

There are no answers to such questions, right now. But that is due to change this December, when the National Centre for Environmental Research and Training (known by its Spanish acronym CENICA) begins a four-month study of the quality of indoor air in this city’s transport system, including the Metro.

“It is the first time that such an extensive study will be carried out to assess the indoor air pollution levels in the transport system,” says Salvador Blanco Jiménez, the co-ordinator of Air Quality Research at CENICA, a government organisation. “We will test for carbon monoxide, heavy metals, lead and particulate matter.”

The winter months were chosen for the study because it is a period when pollution levels in Mexico City’s outdoor air increases, adds Blanco Jiménez. “We want to find out the difference and the relationships between the outdoor and indoor air pollution during this period.”

World public health bodies have long been concerned about the high prevalence of indoor air pollution in homes, offices and closed environments such as transport systems.

According to the World Health Organisation (WHO), close to one billion people, most of them women and children, “are regularly exposed to levels of indoor air pollution exceeding WHO guidelines by up to 100 times”.

What is more, observes Dr. Peter Toft, manager of special projects in the Health and Environmental Division of the Pan American Health Organisation (PAHO), “air pollution indoors is 1,000 times more likely to reach people’s lungs than pollution released outdoors”.

The consequences of that level of exposure have led to a range of illnesses, including respiratory diseases such as asthma, chronic obstructive pulmonary disease, cardiovascular disease and cancer of the lung.

“Indoor air exposure to suspended particulate matter (one of the most common air pollutants) increases the risk of acute respiratory infections,” reveals the Geneva-based WHO.

In India, for instance, where as much as 80 percent of households use solid fuels like wood, coal, charcoal and crop residues for cooking, there are estimates that close to half a million children die annually from indoor air pollution, particularly from acute respiratory infections, adds this United Nations health agency.

And in sub-Saharan Africa, indoor air pollution has been linked to an estimated 300,000 to 500,000 deaths annually.

In Latin American countries, where about one in four household use solid fuels, the WHO estimates that 30,000 people “die each year from acute respiratory infections attributable to indoor air quality”.

But homes with modern fittings and state-of-the-art offices are not immune from the problem of “dirty air” indoors either. “Indoor air pollution can be a problem in Canada and the United States,” says Dr. Toft. “It can result from houses being closed up and there being a build up of air pollution products which normally escape.”

According to a study conducted by the US Environmental Protection Agency in select US schools, poor indoor air quality (IAQ) was linked to children falling ill and causing “acute health symptoms that decrease performance while at school”.

“In addition, recent data suggests that poor IAQ can reduce a person’s ability to perform specific mental tasks requiring concentration, calculation or memory,” states the EPA study, ‘Indoor Air Quality and Student Performance’.

The WHO attributes such a rise in polluted indoor air to the manner in which modern buildings are designed. “In an effort to conserve energy, modern building design has favoured tighter structures with lower rates of ventilation,” remarks the WHO in a study on indoor air quality.

In the developed countries, it adds, important sources of chemical pollutants in indoor environments include “the human body and human activities, emissions from building materials, furnishings and appliances and use of consumer products”.

What is more, the WHO study also identifies badly maintained heating, ventilating and air conditioning systems as sources of indoor pollution, too.

“Improper care of filters can lead to re-emission of particulate contaminants. Biological contamination can proliferate in moist components of the system and be distributed throughout the building.”

Such a situation is compounded further if the indoor environment is polluted with tobacco smoke, since the “particle and vapour phases of environmental tobacco smoke are complex mixtures of several thousand chemicals, including known carcinogens such as nitrosamines and benzene,” notes the study.

Blanco Jiménez has evidence from Mexico City that mirrors such a conclusion. A CENICA investigation last year into the indoor air quality in homes, schools and offices in the Mexican capital had revealed that smoking indoors had contributed to an increase in the indoor air pollution levels, more so in buildings with poor ventilation.

“In buildings with insufficient windows and low ventilation, the pollution level can be higher than outside, in the city,” affirms Blanco Jiménez.

Despite such concern, however, countries in the developing world have still to recognise indoor air pollution as a hazard. “The importance of air pollution as an environmental threat to health is not widely recognised in developing countries,” remarks Dr. Toft.

In that sense, Metro passenger Contreras Díaz welcomes the effort by CENICA to assess the quality of air within this city’s underground commuter trains. “You usually think that the air is clean inside the Metro, but it may not be so, and it is good to know just how bad it is,” she says.