Megacities gasping for air — Environmental and health risks

Millions of private households, industrial and commercial companies, traffic — these are some of the accompanying effects of booming megacities, not to mention the poor quality of air, water and soil. People pay a high price for the damage done to these natural resources, as human health is inevitably affected.

Half of the six billion people on earth today live in cities. Above all the trend towards urban migration in newly industrialised and developing countries continues unbroken. Rapid growth, high population density, industry and traffic all concentrated in a relatively confined area mean that environmental burdens are virtually unavoidable. Particularly affected are air, bodies of water and soil. Environmental standards are generally lacking or the authorities are powerless to enforce them as they simply cannot cope.

Soil and groundwater store pollutants

Toxic heavy metals and other pollutants emitted by traffic as well as by industrial and commercial enterprises reach the soil via the air. Because the soil acts like a filter, the heavy metals mostly do not reach the groundwater. Unlike organic compounds, however, they are essentially non-degradable and therefore build up in the soil. Plants growing there take up some of the heavy metals and so they find their way back into the food chain.

Liquid pollutants are often not retained by the soil. They seep through to the groundwater and burden the drinking water reserves. Industrial and commercial enterprises (e.g. petrol stations) tend to cause localised pollution, whereas leaky sewers are responsible for pollution over a wide area.

Sewage: The legacy of our society

In the year 2000, 400 million city dwellers worldwide had no toilets. This, combined with poor supplies of drinking water, led to deaths from diarrhoeal diseases. The types of sewage disposal developed in the northern hemisphere require a lot of water and are very cost-intensive (up to €150 per inhabitant per year). For poorer countries this technology is unaffordable or not feasible as they lack an adequate water supply. The majority of people living in megacities are still not connected to a public sewage disposal system. Even some European cities today dispose of sewage by flushing it untreated into rivers.

Megacities create mountains of refuse

Especially in megacities, where many people have to live in cramped conditions, there is a refuse problem. A prerequisite for dealing with waste is that it has to be collected and disposed of. If this is not done, there can be serious consequences for health. Mountains of refuse pile up, often where families live or children play. Cramped living conditions and often extremely poor hygiene standards provide ideal breeding grounds and short transmission paths for germs und pathogens. Thus in recent years megacities have increasingly seen the spread of yellow fever, malaria and dengue, diseases that were previously endemic to the countryside.

Thick air over the cities

One of the main problems is diesel soot, a product from the combustion of diesel fuel. Obviously, this comes from vehicles that run on diesel, i.e. cars and buses. The carcinogenic effect of small exhaust particulates is now beyond any doubt. The death rate from lung cancer in Chinese cities is six times higher than the national average.

Nitrous oxides are also an important factor in poor air quality; they are released in combustion processes involving high temperatures, for example when fuel is burned in car engines. During periods of intense sunshine, nitrous oxides also impair health by reacting with other chemical compounds in the air to form ozone, thereby causing increased ground-level ozone values or "summer smog".

The easy spread of infectious diseases

Having lots of people living together in extremely confined quarters makes city dwellers susceptible to infectious diseases. Air pollution, poor nutrition and a lack of medical care means that many people already have seriously impaired health. A person suffering from tuberculosis in the poorest neighbourhoods infects an average of ten to 15 people per year, often family members. Resistant strains of the pathogen and also long and costly treatments mean that this disease is also becoming a problem in major cities in rich countries.

The rapid increase in travel and trade as well as urban drift favour the quick and global spread of diseases. This concerns above all sexually transmitted diseases such as HIV, hepatitis B and C or papilloma virus infections, which can cause cancer.