The living world is made up of a complex system within which species interact with each other and are interdependent. As an integral part of this system humans are tributary to biodiversity for their survival because biodiversity guarantees, amongst other things, the regulation of the quality of the air, climatic stability, soil fertility, etc. Species that die out take with them other living organisms that depend on them.

The major function of the hormonal or endocrine system is to regulate the development, growth and reproduction of living beings. Endocrine disrupters are substances that are foreign to the organism which enter the blood via food, the skin or respiration. Once ingested, the organism mistakes them for hormones which alter numerous essential biological functions.

The worrying increase in cases of infertility, malformations and behavioural problems in both animals and humans has alarmed the World Health Organisation (WHO). Even in very weak doses, that is to say often below legal levels, the combined substances between them represent a dangerous cocktail for living beings.

These elements penetrate our organism through food, breathing, skin contact or irradiation. Occasional exposure to high doses or frequent exposure to low doses provokes a multitude of harmful effects to human health (nervous troubles, lung disease, cancers) and to living organisms in general. In certain countries progress has been made in the decontamination of polluted sites and the protection of workers. This necessitates a considerable financial investment which is rarely to be found in poor or developing countries.

Certain atmospheric gases, known by the name of greenhouse gases, are playing a major role in global warming. Coming essentially from the burning of fossil fuels (coal, petrol and natural gas) the concentration of greenhouse gases in the atmosphere has increased enormously with the intensification of human activities. It is one of the principal processes at the origin of global warming.

Since 1880 an increase of 0.85°C in the average global temperature has been recorded with an acceleration of this trend over the last 60 years. If nothing is done, the Earth could heat up by 4.8°C between now and 2100 causing an acceleration in the melting of ice and a rise in sea level of approximately 1m.

Millions of people living in coastal regions are threatened by rising sea levels. However, the increase in the concentration of greenhouse gases in the atmosphere does not only manifest through more frequent heatwaves or melting glaciers; it is the totality of the climate that becomes unstable, creating an intensification of extreme meteorological events, such as extremes of heat and cold, cyclones or extreme rainfall.

In the same way as the forests and the soil, the oceans are regarded as wells of carbon because they absorb large quantities of atmospheric CO2, the result of burning fossil fuels. In water, carbon dioxide dissolves to form carbonic acid. This latter modifies the chemical balance of seawater, making it more acidic. Over the past two hundred years the oceans have absorbed a quarter of the CO2 emitted through human activity and their acidity has increased by 30%.

Phosphates and nitrates reach water courses by infiltrating the ground water thus polluting drinking water and damaging freshwater and seawater to the point of asphyxiation. Over-nourished algae flourish, greatly reducing the availability of oxygen for other living beings. This process, called eutrophication, brings with it the erosion of biodiversity and the multiplication of harmful species. This infringement alarms scientists who fear a massive extinction of marine species caused by a lack of oxygen in the oceans which will affect the entirety of the food chain. Today, it is estimated that the planetary limit of the nitrogen and phosphorus cycle has already been breached.

Over the past 50 years the rhythm of conversion of forests and other ecosystems into agricultural land has accelerated considerably. Today, the disappearance and fragmentation of natural territories has become the primary cause of attack on biodiversity. Territories that are too small and disconnected make it difficult for fauna to move around for food and to reproduce. The mass destruction of tropical forests is particularly preoccupying.

Solid or liquid, mineral or organic, the particles in suspension are of natural or human origin and of various sizes. Aerosols are naturally emitted into the atmosphere through volcanic eruptions, the mixing of ocean waters, forest fires or the dispersion of pollen. Human activities also diffuse aerosols via the combustion of fossil fuels (coal, petrol), the incineration of refuse and certain industrial processes (metallurgy, manufacture of cement).