Human activities inevitably and increasingly introduce material and energy into the environment; when that material or energy endangers or is liable to endanger man's health, his well-being or his resources, indirectly or directly, it is called a pollutant. A substance may be considered a pollutant simply because it is in the wrong place, at the wrong time, and in the wrong quantity.
Pollutants can affect man with direct effects such as: acute effects from exposure to a toxic pollutant reaching man through air, water or food; long-term effects due to prolonged exposure to a pollutant at levels lower than those giving rise to overt toxic effects; synergistic interaction between pollutants or between a pollutant and malnutrition or disease; genetic effects that are manifested in future generations. Indirect effects on man may result from reduction of the food supply or deterioration of the environment. Such effects include: damage to plants and animals; disruption of ecological cycles such that a previously harmless species becomes a pest; damage to the human habitat (air pollutants that destroy forests and corrode buildings); water pollutants that destroy the recreational value of inland waters; alteration of the global climate (this is considered to be a future threat).
The emissions of sulphur and nitrogen oxides and concentrations of atmospheric ozone have increased, agricultural and industrial wastes have been accumulating, lake acidification has taken place, forests and water quality have been declining. The volume of garbage and waste is constantly increasing, due in particular to increases in population, changes in living habits, increases in packaging material and increases in consumption. The capacity of waste and garbage disposal installations has long been left far behind. Water resources are to an increasing extent being polluted by the constantly growing volume of waste water from households and industry. The river Vistula, which flows through Warsaw, annually disgorges into the Baltic Sea 5,000 tonnes of phosphorus, 90,000 tonnes of nitrogen, 130 tonnes of oil, three tonnes of phenol and lead, as well as unknown quantities of cadmium, mercury and zinc.
Technical progress and mechanization has in recent decades led to a rapid increase in noise. About every fifth worker in Germany is subjected to a noise level of 90 dB or over. The atmosphere is being polluted by dust, smoke and exhaust gases from industry, motor vehicles and domestic heating. In the former Soviet Union fifty million people live in areas where the air pollution levels are 10 times the minimum health standard. In the Urals the city of Nizhny Tagil, for example, industrial enterprises emit nearly 700,000 tons of poisonous substances into the air every year.
According to a recent study by the Lancet, and written by more than 40 international health and environmental experts, pollution killed an estimated 9 million people in the world in 2015.
"Pollution is the largest environmental cause of disease and premature death in the world today. Diseases caused by pollution were responsible for an estimated 9 million premature deaths in 2015—16% of all deaths worldwide—three times more deaths than from AIDS, tuberculosis, and malaria combined and 15 times more than from all wars and other forms of violence. In the most severely affected countries, pollution-related disease is responsible for more than one death in four." (https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(17)32345-0/fulltext)
[Developing countries] Although air, water and noise pollution are not yet matters of primary concern in urban areas of developing countries, such problems will grow more severe as these countries move toward their goals of economic development. Generally the devices and regulations presently in force to control pollution in developed countries are not applied to industrial processes in developing countries with equal efficiency or stringency. In an effort to provide increased economic well-being, environmental safeguards are neglected. Water supplies are not only contaminated with human wastes, but grow increasingly toxic as they receive the effluent from expanding industries. Air pollution increases with the material well-being of the urban population and emanates from power plants, industry, space heating and the growing number of motor vehicles.