Short answers, pulled from the story.
Pollution killed approximately nine million people worldwide in 2019, about one in six deaths that year. About three-quarters of those deaths were caused by air pollution. The Lancet Commission found that toxic air, water, soil, and workplaces kill nine million people annually.
The major forms of pollution include air pollution, water pollution, litter, noise pollution, plastic pollution, soil contamination, radioactive contamination, thermal pollution, light pollution, and visual pollution. Pollution can be a solid, liquid, or gas, or energy such as radioactivity, heat, sound, or light.
Point source pollution comes from a highly concentrated specific site, such as a factory, mine, or construction site. Nonpoint source pollution comes from widespread distributed sources, such as microplastics or agricultural runoff.
Before the 1860s, the word pollution referred to the desecration of something sacred rather than environmental contamination. According to Adam Rome, people described what we now call air pollution as the smoke nuisance, along with variations like the smoke problem, the smoke evil, and the smoke plague.
Pollution generally implies a human source such as manufacturing, extractive industries, poor waste management, transportation, or agriculture. Motor vehicle emissions are among the leading causes of air pollution. Natural events also contribute, with volcanoes and wildfires releasing harmful gases and fine particulates.
The Great Smog of 1952 in London killed at least 4,000 people. It prompted some of the first major modern environmental legislation, the Clean Air Act of 1956.
Polluting industries and toxic waste sites tend to be collocated with populations that have less economic and political power, including children, the elderly, and marginalized communities. This outsized impact is a core reason for the formation of the environmental justice movement, particularly in the Global South.