Gases can be released into the air by accident or by a lack of pollution control in factories. For example, in India in 1984, the pesticide plant in a town called Bhopal leaked just 40 tonnes of toxic gas into the air. This killed eight thousand people in a few days and over the years since then, up to twenty thousand have died from respiratory problems caused by the gas.
Toxic waste dumped in landfill sites seeps into the ground, polluting water supplies and farmland. The toxins can then be eaten and drunk by people, and by animals in the human food chain. It is only during the last quarter of the 20th century that countries like the USA introduced laws to control the dumping of toxic waste in landfill sites.
Factories near the sea will often discharge toxic waste directly into the sea, wrongly assuming that it will be so dilute, it will cause no harm. Small amounts of toxic materials e.g mercury, accumulate in sea creatures. Although the dose they receive is not enough to kill them, people who eat the sea creatures very soon accumulate dangerous levels in their own bodies. Despite 50 countries signing a treaty to halt the disposal of toxic waste at sea, accidents and through illegal shipping to countries with no toxic waste legislation.