Pollution is the release of products not worth recycling, so the extent of any pollution can be reduced by making producers pay the cost of dumping it.
Many halogenated compounds are persistent in nature, in part because they are often soluble in fats, and so may be readily concentrated up the food chain.
The polychlorinated biphenyls are persistent pollutants: the major problem with some persistent pollutants is bioaccumulation up the food chain.
Treatment of sewage before it goes into rivers and lakes reduces eutrophication, and the better the treatment, the less eutrophication there will be.
Large amounts of organic material increase the biological oxygen demand, whether the material comes from eutrophication, sewage, or dumping of waste.
Atmospheric changes spread widely, even crossing the equator into the other hemisphere. Nobody owns the air, nobody has the right to pollute it.
Some substances are biodegradable, which means levels in the environment slowly fall, though sometimes the products are still a problem in the environment.
Eutrophication happens when water has too many nutrients, so plants grow faster than they can be eaten: when these die and rot, they may take all the oxygen.
Salination is a problem with soils all over the world. In large part, it is caused by rising groundwater, itself caused by land-clearing that removes trees.
An ozone hole results from ozone depletion caused by gases released elsewhere in the world: the main one is over the South Pole each southern summer.
Ozone levels in the upper atmosphere are measured with a Dobson spectrophotometer, and these show that ozone levels are dropping, mainly over the Poles.
Land (and soil) is a limited resource, all over the world, it is being degraded, so clearing is needed to get more, leading to a massive loss of habitat.
Laterization is a common problem with soils. This involves the leaching of some of the more soluble soil components to leave iron and aluminium oxides.
There is a limit to the sustainable yield from any ecosystem, sustainability here assuming that conditions will be fully preserved, so the system is unchanged.
Many forms of so-called sustainable harvest do not take into account long-term damage done to soil, biodiversity, and nearby waterways, so are not sustainable.
Aquaculture is a highly productive way of farming, but it brings many problems, mainly because it is intensive, and so produces large amounts of waste.
Pests and feral species can be prevented from entering a new area by maintaining a suitable quarantine system to keep them and their seeds out.
Pests and feral species which have arrived in an area can be prevented from breeding by use of the sterile male technique to limit any breeding that happens.
Conservation of endangered species means maintaining their genetic diversity, but it also means maintaining biodiversity in habitats of many kinds.
The world has many endangered species: some of them are probably more vital to our survival than others, but it is very hard to say which are which.