Widespread contaminationThe use of pesticides, fertilizers and other agrochemicals has increased hugely since the 1950s. For example, the amount of pesticide sprayed on fields has increased 26-fold over the past 50 years.
These chemicals don't just stay on the fields they are applied to. Some application methods – such as pesticide spraying by aeroplane – lead to pollution of adjacent land, rivers or wetlands.
Due to inappropriate water management and irrigation technology, fertilizers and pesticides also commonly run-off from fields to adjacent rivers and lakes and contaminate groundwater sources. These chemicals eventually end up in the marine environment too.
Toxic pesticidesPesticides often don't just kill the target pest. Beneficial insects in and around the fields can be poisoned or killed, as can other animals eating poisoned insects. Pestcides can also kill soil microorganisms.
Pesticide pollution of rivers, lakes and wetlands also directly poisons freshwater species, as well as people.
Some pesticides are suspected of disrupting the hormone messaging systems of wildlife and people, and many can remain in the environment for generations.
Excess nutrientsUnlike pesticides, fertilizers are not directly toxic. However, their presence in freshwater and marine areas alters the nutrient system, and in consequence the species composition of specific ecosystems.
Their most dramatic effect is eutrophication – resulting in an explosive growth of algae due to excess nutrients. This depletes water of dissolved oxygen, which in turn can kill fish and other aquatic life.