Exposure and environmental impact

Examples of environmental impact in aquatic ecosystems

Only a few field studies have investigated how the normal use of pesticides within agriculture can affect aquatic ecosystems. One example where negative ecological effects have been reported is a German study of a stream where 8 of 11 common bottom-dwelling animals completely disappeared and the remaining three species decreased drastically as a result of the use of insecticides (parathion-ethyl and fenvalerate) on neighbouring agricultural land. Insecticides (deltamethrin and permethrin) were also highly likely to have been involved in extensive fish kill-off that particularly affected eels in Lake Balaton in Hungary. Insecticides had been used in the area to control mosquitoes. No similar studies have been carried out in Sweden.

Difficult to detect ecological effects in the environment

In the examples above from Germany and Hungary, the effects of pesticide use are very clear. However, it is not always as easy to detect ecological effects. One possible reason for this is that there is no clear relationship between spraying of a certain compound and the effects in the environment. Several pesticides can e.g. interact and give rise to unexpected effects. Changes in the environment can also take place slowly, making them difficult to detect. The effects may not be detectable for a long time after the exposure. Because of the close interactions between different organisms in aquatic environments, the effects can also influence completely different species or groups of species than the pesticide was originally intended for. It can sometimes be the breakdown products and not the parent compound that cause ecological effects, which further complicates the identification of cause and effect.