Low Dose Effects of Pesticides in the Aquatic Environment

摘要

In contrast to the terrestrial environment, organisms in the aquatic environment are exposed to more complex mixtures of pesticides with high concentrations occurring in pulses associated with spray and rain events. To quantify the effect of these complex mixtures, mixture toxicity models have to be used. The standard is to use Concentration Addition (also called Dose Addition), where all co-occurring pesticides are transformed into one common unit, which is summed and used as the joint exposure concentration. Using this approach, both herbicides and insecticides can reach joint concentrations during storm flow that can cause measurable effects in the plant, algae and invertebrate communities. Fungicide concentrations rarely reach the same level of predicted environmental effects, but this is likely owed to the fact that the traditional ecotoxicological tests do not reflect aquatic fungi communities, which are likely the most sensitive to these pesticides. Except for extreme incidents, pesticide occurrences in agricultural catchments will rarely lead to acute extermination of the majority of species. There is no doubt, however, that peak pesticide concentrations can affect the species communities on sub-lethal endpoints such as growth, emergence times, feeding and drift behaviour which ultimately may translate into altered community structure and function. In addition to the low dose effects of pesticides, other stressors of both chemical and physical nature are also stressing the aquatic communities. Therefore, ensuring a diverse aquatic community, requires a broad focus including both combatting excessive concentrations of pesticides and other chemicals and improving the physical habitat on a local scale as well as on a catchment scale. Only holistic approaches, including all stressors of the aquatic ecosystem, will sufficiently safeguard aquatic ecosystems and potentially recreate lost habitats, as well as increase populations of threatened species.