Pathways of pesticide spread in the environment

Further facts: How biological breakdown occurs

Metabolic breakdown. Breakdown occurs both within organisms and outside. Some microorganisms can adapt to using certain pesticides as an energy source for their own growth (metabolic breakdown). This has been demonstrated for example for the herbicide MCPA, which is a phenoxy acid. The herbicide is then broken down more quickly in the years after the first spraying, i.e. the compound is not as long-lasting. This adaptation in microorganisms can continue even after a field is no longer sprayed. For example, field trials have shown that adaptation to MCPA as an energy source is still detectable after five years.

Co-metabolic breakdown. Breakdown can also occur through microorganisms, plant roots etc. exuding breakdown enzymes (co-metabolic breakdown) to the surrounding soil. These enzymes are actually produced to utilise some other energy substrate but at the same time contribute to the breakdown of pesticides. This type of breakdown does not lead to specific adaptations in soil organisms and therefore breakdown does not occur more quickly after repeated applications of the pesticide. The rate of breakdown is related to the availability of energy substrate in the soil/sediment. General biological activity in a soil (production of carbon dioxide per day) is a rough measure of the ability of a soil to co-metabolically break down pesticides.