Pathways of pesticide spread in the environment

Small recesses in the soil can delay breakdown

The length of time a pesticide remains in the soil without being broken down mainly depends on how accessible it is for breakdown by microorganisms. In the smallest soil recesses, those less than one-tenth of a micrometre, pesticides can survive for a long time. This is because the microorganisms are simply too large to enter these small pores. The pesticide is therefore physically protected against breakdown. It is mainly clayey soils that have a large proportion of such small, inaccessible pores.

In pores so small that microorganisms (green in the pictures) cannot enter them, pesticides can survive for a long time. The upper picture shows pesticide distribution (red dots) from 0-7.7 days. The lower picture shows pesticide distribution after more than 7.7 days. Pictures from: Bergström & Stenström, 1998. Environmental Fate of Chemicals in Soil. Ambio Vol. 27 No 1, Feb. 1998.