Pathways of pesticide spread in the environment

Soil properties have an effect

A number of different soil properties affect the breakdown and mobility of pesticides. Soil composition and properties vary depending on geological origins, position in the landscape, climate zone and the various cropping or soil management practices used. The risk of leaching increases considerably if for example binding is weak due to lack of organic matter in the soil or breakdown is slow due to the microbial activity being low. In soils with a high clay content and high organic matter content, the conditions are often better for rapid breakdown of pesticides. For compounds that are acids or bases, the soil acidity (pH) affects the chemical form of the pesticide and its water solubility and thereby its mobility. For other compounds, the pH affects breakdown.

Lifetime and biological availability

Soil properties also affect the length of time pesticides can remain in the soil without being broken down, i.e. their lifetime or persistence. The soil is a complex and variable environment which greatly affects the soil solution, dissolved compounds, gases and microorganisms. Mineral particles and organic material make up the solid phase of the soil, while soil water and soil air are found in the soil pores between the particles. The soil is continually being affected by temperature changes, weathering, living organisms, water percolation and substances being added from the atmosphere.