The chemical properties of pesticides are listed in the Pesticide Property Database – PPDB (University of Hertfordshire,2017). There is a separate database available for Bio-Pesticides – BPDB. University of Hertfordshire (2016).
The two chemical properties the most commonly used are the DT 50-value and the Koc.
The kinetics of dissipation in soil in the field results in different results depending on the type of reactions observed (abiotic or biotic). A consensus has emerged for the use of a first-order equation for the description of these phenomena (Beulke et al., 2001a, Calvet et al., 2005). In general, only the (bio) degradation data are taken into account, in particular because they are the simplest data to obtain. This first-order equation can use the half-life (DT50) which represents the time to halve the initial amount of product. The DT50 is an indicator of the persistence of the pesticide in the soil. The DT 50-value is thereby often used as a parameter to measure pesticide accumulation.
The partition coefficient Koc is defined as the ratio of pesticide concentration in a state of sorption (i. e. adhered to soil particles) and the solution phase (i. e. dissolved in the soil water). Thus, for a given amount of pesticide, the smaller the Koc value, the greater the concentration of the pesticide in solution. Pesticides with a small Koc value are more likely to leach into groundwater than those with a large Koc value. Sorption for a given pesticide is greater in soils with a higher organic matter content. Thus, pesticide leaching is thought to be slower in soils rich in organic matter than in soils low in organic matter. The Koc is part of several (national) indicators and models (Kookana et al., 2005), sometimes supported by lysimeter studies (Nolting and Schinkel, 1998).
The DT 50-value and Koc-value can be used individually for specific questions such as the environmental test of a certain pesticide in a certain environment or soil type (Kookana et al., 2005, Kucharski and Sadowski, 2009).
Other physical properties, such as water solubility, octanol/water partition coefficient, and volatility from soil, have often been invoked as indicators of leachability, thus affecting the estimated risk of pesticide leaching into groundwater or surface water aquifers.