The objective of the DegT50 module is to provide field results, from which the degradation half-life (DegT50) in top soil at 20oC and at a moisture content corresponding to field capacity can be derived, following inverse modelling procedures (EFSA 2010; http://www.efsa.europa.eu/en/efsajournal/doc/1936.pdf). The geomean DegT50 is used as an input parameter in simulation models for environmental exposure to pesticides (leaching to groundwater, exposure of aquatic and soil organisms), within the EU. In the context of this DegT50 module, the definition of 'degradation' of FOCUS (2006; http://focus.jrc.ec.europa.eu/dk/) is used which considers soil bound residues as degradation products. For the exposure assessments, it is essential that the DegT50 reflects the degradation rate within the soil matrix, so excluding other loss processes such as photodegradation or volatilisation. This can be achieved either by designing the experiment so that the measured decline reflects almost exclusively the degradation within the soil matrix (e.g., by incorporating the dose immediately after application or covering the soil surface after application) or by spraying the substance onto the soil surface combined with an analysis of the data that ensures that other loss processes than degradation do not influence the DegT50 obtained (EFSA 2010). The inverse modelling procedure for estimating a DegT50 is based on the decline of the total mass per surface area that is present in the soil profile. So, the DegT50 module provides guidance for assessing this decline. [Note: The content of this abstract does not necessarily represent the official views of the OECD or of the governments of its member countries and EFSA.]

OECD guidance for pesticide field dissipation studies for obtaining DegT50 value

246th National Meeting (2013)

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