Pesticide Degradation in the Soil Environment – Challenges of Trapping Volatile Components in Anaerobic Studies and a Discussion on Determination of the Bound (Non-extractable) Residue Formation.

In the environment, pesticides are degraded through various pathways that include both biotic and abiotic influences. Often the degradation pathway ultimately lead to formation of volatiles, degradation products (or metabolites in the case of biotic degradation) and bound (non-extractable) residues. Effectively capturing volatiles gases such as methane formed from pesticides exposed to highly anaerobic soil or sediment/water environments in laboratory studies can be challenging. This is particularly the case when such volatile components are formed in high quantities.  This presentation will describe the challenges faced in a case study where a large amount of methane gas and dissolved CO₂ were formed from a pesticide in an anaerobic aquatic environment.  The methods used for the trapping and identifying solubilized and volatiles gases will be presented. 

Degradation of pesticides in soil or sediment often lead to a fraction that is considered bound or non-extractable. The amount of bound residue formed in a given laboratory study is impacted by the method of solvent extraction used. The use of radiotracers (e.g. ¹⁴C-labelled pesticides) in pesticide research provides insight into mechanisms of pesticide bound residue formation. In the pesticide regulatory world, bound residues are sometimes included in a total residue approach for risk assessment, due to uncertainties around the nature of these residues. This presentation will include a discussion on how soil-bound pesticide residues are assessed in laboratory studies, and results seen from extraction procedures now required by the recent EPA guideline on extraction schemes.