Crop metabolism to crop trials: Why conduct radiovalidation?

ACS Fall Conference 2025 -- Crop metabolism studies are conducted to determine the nature of the pesticide residue in raw agricultural commodities. The studies are conducted with radiolabeled pesticide and the total radioactive residue (TRR) in each commodity measured. This means that the extraction method can be designed to ensure that most of the radioactive residues are extracted and both the extractable and non-extractable residue can be quantified and characterized. The residue definition for the consumer toxicological risk assessment is based on the information generated from these studies. It often comprises either just the active substance or the active substance and a limited number of marker metabolites. In subsequent crop residue trials carried out in the field, using the formulated product, the magnitude of the defined pesticide residue in raw agricultural commodities for the proposed uses is determined. These trials are conducted to mimic the proposed use conditions as much as possible with regard to application rate, timing, PHI, etc. Samples of the commodities are extracted and analyzed for the defined residue according to a validated method. Methods are routinely validated using control samples spiked with each component of the defined residue. However, the use of spiked samples in this way can overestimate the efficiency of the extraction procedure compared to extraction of field aged samples. These so-called ‘incurred’ residues may be more difficult to extract as they can include conjugates or be incorporated into the plant matrix. One way to assess the extraction efficiency of the validated residue method is to apply the method to radiolabeled samples from the crop metabolism studies. This allows a comparison to be made of the extractability of the residues of interest from the two types of studies and thus enables the extraction efficiency of the residue method to be calculated.