4.7.4. Precautions when sampling pollen and nectar for residue analyses
Pesticide residue levels in pollen and nectar are generally detected in the range of parts per billion (ppb). These extremely low traces of residues can easily occur due to cross-contamination. Therefore, it is essential that all steps in sample collection and processing, be optimised and quality assurance measures be deployed (e.g., use separate tools for each treatment sample, change disposable gloves between samples, etc.).
To quantify pesticide residues at the lowest level of detection, most analytical laboratories require samples of 3g of pollen or 1.5 ml of nectar, so different male flowers (usually 40-50 for pumpkin) may need to be extracted over the flowering period to collect the required quantities for analysis. In this case, detected residues in nectar and pollen represent the cumulative average level during the entire collection period. For more information on toxicology, see the relevant BEEBOOK paper by Medrzycki et al. (2013).