Optimizing sampling of wheat shipments for better quality monitoring

To ensure that shipments of grain meet international regulations for naturally occurring contaminants and pesticide residues, loads of grain are often monitored and tested as part of a trade transaction. The results of a research study, led by Dr. Sheryl Tittlemier from our Grain Research Laboratory's Trace Organics and Trace Elements program, show how contaminants and residues in large loads of wheat can have different patterns of distribution within and between loads.

The study measured the concentrations of fungal toxins (ochratoxin A, deoxynivalenol, and ergot alkaloids), the heavy metal cadmium, and glyphosate residues in 9 loads of wheat. The loads ranged in size from 4,600 to 55,000 metric tonnes and primary samples were taken by Canadian Grain Commission inspectors using their standard methods. These methods required samples to be taken at approximately 45-second intervals during the entire time the wheat flowed into a vessel hold. The inspectors then prepared composite samples that represented consecutive 500-tonne portions of each load of wheat with the number of composite samples ranging from 11 to 110, depending on the size of the load.

The research team found that within a load, the concentrations of ochratoxin A and ergot alkaloids varied the most, followed by deoxynivalenol and glyphosate residues, and then cadmium. Using statistical tools that measure how similar samples are to each other, the researchers also found that each contaminant and residue was distributed differently within a particular load and that these distributions varied between different loads.

The results of this study show that if sampling is done during only a portion of a loading or unloading process, it can result in composite samples that are not representative of an entire load of grain, increasing the risk of misclassifying a shipment as compliant with international regulations.

To help ensure the quality and safety of Canadian grain exports, the Canadian Grain Commission approves and oversees the operation of all sampling systems used at licensed grain handling facilities to sample grain destined for export (Sampling Systems Handbook and Approval Guide). By using systems that sample a grain stream throughout the entire loading process, the Canadian Grain Commission gives buyers greater confidence in the quality of Canadian grain.

Quote:

“We can't assume that the substances we monitor, such as mycotoxins, cadmium and pesticide residues, are distributed the same way within a single load or between different loads of grain. If sampling plans are designed for the substance with the most uneven distribution, they will work well for all the substances we want to monitor.”

Full research article

Tittlemier, S.A., Blagden, R., Chan, J., Drul, D., Gaba, D., et al. 2024. Contaminants and residues have varied distributions in large volumes of wheat. Food Additives & Contaminants: Part A 42(1):92-102.
https://doi.org/10.1080/19440049.2024.2417394