Research demonstrates reduced chemical contaminants in wheat

Removing bran removes glyphosate residues in wheat

Glyphosate is the active ingredient in a number of herbicide products used by Canadian producers to control invasive weeds. Residues of glyphosate have been found in some grains and grain-based foods, but in almost all instances they were proven to be lower than the maximum glyphosate residue limits set by Health Canada.

We studied glyphosate in Canada Western Red Spring (CWRS) wheat to determine where it accumulates in a wheat kernel and if milling and baking changes the levels of glyphosate residues. Eight samples of CWRS wheat, containing different concentrations of glyphosate, were selected for our study. Each sample was pearled, a process where kernels are abraded to remove their outer layers. The material removed was collected and analyzed, as was the remaining portion of the kernels. We found that 50% of the glyphosate was contained in the outer 16% of a kernel, regardless of the initial concentration in the sample.

We then milled wheat samples to remove all the bran and germ. Our analysis showed that an average of 81% of the glyphosate was contained in the bran, shorts (fine bran), and feeds (germ) milling fractions (Figure 1). The remaining flour contained 19% of the glyphosate, indicating that milling can dramatically reduce exposure to glyphosate residues.

Baking does not affect glyphosate residues

Duplicate batches of dough and bread were prepared from the flours of CWRS wheat samples that had the highest glyphosate concentrations. Dough, fermented dough, and the crust and crumb from baked bread (Figure 2) were all analyzed for glyphosate. There was no difference in glyphosate concentrations when going from flour to finished bread, demonstrating that baking does not affect glyphosate residues, confirming that milling provides the best opportunity for reducing exposure to glyphosate.

Decreased cadmium accumulation in Canadian durum wheat

Cadmium is a heavy metal that is found in soil naturally and as a result of human activities. It can enter the food chain if it is absorbed and stored in edible plants. Some cereal grains accumulate cadmium at higher levels than others, including many durum wheat varieties grown in North America. Since chronic exposure to cadmium can result in negative health effects for humans, a durum breeding program was established in the 1990s to develop varieties that accumulated less cadmium while maintaining valuable quality characteristics. In 2004, low cadmium accumulation was established as a requirement for all new durum cultivars registered in Canada.

We have been monitoring cadmium in durum exports since the early 1990s. As part of our cargo monitoring program, shipments are systematically selected and sampled by Canadian Grain Commission inspectors using approved automated samplers and standardized procedures at terminal grain elevators (Figure 3). Since 1992, 2,239 samples of exported Canada Western Amber Durum (CWAD) wheat and 1,546 samples of exported CWRS wheat have been analyzed for cadmium.

Cadmium concentrations in bulk exports of CWAD wheat, measured in milligrams per kilogram (mg/kg), began to decrease in the mid-2000s. The highest concentrations in CWAD exports (0.16 mg/kg) were from the 2003/2004 shipment year. In the 2019/2020 shipment year, cadmium concentrations were 0.07 mg/kg, representing a decrease of over 56% (Figure 4). We also measured cadmium concentrations in CWRS wheat over the same period of time and found that there was no similar decrease. This is an important finding as it demonstrates that reduced levels of cadmium in CWAD wheat are not related to changes in the procedures and tools used in our analyses.

The decrease in cadmium in durum wheat exports mirrored the decrease in production of higher cadmium accumulating varieties. By 2019, lower accumulating varieties accounted for 98% of the insured CWAD wheat acres. Decreasing durum wheat cadmium concentrations over the past three decades demonstrates the success of the Canadian breeding programs, variety registration requirements, and adoption of low accumulating varieties by producers.