Why and how we monitor cereal contaminants (and why we need to hear from you)

Kristina Grenz explains how we monitor mycotoxins, agrochemical residues and other contaminants in grain, as well as how you can help direct levy investment in this area.

The cereals levy has underpinned the monitoring of contaminants in grain for about 40 years. The work, which measures incidence and levels for many contaminants, can help demonstrate grain safety and guide the improvement of production practices across the supply chain.

The contaminants monitoring project provides open, broad and robust data on grain contaminants.

Each year, the work analyses hundreds of commercial intake samples of wheat, barley and oats destined for food or feed uses, as well as samples of wheatfeed and oatfeed (co-products of milling).

It requires a coordinated approach, achieved through a close collaboration with the project’s four industry partners:

• Agricultural Industries Confederation (AIC)
• British Oat & Barley Millers' Association (BOBMA)
• Maltsters' Association of Great Britain (MAGB)
• UK Flour Millers (UKFM)

The dedicated project page includes statements of support for the work from the project partners, as well as the latest reports.

Take part in a questionnaire to let us know your views on this work (closes Monday 30 September 2024).

ahdb.org.uk/contaminants-review

A contaminant is anything present on or in grain that makes it unfit for consumption. Contaminants can be physical (such as metals), biological (such as insects or pathogens) or chemical (such as pesticide residues).

Each year, the project monitors core grain contaminants (analytes) and conducts further analyses on other priority contaminants (when required). Collectively, the work tracks numerous contaminants, such mycotoxins and pesticide residues, in grain.

In the first seven years of the current project phase (2016–2022), almost 2,500 samples were analysed (nearly 7,000 kg of grain). With 220 different contaminants tested, the work generated over one hundred thousand results.

Most of the mycotoxins studied are associated with in-field pathogen infection, which include ergot alkaloids (produced by Claviceps purpurea) and fusarium mycotoxins (produced by fusarium species) – such as deoxynivalenol (DON), nivalenol (NIV), T-2 and HT-2, and zearalenone (ZON).

The work also monitors storage mycotoxins, such as ochratoxin A (produced by various species of mould).

Most UK grain samples are usually well within the legal limits for all contaminants, according to the project’s long-term results.

In the rare cases where contaminants exceed limits, the supplier labs and trade associations are notified immediately. Subsequent investigations improve production practices, driving down exceedances even further.

For DON, most samples were well below the maximum levels (MLs), even the recently (1 July 2024) lowered MLs that apply to grain traded in the EU.

Feed grains, wheatfeed and oatfeed often recorded the highest levels, which is not surprising, due to agronomic practices and the fact that mycotoxins concentrate in the outer grain layers.

Due to the robust analytical methods used in the project, results are valued by industry to validate and benchmark the methods more commonly used to test commercial grain, such as DON lateral flow tests (LFTs). Thankfully, the results are usually consistent.

When the EU revised the MLs for DON, it also introduced new MLs for T-2/HT-2 toxins (replacing indicative levels) that also apply to grain traded in the EU.

Oats are most severely impacted by T-2/HT-2 toxins, with occurrences highest in oatfeed samples (but still usually within the limits).

Currently, GB has contractual limits for ergot by weight for feed grain and zero tolerance for all other grain. Once again, the EU has recently introduced (1 January 2022) stricter levels for specific cereals and products traded in the EU, which include limits for ergot alkaloids for the first time.

Alkaloids can be detected in grain with no visible ergot symptoms, providing a much tougher test for grain quality.

UK ergot alkaloid data has already been captured by the monitoring project for several years. In most years, levels are low. However, we do detect spikes in some years and in some products. Subsequent investigations are helping the supply chain understand and manage risk better.

We know ergot is associated with wetter growing seasons, like 2023/24. This season also featured many bare patches in fields, boosting grass weed pressures – and many grassweeds are also affected by ergot. 

Black-grass is particularly problematic. It flowers earlier than the main cereal crop, allowing a build-up of inoculum (honeydew phase) that can be readily transferred during the cereal flowering period.

It is unsurprising that AHDB commercial harvest progress reports cite evidence of increased prevalence of ergot in harvest 2024 crops.

Last year, glyphosate was approved for use in the EU for another 10 years, with nations retaining the power to authorise glyphosate-containing products on a case-by-case basis. The active ingredient remains under pressure, with some countries reducing its use (mainly with targeted measures aimed at amateur and amenity uses).

A recent analysis of our UK data (from several harvests) found no exceedances of the maximum residue level (MRL) for glyphosate in the three commodities examined: food oats, malting barley and milling wheat. Milling wheat was generally associated with low incidence and levels, whereas barley had the highest incidence and oats had the highest levels.

Any glyphosate detected would have been due to pre-harvest use, rather than pre-emergence herbicide use.

Interestingly, additional analysis revealed that duller summers were associated with higher glyphosate incidences (which was more influential than higher rainfall or reduced temperatures).

Since the UK withdrew from the EU, the contaminants-monitoring project has become more important, helping the industry navigate the increasing divergence between EU and GB/UK regulations.

Regular horizon scanning also detects and puts us in a stronger position to react to other emerging issues.

The AHDB Cereals & Oilseeds Sector Council recognises the importance of the work and why it should be levy-led.

For example, it is estimated that the costs to industry have been halved through the project’s collaborative approach (when compared to contracting separate commodity-specific tests).

The independent work also frees up the findings from commercial sensitivities, meaning the results can be shared to benefit everyone.

The Sector Council acknowledges that the project needs to move with the times.

With the current project phase (led by Fera) nearly complete, we are asking levy payers to provide their views on the work to help direct future investment.

The questionnaire, which is open until Monday 30 September 2024, can be accessed via: ahdb.org.uk/contaminants-review