September 2022 | Canadian Food Inspection Agency | by Jolette MacAulay, Gina Benedict and Kelly Duong
The Chemistry Section at the Canadian Food Inspection Agency (CFIA) Dartmouth Laboratory in Nova Scotia is responsible for testing fish and other foods for a variety of trace elements and veterinary drug residues. Testing for a long list of compounds involves a variety of methods and instruments, and their effective operation, maintenance and troubleshooting requires specialized skills and expertise.
Streamlining these routine tests can help free up more resources for important research activities and potential food safety investigations. Luckily, the Dartmouth Lab has a great team that is always looking for ways to improve its processes. The team includes two of the CFIA's mighty heroes: Vaughn Arthur and Gina Benedict. Check out their CFIA superhero trading cards!
Overcoming challenges in detecting mercury
Mercury (Hg) is a well-known contaminant that can be found in water, soil and food. Large predatory fish like tuna are known to bioaccumulate Hg over time. When these fish end up on the dinner table, Hg can pose a risk to humans. To protect the health of consumers, Health Canada sets maximum limits for Hg content in fish products. The CFIA regularly tests fish, shellfish and fish products to determine if they meet these standards. If products are found that exceed the limits for Hg, appropriate follow up actions are taken.
Historically, the Dartmouth Lab has analyzed Hg using cold vapour atomic absorption (CVAA), a targeted method for measuring Hg. This is a widely accepted technique that can detect even very low levels of Hg.
The Dartmouth Lab also tests for 23 other trace elements using different methods and an instrument called an inductively-coupled plasma mass spectrometer (ICP-MS). ICP-MS is used to measure trace amounts of elements in food samples, and can analyze almost all the elements in the periodic table in a very short period of time. Hg, however, poses several challenges for analysis by ICP-MS:
- Only a small amount (around 4%) of Hg is able to be detected using ICP-MS.
- Hg has 7 stable forms or isotopes, each accounting for less than 30% of the total that can be detected. This means the total concentration of Hg is divided between these 7 isotopes, some of which may be present at very low levels.
- Hg is known to adsorb to the walls of containers, including the ICP-MS sample introduction system. This is known as a "memory effect" and results in low recovery and long washout times.
- Hg is not stable in a solution and evaporates easily from open containers.
The Dartmouth Lab has implemented multiple solutions to address these challenges:
- New ICP-MS instruments are being used that are more sensitive and able to detect lower levels of Hg.
- To combat the memory effect, the lab started using a gold (Au) washout solution to keep Hg stabilized and to prevent its adherence to the sample introduction system.
- The lab also added hydrochloric acid (HCl) to the sample after digestion and prior to ICP-MS analysis, which helps keep Hg in solution.
After these improvements were made, the ICP-MS method was validated for measuring Hg in food. The Dartmouth Lab is now able to use a single method to test for all 24 trace elements in food samples, including Hg at levels that were previously only achievable using earlier methods like CVAA.
Keeping fish products safe from veterinary drug residues
The Dartmouth Lab is also responsible for analyzing residues of veterinary drugs in fish and fish-based products. Currently, regulatory monitoring programs look for 73 veterinary drug residues in fish products. A number of these residues are banned for use in food, and if present, could pose a risk to public health and safety.
Veterinary drug residue monitoring has historically been very complex, with each class or group of drugs requiring a separate single-class method of analysis that could only target a specific group. This meant the lab had to use 14 methods to monitor for all 73 veterinary drugs. Most of these methods rely on a technique called liquid chromatography tandem mass spectrometry (LC-MS/MS). This is a powerful detection technique that helps to identify suspected residues in food samples.
As testing requirements have increased, the single-class approach has become more difficult and time-consuming to implement. Multi-class, multi-residue methods have since been developed and validated for screening and quantitative purposes. Recent advances in the sensitivity of LC-MS/MS have also made it possible to maintain the required detection limits while incorporating multiple classes into a simple extraction method. This allows the CFIA to test for multiple residues at once, rather than identify them individually. The Dartmouth Lab has successfully developed, validated and adopted 2 multi-class methods that have replaced 11 single-class methods.
Higher efficiency, lower costs
These improvements have significantly increased laboratory efficiency and reduced the cost and time required to perform contaminant and residue analyses. This added efficiency helps the CFIA keep up with testing demands, and allows for the expansion of laboratory testing capacity for other food safety programs.
By innovating and problem-solving, CFIA scientists at the Dartmouth Lab are adapting their methods to help keep food safe and healthy for Canadians.
- Our laboratories [Canadian Food Inspection Agency]
- Food safety testing bulletin and reports [Canadian Food Inspection Agency]
- Mercury in fish – Questions and answers [Canada.ca]
- Do you have what it takes to be a superhero? [Canadian Food Inspection Agency]
- Women in science – podcast with Bree Ann Lightfoot and Dr. Lisa Hodges
- Harnessing the power of spectroscopy for food safety [Science.gc.ca]