POPs are toxic compounds that adversely affect human health and persist for a long time in the environment.
Widely used in crop production, pest control and industry during the boom in industrial production after World War II, these chemicals have caused problems for human health, with some thought to play a role in development of certain cancers, birth defects and damage to the central nervous system.
Because POPs take such a long time to break down and are easily absorbed into the fatty tissues of animals, they can quickly bioaccumulate within the food web.
For humans, this is a problem, as their concentration is at the highest levels in the food chain. Another problem is they can be transported in the environment by wind and water, meaning POPs released in one country can enter the food chain in another.
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Many countries have now recognized the severity of the problem and in 2001 the global community joined forces to reduce or eliminate the production, use and release of 12 key POPs under the Stockholm Convention. The treaty came into force in 2004 and since the signing of the original convention the list of POPs has grown from its original “dirty dozen”.
Dioxins in the food chain
One of the most prevalent classes of POPs are dioxins. They are of particular concern because of their high toxicity and chemical stability.
Dioxins cover a range of compounds based around the chemical structure of dioxin, or 2,3,4,8-tetrachlorodibenzo-para-dioxin (TCDD). While TCDD is the most toxic member of this family, structurally related polychlorinated dibenzo-para-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are also potentially harmful to human health.
Short-term exposure to high levels of dioxins can result in skin lesions and affect liver function, while long-term exposure has been linked to impairment of the immune system, the developing nervous system and reproductive functions.
Over 90% of human exposure to dioxins comes from ingestion of contaminated food with meat, dairy products, fish and shellfish the main offenders.
In many cases dioxin enters the food chain through contaminated animal feed. Several incidences of increased dioxin levels in milk or animal feed have been traced back to clay, fat or citrus pulp pellets used in production of animal feed.
For example, in 1999 a mixture of polychlorinated biphenyls (PCBs) and dioxins was inadvertently added to a Belgian batch of recycled fat used in the production of animal feeds (1). The failure to spot the contamination early resulted in the distribution of dioxin-containing animal feed to around 2,500 pig and poultry farms in the region, with meat found to contain dioxin and PCB at levels 100 times greater than maximal recommended limits.
In light of these dangers, monitoring of food and feed samples for dioxins is routine in many laboratories with most analyses based on gas chromatography in combination with mass spectrometry.
Such analyses must be sufficiently sensitive to determine the trace levels present in samples, and robust enough to handle a range of food and feed matrices.
Until recently, EU legislation for detection of PCDDs and PCDFs in food required gas chromatography-high resolution mass spectrometry (GC-HRMS) for confirmation purposes.
But advances in triple quadrupole mass spectrometry (MS/MS) technology have led to significant improvements in analytical sensitivity and selectivity of such instruments. As a result, GC-MS/MS can now be used under new EU regulations for confirmation.
These advances in analytical performance, combined with the robustness and high throughput offered by triple quadrupole instruments, is helping to make dioxin analysis more cost-effective.
In turn, this can help food safety laboratories analyze more samples and cast their net wider in the interests of public safety.
1) Bernard A, Broeckaert F, De Poorter G, et al. The Belgian PCB/dioxin incident: analysis of the food chain contamination and health risk evaluation. Environ Res. 2002; 988(1): 1-18.
- Khalil Divan is senior director, food and beverage vertical market at Thermo Fisher Scientific