Detecting Polycylic Aromatic Hydrocarbons in Food

The Gulf of Mexico oil spill, the largest in U.S. history, has raised awareness of a food safety issue, namely contamination by polycyclic aromatic hydrocarbons (PAHs). In the future, analytical testing for PAHs in fish, crustaceans, and bivalves will undoubtedly become a routine procedure for many laboratories. PAH exposure, through either environmental pollution or contaminated foodstuffs, and its effects on human health have been the topic of many scientific studies. The recent oil spill again focuses attention on this toxic class of compounds.

PAHs comprise a large group of chemical compounds that are known cancer-causing agents. Some PAHs have been shown to be carcinogenic and mutagenic. The scope of monitored and regulated PAHs is under constant change, influenced by international advisory bodies such as the World Health Organization (WHO) and the European Food Safety Authority (EFSA). Changes in regulations highlight the need for more accurate quantification and improved detail in separation to isolate key PAHs from possible interfering isomers. Gas chromatography (GC), in combination with mass spectrometry (MS), is one of the principal analytical techniques used for identifying and quantifying PAHs in environmental and food-related samples.

During GC/MS analysis, some co-eluting PAHs exhibit an identical MS fragmentation pattern. The possible chromatographic co-elution of some PAHs therefore requires special attention. To obtain unambiguous identification and highly accurate quantification of priority and regulated PAHs, an optimized capillary column is essential.

Here we discuss the possibilities offered by a new generation of dedicated GC columns for PAH analysis, which contribute to more accurate reporting of these compounds for both food and environmental monitoring.

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Table 1. The scientific opinion of the panel on contaminants in the food chain on a request from the European Commission on Polycyclic Aromatic Hydrocarbons in Food (The EFSA Journal, 2008).

EPA Recommendations

Until recently, most analytical methods for PAH monitoring were established for analyzing the 16 priority pollutant PAH compounds recommended by the U.S. Environmental Protection Agency (EPA). They are naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene (see Table 1, p. 38). This list is often targeted for measurement in environmental samples.

The concern about environmental PAH pollution arises from the bioaccumulation risk in the food chain. PAH exposure occurs mainly through air inhalation and food consumption. Sources of airborne PAH include traffic and industry as well as tobacco smoke and open fires. Dietary exposure to PAHs through food consumption has recently gained importance because of general concern about food safety in the European Union and the United States. The oil spill in the Gulf will lead to mounting concern for food safety risks associated with marine organism consumption.

PAH occurrence in food is influenced by the same physiochemical characteristics that determine their absorption and distribution in man. Relative solubility in water and solvents, as well as volatility, determines their capacity for transport and distribution and, consequently, influences their uptake by living organisms. PAHs have a lipophilic nature that contributes to their accumulation in the lipid tissue of plants and animals. The waxy surfaces of vegetables and fruit can concentrate low molecular mass PAHs, mainly through surface absorption. The deposition of small PAH-contaminated airborne particles is the principle route of contamination for vegetables. Atmospheric fallout is also responsible for contamination of less volatile PAHs, which end up in fresh water or marine sediments. PAHs are strongly bound to these sediments, which then become potential reservoirs for PAH release. Filter feeding bivalves have a low metabolic capacity for PAHs, which may lead to their bioaccumulation. Oil spills are the other main cause of PAH contamination of marine organisms.

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Table 2. The most critical peak-pair separations for polycyclic aromatic hydrocarbons.

Smoking and Food Processing

Raw foods rarely contain substantial levels of PAHs, reflected by the relatively low-level background contamination in unprocessed foods from remote rural areas. The produce contamination level is already elevated in more populated regions because of airborne PAH emission by industry and motor vehicles.