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Polycyclic aromatic hydrocarbons ( PAHs )

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Changed on: 08.04.2019

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PAHs (polycyclic aromatic hydrocarbons) is the collective term for aromatic compounds with condensed ring systems (well in excess of 100 substances). PAHs lead to lung cancer following exposure by inhalation, to skin tumours following dermal exposure and are probably carcinogenic in humans following oral exposure.

Origin and incidence

PAHs are produced from incomplete combustion processes or pyrolysis of organic materials (wood, coal, petroleum, oil, tobacco, refuse) or foodstuffs (barbecuing, roasting, smoking, drying). PAHs always occur as mixtures. They are spread via smoke, particulate matter in the air and soot particles.

Given boiling points < 400 °C, PAHs usually occur in the air in gaseous form.
For combustion temperatures of < 1000 °C (e.g. house fire), 3-4-atom PAHs are generally formed.
For temperatures of > 1000 °C (e.g. combustion engines), 5-7-atom PAHs are generally formed.

In the environment PAHs can be of natural or anthropogenic origin. Natural sources can be for example volcanic activity or forest fires. Anthropogenic sources particularly worth mentioning include motor vehicle traffic and industrial processes, but also cigarette smoke.

Chemical properties

PAHs are solid, usually colourless, chemically stable but photosensitive compounds. They are lipophilic (soluble in fat), are almost insoluble in water and have various boiling points depending on molecular mass (e.g. fluoranthene molecular mass = 202 g, boiling point = 383 °C; benzo(a)pyrene molecular mass = 252 g, boiling point = 496 °C).

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Origin and incidence

Given boiling points < 400 °C, PAHs usually occur in the air in gaseous form.
For combustion temperatures of < 1000 °C (e.g. house fire), 3-4-atom PAHs are generally formed.
For temperatures of > 1000 °C (e.g. combustion engines), 5-7-atom PAHs are generally formed.

Chemical properties

Important compounds

The US EPA list primarily takes environmental aspects into account (e.g. industrial emissions) and the selection featured covers PAHs from easily volatile to semi-volatile compounds. The recent EU recommendation targets carcinogenic and genotoxic PAHs in foodstuffs.

As one of the most carcinogenic compounds, benzo(a)pyrene was frequently designated as a guide substance. A conservative approach estimates the carcinogenic potential of the total PAH contamination in foodstuffs to be 10 times the detected concentration of benzo(a)pyrene.

However, the latest findings from foodstuff examinations of EU priority PAHs no longer support the status of benzo(a)pyrene as a guide substance. PAHs have therefore been regulated for certain foodstuffs since 1/9/2012 by using maximum levels of benzo(a)pyrene and the sum of benzo(a)pyrene (BaP), benzo(b)fluoranthene (BbF), benz(a)anthracene (BaA) and chrysene (CHR) as representative for the “EU priority PAHs”. The Scientific Committee on Food (2002) recommends keeping PAH contamination in foodstuffs as low as can reasonably be achieved.

Of the 16 EPA PAHs, routine practice often “only” specifies levels for 12 compounds. Acenaphthene, acenaphthylene, naphthalene and fluorene have low recovery rates due to their volatility. Similarly, some regulations only concentrate on the 6 semi-volatile PAHs benzo(a)pyrene, fluoranthene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene and indeno(1,2,3-cd)pyrene.

U.S. EPA¹	genotoxic (g) / carcinogenic (k)²	EU priority PAH³	genotoxic (g) / carcinogenic (k)²
Acenaphthene	/ ?	Benz(a)anthracene	g / k
Acenaphthylene		Benzo(c)fluorene	/ k
Anthracene	-/-	Benzo(b)fluoranthene	g / k
Benz(a)anthracene	g / k	Benzo(b)fluoranthene	g / k
Benzo(b)fluoranthene	g / k	Benzo(b)fluoranthene	g / k
Benzo(k)fluoranthene	g / k	Benzo(ghi)perylene	g
Benzo(ghi)perylene	g	Benzo(a)pyrene	g / k
Benzo(a)pyrene	g / k	Chrysen	g / k
Chrysene	g / k	Cyclopenta(cd)pyrene	g / k
Dibenz(a,h)anthracene	g / k	Dibenz(a,h)anthracene	g / k
Fluoranthene		Dibenzo(a,e)pyren	g / k
Fluorene	/ -	Dibenzo(a,h)pyrene	g / k
Indeno(1,2,3-cd)pyrene	g / k	Dibenzo(a,i)pyrene	g / k
Naphthalene	?	Dibenzo(a,l)pyrene	g / k
Phenanthrene	?	Indeno(1,2,3-cd)pyrene	g / k
Pyrene	- / ?	5-Methylchrysene	g / k

1 Environmental Protection Agency (EPA): priority list (1982)
2 cit. Scientific Committee on Food (2002)
3 Commission Recommendation 2005/108/EC including benzo(c)fluorene, which was additionally recommended by the experts of the JECFA (Joint FAO/WHO Experts Committee on Food Additives).

PAH regulations (selection)

PAHs in foodstuffs

according to EUR LEX Regulation 1881/2006.

The sampling procedure and the criteria for sample processing and analytical methods for foodstuffs are regulated in Regulation (EC) 333/2007 as amended respectively.

Matrix	Maximum level for	Reference level for	Source
Water for human consumption	Benzo(a)pyrene and sum of benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene and indeno(1,2,3-cd)pyrene		Directive 98/83/EC, Drinking Water Regulation, Federal Legal Gazette No. 304 (2001)
Fertilisers, soil additives, culture substrates and plant additives	Sum of benzo(a)pyrene, fluoranthene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene and indeno(1,2,3-cd)pyrene		Fertiliser Regulation, Federal Law Gazette No. 100 (2004)
Waste compost, certain aggregates	16 EPA PAHs		Compost Regulation, Federal law Gazette No. 292 (2001)
Emission controls: rye grass culture, meadow grass, tree leaves		Benzo(a)pyrene, sum of 6 EPA PAHs (semi-volatile PAHs), sum of 12 EPA PAHs	Öhlinger (2014)

Maximum Levels can be found in the EC Regulation 1881/2006 in its current version:

Food product	Maximum level in µg/kg for benzo(a)pyrene	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)**
Food product Oils and fats (excluding cocoa butter and coconut oil) for direct consumption or as food ingredient	Maximum level in µg/kg for benzo(a)pyrene 2.0	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 10.0
Food product Cocoa beans and derivative products	Maximum level in µg/kg for benzo(a)pyrene 5 µg/kg fat as of 1/4/2013	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 35 µg/kg fat from 1/4/2013 to 31/3/2015 30 µg/kg fat as of 1/4/2015
Food product Coconut oil for direct consumption or as food ingredient	Maximum level in µg/kg for benzo(a)pyrene 2.0	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 20.0
Food product Smoked meat and meat products	Maximum level in µg/kg for benzo(a)pyrene 5.0 until 31/8/2014 2.0 as of 1/9/2014	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 30 µg/kg from 1/9/2012 to 31/8/2014 12 µg/kg as of 1/9/2014
Food product Muscle meat from smoked fish and products; smoked crustaceans: max. level for muscle meat from extremities and rear abdomen; smoked prawns and prawn-like crustaceans (brachyra and anomura): max. level applies to muscle meat from extremities	Maximum level in µg/kg for benzo(a)pyrene 5.0 until 31/8/2014 2.0 as of 1/9/2014	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 30 µg/kg from 1/9/2012 to 31/8/2014 12 µg/kg as of 1/9/2014
Food product Smoked sprats and smoked sprats in tins (spratus spratus); mussels (fresh, refrigerated or frozen); heat-treated meat and meat products that are sold to consumer	Maximum level in µg/kg for benzo(a)pyrene 5.0	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 30.0
Food product Smoked mussels	Maximum level in µg/kg for benzo(a)pyrene 6.0	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 35.0
Food product Processed cereal-based foods and baby food for infants and young children	Maximum level in µg/kg for benzo(a)pyrene 1.0	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 1.0
Food product Infant formula, follow-on formula, baby milk and follow-on milk	Maximum level in µg/kg for benzo(a)pyrene 1.0	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 1.0
Food product Dietetic foods for medical purposes for infants	Maximum level in µg/kg for benzo(a)pyrene 1.0	*Maximum level in µg/kg for sum of BaP, BbF, BaA and CHR (as LB)** 1.0
*Lower concentration limits (LB=lower bound) are calculated assuming that all the values for the four substances lying below the detection level are Zero.

Food product