PAHs – Polycyclic aromatic hydrocarbons

PAHs – Definition

PAHs – (polycyclic aromatic hydrocarbons) is a collective term for a group of substances consisting of organic components.

These consist of two or more (up to seven) benzene rings bonded together, which is why they are also referred to as condensed ring systems. The ring-shaped hydrocarbons often have additional substituents (frequently methyl groups) or derivatives (oxygen or nitrogen).

All these structures are summarized under the term PAHs; several hundred are currently known. Naphthalene is the smallest polycyclic hydrocarbon with the molecular formula _C10H8.

A distinction is made between “lighter” and “heavier” PAHs, whereby compounds of two or three benzene rings belong to the lighter ones and are primarily present in gaseous form. From four cycles upwards, they are particle-bound and are classified as heavier compounds. As the number of benzene rings increases, the molecular weight also increases and thus the volatility at room temperature decreases.
These compounds are also commonly known as “plasticizers”, as they are often added to plastics to make them softer and more flexible.

 

PAHs – formation and occurrence

Polycyclic aromatic hydrocarbons are produced by the incomplete combustion (pyrolysis) of organic material and can therefore be found worldwide. They can also be of natural origin, for example from forest fires. In industry, they are produced during combustion processes in steel or aluminum factories or during crude oil processing. They usually occur as mixtures and are solid and crystalline at room temperature.

In everyday life, PAHs occur in dusty containers, e.g. through rubber abrasion on the road. They can even be found in food, namely in smoked or grilled products. For this reason, grilled food should not be eaten black and contact with glowing coals should be avoided (e.g. by “extinguishing” them).

Danger from polycyclic aromatic hydrocarbons?

Since PAHs compounds are so numerous, the question arises as to what danger they pose. Aromatized hydrocarbons are lipophilic (fat-soluble). The more aromatic rings there are in the compound, the more fat-soluble it becomes and is deposited in the body’s fatty tissue. This fat-solubility leads to irritation on contact with the skin and can cause inflammatory symptoms. Some are considered carcinogenic, mutagenic and in some cases even toxic. This is why they are also classified as “CMR” substances (C – carcinogenic, M – mutagenic, R – toxic for reproduction).
Due to their effect on the environment, many PAHs are referred to as PBT substances.
This stands for:
Persistent: poor or no degradation possibilities in nature
Bioaccumulative: Accumulation in the organism
Toxic: poisonous

The biggest problem with these compounds is their persistence, which means that they remain in the environment for a long time and are hardly degraded. Their hazard potential therefore lingers for a long time.

 

PAHs measurement by GSA Ratingen

As there are so many different PAHs compounds, 16 selected compounds are examined in an analysis, with benzo[a]pyrene serving as the lead substance. The selected substances are representative of the substance group, as they are very toxic and easy to detect chemically. Assuming that other aromatized hydrocarbons are also present when these compounds are detected, this form of analysis is correspondingly meaningful. However, it must be said that this method is not suitable for foodstuffs.

There are currently various individual directives with different limit values for air, water, food or toys (0.5mg/kg). The content of PAHs in soil is differentiated according to use; e.g. 2mg/kg DM (fine soil dry matter) applies to play areas, but a value of 12mg/kg DM applies to commercial areas.
A uniform limit value does not (yet) exist, but PAH-free/lower PAHs substances are already being used in many cases to further reduce pollution.

The measurement of organic components such as PAHs is carried out in accordance with DIN ISO 12884, which describes an outside air measurement with high volume flows (100l/min-250l/min) and a sampling period of 24 hours. The PAHs compounds are then analyzed and broken down using HPLC (high-performance liquid chromatography). For further information please contact us here.

 

How can PAHs be avoided?

Due to the potential dangers, it makes sense to want to avoid polycyclic aromatic hydrocarbons. But is it that simple?
In the private sector, care can be taken to ensure that food is not “burnt” (e.g. grilled food). Furthermore, ovens and boilers can be operated with low levels of pollutants or modernized if necessary. Consumer goods or toys with a high PAHs content often give off a penetrating odor that lingers for a long time. It is therefore advisable to pay attention to quality seals such as the GS mark or the Blauer Engel. The conscious purchasing decision ultimately influences the companies and production.

Sources:
[1]: https://www.umweltbundesamt.de/service/uba-fragen/was-sind-pak
[2]: http://www.chemie.de/lexikon/Polyzyklische_aromatische_Kohlenwasserstoffe.html
[3]: https://www.umweltbundesamt.de/sites/default/files/medien/376/publikationen/polyzyklische_aromatische_kohlenwasserstoffe.pdf
[4]: https://www.bfga.de/arbeitsschutz-lexikon-von-a-bis-z/fachbegriffe-j-r/pak-fachbegriff/
[5]: http://www.gsa-ratingen.de/leistungsangebot/sonstiges.html
[6]: https://www.umweltbundesamt.de/service/uba-fragen/welche-eigenschaften-haben-pak
[7]: https://www.umweltbundesamt.de/service/uba-fragen/wie-werden-pak-bestimmt